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New Proterozoic K-Ar ages for some kimberlites and lamproites from the Cuddapah Basin and Dharwar Craton, South India: Evidence for non-contemporaneous emplacement
Abstract
We report new K-Ar age determinations carded out on mica separates from kimberlites and lamproites that occur within
and adjacent to the intra-cratonic Cuddapah basin in southern India. This work includes the first ages obtained from the
Ramannapeta lamproite (at the northeastern margin of the Cuddapah basin) and from one of the kimberlites in the
Mahbubnagar district. The Ramannapeta lamproite and the Kotakonda kimberlite were both emplaced in the Proterozoic and
have ages of 1384-t- 18 and 1363 + 48 Ma, respectively. These dates are similar to the 1350 -I- 52 Ma age obtained here for
the Chelima lamproite (within the Cuddapah basin). The Muligiripalle kimberlite (Pipe 5 of the Anantapur district) on the
other hand yielded a much lower age of 1153-I- 17 Ma. Our results demonstrate that the emplacement of the Indian
kimberlites and lamproites during the Proterozoic did not take place within the span of 30 Ma around 1090 Ma as some
workers have recently advocated, but occurred over a period of > 300 Ma. The Chelima (within the Cuddapah basin) and
Ramannapeta lamproites represent some of the oldest lamproites world-wide and, together with the Kotakonda kimberlite,
they might constitute a hitherto unrecognised Proterozoic episode of potassic magmatism at ~ 1350-1380 Ma.
... During this time gap, the eastern Dharwar craton witnessed significant events of the Mesoproterozoic magmatic events. (i) The Mesoproterozoic rift related magmatism in the basin is characterized by alkali syenites and lamproites in the central part of NFB (e.g., Crawford and Compston, 1973;Madhavan et al., 1994;Chalapathi Rao et al., 1996, 2012 and (ii) intrusion of ~1575±20 Ma (Rb-Sr) of granites in the northeastern fringes of the NFB (Crawford and Compston 1973;Hazra et al., 2004;Sesha Sai, 2019). ...
... • Subsequent to the major deformational event that resulted in formation of the NFB, the basin witnessed two significant events of magmatism (i) felsic magmatism in the form of emplacement of arc magmatic granites in the NE fringes of NFB around ~1575 ± 20 Ma (Crawford and Compston, 1973) and ~ 1573 ± 59 Ma (Sesha Sai, 2019) and (ii) alkaline magmatism represented by the emplacement of Mesoproterozoic lamproites, alkali syenites (Chalapathi Rao et al., 1996Rao et al., , 1999Rao et al., , 2012. ...
... The Mesoproterozoic lamproite fields, with most of the occurrences predating the~1.1 Gyr kimberlites in the EDC (Chalapathi Rao et al., 1996Rao et al., , 1999Osborne et al., 2011) are located at the northern and northwestern margin of the Cuddapah Basin viz., the Krishna, the Ramadugu and the Vattikod lamproite fields (Fig. 1). Additionally, the EDC also host the Banganapalle (Garledinne) lamproite field and isolated lamproite intrusions at Chelima and Zangamarajupalle-all within the Cuddapah Basin. ...
... Some of the kimberlite pipes from the WKF such as P-12 (Chintalampalle), P-2, P-5 (Muligiripalle), P-13 (Tummatpalle), TK-1 and TK-4 (Timmasamudram) are now reclassified as lamproites based solely on their mineralogy Mitchell, 2013, 2016;Shaikh et al., 2017), however, these rocks are distinct from the 'true lamproites' from the EDC (Krishna, Ramadugu, Vattikod and Cuddapah Basin lamproite fields) as the latter are characterized by the absence of groundmass perovskite as well as ultrapotassic nature (see Chalapathi Rao et al., 2020). Moreover, most of these 'true lamproites' from the Krishna, the Ramadugu, the Vattikod lamproite and the Cuddapah Basin fields pre-date the kimberlite magmatism (Kumar et al., 2001;Chalapathi Rao et al., 1996; unpublished data of the authors). It should be noted that the pipes P-5 (Muligiripalle, ɛNd i = 2.38 and ɛHf i = 3.50), P-12 (Chintalampalle, ɛNd i = 2.16 and ɛHf i = 3.97), and P-13 (Tummatpalle, ɛNd i = 2.38 and ɛHf i = 3.50) have Nd-Hf isotopic compositions similar to those of global kimberlites (Fig. 3b). ...
Kimberlites are volatile-rich deep mantle-derived rocks that often contain diamonds. Numerous Grenvillian (ca. 1.1 Gyr) diamondiferous kimberlites, ultramafic lamprophyres, and lamproites are exposed in the Eastern Dharwar Craton and the Bastar Craton, India, and are aligned almost parallel to the Eastern Ghats (granulite) Mobile Belt (EGMB). The trigger for these kimberlite and related magmatic events still remains an open question. We review the available geochronological and radiogenic isotopic data for the ~1.1 Gyr kimberlites, lamproites, and ultramafic lamprophyres from the Eastern Dharwar Craton and the Bastar Craton of the Indian shield. We show that kimberlites and associated magmas were emplaced for a longer duration (ca. 130 Myr) than previously thought in the Indian shield during the Mesoproterozoic and sampled distinct mantle source regions. The kimberlites and ultramafic lamprophyre are characterized by slightly depleted to chondritic Nd isotopic ratios revealing their origin at deeper sub-lithospheric regions, whereas the lamproites essentially show an enriched Nd isotopic signature suggesting their derivation from enriched sub-continental lithospheric mantle. We argue that the absence of linear age progression, prolonged magmatic activity compared to the time span of coeval large igneous provinces (the Umkondo, the Keweenawan, and the Warakurna) and a cooler ambient mantle as revealed from the entrained xenoliths, constitute important limitations for a plume model earlier proposed for the emplacement of these kimberlites and related magmas. These observations together with a geographical and temporal (Grenvillian) link to the EGMB points towards edge-driven convection as a trigger for kimberlite magmatism- similar to the model proposed for the Mid-Cretaceous kimberlite corridor in North America. However, this model can't explain the coeval formation of sub-continental lithospheric mantle-derived lamproites. As the timing of kimberlite and related magmatism coincides with that of the Grenvillian orogeny and succeeded a magmatic lull of ~360 Myr in the Dharwar Craton during the Mesoproterozoic, we instead, propose that small scale partial melting of heterogeneous mantle caused by plate reorganization during Columbia to Rodinia supercontinent extroversion served as a trigger for this ca. 1.1 Gyr magmatism in the southeastern Indian shield.
... Lamproites and associated rock suites have been reported from a number of regions in Peninsular India including the Eastern Dharwar Craton (Cuddapah, Krishna, Ramadugu and Vattikod) and Bastar Craton (Nuapada and Khadka) in central India, Bundelkhand Craton (Majhgawan, Hinota and Saptarshi lamproites) in northern India, Chhotanagpur in eastern India and Kutch basin in NW India (Chalapathi Rao et al., 1996, 2013, 2014a, 2014b, 2016a, 2016bYellappa et al., 2010;Karmalkar et al., 2014;Sahu et al., 2013;Satyanarayanan et al., 2017, and references therein). However, precise geochronological data are scarce on these rocks except for the Early Cretaceous (124-117 Ma) lamproites in the Damodar Valley and Kutch Basin (Kent et al., 1998;Karmalkar et al., 2014). ...
... Paleoproterozoic (ca. 1.88 Ga; Yellappa et al., 2010) to Mesoproterozoic ages (1500 Ma to 1090 Ma; Chalapathi Rao et al., 1996Rao et al., , 2014aRao et al., , 2014bOsborne et al., 2011;Sahu et al., 2013) have been assumed for the other occurrences. Sahu et al. (2013) reported an age of 1055 ± 10 Ma from the Nuapada lamproites in Bastar Craton based on whole rock 40 Ar/ 39 Ar isotopic analysis. ...
Potassic and ultrapotassic magmatism from deep lithospheric sources in intra-cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of Large Igneous Provinces (LIPs) triggered by mantle plumes. Here we report for the first time, precise zircon U–Pb age data from a suite of lamproites in the Bastar Craton of central India that mark the onset of Paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major LIP events
during the Precambrian evolution of the Indian shield. The lamproites from the Nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile, apatite and
zircon. The rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite. Geochemical features of the lamproites correlate with their counterparts in Peninsular India and other similar suites elsewhere in the world related to rift settings, and also indicate OIB-like magma source. The associated syenite shows
subduction-related features, possibly generated in a post-collisional setting. Magmatic zircon grains with high Th/U ratios in the syenite from the Nuapada lamproite form a coherent group with an upper intercept age of 2473 ± 8 Ma representing the timing of emplacement of the magma. Zircon grains in three lamproite samples yield four distinct age groups at ca. 2.4 Ga, 2.2 Ga, 2.0 Ga and 0.8 Ga. The 2.4 Ga group corresponds to xenocrysts entrained from the syenite whereas the 2.2 Ga group is considered to represent the timing of emplacement of the lamproites. The ca. 2.0 Ga zircon grains
correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern Bastar and the adjacent Dharwar Cratons. A few young zircon grains in the syenite and lamproites show a range of early to middle Neoproterozoic ages
from 879 to 651 Ma corresponding to younger thermal event(s) as also represented by granitic veins cutting across these rocks and extensive silicification. Zircon Lu–Hf isotope
data suggest magma derivation from a refertilized Paleo-Mesoarchean sub-continental lithospheric mantle, or OIB-type sources. The differences in Hf-isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale. A combination of the features from geochemical and zircon Hf isotope data is consistent with asthenosphere-lithosphere interaction during the lamproite magma evolution. The timing of lamproite emplacement in central India correlates with the global 2.2 Ga record of LIPs. We link the origin of the related mantle plume to the recycling of subducted
slabs associated with the prolonged subduction-accretion history prior to the Neoarchean cratonization, as well as the thermal blanket effect of the Earth’s oldest supercontinent. Pulsating plumes and continued rifting generated voluminous dyke swarms across the Bastar and Dharwar Cratons, forming part of a major global rifting and LIP event.
... Other kimberlites could also be the source of the diamonds. However, all the known kimberlites in the area have late Mesoproterozoic ages (Kumar et al. 1993(Kumar et al. , 2001Chalapathi Rao et al. 1996Kumar, Heaman & Manikeyamba, 2007;Babu et al. 2008), so if the occurrence of diamond in the Banganapalle Quartzite and that of sedimentary carbonate xenoliths in the kimberlites are to be reconciled with this, then the source of diamonds will apparently be the lamproites. Chalapathi Rao et al. (2010) suggested lamproitic rocks analogous to the ∼1417 Ma Chelima lamproites (Chalapathi Rao et al. 1999) as the source of the diamonds in the Banganapalle Quartzite. ...
... The sediments in the Kurnool sub-basin were probably deposited later in the Mesoproterozoic, most likely after the emplacement of the kimberlites of the EDC at c. 1100 Ma (Kumar et al. 1993(Kumar et al. , 2001Chalapathi Rao et al. 1996Kumar, Heaman & Manikeyamba, 2007;Babu et al. 2008), consistent with diamond occurrence in the Banganapalle Quartzite in the Kurnool sub-basin as well as with the report of Ediacaran fossils in the Owk Shale (Sharma & Shukla, 2012). ...
The Cuddapah basin in southern India, consisting of the Palnad, Srisailam, Kurnool and Papaghni sub-basins, contains unmetamorphosed and undeformed sediments deposited during a long span of time in the Proterozoic. In the absence of robust age constraints, there is considerable confusion regarding the relative timing of sedimentation in these sub-basins. In this study, U–Pb isotopic dating of zircon and U–Th–Pb total dating of monazite and uraninite from the gritty quartzite that supposedly belongs to the formation Banganapalle Quartzite have been used to constrain the beginning of sedimentation in the Palnad sub-basin. Magmatic and detrital zircons recording an age of 2.53 Ga indicate that the sediments were derived from the granitic basement or similar sources and were deposited after 2.53 Ga. Hydrothermally altered zircons both in the basement and the cover provide concordant ages of 2.32 and 2.12 Ga and date two major hydrothermal events. Thus, the gritty quartzite must have been deposited sometime between 2.53 and 2.12 Ga and represents the earliest sediments in the Cuddapah basin. Monazite and uraninite give a wide spectrum of ages between 2.5 Ga and 150 Ma, which indicates several pulses of hydrothermal activity over a considerable time span, both in the basement granite and the overlying quartzite. The new age constraints suggest that the gritty quartzite may be stratigraphically equivalent to the Gulcheru Quartzite that is the oldest unit in the Cuddapah basin, and that a sedimentary/erosional hiatus exists above it.
... All the kimberlites and lamproites so far discovered in south India are on the Eastern Dharwar Craton (Fig. 1). Reddy (1987) has suggested previously P-2 and P-5 kimberlites to be lamproites and recent reports on detailed mineralogy of P-2 kimberlite from the Wajrakarur kimberlite field (Mitchell 2010;Fareeduddin and Mitchell 2012) indicates its affinity more towards a lamproitic magma in contrast to a archetypal kimberlite as suggested by earlier workers (Rao and Phadtre 1966;Murthy et al. 1980;Smith 1989;Chalapathi et al. 1996;Fareeduddin 2008;Ravi et al. 2009). These new results on P-2 kimberlite from Wajrakarur have prompted detailed petrographic studies of the other kimberlite bodies in the region with a view to classifying them in their appropriate slots in the mineralogic-genetic classification scheme of ultrapotassic rocks. ...
... The kimberlites are capped by 0.5 m-1.5-m thick calcrete. Kimberlites of WKF are of middle to late Proterozoic age ranging from 840 to 1,153 Ma (Paul et al. 1975;Kumar et al. 1993Kumar et al. , 2007Chalapathi Rao et al. 1996Paul et al. 2006;Ravi et al. 2009;Fareeduddin and Mitchell 2012). ...
To date, all the potassic-ultramafic pipes from the Wajrakarur Kimberlite Field (WKF),
Eastern Dharwar Craton (EDC), India, have been classified as kimberlites. Recent
reclassification of a kimberlite pipe P-2 from the WKF as a lamproite necessitated a reexamination
at the other kimberlite bodies in the region with a view to placing them in their
appropriate slots in the mineralogic-genetic classification scheme of ultrapotassic rocks. The
Pipes P-5 and P-13 of Lattavaram cluster in WKF were chosen for this present work. Both
pipes exhibit macrocrystal textures and have two generations of olivine. The prominent
groundmass minerals constitute spinel, perovskite, phlogopite, apatite, pyroxene, serpentine,
chlorite and calcite/magnesite. The phlogopites from both the pipes are low in aluminium and
barium, are high in total iron in comparison to archetypal kimberlites and follow lamproite
trends. The pipes are characterized by the groundmass spinels of four varieties, for example,
ulvöspinel, Mg-ulvöspinel, Mg-Cr-spinel and magnetites. Both the pipes have atoll and
necklace-textured spinels besides the euhedral groundmass spinels. These spinels exhibit
compositional trends identical to those found in kimberlite magmatic trend T2. Perovskites
with bimodal size distribution occur as discrete grains throughout the rock. The two pipes
represent polyphase intrusions that are in close proximity within Lattavaram region. The
mineral chemistry data of phlogopites, spinels, perovskites and pyroxenes from these pipes
are more akin to those in lamproite magmas rather than that in archetypal (Group-1)
kimberlites. Thus, a careful reassessment of the petrological characteristics of all the
45 kimberlitic pipes so far discovered in the EDC is necessary keeping in view the economic
and academic importance of these pipes due to their diamond and mantle xenolith potential.
... All the kimberlites and lamproites so far discovered in south India are on the Eastern Dharwar Craton (Fig. 1). Reddy (1987) has suggested previously P-2 and P-5 kimberlites to be lamproites and recent reports on detailed mineralogy of P-2 kimberlite from the Wajrakarur kimberlite field (Mitchell 2010;Fareeduddin and Mitchell 2012) indicates its affinity more towards a lamproitic magma in contrast to a archetypal kimberlite as suggested by earlier workers (Rao and Phadtre 1966;Murthy et al. 1980;Smith 1989;Chalapathi et al. 1996;Fareeduddin 2008;Ravi et al. 2009). These new results on P-2 kimberlite from Wajrakarur have prompted detailed petrographic studies of the other kimberlite bodies in the region with a view to classifying them in their appropriate slots in the mineralogic-genetic classification scheme of ultrapotassic rocks. ...
... The kimberlites are capped by 0.5 m-1.5-m thick calcrete. Kimberlites of WKF are of middle to late Proterozoic age ranging from 840 to 1,153 Ma (Paul et al. 1975;Kumar et al. 1993Kumar et al. , 2007Chalapathi Rao et al. 1996Paul et al. 2006;Ravi et al. 2009;Fareeduddin and Mitchell 2012). ...
To date all the potassic-ultramafic pipes from the Wajrakarur Kimberlite Field, Eastern
Dharwar Craton, India, have been classified as kimberlites. Recent reclassification of a
kimberlite pipe P-2 from the Wajrakarur kimberlite field as a lamproite necessitated a
re-examination at the other kimberlite bodies in the region with a view to placing them
in their appropriate slots in the mineralogic-genetic classification scheme of
ultrapotassic rocks. The Pipes P-5 and P-13 of Lattavaram cluster in Wajrakarur
Kimberlite Field were chosen for this present work. Both pipes exhibit macrocrystal
textures and have two generations of olivine. The prominent groundmass minerals
constitute spinel, perovskite, phlogopite, apatite, pyroxene, serpentine, chlorite and
calcite/magnesite. The phlogopites from both the pipes are low in aluminium and
barium, and are high in total iron in comparison to archetypal kimberlites and follow
lamproite trends. The pipes are characterized by the groundmass spinels of four
varieties, e.g., ulvöspinel, Mg-ulvöspinel, Mg-Cr-spinel and magnetites. Both the pipes
have atoll and necklace textured spinels besides the euhedral groundmass spinels.
These spinels exhibit compositional trends identical to those found in kimberlite
magmatic trend T2. Perovskites with bimodal size distribution occur as discrete grains
throughout the rock. The two pipes represent polyphase intrusions that are in close
proximity within Lattavaram region. The mineral chemistry data of phlogopites, spinels,
perovskites and pyroxenes from these pipes are more akin to those in lamproite
magmas rather than that in archetypal (Group I) kimberlites. Thus a careful
reassessment of the petrological characteristics of all the 45 kimberlitic pipes so far
discovered in the Eastern Dharwar Craton is necessary keeping in view the economic
and academic importance of these pipes due to their diamond and mantle xenolith
potential.
... See Analytical Techniques in Chalapathi Rao et al. (2004) for further details of procedures. Ages of emplacement (Chalapathi Rao et al., 1996Rao et al., , 1998 The comments relating to the analytical procedures used in the determination of Sr isotopes are almost identical to those raised by and we refer the reader to Chalapathi Rao et al. (1999a) for our responses. We state clearly in Chalapathi Rao et al. (2004) that 'we are cautious about interpreting the petrogenetic significance of these (Sr isotope) ratios' and our interpretations of melt generation processes and mantle source characteristics are based on rare-earth elements (REE) and Nd isotopic ratios, which are less susceptible to alteration. ...
... Nevertheless, Anil Kumar & Gopalan (2005) disagree with the ages that we have used to correct Sr and Nd isotopic ratios from measured to initial values. They state that Rb-Sr ages published for the lamproites by Anil Kumar et al. (2001) are 'only provisional' and we therefore prefer to use our previously published age determinations (Chalapathi Rao et al., 1996Rao et al., , 1999b as we are familiar with the petrography of the dated samples and are able to assess the quality of the data. The phlogopites in the groundmass of our samples from the Chelima lamproite have not undergone extensive secondary carbonation and we did not [as implied by Anil Kumar & Gopalan (2005)] undertake acid leaching on this phase prior to Ar/Ar age dating. ...
Proterozoic mafic potassic and ultrapotassic igneous rocks implaced at the Cuddapah Basin and Dharwar Craton of the southern Indian shield are among the earliest recorded on Earth. Lamproiles intrude the basin and its NE margin, whereas kimberlites intrude the craton to the west of the basin. Kimberlites occur in two spatially separate groups: the non-diamondiferous Mahbubnagar cluster that was emplaced at 1400 Ma and is of a similar age to the Cuddapah lamproites, and the predominantly diamondiferous Anantapur cluster, emplaced at ∼1100 Ma. Despite their Proterozoic ages, some of the kimberlites are petrographically fresh. Distinct variations are evident in the major and trace element concentrations ofthe diamondiferous and non-diamondiferous kimberlites. The latter have higher concentrations of Fe, Ti, Zr, Hf and Sc, and lower Ni contents and La/Sm ratios. All of the kimberlites have high La/Yb ratios (65-180) and positive εNdi values (0.5-4.5), which suggests that their source regions were metasomatized by small-fraction melts derived from the depleted upper mantle, shortly prior to kimberlite genesis. Cuddapah Basin lamproites have similar La/Yb ratios but much lower εNdi values (-6 to -7) and appear to have been derived from ancient metasomatized sub-continental lithospheric mantle. The Proterozoic ambient mantle is believed to have had a higher potential temperature than at the present day such that small amounts of lithospheric extension may account for the genesis of the kimberlites and lamproites of southern India without the need for a mantle plume.
... The EDC is relatively younger and lesser in thickness in comparison of WDC ( Kaila et al., 1979 ) and comprises of long linear regional structures such as CG, greenstone belts and mafic dyke of different episodes of Paleo-proterozoic magmatic activities together with Meso-proterozoic intrusions of Kimberlite Clan of Rocks (KCR). The age of these KCR is in between 1.38 and 1.1 Ga as per existing geo-chronological data set ( Paul et al., 1975 ;Basu and Tatsumato, 1979 ;Kumar et al., 1993 ;Chalapathi Rao et al., 1996 ;Kumar et al., 2007 ;Babu et al., 2008 ;Chalapathi Rao et al., 2012 ;Osborne et al., 2011Osborne et al., , 2013. The WKF is a classic example of Archaean Granite-Greenstone terrain ( Murthy et al., 1987 ; imposed by quartz reefs, dykes and basement rock PGC-II of EDC. ...
The Ground magnetic study in the Wajrakarur Kimberlite Field and adjoining area has unveiled prominent
geological variations, including felsic doming beneath the PGC-II formation to the west of the Cuddapah
Basin and mafic doming beneath the Closepet Granite zone. These doming features within the upper
mantle are identified as sources of mantle upwelling, which influence the emplacement of corresponding
intrusive rocks. The presence of mafic chambers enhances the magnetic response, leading to localized
high signatures in magnetic data and contributes to a better understanding of the subsurface composition and distribution of rock types. The present magnetic data throw lights to study the complexity
of the sub-surface structure and geological activities, have shaped the study area and serve as valuable
markers for understanding the geological evolution of the area. The intersections of magnetic lineament
oriented in NW-SE, NE-SW, E-W yield crucial insights into geological structures and the emplacement of
Kimberlite intrusions. Through comprehensive magnetic data analysis, the study offers a unique cross-sectional view of the subsurface, reaching depth up to 60 km. This perspective unveils magnetic sources
and structures, revealing shallow features, interfaces of the Archaean basement, crustal roots, and upper mantle configuration. Profound magnetic gradients observed in the study area serve as indicators of
fault lines influenced by tectonic activity, kimberlite intrusion, and other fault-related mineralization if
any. These features contribute to a deeper understanding of the structural configurations and geological
history of the area. The present study provides information about the lateral and vertical layouts of major structures as well as the deep-seated channels. It also introduces the mafic and felsic categories of
rocks, explaining the complex relationships between underlying structures, geological characteristics, and
magnetic anomalies.
... The ca. 1.2 Ga kimberlites in the Indian craton (Paul et al., 1975;Chalapathi Rao et al., 1996) indicate an important mantle upwelling episode that resulted in the final disintegration of the Columbia supercontinent (Zhao et al., 2002(Zhao et al., , 2004. The fragments from the breakup of Columbia were proposed to re-amalgamate to form Rodinia at ca. 1.2-0.9 ...
The Meso-Neoproterozoic Rodinia supercontinent formed a coherent large landmass, which was later dispersed over all current major continents and a number of microcontinents. The Qinling block is a Precambrian continental mass, located in the Qinling orogenic belt, which marks the junction of the North China and South China cratons. In this paper, we present a systematic study of the petrology, whole-rock geochemistry and geochronology of metasedimentary rocks from the Xiahe Group, which is a key unit of the Precambrian basement in the Qinling block, to constrain the paleogeographic reconstruction of Rodinia. The studied metasedimentary rocks have detrital zircon ages of 3054–1082 Ma that peak at 1172 Ma and 1582 Ma. The protoliths of the metasedimentary rocks are mainly shales and wackes with maximum depositional ages from 1147 to 1082 Ma, representing a part of a continental arc-related sedimentary sequence. Combining our results with existing data, we propose that their protoliths constituted a sedimentary series including an older sequence of basement and a younger sequence with depositional ages between 1262 and 840 Ma. The detritus that is older than 1266 Ma was sourced from the continental margin of the Indian craton, which was part of the Columbia supercontinent. There was a Paleo-Mesoproterozoic continental nucleus in the Qinling block that split from the margin of the Indian craton during the breakup of Columbia. The source rocks for the younger detritus were arc magmatic rocks in the Qinling block, which formed in a continental arc by oceanic lithosphere subduction during the assembly of Rodinia. A sequence of oceanic subduction beneath the continental nucleus of the Qinling block (1262–981 Ma), arc-continent collision between the continental nucleus and the Indian craton (981–911 Ma), continuous subduction of oceanic crust beneath the block with formation of a mature volcanic arc (929–833 Ma), and continental rifting (833–774 Ma) during the formation of the Qinling block was identified. The block faced the Neoproterozoic ocean during the assembly of Rodinia, and finally rifted off the supercontinent during its breakup to form an isolated arc terrane
... The WKF kimberlites are of Mesoproterozoic age, ca. 1110 Ma, and are hosted in gneisses of the southern part of the Dharwar Craton (Chalapathi Rao et al., 1996). The EDC of southern India host a large number of Proterozoic kimberlites intrusions, and > 100 kimberlites were reported (Gopalan and Kumar, 2008;Ravi et al., 2018), Fig. 1. ...
... Zachariah et al. (1999) proposed 1756±29 Ma, Pb-Pb date of the dolomite hosted Ur mineralized horizons of Vempalle and Tadpatri Formation. An upper age constraint of 1400 Ma for the Cuddapah deposition is provided by the ages for lamproite dykes intrusive to Cumbum shale, between 1354 and 1418 Ma (Chalapathi Rao et al., 2016Rao et al., , 1996Kumar et al., 2001). The uppermost limit of the sedimentation in the Kurnool Group is assumed to be >1.1Ga, ...
The Proterozoic cratonic basins of peninsular India
preserve records of repeated opening and closing of rifts
along the zone of Neoarchean sutures and/or along the
weak zones. These sedimentary basins, ranging in age
from late Palaeoproterozoic through Neoproterozoic are
traditionally referred to as Purana basins in Indian
literature. The successions of each of the basins may be
represented by successive unconformity-bound
sequences, which represent several cycles of fluvial-
shallow marine to shelf-slope-basin sedimentation
punctuated by local hiatuses and/or volcanic upheavals.
The advance retreat of ancient seaways and their complex
are recorded in the sedimentary successions of Purana
Basins.
Papaghni-Chitravati; Kaladgi-Badami; Lower
Vindhyan record the oldest cycle of sedimentation. These
basins opened after 2.0 Ga and closed by 1.55 Ga. The
Chattisgarh and its satellite basins, namely Indravati;
Khariar; Ampani opened after the 1.6 Ga. and closed
shortly after the 1000 Ma. Albaka; Mallampalli;
Kurnool; Bhima preserve Neoproterozoic sedimentation
history. The upper Vindhyan basin likely opened after
1.4 Ga. and continued through the Neoproterozoic. The
sequence of events indicates a close relationship of craton
interior histories with plate tectonics and variations in
the heat flow regime underneath the continental crust.
Periods of formation of the cratonic basins are coincident
with the amalgamation or fragmentation of
supercontinents further indicates genetic linkage between
the two processes. Synchronous development of the
cratonic basins with closely comparable stratigraphy and
basin development events, in different small continents, strengthens the view that basin formation processes
operated on a global scale, and stratigraphic basin
analysis on a regional scale is a significant tool in
evaluating the basins’ history. The available
stratigraphic, geochronologic or palaeomagnetic data
from India is still inadequate, and further information is
required to constrain its definite position in the context
of global tectonics.
... Zachariah et al. (1999) proposed 1756±29 Ma, Pb-Pb date of the dolomite hosted Ur mineralized horizons of Vempalle and Tadpatri Formation. An upper age constraint of 1400 Ma for the Cuddapah deposition is provided by the ages for lamproite dykes intrusive to Cumbum shale, between 1354 and 1418 Ma (Chalapathi Rao et al., 2016Rao et al., , 1996Kumar et al., 2001). The uppermost limit of the sedimentation in the Kurnool Group is assumed to be >1.1Ga, ...
... The Proterozoic rock successions of EDC constitute of mafic dike swarms, Cuddapah Basin, and potassic to ultrapotassic alkaline rocks (Chalapathi Rao, 2008;Chalapathi Rao, Miller, Pyle, & Madhavan, 1996;Chalapathi Rao, Miller, Gibson, Pyle, & Madhavan, 1999;Kumar, Heaman, & Manikyamba, 2007, and references therein;Chalapathi Rao, Wu, et al., 2013). Recent studies show that the Eastern Dharwar Craton is furthur subdivided into central and eastern Dharwar Province (Dey, 2013;Jayananda et al., 2013;Jayananda, Santosh, & Aadhiseshan, 2018). ...
... The western Dharwar craton (WDC) hosts Paleo-Mesoarchean granitoids and older greenstone belts as compared to the eastern Dharwar craton (EDC) with Neoarchean granitoids, known as the Dharwar Batholith and parallel trending intra arc originated greenstone belts (Chadwick et al., 2000). Five distinct Paleoproterozoic mafic dyke swarms, Paleo-Mesoproterozoic crescent shaped Cuddapah Basin and Mesoproterozoic (1.3-1.1 Ga) alkaline rocks such as kimberlites and lamproites constitute the Proterozoic lithostratigraphy of the EDC (Chalapathi Rao et al., 1996Rao et al., , 1999Kumar et al., 2007;Osborne et al., 2011). ...
Lamprophyres from the greenstone belts play a crucial role in deciphering tectonic and geodynamic processes operating during the Archean. This study presents a comprehensive mineralogical and geochemical study of three lamprophyre dykes with calc-alkaline to shoshonitic affinities from the Neoarchean Kadiri schist belt, eastern Dharwar craton, southern India. These rocks display porphyritic-panidiomorphic texture, typical of the lamprophyres with amphibole (magnesio-hornblende) as phenocrysts, biotite as microphenocrysts and feldspar, epidote, titanite and apatite confined to the groundmass. Alteration of biotite to chlorite is observed along with mild deformation in the amphibole phenocrysts. Based on mineralogy and major oxide geochemistry, these rocks are classified as the calc-alkaline lamprophyres. Higher Ba/Nb and low Nb/La points to their derivation from an enriched lithospheric mantle source and higher Th/Yb ratio along with negative TNT (Ti-Nb-Ta) and Zr-Hf anomalies on the primitive mantle (PM) normalized multi-element diagram indicates dehydrated fluids from the foundering slab could be the possible metasomatic agent. Fractionated HREE ratios (GdN/YbN >1.9) and higher SmN/YbN suggests that the source region lies in the garnet stability field. Higher than PM Rb/Sr along with positive correlation between K/La and Rb/La reveals presence of metasomatic phlogopite in the source region. Strong negative initial εNd along with radiogenic 87Sr/86Sr ratios further support an enriched mantle reservoir involved in their genesis. Non-modal batch melting (1–5%) of a mixed source (phlogopite-garnet peridotite) assuming 5% mixing of subducted sediment with ambient mantle wedge (depleted mantle) satisfies the multi-element concentration pattern shown by the Kadiri lamprophyres. The source enrichment can be linked to the accretion-related growth of Dharwar craton and its schist belts during Neoarchean. Our study shows that a majority of lamprophyres associated with the Archean greenstone belts display a shoshonitic character; this highlights the role of subduction-related processes in the growth and evolution of the greenstone belts
... The VLF is a separate cluster a few kilometers east of the RLF and, therefore, allows to study the relation between these two fields. The lamproites in the EDC range from 1.25 to 1.4 Ga in age, preceding the kimberlite magmatism at ~ 1.1 Ga (Chalapathi Rao et al. 1996Rao et al. , 1999Rao et al. , 2013Rao et al. , 2014Rao et al. , 2016aKumar et al. 2001;Osborne et al. 2011;Phillips 2012). ...
... The VLF is a separate cluster a few kilometers east of the RLF and, therefore, allows to study the relation between these two fields. The lamproites in the EDC range from 1.25 to 1.4 Ga in age, preceding the kimberlite magmatism at ~ 1.1 Ga (Chalapathi Rao et al. 1996Rao et al. , 1999Rao et al. , 2013Rao et al. , 2014Rao et al. , 2016aKumar et al. 2001;Osborne et al. 2011;Phillips 2012). ...
Numerous lamproite dykes are hosted by the Eastern Dharwar Craton, southern India, particularly towards the northwestern
margin of the Cuddapah Basin. We present here a comprehensive mineralogical and geochemical (including Sr and Nd
isotopic) study on the lamproites from the Vattikod Field, exposed in the vicinity of the well-studied Ramadugu lamproite
field. The Vattikod lamproites trend WNW–ESE to NW–SE and reveal effects of low-temperature post-magmatic alteration.
The studied lamproites show porphyritic texture with carbonated and serpentinized olivine, diopside, fluorine-rich phlogopite,
amphibole, apatite, chromite, allanite, and calcite. The trace-element geochemistry (elevated Sr and HFSE) reveals
their mixed affinity to orogenic as well as anorogenic lamproites. Higher fluorine content of the hydrous phases coupled
with higher whole-rock K2O
highlights the role of metasomatic phlogopite and apatite in the mantle source regions. Traceelement
ratios such as Zr/Hf and Ti/Eu reveal carbonate metasomatism of mantle previously enriched by ancient subduction
processes. The initial 87Sr/86Sr-isotopic ratios (calculated for an assumed emplacement age of 1350 Ma) vary from 0.7037 to
0.7087 and ɛNd range from − 10.6 to − 9.3, consistent with data on global lamproites and ultrapotassic rocks. We attribute
the mixed orogenic–anorogenic character for the lamproites under study to multi-stage metasomatism. We relate the (1)
earlier subduction-related enrichment to the Paleoproterozoic amalgamation of the Columbia supercontinent and the (2)
second episode of carbonate metasomatism to the Mesoproterozoic rift-related asthenospheric upwelling associated with the
Columbia breakup. This study highlights the association of lamproites with supercontinent amalgamation and fragmentation
in the Earth history.
... The earliest attempt to date magmatic rocks of the Cuddapah basin by radiometric systematics was made by Aswathanarayana (1962a, b) and was followed by a number of workers (e.g., Crawford and Compston, 1973;Murthy et al., 1987;Bhaskar Rao et al., 1995;Chalapathi Rao et al., 1996. Crawford and Compston (1973) proposed an Rb-Sr age of w1550 AE 147 Ma for the mafic flows of Vempalle Formation later on revised by Bhaskar using the same Rb-Sr systematics on differentiated sills from Tadpatri Formation and gave a much older age of 1817 AE 24 Ma. ...
This study reports major, trace, rare earth and platinum group element compositions of lava flows from the Vempalle Formation of Cuddapah Basin through an integrated petrological and geochemical approach to address mantle conditions, magma generation processes and tectonic regimes involved in their formation. Six flows have been identified on the basis of morphological features and systematic three-tier arrangement of vesicular-entablature-colonnade zones. Petrographically, the studied flows are porphyritic basalts with plagioclase and clinopyroxene representing dominant phenocrystal phases. Major and trace element characteristics reflect moderate magmatic differentiation and fractional crystallization of tholeiitic magmas. Chondrite-normalized REE patterns corroborate pronounced LREE/HREE fractionation with LREE enrichment over MREE and HREE. Primitive mantle normalized trace element abundances are marked by LILE-LREE enrichment with relative HFSE depletion collectively conforming to intraplate magmatism with contributions from sub-continental lithospheric mantle (SCLM) and extensive melt-crust interaction. PGE compositions of Vempalle lavas attest to early sulphur-saturated nature of magmas with pronounced sulphide fractionation, while PPGE enrichment over IPGE and higher Pd/Ir ratios accord to the role of a metasomatized lithospheric mantle in the genesis of the lava flows. HFSE-REE-PGE systematics invoke heterogeneous mantle sources comprising depleted asthenospheric MORB type components combined with plume type melts. HFSE-REE variations account for polybaric melting at variable depths ranging from garnet to spinel lherzolite compositional domains of mantle. Intraplate tectonic setting for the Vempalle flows with P-MORB affinity is further substantiated by (i) their origin from a rising mantle plume trapping depleted asthenospheric MORB mantle during ascent (ii) interaction between plume-derived melts and SCLM (iii) their rift-controlled intrabasinal emplacement through Archean-Proterozoic cratonic blocks in a subduction-unrelated ocean-continent transition zone (OCTZ). The present study is significant in light of the evolution of Cuddapah basin in the global tectonic framework in terms of its association with Antarctica, plume incubation, lithospheric melting and thinning, asthenospheric infiltration collectively affecting the rifted margin of eastern Dharwar Craton and serving as precursors to supercontinent disintegration.
... We have used the published data sets of CIP as well as Mudigubba lamprophyres throughout this paper for making an effective comparison with the lamprophyre under this study. The lamprophyre dyke of this study was reported by the Geological Survey of India (Ravi et al., 1998) Rao et al., 1996Rao et al., , 2016Kumar et al., 1993Kumar et al., , 2007Osborne et al., 2011). The ...
Mineralogy and geochemistry of the Udirpikonda lamprophyre, located within the Mesoproterozoic diamondiferous Wajrakarur kimberlite field (WKF), towards the western margin of the Paleo-Mesoproterozoic Cuddapah basin are presented. The lamprophyre is characterised by a panidiomorphic-porphyritic texture imparted by clinopyroxene, olivine and biotite set in a groundmass of feldspar and spinel. Olivine occurs as the microphenocrysts with a composition range of Fo87–78. Clinopyroxenes display reverse as well as oscillatory optical zoning and are diopsidic in nature with a variation in the composition from core (Wo47 En28 Fs20Ac5) to rim (Wo46En41Fs11Ac3). Biotite (Mg# < 0.6) is the only mica present and spinels are titano-magnetites showing ulvospinel- magnetite solid solution. Plagioclase is the dominant feldspar with a variable compositional range of An41–8Ab82–56Or33–3. Based on the mineralogy, the lamprophyre can be classified to be of calc-alkaline variety but its geochemistry display mixed signals of both alkaline and calc-alkaline lamprophyres. K2O/Na2O ranges from 1.49 to 2.79, making it distinctly potassic and highlights its shoshonitic character. Moderate Mg# (60–65), Ni (110–200 ppm) and Cr (110–260 ppm) contents in the bulk-rock indicate substantial fractional crystallization of olivine and clinopyroxene. Fractionated chondrite normalized REE patterns (average (La/Yb)N = 37.56) indicates involvement of an enriched mantle source from within the garnet stability field whereas slightly negative Ta-Nb-Ti and Hf anomalies displayed on the primitive mantle normalized multi-element spider gram highlight involvement of a subducted component in the mantle source. Given the spatial disposition of the studied lamprophyre, the age of the emplacement is considered to be coeval with WKF kimberlites (~ 1.1 Ga) and the initial ¹⁴³Nd/¹⁴⁴Nd (0.510065–0.510192) and ⁸⁷Sr/⁸⁶Sr (0.705333–0.706223) are strikingly similar to those observed for the Smoky Butte lamproites, Montana, USA. Fluid-related subduction enrichment of the mantle source is apparent from the enriched ratios of La/Nb, Ba/Nb and (Hf/Sm)N, (Ta/La)N < 1. Petrogenetic modelling reveals melt generation from 1 to 2% partial melting of an enriched mantle source that subsequently underwent fractional crystallization. Our study provides geochemical and isotopic evidence for a sub-continental lithospheric mantle (SCLM) modified by subduction and asthenospheric upwelling in the Eastern Dharwar Craton. The partial melting of a resulting heterogeneous Eastern Dharwar Craton SCLM to generate Udiripikonda lamprophyre and Wajrakarur kimberlites has been attributed to the Mesoproterozoic regional lithospheric extension event.
... Shaded field represents P-T data form mantle xenoliths reported by Ganguly and Bhattacharya (1987) and Nehru and Reddy (1989 Rao et al., 2013b and references therein), only six intrusions including two each from the KLF, NLF and RLF, have so far been dated among the lamproites. These dated lamproites have yielded Rb-Sr phlogopite ages in the range of 1400-1070 My (Anil Kumar et al. 2001), and K-Ar and 40 Ar/ 39 Ar phlogopite ages in the range of 1500-1400 My (Chalapathi Rao et al. 1996Osborne et al. 2011). However, Phillips (2012 noted that the age of1 500 Ma reported by Osborne et al. (2011) was an overestimate and that the studied lamproite was emplaced at b 1400 Ma. ...
A mineralogical study of the hypabyssal facies, late Cretaceous macrocrystic pulse of TK1 intrusion and the Mesoproterozoic aphanitic pulse of TK4 intrusion in the Wajrakarur Kimberlite Field of southern India shows that the rocks contain macrocrysts of forsteritic olivine, phenocrysts and microphenocrysts of AlNa-poor diopside and phlogopite set in a groundmass mainly of AlNa-poor diopside and phlogopite. Other groundmass minerals are spinel, perovskite and fluorapatite in TK1, and spinel, titanite, chlorite, calcite and gittinsite in TK4. K-richterite and perovskite occur only as inclusions in phlogopite and titanite, respectively in TK4. Late-stage deuteric phases include pyrite and barite in TK1, and strontianite, chalcopyrite, galena and pentlandite in TK4. Diopside microphenocrysts in TK4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth. TK1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite, whereas TK4 spinels are less evolved with magnesiochromite composition only. TK1 phlogopites show a simple compositional trend that is typical of lamproite micas, while four distinct growth zones are observed in TK4 phlogopites with the following compositional characteristics: zone I: high Cr2O3 and TiO2 and low BaO; zone II: low Cr2O3; zone III: low TiO2 and high BaO; zone IV: low BaO. Forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for TK1 olivines. Mineralogically, both TK1 and TK4 are classified as diopside–phlogopite lamproites rather than archetypal kimberlites. The two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions. With elevated content of Fe3 + in phlogopite, spinel and perovskite, TK1 appears to have crystallised in a relatively high oxygen fugacity environment. Multiple growth generations of phlogopite, spinel and fluorapatite in TK4 indicate a complex evolutionary history of the magma. Close spatial and temporal associations of Mesoproterozoic kimberlites and lamproites in southern India can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting.
... 1,100 Ma that have been obtained for a number of kimberlites and lamproites of the Dharwar Craton (Chalapathi Rao et al. 1999;Kumar et al. 2007). The Krishna lamproites have yielded Rb-Sr phlogopite ages in the range of 1,100-1,400 My (Kumar et al. 2001) and K-Ar and 40 Ar/ 39 Ar phlogopite ages in the range of 1,400-1,500 My (Chalapathi Rao et al. 1996;Osborne et al. 2011). However, Phillips (2012) commented that the age of *1500 Ma reported by Osborne et al. (2011) was an overestimate and that the studied lamproite was emplaced at \1,400 Ma. ...
This work presents the first mineralogical, geochemical and 40Ar/39Ar geochronological data on hypabyssal facies lamproites near Kalmidadar and Darlimunda in the Nuapada Lamproite Field of the Bastar Craton. The Kalmidadar lamproite is a diamondiferous intrusion with surface dimension of ~320 m × 160 m, whereas the Darlimunda lamproite is a dyke swarm comprising clusters of several narrow (<5 m wide) and elongated bodies. Indicator mineral suite around the Kalmidadar lamproite is marked by abundance of Cr-spinel, rarity of garnet and absence of Cr-diopside and picroilmenite. Mineralogically, the Kalmidadar lamproite comprises phenocrysts of olivine (pseudomorphed by calcite and talc) and microphenocrysts of phlogopite set in a groundmass of chlorite and calcite. The phlogopite is Ti rich (5.4–7.4 wt % TiO2), and the relationship between its Ti content and octahedral site deficiency indicates two substitution mechanisms, viz. Ti + ▭ ↔ 2 Mg and Ti + 2Al ↔ Mg + 2Si. The Darlimunda lamproites have undergone pervasive hydrothermal and/or deuteric alteration, which has resulted in complete chloritisation of phlogopite and extensive silicification of the rocks. Tiny grains of rutile and apatite are commonly scattered in the groundmass of both Kalmidadar and Darlimunda lamproites. The Nuapada lamproites have high contents of compatible elements such as V, Cr and Ni and of incompatible elements such as Ba, Zr, Nb and Hf. They also show high abundance of REE and enrichment in LREE relative to HREE. The incompatible element distribution patterns of the lamproites are marked by Nb, Sr, P, Hf and Zr anomalies relative to REE. The observed petrological and geochemical characteristics of the Nuapada lamproites are consistent with the derivation of the magma from a metasomatised subcontinental lithospheric mantle source. Whole-rock 40Ar/39Ar isotopic data yields an age of 1055 ± 10 Ma for the Nuapada lamproites.
... Ultrapotassic rocks belonging to four distinct ages have so far been recorded from the Indian cratons and mobile belts ( Fig. 1a): (i) Mesoproterozoic (ca. 1350-1400 Ma) lamproites from the Eastern Dharwar craton and the Cuddapah basin, southern India (Chalapathi Rao et al. 1996Rao et al. , 1999Kumar et al. 2001;Osborne et al. 2011); (ii) Mesoproterozoic (ca. 1055-1090 Ma) lamproites from the Bundelkhand and Bastar cratons, central India, and the Cuddapah basin, southern India (Anil Kumar et al. 1993;Chalapathi Rao 2005;Masun et al. 2009;Sahu et al. 2013), (iii) Neoproterozoic (ca. ...
We report the mineralogy, bulk-rock geochemistry, 40Ar/39Ar (whole-rock) age and radiogenic (Sr and Nd) isotope composition of an ultrapotassic dyke from Sakri (Nuapada lamproite field) located at the tectonic contact between the easternmost margin of the Bastar craton and Eastern Ghats Mobile Belt, India. The Sakri dyke has a mineralogy which strongly resembles a lamproite sensu stricto (viz.,Ti-rich phlogopite, Na-poor diopside, Fe-rich sanidine, ulvospinel trend and Sr-rich apatite). However, its bulk-rock major element geochemical characteristics (viz., extreme silica-undersaturated nature) resemble sensu lato kamafugite from Toro Ankole, Uganda, East African Rift, and Alto Paranaiba Province, Brazil. The Sakri dyke also displays certain compositional peculiarities (viz., high degree of evolution of mica composition from phlogopite to biotite, elevated titanium and aluminum in clinopyroxene and significantly lower bulk Mg#) when compared to the ultrapotassic rocks from various Indian cratons. 40Ar/39Ar dating gave a plateau age of 1045 ± 9 Ma which is broadly similar to that of other Mesoproterozoic (i) lamproites from the Bastar and Bundelkhand cratons, and (ii) kimberlites from the Eastern Dharwar craton. Initial bulk-rock Sr (0.705865–0.709024) and Nd (0.511063–0.511154) isotopic ratios reveal involvement of an ‘enriched’ source region with long-term incompatible element enrichment and a depleted mantle (TDM) Nd model age of 2.56 Ga straddling the Archaean-Proterozoic chronostratigraphic boundary. The bulk-rock incompatible trace element ratios (Ta/Yb, Th/Yb, Rb/Ba and Ce/Y) of the Sakri ultrapotassic dyke negate any significant influence of crustal contamination. Small-degree melting (1 to 1.5 %) of a mixed garnet-facies and spinel-facies phlogopite lherzolite can account for its observed REE concentrations. Whereas the emplacement of the Sakri ultrapotassic dyke is related to the amalgamation of the supercontinent of Rodinia, its overlapping geochemical characteristics of lamproite and kamafugite (also displayed by two other lamproites of the Nuapada field at Amlidadar and Parkom) are linked to the emplacement in a unique geological setting at the craton-mobile belt contact and hence of geodynamic significance.
... The Vempalle lavas, sills and dykes have been dated between 1879 and 1899 Ma (Chatterjee and Bhattacharji, 2001;Anand et al., 2003). An upper age constraint of $1400 Ma for the Cuddapah deposition is provided by the ages for lamproite dykes intrusive to Cumbum shale, between 1354 and 1418 Ma (Kumar et al., 2001;Chalapathi Rao et al., 1996. Collins et al. (2014) presented 21 stratigraphically constrained detrital zircons samples from the Cuddapah basin and 12 Ar/Ar samples from Srisailam Formation, providing the maximum deposition age of different sediment units in the Cuddapah Supergroup and Kurnool Group (Fig. 2). ...
... Ga (Halls et al., 2007;French et al., 2008;French and Heaman, 2010;Kumar et al., 2012). Kimberlite (1.1 Ga) and lamproite (1.4-1.1 Ga) magmatism is restricted to the EDC Griffin et al., 2009;Chalapathi Rao et al., 1996). The craton witnessed affects of Meso-and Neoproterozoic collisional orogenies at its margins along mobile belts -Eastern Ghat Granulite Terrane (EGGT) and Southern Granulite Terrain (SGT) (Figs. 1 and 2) and a series of Phanerozoic (ca. ...
... Radiometric ages (K–Ar, Rb–Sr and Ar–Ar) on phlogopite separates reveal that the lamproite emplacement in the EDC and Cuddapah basin took place between ca. 1225 and 1500 Ma and clearly preceded that of the EDC kimberlites (Chalapathi Rao et al., 1996, 1999 Anil Kumar et al., 2001; Osborne et al., 2011). Apart from the report of a solitary microdiamond from the Chelima lamproites (Sen and Narasimha Rao, 1970), none of the Eastern Dharwar craton lamproites are reported to be diamondiferous. ...
We report the first Re-Os isotope data for samples from Mesoproterozoic kimberlite and lamproite occurrences from the Eastern Dharwar craton and end-Cretaceous Kodomali orangeite from the Bastar craton, India. The Re concentrations of the kimberlites (n = 10) range from 0.077 to 0.290 parts per billion (ppb) whereas the Os contents vary from 0.312 to 1.98 ppb. The measured Os-187/Os-188 ratios range from 0.1143 to 0.1655. The calculated initial Os-187/Os-188 ratios range from 0.0967 to 0.1260, with low values indicating Re mobility on the whole-rock scale since crystallisation. The orangeite has a measured Os-187/Os-188 ratio of 0.1342 and a slightly higher initial Os-187/Os-188 value of 0.1330. On the other hand, the lamproites (n = 3) display lower Re (0.031 to 0.279 ppb) and Os (0.060 to 0.129 ppb) contents. Their measured Os-187/Os-188 ratios (0.2398 to 0.7521) and their initial Os-187/Os-188 ratios (0.1891 to 0.5499) are significantly higher. A majority of the kimberlites display gamma Os-i of -2.7 to -22.7 and imply their interaction with a depleted or unradiogenic source such as cratonic lithosphere. A regression age (involving Re-187/Os-188 vs Os-187/Os-188) of 1008 +/- 410 Ma for eight least altered kimberlites corresponds, within the error limits, to their emplacement age (1.1 Ga) and negates mixing of a highly radiogenic low Os melt, similar to the lamproites, and lithospheric mantle in their genesis. The most Re-depleted kimberlite sample with the lowest present-day Os-187/Os-188 (0.1143) yields a model age (T-MA) of 3.2 Ga and a Re-depletion model age (T-RD) of 2 Ga. The T-RD age reveals: (i) the involvement of Proterozoic lithosphere in the genesis of the kimberlites, (ii) coupling of the continental crust of the Eastern Dharwar craton and the underlying sub-continental lithospheric mantle from 2.5 Ga to at least 1.1 Ga, and (iii) its similarity with the emplacement age of large igneous provinces of similar age and magmatism in the Eastern Dharwar and Bastar cratons (India), the Superior Craton (Canada) and the Kaapvaal craton (southern Africa). However, two of the kimberlite samples (from Raichur and Narayanpet kimberlite fields) show positive gamma Os values ranging from 2.9 to 3.6 suggesting involvement of multiple sources (e.g., subduction, plume or metasomatised lithosphere) in their genesis. An enriched mantle source for the Kodomali orangeite (gamma Os = 3) is also supported by its lower epsilon Nd-i values. The lamproites have very radiogenic gamma Osi values of 56 to 355, similar to those displayed by the lamproites of the Italian peninsula, and indicate a source with elevated Re/Os, possibly a subducted component. Our study provides strong evidence for contrasting mantle sources for kimberlites and lamproites in the Eastern Dharwar craton, southern India. (c) 2012 Elsevier B.V. All rights reserved.
... As a result, most of the current lamproite petrogenetic models are strongly influenced by studies on Phanerozoic lamproites (e.g., Leucite Hills, Smoky Butte, West Kimberley, Gaussberg, and the Mediterranean region; Murphy et al. 2002;Carlier and Lorand 2003;Coban and Flower 2006;Mirnejad and Bell 2006;Davies et al. 2006;Prelević et al. 2012). A significant number of Mesoproterozoic lamproites occur in the Eastern Dharwar, the Bastar and the Bundelkhand cratons of the Indian shield (Chalapathi Rao et al. 1996Rao et al. , 1999Kumar et al. 2001;Osborne et al. 2011;Sahu et al. 2013) and they provide a unique opportunity to understand the tectonomagmatic processes when these cratons constituted a part of Proterozoic supercontinents such as Columbia and Rodinia. Furthermore, the spatial association of Mesoproterozoic lamproites, some of which are diamondiferous, with two of the major Proterozoic Purāna sedimentary basins of peninsular Indiathe Vindhyan (Chalapathi Rao 2005 and references therein; Masun et al. 2009) in central India and the Cuddapah (Bergman 1987;Chalapathi Rao 2007) in southern Indiaremains one of the puzzling aspects of Indian geology. ...
We report mineral chemistry and whole-rock major and trace-element geochemistry for a recent find of Mesoproterozoic (~1.4 Ga) lamproites from the Garledinne (Banganapalle) cluster, south-western part of the Paleo-Mesoproterozoic Cuddapah Basin, southern India. The Garledinne lamproites occur as WNW–ESE-trending dykes that have undergone varying degree of pervasive silicification and carbonate alteration. Nevertheless, their overall texture and relict mineralogy remain intact and provide important insights into the nature of their magmas. The lamproite dykes have porphyritic to weakly porphyritic textures comprising pseudomorphed olivine macrocrysts and microphenocrysts, titanian phlogopite microphenocrysts, spinel having a compositional range from chromite to rarely magnesiochromite, Sr-rich apatite and niobian rutile. The Garledinne and other Cuddapah Basin lamproites (Chelima and Zangamarajupalle) collectively lack sanidine, clinopyroxene, potassic richterite, and titanite and are thus mineralogically distinct from the nearby Mesoproterozoic lamproites (Krishna and Ramadugu) in the Eastern Dharwar Craton, southern India. The strong correlation between various major and trace elements coupled with high abundances of incompatible and compatible trace elements imply that alteration and crustal contamination have had a limited effect on the whole-rock geochemistry (apart from K2O and CaO) of the Garledinne lamproites and that olivine fractionation played an important role in their evolution. The Garledinne lamproites represent small-degree partial melts derived from a refractory (previously melt extracted) peridotitic mantle source that was subsequently metasomatised (enriched) by carbonate–rich fluids/melts within the garnet stability field. The involvement of multiple reservoirs (sub-continental lithospheric mantle and asthenosphere) has been inferred in their genesis. The emplacement of the Garledinne lamproites is linked to extensional events, across the various Indian cratons, related to the break-up of the Proterozoic supercontinent of Columbia.
... rite sills , basaltic - andesitic and rhyolitic lava flows , and tuffs of different episodes / ages ( Murthy et al . , 1987 ) . Geochronological studies have been conducted on the mafic dyke swarms , kimberlite and lamporites in and around the Cuddapah basin ( Crawford & Compston , 1973 ; Murthy et al . , 1987 ; Kumar et al . , 1996 and Chalapathi Rao et al . , 1996 ) . K - Ar ages older than 1700 Ma have been reported for dykes of tholeitic ...
The Vempalle and the Tadpatri formations of the Cuddapah Supergroup of India are well known for their stromatolites. Absolute dates of the rock containing these stromatolites range between < 1800 Ma to > 1550 Ma. The stromatolites have been grouped into three assemblage zones. The characteristic forms of these three assemblages are (1) Pilbaria-Asperia, (2) Gymnosolen-Tibia and (3) Conophyton-Collumnocollenia in a younging sequence at different stratigraphic levels of the Cuddapah Supergroup. The assemblages consist of some typical Palaeoproterozoic stromatolites, viz., Asperia, Microstylus, Alcheringa, Paraboxonia and Tibia. The morphological features, microstructure and microfabric of these assemblages are comparable with Chinese forms and are characteristic of the Palaeoproterozoic age. Banded and streaky types dominate the microstructures and microfabrics are characterized by the granular, vermiform, pelloidal and tussocky types, and are similar to those recorded in Chinese forms. These microstructure and microfabrics are described and their genesis have been discussed. Comparison of the microstructure and microfabric with microstructure and microfabric of Chinese Palaeoproterozoic and younger stromatolite forms suggest that they may be identical to Chinese forms but these could not exclusively be considered as characteristic of Palaeoproterozic stromatolite assemblage. On the contrary morphological forms of the stromatolites are more reliable from the biostratigraphic point of view and are not frequently repeated in the earth history.
... Only one occurrence (Ramannapeta-1) from the KLF has so far been dated. Groundmass phlogopite gave contrasting K-Ar (1384 ± 18 Ma; Chalapathi Rao et al., 1996Rao et al., , 1999 and Rb-Sr (1224 ±14 Ma; Anil Kumar et al., 2001) ages, both of which are essentially Mesoproterozoic. ...
Diamond prospectivity of Mesoproterozoic lamproites in the Krishna valley at the northern and north-eastern margin of the Cuddapah Basin, southern India, is a matter of significance since several historically world-famous alluvial diamonds were recovered from their near vicinity. As the Krishna lamproites presently expose their root zones the possibility of diamond occurrence in their now-eroded uppermost portions remains an open question and renders assessment of their diamond prospectivity a challenging task. Based on newly developed models from a global data base, that predict diamond potential of hypabyssal facies lamproite/kimberlite from whole-rock geochemistry, we infer the Krishna lamproites to be non-diamondiferous. The non-prospective nature of Krishna lamproites is also additionally corroborated by the (i) non-recovery of macro diamond from bulk processing of samples to date, (ii) relatively larger degree melting of their source regions compared to those of diamondiferous kimberlites from Wajrakarur kimberlite field (Dharwar craton) and also the poorly diamondiferous lamproites from Chelima and Zangamarajupalle (Cuddapah basin) and (iii) their relatively highly fractionated nature. If our proposal is correct, then the primary source(s) for the historically renowned diamonds recovered from the Krishna valley may lie elsewhere or be from host rocks yet to be discovered.
... Presence of xenoliths of granite, gneiss, dolerite, and probably phyllite and quartzite, indicate that the lamproites intruded the basement rocks as well as the sediments. K-Ar ages of the Ramannapeta lamproite body (Chalapathi Rao et al. 1996) yielded ages of 1384±18 Ma. However, recent Rb-Sr isotopic age determination of the Ramannapeta body (Anil Kumar and Gopalan, 1998) has shown that the emplacement of lamproites took place around 1224±14 Ma. ...
Search for primary source rocks of diamond in close proximity of the well known alluvial gravel workings for diamonds along the palaeochannels of the River Krishna, has resulted in the discovery of a lamproite field comprising several lamproite clan rocks in parts of Krishna and Nalgonda districts of Andhra Pradesh (South India). These rare rock types are defined in this work as 'lamproites', on the basis of their occurrence in a unique tectonic setting and containing one or more of the typomorphic minerals and having the requisite rock geochemical characters of members of the suite as a whole. These bodies with an exotic and diagnostic mineralogy, composition and textures occur in a complex tectonic setting with unique intrusive history. The discovery of this lamproite field is considered very significant from the point of diamond exploration as it is located very close to the famous Golconda Mines along the banks of the River Krishna which yielded many of the celebrated diamonds in the past. This field is christened "Krishna Lamproite Field", in view of the proximity of the lamproite occurrences to the Krishna River having the alluvial placer diamonds. These rocks are emplaced along the eastern margin of the Precambrian Dharwar Craton, at the contact between the northeastern periphery of the Proterozoic Cuddapah Basin and the Archaean crystalline basement rocks, in the form of dykes (usually in clusters) and plugged conduits. The emplacement is controlled by major faults/fractures, trending in NNW-SSE and WNW-ESE directions and occur closely associated with mafic (dolerite) dykes and followed the same channels for their emplacement. The lamproites contain glass, numerous vesicles, and xenoliths of the basement granite-gneiss, dolerite and probably platformal sediments of the Cuddapah Basin, besides exhibiting fragmental and pyroclastic textures suggestive of near-surface emplacement. Radiometric age determinations suggests emplacement of these lamproites took place around 1224±14 Ma, probably during the reactivation of major crustal lineaments coinciding with the uplift of the mid-Proterozoic Nallamalai sediments of the Cuddapah Basin. Diopside, phlogopite, tetra-ferri phlogopite, richterite, sanidine, apatite and pseudomorphs of leucite, enstatite and olivine are the major primary constituent minerals present. Diopside-leucite-lamproite, phlogopite-leucite-lamproite, olivine-lamproite and richterite-phlogopite-lamproites are the variants. The bodies are ultrapotassic (molar K 2 O/Na 2 O >10), and contain high TiO 2 , P 2 O 5 , K 2 O, MgO, Ba, Sr, Zr, Cr, Ni, La and Ce, pointing to crystallisation from typical lamproite magma. The presence of mantle peridotite xenoliths and xenocrystic minerals such as chrome-diopside, spinel and garnet indicate deep seated mantle derivation of the Krishna lamproites.
... The lamproite occurrences at Majhgawan, Bhander in the Bundelkhand Craton and Zangamrajupalle in the Dharwar Craton also are dated at 1.1 Ga (Anil Kumar et al., 2001;Gregory et al., 2006;Masun et al., 2009), while those from Chelima in the Dharwar craton are dated at 1.38 Ga (e.g. Murthy et al., 1987;Chalapathi Rao et al., 1996, 1999Anil Kumar et al., 2001, etc.). ...
The Phanerozoic tectonic evolution of the Kutch region (NW India) has been attributed to rifting processes. In situ U-Pb perovskite dates (all data = 124 +/- 4 Ma, MSWD = 42) obtained on three samples of a newly discovered lamproite dyke emplaced in the Kutch rift setting identify a previously unknown and relatively young (Mid-Cretaceous) magmatic event in this part of India. The dyke was emplaced into the Katrol Formation of Upper Jurassic to very early Cretaceous age. The presence of xenocrystic garnet and fractionated REE distribution patterns (low HREE/LREE) in the lamproite, along with high contents of transition metals and low Al2O3, suggest that it was derived from the garnet stability field in the mantle. Extreme impoverishment in HREE and HFSE suggest a mantle source region that has experienced both depletion and later enrichment. In situ analysis of Nd isotopes in perovskite of three samples gives a mean epsilon Nd = 0.4 +/- 1 and a TOM model age of 598 +/- 64 Ma, while in situ Sr-isotope analysis gives a mean Sr-87/Sr-86 = 0.70388 +/- 2 (2SE), corresponding to epsilon Sr = 8.6 +/- 03; both datasets suggest mixing between lithospheric-mantle and depleted-mantle components. The fault-controlled emplacement of this body highlights the role of deep-penetrating fault systems in providing a pathway and initiating decompressional melting of the mantle source rocks. The lamproite represents an earlier phase of rift related magmatism, different from the emplacement of the melanephelinite-basanites and basalts that dominate the igneous activity related to the Deccan volcanism in the Kutch mainland.
... In addition, the widespread Mid-Mesoproterozoic (1.4-1.2 Ga) continental rifting, anorogenic magmatism and emplacement of mafic dyke (or sill) swarms are also preserved in all the cratonic blocks which were part of the Columbia supercontinent (e.g., Zhao et al., 2003aZhao et al., , 2004Zhao et al., , 2006Hou et al., 2008;Goldberg, 2010), such as North America (e.g., Heaman, 1989, 1991;Ernst et al., 1995;Buchan, 2001, 2003), Greenland (e.g., Nielsen, 1987;Cadman et al., 2001), South America (e.g., Raposo and D'Agrella, 2000), Australia (e.g., Mortimer et al., 1988;Pidgeon and Nemchin, 2001), east Antarctica (e.g., Sheraton et al., 1990), Africa (e.g., Hunter and Reid, 1987), and India (e.g., Chalapathi Rao et al., 1996;Chalapathi Rao, 2007;Dharma Rao et al., 2010). All these observations stated above provide compelling suggestion that the 1.35-1.32 ...
... age and were emplaced close to 1 Ga (e.g. Chalapathi Rao et al., 1996Rao et al., , 1999Anil Kumar et al., 2001Gopalan and Anil Kumar, 2008;Anand et al., 2008). ...
The Mesoproterozoic Narayanpet Kimberlite Field (NKF) is located ~200 km north of the well-known Wajrakarur Kimberlite Field (WKF) in the Eastern Dharwar Craton, southern India. Whereas a majority of the WKF occurrences are diamondiferous and contain mantle xenoliths and xenocrysts, their paucity is a characteristic feature of the NKF. This has been attributed alternately to the derivation of NKF magmas from a shallower depth, or to variability in thickness of the Sub-Continental Lithospheric Mantle (SCLM) beneath the Eastern Dharwar Craton. Recently, exploration by De Beers resulted in the discovery of a number of new kimberlite occurrences from the NKF, with some of their geochemical features and radiogenic isotope systematics subsequently becoming available. In this paper, we present detailed petrography, groundmass mineral composition and new bulk-rock geochemistry data for a number of NKF rocks and attempt to further constrain their origin. We also investigate the influence of redox conditions on diamond prospectivity by estimating oxygen fugacity (fO2) from Fe–Nb oxybarometry on NKF groundmass perovskites. We identify for the first time in the NKF the presence of volcaniclastic (fragmental textured) facies kimberlite belonging to the diatreme portion of the intrusion. Rarity of olivine macrocrysts and the presence of diopside are hallmarks of the NKF kimberlites, in contrast to archetypal kimberlites of southern Africa. Mineral components of the groundmass display features that are characteristic to both archetypal kimberlites and to orangeites, and it is not straight forward to apply conventional mineral-genetic schemes in the nomenclature of the NKF pipes. Low fO2 of the NKF magma (ΔNNO (nickel–nickel oxide) = −1.9 to −3.2), indistinguishable from that of diamondiferous kimberlites world-wide, indicates that redox conditions were favourable for diamond prospectivity, and that magmatic emplacement could, instead, have played a major role in their low diamond potential. Copyright © 2011 John Wiley & Sons, Ltd.
... The Wajrakarur cluster principally hosts poorly-diamondiferous kimberlites, whereas the Narayanpet and Raichur kimberlites are essentially non-diamondiferous with reports of a few microdiamonds from the latter (Lynn, 2005; Chalapathi Rao et al., 2013). The kimberlites are mostly of Middle-to-Late Proterozoic age, whereas the lamproites were emplaced between ~1225 and 1500 Ma and thus are older than the kimberlites (Chalapathi Rao et al., 1996 Anil Kumar et al., 1997 (93?), 2001 Osborne et al., 2011). ...
A detailed mineralogical examination of representative material from the P2-West 'kimberlite' located in the Wajrakarur Kimberlite Field (India) demonstrates that significant differences exist between these rocks and archetypal hypabyssal kimberlite. The intrusion consists of an olivine-phyric facies which has been transected by, and includes clasts of, a consanguineous phlogopite-rich pegmatitic facies. The olivine-rich parts of P2-West are relatively fresh and consist of euhedral-to-subhedral microphenocrystal olivine set in a groundmass of fine-grained anhedral monticellite, amoeboid apatite, and subhedral-to-euhedral perovskite within a partially chloritized-to-fresh phlogopite-rich mesostasis. The rock lacks the abundant olivine macrocrysts characteristic of kimberlite. Monticellite crystals are commonly partially or completely replaced by pectolite and hydrogarnet. Similar material occurs as irregular aggregates randomly scattered throughout the groundmass. The groundmass, in contrast to that of hypabyssal kimberlites, is relatively poor in spinels. Atoll spinels are absent, with the majority of spinels occurring principally as mantles upon microphenocrystal olivine. Disaggregated cumulate-like assemblages of intergrown anhedral perovskite and spinel are common. Spinel compositions are unlike those of kimberlites and their evolutionary trend is similar to that of lamproite and lamprophyre spinels. The pegmatitic facies of the intrusion are highly and pervasively altered, and characterized by the presence of large clasts, veins, and irregular aggregates consisting of large (1–5 mm) crystals of pinkish-bronze Al-poor phlogopite intergrown with and/or including: apatite; pectolite-hydrogarnet pseudomorphs after an unidentified euhedral phase; chlorite laths; barytolamprophyllite; perovskite; tausonite; diverse Sr-Ba-carbonates; and baryte. The presence of barytolamprophyllite and tausonite are typical of potassic undersaturated alkaline rocks and have never been reported from kimberlite; however, neither feldspar nor feldspathoids are present in P2-West. Micas in fresh and altered rocks are Al2O3- and BaO-poor, and exhibit compositional evolutionary trends towards tetraferriphlogopite rather than kinoshitalite. On the basis of these mineralogical data it is suggested that P2-West represents an unusual lamproite-like intrusion which has undergone extensive hydrothermal deuteric alteration and should not be considered a bona fide kimberlite.
... The relationship between this thrusting event and its relationship, if any, with the lamproite emplacement is yet to be evaluated. Ramannapeta lamproite is the only yet dated lamproite from KLF and its age range from 1384± 18Ma (K-Ar; method ;Chalapathi Rao et al., 1996) to 1224 ± 14 Ma (Rb-Sr method; Anil Kumar et al., 2001). Lack of detailed description of the individual occurrences in KLF (Reddy et al., 2003) is less informative to workers interested in locating them (see Nambiar, 2003) as our own field experience in KLF has shown. ...
A suite of about thirty lamproites outcrop in the Krishna valley at the Northern and North-Eastern
margin of the Cuddapah Basin, southern India. They occur as dykes as well as plugs and intrude the
basement Archaean granite-gneissic rocks. These lamproites are characterised by the varying
proportions of serpentinised olivine, phlogopite, clinopyroxene, amphibole, sanidine, titanite, leucite
(?), apatite, perovskite, spinels and a number of secondary phases like talc, chlorite, carbonate and
quartz and also exhibit remarkably diverse textures viz., flow, pyroclastic (tuffaceous), inequigranular,
microporphyritc and equigranular. The available geochemical data favour involvement of a similar
magma in the genesis of all these lamproites. Thus, the Krishna valley lamproites constitute an
extremely rare example of their kind in the world exhibiting the well known phenomenon, exhibited
mostly by lamprophyres, of heteromorphism wherein a magma of similar composition can give rise to
petrographically diverse rock types. The observed petrographic diversity of Krishna lamproites is
attributed to the differences in the volatile contents in their respective source regions and the
subsequent low -pressure crystallisation of these magmas.
This article presents field description of lamprophyres of the Wajrakarur Kimberlite Field (WKF) emphasising their geoscientific potential to develop and popularize them as geoparks. Also presented are other places of geological importance and heritage sites to visit, such as kimberlite pipe locations, syenite body at Danduvaripalli, ancient Hindu shrines and Batrepalli waterfall etc. to develop as a geotourism corridor. The WKF is largest of all kimberlite fields in the Indian shield and is bestowed with all types of rare mantle derived lamprophyre clan rocks (LCRs) such as lamprophyres, lamproites and kimberlites. The LCRs represent geological anomalies and act as the focal points of diamond exploration. They have been significant in mantle petrological research. The geopark evaluation reveals that the lamprophyre sites deserve to be considered for geopark development. A geotoruism strategy through SWOT evaluation of eligibility criteria of lamprophyres shows that they have geoscientific potential to be developed as geoparks in conjunction with other geological and cultural sites in the proximity. As the outcrops are small, developing them as geoparks and their maintenance is not tough, however, it requires investment, maintenance and wide publicity. If developed as geoparks, these will attract geology researchers and enthusiasts and stands as an example for other similar sites in the country to inculcate awareness of geotourism. Aggressive involvement of national geological organisations and institutes is inevitable to achieve the goal of unraveling new geoparks of this sort.
36-IGC-Field-Trip-Guide- Book: A Journey from Paleo to Neoproterozoic : Sedimentation, magmatism and mineralization in the Cuddapah Basin, India.
https://36igc-virtual.in/wp-content/uploads/2022/03/SR007_36-IGC-Field-Trip-Guide-compressed.pdf
We report Mesoproterozoic ⁴⁰ Ar- ³⁹ Ar (whole-rock) ages of lamproites from (i) the Ramadugu field (R4 dyke : 1434 ± 19 Ma and R5 dyke: 1334 ± 12 Ma) and the Krishna field (Pochampalle dyke: 1439 ± 3 Ma and Tirumalgiri dyke: 1256 ± 12 Ma) from the Eastern Dharwar Craton (EDC) and (ii) the Garledinne (1433 ± 8 Ma) and the Chelima (1373 ± 6 Ma) dykes from within the Paleo-Mesoproterozoic Cuddapah Basin, southern India. The ages reported for the Ramadugu and Tirumalgiri lamproites constitute their first radiometric dates. Ages of the Pochampalle and the Chelima lamproites from this study are broadly comparable to their previously reported ⁴⁰ Ar- ³⁹ Ar (phlogopite) ages of c . 1500 Ma and 1418 ± 8 Ma, respectively. The ages of all these lamproites are much older than those of the (i) c . 1.1 Ga kimberlites from the Wajrakarur and Narayanpet fields of the EDC and (ii) c . 1.09 Ga lamproitic dykes at Zangamarajupalle which intrude the Cumbum Formation of the Cuddapah Basin. However, the age of the Tirumalgiri lamproite ( c . 1256 Ma) is similar to that of the Ramannapeta lamproite ( c . 1224 Ma) within the Krishna field. Our study provides evidence for protracted ultrapotassic (lamproitic) magmatism from c . 1.43 to 1.1 Ga over a widespread area ( c . 2500 km ² ) in and around the Cuddapah Basin and the EDC. Implications of the obtained new ages for the diamond provenance of the Banganapalle Conglomerates, the age of the Kurnool Group and for the timing of break-up of the Paleo-Mesoproterozoic supercontinent of Columbia/Nuna are explored.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.5289354
The Pictorial Atlas on Cuddapah Basin is an attempt by the Geological Survey of India to display one of the largest Proterozoic sedimentary basins of India. This pictorial atlas is prepared with the hope to cater a bridge in understanding of the basin in visual way for the geoscientific community and young research fellow. Known for its rich mineral wealth, the Proterozoic Cuddapah Basin of Eastern Dharwar Craton is charecterised by the presence of thick sequences of clastic and non clastic sedimentary rocks. The atlas covers the geological details of the rudaceous, arenaceous, argillaceous and carbonate sequences from the type sections in the basin. The atlas also covers succint details pertaining to the field aspects of the magmatic rocks and associated mineral deposits. The atlas illustates the sedimentary sequences comprising both major stratigraphic units of the Paleoproterozoic Cuddapah Supergroup and the younger Neoproterozoic Kurnool Group. The Cuddapah basin is sub divided into (a) Papaghni sub-basin (b) Nallamalai sub-basin (c) Srisailam sub-basin (d) Kurnool and Palnad sub-basins. Stratigraphically, the Cuddapah Supergroup is unconformably overlain by the Kurnool Group, a 500 m thick orthoquartzite–carbonate–shale association with a basal conglomerate.
Mesoproterozoic kimberlite pipes designated as Kl-4 and P-5, along with several other well-known diamondiferous (ca. 1110 Ma) kimberlites in the Wajrakarur kimberlite field (WKF) intruded into the cratonic roots of Eastern Dharwar craton (EDC) in southern India. The groundmass minerals of the kimberlites exhibit inequigranular texture with spinel showing straddle between MUM and Mag trend, Ti-rich schorlomite garnet, two generations of olivine (macrocrysts and groundmass microphenocrysts), phlogopite, perovskite, clinopyroxene (diopside), ilmenite (low Mn) and rare apatite. We identified three distinct spinel associations in Kl-4 and P-5: (i) finer-grained (<50 μm) microcrysts in the groundmass; (ii) resorbed euhedral atoll spinel, consisting of titanomagnetite (magnesian-ulvospinel-magnetite to titanian-chrome-magnetite) which is isolated from the rim of magnetite by spongy lagoon phase of schorlomite, and (iii) larger chrome spinel macrocrysts/xenocrysts (>500 μm). The schorlomite garnet in both P-5 and Kl-4 represents solid solution of schorlomite-pyrope-almandine-grossular. Additionally, Kl-4 contains another Cr-rich schorlomite-pyrope-almandine-uvarovite solid solution. Macrocrystic spinel exhibits distinct composition of chromium (Cr2O3 up to 59.62 wt%), and TiO2-poor (<1.19 wt%). The high chromium spinel macrocrysts from Kl-4 are confirmed to be fragments of mantle xenocrysts and their composition falls within the diamond stability field. Atoll-textured epitaxial mantled resorbed spinel associated with schorlomite suggests that they formed through the replacement of spinel possibly through interaction of late residual fluids/melts in the final stages of crystallization of the kimberlite magma. The significant enrichment of Fe and Ti in schorlomite suggests the involvement of metasomatized sub-continental lithospheric mantle. It is also inferred that spinel immiscibility played an important role in the metasomatic replacement. The Ti-rich minerals have orangeitic affinity, similar to those in the Kaapvaal craton of South Africa, and suggest the high Ti-, high Ca- and the low Al-bearing nature of the parent magma (Group II kimberlites). The groundmass tetraferriphlogopite is Al- and Ba-poor and the spinel from P-5 and Kl-4 kimberlites investigated in this study show compositions straddling between magnesian ulvöspinel (Group I kimberlite) and titanomagnetite (Group II kimberlite) comparable with orangeite and lamproites. The results presented in this study suggest that the P-5 and Kl-4 has orengeitic or lamproitic affinity. Our findings can be useful as an indicator mineral in diamond prospecting.
Petrological and geochemical studies have been carried out on Pulivendla and Gandikota Quartzite from Chitravati Group of Cuddapah Supergroup to decipher the provenance and depositional environment. Both the units are texturally mature with sub-rounded to well-rounded and moderately to well-sorted grains. Majority of the framework grains are quartz, in the form of monocrystalline quartz, followed by feldspars (K-feldspar and plagioclase), mica, rock fragments, heavy minerals, with minor proportion of the matrix and cement. Based on major element geochemical classification diagram, Pulivendla Quartzite is considered as quartz-arenite and arkose to sub-arkose, whereas Gandikota Quartzite falls in the field of lith-arenite and arkose to sub-arkose. Weathering indices like CIA, PIA, CIW, ICV, Th/U ratio and A–CN–K ternary diagram suggest moderate to intense chemical weathering of the source rocks of these quartzites. Whole rock geochemistry of quartzites indicate that they are primarily from the first-cycle sediments, along with some minor recycled components. Also their sources were mostly intermediate-felsic igneous rocks of Archean age. The tectonic discrimination plots, Th–Sc–Zr/10 of both these formations reflect active to passive continental margin setting. Chondrite-normalized rare earth element (REE) patterns, and various trace element ratios like Cr/Th, Th/Co, La/Sc and Th/Cr indicate dominantly felsic source with minor contribution from mafic source. Th/Sc ratios of Pulivendla and Gandikota Quartzite are in close proximity with average values of 2.83, 3.45 respectively, which is higher than AUCC (Th/Sc = 0.97 ), demonstrating that the contributions from more alkali source rocks than those that contributed to AUCC.
Bayan Obo ore deposit is the largest rare earth element (REE) resource and the second largest niobium (Nb) resource in the world. The REE enrichment mechanism and genesis of this giant deposit still remains intense debated. The deposit is hosted in the massive dolomite, and nearly one hundred carbonatite dykes occur in the vicinity of the deposit. The carbonatite dykes can be divided into three types from early to late: dolomite, coexisting dolomite–calcite, and calcite type, corresponding to different evolutionary stages of carbonatitic magmatism, and the latter always has higher LREE content. The origin of the ore-hosting dolomite at Bayan Obo has been addressed in various models, ranging from a normal sedimentary carbonate rocks to volcano-sedimentary sequence, and a large carbonatitic intrusion. More geochemical evidences and field interspersed relationship show that the coarse-grained dolomite represents a Mesoproterozoic carbonatite pluton and the fine-grained dolomite resulted from the extensive REE mineralization and modification of the former one. The ore bodies, distributed along an E-W striking belt, occur as large lenses and underwent more intense fluoritization and fenitization with wall rocks. The first episode mineralization is characterized by disseminated mineralization in the dolomite. The second or main-episode is banded or massive mineralization, cut by the third episode consisting of aegirine-rich veins. Various dating methods gave different mineralization ages at Bayan Obo, resulting in long and hot debates. Compilation of available data suggests that the mineralization is rather variable with two peaks at ~1400 and 440 Ma. The early mineralization peak closes in time to the intrusion of the carbonatite dykes. A significant thermal event at ca. 440 Ma resulted in the formation of late-stage veins with coarse crystals of REE minerals. Fluids involving in the REE-Nb-Fe mineralization at Bayan Obo might be REE-F-CO2-NaCl-H2O system. The presence of REE-carbonates as an abundant solid in the ores shows that the original ore-forming fluids are very rich in REE, and therefore, have the potential to produce economic REE ores at Bayan Obo. The Bayan Obo deposit is a product of mantle-derived carbonatitic magmatism at ca. 1400 Ma, which was likely related to the breakup of the supercontinent Columbia. Some remobilization of REE occurred due to subduction of the Palaeo-Asian oceanic plate in the Early Paleozoic, forming weak vein-like mineralization.
The kimberlite body near Undraldoddi, towards eastern part of Raichur Kimberlite Field of South Indian Diamond Province (SIDP) within the Neoarchaean Eastern Dharwar Craton, has been identified as ‘Tuffisitic kimberlite’. It is primarily composed of macrocrysts/microcrysts of abundant pseudomorphed olivine, minor spinels, rare phlogopite, Cr-diopside and abundant magmaclasts set in a cryptocrystalline chlorite–phlogopite–diopside dominated interclast matrix. The pre-existing crysts and clasts are rimmed by thin mantle of microlites of diopside–phlogopite–titanite which are considered to represent selvages of rapidly cooled and evolved kimberlite-melt. Magmaclasts, with kernels of both olivine (dominant) and xenoliths (mantle and crustal), consist of microcryst/phenocryst of pseudomorphed olivine and rare K-feldspar is set in very fine-grained groundmass of diopside–mica (phlogopite)–spinel–apatite–perovskite comparable to hypabyssal kimberlite. Olivine is completely altered to chlorite-smectite-talc aggregates, phlogopite to chlorite, perovskite to Ca–Ti silicate (titanite) and Al–Mg–Cr spinel to a garnet phase. The development of secondary mineral phases like chlorite–smectite–talc, diopside, titanite and andradite in this kimberlite is the characteristic feature and is probably related to the evolution of ascending kimberlite magma by degassing of CO2, country rock assimilation at higher level and alterations. Spinels can be classified either as high-chromium spinel (chromite) or as Al–Mg–Cr spinel with a growth rim of Ti-magnetite suggesting kimberlitic trend. Chromite (xenocryst) with Cr2O3 ranging from 55 to 59% falls very near to diamond stability field indicating deep source. Some of the xenocrystal phlogopite shows a Group-I kimberlite trend, whereas majority show Group-II kimberlite trend. The whole rock REE patterns of these kimberlites show a Group-I kimberlite trend. The data on whole rock chemistry and individual mineral phase chemistry have been utilised to suggest that a continuum of crystallisation of kimberlite magma was maintained both by gradual increase in silica and H2O in the residual phase as well as contribution from the country rock. The remarkable similarity recorded between Undraldoddi kimberlite and the diamondiferous tuffisitic kimberlites of Wesselton Mine, South Africa is expected to renew the interest in kimberlite search as well as diamond exploration in this part of the Eastern Dharwar Craton.
A suite of potassic ultramafic rocks occurs in the Krishna district in the southern Indian craton along with clusters of kimberlite. The principal minerals include olivine, pyroxene, amphibole and phlogopite. Compositional variation exists in the phlogopite of the different occurrences of the region. Mg number varies from 0.37 to 0.56 and the groundmass phlogopites are enriched in Fe and Ti and poor in Al compared to the phenocrysts. Major and trace element data indicate enrichment of LILE and LREE (La/Yb = 24 - 104; Gd/Yb = 3.8 - 8.02). Ba contents vary from 132 to 5327 ppm, which is rather low compared to literature values for lamproite. However, the abundances of Zr (> 500 ppm), Sr (> 1000 ppm) and La (>200 ppm) are similar to those in the lamproite. The potassic ultramafic rocks have variable but high U/Pb (2-37, average 17.2) and Th/U (4.6-10.7) ratios. Concentrations of Platinum Group Elements (PGE) are quite variable with Ir, Pt and Pd varying by >9, 21 and 15 times respectively over the suite. Significant features include differences in fractionation between PGE and enrichment of Cu relative to the mantle source region. Some of the samples are not ultrapotassic and peralkaline. However, combining their mineralogical and geochemical properties, these rocks of the Krishna region may be considered as a member of the lamproite clan. There is no evidence of significant crustal contamination, but fractional crystallisation of olivine and perovskite is suggested from the geochemical relations. Available isotopic age data indicate that the ca. 1220 Ma old Krishna lamproite preceded kimberlite emplacement in the region by about 160 million years. Partial melting of a mantle metasomatically enriched in Ti and Fe would yield the Krishna lamproite magma. Amphibole contributed to the melt, but the HREE abundance data preclude garnet involvement. The depth of melt formation was likely to be shallower than that of kimberlites.
We report new U-Pb ages of groundmass perovskite determined by secondary ion mass spectrometry, trace element, and Sr and Nd isotopic compositions for twelve kimberlites emplaced in three different fields from the Eastern Dharwar craton, southern India. Diamondiferous kimberlites from the Wajrakarur field gave ages ranging from 1099 +/- 12 Ma to 1129 +/- 12 Ma. The non-diamondiferous kimberlites from the Narayanpet field gave ages ranging from 1123 +/- 17 Ma to 1141 +/- 18 Ma. One kimberlite (Siddanpalle cluster) from the poorly-diamondiferous Raichur field has an indistinguishable age of 1093 +/- 18 Ma. Our data contribute to the evidence for a near-synchronous late Mesoproterozoic kimberlite emplacement event in the Eastern Dharwar craton at 1.1 Ga and increases the spatial extent of this tectonomagmatic event. The perovskite U-Pb ages of kimberlites determined in this study are similar to those of the diamondiferous Majhgawan and Bunder lamproites of the Bundelkhand craton (northern India) and Nuapada lamproites of Bastar craton, (central India), but are clearly much younger than the 1.5 Ga ages recently reported for some of the Krishna lamproites of the Eastern Dharwar Craton. Regardless of their contemporaneous ages, initial Sr-87/Sr-86 ratios of Narayanpet perovskites are notably higher (0.70302-0.70339) than those (0.70240-0.70255) from the Wajrakarur Field. Similarly, the epsilon(Nd)(t) of Narayanpet perovskite (+0.6 to +1.9) is relatively lower than that (+2 to +2.9) of the Wajrakarur perovskites and provides clear evidence for the involvement of distinct isotopic mantle sources for these different kimberlite fields. The Raichur kimberlite has an indistinguishable initial Sr-87/Sr-86 ratio (0.70305) and epsilon(Nd)(t) (+1.4) to the Narayanpet kimberlites. The perovskite depleted mantle model ages (T-DM) of the Wajrakarur and Narayanpet kimberlites range from 1.3 to 1.5 Ga and are inferred to be distant effects related to the break-up of the Columbia supercontinent and separation of the North China craton and Indian shield from the Laurentia continent. A variably-enriched metasomatised sub-continental lithospheric mantle overprinted by an asthenospheric signature within a short time-span can account for the distinct isotopic signals of kimberlites in different fields of the Eastern Dharwar Craton and their "transitional" petrological and geochemical characteristics compared to archetypal kimberlites. (c) 2012 Elsevier B.V. All rights reserved.
The Proterozoic Cuddapah Basin of south India is one of the most important Purana basins of Peninsular India. It hosts the Cuddapah Supergroup and the Kurnool Group of rocks. The structure of the Cuddapah Basin reveals that it forms the frontal part of a larger fold–thrust belt, named the Cuddapah fold–thrust belt (CFTB). The CFTB formed in response to the amalgamation of the Prince Charles Mountains–Rayner Complex of Antarctica with the Krishna province of India during the formation of the Rodinia Supercontinent.
The CFTB, bounded by the Nellore–Khammam schist belt and Eastern Ghats terrane in the east and Peninsular Gneissic complex of the Dharwar Craton to the west, includes two frontal thrusts and foreland of an orogen. The frontal Nallamalai thrust structurally separates the basin into two blocks – the eastern Nallamalai fold belt and the western foreland. A model of evolution of the CFTB has been proposed. The CFTB, forming the front-most segment of a larger orogen associated with the intercratonic deformation related to the formation of the Rodinia Supercontinent, is the result of fault-propagation folding, forming an overturned anticline–syncline pair at
the tip of the propagating Velikonda thrust which later cuts through the common limb of the fold pair.
Osborne et al. (2011; Precambrian Res. 189, 91–103) report new 40Ar/39Ar age results for two kimberlites (Muligiripalle pipe 5 and Tummatapalle pipe 13) and one lamproite (Pochampalle), from the Archaean Dharwar craton in southern India. Previous studies indicate that kimberlites and related rocks are highly susceptible to extraneous argon contamination, leading to anomalously old ages; although reliable 40Ar/39Ar ages can be obtained from step-heating analyses of groundmass phlogopite grains. Osborne et al. (2011) carried out single-step 40Ar/39Ar fusion analyses on phlogopite phenocrysts and xenocrysts. This approach is not favoured, because it does not allow identification of argon loss/gain effects, thus complicating data interpretation and reducing confidence in the reliability of the reported ages. In particular, it is suggested that the Pochampalle lamproite was emplaced <1400 Ma ago, rather than ca.1500 Ma, as suggested by Osborne et al. (2011). It is recommended that 40Ar/39Ar geochronology of kimberlite and lamproites include step-heating analyses of matrix phlogopite grains, with anomalous or contentious results verified using other dating methods.
Widespread distribution of mafic dykes and scanty occurrence of ultrabasic intrusives of kimberlitic affinity around Proterozoic Cuddapah basin, parts of Eastern Dharwar craton of south India has been the focus of attention since their discovery, to understand the structural fabric in relation to their emplacement in geological time. Satellite Imagery, geomorphological, geophysical and radiometric age data of Narayanpet area, northwest of Cuddappah basin, have clearly displayed the alignments and structures of geological significance, such as deep seated fault / fracture / shear zones, stratigraphic / lithological contacts, basic / ultrabasic intrusives and younger granites etc,. Based on the field observations such as emplacement of mafic dykes, their cross cutting relationship, study of morphological and geophysical signatures, inferred linears drawn from satellite imagery, aeromagnetic and gravity maps are arranged in a chronological order. A system of long, narrow and widely spaced dykes trending NW-SE direction conformable to gneissic foliation, typically associated with migmatites in the southwestern part of the study area are the oldest. Followed by E-W dykes, cut across by the sparsely distributed dykes associated with NW-SE and N-S features and in turn off set by dykes of NE-SW trends are the youngest. Kimberlites of Narayanpet area, belongs to hypabysal facies, which are essentially controlled by E-W to ENE-WSW deep seated fault / fracture zone, their intersection with NW-SE, NE-SW to N-S trends, which may have been reactivated during Proterozoic period as indicated by the intrusion of mafic dykes.
Detailed petological and geochemical studies pertaining to the lamproitic body recorded by the Geological Survey of India at Ramannapeta-Ustapalle, Krishna district Andhra Pradesh, are presented. Unmistakable lamproite signatures like the presence of Ti-rich potassic richterite, abundance of Ti-rich, Al-poor phlogopite and Ca-rich, Al-poor clinopyroxene, absence of primary calcite, paucity of typical kimberlite indicator minerals and the ultra potassic nature are recognised. Major oxide as well as the trace elemental abundances of the body are observed to be similar to those of the Chelima lamproites occurring within the intra-cratonic Cuddapah basin. The available radiometric ages of all the known Indian lamproites and kimberlites are taken into consideration and a mid-Proterozoic lamproite event in the Indian sub-continent is postulated.
Evidence which includes Landsat images is presented for prolonged periods of tectonism, marginal to and extending within the intracratonic region of the West African platform. Also found are indications of intermittent, or perhaps even sustained activity, dating back to more than three billion years. The petrology and mineral chemistry of kimberlites, and their associated nodule suites in the present region, are broadly similar to those from kimberlite localities throughout the African continent, and should therefore be considered as part of a major province. Attention is drawn to the lineament control of kimberlites, and the coincidence of these lineaments with the basement fabric and with faults. The proposed interpretation for the distribution of West African kimberlites is in essential agreement with the intraplate and intracratonic model of Dawson (1970) and Sykes (1978), which calls upon the reactivation of paleofaults and sutures during plate tectonism.
When the subcontinental lithospheric mantle undergoes heating and/or extension, some of the earliest mafic melts to be generated are those rich in volatUes and potassium. In some cases, e.g. when a plume impinges on thick cratonic lithosphere or when the amount of extension is very small, K-rich mafic igneous rocks may be the only surface expression of mantle melting. The Alto Paranaiba Igneous Province, in SE Brazil, is one of the world's most voluminous mafic potassic provinces (>15000km3), which until recently was relatively unknown. The magmas were emplaced into a narrow Proterozoic mobile belt close to the surface margin of the Sao Francisco craton, and it is one of several Cretaceous alkaline igneous provinces that are located around the margin of the Parana sedimentary basin in Brazil and Paraguay.Detailed geochemical analyses of samples from throughout the Alto Paranaiba Igneous Province show that it is composed of a relatively diverse suite of ultrapotassic-potassic, ultramaficmqfic, silica-undersaturated lavas and hypabyssal intrusions, i.e. kimberlites, madupitic olivine lamproites and kamafugitic rocks. These all have very high concentrations of incompatible trace elements and are all strongly enriched in light rare earth relative to heavy rare earth elements (e.g. La/Yb=50-230). Wide variations in major element ratios, which are unrelated to the effects of crystal fractionation in these magmas (e.g. CaO/Al 2 O 3 ), suggest that the mafic potassic rocks were derived from a heterogeneous mantle source. They show relatively restricted ranges of initial 87Sr/86Sr (0�70436-0�70588) and ϵNd 25 values of -4 to -8, intermediate between Group I and II South African kimberlites. T DM Nd isotope model ages of ∽900 Ma suggest that the magmas were derived by the remobilization of subcontinental lithospheric mantle that had been enriched by small-volume K-rich melt fractions since the Late Proterozoic.New K/Ar ages for mica separates show that the kimberlites, madupitic olivine lamproites and kamafugitic rocks were emplaced together with large carbonatite-bearing plutonic complexes at ∽85 Ma. Reconstructions of plate motions show that, at this time, the location of the Alto Paranaiba Igneous Province coincided with the postulated position of the present-day Trindade(or Martin Vaz) plume. We propose that the widespread Late Cretaceous alkaline magmatism in SE Brazil may have been caused by impingement of this plume on the base of the subcontinental lithosphere. Heat penetrating the lithosphere, both by conduction and advection by asthenospheric-source decompression melts, may have caused melting of the readily fusible parts of the lithospheric mantle and the genesis of mafic potassic and (after fractionation) carbonatite magmas. The Proterozoic mobile belt (the Brasilia Belt) appears to have acted as a Hhinspof relative to the adjacent Sao Francisco craton, allowing greater upwelling and melting of the asthenosphere. Subsequently, as the craton passed over the plume, volcanism was switched off' until the Early Tertiary when the plume reemerged from beneath the westward drifting South America continent and was the magma source for oceanic-islands and seamounts of the Trindade-Vit�ria chain.
Strontium isotopic studies on twenty three whole rock kimberlites from two petrographic provinces in India show variation of initial 87 Sr / 86 Sr ratios from 0.7027 to 0.7102. The variation is unrelated to the degree of alteration. Between the micaceous and basaltic varieties there is some overlap in the Sr isotopic ratios. Leaching experiments on whole rock samples showed more highly radiogenic Sr in leaches compared to the bulk samples. In two diatremes, the initial 87 Sr / 86 Sr ratios show a positive correlation with Rb / Sr which is believed to reflect a source event earlier than the formation of the kimberlites. The observed Sr isotopic data can be caused by (i) melting of a heterogeneous source or (ii) disequilibrium partial melting in the source region. In the former case, variable isotopic composition would be a necessary consequence of melting in small subsystems.
Argon isotopic analyses were undertaken on phlogopite from the Swartruggens kimberlite dyke and a Premier kimberlite (1200 Ma) peridotite xenolith. Groundmass phlogopite from Swartruggens yields a plateau age of 145.0± 0.4 Ma, consistent with previous age determinations. Phlogopite phenocrysts from Swartruggens and macrocrysts from the Premier xenolith yield complex age spectra, with anomalously old ages, attributed to incorporation of excess radiogenic argon.Laser probe analyses on single phlogopite grains reveal systematic zonations in excess Ar and CI concentrations across (001) cleavage surfaces. One Premier macrocryst exhibits ages in excess of 2.3 Ga and CI levels of 1600 ppm at its centre. These values decrease systematically to 1.2 Ga and 1300 ppm Cl along grain margins. Similar results were obtained from a single Swartruggens phenocryst, which exhibits a range in values of 340—800 Ma and 300—1300 ppm Cl. A second Swartruggens phenocryst is characterised by smaller variations in age (140–230 Ma) and CI content (390–470 ppm ). Fluorine concentrations, determined by electron microprobe, are relatively constant or increase slightly towards grain edges. The laser probe profiles cannot be reconciled with the step-heating results, probably due to phlogopite degradation during invacuo furnace heating.Transport of Ar and CI in kimberlitic phlogopite appears to be dominated by radial diffusion (cylindrical geometry). The variety of laser probe profiles obtained suggests that Ar and Cl diffusion is governed by factors such as lattice diffusion, diffusion anisotropy, and structural defects, which reduce the effective radii of diffusion and may impart a component of pipe diffusion.It is suggested that the xenolith phlogopite entrapped excess 40Ar and halogens in the mantle lithosphere, in response to elevated Ar and halogen fluid pressures. Swartruggens phenocrysts appear to have crystallised from a volatile-rich kimberlite melt. Subsequent magma devolatilisation prior to emplacement reduced Ar partial pressure and CI content. Possible reasons for enhanced F levels after devolatilisation include increased F solubility in the kimberlite melt, extraction of F from infiltrating hydrothermal fluids and local heterogeneities in fluid composition.The final distributions of Ar, Cl and F in kimberlitic phlogopite are variably dependent on several parameters, including local fluid composition, timing of melt devolatilisation, diffusion/ exchange mechanisms, and mineral composition.
New isotopic data, mainly Rb-Sr, are given for the Vindhyan System of Peninsular India, the underlying Gwalior Series and Bijawar Series, and a pipe of kimberlitic affinities which intrudes the Upper Vindhyan. The Vindhyan System is shown to have a base with an age of at least 1200 and possibly 1400 m.y. The Gwalior Series is shown to have an age of between 1600 and 2000 m.y. while the Bijawar Series is very much older at about 2500 m.y. The necessity for revision of palaeomagnetic interpretations based on very different age estimates is shown, and it is recommended that because of its probable long time span any evidence for glaciation in the Vindhyan, at present poor, needs to be carefully attributed stratigraphically.
Kimberlite occurs as intrusive pipes in the Precambrian shield area of India. Regional mineralogical and chemical variation with highly significant differences in AL2O3, MgO, CaO, and P2O5 exist between the localities. New K-Ar ages on eight whole-rock analyses suggest that the known Indian occurrences are of Precambrian age.
The evolution of the Indian Shield has been envisaged from the analysis of available tectono-lithostratigraphic, geochronological, geochemical and geophysical data. It appears that the Dharwar schist belts and their equivalents, except the Kolar schist belt, are not typical greenstone belts, but are representative of a transitional era of rapid transformation from simatic to sialic crust. In the Archaean—Proterozoic tract of India, relics of rocks older than 3.0 b.y. are identified in five widely separated regions of distinct tectono-litho-stratigraphic assemblages which probably represent the primordial continental nucleii. It is suggested that the growth of the Indian Shield has taken place through nucleation, accretion and merger into three protocontinents named Dharwar, Aravalli and Singhbhum. The cratonisation of the Indian unit seems to have been rapid and almost completed by the middle Proterozoic, as there is no significant variation in the composition of the clastic sediments and basalts from middle Proterozoic onwards. The continental nucleii appear to merge along the deep-seated lineaments, which are reflected on the tectonic map of India. Further, the Dharwar, Aravalli and Singhbhum protocontinents also seem to merge along a Y=shaped Narmada—Son—Godavari lineament which along with the Mahanadi lineament, between the two continental nucleii of the Singhbhum protocontinent have later developed into rift valleys.
Recently discovered kimberlitic dykes and sills in the Guaniamo area of Bolivar Province (Guyana Craton) are the source of nearby extensive alluvial diamonds occurring in Recent gravels and in the Roraima sedimentary group (ca. 1.7 Ga) to the south. The intrusives are altered to nontronite and saponite but texturally are identified as Group I macrocrystic olivine rich kimberlites with identifiable monticellite and phlogopite. The REE show steep patterns and high (La/Yb)n up to 480; Cr, Ni and Nb are enriched, but LILE and Ti, Zr depleted with respect to average kimberlite, partly as a result of weathering. Leached samples yield a Rb-Sr isochron age of 1732 ± 82 Ma making them the oldest kimberlites on record. Sr and Nd isotope data are more consistent with a Group II, rather than a Group I kimberlite paragenesis. Discrete nodules (megacrysts) which typify Group I kimberlites have not been identified. There are no mantle xenoliths but mantle xenocrysts of chromium-rich pyropes and spinels, similar to those from cratonic harzburgite xenoliths of diamond facies, are abundant. The spinels show metasomatic alteration to yimengite.The kimberlites are intruded by micaceous dykes enriched in K, Ba, Sr, Zr and F indicative of a second phase of alkaline igneous activity. These igneous and metasomatic events are discussed in the context of the evolution of the Guyana Craton.Archaean metamorphism associated with the Imataca Complex spans the harzburgite chromium pyrope model Nd age (2.6 Ga). The widespread Trans-Amazonian metamorphic event (ca. 2.1 Ga) was possibly contemporaneous with mantle metasomatism indicated by yimengite formation. The kimberlites were emplaced thereafter (1.7 Ga). The micaceous dykes (0.85 Ga, ) were generated in a mantle enriched in elements similar to those found in the earlier formed yimengite (K, Ba, Sr).
Rb/Sr isotopic analysis of phlogopite micas has commonly been used to determine the emplacement ages of kimberlite and other alkaline intrusives.Leaching of fresh as well as partially altered phlogopite samples in dilute (∼ 2 N) HCl, prior to isotopic analysis, increases the precision of the calculated ages significantly without disturbing the RbSr isotope systematics of the micas. The leaching step removes trace amounts of carbonate, which typically has a high Sr concentration (2000–9000 ppm), from the mica separates and thus increases the 87Rb/86Sr and 87Sr/86Sr ratios of the analysed samples. Leaching for a period of 10 min. had no affect on the Rb concentrations of the analysed phlogopite samples. However, leaching for a period of 12 hr. lowered the Rb contents of the phlogopites by a few per cent. All but one of the phlogopite samples leached for 12 hr. plot on an isochron. The slight loss in Rb content of these samples was thus complemented by loss of radiogenic Sr, which occurred along with the Rb in the large interlayer cation sites of the mica lattice.The emplacement age of the Makganyene kimberlite pipe is 121.2 ± 1.2 Ma, given by a RbSr isochron, including 19 phlogopite samples and one whole-rock sample. The initial 87Sr/86Sr ratio of 0.7100 ± 0.0002, in conjunction with the phlogopite mineralogy, indicates that the kimberlite is a Group-II kimberlite.
Geologic data, especially conodont paleotemperatures, imply that southeastern Canada and New England have been elevated at least 4 km relative to the central Appalachian region. Apatite fission-track ages suggest that the uplift and consequent erosion occurred in Cretaceous-early Tertiary time, consistent with the formation of a broad swell as North America moved northwestward over the Great Meteor hotspot.
In southern India the older Precambrian is overlain unconformably in the Cuddapah Basin by the Cuddapah and Kurnool Systems. The former is tilted and unmetamorphosed in the west but eastwards becomes strongly folded and metamorphosed. It contains lavas and sills, particularly in the lower two groups, is intruded by dolerites and at Chelima by diatremes of kimberlitic affinities related to those intruding the older gneisses west of the Cuddapah Basin in the Wajrakarur area. The Kurnool System lacks any igneous rocks; its basal conglomerate is diamondi‐ferous.Rb‐Sr dating of lava samples from the lowest group of the Cuddapah System shows that the age of the base of the system may be as great as 1,700 m.y. Together with data for a granite which intrudes probable Cuddapah rocks near the disturbed eastern margin of the basin the data imply that the base is unlikely to be younger than 1,555 m.y. Metamorphism affected some lavas at about 1,360 m.y. The diatremes have two ages of intrusion, about 1,225 m.y. and 1,140 m.y., the latter being the age of the Majhgawan pipe near Panna in northern India. Pre‐Kurnool dolerites have an age of 980 ±110 m.y.The lavas and dolerites show a range of initial Sr/Rb ratios from about 0.704 to 0.708 and possibly 0.712.The age data suggest that no simple correlation can be made with other Precambrian sequences in northern peninsular India. Deposition of the Cuddapah System appears to have started well before the start of the deposition of the Vindhyan System, while the Kurnool System is coeval with only part of the Upper Vindhyan. The data also suggest that present interpretations of the structural development of the Cuddapah Basin may need some revision.
The kimberlite pipe at De Beers Mine, Kimberley is a complex, multiple structure. Three concordant argon-40/argon-39 age spectra have been obtained from samples from the 720 m level in the East Peripheral kimberlite. Each spectrum is dominated by a major plateau-feature between 84 and 89 Ma and none shows significant evidence of either excess argon or argon loss discrepancy. The available evidence suggests that the K-Ar age of normal magmatic emplacement-cooling of the East Peripheral kimberlite at De Beers Mine was close to 86 ± 2 Ma.
Major-element geochemical data from fresh biotites are used to distinguish an “invariant” parameter, Σ, which is the scaled sum of elemental concentrations, 0.7 (Fe 2+ + Mg + Ti + Al + Si) + 0.3K, having the value 35.3 ± 0.5 wt.%. Analyses of biotites from a sub-tropical modern weathering section of the Beni-Toufout Granite (northern Algeria) (K-Ar age 17.5 ± 0.2 Ma) are used to demonstrate that, during weathering, Σ is reduced in a fashion which is linearly correlated with radiogenic Ar loss. By this means, a quantification of the effect of weathering on the K-Ar age system is established, and used to “correct” conventional K-Ar ages of detrital biotites from Middle Triassic sandstones of the Cheshire Basin, U.K. Following “correction”, the biotite ages are in closer accord with K-Ar ages of coexisting detrital muscovite than they were previously. The “corrected” ages support the view that the palaeo-drainage system transporting the micas originated in the Armorican uplands lying to the south, where both the Cadomian and Variscan orogenic belts are represented. No evidence is found to indicate significant “Caledonian” input to the “Keuper” of the Cheshire Basin.
This paper describes partly successful attempts to determine emplacement ages of kimberlites by U−Pb and Pb−Pb methods, involving groundmass minerals with high U content (notably perovskite) and whole-rock kimberlite samples. U/Pb ratios in perovs-kite in the matrix of kimberlites can be two orders of magnitude larger than in the rest of the kimberlite material, and with simple mineral separation techniques moderate success was achieved in U−Pb dating of fresh samples of younger kimberlites (around 100 Ma). The differences in U/Pb ratios between kimberlite samples from different parts of the same pipe have also been found to be large enough, in some cases, to allow reasonably accurate U−Pb age determination.In older kimberlites the U−Pb ages obtained were mostly incompatible with geological constraints and results obtained by other methods. However, for such pipes use of Pb−Pb systematics yields realistic age limits in some cases.
Kimberlites, carbonatites and ultramafic, mafic and potassic lamprophyres have been produced in West Greenland in recurrent events since the Archaean. Five distinct age groups are recognised: Archaean (>2500 Ma). Early Proterozoic (1700–1900 Ma), Middle Proterozoic (Gardar, c. 1100–1300 Ma), Late Proterozoic (600 Ma) and Mesozoic-Tertiary (200-30 Ma) The rocks comprise two large and four small carbonatite occurrences, four kimberlite dyke swarms, one lamproite dyke swarm and one lamproite pipe, one dyke swarm of potassic lamprophyre (shonkinite) and some ten dyke swarms of ultramafic lamprophyre and monchiquite. Geochemical data for the various rock groups are presented. Some of the carbonatites may represent relatively unmodified mantle-derived melts. The kimberlites range from primitive to differentiated compositions, and there are regional differences between kimberlites within Archaean and Proterozoic basement. The ultrapotassic lamproites and shonkinites have strong negative Nb spikes in their trace element spectra. The ultramafic and monchiquitic lamprophyres encompass a large compositional variation; however, several of the dyke swarms have individual chemical characters.
Available age data support the hypothesis that kimberlite intrusions are formed by mantle hotspots. The hypothesis has been tested by inverting the volcanic traces formed by three hotspots to determine the post-Triassic motions of Africa, South America, and North America relative to these hotspots. Then, using these motions, the kimberlites intruded on these continents within the last 150 m.y. are relocated to their place of origin in the present hotspot reference frame. The result indicates that a majority of the kimberlites formed within 5° of a mantle hotspot. Statistical analysis shows that this kimberlite/hotspot correlation is significant at above the 90% level.
RbSr analyses of leached phlogopite macrocrysts from kimberlite pipes 1, 2, 5 and 7 in south India give concordant ages of 1091±20, 1092±15, 1093±20 and 1091±10 Ma, respectively, indicating contemporaneous emplacement of these pipes. The present results are in contradiction with earlier measurements. Groundmass mineral assemblages with low ratios give a tight set of initial Sr ratios at 0.7029±2, 0.7019±2, 0.7029±2 and 0.7030±4 suggesting derivation of the primary kimberlite magma from a relatively uniform and depleted mantle source. A similar age and initial Sr isotopic ratio of one sample of the Majhgawan lamproite from Central India imply that the Proterozoic kimberlite/lamproite activities in India, though widely separated in space, were nearly contemporaneous.
Potassium-argon ages are reported for 16 muscovite and 14 biotite samples separated from Triassic sandstones of the Manx-Furness, Carlisle-Solway Firth and Lough Neagh-Arran Basins. Disturbance of the K-Ar isotopic system in these minerals during weathering, erosion, transport and lithification is discussed and loss of potassium shown to be as important a parameter as argon loss. Published data from tropical weathering profiles are used to establish the pattern of loss for these two elements during the formation of clay minerals from biotite, the data being displayed in a “potassium-argon loss diagram”. The loss curve so produced is then used to interpret our new biotite data and previously published age data for detrital biotite from the Cheshire Basin. The limit of interdigitation of northerly and southerly derived materials in the Irish Sea Basins is shown to lie north of the Fylde district of Lancashire. Age data from detrital muscovite are used to establish a potassum-argon loss curve for muscovite. The features of the two curves are markedly similar. Little effect on the apparent K-Ar age is observed until about 20% loss of potassium occurs. At this point massive argon loss takes place with little loss of potassium, due to either potassium “stabilisation” or structural expansion. The suitability of micas as K-Ar chronometers may be a consequence of the correlated potassium-argon loss rather than intrinsic high argon retentivity. If both mica curves are applied to detrial micas of the Namurian Millstone Grit series, a source area of age of ca. 900 Ma is indicated for both muscovite and biotite, indicating a probable pre-Cambrian age source area, probably in Scandinavia.
The emplacement of kimberlites in the North American and African continents since the early Palaeozoic appears to have occurred during periods of relatively slow motion of these continents. The distribution of kimberlites in time may reflect the global pattern of convection, which forces individual plates to move faster or slower at different times. Two-dimensional numerical experiments on a convecting layer with a moving upper boundary show two different regimes: in the first, when the upper boundary velocity is high, heat is transferred by the large-scale circulation and in the second, when the upper boundary velocity is lower, heat is predominantly transferred by thermal plumes rising from the lower boundary layer. For a reasonable mantle solidus, this second regime can give rise to partial melting beneath the moving plate, far from the plate boundaries. The transition between these modes takes place over a small range of plate velocities; for a Rayleigh number of 1,000,000 it occurs around 20 mm/yr. It is suggested that the generation of kimberlite magmas may result from thermal plumes incident on the base of a slowly moving plate.
The initial ratios of neodymium-143 to neodymium-144 in kimberlites ranging in age between 90 x 106 to 1300 x 106 years from South Africa, India, and the United States are different from the corresponding ratios in the minerals of peridotite
inclusions in the kimberlites but are identical to the ratios in the basaltic achondrite Juvinas at the times of emplacement
of the respective kimberlite pipes. This correlation between the kimberlites and Juvinas, which represents the bulk chondritic
earth in rare-earth elements, strongly indicates that the kimberlite's source in the mantle is chondritic in rare-earth elements
and relatively primeval in composition.
Rb-Sr ages of Indian kimberlites
- Anil Kumar
- T V Sivaraman
- K Gopalan
- D S N Murthy
Anil Kumar, Sivaraman, T.V., Gopalan, K. and Murthy, D.S.N.,
1990. Rb-Sr ages of Indian kimberlites. NGRI Annu. Rep.,
1989-1990: 19.
Chelima dykes-a source for diamonds in Kumool district
- S N Sen
- Ch Rao
Sen, S.N. and Narasimha Rao, Ch., 1971. Chelima dykes-a
source for diamonds in Kumool district, Andhra Pradesh.
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R-Phl) 1200 a K-Ar (Phl)
- Rb-Sr
Rb-Sr (W.R-Phl)
1200 a
K-Ar (Phl)
1319-1391
The multifaceted manifestations of an intrusive province around the intra cratonic Cuddapah basin
- V Madhavan
- J Mallikharjuna Rao
- N V Chalapathi Rao
- M Srinivas
Madhavan, V., Mallikharjuna Rao, J., Chalapathi Rao, N.V. and
Srinivas, M., 1995. The multifaceted manifestations of an
intrusive province around the intra cratonic Cuddapah basin,
India. In: Rajesh K. Srivastava and R. Chandra (Editors),
Magmatism in Relation to Diverse Tectonic Settings. Oxford
and IBH Publishers, New Delhi, pp. 93-105.
Precise Rb-Sr ages of South Indian kimbedites and Central Indian lamproites
- Anil Kumar
- K Gopalan
Anil Kumar and Gopalan, K., 1992. Precise Rb-Sr ages of South
Indian kimbedites and Central Indian lamproites. Proceedings
of the International Round Table Conference on Diamond
Exploration and Mining. Organised by NMDC and UNESCO,
26th and 27th November, 1992, New Delhi (unpaginated).
Chelima dykes-a source for diamonds in Kumool district, Andhra Pradesh
- S N Sen
- And Narasimha Rao
- Ch
Sen, S.N. and Narasimha Rao, Ch., 1971. Chelima dykes-a source for diamonds in Kumool district, Andhra Pradesh. Geol. Surv. India Misc. Publ., 19: 92-94.
Samarium-neodymium systematics in kimberlites and in the minerals of garnet lherzolite inclusions
- A R Basu
- M Tatsumato
Basu, A.R. and Tatsumato, M., 1979. Samarium-neodymium
systematics in kimberlites and in the minerals of garnet lherzolite inclusions. Science, 205: 389-401.
The multifaceted manifestations of an intrusive province around the intra cratonic Cuddapah basin, India
- Madhavan
Chelima dykes-a source for diamonds in Kurnool district, Andhra Pradesh
- Sen
RbSr ages of Indian kimberlites
- Anil
Precise RbSr ages of South Indian kimberlites and Central Indian lamproites
- Anil