No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Precise measurement of 143Nd/144Nd and Sm/Nd ratios using multiple-collectors inductively couple plasma-mass spectrometer (MC-ICP-MS) [in Chinese with English abstract]
... Separation of Hf and Nd was carried out on a HDEHP-coated Kef column. The Sr-Nd isotopic analysis methods follow Wei et al. (2002) and Liang et al. (2003). 87 Nd/ 144 Nd is reported relative to JNdi-1 ( 143 Nd/ 144 Nd = 0.512115), and 176 Hf/ 177 Hf is reported relative to JMC 14374 ( 176 Hf/ 177 Hf = 0.282189; corresponding to 0.282158 for JMC475). ...
... The Sr-Nd-Hf-Pb isotope ratios of the purified solution were analyzed by a Neptune Plus MC-ICP-MS at GIG-CAS, and the analytical procedures were the same as those described in Wei et al. (2002) and Liang et al. (2003). The analytical precisions of the isotopic ratio were reported as 2σ standard errors, and normalizing factors of 86 Sr/ 88 Sr = 0.1194, 146 Nd/ 144 Nd = 0.7219, and 179 Hf/ 177 Hf = 0.7325 were adopted to correct the mass fractionations of Sr, Nd and Hf during the measurements, respectively. ...
The ancient sub-continental lithospheric mantle (SCLM) of the eastern North China Craton (NCC) underwent metasomatism in the Triassic due to fluids derived from subducted Yangtze continental crust, followed by further metasomatism during the Jurassic–Cretaceous caused by fluids originating from subducted Paleo-Pacific oceanic slabs. However, the occurrence of carbonate metasomatism during these two geological events is a subject of debate, and the origin of carbonate-bearing metasomatic agents remains ambiguous. Here, we present an integrated study of petrography, whole-rock trace element data and Sr–Nd–Hf–Pb isotope data for the Jinan gabbros in the Luxi block of the eastern NCC. The Jinan gabbros show arc-like trace element patterns and enriched Sr–Nd–Hf–Pb isotopic compositions, suggesting that they originated from partial melting of the enriched ancient SCLM. In addition, there are remarkable similarities in Sr–Nd–Hf–Pb isotopes between the Jinan gabbros and HP–UHP metamorphic rocks in the Dabie–Sulu orogenic belt, indicating the involvement of continental crustal components from the subducted Yangtze block in the mantle source of the Jinan gabbros. The gabbro samples show decoupled Nd–Hf isotopes with positive ∆εHf values (∆εHf = εHf – 1.55 × εNd – 1.21; Vervoort et al., 2011), which were mainly caused by a metasomatic agent with high Nd/Hf ratios. The increase in εNd values with increasing Hf/Hf* (Hf/Hf* = HfPM/[(NdPM × SmPM)0.5]) and Nb/La further indicates that the metasomatic agent in the mantle source was depleted in high field strength elements (HFSEs) but enriched in rare earth elements (REEs), resembling the mantle-derived carbonatites in the Luxi area. The Jinan gabbros show significant variations in εNd and εHf, which cannot be explained by the involvement of C–O–H fluids and pure carbonatitic melts in their mantle source. Instead, carbonate-bearing felsic melts from the deeply subducted Yangtze continental crust are proposed to have acted as metasomatic agents. Carbonate metasomatism can significantly weaken the strength and decrease the melting temperature of the overlying ancient SCLM. Therefore, carbonate metasomatism that occurred in the lithospheric mantle of the eastern NCC during the Triassic, likely associated with deep subduction of the Yangtze block, might have played a significant role in promoting lithospheric thinning and mafic magmatism in the late Mesozoic.
... The solution was dried, redissolved in HCl, and then separated using the conventional cation exchange technique. Sample preparation and chemical separation were performed as described by Liang et al. [41,42]. The Sr-Nd isotope ratios were measured using a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Dreieich, Germany). ...
The Huayangchuan U-polymetallic deposit in the Qinling Orogen is a newly verified carbonatite-hosted deposit on the southern margin of the North China Craton (NCC) in Central China. Granitic magmatism is extensively developed in the Huayangchuan deposit area and is lacking analysis on the reasons for these situations; however, its ages, petrogenesis, and relationship with uranium mineralization are not well constrained. Zircon U–Pb ages for the hornblende-bearing granite porphyry and medium-fine-grained biotite granites in close proximity to carbonatite rocks are 229.8 ± 1.1 and 135.3 ± 0.6 Ma, respectively. High-K calc-alkaline series and weakly peraluminous Triassic hornblende-bearing granite porphyry are slightly enriched in light rare earth elements (LREE) with flat heavy rare earth element (HREE) patterns, enriched in Ba and Sr, and depleted in Nb, Ta, P, and Ti, i.e., geochemical characteristics similar to those of adakite-like rocks. The Early Cretaceous medium-fine-grained biotite granites are characterized by LREE enrichment and flat HREE patterns, which belong to high-K calc-alkaline series, and metaluminous belong to weakly peraluminous I-type granite, with U and large ion lithophile element (LILE) enrichment and high field strength element depletion. The high initial 87Sr/86Sr ratios and enriched Nd (εNd(t) = −10.7 to −9.5 and −19.9 to −18.9, respectively) and Hf (εHf(t) = −21.8 to −13.0 and −30.5 to −19.0, respectively) isotopes revealed that both granitic rocks from the Huayangchuan deposit mainly originated from lower crustal materials, generated by partial melting of the ancient basement materials of the Taihua Group. Triassic hornblende-bearing granite porphyry is significantly different from the mantle origin of the contemporaneous U-mineralization carbonatite. In combination with tectonic evolution, we argue that the Qinling Orogenic Belt was affected by the subduction of the North Mianlian Ocean during the Late Triassic. The ongoing northward subduction of the Yangtze Craton resulted in crustal thickening, forming large-scale Indosinian carbonatites, U-polymetallic mineralization, and contemporaneous intermediate-acid magmatism. Additionally, due to the tectonic system transformation caused by Paleo-Pacific Plate subduction, intracontinental lithosphere extension and lithospheric thinning occurred along the southern NCC margin in the Early Cretaceous. Intense magma underplating of the post-orogeny created a large number of magmatic rocks. The tremendous heat could have provided a thermal source and dynamic mechanism for the Yanshanian large-scale U-polymetallic mineralization events.
... Two USGS reference materials W-2a and BHVO-2 were also processed for Sr-Nd isotopes to monitor the analytical accuracy and gave ratios of 0.706957 ± 10 and 0.703480 ± 14 for 87 Sr/ 86 Sr, respectively, and of 0.512509 ± 10 and 0.512989 ± 18 for 143 Nd/ 144 Nd, respectively, which are in agreement within error of the recommended values (Fourny et al. 2016). The analytical procedures are principally similar to the description in Wei et al. (2002) and Liang et al. (2003). ...
Pre-Cenozoic high-Mg andesites (HMAs) are mostly present in continental interiors, but their genetic relationship with continental lithosphere evolution remains unclear because of uncertainties of their mantle source, magmatic processes, and physicochemical conditions of formation. Early Cretaceous high-Mg dioritic rocks (HMDs, analogs of HMAs) of the Jinling complex in the Luxi area are typical intra-plate intrusions of the eastern North China Craton (NCC) and can be subdivided into two groups (Group-I and -II) on the basis of their petrographic and geochemical features. Group-I HMDs show low SiO2 contents (52.47–56.10 wt%) and Sr/Y (34.5–39.6) and (La/Yb)N (10.3–13.6) ratios but high contents of MgO (7.86–9.13 wt%), Y (18.3–20.3 ppm), Yb (1.43–1.47 ppm), and compatible elements (Cr = 407–585 ppm; Ni = 117–216 ppm), classifying as sanukitic rocks. Group-II HMDs are characterized by high SiO2 contents (63.81–64.87 wt%) and Sr/Y (47.1–63.4) and (La/Yb)N (16.1–17.5) ratios with low MgO (2.90–3.08 wt%), Y (0.88–1.04 ppm), Yb (0.88–1.04 ppm), and compatible elements (Cr = 201–213 ppm; Ni = 55–57 ppm) contents, belonging to adakitic rocks. Group-I and Group-II HMDs of the Jinling complex are closely related in spatial and temporal distribution, and all have enriched Sr-Nd isotopic compositions and arc-like trace element patterns with abundant hydrous minerals. Therefore, the Jinling HMDs should share a common source of ancient sub-continental lithospheric mantle that was metasomatized by aqueous fluids derived from the subducted Paleo-Pacific slab. The Jinling HMDs were not formed from interaction between slab-derived melts and mantle-wedge peridotites but were instead derived from partial melting of hydrous mantle peridotites in the continental interior of the eastern NCC. The distinctly different petrography, geochemistry, and mineralogy of the two groups of rocks resulted mainly from differing magmatic processes at crustal depths. Thus, Pre-Cenozoic intra-plate HMAs/HMDs are genetically distinct from Cenozoic HMAs that were mostly present in arc settings and generally represent juvenile crust growth. In a way, Archean tonalitic-trondhjemiticgranodioritic rocks (TTG) and sanukitoids, geochemically similar to HMAs/HMDs, could also be derived from interaction between slab-derived melts and mantle-wedge peridotites in arc settings or partial melting of hydrous mantle peridotites in continental interiors, and thus might not always be related with continental crustal growth and the onset of plate subduction.
... Samples for whole-rock Nd isotope analysis were separated and purified by specified cationexchange techniques at GIGCAS. Neodymium isotope compositions were measured by MC-ICP-MS at GIGCAS, following the analytical procedures described by Liang et al. (2003). Measured 143 Nd/ 144 Nd ratios were normalized to 146 Nd/ 144 Nd = 0.7219. ...
Widespread crust-derived granitoids in North China provide evidence of Mesozoic lithospheric thinning and destruction of the North China Craton. However, the link between lower crust and lithospheric mantle reactivation remains poorly understood. We present whole-rock geochemistry and zircon O-Hf isotopes for Early Cretaceous peralkaline A-type granites (i.e., Xiwanzi, Xiangshan, and Yansehu) from the Yanshan Mountains of the eastern block of the North China Craton. The Xiwanzi granite has a U-Pb age of 134.3 ± 0.4 Ma, with homogeneous whole-rock Nd isotopes [εNd(t) = −7.7 to −7.5] but highly variable zircon O-Hf isotopes [δ18O = 5.1‰ to 7.2‰ and εHf(t) = −7.7 to +9.6]. Such isotopic variations likely resulted from a hybrid juvenile source consisting of partial melting of newly underplated basaltic rocks derived from both the metasomatized ancient and juvenile sub-continental lithospheric mantle. In contrast, the Xiangshan (117.4 ± 1.0 Ma) and Yansehu (116.3 ± 1.4 Ma) granites have relatively uniform isotopic compositions [whole-rock εNd(t) = −12.2 to −10.8, zircon δ18O = 5.2‰ to 6.4‰, and εHf(t) = −17.1 to −4.7], close to those of the Proterozoic mafic granulite xenoliths from the ancient lower crust. The isotopic variations of the Early Cretaceous A-type granites suggest a continuous change in the melting model from the underplated juvenile lowermost crust to the overlying ancient lower crust at high temperatures in an extensional environment. Our results indicate that A-type granites can be used to probe the nature and reactivation of the lower crust of an Archean craton. Significantly, large-scale continuous thinning of lower continental crust provides key insights into the generation of the widespread Mesozoic crust-derived granitoids in North China.
... Whole-rock Sr-Nd isotope analyses were undertaken at the SKLaBIG, GIGCAS, with a Thermo-Fisher Scientific Neptune Plus multi-collector ICP-MS (MC-ICP-MS) instrument. The analytical procedures were identical to those described by Wei et al. (2002) and Liang et al. (2003). Instrumental mass bias was corrected by normalization to 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219. ...
The origins of Cenozoic granites in the Himalaya are key to understanding the evolution of the Himalayan orogen. However, it is unclear whether these granites represent primary melts, and the nature of their magma source is controversial. Here, we present a systematic element and Sr–Nd–B–Mo isotope study of Cenozoic granites from the Yardoi area in the eastern Tethyan Himalaya, China. These granites can be divided into two groups: mid‐Eocene porphyritic two‐mica granites with low SiO2 contents (65.9−69.6 wt.%) and adakitic geochemical signatures, and mid‐Eocene to Miocene equigranular granites with high SiO2 contents (71.6−75.5 wt.%). The high‐SiO2 granites (HSG) have similar Sr−Nd isotope compositions to the low‐SiO2 granites (LSG), but they have distinct δ¹¹B values of −19.4‰ to −11.4‰ and −10.6‰ to −6.89‰. This indicates that the two groups have different sources, with the LSG derived by partial melting dominantly of metamafic rocks at thickened lower crustal conditions, and the HSG generated by partial melting of the mid‐crust metasedimentary rocks with less enriched Nd isotope compositions. The δ98/95Mo of the LSG and HSG are highly variable with values of −0.68‰ to 0.12‰ and −1.13‰ to 0.46‰, respectively. δ¹¹B values of the HSG correlate positively with δ98/95Mo and Sr/Y values and correlate negatively with K2O, Rb, Zr, and Rb/Sr, reflecting the addition of external metamorphic fluids during anatexis of the metapelites. The B–Mo isotope data robustly suggest source‐controlled compositional diversity of the Himalayan granites, which could provide clues to the physical and geochemical responses during the evolution of a large orogen.
... Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/doi/10.1130/B36729.1/5814704/b36729.pdf by Guangzhou Institute of Geochemistry CAS user compositions were determined on the Neptune Plus multiple collector−inductively coupled plasma−mass spectrometer (MC-ICP-MS) at the Sate Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), following the procedures described in Wei et al. (2002) and Liang et al. (2003). The mass bias during the analysis was normalized to 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219. ...
Recycling of Fe-rich materials through subduction may affect the element budgets and redox properties of the mantle, thus influencing the differentiation trends and mineralization types of mantle-derived magmas. However, the effects of different recycled Fe-rich materials on the mantle are dependent on their lithologies, which are still poorly constrained. Stable Fe isotopes can act as useful tracers for distinguishing among different recycled Fe-rich lithologies, and their imprints may be documented in mantle-derived magmas. This study focuses on the Fe isotopes of ferrobasalts and the associated dacites and magnetite ores in the Chagangnuoer Fe deposit of the Awulale Arc, Central Asia, to identify recycled Fe-rich materials and explore the Fe enrichment mechanism in continental arcs. Our results indicate that the ferrobasalts and dacites possess the lowest known δ56Fe, −0.40‰ ± 0.04‰ (2SE), among their counterparts worldwide. The low δ56Fe signatures are considered to originate from a hybridized mantle source, which may have been modified by recycled ferrocarbonates. The recycled ferrocarbonates may have melted during the decompressional heating stage of the slab subduction of the South Tianshan Ocean, coupled with asthenospheric upwelling under “wet” mantle conditions. The addition of ferrocarbonate melts to the mantle might have decreased the oxygen fugacity of the mantle wedge to below the fayalite−magnetite−quartz buffer, accounting for the Fe enrichment in arc tholeiites and large-scale Fe mineralization along the Awulale. Notably, our study reveals a novel carbonate recycling pathway in the cold subduction zones, where ferrocarbonates were subducted into the mantle and then recycled by the upwelling asthenosphere to mix with the fluid-metasomatized mantle through mantle convection.
... The purified solution Sr-Nd-Hf-Pb isotope ratios were measured using a Neptune Plus MC-ICP-MS at GIG-CAS, the analytical procedures are principally similar to the description in Wei et al. (2002) and Liang et al. (2003). The analytical precisions of isotopic ratio were reported as 2σ standard errors. ...
Recycled crustal materials play an important role in modifying chemical composition of the overlying mantle wedge in oceanic and continental subduction channels. It is widely recognized that the eastern North China Craton (NCC) experienced a complex evolutional history in Phanerozoic and may have undergone multi-stage fluid- and/or melt-related metasomatism from the subducted continental blocks and oceanic slabs. However, the nature and origin of metasomatic agents for the sub-continental lithospheric mantle (SCLM) of the eastern NCC remain in debate. Here, we present an integrated study of zircon U-Pb dating, whole-rock trace elements and Sr-Nd-Hf-Pb isotopes for the Zouping gabbroic diorites in the Luxi area in continental interior of the eastern NCC. The Zouping gabbroic diorites were emplaced into Paleozoic-Mesozoic volcanic-sedimentary sequences at 127±1 Ma. The studied samples geochemically belong to gabbroic diorites and show arc-like trace element patterns with enriched Sr-Nd-Hf-Pb isotopic compositions. Sr-Pb isotopes of the Zouping gabbroic diorites are uncorrelated with Nd-Hf isotopes, denoting a remarkable decoupling between Sr-Pb and Nd-Hf isotopes. Nd-Hf isotopic compositions of the Zouping gabbroic diorites are similar to those of the eclogites in the Dabie-Sulu orogenic belt, suggesting that their mantle source had been metasomatized by felsic melts possibly derived from the UHP metamorphic rocks (i.e., eclogites) in the Dabie-Sulu orogenic belt. Thus, Triassic continental subduction of the Yangtze Block should have arrived beneath the continental interior of the eastern NCC. Furthermore, the Zouping gabbroic diorites have significantly variable Pb isotopic compositions that are correlated with Ba/La and Ba/Th ratios, suggesting the involvement of two types of aqueous fluids with different Pb isotopic compositions in the mantle source. The high 206Pb/204Pb fluid was directly derived from dehydration of the subducted Paleo-Pacific oceanic crust, while the low 206Pb/204Pb aqueous fluid was originated from dehydration of the subducted Yangtze continental crust. Therefore, the SCLM of the eastern NCC should have been successively metasomatized by aqueous fluids released from the subducted Yangtze continental crust in Triassic and Paleo-Pacific oceanic slabs in Jurassic−Cretaceous. These processes not only resulted in various mantle metasomatites with distinct radiogenic isotopic compositions but also weakened the overlying lithospheric mantle by reducing its viscosity and strength, which should also be regarded as a critical factor for Mesozoic descratonization of the eastern NCC.
... Whole-rock Sr-Nd-Hf isotopes were determined using a Finnigan Neptune multi-collector (MC)-ICP-MS, following the procedure described by Wei et al. (2002), Liang et al. (2003), and Li et al. (2005), respectively. Reference standard BHVO-2 analyzed along with the unknowns gave 87 Sr/ 86 Sr = 0.703456 ± 0.000028 (n = 10; 2σ ), 143 Nd/ 144 Nd = 0.512984 ± 0.000011 (n = 8; 2σ ), and 176 Hf/ 177 Hf = 0.283095 ± 0.000004 (n = 4; 2σ ) (Supplementary Weis et al., 2005). ...
Understanding the petrogenesis of alkaline syenites is important for constraining the mechanisms of rare earth element (REE) and rare-metal mineralization. Here we report a detailed petrological and geochemical study of early Permian syenitic rocks from the southwestern Tarim large igneous province (TLIP) in the Wajilitag area (China). We use these data to investigate the complex magmatic processes responsible for the enrichment of incompatible elements (e.g., REEs and rare-metals) in these rocks. The Wajilitag syenitic rocks comprise early hornblende syenite (281 Ma) and later nepheline syenite (278 Ma), both of which are spatially and temporally associated with mafic intrusions (i.e., gabbro and diabase). These syenitic rocks show continuous variations in major elements with the mafic rocks. They also have similar Sr–Nd–Hf isotopic compositions with the nearby mafic rocks, denoting that the Wajilitag syenitic rocks should be derived from the melts represented by these mafic rocks. However, these syenitic rocks, particularly the nepheline syenites, are typically characterized by extreme enrichment of incompatible elements, which is hard to be accounted by simple fractional crystallization of mafic magmas. Some clinopyroxene phenocrysts in the Wajilitag nepheline syenites show oscillatory zoning with strikingly increasing and then gradually decreasing MgO contents, which recorded replenishment of mafic magma at the interval. Low-MgO clinopyroxene mantles and/or rims have much higher incompatible element contents (e.g., Nb, Ce, and Zr) and ratios (e.g., Ce/Y) than their cores, which could reflect melt injection controlled by reactive porous flow in a mush reservoir of a crustal magma chamber. Such processes may also cause the high Ce and/or Nb contents of the mantles and/or rims of zoned titanite and apatite phenocrysts. The injection of reactive porous flow melts is the key process that produces the extreme enrichment of incompatible elements in the alkaline syenites from the western TLIP, as well as other plume-related alkaline syenites that host world-class REE and rare-metal deposits.
... The isotopes were separated via ESI Prep Fast-MC (ESI, America). Sr and Nd isotopic analyses were performed using a Neptune Plus multicollector ICP-MS (MC-ICP-MS) (Liang et al., 2003;Wei, 2002). Sr and rare earth elements (REE) were separated using a cation column, and the Nd fraction was further separated using a HDEHP-coated Kef column. ...
Rare Earth Element and Yttrium (REY)-rich deep sea sediments have been estimated to be a highly important potential resource. However, the main material sources that supply the huge amount of REY resources, as well as geochemical procedure determines the distinct REY patterns of these sediments, remain unclear. To fill this research gap, in this study, three sediment cores (GC02, GC04, and GC11) collected from the Central Indian Ocean Basin (CIOB) and a core (GC03) from eastern of the 90° E Ridge (NER) were sampled for mineral identification and elemental (major, trace, and rare earth elements) analyses. Fish teeth and detrital minerals were isolated from the sediments, and their ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios were measured. Accumulation of REY is revealed in three cores of GC02, GC04, and GC11 from CIOB with mean value of 511.93μg/g, 614.79 μg/g, and 1036.14 μg/g, respectively. Most REY rich sediment exhibit obvious to slight negative Ce abnormal, slight positive Eu and Y abnormal. The detrital fraction of the REY rich sediments exhibit less radioactive εNd values of −8.36295 and more radioactive ⁸⁷Sr/⁸⁶Sr of of 0.71651. On the contrary, the fish teeth exhibit less radiogenic ⁸⁷Sr/⁸⁶Sr ratio of 0.70915 but more radiogenic εNd values of −5.13511 than those of the sea water of the Indian Ocean. The results reveal that the REY-rich sediments in the CIOB are characterized by multiple material sources including weathering continental products, alteration of volcanogenic glasses, hydrothermal and marine authigenic materials. Distinct volcanogenic materials input are obvious in the CIOB evidenced with radiogenic ¹⁴³Nd/¹⁴⁴Nd ratios of the fish teeth, the wide occurrence of clinoptilolite and high Te contents contained. The volcanogenic related hydrothermal materials are then indicated to provide most part of REY for the fish teeth, which contribute the most amount of REY of the sediments. However, the terrestrial input of REY cannot be neglected, which indicates the REY-rich deep sediments were formed under multi-source supply system. The study indicated that continuous exchange of Sr between fish teeth and ambient pore water after deposition, and ambient pore water was concluded to contain an abundance of released radiogenic terrestrial Sr. However, the exchange of Nd between fish teeth and bottom sea water ceased after buried in depth. Nd ratios on the fish teeth recorded the more radioactive hydrothermal material carried by bottom seawater at the early stage of precipitation.
... All measured 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios were fractionationcorrected to 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219, respectively. The details of the analytical procedures were described by Wei et al. (2002) and Liang et al. (2003). ...
A world-class Sn province in South China contains granite- and porphyry-related Sn deposits. In this paper, we investigate the source of Sn, based on a study of Early Cretaceous (145–134 Ma) ore-barren granites and granite porphyries, ore-barren rhyolites, and Sn-bearing granite porphyries in the Mikengshan (MKS)–Qingxixiang (QXX)–Yanbei (YB) area of South China. The ore-barren rhyolites have enriched whole-rock Nd and zircon Hf isotopic compositions [εNd(t) = −9.1 to −10.5; εHf(t) = −5.9 to −13.8]. The ore-barren granites and granite porphyries have A-type granite characteristics and less enriched Nd–Hf isotopic compositions [εNd(t) = −4.9 to −3.2; εHf(t) = −6.0 to +1.7] than the ore-barren rhyolites. The Sn-bearing granite porphyries have similar rare earth element and trace element patterns to the ore-barren rhyolites. In addition, they have similar Nd but less enriched Hf isotopic compositions [εNd(t) = −8.9; εHf(t) = −3.3 to +0.4] compared with the ore-barren rhyolites. The average ΔFMQ values of the studied volcanic (–0.50) and intrusive (–0.21) rocks indicate reduced condition during magma evolution. We suggest that the ore-barren rhyolites were likely derived by partial melting of Paleoproterozoic to Mesoproterozoic crustal metasedimentary rocks and that the Sn-bearing granite porphyries were possibly formed by partial melting of Paleoproterozoic metasomatized mantle-derived crustal rocks. Whereas, the ore-barren granites and granite porphyries were likely generated by partial melting of a hybridized source consisting of ancient and late Mesozoic juvenile crustal rocks. We propose that the reduced redox state and ancient crustal sources played an important role for Sn mineralization in the MKS–QXX–YB area.
... The precision of the 147 Sm/ 144 Nd ratios was better than 0.5%, and the accuracy of the measured Nd isotopic ratios was better than 0.003%. Details of the experimental procedures and the analytical precision were discussed by Liang et al. [95]. ...
The Jinshajiang–Ailaoshan–Song Ma orogenic belt (JASB), as a vital segment of the eastern Paleo-Tethyan tectonic zone, is one of the most important zones in which to study the Paleo-Tethyan tectonic evolution. We have undertaken an integrated geochronological, petrological, and geochemical study of mafic rocks from the JASB to reveal the subduction and closure processes of the eastern Paleo-Tethyan Ocean during the Permian to Triassic. In conjunction with previous magmatic and metamorphic records in the JASB, three important tectonic stages are identified: (1) Early Permian to Early Triassic (ca. 288–248 Ma). Most of the Early Permian to Early Triassic mafic rocks have normal mid-ocean ridge basalt (N-MORB)- or enriched MORB (E-MORB)-like rare earth elements (REE) and trace element-normalized patterns with positive εNd(t) and εHf(t) values and negative Nb and Ta anomalies. Their La/Nb ratios and εNd(t) values show that approximately 3%–15% of slab-derived fluid accounts for the generation of these rocks. These characteristics suggest that the mafic rocks formed in an arc/back-arc basin setting at this stage. Additionally, the Early Permian mafic rocks are mainly exposed in the Jomda–Weixi–Yaxuanqiao–Truong Son magmatic rock belt (JYTB) on the western side of the JASB, indicating that the westward subduction of the Jinshajiang–Ailaoshan–Song Ma Paleo-Tethys Ocean (JASO) began in the Early Permian. Middle Permian mafic rocks are exposed in the Ailaoshan-Day Nui Con Voi metamorphic complex belt and the JYTB on both sides of the JASB. We propose that the bipolar subduction of the JASO occurred in the Middle Permian and ended in the Early Triassic. (2) Middle Triassic (ca. 248–237 Ma). The mafic rocks at this stage have LREE- and LILE-enriched patterns, negative Nb and Ta anomalies and negative εNd(t) values. Their variable εHf(t), εNd(t) values and La/Nb ratios show that these mafic rocks were highly affected by crustal material (ca. 16%). Considering the Middle Triassic high-pressure (HP) metamorphism and massive Al-enriched felsic magmatism in the JASB, these rocks may have formed in a collisional setting between the South China Block (SCB) and the North Qiangtang–Simao–Indochina Block (QSIB) during the Middle Triassic. (3) Late Triassic (ca. 235–202 Ma). The mafic rocks at this stage have negative εNd(t) and εHf(t) values and show terrestrial array characteristics. The εNd(t) values and La/Nb ratios show that approximately 30% of crustal components account for the generation of these rocks. Combined with the contemporaneous bimodal magma and metamorphism during the Late Triassic, we suggest that these rocks may have formed in a postcollisional extensional setting associated with magma diapir.
... Sr and Nd isotopic compositions were assessed with Neptune plus MC-ICPMS, following procedures described by Wei et al. (2002) and Liang et al. (2003) ...
Previous studies have shown that the formation of Maoniuping giant rare-earth elements (REE) deposit is closely related to the protracted magmatic evolution (>2 Myr) of syenite–carbonatite magma. However, the reasons responsible for the protracted magmatic evolution of the Maoniuping deposit has not yet been well constrained. The REE-barren alkaline granite intruding the Cenozoic REE-mineralized syenite−carbonatite complex provides an opportunity to resolve this problem. In this study, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf isotope analyses of the alkaline granite and syenite were undertaken to elucidate the long timescales of magmatic evolution in the Maoniuping deposit. Zircon U–Pb dating indicates that the alkaline granite formed slightly later (25.5 ± 0.4 Ma) than the syenite (27.2 ± 0.6 Ma). The former is characterized by high SiO2 (72.8–75.8 wt.%), Na2O + K2O (10.5–11.6 wt.%), and FeOT (2.24–2.87 wt.%) contents, low Al2O3 (10.3–11.8 wt.%), MgO (0.08–0.20 wt.%), and CaO (0.04–0.33 wt.%) contents, and negative Eu, Ba, Sr, Ti, and P anomalies. It has characteristics typical of A-type granitoids, such as high 10000Ga/Al (3.46–5.16) and FeOT/(FeOT + MgO) (0.93–0.97) ratios, and high (Zr + Nb + Ce + Y) contents (650–1065 ppm). The distinct Sr–Nd–Hf isotopic and compositional signatures of the alkaline granite and syenite indicate that the former is likely a product of direct high-temperature partial melting of shallow crust induced by the upwelling of asthenospheric mantle in a transtensional setting. Combining our results with those of previous studies, we suggest that shallow-seated, continuous underplating of mantle-derived magmas and stable regional thermal anomalies were responsible for the prolonged magmatic evolution and REE mineralization of the Maoniuping syenite–carbonatite complex.
... Whole-rock Sr and Nd isotopic analyses were conducted on a subset of whole-rock sample powder using a Neptune plus MC-ICP-MS at the SKLaBIG, GIG-CAS. Detailed procedures of sample preparation and chemical separation are same as those described by Liang et al. (2003) and Wei et al. (2002). The REEs were separated using the cation exchange columns, and the Nd fractions were further separated by HDEHP-coated Kef columns. ...
The early Paleozoic Wuyi-Yunkai Orogen (WYO) developed in the inner part of the South China Block (SCB) and underwent large scale felsic magmatism. Different tectonic models have been proposed to explain the evolution of the WYO, including intracontinental and collisional orogenesis. The debates focus on whether the asthenospheric materials were involved during evolution of the WYO. We conducted detailed petrographic and geochemical analyses on gabbros from the Qiaotou pluton and granodiorites and the hosted MMEs from the Xinsi pluton in the eastern WYO, and present the first evidence of asthenosphere upwelling that induced significant lithosphere remobilization in the SCB during early Paleozoic. Granodiorites from the Xinsi pluton (441±2 Ma) contain abundant amphibole and are metaluminous, which originated from the igneous basement in the Cathaysia Block. The hosted MMEs (440±2 Ma) have variable SiO2 and enriched Sr-Nd isotopic compositions with high zircon δ¹⁸O values, which were formed through hybridization of felsic melts and mafic magmas from the enriched lithosphere mantle. Gabbros from the Qiaotou pluton (448±8 Ma) have low K2O with insignificant Nb-Ta-Ti anomalies and show variable Sr-Nd-O isotopic compositions. They were derived from the depleted asthenosphere and underwent crustal assimilation. The asthenosphere upwelling may be induced by slab breakoff during the collision between the western Cathaysia Block and an unknown block near northern Gondwana. The continental collision possibly transferred compressional stress and caused crustal uplifting along the weak zone in the inner SCB. The asthenosphere upwelling provided tremendous heat for the lithosphere remobilization and voluminous magmatism in the WYO.
... Sr was further purified using Sr-specific resin, while Nd was separated from other REEs with LN-specific resin. The analytical methods were described in detail by Liang et al. (2003). Isotopic ratios were corrected for instrumental mass fractionation using 88 Sr/ 86 Sr = 8.375209 for the 87 Sr/ 86 Sr ratios, 146 Nd/ 144 Nd = 0.7219 for the 143 Nd/ 144 Nd ratio. ...
Revealing the origin of explosive eruptions of silica-rich magma is of paramount importance for understanding the evolution of continental crust and volcanic hazards. However, it remains controversial as to how the erupted magmas form and how they connect with plutonic realms, partly owing to the rarity and the obscurity of the “cumulate” complementary to such eruptions of silica-rich magmas. Here the issues are explored by comparing the volcanic rocks (rhyodacite + rhyolite) and their associated subvolcanic intrusions (monzodiorite + monzonite + quartz monzonite) within Tonglu volcanic basin (SE, China). The Tonglu plutonic and volcanic units are consistent with each other in age (~130 Ma), space and source materials (e.g., Sr-Nd-Hf isotopes), strongly suggesting that they are cogenetic. Mineral mapping demonstrates that abundant plagioclase clusters (and chains in monzodiorite) occur in plutonic units, implying the processes of crystal gathering and/or accumulation. Rhyolite-MELTS modeling, and geochemical studies coupled with textural observations suggest that the Tonglu volcanic and plutonic rocks represent the residual melts and the complementary cumulate residues, respectively. The compositional and mineral variations in the plutonic rocks can be explained by two-stage, low-pressure crystal-melt separation of a dacitic magma. The monzodiorite represents the first-stage cumulate that was unsaturated in zircon and biotite/K-feldspar on the basis of low Zr and Ba concentrations and the occurrence of these two phases in the interstices between plagioclase and amphibole. The monzonite and quartz monzonite are the second-stage cumulates after saturation of zircon and biotite/K-feldspar as indicated by abrupt increases in Zr and Ba concentrations and zircon inclusions within euhedral biotite. Mass balance calculation and textural estimation indicate that the cumulates actually are a mixture of crystals and melt, containing ~40 vol% interstitial melt. Interstitial zircons from monzodiorite, largely crystallized from trapped melt, show contrasting trace-element trends (e.g., Ti, Zr/Hf, Eu/Eu*, Gd/Yb) to those of the other rock types (i.e., monzonite, quartz monzonite, rhyodacite and rhyolite), consistent with fractional crystallization. We interpret these divergences to heating-induced partial dissolution of a basal crystal framework of monzodiorite due to recharges of hot mafic magmas, but the limited dissolution fails to rejuvenate the crystal mush. The Tonglu volcanic-plutonic system demonstrates that compositional distillation via crystal-liquid separation within the upper crust is an effective mechanism by which a potentially eruptible rhyolitic cap can be generated. Recharges of hot mafic magmas at shallow crustal levels may prolong the lifespan of granitic magma reservoirs. A combined study including texture, geochemistry, thermodynamic modeling and mass-balance calculations can help us identify the fingerprints of cumulates in felsic magma systems and thus track the processes responsible for producing large eruptions of silica-rich magmas.
... Secondly, REEs were separated using cation columns, and then Nd fractions were further separated using HDEHP-coated columns. Nd isotopic compositions were analyzed on the Neptune Plus multi-collector mass spectrometer at GIGCAS, following procedures similar to those of Wei et al. (2002) and Liang et al. (2003). Measured 143 Nd/ 144 Nd ratios were normalized to 146 Nd/ 144 Nd = 0.7219. ...
Relative contribution of magmatic and hydrothermal processes to rare metal enrichment has been a key issue for the alkaline-associated rare metal deposits. Till now, our understanding on the rare metal concentration of extrusive peralkaline magmatic systems is rather limited. We try to address this issue by studying the Tudiling trachyte Nb-Ta-Zr-REE deposit in the South Qinling (SQ), which is well endowed with abundant alkaline-associated rare metal deposits. Four lithofacies (i.e., trachyte, trachytic tuff, trachytic phyllite and trachytic ignimbrite) with rare metal mineralization were thoroughly investigated on their emplacement ages, whole-rock geochemistry, and Nb-REE mineralogy to decipher the evolution of the system and the concentration mechanisms for the rare metals. Zircon U-Pb dating indicates that the former three lithofacies developed during the Early Silurian (445 − 442 Ma) and are coeval with their intrusive counterparts, i.e., the Miaoya and Shaxiongdong syenites in the SQ. They share similar element distribution patterns (Nb-Ta, Zr-Hf, LREE enrichments, and Sr, P, Ti depletions) and moderately depleted Nd isotopes (εNd(t) values: 2.3 – 3.1), indicating a common mantle source. In contrast, the trachytic ignimbrite erupted during the late Jurassic (157 ± 1.9 Ma) and has enriched Nd isotope compositions (εNd(t) values: -2.9 − -2.8), implying an enriched mantle source, which had probably been modified by the residuals of the Mianlue oceanic sediments. Their bulk-rock rare metal concentrations indicate that the former three lithofacies are characterized by Nb-Ta-Zr mineralization/enrichment with the phyllite containing the highest grades, while the latter one has REE mineralization as well as Nb-Ta-Zr mineralization/enrichment. Our geochemical and mineralogical results suggested that rare metal enrichment in these trachytic rocks was initially attributed to the partial melting of an enriched mantle source and subsequent protracted fractional crystallization of alkaline basaltic magmas. Effects of late-stage hydrothermal alteration on rare metal upgrading are highly dependent on rock structures and distinct on the intensively altered phyllite and ignimbrite.
... Sr-Nd isotopic compositions were performed by the MC-ICPMS at the State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China, following the chemical separation outlined by Liang, (2003). The mass fractionation corrections are based on 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219 and the total procedure blanks for Sr and Nd are in the range of 200-500 pg and < 50 pg, respectively. ...
A combined U-Pb geochronology, whole-rock geochemistry, and Sr-Nd isotopic study give new insights into the nature of the protolith, tectonic setting, and petrogenetic history of Cadomian orthogneisses from the Tutak metamorphic complex (TMC), Sanandaj-Sirjan Zone, Iran. U–Pb zircon dates of 535 ± 4 Ma suggest an Early Cambrian crystallization age for the orthogneiss protoliths. Geochemical data indicate that the orthogneisses have I-type, high-K calc-alkaline, and peraluminous signatures. Depletion in Nb, Ta, Ti, Sr, and enrichment in Nd, Th, K, U relative to the primitive mantle, suggest derivation in a subduction zone environment in an active continental margin. Initial ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios vary from 0.7045 to 0.7092 and from 0.5116 to 0.5117, respectively. Moreover, εNd(t) values range from − 2.95 to − 5.29, and two-stage model ages vary from 1.4 to 1.6 Ga. Taken together, these data suggest derivation of TMC orthogneisses from a metasomatic lithospheric mantle with a contribution of a crustal component generated via partial melting of a metabasite (i.e., amphibolite).
... Whole-rock Sr-Nd isotope compositions were measured by a Multicollector Inductively-Coupled plasma Mass Spectrometry (MC-ICP-MS) at University of Science and Technology of China. Chemical separation and purification were conducted at SKLIG-GIG-CAS following Liang et al. (2003) and Wei et al. (2002). An international standard BHVO-2 was used as the standard solution for isotopic ratio analysis. ...
Accretionary orogens are the primary sites for continental growth, but the rate and amount of crust generation throughout its evolution are poorly constrained. In this contribution, our new results about the genesis of two intermediate-felsic plutons are combined with a compiled granitoid dataset to evaluate the amount and rate of crustal growth throughout the evolution of the Western Kunlun orogen, which is a typical accretionary orogen associated with the consumption of the Proto-Tethys during the Early Paleozoic. The ca.446 Ma Sanshili pluton was formed through interactions between metasomatized mantle wedge-derived oxidized magmas and the lower arc crust, as indicated by high whole-rock Mg#, high Ce⁴⁺/Ce³⁺ ratios (308–861) of ca.446 Ma zircons, and the existence of inherited zircons with ages of 546–472 Ma. The Yirba dioritic to granodioritic pluton was emplaced at 474 ± 3 Ma. Samples from the Yirba pluton are characterized by high K2O content, higher Mg# (40–49) than pure crustal melts, slightly higher Y + Nb concentrations, and high Th/Nb ratios, and slightly enriched to depleted HfNd isotopes. Combined with the presence of the 502–531 Ma inherited zircons, the Yirba pluton is suggested to from through differentiation of the metasomatized lithospheric mantle derived-magmas beneath the juvenile intra-oceanic arc in combination with crustal reworking during regional extensions. The Yirba pluton, together with contemporary A1-type granites, thus marks an extension event at ca. 475 Ma in the Western Kunlun orogen. The compiled dataset reveals three magmatic flare-ups at 530–500 Ma, 480–470 Ma, and 445–430 Ma, corresponding to two slab rollback events and the slab break-off after the final closure of the Proto-Tethys. The three episodes of more intensive magmatism are associated with more radiogenic HfNd isotopes and increased Nb/La and Nb/Y ratios, indicating more contributions from intraplate-like sources during lithospheric extensions. Meanwhile, element ratios (La/Yb, Sm/Yb, and Sr/Y) that are sensitive to crustal thickness are also elevated. These phenomena are consistent with rapid juvenile crust generation during extensional stages of accretionary orogens. Our study has also shown that the rate of new crust production is quite uniform for different extensional events. The crustal generation rate during slab break-off is much higher than that during slab rollback, although the proportions of juvenile inputs in granitoids formed during slab rollback are relatively higher. This may reflect extra inputs from partial melting of oceanic slabs and subducting sediments like those in continental collision zones and/or rapid asthenospheric upwelling coupled with enhanced crust reworking during slab break-off.
... Strontium and REE were separated using cation exchange columns, and Nd fractions further separated using HDEHP-coated Kef columns. Isotopic analyses involved multi-collector-ICP-MS (MC-ICP-MS; Neptune Plus), following procedures described by Wei et al. (2002) and Liang et al. (2003). Measured 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios were normalised to 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219, respectively. ...
The Maoniuping giant rare earth element deposit is genetically related to a Cenozoic alkaline syenite–carbonatite complex. However, the origin of the alkaline complex and the genesis of the Maoniuping deposit are still unclear. In this study, the origin of the Maoniuping complex was constrained through B–Sr–Nd–Pb isotopic data for fresh/unaltered alkaline syenites. Our results indicate that the Maoniuping alkaline syenite has arc-like trace element patterns with elevated initial ⁸⁷Sr/⁸⁶Sr (0.706040–0.706541), ²⁰⁶Pb/²⁰⁴Pb (18.00–18.32), ²⁰⁷Pb/²⁰⁴Pb (15.53–15.60), and ²⁰⁸Pb/²⁰⁴Pb (38.25–38.78) ratios, and relatively low εNd(t) values (–4.92 to –2.66), suggesting derivation by partial melting of fertile mantle source. It also has higher B contents (1.06–7.65 ppm) and heavier δ¹¹B values (−5.38‰ to − 2.46‰) than the upper mantle, indicating modification of the mantle source by interaction with carbonatitic melts/fluids derived from marine sediments and altered oceanic crust within the subducting Indian slab. Our results, together with recently acquired seismic tomographic data, indicate that hybridisation in the mantle source was likely induced by subduction input of marine sediments to the mantle transition zone. Boron isotopes provide a novel indicator of the deep recycling of subducted crustal materials in the sources of alkaline magmas.
... Detailed sample preparation and chemical separation procedures were similar to those outlined by Wei et al. (2002). Ratios of Sr-Nd isotopes were measured with a VG-354 Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) at GIGCAS, with the analytical procedures following those of Liang et al. (2003). Mass fractionation corrections of the Sr and Nd isotope ratios used 86 Sr/ 88 Sr = 0.1194 and 156 Nd/ 144 Nd = 0.7219, respectively. ...
The Mesozoic South China is characterized by extensive magmatism, transition from Jurassic intraplate magmatism to Cretaceous active continental margin magmatism. However, the time and deep geodynamic processes accounting for the Mesozoic magmatism remains controversial. In this study, we presented new SIMS zircon UPb ages, in-situ Sr isotope of plagioclase, whole-rock geochemical and Sr–Nd–Pb isotopic data on three suites of mafic dikes in eastern Guangdong, namely Anliu (AL) and Sanjiaowo (SJW) and Jishuimen (JSM) mafic dikes. The AL (154.3 ± 3.4 Ma) and SJW (141.3 ± 4.0 Ma and 143.2 ± 2.3 Ma) dikes show arc-like geochemistry and “crust-like” isotopic signatures, likely derived from partial melting of a subduction metasomatized lithospheric mantle. Meanwhile, the JSM dikes (141.7 ± 3.2 Ma) exhibit OIB-type geochemical and isotopic features, and were likely derived from partial melting of an enriched asthenospheric mantle. The development of late Jurassic AL lamprophyre may represent the oldest Paleo-Pacific subduction-related arc-type mafic rocks so far recorded in South China. Development of dikes (SJW vs JSM) with different geochemical signatures (Arc vs OIB) at the same time within a limited space indicates that asthenosphere-related process overprint and co-operate with subduction-related magmatism and imply the initiation of Paleo-Pacific subduction roll-back was potentially at least ca.141 Ma.
... After sample decomposition, Sr and rare earth element (REE) were separated using cation exchange columns, and then the Nd fractions were further separated using HDEHP-coated Kef columns. The analytical methods for Sr-Nd isotopes follow the procedure of Wei et al. (2002) and Liang et al. (2003). Normalizing factors used to correct the mass fractionation of Sr and Nd during the measurements are 86 Sr/ 88 Sr ¼ 0Á1194 and 146 Nd/ 144 Nd ¼ 0Á7219. ...
Ultrapotassic rocks are volumetrically minor, but widely distributed in different geological settings. Extensive studies have concerned about mantle melting processes that generated these rocks. However, crustal processes that they may have involved are poorly known. In this paper, we describe complex oscillatory zoning patterns of clinopyroxene (Cpx) macrocrysts from an ultrapotassic lamprophyre dyke in the Kyrgyz North Tianshan orogen. These macrocrysts commonly have a corroded or patchy-zoned core surrounded by a mantle with distinct oscillatory zoning, which is, in turn, surround by a euhedral rim. The oscillatory zoning of the mantle is composed of alternating coarse and fine layers with clear resorption surface, or closely-packed layers with straight or wavy boundary under the back-scattered electron images. High-amplitude oscillation of Mg#, Ti, Al, Cr and Sr across the layers of the mantle is attributed to magma mixing. Low-amplitude, high-frequency oscillation of Mg# across the closely-packed layers was likely developed due to kinetic effects or crystal movement under the thermal and chemical gradients. In addition, cryptic sector zoning of some macrocrysts clearly shows Si- and Mg-rich hourglass sector and Al- and Ti-rich prism sector. The sector zoning indicates crystallization of these macrocrysts under low degrees of undercooling, and the presence of concentric Cr-rich and Cr-poor layers within the same grain indicate that the growth process was disrupted by multiple magma recharging events. The core parts of the macrocrysts have Mg# with three distinctive ranges, i.e., <84 to 90 (Core I), 74 to 84 (Core II) and 60 to 70 (Core III). The mantle parts have Mg# ranging from 64 to 90 without a distinct gap. The rim parts have a narrow range of Mg# from 76 to 80. The core and mantle parts with high Mg# (≥85) have variable La/Yb from 1.8 to 5.0 and Dy/Yb from 2.3 to 4.6. The macrocrysts overall have variable 87Sr/86Sr from 0.7072 to 0.7084. Highly variable trace elements and 87Sr/86Sr within a single grain indicate that both primary and evolved magmas with different compositions were periodically recharged into the crustal magma reservoirs. Modelling results reveal that the melts in equilibrium with the Cpx macrocrysts may have been derived from the magma reservoirs at three different depths equivalent to crystallization pressures of ∼5.4, ∼3.3 and ∼1.6 kbar, respectively, making up a transcrustal magmatic system. The Cpx-laden melts in deep magma reservoirs may have been frequently transported to shallower reservoirs. Magma mixing in the shallower reservoirs led to heterogeneous magmas with different cooling rates and chemical compositions. Early crystallized Cpx crystals were overprinted with diverse zoning patterns during overgrowth and accumulation. Thus, the complex zoning patterns and compositions of the Cpx macrocrysts have important implications for a transcrustal magmatic system in the formation of ultrapotassic rocks.
... Rare-earth-elements (REEs) were separated by cationexchange chromatography using procedures of Wei et al. (2002). Nd isotopic ratios were determined by multicollextor (MC) -ICP-MS (VG-354) at GIG-CAS using procedures described by Liang et al. (2003). The mass-fractionation correction was based on 156 Nd/ 144 Nd = 0.7219 Shin Etsu JNdi-1 was used as a standard with 143 Nd/ 144 Nd = 0.512090 ± 0.000003 (2σ; n = 3). ...
... The mass fractionation corrections for Sr and Nd isotopic ratios are based on 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219, respectively. The 87 Sr/ 86 Sr ratio of the NBS987 Sr standard and 143 Nd/ 144 Nd ratio of the La Jolla Nd standard determined using the same analytical procedure in this study were 0.710248 and 0.512115, respectively [29]. ...
Cenozoic alkali basalts in Southeast (SE) China generally are genetically related to intracontinental rifting. Hence, they can be used to probe the nature of their underlying mantle sources and aid studies of the tectonic background in this region. This paper focuses on the Shanhoujian alkali basalts located in Bailing County, northeastern Fujian, SE China. We herein report their petrology, whole-rock major, and trace element geochemistry, and Sr-Nd isotopic composition and provide a new zircon U-Pb age for the basalts (~40 Ma, Eocene). These data help to constrain the petrogenesis of alkali basalts, their mantle source, and tectonic settings. The basalts are characterized by high Mg# (58.21–63.52) with Na2O/K2O > 1. MgO content is weakly correlated with CaO and Cr content but shows no correlation with Ni and Fe2O3 (total). Such features suggest that fractionation of clinopyroxene rather than olivine was important. In terms of trace elements, the alkali basalts display: (1) enrichment in La, Ce, Rb, Ba, Nb, and Ta and depletion in K, Pb, Zr, Hf, and Ti and (2) notable fractionation of light rare earth elements from heavy rare earth elements. Determined (87Sr/86Sr)i is in the range of 0.7041–0.7040 and εNd (t) is between +3.2 and +3.3. The Shanhoujian alkali basalts show a notable affinity to oceanic island basalts (OIBs) with little assimilation of crustal materials. They were derived from a pyroxenite and carbonated peridotite mantle source metasomatized by sediments carried by the subduction plate at different depths. The primary magmas of these basalts were derived from partial melting of this metasomatized mantle source during upwelling of the asthenospheric mantle as an intracontinental rift formed through extension in this part of SE China.
... The Sr-Nd isotopic compositions of selected samples were determined using a Micromass Isoprobe Neptune Plus multi-collection ICP-MS equipped with nine Faraday cup collectors and eight ion counters at the State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. The analytical procedures were similar to those described in Liang et al. (2003). Sr and rare Earth elements (REEs) were separated using standard cation exchange columns, and the Nd fraction was isolated from the other REEs using Di-(2ethylhexyl)phosphoric acid (HDEHP) ...
The Datong pluton, the largest early Palaeozoic granitoid in the Western Kunlun Orogenic Belt (WKOB) in NW China, is a typical appinite-granite complex. It consists of diorites, quartz dior-ites, monzodiorites, quartz monzodiorites, monzonites, quartz monzonites, syenites, granodiorites and monzogranites. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yielded crystallization ages of 459 ± 3 Ma for the quartz monzonites and 452 ± 5 Ma for the monzogranites (Late Ordovician). The rocks possess a wide range of SiO 2 (56.0-73.4 wt %), MgO (0.17-4.55 wt %) and Mg no. (25-60), with high K 2 O (2.83-5.29 wt %) contents, exhibiting high-K calc-alkaline to shoshonitic traits. They are characterized by enrichments in large-ion lithophile elements (LILEs) and light rare Earth elements (LREEs), as well as depletions in high-field-strength elements (HFSEs). The rocks have initial 87 Sr/ 86 Sr ratios of 0.7086-0.7185, negative ε Nd (t) values of-3.72 to-1.79 and ε Hf (t) values vary from-1.6 to +4.7. These features are modelled to show that they were most likely derived from an enriched lithospheric mantle source and that fractional crystal-lization with minor crustal contamination was involved in their petrogenetic process. Considering the distribution and chronology of the Palaeozoic intrusions-such as Kegang, Bulong, Qiukesu, Yierba, North Kudi, Dongbake, Buya, Ayilixi and Warengzilafu granitoid plutons with ages of c. 420-530 Main conjunction with the Palaeozoic metamorphic overprinting in the WKOB, we propose a divergent double-subduction model to explain the destruction of the Proto-Tethys Ocean and suggest that the Datong pluton was likely emplaced in a post-collisional setting following the termination of subduction in response to slab break-off.
... The Sr-Nd isotopic compositions of selected samples were determined using a Micromass Isoprobe Neptune Plus multi-collection ICP-MS equipped with nine Faraday cup collectors and eight ion counters at the State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. The analytical procedures were similar to those described in Liang et al. (2003). Sr and rare Earth elements (REEs) were separated using standard cation exchange columns, and the Nd fraction was isolated from the other REEs using Di-(2ethylhexyl)phosphoric acid (HDEHP) ...
... Lead was separated and purified by a conventional cation-exchange technique (AG18, 200-400 resin) with diluted HBr and HCl used as the eluants. Sr-Nd-Pb isotopic measurement was performed on a Thermo-Fisher Scientific Neptune Plus Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICP-MS) at the CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China (USTC), following similar analytical procedures described by Wei et al. (2002), Liang et al. (2003) and Wu et al. (2017a). Whole procedure blanks for Sr, Nd and Pb during the course of this study are 0.1-0.4 ...
The westward subduction of the Pacific plate interacted with the northward subduction of the eastern Neo-Tethys plate in the Early Cretaceous. However, the subduction polarities between these two plates in the Early Cretaceous is not well constrained. The proto-Philippine arc is suggested to have originated at the Pacific – Neo-Tethys intersection in the SW Pacific in the latest Jurassic – Early Cretaceous, and can provide information about the ancient interaction between these two plates. In this study, the oldest known Early Cretaceous mantle-derived arc volcanic rocks and slab-melting generated adakites occurring in the Philippine arc have been studied for Pb, Sr, Nd and Hf isotopes to discriminate the provenance of their mantle sources and/or subduction components.
The 126 – 118 Ma Kansi island arc volcanics have Pacific-type Pb isotopes, suggesting that the subduction components in the source are mainly from the subducted Pacific plate. Their Hf-Nd isotopes give support to a mantle source that is isotopically transitional Pacific-Indian type. The formation of the Kansi volcanics dates the subduction of the Pacific Plate under the transitional Pacific-Indian mantle as Early Cretaceous. The subsequent generation of the 110 Ma Kansi adakitic diorites with the similar Pacific-type Pb isotopes indicates further partial melting of the subducted Pacific plate. In contrast, the post-110 Ma Lutopan adakitic diorites have Indian-type Pb isotopes, indicating the subsequent subduction of an Indian-type oceanic slab in the eastern Neo-Tethys tectonic regime. Therefore, the proto-Philippine arc is constrained to have originated at the intersection between Indian-type and Pacific-type oceanic crusts and mantle domains. The successive generation of these Early Cretaceous arc rocks in the Philippines indicates that a transformation of the tectonic regime from southwestward Pacific subduction to northeastward subduction of the eastern Neo-Tethys in the SW Pacific Ocean occurred at ca. 110 Ma, due to the abrupt change in drifting direction of the Pacific plate.
The North Qinling Orogenic Belt (NQB) records the pivotal geological information for understanding the Palaeozoic evolution of the Qinling Orogenic Belt (QOB). Previous studies mainly focused on the subduction-collision process along the Shangdan suture zone before the Early Devonian. However, as the significant interim period between the Early Palaeozoic and Mesozoic orogeny, the Late Palaeozoic tectonic evolution of the NQB remains poorly understood. Fortunately, the Carboniferous magmatic rocks discovered this time provide substantial geological evidence for revealing the Late Palaeozoic tectonic history of the Qinling Orogenic Belt. This paper will provide a detailed analysis of zircon U-Pb ages, geochemical characteristics and Sr-Nd-Hf isotopic compositions of Carboniferous rocks. The Carboniferous magmatic rocks are categorized as highly differentiated S-type granite and monzo-diorite, formed at 350 ± 2.4 Ma and 353 ± 5.2 Ma, respectively. The granite shows weak peraluminous (A/CNK = 1.02-1.11) and shoshonite nature. Based on the isotopic composition and trace element characteristics, we propose that the Qinling Group paragneiss is the primary source of the Carboniferous granite. Monzodiorite is characterized by enriched LREEs and LILEs (Ba, K and Pb), depleted HFSEs (Th, Nb, Ta and Ti) and enriched Sr-Nd isotopic composition. Monzodiorite magma source region consists of continental crustal material and lithospheric metasomatized mantle. Carboniferous magmatic rocks are the product of an extensional tectonic setting, which indicates the NQB tectonic regimes transition from compression to extension during the Carboniferous.
Late Paleozoic magmatic rock outcrops are common in the Northern Alxa, Southern Central Asian Orogenic Belt (CAOB), which is a key area for understanding tectonic processes and defining the final closure time of the Paleo-Asian Ocean (PAO). We present zircon U‒Pb chronology and whole-rock geochemistry data for late Paleozoic magmatic rocks from the Yagan area of northern Alxa. This paper reveals two periods of magmatism: syenogranite (374.8 Ma) and bimodal intrusive rocks, which consist of gabbro (261.4 Ma), diabase (262.9 Ma) and biotite monzogranite (263.4 Ma). The syenogranite is high-K calc-alkaline and shows enrichments in Th, Zr, Hf and LREEs; depletions in Sr, Nb, Ta, and Ti; and low Mg# values (6.9–13.2); the syenogranite was derived from partial melting of the crust and has volcanic arc characteristics. The gabbro and diabase have similar geochemical characteristics, such as enrichments in Pb, Rb, Sr, Zr, and Hf and depletions in Nb, Ta, and Ti, with positive εHf(t) values (+0.9–+2.7 and +2.6–+3.6, respectively), indicating that they originated from partial melting of depleted mantle and experienced crustal contamination during magma emplacement. The biotite monzogranite shows depletions in Nb, Ta, and Ti and εNd (t) values of -2.6 to −2.4 and resulted from partial melting of the lower crust caused by asthenospheric underplating. The bimodal intrusive rocks formed in a postcollision extensional setting. Combined with previous data, we conclude that northern Alxa was an active continental margin during the late Devonian and that the final closure of the Yagan branch ocean of the PAO occurred prior to the middle Permian.
Several important processes in the petrogenesis of granite are still debated due to poor understanding of complex interactions between minerals during the melting and melt segregation processes. To promote improved understanding of the mineral-melt relationships, we present a systematic petrographic and geochemical analysis for melanosome and leucosome samples from the Triassic Jindong migmatite, South China. Petrographic observations and zircon U-Pb geochronology indicate that the Jindong migmatite was formed through water-fluxed melting of the Early Paleozoic gneissic granite (437±2 Ma) during the Triassic (238±1 Ma), with the production of melt dominated by the breakdown of K-feldspar, plagioclase and quartz. The Jindong leucosomes may be divided into lenticular and net-structured types. Muscovite, plagioclase and K-feldspar in the net-structured leucosome show higher Rb and much lower Ba and Sr contents than those in the lenticular leucosome. This may be attributed to elevation of Rb and decreasing Ba and Sr abundances in melts during the segregation process, due to early fractional crystallization of K-feldspar and plagioclase. These leucosomes show negative correlation between εNd(t) and P2O5, reflecting increasing dissolution of low εNd(t) apatite during melting process. The continuous dissolution of apatite caused saturation of monazite and xenotime in melt, resulting in the growth of monazite and xenotime around apatite in the melanosome. This process resulted in a sharp decrease of Th, Y and REE with increasing P2O5 in the leucosome samples. This complex interplay of accessory mineral reactions in the source impact REE geochemistry and Nd isotope ratios of granites. As the granites worldwide exhibit similar compositional and isotopic patterns with the Jindong leucosomes, we suggest that both the melting and melt segregation processes strongly control the granitic melt compositions.
The Fangshan intrusive suite is a composite pluton in the North China Craton that resulted from incremental assembly of small magma batches. The pluton consists of four intrusive units with abundant mafic enclaves. Here we clarify its crystallisation history through zircon UPb dating, which indicates prolonged crystallisation of each intrusive unit at upper-crustal levels between 132.5 and 128.7 Ma. The magmas were episodically extracted from a deep storage area and ascended to the final intrusion level at a palaeo-depth of 10–16 km. Zircon trace element and Hf isotopic compositions and Ti-in-zircon temperature of the four intrusive units and mafic enclaves show significant differences and suggest that their crystallisation occurred in isotopically and chemically diverse magma batches. These magma batches formed in the lower crust from the mingling and mixing of various proportions of residual melts, derived from the fractional crystallisation of mafic magmas, with crustal partial melts at high temperatures. Four type of zircons were observed in mafic enclaves based on a simple textural classification, including antecrysts (type 1), xenocrysts (type 2 and type 3), and recrystallised zircon (type 4). Type 1 zircons were not formed at the emplacement level and are “antecrystic”, having formed at a deeper, hotter level and been entrained into the ascending melts. Most type 2 zircons were captured from coarse-grained monzonite, and a very small number of grains were sourced from porphyritic granodiorite. Type 3 zircons display a core-rim texture, illustrating that xenocrysts may successively grow in mafic melts. Type 4 zircons display patchy zoning that represents a disequilibrium texture, manifested by the replacement of U–Th–REE-rich zircon by U–Th–REE-poor zircon, which occurred in response to magma mixing between mafic and felsic melts. This study shows that zircon chemistry coupled with detailed textural analyses can provide a powerful tool to elucidate the complex evolution of a magmatic system.
The Lhasa terrane records voluminous magmatism related to the subduction of the Neo-Tethyan oceanic lithosphere, the study of which constrains the tectonomagmatic evolution of the region. We report zircon U-Pb ages, whole-rock compositions and Sr-Nd isotopic data from volcanic rocks in the Bangba district within the central Lhasa subterrane to constrain their magmatic source and petrogenesis. Zircon U-Pb dating of two volcanic rock samples yields End Cretaceous ages of 70.0 ± 0.8 and 74.3 ± 1.2 Ma. The rocks have high SiO2 (65.41 wt.%–68.45 wt.%), Al2O3 (16.16 wt.%–16.59 wt.%) and K2O (5.00 wt.%–6.73 wt.%) contents, and low TFe2O3 (2.33 wt.%–2.79 wt.%), MgO (0.64 wt.%–1.44 wt.%) and TiO2 (0.61 wt.%–0.65 wt.%) contents, with aluminium saturation indices (A/CNK) of 0.99–1.06. The major- and trace-element compositions of the rocks show they are metaluminous to slightly peraluminous high-K calc-alkaline trachydacite. The relatively high SiO2 and Sr-Nd isotopic compositions ((87Sr/86Sr)i = 0.722 654, 0.722 038 and 0.725 787 and εNd(t) = −12.27, −12.36 and −6.09, respectively) indicate that the trachydacites formed by partial melting of crustal material. The trachydacites are relatively enriched in light rare earth elements, depleted in heavy rare earth elements, have high (La/Yb)N and (Gd/Yb)N ratios (>61 and >6, respectively), and low Y (<18 ppm) and Yb (<18 ppm) contents, indicating they most likely formed from partial melting of lower crust in the garnet stability field. Considering the geodynamic setting of the region during this period, partial melting of the ancient Lhasa crust was likely triggered by underplating mafic magmas during rollback of the Neo-Tethyan slab.
South Qinling hosts abundant alkaline igneous rocks characterized by rare metal mineralization, which, however, is not well understood, particularly for those extrusive alkaline magmatic systems. This study focuses on the Tianbao trachyte Nb(-REE) deposit located in the North Daba Mountains (South Qinling) and investigates textures and geochemistry of ore-bearing trachytes and Nb-REE minerals to reveal relative contributions of magmatic and hydrothermal processes to rare metal enrichment. Low K2O/Na2O ratios (0.26 − 1.64), depletions of Ba, Sr, and enrichments of Nb, Ta, Zr, Hf in the Tianbao trachytic complex resemble geochemical signatures of rifting-related alkaline igneous rocks, highlighting an intraplate rifting origin. Positive εNd(t) values (3.1 – 3.6) and constrained La/Yb (21.2 – 35.8) and Nb/Zr (3.7 – 4.8) ratios indicate that they might have originated from mixing of the asthenospheric mantle and metasomatized lithospheric mantle and formed due to protracted magmatic differentiation of coeval mafic magmas. Niobium and REEs in the Tianbao trachytic complex primarily originated from an enriched mantle source, and then upgraded to initial enrichment due to intense differentiation of the trachytic magmas. Niobium and REEs in the trachytic magmas were firstly incorporated into magmatic mineral phases (e.g., biotite, niobian titanite, niobian ilmenite and apatite) under relatively reduced (below the Ni-NiO oxygen fugacity buffer) conditions. With the differentiation of trachytic magmas, niobium, REEs and anion ligands (F⁻, CO3²⁻ and PO4³⁻) got saturated in the late-stage alkaline melts and then entered the exsolved fluids. Ca-rich components should have been leached from the magmatic minerals during the hydrothermal stage and reacted with these ligands to develop Ca-rich hydrothermal mineral phases, including fluorite and calcite veins, allanite and apatite overgrowth under relatively oxidized (between the Ni-NiO and hematite-magnetite oxygen fugacity buffer) conditions. The remaining Nb and REEs finally precipitated as the economic minerals (e.g., allanite-(Ce), loparite-(Ce) and niobian Y-rich zircon) along fractures. Mass balance calculations indicate that these hydrothermal economic mineral phases account for the majority of Nb-REE reserve in the trachytic complex, and thus, the hydrothermal process might have played the key role in leading to Nb and REE concentrating to ore grade.
The medium-sized Tashan Sn deposit, mainly hosted in the Tashan granite porphyry, is located in eastern Guangdong, Southeast China. Zircon U–Pb dating of the granite porphyry yielded a concordant age of 138.0 ± 1.1 Ma, which is consistent with the cassiterite U–Pb age of 138.0 ± 2.3 Ma from the Sn ores, indicating a temporal link between the emplacement of granitic pluton and Sn mineralization. The contents of Fe³⁺, Fe²⁺, and Mg²⁺ in biotite, low calculated zircon Ce⁴⁺/Ce³⁺ of 4.4–71.6, low Eu/Eu* ratios of 0.06–0.35, and low whole-rock Fe2O3/FeO of 0.04–0.13 of the granite porphyry reveals its low oxygen fugacity, which may have facilitated the Sn enrichment during magma evolution and played a key role in the Sn mineralization. Low K/Rb (150–175, aver. = 160), Nb/Ta (7.3–8.2, aver. = 7.8), and Zr/Hf (23.2–25.1, aver. = 23.9) values were observed for the granite porphyry, indicating its high fractionation and probable interaction with an aqueous fluid phase to some extent. The reduced and highly fractionated features and high F and Sn contents of the granite porphyry thus indicate it is a typical Sn-fertile granite. The granite porphyry is weakly peraluminous and belongs to high-K calc-alkaline type. The rocks are characterized by high SiO2, K2O + Na2O, F, and Zr + Nb + Ce + Y (360–410 ppm) contents; and 10000 Ga/Al (2.31–3.06) ratios and low CaO, MgO, TiO2, and P2O5 contents; Rb, Cs, Th, and U enrichment; and Ba, Sr, Zr, Ti, and P depletion, exhibiting an A-type affinity. Moreover, the rocks display whole rock initial ⁸⁷Sr/⁸⁶Sr values of 0.70927–0.71218, εNd(t) of −6.5 to −6.3, and zircon εHf(t) values from −5.7 to −1.5 with Mesoproterozoic TDM2 ages for both Nd and Hf isotopes, indicating their formation by partial melting of a crustal source of Mesoproterozoic overall residence ages with minor input of mantle materials. By integrating new and published data on tectonic evolution, we suggest that the granite porphyry and associated Sn mineralization in the Tashan deposit that was formed in a back-arc extensional environment started before ∼141 Ma, related to the rollback of the paleo-Pacific Plate.
Five Late Cretaceous tungsten-tin ore clusters (Gejiu, Dulong, Bainiuchang and Dachang tin deposits and Damingshan tungsten deposit) have been identified in the Youjiang Basin, South China. However, litter attention has been paid to such W-Sn metallogenetic specialization in the Youjiang Basin, as well as the geodynamic setting of mineralization and related magmatism. This study presents petrographical, geochronological, zircon Lu-Hf isotopic and whole-rock geochemical analyses for the Kunlunguan (KLG) biotite granites from the Damingshan ore cluster in the eastern part of the Youjiang Basin, and synthesizes previously published data from other ore clusters. The KLG granites yield crystallization ages of ∼100.2-98.6 Ma, and are characterized by high SiO2 and low A/CNK, Rb/Sr and 10000*Ga/Al, belonging to metaluminous to weakly peraluminous unfractionated I-type granite. The granites have initial ⁸⁷Sr/⁸⁶Sr ranging from 0.70919 to 0.71133 and εNd(t) from -9.3 to -6.8 with zircon εHf(t) ranging from -13.2 to -3.1, Eu/Eu* from 0.18 to 0.42 and Ce/Ce* from 7.43 to 254. Such signatures suggest that the KLG granites originated from partial melting of lower crustal mafic rocks with a minor mantle component. Overall, the W-Sn metallogenic specialization in the Youjiang Basin was first-order controlled by crustal sources of ore-host granites. The metallogenic age of the W-Sn deposits (∼97-75 Ma) is similar to the crystallization age of the granites (∼100-77 Ma), and the ages of mineralization and granites in the west of the Youjiang Basin are relatively younger than those in the east. The Late Cretaceous W-Sn mineralization system in the Youjiang Basin belongs to a part of an EW-trending Sn-W-Cu mineralization belt from Myanmar to Guangdong, forming in an extensional setting caused by the Neo-Tethys oceanic slab roll-back.
The porphyry Cu deposits in the Gangdese metallogenic belt were mainly formed in the eastern portion. The Beimulang is a newly discovered deposit formed in post-collisional setting in the western part of the belt and adjacent to the super-large Zhunuo porphyry Cu deposit. There are three epochs of magmatism at Beimulang, including pre-mineralization quartz porphyry (PQP; 49.7 ± 0.4 Ma), inter-mineralization monzogranite porphyry (IMGP; 14.8 ± 0.2 Ma), monzogranite (IMG; 14.1 ± 0.2 Ma), and late-mineralization granite porphyry (LGP; 11.7 ± 0.1 Ma). The various degrees of alteration and sulfide occurred at the IMG(P) and LGP indicate that there are at least two episodes of fluid exsolution events associated with different intrusions spanning ∼3 m.y. at Beimulang, which are unlike other Gangdese porphyry Cu deposits showing single fluid exsolution around only one porphyry at Miocene (e.g., Qulong, Zhunuo, Dabu). The PQP is characterized by high SiO2 (75.6-81.4 wt.%) and K2O (2.1-4.3 wt.%) concentrations, high Nb/Ta (8.4-11.3) ratios, and low Mg# (22-43), Ni (1.5-2.7 ppm) contents. They have high (⁸⁷Sr/⁸⁶Sr)i (0.705098-0.707767) ratios and low εNd(t) (-4.9 to -1.9) values. These geochemical characteristics indicate that they were probably derived from a juvenile basaltic lower crust during the ongoing Indian-Asian collision. The IMGP and IMG show similar petrography and geochemical characteristics, such as high SiO2 (65.0-69.8 wt.%), K2O (3.6-4.3 wt.%), Sr (550-809 ppm) contents, high Sr/Y (79-89) ratios, and low Mg# (43-48), Th/Yb, and Nb/Yb values, combined with high (⁸⁷Sr/⁸⁶Sr)i (0.707254-0.708017) and low εNd(t) (-7.9 to -6.0), implying a similar source probably originated in the subduction-modified lower crust metasomatized by Neo-Tethyan oceanic slab-derived fluids. The LGP displays trends produced by fractionation of magma with a composition similar to the IMG(P), but wall rock assimilation plays a significant role during magmatic evolution. Zircons from the IMG(P) show higher Eu/Eu* (>0.3), 10000*(Eu/Eu*)/Y (>4), and (Ce/Nd)/Y (>0.04) ratios than those of the PQP, indicating the fertile magmas were more oxidized and hydrous. The high magmatic oxidation state for the IMG(P) is also supported by using the zircon (ΔFMQ = +4.1 to +6.1), and amphibole (ΔFMQ =+2.6 to +3.4) oxybarometers. Their high magmatic water contents are supported by evaluations using amphibole (∼3.5 wt.%) and plagioclase (∼6.7 wt.%) compositions, respectively. However, the LGP has higher magmatic oxygen fugacity (Eu/Eu* >0.3, ΔFMQ = +4.2 to +7.3) caused probably by auto-oxidation of the magmas, but lower magmatic water contents (Sr/Y = 31 ± 15; V/Sc=6 ± 4) caused presumably by previous fluid exsolution and/or fractionation of hydrous silicate minerals during magma ascent than those of the IMG(P). Therefore, the highly hydrous and oxidized magmas with juvenile material are favorable to form porphyry Cu deposits in Tibetan orogen. On the contrary, magmatic evolution can probably reduce the water content of magma chamber, which is not beneficial to porphyry Cu mineralization.
The amalgamation process and suture boundary of the Yangtze and Cathaysia blocks have been in hot dispute and attracted considerable attention. Overall, controversies remain on where the closure boundary of the Paleo-Huanan Ocean was and how the Jiangshan-Shaoxing fault southwesterly extended. This paper presents a set of new geochronological, geochemical and Nd isotopic data for the igneous rocks from the Zhoutan and Shenshan groups in Central Jiangxi. The Zhoutan amphibolites formed during the Neoproterozoic (∼850–830 Ma) and experienced the Silurian (∼430 Ma) metamorphism. They have low SiO2 (49.5–52.9 wt%), Al2O3 (13.48–14.38 wt%), and TiO2 (0.99–1.57 wt%) contents and K2O/Na2O values (<1.0), and show E-MORB-resembling REE and PM-normalized pattern, with Nb/La of 0.59–0.88. Their εNd(t) values range from + 4.8 to + 5.9, and they were originated from a slab fluid-modified E-MORB-like mantle source. The high-Mg meta-andesite and -dacite rocks from the Zhoutan Group and Lower Shenshan subgroup yield zircon U–Pb mean ages of 850–837 Ma and exhibit 61.4–75.2 wt% SiO2 and 2.0–4.1 wt% MgO. They are enriched in LILEs and depleted in HFSEs, with Nb/La = 0.21–0.42 and εNd(t) = − 3.1 to − 8.9. These high-Mg volcanic rocks were derived from a sediment- modified wedge source. The Shenshan Group is likely to be an equivalent of the Yingyangguan volcano-sedimentary sequence that was split into Lower (853–830 Ma) and Upper (810–740 Ma) subgroups. The Zhoutan and Lower Shenshan igneous rocks formed in a fore-arc setting at the Neoproterozoic period in response to the westward consumption of the Paleo-Hunan Ocean. The Jiangshan–Shaoxing suture extends southwardly into the Yingyangguan area across the Zhoutan–Yangtian area near to the Chenzhou-Linwu fault.
The magma source, petrogenesis, tectonic setting and its geochronology of the Late Paleozoic A-type granites, which widely exposed in Zhaheba area, East Junggar, have not been well constrained so far. A better understanding of these issues above will help us to reveal the magmatic processes and the continental growth of Central Asia. The A-type granites in Zhaheba include the Ashutasi alkaline granites and Yuyitasi syenogranites, which were emplaced in 321.5±4.8 and 321.7±0.6 Ma, respectively. The major rock-forming minerals are orthoclase, perthite, arfvedsonite and quartz, and exhibit the following main geochemical characteristics of A2-type granites. (1) Their REE distribution curves each exhibit a “V”-shaped pattern and a marked depletion in Eu. They are rich in large-ion lithophile elements Rb, Th, and U as well as high-field-strength elements Nb, Ta, Zr, and Hf but significantly depleted in Ba, Sr, P, and Ti. (2) Their (⁸⁷Sr/⁸⁶Sr)i values (0.7021–0.7041), εNd(t) values (4.57–5.16), and REE distribution patterns are in basic agreement with those of the Kalamaili A-type granite belt in East Junggar. The TDM2 values of the alkaline granites and syenogranites range from 661 to 709 Ma. The A-type granits may be the products of upwelling asthenosphere triggered partial melting of juvenile lower crust. . The alkaline granites were later-stage products of crystallization and differentiation. Compared to the syenogranites, the alkaline granites are significantly lower in K2O, Na2O, Al2O3, FeO, MgO, and CaO but significantly higher in incompatible elements (e.g., SiO2, Rb, and Sr). The magmatic crystallization temperatures of the syenogranites and alkaline granites are 874 ℃ and 819 ℃, respectively. As their age gradually decreases (peak ages: 322 Ma and 307 Ma, respectively), there is a gradual decrease in the TDM2 of the A-type granites and a gradual increase in their εNd(t) value from the Ulungur belt to the Kalamaili belt in East Junggar. Therefore, the study of A-type granites is one of the keys to understanding the laws and mechanisms of crustal accretion during the Phanerozoic period, and is also of great significance for understanding the Paleozoic accretion.
Late Jurassic (~ 160 Ma) granitoids are widely distributed across the South China Block. These granitoids are mainly biotite granites, with subordinate amphibole-bearing and two-mica or muscovite-bearing granites. Previous studies have shown that a clear negative correlation exists between SiO2 and P2O5 contents in the amphibole-bearing, biotite, two-mica, and muscovite-bearing granites, and suggested that these granitoids are I-type (metaigneous-rock-derived) or fractionated I-type granites. However, whether the Late Jurassic two-mica granites were formed by fractional crystallization of S-type (metasedimentary-rock-derived) granitic magmas in addition to fractional crystallization of I-type granitic magmas, and the role of mantle-derived magma in the generation of the Late Jurassic granitoids, are still debated. We present data for two-mica granites in the Maofengshan area of Guangzhou, Guangdong Province, southeastern China. Zircon U–Pb ages show that these rocks were formed during the Late Jurassic (159 Ma). The Maofengshan two-mica granites have high SiO2 contents (73.1–74.1 wt.%) and peraluminous compositions (A/CNK = 1.08–1.11). They are enriched in Rb, Th, U, and Pb, depleted in Ba, Sr, Nb, and Ti, and have pronounced negative Eu anomalies. The Maofengshan granites also have enriched Sr–Nd–Hf isotopic compositions [(87Sr/86Sr)i = 0.7103–0.7118, εNd(t) = − 10.3 to − 10.1, and εHf(t) = − 14.2 to − 7.5)] and heavy zircon O isotopic compositions (δ18O = 8.2‰–10.2‰). We suggest that these granites were formed by fractional crystallization of metasedimentary-rock-derived granitic magmas in the middle crust (16.5–20.0 km), as they have similar major and trace element and isotopic characteristics to S-type granites and show relatively higher FeOT/MgO (5.2–5.6 > 4), (K2O + Na2O)/CaO (8.2–9.3 > 7), Rb/Sr (5.4–6.4), and Rb/Ba (1.2–1.5) and lower Nb/Ta (5.6–7.3 < 11) ratios than normal unfractionated granites. Mantle-derived mafic magma mainly provided the heat for their generation.
The Youjiang Basin is usually regarded as an important foreland basin in the southern part of the South China Block that is related to the convergence of the South China and Indochina blocks during the Permian-Triassic. However, the nature of the basin remains controversial due to questions about the subduction polarity and suture boundary between these two blocks. Permian-Triassic felsic volcanics across the Dian-Qiong and Song Ma suture zones could offer new insights into the convergent processes of the South China and Indochina blocks. This study presents detailed petrological, zircon U-Pb dating, and Hf-O isotope and whole-rock geochemical analyses for the Triassic felsic volcanics of the Youjiang Basin (northeast of the Dian-Qiong). The dacites and rhyolites from the Beisi and Baifeng Formations were dated at ca. 240−245 Ma. All of the felsic volcanics are characterized by high SiO2 (69.40−73.15 wt%), FeOt/MgO, 10000*Ga/Al, and TZr, δ18O (9.7−11.8‰) and negative εNd(t) (from −9.6 to −12.3) and zircon εHf(t) (from −6.2 to −14.5) with A-type granitoid geochemical affinities, suggesting the reworking of crustal rocks in an extensional setting. Permian-Triassic felsic igneous rocks display similar geochemical signatures across the Dian-Qiong suture zone, whereas they show distinctive Sr-Nd and zircon Hf-O isotopes across the Song Ma suture zone. The felsic igneous rocks to the northeast of the Song Ma suture zone have much lower εNd(t) and higher δ18O with negative zircon εHf(t) than those to the southwest, which have positive zircon εHf(t). Combined with other geological and geophysical features, it is inferred that the Song Ma suture zone was probably the suture boundary between the South China and Indochina blocks, and the Youjiang Basin was likely a peripheral foreland basin in response to the southwestward convergence of the South China Block toward the Indochina Block.
The Cathaysia Block amalgamated with the Yangtze Block along the Jiangnan orogenic belt to form the South China Craton during early Neoproterozoic time. However, the origin of the Cathaysia Block and its position in the Nuna supercontinent remain controversial. This paper synthesizes geochronological, geochemical and isotopic data from late Paleoproterozoic igneous rocks in the Wuyishan Domain of the Cathaysia Block (SE China). Two-phases of late Paleoproterozoic A- and S-type granitoids were identified and dated at 1925–1848 Ma and 1816–1750 Ma. The A-type granites in the Wuyishan Domain were likely derived from partial melting of mafic lower crust with a tonalitic to granodioritic geochemical composition, and the S-type granites were derived from partial melting of a meta-sedimentary source. These late Paleoproterozoic granitoids were emplaced in a continental arc/back-arc setting and the two-phased arc/back-arc magmatism was related to the assembly of the Paleoproterozoic Nuna supercontinent. Combining our results with previous late Paleoproterozoic geochemical and age data, we suggest that the Cathaysia Block was located close to northern India Shield during Proterozoic time until the breakup of the Rodinia Supercontinent in the late Neoproterozoic.
The Shangbao mining district, located in Nanling Range, South China, includes a series of middle-large scale granite-related W–Sn–Nb–Ta deposits. The genesis for W-Sn-Nb–Ta mineralization in this region is in fact ambiguous. In addition, the research of the latest mineralized granites in Nanling Range may be contributed to further understand the mineralization mechanism. In this study, we report the geochronological, geochemical and isotopic compositions of the Shangbao granite, together with the texture and element of Nb–Ta bearing minerals. LA-MC-ICP-MS U–Pb dating of zircon and columbite in granite from Shangbao Nb–Ta deposit yields weighted mean ²⁰⁶Pb/²³⁸U age of 87.3±0.9 Ma and 86.83±0.8 Ma, respectively, revealing the emplacement of the granites and their mineralization during Late Cretaceous. The major elements of these granites show high contents of K2O+Na2O, Fe2O3, SiO2 and F, low contents of P2O5, CaO, TiO2 and MgO, suggesting high-K calc-alkaline series with slightly peraluminous signature. Besides, they exhibit flat REE pattern and high content of Zr+Nb+Ce+Y, revealing the Shangbao granite affinity of highly fractionated A-type granite. Lu–Hf and Sr–Nd isotopes indicate that the Nb–Ta bearing magma was formed by the mixing crust-mantle materials. Combined with the previous studies, emplacement of Shangbao granite is linked to an expansional geodynamic setting, likely caused by the roll-back of the paleo-Pacific plate subduction.
The principal economic Nb–Ta oxides of Shangbao granite are columbite group minerals (CGM). Three major groups are identified given textural and chemical characteristics of CGM, i.e., (i) Group I displays systematic core-rim evolution from columbite to tantalite, and eventually to columbite; (ii) Group II shows that the columbite and tantalite have undergone metasomatism through the wolframoixiolite, and numerous REE-mineral were contained; (iii) Group III is anhedral columbite crystallized together with rutile. As revealed from geochemical characteristics of these three groups, the formation of Nb–Ta oxides within Shangbao granite display three generating stages, supporting the magmatic-hydrothermal origin. The high-degree fractional crystallization of Shangbao granitic magma is the main factor leading to the enrichment of Nb to allow saturation of columbite.
Numerous leucogranite dykes, and spatially associated high-grade metamorphic rocks, are well-preserved in the Chinese Altai orogenic belt. Integrated petrological, geochronological, and geochemical results of the leucogranite dykes are presented to decipher their petrogenesis and constrain the tectono-thermal setting of the Altai orogen. The leucogranite dykes have high SiO2 (71.9–81.2 wt%) and Al2O3 contents (11.1–15.7 wt%), and low CaO, MgO and TiO2 contents, with a total alkali content (K2O + Na2O) of 4.55–9.88 wt%. All leucogranites show weakly to strongly peraluminous S-type granite affinities with A/CNK ratios of 1.0–2.2. Trace element concentrations indicate a characteristic high Rb content, low Ba and Sr contents, and Rb/Sr ratios of 0.43–35.8. They exhibit nearly flat REE patterns with strong negative Eu anomalies on chondrite-normalized REE patterns. Considering their low zircon saturation temperatures (682–758 °C) and low εNd(t) values (˗12.4 to ˗2.7), as well as the presence of Al-rich minerals (muscovite and garnet), we infer that the leucogranites were low-temperature granites and generated mainly by fluid-absent muscovite dehydration melting of metasediments. LA-ICPMS zircon and monazite U-Pb dating suggests crystallization ages of 279–267 Ma, which places these leucogranite dykes in temporal association with the ultrahigh- to high-grade metamorphic rocks and implies a prolonged heat budget in the region. Together with contemporary magmatic activities and metamorphism in the Chinese Altai orogen, the generation of the leucogranite dykes may have been attributed to long-lasting high heat flow in the early Permian, most likely related to the assembly of the Junggar plate and the Chinese Altai.
The clay mineralogy and Sr-Nd isotopic composition of sediments collected in the northwestern South China Sea (SCS) were investigated to understand sediment provenance and changes in the SCS since the Late Pleistocene. Our results show that the clay mineral assemblages of the surface sediments are characterized by high amounts of illite and smectite, and low amounts of kaolinite and chlorite. The ⁸⁷Sr/⁸⁶Sr ratios of the surface sediments vary from 0.709617 to 0.734416, and εNd values range from –11.6 to –8.3. The clay minerals and Sr-Nd isotope records suggest that sediments in the northwestern SCS are derived from multiple sources. The sediments deposited in the eastern shelf offshore of Hainan originate predominantly from Hainan Island and South China, whereas sediments in the western shelf offshore of Hainan are derived mainly from Indochina and Hainan Island. However, sediment source and transport mechanisms in the northwestern slope of the SCS are more complicated. Our results suggest that input from the west may be the major sediment source, but regions in the east (Taiwan and Luzon) also contribute part of the terrigenous materials. Downcore variations of Sr-Nd isotopic composition in core sediments show clear glacial–interglacial fluctuations. Higher ⁸⁷Sr/⁸⁶Sr ratios occur during glacial period, indicating that the input of terrigenous materials from old continental rocks becomes one of the important sediment sources during these periods. The exposure of continental shelf and southward migration of the coastline during the glacial sea-level lowstand led to an increase of terrigenous supply to the northwestern slope of the SCS. The paleo-Red River and Indochina are also potentially important contributors.
The newly discovered early Paleozoic Delenuoer ophiolite, in the western margin of the Central Qilian Shan, is composed of serpentinized peridotite, cumulate gabbro, diabase, massive basalt, and pillow basalt. This study presents geochronological and geochemical data for the cumulate gabbro and basalt. LA–ICP–MS U–Pb dating of zircons from the cumulate gabbro yielded a magmatic crystallization age of 472 ± 4 Ma. The basalts have normal mid-ocean ridge basalt (N-MORB) compositions and a narrow range of εNd(t) values (+4.5 to + 5.3), which indicates they were derived from a depleted mantle source. On the basis of regional geological constraints, it is proposed that the Delenuoer ophiolite is a westward extension of the South Ophiolite Belt (Yushigou–Youhulugou–Donggou–Dongcaohe Ophiolite Belt) in the North Qilian Shan. The Delenuoer ophiolite, along with the Gulangxia–Delenuoer fault, defines the westernmost part of the tectonic boundary between the North and Central Qilian Shan. This ophiolite may have formed during southward subduction of the Qilian Ocean slab during the early Paleozoic.
ResearchGate has not been able to resolve any references for this publication.