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Morphology, architecture and emplacement of the Central Atlantic Magmatic Province (CAMP) basaltic successions in Morocco, and comparisons with the Deccan (India) and Parana (Brazil) traps. Proposal of a new facies model for the emplacement of the Continental Flood Basalt.

Authors:
Nasrrddine Youbi at Cadi Ayyad University
Nasrrddine Youbi
Hind El Hachimi at Chouaib Doukkali University
Hind El Hachimi
  • Chouaib Doukkali University
Mohamed Khalil Bensalah at Cadi Ayyad University
Mohamed Khalil Bensalah
José Madeira at University of Lisbon
José Madeira
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Abstract

Once considered to be composed by monotonous stacks of basaltic lava, continental flood basalt (CFB) provinces are now known to display considerable diversity in lava flow morphology. Whereas most initial studies of flood basalt morphology and emplacement focused on younger provinces such as the Columbia River Basalt (e.g., Self et al. 1996; Thordarson and Self 1998), subsequent investigations have also targeted older provinces such as the Central Atlantic Magmatic Province (CAMP, e.g., Kontak, 2008; Martins et al., 2008; El Hachimi et al., 2011), Paranà-Etendeka (Jerram et al., 1999a, b; Waichel et al., 2006, Waichel et al., 2008; Waichel et al., 2012; Rossetti et al., 2014), and the Deccan Volcanic Province (DVP, e.g., Keszthelyi et al. 1999; Duraiswami et al., 2001, Duraiswami et al., 2003; Bondre et al., 2004a,b; Sheth 2006; Sheth et al., 2011; Duraiswami et al., 2014). It is becoming increasingly clear that every CFB province is unique in terms of its tectono-magmatic evolution as well as in the types of lava flows and their proportions. Bondre et al. (2004a,b) have cautioned against using only the Columbia River Basalt province as an analogue for all CFB provinces. They stressed the need to document the morphology of lava flows from each individual province in order to obtain insights into their emplacement and eruptive histories. An important reason for documenting flow morphology in older provinces is to uncover lava types and modes of emplacement that are not observed in younger and active volcanic provinces. Indeed, recent studies from CFB provinces have led to the recognition of distinct lava types that have few young analogues (e.g. rubbly pahoehoe; Keszthelyi et al. 2006). Here we compare the morphology, architecture and emplacement of the CAMP basaltic successions in Morocco with the DVP (India) and Parana (Brazil) traps and propose a new facies model for the emplacement of the CFB. Our comparison on the physical volcanology of these key provinces and others CFB indicate that they do not have a simple, ‘layer-cake stratigraphy’, but contain complex internal and external architectures. Such architectures are governed by the volume of individual eruption events, the location and abundance of volcanic centers, and the evolution of these centers through time. The architecture of most, if not all, CFB provinces reveals that the production of compound pahoehoe flows was followed by flows with a simpler, sheet-like geometry indicating a fundamental temporal change in the emplacement process of lava flows. Accordingly, it appears that flood basalt volcanism initially starts out at relatively low effusion rate, which gradually accelerate to high effusion rate, high-volume eruptions. This worldwide similarity suggests that the magma genesis and/or magma ascension processes are similar in all CFB provinces (Jerram 2002; Jerram et al. 1999a, b; Planke et al. 2000; White et al. 2009; Jerram and Widdowson 2005; Martins et al., 2008; El Hachimi et al., 2011; Waichel et al., 2012; Rossetti et al., 2014; Duraiswami et al., 2014), although local conditions (coeval regional geomorphology, surface and underground water availability) may constrain the details of the internal architecture of each province (Luchetti et al., 2014; El Ghilani et al., 2017). References Bondre NR, Duraiswami RA, Dole G (2004a) Morphology and emplacement of flows from the Deccan Volcanic Province, India. Bull Volcanol 66:29-45 Bondre NR, Duraiswami RA, Dole G (2004b) A brief comparison of lava flows from the Deccan Volcanic Province and the Columbia-Oregon Plateau flood basalts: Implications for models of flood basalt emplacement. In: Sheth HC, Pande K (eds) Magmatism in India through time. Proc Ind Acad Sci (Earth and Planet Sci) 113:809-817. Duraiswami RA, Bondre NR, Dole G, Phadnis VM, Kale VS (2001) Tumuli and associated features from the western Deccan Volcanic Province, India. Bull Volcanol 63:435-442. Duraiswami RA, Dole G, Bondre NR (2003) Slabby pahoehoe from the western Deccan Volcanic Province: evidence for incipient pahoehoe–aa transitions. J Volcanol Geotherm Res 121:195-217. Duraiswami, R.A., Purva Gadpallu, Shaikh, T.N. and Neha Cardin (2014). Pahoehoe-a’a transitions in the lava flow fields of the western Deccan Traps, India- implications for emplacement dynamics, flood basalt architecture and volcanic stratigraphy. Jour. Asian Earth Sci., v.84, pp.146-166 El Ghilani, S.; Youbi, N.; Madeira, J.; Chellai, E.H.; Lopez-Galindo, A.; Martins, L. and Mata, J. (2017) Environmental implication of subaqueous lava flows from a continental Large Igneous Province: examples from the Moroccan Central Atlantic Magmatic Province (CAMP). J. African Earth Sci. 127: 211–221. El Hachimi H, Youbi N, Madeira J, Bensalah MK, Martins L, Mata J, Bertrand H, Marzoli A, Medina F, Munhá J, Bellieni J, Mahmoudi A, Ben Abbou M, Assafar H (2011) Morphology, internal architecture, and emplacement mechanisms of lava flows from the Central Atlantic Magmatic Province (CAMP) of Argana basin (Morocco). In: Van Hinsbergen DJJ, Buiter SJH, Torsvik TH, Gaina C, Webb SJ (eds) The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History. Geol Soc Lond Spec Publ 357, 167-193. Jerram DA, Mountney N, Stollhofen H. (1999a) Facies architecture of the Etjo Sandstone Formation and its interaction with the Basal Etendeka food basalts of NW Namibia: Implications for offshore analogues. In: Cameron N, Bate R, Clure V (eds) The Oil and Gas Habitats of the South Atlantic. Geol Soc Lond Spec Publ 153, 367-380.
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filoniennes renfermant des roches basiques à intermédiaires allant même jusqu'aux termes
différenciés acides.
A ce stade de l'étude, plusieurs types pétrographiques sont distingués :
- Un ensemble filonien allongé dans un couloir de 60 km de long et 5 km de large,
orienté NE –SW. La texture et la composition des filons sont variables d’un dyke à
l’autre, microgrenue à grenue porphyrique avec quartz, K-feldspath, plagioclase,
biotite et amphibole en plus des minéraux accessoires ;
- Un granite mis en place en massifs circonscrits et protrusions d'amplitude
hectométrique, alignés suivant une direction méridienne à l'intérieur du CST. Ces
pointements semblent constituer des apophyses d'un batholite plus ample encore
enfoui, générateur d'une large auréole de métamorphisme de contact. Cet épisode
granitique semble synchrone d'un magmatisme tonalitique avec lequel il développe un
contact sinueux et progressif, permettant une migration de cristaux entre les deux
faciès;
- Des lentilles de microleucogranites d'origine supracrustale, mises en place dans des
couloirs de cisaillement subparallèles à jeu senestre, récurrents à l'échelle de CST.
La cartographie des occurrences magmatiques suivant une approche de pétrologie
structurale a permis de classifier les différents épisodes magmatiques et préciser leur
filiation génétique.
Morphology, architecture and emplacement of the Central Atlantic Magmatic
Province (CAMP) basaltic successions in Morocco, and comparisons with the
Deccan (India) and Parana (Brazil) traps. Proposal of a new facies model for
the emplacement of the Continental Flood Basalt
N. Youbi1,2, H. El Hachimi3, M. Kh. Bensalah1,2, J. Madeira2, M. A. Boumehdi1,2, H. Sheth4, R.
Duraiswami5, J. Mata2, L. Martins2, El. H. Chellai1, A. Marzoli6, H. Bertrand7, F. Medina8, M.
Ben Abbou9, F. Zouita1, H. Khounch1
1 Department of Geology, Faculty. of Sciences-Semlalia, Cadi Ayyad University, Prince Moulay Abdellah
Boulevard, P.O. Box 2390, Marrakech, 40 000, Morocco, e-mail: youbi@uca.ma; boumehdi@uca.ac.ma;
2 Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
Email : jmadeira@fc.ul.pt; jmata@fc.ul.pt
3 Department of Geology, Faculty of Sciences, Chouaïb Doukkali University, 24000 El Jadida, Morocco.
Email : elhachimi_hind@yahoo.fr
4 Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, India. Email:
hcsheth@iitb.ac
5 Department of Geology, Savitribai Phule Pune University, Pune 411 007, India. Email:
raymond.duraiswami@gmail.com
6 Dipartimento di Geoscienze, Università di Padova, 35131 Padova, Italy. Email : andrea.marzoli@unipd.it
7 Laboratoire de Géologie de Lyon, ENS de Lyon, Université Lyon 1, CNRS, UMR 5276, Lyon 69364, France.
Email : herve.bertrand@ens-lyon.fr
8 Moroccan Association of Geosciences, Rabat, Morocco
9 Department of Geology, Faculty of Sciences Dhar Al Mahraz, Sidi Mohammed Ben Abdellah University,
Fès, Morocco
Once considered to be composed by monotonous stacks of basaltic lava, continental flood
basalt (CFB) provinces are now known to display considerable diversity in lava flow
51
Abstract Book
morphology. Whereas most initial studies of flood basalt morphology and emplacement
focused on younger provinces such as the Columbia River Basalt (e.g., Self et al. 1996;
Thordarson and Self 1998), subsequent investigations have also targeted older provinces
such as the Central Atlantic Magmatic Province (CAMP, e.g., Kontak, 2008; Martins et al.,
2008; El Hachimi et al., 2011), Paranà-Etendeka (Jerram et al., 1999a, b; Waichel et al., 2006,
Waichel et al., 2008; Waichel et al., 2012; Rossetti et al., 2014), and the Deccan Volcanic
Province (DVP, e.g., Keszthelyi et al. 1999; Duraiswami et al., 2001, Duraiswami et al., 2003;
Bondre et al., 2004a,b; Sheth 2006; Sheth et al., 2011; Duraiswami et al., 2014). It is
becoming increasingly clear that every CFB province is unique in terms of its tectono-
magmatic evolution as well as in the types of lava flows and their proportions. Bondre et al.
(2004a,b) have cautioned against using only the Columbia River Basalt province as an
analogue for all CFB provinces. They stressed the need to document the morphology of lava
flows from each individual province in order to obtain insights into their emplacement and
eruptive histories. An important reason for documenting flow morphology in older provinces
is to uncover lava types and modes of emplacement that are not observed in younger and
active volcanic provinces. Indeed, recent studies from CFB provinces have led to the
recognition of distinct lava types that have few young analogues (e.g. rubbly pahoehoe;
Keszthelyi et al. 2006). Here we compare the morphology, architecture and emplacement of
the CAMP basaltic successions in Morocco with the DVP (India) and Parana (Brazil) traps and
propose a new facies model for the emplacement of the CFB. Our comparison on the
physical volcanology of these key provinces and others CFB indicate that they do not have a
simple, ‘layer-cake stratigraphy’, but contain complex internal and external architectures.
Such architectures are governed by the volume of individual eruption events, the location
and abundance of volcanic centers, and the evolution of these centers through time. The
architecture of most, if not all, CFB provinces reveals that the production of compound
pahoehoe flows was followed by flows with a simpler, sheet-like geometry indicating a
fundamental temporal change in the emplacement process of lava flows. Accordingly, it
appears that flood basalt volcanism initially starts out at relatively low effusion rate, which
gradually accelerate to high effusion rate, high-volume eruptions. This worldwide similarity
suggests that the magma genesis and/or magma ascension processes are similar in all CFB
provinces (Jerram 2002; Jerram et al. 1999a, b; Planke et al. 2000; White et al. 2009; Jerram
and Widdowson 2005; Martins et al., 2008; El Hachimi et al., 2011; Waichel et al., 2012;
Rossetti et al., 2014; Duraiswami et al., 2014), although local conditions (coeval regional
geomorphology, surface and underground water availability) may constrain the details of the
internal architecture of each province (Luchetti et al., 2014; El Ghilani et al., 2017).
References
Bondre NR, Duraiswami RA, Dole G 2004a.Morphology and emplacement of flows from the Deccan Volcanic
Province, India. Bull Volcanol 66:29-45
Bondre NR, Duraiswami RA, Dole G 2004b.A brief comparison of lava flows from the Deccan Volcanic Province
and the Columbia-Oregon Plateau flood basalts: Implications for models of flood basalt emplacement. In: Sheth
HC, Pande K (eds) Magmatism in India through time. Proc IndAcadSci (Earth and Planet Sci) 113:809-817.
Duraiswami RA, Bondre NR, Dole G, Phadnis VM, Kale VS 2001.Tumuli and associated features from the
western Deccan Volcanic Province, India. Bull Volcanol 63:435-442.
Duraiswami RA, Dole G, Bondre NR 2003.Slabby pahoehoe from the western Deccan Volcanic Province:
evidence for incipient pahoehoe–aa transitions. J VolcanolGeotherm Res 121:195-217.
Duraiswami, R.A., PurvaGadpallu, Shaikh, T.N. and Neha Cardin 2014. Pahoehoe-a’a transitions in the lava
flow fields of the western Deccan Traps, India- implications for emplacement dynamics, flood basalt
architecture and volcanic stratigraphy. Jour.Asian Earth Sci., v.84, pp.146-166
52
Abstract Book
El Ghilani, S.; Youbi, N.; Madeira, J.; Chellai, E.H.; Lopez-Galindo, A.; Martins, L. andMata, J.
2017.Environmental implication of subaqueous lava flows from a continental Large Igneous Province: examples
from the Moroccan Central Atlantic Magmatic Province (CAMP). J. African Earth Sci. 127: 211–221.
El Hachimi H, Youbi N, Madeira J, Bensalah MK, Martins L, Mata J, Bertrand H, Marzoli A, Medina F, Munhá
J, Bellieni J, Mahmoudi A, Ben Abbou M, Assafar H 2011. Morphology, internal architecture, and emplacement
mechanisms of lava flows from the Central Atlantic Magmatic Province (CAMP) of Argana basin (Morocco). In:
Van Hinsbergen DJJ, Buiter SJH, Torsvik TH, Gaina C, Webb SJ (eds) The Formation and Evolution of Africa: A
Synopsis of 3.8 Ga of Earth History. Geol Soc Lond Spec Publ 357, 167-193.
Jerram DA, Mountney N, Stollhofen H. 1999a. Facies architecture of the Etjo Sandstone Formation and its
interaction with the Basal Etendeka food basalts of NW Namibia: Implications for offshore analogues. In:
Cameron N, Bate R, Clure V (eds) The Oil and Gas Habitats of the South Atlantic. GeolSocLond Spec Publ 153,
367-380.
Jerram DA, Mountney N, Holzförster F, Stollhofen H 1999b. Internal stratigraphic relationships in the Etendeka
Group in the Huab Basin, NW Namibia: understanding the onset of food volcanism. J Geodyn 28, 393-418.
Jerram, D. A. & Widdowson, M. 2005. The anatomy of Continental Flood Basalt Provinces: geological
constraints on the processes and products of flood volcanism. Lithos, 79, 385-405.
Jerram, D. A. 2002. Volcanology and facies architecture of flood basalts. In: Menzies, M. A., Klemperer, S. L.,
Ebinger, C. J. & Baker, J. (eds) Volcanic Rifted Margins. Geological Society of America, Boulder, Special Paper,
362, 121-135.
Keszthelyi L, Self S, Thordarson T 1999. Application of Recent studies on the emplacement of basaltic lava
flows to the Deccan Traps. In: Subbarao KV (ed) Deccan Volcanic Province, Mem GeolSocInd 43, 485-520.
Keszthelyi L, Self S, Thordarson T 2006. Flood lavas on Earth, Io and Mars. J GeolSocLond 163, 253-264.
Kontak DJ 2008. On the edge of CAMP: Geology and volcanology of the Jurassic North Mountain Basalt, Nova
Scotia. In: Dostal J, Greenough JD, Kontak DJ (eds) Rift-related Magmatism. Lithos 101, 74-101.
Luchetti, A.C.F.; Nardy, A.J.R.; Machado, F.B.; Madeira, J. & Arnósio, J.M. 2014.New insights on the
occurrence of peperites and sedimentary deposits within the silicic volcanic sequences of the Paraná Magmatic
Province, Brazil. Solid Earth 5, 121-130.
Martins LT, Madeira J, Youbi N, Munha J, Mata J., Kerrich R 2008. Rift-related magmatism of the Central
Atlantic Magmatic Province in Algarve, Southern Portugal. In: Dostal J, Greenough JD, Kontak DJ (eds) Rift-
related Magmatism. Lithos 101, 102-124.
Planke, S., Symonds, P. A., Alvestad, E. &Skogseid, J. 2000. Seismic volcanostratigraphy of large-volume
basaltic extrusive complexes on rifted margins. Journal of Geophysical Research, 105, 19,335-19,351.
Rossetti, L.M.L.M., Lima, E.F.E.F., Waichel, B.L.B.L., Scherer, C.M.C.M., Barreto, C.J.C.J. 2014. Stratigraphical
framework of basaltic lavas in Torres syncline main valley, southern Parana-Etendeka Volcanic Province. J. S.
Am. Earth Sci. 56:409-421.
Self S, Thordarson T, Keszthelyi L 1996. A new model for the emplacement of Columbia River basalts as large,
inflated pahoehoe lava flow fields. Geophys Res Lett 23:2689–2692.
Sheth , HC. 2006. The emplacement of pahoehoe lavas on Kilauea and in the Deccan Traps. J Earth SystSci 115,
615-629.
Sheth HC, Ray JS, Senthil Kumar P, Duraiswami RA, Chatterjee RN, Gurav T 2011. Recycling of flow-top breccia
crusts into molten interiors of flood basalt lava flows: Field and geochemical evidence from the Deccan Traps.
In: Ray J, Sen G, Ghosh B (eds) Topics in Igneous Petrology. Springer, Ch 8, 161-180.
Thordarson T, Self S 1998. The Roza Member, Columbia River Basalt Group: A gigantic pahoehoe lava flow field
formed by endogenous processes? J Geophys Res 103:27411-27445
Waichel PL, Lima EF, Lubachesky R, Sommer CA 2006. Pahoehoe flows from the central Parana Continental
Flood Basalts. Bull Volcanol 68, 599-610
Waichel PL, Scherer CMS, Frank HT 2008. Basaltic lava flows covering active aeolian dunes in the Parana Basin
in southern Brazil: Features and emplacement aspects. J VolcanolGeotherm Res 171, 59-72.
Waichel, B.L., Lima, E.F., Viana, A.R., Scherer, C.M., Bueno, G.V., Dutra, G., 2012. Stratigraphy and volcanic
facies architecture of the Torres Syncline, Southern Brazil, and its role in understanding the Parana-Etendeka
Continental Flood Basalt Province. J. Volcanol. Geotherm. Res. 216, 74-82.
White, J. D. L., Bryan, S. E., Ross, P. S., Self, S. &Thordarson, T. 2009. Physical volcanology of large igneous
provinces: update and review. In: Thordarson, T., Self, S., Larsen, G., Rowland, S. &Hoskuldsson, A. (eds) Studies
in Volcanology: The Legacy of George Walker. Special Publications of IAVCEI, 2. Geological Society, London,
291-321.
ResearchGate has not been able to resolve any citations for this publication.
The emplacement of pahoehoe lavas on Kilauea and in the Deccan Traps (2006)
Article
Full-text available
  • Dec 2006
  • J EARTH SYST SCI
There is a growing interest in deciphering the emplacement and environmental impact of flood basalt provinces such as the Deccan, India. Observations of active volcanism lead to meaningful interpretations of now-extinct volcanic systems. Here, I illustrate and discuss the morphology and emplacement of the modern and active lava flows of Kilauea volcano in Hawaii, and based on them, interpret the compound pahoehoe lavas of the Deccan Traps. The latter are vastly larger (areally extensive and voluminous) than Kilauea flows, and yet, their internal architecture is the same as that of Kilauea flows, and even the sizes of individual flow units often identical. Many or most compound flows of the Deccan Traps were emplaced in a gentle, effusive, Kilauea-like fashion. Bulk eruption rates for the Deccan province are unknown, and were probably high, but the local eruption rates of the compound flows were no larger than Kilauea's. Large (≥ 1000 km 3) individual compound pahoehoe flows in the Deccan could have been emplaced at Kilauea-like local eruption rates (1 m 3 /sec per metre length of fissure) in a decade or less, given fissures of sufficient length (tens of kilometres), now exposed as dyke swarms in the province.
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Recycling of Flow-Top Breccia Crusts into Molten Interiors of Flood Basalt Lava Flows: Field and Geochemical Evidence from the Deccan Traps
Article
Full-text available
  • Nov 2011
Thick flood basalt lava flows cool conductively inward from their tops and bases, usually developing columnar jointing. Although relatively rapid cooling in such flows due to meteoric water circulation has been previously demonstrated, mixing of the surface crust with the interior – as observed in active lava lakes – has not been shown. Here we report large radial columnar jointing structures (rosettes) with cores of highly brecciated, weathered and amygdaloidal material within Deccan flood basalt lava flows. The morphology of such breccia-cored rosettes, petrographic observations, and geochemical data, particularly Nd–Sr isotopic ratios, all suggest that the features formed due to the sinking of the flow-top breccia crusts into these flows' molten interiors and the resultant warping of isotherms around these "cold anchors". Thus, cooling in some thick flood basalt lava flows may be accelerated by sinking of cooler upper crusts into hotter, molten interiors.
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Pahoehoe–a′a transitions in the lava flow fields of the western Deccan Traps, India-implications for emplacement dynamics, flood basalt architecture and volcanic stratigraphy
Article
Full-text available
  • Apr 2014
  • J ASIAN EARTH SCI
Unlike pahoehoe, documentation of true a′a lavas from a modern volcanological perspective is a relatively recent phenomenon in the Deccan Trap (e.g. Brown et al., 2011, Bull. Volcanol. 73(6): 737–752) as most lava flows previously considered to be a′a (e.g. GSI, 1998) have been shown to be transitional (e.g. Rajarao et al., 1978, Geol. Soc. India Mem. 43: 401–414; Duraiswami et al., 2008 J. Volcanol. Geothermal. Res. 177: 822–836). In this paper we demonstrate the co-existence of autobrecciation products such as slabby pahoehoe, rubbly pahoehoe and a′a in scattered outcrops within the dominantly pahoehoe flow fields. Although volumetrically low in number, the pattern of occurrence of the brecciating lobes alongside intact ones suggests that these might have formed in individual lobes along marginal branches and terminal parts of compound flow fields. Complete transitions from typical pahoehoe to ‘a′a lava flow morphologies are seen on length scales of 100–1000 m within road and sea-cliff sections near Uruli and Rajpuri. We consider the complex interplay between local increase in the lava supply rates due to storage or temporary stoppage, local increase in paleo-slope, rapid cooling and localized increase in the strain rates especially in the middle and terminal parts of the compound flow field responsible for the transitional morphologies. Such transitions are seen in the Thakurwadi-, Bushe- and Poladpur Formation in the western Deccan Traps. These are similar to pahoehoe–a′a transitions seen in Cenozoic long lava flows (Undara ∼160 km, Toomba ∼120 km, Kinrara ∼55 km) from north Queensland, Australia and Recent (1859) eruption of Mauna Loa, Hawaii (a′a lava flow ∼51 km) suggesting that flow fields with transitional tendencies cannot travel great lengths despite strong channelisation. If these observations are true, then it arguably limits long distance flow of Deccan Traps lavas to Rajahmundry suggesting polycentric eruptions at ∼65 Ma in Peninsular India.
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New insights on the occurrence of peperites and sedimentary deposits within the silicic volcanic sequences of the Paraná Magmatic Province, Brazil
Article
Full-text available
  • Mar 2014
The PMP (Paraná Magmatic Province) is characterized by lava flows of the Early Cretaceous Serra Geral Formation which covers about 75% of the Paraná Basin (southern and southeastern Brazil), composed of a thick (up to 1600 m) volcanic sequence formed by a succession of petrographically and geochemically distinct units of basic and silicic composition. The whole package must have been emplaced during approximately 3 million years of nearly uninterrupted activity. A few aeolian sandstone layers, indicating arid environmental conditions (the Botucatu Formation), are interlayered in the lower basalts. Above the basalts, the Palmas and Chapecó Members are composed of silicic volcanic rocks (quartz latites, dacites, rhyodacites and rhyolites) and basalts. This paper presents new evidence of sedimentation episodes separating silicic volcanic events, expressed by the occurrence of sedimentary deposits. Interaction between the volcanic bodies and the coeval unconsolidated sediments formed peperites. The sediments were observed between basaltic lava flows and silicic rocks or interlayered in the Palmas-type rocks, between the Chapecó-type rocks and overlying basaltic flows, between silicic bodies of the Palmas and Chapecó types, and interlayered within Palmas-type units. The observed structures indicate that the sediments were still wet and unconsolidated, or weakly consolidated, at the time of volcanism, which, coupled with the sediment features, reflect environmental conditions that are different from those characterizing the Botucatu arid conditions.
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Stratigraphy and volcanic facies architecture of the Torres Syncline, Southern Brazil, and its role in understanding the Paraná–Etendeka Continental Flood Basalt Province
Article
Full-text available
  • Feb 2012
  • J VOLCANOL GEOTH RES
The Torres Syncline is a large structure that constitutes the eastmost outcrop of the Paraná–Etendeka CFB in South American side, and this work focuses the stratigraphy and facies architecture of the volcanic pile in the syncline. The volcanic sequence along the study area permits the division of three regions: main valley, intermediate zone and south hinge, each of them with distinct stratigraphy, which probably reflects the structural evolution of the syncline. The stratigraphy of the Torres Syncline is composed by: 1 — Botucatu palaeoerg; 2 — Basic volcanic episode I; 3 — Basic volcanic episode II, 4 — Acidic volcanic I, 5 — Basic volcanic episode III and 6 — Acidic volcanic episode II. The five volcanic episodes recognized in study area can be related to five volcanic facies architecture: compound-braided, tabular-classic, tabular/lobate escoriaceous, dome-field (acidic lavas) and tabular flows (acidic lavas). The basic episode I is composed by pahoehoe flows with a compound-braided facies architecture that covered the Botucatu palaeoerg. The basic episode II is a tabular-classic facies architecture predominantly composed by simple flows (10–20 m thick) reaching the total thickness of ~ 500 m in main valley. The acidic episode I is exposed in main valley and south hinge, and is composed by acidic lavas forming lava dome-field facies architecture with a thickness of ~ 150 m. The basic episode III is predominantly constituted by ‘a’ā flows with tabular/lobate escoriaceous facies architecture. The acidic episode II is constituted by tabular flow volcanic facies (acidic flows) and outcrops all along the study area. The Torres Syncline constitute the eastmost on-shore exposures of the Paraná–Etendeka CFB in South American side and detailed stratigraphic, volcanological and structural studies in these area, coupled with correlation with Huab Basin (NW Namíbia, Africa) will aim the understanding of the Gondwana breakup process and the early stages of the South Atlantic margin opening.
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Facies architecture of the Etjo Sandstone Formation and its interaction with the basal Etendeka flood basalts of NW Namibia: Implications for offshore analogues
Article
Full-text available
  • Sep 1999
The Basal Etendeka Flood Basalt stratigraphy in the Huab Basin of northwest Namibia comprises a series of lava flows interleaved with aeolian sandstone bodies of the Etjo Sandstone Formation. The sandstone units are characterized by three main types: (1) the major erg — a mixed aeolian and fluvial facies up to 150 m thick; (2) minor ergs — aeolian facies which occur directly above the first volcanic units and are up to 60 m thick; (3) isolated bodies — multidune, single dune and lava topography infills. A variety of bypass surfaces identified by sand-filled cracks and sediment-lava breccias occur on lava top surfaces. Preserved ripples and pahoehoe lava imprints indicate that the aeolian sand dunes were actively migrating during basalt emplacement. Observations recorded in the Basal Etendeka Flood Basalts which may be of relevance to offshore hydrocarbon exploration include: a major-minor erg relationship resulting in large sandbodies up to 60 m thick which occur directly after the first volcanic units; the occurrence of sand-filled fissures up to 36 m in depth which would greatly influence connectivity in an offshore setting; the identification of bypass surfaces as marker horizons which may laterally correlate with isolated sandbodies.
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Slabby pahoehoe from the western Deccan Volcanic Province: Evidence for incipient pahoehoe-aa transitions
Article
  • Mar 2003
The pahoehoe-aa transition for a flow exposed near Bodshil village from the western part of the Deccan Volcanic Province (DVP) is reported for the first time. The ∼ 1-km-long Bodshil flow issued as a small sheet from a preexisting lobe. Near the source, the crust is characterised by numerous squeeze-ups. A number of gaping fractures, parallel to sub-parallel to the flow direction, are exposed on the surface in the medial portion of the flow. About 800 m away, the flow completely transforms to slabby pahoehoe. The terminal portion of the flow is characterised by concentrations of slabs, blocks and lava balls. The size and concentrations of the slabs and lava balls appear to increase along the length of the flow. Petrographic studies reveal a dominant hypohyaline texture. The flow core is coarse and is characterised by plagioclase set in a glassy matrix. The presence of clinopyroxene in addition to plagioclase and glass distinguishes the crust and interslab crust from the core. On the basis of mineralogy, a temperature range of 1146 ± 15°C to 1169 ± 15°C is inferred for the Bodshil flow. Increased vesicle deformation across the transition is discernible and an average D-value of 60.4 indicates moderate strain rates during emplacement. In light of the morphology and petrography, the cooling history and the mode of emplacement of the Bodshil flow is discussed. The flow originated as a small toe at the leading edge of a pahoehoe flow, and grew into a sheet by the mechanism of inflation. Continuous inflation caused the brittle crust to uplift and produce a network of inflation clefts that were subsequently occupied by squeeze-ups. Temporary stagnation of the flow due to cessation of lava supply or storage allowed the crust to grow and thicken. Renewed movement of the stored and cooled lava to the flow front at a fairly high volumetric rate was responsible for the initial disruption of the crust. High rates of crustal disruption induced higher rates of degassing and cooling, which resulted in rapid crystallisation of the fluid core. Increase in crystallinity lead to the onset of yield strength, and it is envisaged that at least the terminal parts of the flow behaved as a Bingham fluid. The Bodshil flow is unique to the DVP because it is the first to record slabby pahoehoe and provide evidence for the incipient transformation of basaltic lava from pahoehoe to aa.
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Environmental implication of subaqueous lava flows from a continental Large Igneous Province: Examples from the Moroccan Central Atlantic Magmatic Province (CAMP)
Article
  • Mar 2017
  • J AFR EARTH SCI
The Late Triassic-Early Jurassic volcanic sequence of the Central Atlantic Magmatic Province (CAMP) of Morocco is classically subdivided into four stratigraphic units: the Lower, Middle, Upper and Recurrent Formations separated by intercalated sediments deposited during short hiatuses in volcanic activity. Although corresponding to a Large Igneous Province formed in continental environment, it contains subaqueous lava flows, including dominant pillowed flows but also occasional sheet flows. We present a study of the morphology, structure and morphometry of subaqueous lava flows from three sections located at the Marrakech High-Atlas (regions of Aït-Ourir, Jbel Imzar and Oued Lhar-Herissane), as well as an analysis of the sediments, in order to characterize them and to understand their environmental meaning.
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Volcanology and facies architecture of flood basalts
Article
  • Jan 2002
In terms of their detailed volcanology and facies architecture, continental flood basalts and associated volcanic rifted margins reveal important information to help our understanding of their evolution. Mafic volcanism, which makes up the majority of preserved material, is characterized by flows 2-3 m to several tens of meters thick, with ponded flows and occasional massive flow events of ∼100 m thick. Although most of the flows are emplaced by the same mechanism as passive inflated sheets, a variety of different facies associations are dependent on flow volumes and to some extent flow composition. The largest silicic volcanic events in continental flood basalts are larger in volume than the largest recorded mafic events, and they are potentially more catastrophic if erupted as ignimbrite flows. The architecture of continental flood basalts and associated volcanic rifted margins is recorded by facies types and facies associations. Facies types, such as tabular-classic flows, braided-compound flows, or hyaloclastites, represent genetically related building blocks of the volcanic stratigraphy. Facies associations, such as downlap, onlap, and disconformities, relate how the volcanic facies are stacked together. Many of the facies associations occur on an intermediate to large basin-wide scale and may only be revealed by detailed field work, photogrammetry, and three-dimensional geological models.
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