Petrogenesis and geochemical characteristics of plagiogranites from Naga Ophiolite Belt, northeast India: Fractional crystallization of MORB-type magma

Nayak, Ranjit; Rao, B. Veeranarayana

doi:10.1016/j.chemer.2016.11.001

Cited by 6 publications

(5 citation statements)

References 49 publications

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“…(a) and (b) Mafic rocks; (c) and (d) Plagiogranites; whereas (e) and (f) represent Ultramafic rocks. Published data shown for comparison are from: basalt (Imchen et al, 2015; Khogenkumar et al, 2016; Nayak & Rao, 2017; Sengupta et al, 1989; Srikanth et al, 2004), gabbro (Singh et al, 2012; Singh et al, 2016), plagiogranite (Nayak & Rao, 2017; Singh, Chung, Bikramaditya, & Lee, 2017). Normalizing REE and primitive mantle (PM) compositions are after McDonough and Frey (1989) [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Resultsmentioning

confidence: 99%

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Subduction versus non‐subduction origin of the Nagaland‐Manipur Ophiolites along the Indo‐Myanmar Orogenic Belt, northeast India: Fact and fallacy

et al. 2020

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The Nagaland‐Manipur Ophiolites (NMO) in northeast India is known for its complex geological history. Tough terrain, thick vegetation, and dismembered exposure of ophiolitic suite of rocks in the region made uneasy for geological investigation and put it in a deadlock for a long time. Only in the last decade has seen an appreciable amount of publications but the results boil down to a hot debate between two opposite schools of thoughts of subduction origin versus non‐subduction origin of the NMO. In this article, we revisit the literature data and compare it with our new geochemical data with an attempt to provide fresh insight into the long‐standing debate on the geodynamic evolution of the NMO. Our investigation arrives at the conclusion that the NMO as a whole cannot be considered as 100% subduction or 100% non‐subduction origin. It is indeed a combination of both. The non‐subduction group of mafic rocks shows a high ratio of incompatible elements (Nb/Yb >1), high‐Ti, enriched LILE, and HFSE with primitive mantle normalized values >5. Their bulk‐rock geochemical composition is equivalent to mid‐ocean ridge basalt (MORB) and ocean island basalt (OIB). The subduction group of rocks, on the other hand, shows a low ratio of incompatible elements (Nb/Yb <1), low‐Ti, depleted LILE, and HFSE with primitive mantle normalized values <1, affinity to the fore‐arc depleted N‐MORB type. Similarly, spinels present in subduction‐influenced mantle rocks show high chromium content (Cr# >50) but it is lower (Cr# <50) in non‐subduction abyssal peridotites of the NMO. Such geochemical variations cannot simply be explained by fractional crystallization or variable degree of partial melting of a single source, but rather signifies derivation from different tectonic settings of subduction and non‐subduction magma factories. We further conclude that the primary compressional force of India‐Myanmar Plate collision and secondary strike‐slip faults running along this ophiolite belt jeopardized the accretionary process which led to distortion and dismembering of the rocks like a scrambled bread.

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Section: Resultsmentioning

confidence: 99%

“…Published data shown for comparison are available in Supporting Information. Data are from Sengupta et al (1989), Srikanth et al (2004), Imchen et al (2015), Khogenkumar et al (2016), Nayak and Rao (2017), Singh et al (2012), Singh et al (2016). The data sources are listed in Appendix S1.…”

Section: Mineral Chemistrymentioning

confidence: 99%

Subduction versus non‐subduction origin of the Nagaland‐Manipur Ophiolites along the Indo‐Myanmar Orogenic Belt, northeast India: Fact and fallacy

et al. 2020

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“…In recent years, several workers have contributed to the geology, tectonics, geochemistry, and effects of metamorphism on the different rocks of the ophiolite sequence (Abdullah, Misra, & Ghosh, 2018; Acharyya, 2007; Aitchison et al, 2019; Chattopadhyay, Venkataramana, Roy, Bhattacharya, & Ghosh, 1983; Dey, Hussain, & Barman, 2018; Ghose, 2014; Ghosh, Ray, & Morishita, 2014; Imchen et al, 2015; Kingson, Bhutani, Balakrishnan, Dash, & Shukla, 2019; Nayak & Rao, 2017; Singh et al, 2016; Steckler et al, 2016; Verencar, Saha, Ganguly, & Manikyamba, 2021). However, no detailed work has so far been carried out on the NHO chert, barring a few paleontological studies.…”

Section: Introductionmentioning

confidence: 99%

Geochemical evidences on the origin and paleo‐oceanic depositional setting of the Naga Hills Ophiolite cherts, North East India

2022

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The Jurassic‐Cretaceous chert of the Naga Hills Ophiolite (NHO) is tectonically juxtaposed with the mafics (mostly basalts) and ultramafics along the Indo‐Myanmar Ranges (IMR), which constitute the southeastern extension of the Indus‐Yarlung‐Tsangpo Suture. Petrographic and geochemical studies were taken up to determine their origin and paleo‐oceanic depositional environments. Cryptocrystalline quartz is intimately mixed with iron oxides and clay minerals containing poorly preserved radiolarians. Geochemical signatures indicate a predominantly biogenic origin for the NHO cherts, which were derived from radiolarians and other siliceous microfossils. Rare earth elements and trace element abundances indicate predominant contribution by scavenging from seawater with the minor influence of low‐temperature hydrothermal activity. Most of the NHO cherts were deposited in an open ocean basin where oxic conditions prevailed. Geochemical signatures endorsed by field relations of chert, pillow basalts, and limestone within the oceanic plate indicate that chert formation continued in the vicinity of oceanic islands. Organic matter played a pivotal role in regulating oxic‐anoxic conditions during deposition, as evidenced by redox‐sensitive trace elements. These cherts, envisaged to have been originally part of the Tethys, were tectonically emplaced during the Middle Eocene. They now constitute part of the NHO along the IMR.

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“…Plagiogranites constitute only a minor part of ophiolite sequences and typically occur as intrusive masses or tectonic blocks with an unclear relationship with the ophiolite matrix. The petrogenesis of oceanic plagiogranite is controversial, and there are four hypotheses for its formation: (1) partial melting of preexisting basaltic crust (Anenburg et al, 2015;Borsi et al, 1996;Gerlach et al, 1981;Gillis & Coogan, 2002;Koepke et al, 2004;Malpas, 1979;Nicholson et al, 1991;Spulber & Rutherford, 1983;Stakes & Taylor, 2003); (2) fractional crystallization of mid-ocean ridge basalt (MORB)-type magmas (Coleman & Peterman, 1975;Coleman & Donato, 1979;Pallister & Knight, 1981;Floyd et al, 1998;Haase et al, 2006;Freund et al, 2014;Whattam et al, 2016;Nayak, 2016); (3) assimilation of seawater-altered components (Wanless et al, 2010); and (4) silicate melt immiscibility under certain conditions (Dixon & Rutherford, 1979). In addition, some silicic rocks in ophiolites can form by partial melting of sedimentary wall rocks during tectonic emplacement of the ophiolite (Li et al, 2008;Sorensen & Grossman, 1989), which should be distinguished from typical plagiogranites.…”

Section: Introductionmentioning

confidence: 99%

Diversity of Felsic Rocks in Oceanic Crust: Implications From the Neoproterozoic Plagiogranites Within the Northeast Jiangxi Ophiolite, Southern China

et al. 2020

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Silicic igneous rocks in the oceanic crust provide insights into the formation of proto‐continental crust, which can be investigated by studying rare silicic rocks within ophiolite complexes. This study focuses on plagiogranites that crop out as lenses and blocks in the northeast Jiangxi ophiolite (NJO), located in the eastern segment of the Neoproterozoic Jiangnan Orogen, southern China. The plagiogranites yield a mean SHRIMP U‐Pb zircon crystallization age of ca. 995 Ma and also record a late thermal event at ca. 220 Ma. The plagiogranites have high Na, very low K, and highly variable rare earth element (REE) concentrations from extremely depleted total REEs to strong enrichment in light REEs. Some samples have adakitic characteristics. Zircons from the plagiogranites have positive εHf(t) values (9.96 to 16.6) and mantle‐like δ18O values (5.13 ± 0.21‰), indicating a juvenile crustal or mantle source. Based on REE modeling, we propose a two‐stage model for the formation of the geochemically variable NJO plagiogranites: (1) High‐REE adakitic magmas plagiogranites were generated by 20% partial melting of basaltic oceanic crust; and (2) subsequent fractional crystallization (up to 50%) of these magmas and crystal accumulation produced the low‐REE plagiogranites. Our results show that granitic magmas can become highly differentiated in an oceanic setting. The diversity of silicic rocks in the oceanic crust is mainly the result of partial melting of subducted basaltic rocks and subsequent differentiation rather than just fractional crystallization of basaltic magmas.

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Petrogenesis and geochemical characteristics of plagiogranites from Naga Ophiolite Belt, northeast India: Fractional crystallization of MORB-type magma

Cited by 6 publications

References 49 publications

Subduction versus non‐subduction origin of the Nagaland‐Manipur Ophiolites along the Indo‐Myanmar Orogenic Belt, northeast India: Fact and fallacy

Subduction versus non‐subduction origin of the Nagaland‐Manipur Ophiolites along the Indo‐Myanmar Orogenic Belt, northeast India: Fact and fallacy

Geochemical evidences on the origin and paleo‐oceanic depositional setting of the Naga Hills Ophiolite cherts, North East India

Diversity of Felsic Rocks in Oceanic Crust: Implications From the Neoproterozoic Plagiogranites Within the Northeast Jiangxi Ophiolite, Southern China

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