Browsing by Author "Govind Oinam"

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Continental extension of northern Gondwana margin in the Eastern Himalaya: Constraints from geochemistry and U-Pb zircon ages of mafic intrusives in the Siang window, Arunachal Himalaya, India
(Academie des sciences, 2020) Govind Oinam; A. Krishnakanta Singh; Mallickarjun Joshi; Amrita Dutt; M. Rajanikanta Singh; N. Lakhan Singh; R.K. Bikramaditya Singh
We report new U-Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, eastern Himalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende + Fe-Ti oxides) that retain granular and interlocking texture. Geochemically, they display enriched-mid oceanic ridge basalt (E-MORB) affinity characterized by moderate to slightly fractionated REE patterns marked by (La/Yb)N = 2.65 − 3.99. Their geochemical characteristics suggest that the parental magmas of these rocks were formed by medium to higher degrees (∼12-28%) of partial melting similar to that of the asthenospheric mantle in the garnet-spinel transition zone. Magmatic zircons from two gabbros yield U-Pb ages of 521.50 ± 2.53 Ma and 568 ± 2 Ma. This new age reveals two pulses of Late Neoproterozoic and Early Cambrian mafic magmatism that are inconsistent with the temporal distribution of Paleozoic magmatism in the Siang window of the Eastern Himalayas. However, based on the results of this study and the correlation of continental extensional mafic magmatism in the Northwest Himalaya, we suggest that investigated mafic intrusive rocks might have been generated in an extensional tectonic environment during the long-lasting Pan-African orogenic cycle of the late Neoproterozoic to early Cambrian which ended with the formation of the Gondwana supercontinent. © Académie des sciences, Paris and the authors, 2020. Some rights reserved.
Depositional environment and tectonic backdrop of meta-carbonates in the Eastern Himalayan ophiolites, India: insights from calcite microstructures, whole-rock elements and stable isotopes
(Springer Science and Business Media Deutschland GmbH, 2021) Amrita Dutt; A. Krishnakanta Singh; Govind Oinam; Rajesh K. Srivastava
Tuting–Tidding Suture Zone (TTSZ) is the eastern extension of the Indus–Tsangpo Suture Zone (ITSZ) and is exposed in the Arunachal Himalaya, India. It comprises rocks of ophiolitic affinity associated with amphibolites, volcano-sedimentary units and meta-carbonates, occurring as a folded sequence of dismembered outcrops. The meta-carbonates are banded and massive in nature and appear devoid of any microfossils. We present whole-rock geochemistry and stable isotopes of these meta-carbonates to explain their depositional as well as post-depositional characteristics. REE patterns (ƩREE = 3.63–47.10), with almost flat to slight enrichment of HREE as compared to LREE [(La/Yb)SN = 0.60–1.37] are comparable with REE patterns of marine carbonates. The δ13CPDB and δ18OPDB values range between 0.33 and 4.29‰ and − 13.90 and − 6.50‰, respectively. Poor correlations between isotopic ratios of δ13CPDB and δ18OPDB, values of whole-rock elemental ratios (Mg/Ca, Fe/Sr, Mn/Sr, Ca/Sr), and extremely low Na/Ca indicate that these rocks were formed in a hypersaline environment with least effect of post-depositional diagenetic processes. Calcite microstructural studies of the TTSZ meta-carbonates suggest that they have undergone deformation up to mylonitic stage, which generally occurs at temperatures above 400 °C. This deformation can be correlated with the metamorphism and deformation event of the ophiolite that occurred during accretion and exhumation of the sequence in the cold subduction zone. Thus, based on the microstructural, geochemical, and isotopic evidences, we propose that the TTSZ meta-carbonates were formed in a shallow marine environment during the late stage of an intra-oceanic subduction and were later deformed along with the rest of the ophiolitic rocks during accretion and exhumation. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Evidence of melt– and fluid–rock interactions in the refractory forearc peridotites and associated mafic intrusives from the Tuting–Tidding ophiolites, eastern Himalaya, India: Petrogenetic and tectonic implications
(John Wiley and Sons Ltd, 2021) Amrita Dutt; Athokpam Krishnakanta Singh; Rajesh K. Srivastava; Govind Oinam
We present a comprehensive geochemical data set of whole-rock geochemistry and mineral phases from the mantle peridotites and mafic intrusives of the Tuting–Tidding Suture Zone (TTSZ) ophiolites, eastern Himalaya, north-east India. Modal mineralogy, low Al2O3 and CaO, high Cr# of Cr-spinels, and forsterite number (Fo90–92) in primary olivine indicate the highly refractory nature of the TTSZ peridotites. LREE-enriched patterns, cumulative olivines in dunites, and Cr-spinel and olivine compositions further suggest that the peridotites were subjected to high-temperature melt–rock interaction from a percolating boninitic melt in the nascent forearc of an intra-oceanic subduction zone. The associated mafic intrusives are tholeiitic in nature and their geochemical characteristics [∑REE = 23.34–59.12; nearly flat rare earth elements (REE) pattern (LaN/YbN = 1.49–2.58); negative anomalies of Nb and Ti] show mid-oceanic ridge basalt affinity. Trace elemental modelling of the mafic intrusives along with their mineralogy and geochemistry suggests that they formed due to different degrees of partial melting with the involvement of a subduction component in the spreading regime of the forearc region. Based on the presence of hydrous minerals like Cr-chlorite and tremolite in the peridotites and P–T modelling (525–575°C, 1.05–1.09 GPa) of the mafic intrusives, it is considered that TTSZ ophiolites underwent low-temperature metamorphism by fluid–rock interaction either during the later phase of subduction (in a cool mature subduction zone) or during Himalayan Orogeny. We also infer that the TTSZ ophiolites resemble other Neo-Tethyan ophiolites of the Indus-Tsangpo Suture Zone in terms of their geochemical and petrogenetic aspects. © 2020 John Wiley & Sons Ltd.
Evolution of Late Cretaceous to Palaeogene basalt–andesite–dacite–rhyolite volcanic suites along the northern margin of the Ladakh magmatic arc, NW Himalaya, India
(Springer, 2020) Nongmaithem Lakhan; A Krishnakanta Singh; B.P. Singh; Kshetrimayum Premi; Govind Oinam
This paper describes a comprehensive geochemical study of basalt–andesite–dacite–rhyolite volcanic association in the Khardung volcanic suite along the northern margin of the Ladakh magmatic arc. This volcanic association is outcropped mainly in the segment of the further north of the Khardung village to Khalsar delineating from the Ladakh magmatic arc by ~2 km thick porphyritic sill. The closed association of basalt–andesite–dacite–rhyolite volcanic within a volcanic suite suggests that these rocks may be genetically inter-related and might have derived from the same parental magma source. Felsic lavas (dacite–rhyolite) show SiO2 range from 64.75 to 79.11 wt.%, while intermediate lavas (basaltic andesite–andesite) ranges from 50.80 to 51.81 wt.% with mafic lavas (basalt) span from 53.39 to 62.05 wt.%. These volcanic suites show enrichment in LIL elements (Rb, Ba, Th, U, and Pb) and depletion in Nb, P, and Ti, which can be evident in spider diagrams with pronounced to mild Eu negative anomalies in REE patterns. Previous reports on zircon U–Pb ages of the Khardung volcanics range between 60 and 69.7 Ma confirm an upper bound eruption age of this volcanic suite as pre-collision continental arc magmas. Hence, the results of geochemical modelling suggest that the Khardung mafic–intermediate-felsic lavas were generated from the melting of 1–4% spinel and garnet-bearing lherzolite sources. The generated parental magmas were modified by crustal materials during the magma ascent along with fractional crystallization and were metasomatized by slab-derived fluids released from the subducting Neo-Tethyan oceanic crust during the Late Cretaceous to Palaeogene in the northern margin of the Ladakh magmatic arc. © 2020, Indian Academy of Sciences.
Geochemical and metamorphic record of the amphibolites from the Tuting-Tidding Suture Zone ophiolites, Eastern Himalaya, India: Implications for the presence of a dismembered metamorphic sole
(Cambridge University Press, 2021) Amrita Dutt; A Krishnakanta Singh; Rajesh K Srivastava; Govind Oinam; R.K. Bikramaditya
The Tuting-Tidding Suture Zone (TTSZ), exposed along Dibang and Lohit river valleys in Arunachal Himalaya, NE India, is the easternmost continuation of the Indus-Tsangpo Suture Zone (ITSZ) and consists of ophiolites associated with metabasics and carbonates. Amphibolites, existing at the base of the ophiolite complex, were studied using whole-rock, mineral chemical analyses and pressure-temperature (P-T) pseudosection modelling to understand their metamorphic and petrogenetic history, and interpret the tectonic environment of their formation. They exhibit two-stage deformation, where D1 is depicted by polymineralic inclusion trails in former melt pools and the main foliation represents D2. Sub-alkaline tholeiitic character, high-field-strength element (HFSE) ratios and mid-oceanic ridge basalt (MORB) -like rare earth element (REE) patterns with negative Eu anomaly indicate that the protolith of these amphibolites originated in a spreading regime by extensive partial melting of a depleted mantle source at shallow depth. Petrography, mineral chemistry and P-T modelling indicate a three-stage metamorphic history for them. M1 is the prograde (c.A 2.1 GPa, c.A 450°C) defined by garnet centre compositions corresponding to the D1 event. The existence of former melts in the samples demarcates the M2 stage (1.4-1.8 GPa, c.A 600°C). The rocks later underwent retrogression (M3: 0.8-1.0 GPa, 480-520°C), which corresponds to the D2 event. These observations suggest that the protolith of the TTSZ amphibolites originated in a mid-oceanic ridge setting, which accreted below a subduction zone where it underwent M1 metamorphism followed by M2 metamorphism, corresponding to partial melting of the rocks. Finally, the M3 event occurred during the obduction phase of the ophiolite complex, where the amphibolites were obducted as the metamorphic sole of the TTSZ ophiolites. © The Author(s), 2020. Published by Cambridge University Press.
Magmatic evolution of the Paleoproterozoic A2-type granite along the northern Indian margin: Insights from geochemistry and U-Pb geochronology of Baijnath Klippe, NW Himalaya
(Cambridge University Press, 2025) Shubham Patel; Mallickarjun Joshi; Govind Oinam; Biraja P. Das; Alok Kumar; Tanya Srivastava
Paleoproterozoic granitoids of the lesser Himalayan belt are keys to understanding the evolution of the northern Indian continental margin and its position in the Columbia supercontinent assembly. We present whole-rock chemistry and zircon U-Pb geochronological data for Gwaldam Biotite Granite (GBGr) from the Baijnath Klippe (BK) in Kumaun Himalaya to elucidate their petrogenesis and geodynamic implications. Granites are characterized by ferroan, weakly peraluminous nature with high SiO2 and K2O contents, enrichment in LILE (Rb, Th, K and Pb), and depletion in Ba, Nb, P, Hf and Ti. Granites show enrichment in light rare earth element relative to heavy rare earth elements and pronounced negative Eu anomalies. Such chemistry suggests typical A-type granite with high Y/Nb >2 values that characterize it as A2-type granite. Zircon U-Pb ages for the granite yield upper intercept at 1900 ± 3 Ma (core) and 1854 ± 2 Ma (rim). Integrating the chemical and geochronological data, we propose a two-stage evolution model for the area. In the GBGr, the ∼1900 Ma date of zircon core is likely the date of crystallization of the melts presumably formed during the first extensional stage at uppermost mantle - lower crust levels caused by slab break-off/rollback, which followed a post-collisional setting. The second incipient rifting stage produced melt that entrained the zircon cores (∼1900 Ma) during its ascendance and crystallized as the GBGr at ∼1854 Ma when the zircon rims crystallized. It is further proposed that the Paleoproterozoic Northern Indian continental margin later underwent at least two crustal extensions during the Columbia supercontinent agglomeration. © The Author(s), 2025. Published by Cambridge University Press.
Magmatic records of Gondwana assembly and break-up in the eastern Himalayan syntaxis, northeast India
(Elsevier Inc., 2022) Govind Oinam; A. Krishnakanta Singh; Amrita Dutt; Shoraisam Khogenkumar; Mallickarjun Joshi; Saurabh Singhal; R.K. Bikramaditya
The Indian sub-continent was an integral part of the Gondwana supercontinent with multiple magmatic episodes during the Gondwana assembly and break-up events. However, most of these vital records to understand the past magmatism were obliterated during the Himalayan orogeny due to the subduction of the Indian plate. In this contribution, we attempt to tackle this issue by investigating the Abor magmatic rocks from the eastern Himalayan syntaxis, which are likely to represent the leftover fragments of the eastern Gondwana continental margin. This study uses zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotopic ratios data of the mafic intrusive and felsic volcanic rocks of the Abor magmatism. The mafic intrusive rocks have zircon ages of 500–473 Ma, while the felsic rocks yield ages of 145–132 Ma, indicating two temporally separated episodes of magmatism. The mafic intrusives are sub-alkaline/tholeiitic (Nb/Y < 0.65), with high TiO2 (1.63–3.42 wt%) and ocean island basalt to enriched-mid oceanic ridge basalt affinities. A relatively narrow range of initial 87Sr/86Sr (0.703887–0.705513), 143Nd/144Nd (0.511978–0.512118), and εNd(t) (-0.323–+2.43) of the mafic intrusives suggest fractional crystallization with negligible crustal contamination, generated by low degree (∼3–13 %) partial melting of a primitive mantle (garnet and spinel lherzolite). The felsic rocks display low MgO (0.38–1.17 wt%), CaO (1.06–5.31 wt%), LREE and LILE (Rb, K, Pb) enrichment, depletion in HREE, Sr, Nb, Ti, with strong negative Eu-anomaly (0.48–0.73), high initial 87Sr/86Sr (0.707878–0.717650), and negative εNd(t) (-14.35 to −9.21), suggesting A-type felsic magmatism. The older mafic intrusions were thus attributed to the events of the Gondwana assembly and were inferred to form in an extensional passive margin during the early Paleozoic. However, the younger felsic rocks were likely to have been generated by the interaction of the upwelling Kerguelen mantle plume and the pre-existing crust during the initiation of the eastern Gondwana break-up during the early Cretaceous. Our new findings reveal that two episodic magmatic events related to the eastern Gondwana assembly and the subsequent Gondwana break-up are responsible for the magmatism in the Siang window of eastern Himalayan syntaxis, northeast India. © 2022 International Association for Gondwana Research
Magmatism in the Siang window of the Eastern Himalayan Syntaxis, NE India: a vestige of Kerguelen mantle plume activity
(Geological Society of London, 2022) Athokpam Krishnakanta Singh; Govind Oinam; Sun-Lin Chung; R.K. Bikramaditya; Hao-Yang Lee; Mallickarjun Joshi
We report new U–Pb zircon ages for mafic plutonic (gabbro) and volcanic (andesite) rocks, along with the whole-rock chemistry of a mafic–felsic suite of volcanic rocks from the Siang window of the Eastern Himalayan Syntaxis, NE India. Field relationships, and mineralogical and geochemical characteristics, of the studied mafic–intermediate–felsic rocks suggest their co-magmatic linkage that was generated in an extensional tectonic environment. Incompatible trace elements and low concentrations of large ion lithophile elements (LILEs) and REE behaviour reflect both the enriched nature of the mafic rocks and the limited influence of crustal contamination in their genesis. Partial melting and fractional crystallization processes have played a major role during the genesis of these felsic volcanics from the parental mafic magma. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages suggest that the mafic plutonic rock was emplaced at c. 121.18 + 1 Ma and intermediate volcanic rock was emplaced at c. 135.48 + 0.50 Ma during the Early Cretaceous period. The new ages are consistent with earlier reported zircon U–Pb ages (133.0 + 1.9–130.7 + 1.8 Ma) of felsic volcanic rocks from the present study area. Our new field observations, and mineralogical and geochemical characteristics, in conjunction with the U–Pb isotopic database suggest that the major magmatic event in the core of the Siang window of the Eastern Himalaya is coeval with the Raj-mahal–Sylhet–Mikir–Shillong flood basalts of eastern and northeastern India, and the Comei–Bunbury Large Igneous Province of southeastern Tibet and SW Australia. These events are related to the break-up of eastern Gondwana and outbreak of the Kerguelen plume. © 2021 The Author(s).
New constraints on the tectono-magmatic evolution of the Tidding-Mayodia ophiolites, eastern Himalaya, northeast India
(John Wiley and Sons Ltd, 2022) Athokpam Krishnakanta Singh; Amrita Dutt; Bibhuranjan Nayak; Raj Kumar Bikramaditya; Govind Oinam; Satyajeet S. Thakur; Rajesh K. Srivastava; Shoraisam Khogenkumar; Manoj Kumar
The Tidding-Mayodia ophiolites (TMO) exposed along the Lohit and Dibang river valleys in eastern Himalaya that have been considered as the extension of the Indus-Tsangpo Suture Zone ophiolites are revisited to review their petrogenetic-tectonic origin. The ophiolites consist of depleted harzburgite and dunite with lesser amounts of mafic rocks (gabbro intrusives, mafic dykes) and carbonates. The serpentinized peridotites consist of antigorite, lizardite, olivine, Cr-spinel, and bastite with minor sulfide minerals. From SEM-EDS studies, sulfide minerals were observed to be associated mainly with magnetites. The main sulfide mineral is pentlandite with minor millerite that exists as inclusions inside the pentlandite grains. Elemental mapping of these sulfides shows that they are mainly Ni-(Co-)-bearing sulfides. The olivines are highly forsteritic (Fo = 95–96) while the Cr-spinels show distinct Cr-magnetite rims with a chromite core (Cr# = ~93). The serpentinized peridotites have whole-rock compositions of SiO2 <47 wt% and high MgO (>36.37 wt%) and low Al2O3 (<1.21 wt%), CaO (<0.82 wt%), indicating the depleted nature of the parent rocks. Highly fractionated LREEs as compared to HREEs [(La/Yb)N = 2.62–13.22], and REE and Cr spinel chemistry modelling suggests that the studied peridotites have formed from ~22% partial melting of a depleted spinel lherzolite source which later underwent interactions with a high-temperature silicate melt that caused enrichment in LREE and Cr of spinels. The parental melt compositions of Cr spinel yield their formation during arc tectonism (Al2O3melt = 6.28–7.65 wt%, FeO/MgO = 1.00–1.33). Furthermore, Mn and Zn concentrations in spinels, the occurrence of Cr magnetite rim in Cr-spinels, presence of secondary olivine with higher Fo (~98), and occurrence of low-temperature re-equilibrated sulfide minerals, indicate that the rocks were subject to low-temperature metamorphism. Based on this evidence, combined with data from previous studies, a tectonic model has been proposed for the genesis of the studied ophiolites. This model shows that the ophiolites have formed from the entrapment of depleted N-MORB mantle in the mantle wedge of an intra-oceanic subduction zone. During the nascent forearc regime, this mantle wedge underwent interactions with high-temperature melts, which caused changes in their chemistry. Moreover, the rocks underwent interactions with low-temperature fluids in the mature forearc, which caused the formation of sulfides and metamorphozed these rocks. © 2021 John Wiley & Sons Ltd.
P–T Evolution of Paleoproterozoic Dangoli Pelitic Gneisses, Baijnath Klippe, NW Himalaya: Insights From the Geochemistry and Zircon U–Pb Geochronology
(John Wiley and Sons Inc, 2025) Mallickarjun Joshi; Shubham Patel; Biraja P. Das; Govind Oinam; Tanya Srivastava; Alok Kumar
The Cenozoic Himalayan orogeny resulted from the continental collision between the Tibetan block and the northern Indian Precambrian shield. The latter, replete with evidence of Columbian supercontinent assembly, likely comprised the north Indian continental margin that was reworked mechanically and thermally during the Himalayan orogeny, and still survives as Precambrian vestiges in the Himalaya. Parts of this Paleoproterozoic crust, which now occur as nappes and klippen, were tectonically transported by the Main Central Thrust southwards over the Lesser Himalayan sedimentaries during the orogeny. The Absence of Columbian metamorphic signatures in these thrust sheets has intrigued geologists for long. We present evidence for a Middle Orosirian metamorphic event from the pelitic gneisses of the Almora Group in the Baijnath Klippe from NW Himalaya. The physical conditions of metamorphism have been inferred using mineral chemistry, bulk-rock chemistry, and phase section modeling using Perple_X software in the MnNKCFMASHT model system. Zircon U–Pb geochronology for the Dangoli pelitic gneisses yielded a robust upper intercept at 1891 ± 12.82 Ma. The P–T phase diagram indicates that the peak mineral assemblage stabilized in the P–T range of 0.41–0.46 GPa and 675°C–700°C suggesting upper amphibolite facies metamorphism. Integrated metamorphic and geochronological results indicate that the Dangoli pelitic gneisses were derived by muscovite dehydration melting of metasediments during the peak metamorphism related to syn-collisional setting broadly coeval with the Paleoproterozoic magmatism during the Columbia supercontinent assembly. The evidence for definite involvement of Paleoproterozoic high-grade metamorphic rocks of the northern Indian shield in the Himalayan orogeny is being documented. © 2025 John Wiley & Sons Australia, Ltd.
Plagioclase ultraphyric basalts of the Abor magmatic complex: Implications for a plumbing system at the eastern Himalaya
(Elsevier B.V., 2024) Govind Oinam; A. Krishnakanta Singh; M. Santosh; Mallickarjun Joshi; Amrita Dutt; Shoraisam Khogenkumar; Biraja Prasad Das; R.K. Bikramaditya
Plagioclase ultraphyric basalts (PUBs) are an important unit of the Abor magmatic complex (AMC) of the eastern Himalaya, containing ≥35 vol% plagioclase phenocrysts. Apart from the eastern region, PUBs have not been reported in any other part of the Himalayas. However, very little information is available about their origin and significance in the evolution of the eastern margin of the Indian plate and the Himalayan orogeny. In this contribution, we present the first zircon U[sbnd]Pb age data of the PUBs along with whole-rock geochemistry, Sr[sbnd]Nd isotopic ratios, mineral chemistry, and quantitative textural analysis, to understand the evolutionary history of the AMC and subsurface magma chamber activities. The PUBs formed from highly evolved magma (<6 MgO wt%), having high Fe2O3 (9.06–12.29 wt%) and Ti/Y ratios (>500). Their εNd (t) values (−0.02 to +2.66) suggest plume magma source. A small difference in anorthite contents (<5 mol%) is observed from the thick core (An47–58) with lower anorthite contents towards the rim (An34–47) of the plagioclase phenocrysts, which is an indication of weakly zoned characteristics. Crystal size distribution shows a non-linear and concave upward trend with a relatively gentler slope towards the coarser plagioclase populations, which can be attributed to the hybrid crystallization of plagioclase-bearing magma and its subsequent differentiation with cumulates of plagioclase inside the magma chamber. The zircon U[sbnd]Pb age of these PUBs records two magmatic events - Early Paleozoic (505–473 Ma) at the core and Early Cretaceous (134–126 Ma) at the rim that are consistent with the previously proposed magmatic events of AMC with Gondwana assembly and break-up. Encounter of such dual ages in zircons does not support the usual condition of PUBs formation through crystal floatation in a slow cooling process of a single magma chamber. Therefore, considering the evidences observed in crystal size distribution, core-rim anorthite variation, geochemistry, and age data, we propose that the PUBs of AMC, eastern Himalaya were formed due to injection of a hot and young magma during the Early Cretaceous into an old and cold mush zone containing pre-existing plagioclase phenocrysts formed during the Early Paleozoic. The results further support that the newly injected magma formed the rim of the plagioclase phenocrysts and the groundmass of the PUBs. © 2024
Tectonic evolution of the neoproterozoic tusham ring complex, Northwestern India: Constraints from geochemistry and zircon U–Pb geochronology, and implications for Rodinia supercontinent history
(Elsevier B.V., 2023) A. Krishnakanta Singh; Naveen Kumar; Sun-Lin Chung; Hao-Yang Lee; M. Santosh; Radhika Sharma; Naresh Kumar; R.K. Bikramaditya; Govind Oinam; Nongmaithem Lakhan
Neoproterozoic felsic magmatic suites are important proxies to investigate the breakup history of the Rodinia supercontinent which likely coincided with the emplacement of voluminous Silicic Large Igneous Provinces (SLIPs). Here we report new zircon U–Pb ages with comprehensive whole-rock and mineral chemistry data on the felsic volcano-plutonic rocks from the Tusham Ring Complex (TRC) that forms part of the anorogenic Malani Igneous Suite (MIS) (∼780–750 Ma) in NW India. The plutonic rocks (granites) and contemporaneous volcanic rocks (rhyolites) show affinity to A-type granitoids, hypersolvus to subsolvus, and metaluminous to peraluminous. The granitoids investigated in this study are enriched in SiO2, Na2O + K2O, Fe/Mg, Ga/Al, U, Th, REE (except Eu), and depleted in MgO, CaO, Cr, Ni, P, Ti, Sr, and Eu contents. The zircon U–Pb dating for felsic volcanic rocks (four rhyolite samples) yielded Neoproterozoic ages ranging from 827 to 764 Ma whereas zircon in five felsic plutonic rocks (granite) shows ages ranging from 830 to 787 Ma, indicating coeval nature of the intrusive and extrusive rocks. The zircon grains have mostly negative εHf(t) values up to −3.62 and yield crustal Hf model ages from 1.6 Ga to 1.9 Ga, suggesting that the magmatic event involved melting of a Paleoproterozoic source. Based on geochemical features, we propose that the partial melting of crustal protoliths, fractional crystallization, and crustal contamination played a significant role in the magmatic evolution of these rocks. We also infer that the felsic anorogenic magmatism in the TRC occurred in an extensional tectonic regime, possibly associated with a mantle plume event. Our results, in conjunction with previous studies, support the model of anorogenic magmatism linked with the disruption of the Neoproterozoic Rodinia supercontinent. © 2023 Elsevier B.V.
Zircon U–Pb geochronology, mineral and whole-rock geochemistry of the Khardung volcanics, Ladakh Himalaya, India: Implications for Late Cretaceous to Palaeogene continental arc magmatism
(John Wiley and Sons Ltd, 2020) Nongmaithem Lakhan; Athokpam Krishnakanta Singh; Birendra Pratap Singh; Koushik Sen; Mutum Rajanikanta Singh; Shoraisam Khogenkumar; Saurabh Singhal; Govind Oinam
In this study, we present new mineral and whole-rock geochemical data with zircon U–Pb ages of the Khardung volcanics (KV) from the western Himalaya and discuss their tectono-magmatic evolution. These volcanics are sandwiched between the Ladakh batholith and Karakoram batholith and classified as intermediate volcanics (basaltic andesite-andesite) and felsic volcanics (dacite-rhyolite). The intermediate volcanics are marked by low SiO2 (52.80–61.31 wt.%), enriched LREEs, and depleted HFSEs (Nb, Ti, Zr), whereas more evolved felsic volcanics exhibit quartz, K-feldspar, and plagioclase as dominant mineral phases and felsic compositions are characterized by high SiO2 (64.52–79.19 wt.%) content with pronounced negative Eu anomalies, enriched LREEs, and depleted HREEs and HFSEs (Nb, Ti). New zircon U–Pb ages of intermediate volcanics (andesite) yield 69.71 Ma, whereas felsic volcanics (rhyolites) range between 62.49 and 66.55 Ma, indicating that the Khardung magmatism overlaps with the last phase of the Ladakh batholith magmatism. Geochemical characteristics indicate that the KV were generated from a same parental magma source through fractional crystallization along with crustal assimilation from an older crust, and they show genetic affinity with the adjacent Ladakh batholith. Therefore, the KV and Ladakh batholith could be considered as a product of the mature stage arc magmatism generated during subduction of the Neo-Tethyan oceanic crust prior to the main collision between the Indian and Eurasian continents. © 2019 John Wiley & Sons, Ltd.