Understanding the tempo and duration of orogenesis remains a fundamental challenge in reconstructing ancient convergent plate margin processes. A critical debate concerns whether mountain belts, particularly those of Precambrian age, formed through single, protracted orogenic cycles spanning hundreds of millions of years, or through multiple discrete tectonothermal pulses separated by periods of tectonic quiescence. This distinction has profound implications for interpreting continental growth, plate interactions, and geodynamic processes in deep time. However, the fragmentary nature of the Precambrian rock record and the limitations of conventional geochronological interpretations have made resolving this question particularly challenging. In this perspective, we analyze the thermo-tectonic evolution of key Precambrian orogens, including the Eastern Ghats Mobile Belt, the Central Indian Tectonic Zone, and the Napier Complex, by critically integrating available geochronological, petrological, and diffusion chronometry datasets. Our synthesis reveals that what appears as a single prolonged orogenic event in the geological record may actually preserve multiple short-lived tectonic cycles that episodically reworked the same crustal segments over extended periods (e.g., the Central Indian Tectonic Zone). This interpretation challenges the prevailing paradigm of continuous high-temperature orogenesis in Precambrian terranes and suggests more dynamic plate interactions during ancient continental assembly. However, in certain cases, long-lived orogenesis do represent the true situation (e.g., the Napier Complex), where prolonged residence at high-temperature conditions in the deep crust seems unequivocal. Our study further highlights the importance of distinguishing between the duration of individual metamorphic-magmatic-deformation events and the overall lifespan of an orogenic belt. We thus introduce a hierarchy of timescales for re-interpreting the tempo of orogenesis. This hierarchical framework distinguishes three temporal scales: Asimus et al. (2024) (1) individual tectonothermal events (1 s–10s Myr), Axelsson et al. (2020) (2) orogenic duration comprising multiple tectonothermal events (10s–100s Myr), and (Banerjee et al., 2023 (3)) supercontinental cycles encompassing several orogenies (100 s–1000 Myr). This perspective has significant implications for understanding how continental lithosphere was assembled and stabilized during Earth's history.

This study investigates the co-occurrence of ferric illite and glauconite in the Deodongar sandstone of the Mesoproterozoic Chattisgarh Supergroup in India. Forming a Member within the stromatolitic Chandi Formation, these glauconitic arenites were deposited in a shallow marine setting, as revealed by field relationships. Electron Probe Micro Analyzer (EPMA) data shows that these ferric illites and glauconites are rich in magnesium and aluminum, although they exhibit considerable variation in iron and potassium content. Oxide cross-plots indicate that ferric illite and glauconite followed different geochemical pathways of formation. Textural observations indicate that these minerals formed over K-feldspar, quartz and chert fragments as authigenic phases. Mass balance calculations suggest that potassium released during the conversion of K-feldspar to glauconitic minerals may aid in transforming quartz/chert fragments to these minerals, though additional sources for iron, magnesium and aluminum ions are necessary. Thermodynamic calculations show that ferric illite formation is favorable than glauconite at 1 atmospheric pressure and 298 Kelvin temperature. Yet, occurrence of ferric illite and glauconite forming over adjacent substrates suggests that each substrate acted as a closed independent chemical system for mineral authigenesis.

Petrology, geochemistry and geochronology of a metapelite (sillimanite-garnet-biotite-plagioclase-quartz) from the vicinity of the Archean Mercara Shear Zone in Coorg, S. India show that metamorphism at temperatures > 850 °C occurred between 2700–3300 Ma (Phase equilibria, thermobarometry, U-Pb dating of zircons and Lu-Hf dating of garnets). Subsequently, the rocks experienced thermal events at lower temperatures at 2400-2600 Ma as well as at 600-640 Ma (U-Pb dates from rutile). There are indications of multiple episodes of metasomatic/ (high temperature) hydrothermal activity during the Archean events. Residence of the rocks at lower temperatures between the high temperature events is indicated by the kinetics of dissolution of zircon in melt. Taken together, this history shows that (a) P-T-t evolution in this Archean collisional setting happened along an overall clockwise path but not in a single continuous loop - episodes at high temperatures were interspersed with residence at cooler temperatures in between, (b) subtle effects of metamorphism that occurred at temperatures below the peak temperature could help to resolve some controversies related to tectonothermal reconstructions in the region (e.g. whether signatures of both - amalgamation of Dharwar and Coorg cratons and activity along an equivalent of the Betsimisaraka suture zone in east-central Madagascar may be present in the region), and (c) the duration of high-temperature events (several 100 million years at 800 °C) are consistent with an early Earth peel-back style of plate tectonics, rather than modern day plate tectonics, operating in the region at the time.

Widespread occurrence of geogenic groundwater contaminants, such arsenic (As), poses a significant health risk to millions of people worldwide through ingestion of contaminated drinking water. However, the (co)occurrence of other, less studied contaminants that may be sourced from similar geological settings, are less documented. Here, for the first time, we document the (co)occurrence of excess concentrations of nickel (Ni) in the intensely As-enriched groundwater from the alluvial aquifers of the Brahmaputra River Basin (BRB). Approximately 30 % of the sampled groundwater (n = 70) exceeds the drinking water guideline value of 20 mu g/L for Ni, while around 20 % of samples contain both Ni (>20 mu g/L) and As (>10 mu g/L). Furthermore, the groundwater also has elevated levels of Fe (up to 19 mg/L) and Mn (up to similar to 5 mg/L). The groundwater is mildly oxidizing to strongly reducing (Eh 234 mV to -72 mV), with dominant hydrogeochemical facies ranging from Ca-Mg-HCO3 to Na-HCO3 type. Linear correlation shows that Ni has a strong positive correlation with Fe (r = 0.9), As (r = 0.84), and Mn (r = 0.68) in the northern bank of the Brahmaputra River, while having a less prominent relationship with Fe (r = 0.78), As (r = -0.35) and Mn (r = 0.46) in the southern bank. We hypothesize that Ni-rich rocks from the IndusTsangpo suture zone and the Tidding suture serve as the primary sources of geogenic Ni in the BRB, later weathered, transported and deposited by the Brahmaputra (Siang/Tsangpo) and Lohit rivers, forming extensive alluvial plains. We suggest that the reductive dissolution of Fe-oxyhydroxides is the primary mechanism of Ni and As release in the groundwater on the northern bank of BRB. At the same time, Fe and SO42- -reduction play an active role in the contaminant mobilization in the southern bank. The emergence of (co)occurring geogenic contaminants, such as Ni, increases the health risk for millions of residents in the study area, who are already exposed to excessive levels of As in groundwater-sourced drinking water at BRB.

The Mesoarchaean Coorg granulite block-Mercara Shear Zone (MRSZ) - Meso- to Neoarchaean Western Dharwar Craton (WDC) crustal section is ideally suited to study the Early Earth tectonics, and in particular, to establish collisional tectonics that led to their amalgamation. However, despite numerous petrological and geochronological studies, the nature of tectonic relationships among the three litho-tectonic domains is not well understood. Importantly enough, there is a dearth of metamorphic studies from the western part of the WDC, and in its absence, the amalgamation tectonics between the WDC and the Coorg block is poorly constrained. The south-western part of the Western Dharwar Craton (WDC), in contact with the Mesoarchaean Coorg Granulite Massif, consists of NNW-SSE trending mafic to ultramafic dyke swarm that is variably metamorphosed. Based on field observations and petrographic study, we have classified the metamafic dykes into two broad types: (a) Undeformed to foliated metagabbro, locally with coarse coronal Grt around Cpx, Pl, Ilm, and Hbl1 (mineral abbreviations after Kretz, 1983) and differentially preserved igneous textures (Type-1) and (b) well-foliated and banded metamafites that lack magmatic textures and mineralogy, locally migmatitic with porphyroblastic Grt and Cpx and in others, garnetiferous amphibolite with porphyroblastic garnet (Type-2). Based on the degree of foliation development in these metamafites, we observe a south-westward increase in strain. Type-1 metamafites record a sequence of textural evolution, namely recrystallization of the magmatic Cpx±Opx+Pl assemblage→partial high-T hydration, producing Ti-Hbl (Ti=0.24-0.28)→growth of coarse coronal Grt [with a broad homogeneous magnesian core (XMg=0.25-0.23, XGrs=0.20-0.22) and slightly ferroan rim (XMg=0.21-0.22, XGrs=0.21-0.22), particularly in contact with Cpx] on the recrystallized matrix→a late Hbl-defined foliation (Ti=0.19-0.23). Type-2 metamafites show the development of a pervasive titaniferous Hbl-defined foliation (Ti=0.14-0.19), followed by the growth of compositionally homogeneous porphyroblastic Grt (XMg=0.21-0.22; Prp14-15Grs22-27) with or without Cpx (XMg=0.65-0.70, Altotal=0.03-0.08, and Natotal=0.01-0.03), and including localised crustal anataxis, producing tonalitic melt at the metamorphic peak. This was followed by the formation of late low Ti-Hbl (Ti=0.04-0.05). Using conventional thermobarometry, the peak P-T of type-1 metamafite has been estimated at ~ 8kb and 800°C. In the type-2 metamafites, the peak and retrograde P-T is estimated at ~9kb and 800°C and ~7kb and 500°C respectively. The effective bulk rock composition has been used to calculate the phase equilibria modelling of the type-2 metamafite, in which the intersections of compositional isopleths of XMg(Grt), XGrs(Grt), XAn(Pl), Al(Cpx), Ti(Hbl) defines a peak P-T of 9.4 kb and 800°C which is similar to that calculated by conventional thermobarometry. The peak and retrograde P-T conditions together record the retrograde segment of a clockwise P-T path of evolution. We relate the textural sequence, results of thermobarometric computations and phase equilibria modelling, and strain patterns in the metamafic dykes to suggest a pervasive thermo-tectonic event that led to the prograde burial of the extended cratonised WDC beneath the Coorg Granulite Block to high-pressure upper amphibolite to granulite facies metamorphic conditions. We link this event with continental collisions between the WDC and Coorg Block at the dawn of the Proterozoic.

The contact between the Archean Bastar craton (BC) and Proterozoic Eastern Ghats Province (EGP), central India, is marked by a suture zone termed Terrane Boundary Shear Zone (TBSZ). BC in this area is largely composed of hornblende-biotite granite with some mafic dykes. Rocks in the TBSZ include quartzofeldspathic (leptynite) gneiss, garnet-orthopyroxene-bearing granitoid, mafic granulites (Group A of cratonic affinity, and Group B of EGP affinity), Mg-Al granulite and an isolated exposure of orthopyroxene-bearing gneiss. Detailed geochemical analysis shows remarkable similarity between Hbl-Bt granite and Grt-Opx-bearing granitoid, with A-type affinity, and between mafic dykes and Group A mafic granulites. However, the Opx-bearing gneiss is geochemically distinct having I-type affinity, similar to TTG gneisses described from BC. Metamorphic phase equilibria analysis and trace element modelling shows that (i) melting of Opx-bearing gneiss would produce a ferroan granitic melt resembling the Hbl-Bt granite, (ii) metamorphism at appropriate P-T conditions would convert the granite to Grt-Opx-bearing granitoid and the mafic dyke to Group A mafic granulite. U-Pb geochronology of zircon constrains emplacement ages of the magmatic precursors of Opx-bearing gneiss and Grt-Opx-bearing granitoid as ca. 2.73 and ca. 2.5 Ga, respectively. These rocks were subjected to an early granulite facies metamorphism, followed by an amphibolite facies metamorphism, shearing and hydrous fluid flux. Geochronological data shows that the latter event took place at ca. 0.52 Ga, while the earlier granulite facies event can only be tentatively suggested to be of late Stenian/Tonian age. Collating all the evidence (including published geophysical and geochronological data), we suggest that the initial collision between BC and EGP took place during late Stenian/Tonian time as a consequence of formation of the Greater Indian Landmass, a part of Rodinia supercontinent. The TBSZ, probably initiated due to the late Stenian/Tonian collision, was reactivated and reworked tectonothermally at ca. 0.52 Ga, caused by far field stress effect of the Kuunga orogeny, which was strong enough to obliterate most of the imprints of the late Stenian/Tonian orogeny.

The Proterozoic orogenic belts incorporated in and around the present-day continents preserve complex magmatic, metamorphic, and geophysical signatures of the ancient supercontinents. One such orogenic belt, the Eastern Ghats Belt (EGB) is amalgamated with the Archean cratons of India along a crustal-scale suture zone known as the Terrane Boundary Shear Zone (TBSZ). The continental margin – orogenic belt interfaces, such as the TBSZ, are the black boxes of ancient tectonic processes, since they are rheologically weakened crustal discontinuities that undergo intense deformation and metamorphism recording the complete orogenic history. There have been two schools of thought on the age of final amalgamation of the EGB with the Bastar craton, as the TBSZ records two major tectonothermal events at ~950Ma and ~550Ma, coeval with the formation of supercontinents Rodinia and Gondwana, respectively. The age and mechanism of this amalgamation have implication on the crustal architecture of the Proterozoic supercontinents.Recent studies confirmed the presence of felsic and mafic granulites of Archean Sm-Nd model ages (3.3 – 3.1 Ga) from the TBSZ that have undergone high-pressure granulite facies metamorphism. It is speculated that these rocks are of Bastar craton in origin and the underthrusting of the Bastar craton beneath the EGB, during the final collision, led to the high-pressure metamorphic conditions. In this communication, we have carried out a comparative petrological and geochemical investigation of the Archean felsic rocks (Grt-bearing charnockites) from the TBSZ and the Hbl-Bt granites from the adjacent regions of the Bastar craton to understand origin and tectonic significance of the charnockites. The garnet-bearing charnockites from the TBSZ are characterised by coarse grained Grt + Opx + Pl + Qz + Kfs + Hbl + Bt ± Ilm. The Hbl-Bt granites of the Bastar craton, adjacent to the TBSZ, are characterized by coarse grained Hbl + Bt + Qz + Kfs + Pl, with small Opx grains forming around Hbl in few places at the interface. The Grt-bearing charnockites and the Hbl-Bt granites are both ferroan and metaluminous to slightly peraluminous in nature. The high concentrations of trace elements, high Y/Nb (>1.2) ratio and pronounced negative anomalies of Eu, Sr and Ti in both the rocks are characteristic of A2-type within plate granitoids, similar to the other reported granitoids from the Bastar craton. The strong similarity in the geochemistry of Grt-bearing charnockites and Hbl-Bt granites along with the available Archean model ages of the charnockites indicate that the Grt-bearing charnockites of the TBSZ are granulite-facies equivalents of the Hbl-Bt granites and hence represent the remnants of cratonic margin in the TBSZ. This geochemical study along with the Tonian ages (~950 Ma) from monazite cores and inclusions in garnet within the co-exposed metapelites in the suture zone indicate that the Bastar craton underthrusted beneath the EGB during the formation of Rodinia. The ~500 Ma ages reported from the strongly recrystallized monazite rims might represent the reactivation of the intracontinental suture zone due to the far-field stress from the Kuunga orogeny (~530 – 490 Ma) during the formation of East Gondwana.

Knowledge of pressure-temperature-time (P-T-t) evolution of Archean high-grade (deep crustal) metamorphic rocks is important for deciphering the nature of Archean tectonic processes. However, exposures of such rocks are limited in the present rock record. Here, we study a suite of high-grade, mafic rocks that are present along a crustal-scale shear zone (called the Mercara Shear Zone) between two Archean terrains of India, the Coorg block and the Dharwar Craton. Given that the Mercara Shear Zone is dated to be Mesoarchean, these shear zone rocks are well suited to elucidate Archean orogenic processes. Petrological investigation shows that these mafic rocks are characterized by a granulitic assemblage of orthopyroxene, clinopyroxene, plagioclase, quartz and amphibole +/- garnet, and with accessory phases such as apatite, ilmenite, magnetite and rutile in some cases. We distinguish the investigated rocks into low-Mg and high-Mg varieties based on their whole-rock composition as well as their mode of occurrence in the field and mineral chemistry. This difference in the bulk composition led to different reaction histories-for example, the low-Mg mafic granulites underwent partial melting while high-Mg granulites were less fertile. Combining these observations with the results of geothermobarometry, phase equilibria modeling, geochronology (U-Pb in zircon and Lu-Hf in garnet ) and diffusion modeling, we have reconstructed a multi-stage P-T-t history for these rocks. The first phase (Stage 1) is represented by granulite-grade metamorphism at similar to 750-900 degrees C and 8-13 kbar during similar to 3100 Ma (with uncertainties permitting a timing as recent as similar to 2700 Ma), after which they resided at T <500 degrees C, likely at lower crustal levels (Stage 2). Subsequently, these rocks were reheated to a T of 700-750 degrees C at 7-10 kbar at similar to 2400 Ma (Stage 3) and then again cooled down to similar to 500-600 degrees C at 6-8 kbar (Stage 4). Application of diffusion chronometry shows that (1) the cooling rates of these granulites at high temperatures (>600 degrees C) varied in the range of 25-50 degrees C/Ma, and (2) the rocks resided for a long duration (similar to 500 million years) at the Stage 2 metamorphic conditions, i.e. at T <500 degrees C. We infer that such a protracted, high-T metamorphic history involving at least two heating pulses, and the relatively slow cooling rates on the order of 10's degrees C/Ma are consistent with the operation of peel-back styled orogenesis (an embryonic form of plate tectonics) on an early hotter Earth (Mesoarchean to Paleoproterozoic). Moreover, the controls of bulk rock compositions on reaction histories provide a mechanism for intracrustal differentiation and generating Mg-rich, refractory material that may have eventually formed the lower continental crust over a protracted and pulsed thermal evolution spanning several hundred million years.

Mg-Al granulites and associated metapelites occurring in a shear zone at the contact of the Archean Bastar Craton and the Proterozoic Eastern Ghats Province (EGP) have been studied here. Reaction textures, geothermobarometry and P-T pseudosection studies reveal that the rocks record ultrahigh peak temperatures (>900 °C) at pressures of 8–8.5 kbar and were exhumed along a retrograde decompression-cooling trajectory reaching ∼770 °C and 5–6 kbar following an overall clockwise P-T path. Texturally constrained in-situ monazite chemical dates establish the age of peak metamorphism at 920 ± 11 Ma. Another prominent age cluster is at ∼500 Ma, which is ascribed, on the basis of petrographic characteristics, to tectonothermal reworking in the presence of reactive fluid. UHT metamorphism at ∼920 Ma along a clockwise path and extensive amphibolite facies reworking accompanying fluid infiltration at ∼500 Ma for the studied rocks contrast with the known petrological history of the EGP. We tentatively correlate these features in the contact shear zone to Tonian age amalgamation of the Bastar craton with the EGP and subsequent tectonothermal reworking, aided by fluid infiltration, during the Kuunga orogeny.

The Hole Narsipur Greenstone Belt (HGB), in the Western Dharwar Craton, South India, preserves evidence for three cycles of metamorphism spanning the Archaean-Proterozoic transition. Changes in metamorphic style across the transition are investigated using integrated petrographic, mineral chemical, metamorphic evolutionary history, conventional geothermobarometry, and phase equilibria modeling studies of rocks of diverse bulk rock composition from the belt. These rocks record signatures of three overprinting metamorphic cycles (M-2 -> M-3 -> M-4 in sequence), postdating a Mesoarchaean, M-1 event in the craton. The M-2 cycle represents characteristic LP-HT metamorphism along a counterclockwise (CCW) metamorphic P-T path, peak metamorphism at 4-5 kbar, 515-595 degrees C, and high thermobaric ratios (T/P similar to 1050-1525 degrees C/GPa) at the M-2 peak. The intermediate M-3 metamorphic cycle records a prograde burial of partially cooled M-2 rocks to middle-lower crustal depths, peak metamorphism at P similar to 7.5-10.2 kbar, T similar to 630-655 degrees C, and corresponding intermediate T/P ratios (T/P similar to 620-875 degrees C/GPa) and a retrograde stage, marked by combined exhumation and cooling to P similar to 5.3-6.4 kbar, T similar to 530-575 degrees C. The resultant P-T paths of evolution show variability of clockwise (CW) paths from classical hairpin type to two-stage prograde heating segments. During the M 4 metamorphism (T-Max similar to 630-640 degrees C at similar to 8.9-10.3 kbar and with lower T/P ratios at similar to 610-720 degrees C/GPa), the partially exhumed M 3 crust is re-buried to lower crustal depths along an intermediate thermal gradient as during the M-3 metamorphic cycle. We interpret the thermal transition, tectonic thickening along a cooler thermal gradient, repeated burial-exhumation cycles in the orogenic wedge, and tectonic mixing of the three metamorphic cycles in terms of a three-stage tectonic evolution of the HGB. These in a sequence are (a) the development of a hot and thinned crust (cf. M ( )cycle), (b) the transition to a thickened crustal zone tectonic domain (cf. M-3 cycle), with both the domains being part of the lithospheric peel-back driven convergence setting and (c) finally continental collision tectonics (cf. M-4 cycle). The pulsating nature of orogenesis at the Archaean-Proterozoic boundary deduced here distinguishes the Western Dharwar Craton from other cratonic blocks globally at the same time frame.

The Bastar Craton at the interface of Eastern Ghats Belt (EGB) contains a mélange of rocks from both the Archean cratonic domain and the adjacent Proterozoic mobile belt domain marking a broad shear zone, known as the Terrane Boundary Shear Zone (TBSZ). The TBSZ preserves a very rare occurrence of high-grade metamorphosed Archean cratonic rocks, whose ancestry has been constrained by Nd model ages. This study presents the petrological and geochemical characterization of mafic granulites and orthopyroxene bearing granitoids from the shear zone and its implications on the tectonic evolution of the craton – mobile belt boundary. Detailed petrographic, geothermobarometric and P-T pseudosection studies indicate that the Bastar cratonic rocks underwent high-pressure granulite facies metamorphism along a clockwise P-T path, reaching ~900°C and 9-10 kbar. The originally amphibolite facies rocks, metamorphosed through dehydration-melting of hornblende (mafic rocks) and biotite (felsic rocks), to attain the peak P-T conditions. We suggest that this high-grade metamorphism was due to the subduction/underthrusting of the Bastar Craton beneath the EGB, supported by the available seismic data, which resulted from far-field stress related to the Kuunga orogeny in an intraplate setting.

Different criteria used to classify metamorphism are reviewed, and it is suggested three of these (plate tectonic setting, agents of metamorphism and geological setting) can be used to characterize most of the common types of terrestrial metamorphism. Accordingly, the nature of plate tectonic setting (convergent/divergent/transform/interior), thermal/baric gradients, geologic setting (igneous intrusion, meteorite impact, etc.) and agents (pressure variables, temperature and fluid-driven mass transfer) are used to classify the types of metamorphism. The classification uses vast amount of data collected over the last half-century, in conjunction with those available earlier, and improved understanding of metamorphic processes to characterize each type of metamorphism. Additionally, metamorphism in asteroidal bodies is considered.

Nd model ages show that the suture between the Archean Bastar craton and Proterozoic Eastern Ghats Province (a part of the Eastern Ghats Belt), India is marked by a broad shear zone that contains a mixture of rocks from both the blocks. In this suture zone, amphibolite facies rocks of the Bastar craton were subjected to high pressure granulite facies metamorphism possibly at similar to 500 Ma (published isotopic data). New petrological, geothermobarometric and P-T pseudosection studies show that dehydration-melting of amphibole (in mafic proto-lith) and of biotite (in quartzofeldspathic protolith) along a clockwise P-T path led to peak metamorphic conditions of 9.75 +/- 0.5 kbar; 875 +/- 30 degrees C. Mafic granulites from the Eastern Ghats Province had an earlier metamorphic history of isobaric cooling from unknown peak metamorphic conditions, but currently record P-T maximum values of 9.25 +/- 0.25 kbar; 825 +/- 25 degrees C. Followed by cooling through similar to 100 degrees C from the peak metamorphic conditions, mafic granulites from the Bastar craton were exhumed to mid-crustal levels by decompression-cooling, probably as a tectonic wedge. This decompression-cooling is also shared by charnockitic rocks of the Bastar craton and mafic granulites of the Eastern Ghats Province. We interpret further burial of the Bastar craton rocks as a result of underthrusting beneath the Eastern Ghats Province, consistent with available seismic data. Total absence of any evidence of ocean opening or closure between the Bastar craton and the Eastern Ghats Province at around 500 Ma, coupled with interpretation of deduced P-T paths, suggest the shear zone resulted from far-field stress related to the Kuunga orogeny in an intraplate setting. This would support a model of Tonian age amalgamation of the Bastar craton and the Eastern Ghats Province as a part of the Greater Indian Landmass.

The present communication aims at an assessment of the current status on petrological evolution of the Eastern Ghats Belt in the context of its correlation with three supercontinents, namely Columbia, Rodinia and East Gondwana. Despite intensive research by different groups over the last three decades, various issues remain unresolved. Some major outstanding issues include, the nature of the basement for the Eastern Ghats rocks, isotopic and / or lithotectonic subdivisions of the belt, nature of the retrograde path of UHT metamorphism and timing of juxtaposition of the mobile belt with the adjacent cratons.

Acta Geologica Sinica - English EditionVolume 93, Issue S1 p. 37-37 Session 1: Deep structure and dynamics of the Himalaya – Tibet orogen and global collision zonesFree Access Tectonothermal modelling for Sikkim Himalaya: Implications for channel flow to thrust tectonics in collision zones Dilip K. Mukhopadhyay, Dilip K. Mukhopadhyay dilipfes@gmail.com Department of Earth Sciences, Indian Institute of Technology, Roorkee 247667 IndiaSearch for more papers by this authorSumit Chakraborty, Sumit Chakraborty Institute for Geology, Mineralogy and Geophysics, Ruhr Iniversity, D-44780 Bochum GermanySearch for more papers by this authorSomnath Dasgupta, Somnath Dasgupta Indian Institute of Science, Education and Research Kolkata, Mohanpur 741246 IndiaSearch for more papers by this author Dilip K. Mukhopadhyay, Dilip K. Mukhopadhyay dilipfes@gmail.com Department of Earth Sciences, Indian Institute of Technology, Roorkee 247667 IndiaSearch for more papers by this authorSumit Chakraborty, Sumit Chakraborty Institute for Geology, Mineralogy and Geophysics, Ruhr Iniversity, D-44780 Bochum GermanySearch for more papers by this authorSomnath Dasgupta, Somnath Dasgupta Indian Institute of Science, Education and Research Kolkata, Mohanpur 741246 IndiaSearch for more papers by this author First published: 31 May 2019 https://doi.org/10.1111/1755-6724.13919AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume93, IssueS1Special Issue: Abstracts of the International Symposium on Deep Earth Exploration and Practices, 24–26 Oct 2018, Beijing, ChinaMay 2019Pages 37-37 RelatedInformation

In this study, we utilize high-alumina pelitic schist samples from the Holenarsipur Greenstone Belt, a component of the ca. 3.30-3.15 Ga Sargur Supergroup in the Western Dharwar Craton, South India to establish a Mesoarchaean metamorphic history in the terrane. On the basis of integrated textural, mineral compositional, metamorphic reaction history and P-T pseudosection modelling studies, garnet-monazite trace element thermometry and coupled monazite electron probe micro-analyzer and sensitive high-resolution ion microprobe U-Pb dating results, we constrain for the first time a Mesoarchaean metamorphism along a hairpin clockwise metamorphic P-T path in the Dharwar Craton. The path reveals a two-stage prograde segment with an initial phase of heating accompanying burial (dP/dT gradient similar to 30 bar/degrees C) and a later phase of steep burial (Delta P similar to 1.1 kbar, dP/dT gradient similar to 110 bar/degrees C), peak metamorphism at 7.5 kbar, 640 degrees C and a post-peak, steep decompression stage (P similar to 63 kbar at 635 degrees C). Chemically zoned monazite grains shielded within garnet or occurring in low-strain matrix domains were formed in two stages during the Mesoarchaean metamorphism: (a) Monazite cores with relatively lower Y concentrations, higher Th/U ratios, a strong negative Eu anomaly; their REE partitioning relationships with the garnet inner rim reveal their crystallization was synchronous with the growth of garnet. (b) Monazite rims with higher Y and uraniferous compositions and lower Th/U ratios which, combined with Y and HREE enrichments in the outer rim of garnet, indicate their formation during the post-peak decompression stage associated with coupled decompositions of garnet and zircon. We correlate U-Pb monazite core and rim ages at 3144 +/- 7 Ma and 3105 +/- 10 Ma respectively with the timings of peak and retrograde metamorphism. Our findings, when evaluated with the available geological, isotopic, geochronological data of Meso- to Palaeoarchaean extant and extinct felsic crust as well as thermo-mechanical models, predict the ca.3.14-3.11 Ga metamorphism in the Holenarsipur Greenstone Belt as part of a widespread tectono-thermal event in the Western Dharwar Craton. The event marks late stages of sagduction tectonics in the craton as it evolves from a predominantly vertical to a horizontal shortening mode. (C) 2019 Elsevier B.V. All rights reserved.

The configuration of the Greater Indian Landmass was achieved during the late Proterozoic era (Grenvillian-age) through tectonic cycles involving cratonic blocks of India and East Antarctica in the broad framework of the assembly of the supercontinent Rodinia. Geological evidences are recorded from orogenic belts separating southern, northern and western cratonic blocks of India and its transcontinental neighbor East Antarctica. Eastern Ghats Belt of India played a pivotal role in the continental amalgamation process and it evolved in tandem with the Central Indian Tectonic Zone and the Aravalli Delhi Mobile Belt. We have collated geological and geochronological evidences from the cratonic blocks and the bounding orogenic belts to trace back the Grenvillian-age tectonics surrounding India and its eventual manifestation as the configuration of the Greater Indian Landmass. The status of the Greater Indian Landmass as a part of Rodinia is debated and unresolved issues are highlighted.