Ultrametamorphism in Precambrian granulite terranes: Evidence from Mg‐AI granulites and calc‐silicate granulites of the Eastern Ghats, India

Dasgupta, Somnath; Sengupta, P.

doi:10.1002/gj.3350300310

Cited by 30 publications

(6 citation statements)

References 54 publications

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“…The EGP is a type locality for long‐lived UHT metamorphism (e.g. Dasgupta & Sengupta, ; Dasgupta et al., ; Korhonen, Brown, et al., ; Korhonen, Clark, et al., ; Korhonen et al., ; Rickers, Mezger, et al., ). The EGP was interpreted to be formerly contiguous with the Rayner Complex in east Antarctica, and together they formed a vast Mesoproterozoic–Neoproterozoic orogenic belt that was over 500 km wide (e.g.…”

Section: Background and Geologicalsettingmentioning

confidence: 99%

“…The M1 event in the EGP was interpreted to involve UHT metamorphism followed by near‐isobaric cooling (e.g. Bhowmik, ; Bose & Das, ; Bose, Das, Dasgupta, Miura, & Fukuoka, ; Bose, Fukuoka, Sengupta, & Dasgupta, ; Das, Bhattacharya, Raith, Bhadra, and Banerjee, ; Das, Bose, Ohnishi, & Dasgupta, ; Dasgupta & Ehl, ; Dasgupta & Sengupta, , ; Dasgupta, Sengupta, Fukuoka, & Bhattacharya, ; Dasgupta et al., ; Dharma Rao et al., ; Grew, ; Kamineni & Rao, , 1988b; Korhonen, Brown, et al., ; Korhonen et al., ; Lal, Ackermand, & Upadhyay, ; Mohan, Tripathi, & Motoyoshi, ; Mukhopadhyay & Bhattacharya, ; Nasipuri, Bhattacharya, & Das, ; Pal & Bose, ; Prakash et al., ; Sarkar, Dasgupta, & Fukuoka, ; Sengupta, Karmakar, Dasgupta, & Fukuoka, ; Sengupta, Raith, & Dasgupta, ; Sengupta et al., ; Shaw & Arima, , ). Most researchers consider M1 to be characterized by an overall counter‐clockwise P–T path (see Table and preceding references).…”

Section: Background and Geologicalsettingmentioning

confidence: 99%

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Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province, India

Kelsey

Morrissey

Hand

et al. 2017

Journal Metamorphic Geology

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Ultrahigh temperature (UHT) granulites in the Eastern Ghats Province (EGP) have a complex P–T–t history. We review the P–T histories of UHT metamorphism in the EGP and use that as a framework for investigating the P–T–t history of Mg–Al‐rich granulites from Anakapalle, with the express purpose of trying to reconcile the down‐pressure‐dominated P–T path with other UHT localities in the EGP. Mafic granulite that is host to Mg–Al‐rich metasedimentary granulites at Anakapalle has a protolith age of c. 1,580 Ma. Mg–Al‐rich metasedimentary granulites within the mafic granulite at Anakapalle were metamorphosed at UHT conditions during tectonism at 960–875 Ma, meaning that the UHT metamorphism was not the result of contact metamorphism from emplacement of the host mafic rock. Reworking occurred during the Pan‐African (c. 600–500 Ma) event, and is interpreted to have produced hydrous assemblages that overprint the post‐peak high‐T retrograde assemblages. In contrast to rocks elsewhere in the EGP that developed post‐peak cordierite, the metasedimentary granulites at Anakapalle developed post‐peak, generation ‘2’ reaction products that are cordierite‐absent and nominally anhydrous. Therefore, rocks at Anakapalle offer the unique opportunity to quantify the pressure drop that occurred during so‐called M2 that affected the EGP. We argue that M2 is either a continuation of M1 and that the overall P–T path shape is a complex counter‐clockwise loop, or that M1 is an up‐temperature counter‐clockwise deviation superimposed on the M2 path. Therefore, rather than the rocks at Anakapalle having a metamorphic history that is apparently anomalous from the rest of the EGP, we interpret that other previously studied localities in the EGP record a different part of the same P–T path history as Anakapalle, but do not preserve a significant record of pressure decrease. This is due either to the inability of refractory rocks to extensively react to produce a rich mineralogical record of pressure decrease, or because the earlier high‐P part of the rocks history was erased by the M1 loop. Irrespective of the specific scenario, models for the tectonic evolution of the EGP must take the substantial pressure decrease during M2 into account, as it is probable the P–T record at Anakapalle is a reflection of tectonics affecting the entire province.

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Section: Background and Geologicalsettingmentioning

confidence: 99%

Section: Background and Geologicalsettingmentioning

confidence: 99%

Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province, India

Kelsey

Morrissey

Hand

et al. 2017

Journal Metamorphic Geology

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“…UHT rocks have been reported from various terrains in the world, and are particularly common in the East Gondwana crustal fragments including the Napier Complex in East Antarctica (e.g., Harley and Motoyoshi, 2000), Eastern Ghats in India (e.g., Dasgupta and Sengupta, 1995) and Highland Complex in Sri Lanka (e.g., Osanai et al, 2000). The dry mineral assemblages which characterize these rocks require that the water activities were buffered to low levels during peak metamorphic P T conditions.…”

Section: Introductionmentioning

confidence: 99%

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

Santosh

Tsunogae

Yoshikura

2004

Journal of Mineralogical and Petrological Sciences

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Ultrahigh temperature (UHT) granulites in Tonagh Island, Napier Complex, East Antarctica record peak metamorphic pressure temperature (P T) conditions of up to 9 kbar and 1100°C. Sapphirine, garnet, orthopyroxene and quartz in these rocks contain very high density fluid inclusions with melting temperatures close to that of pure CO 2 (−56.6°C) and homogenization temperatures down to −34.9°C translating into high CO 2 densities (up to 1.07 g/cm 3 ). The UHT granulites of Vizianagram in Eastern Ghats Belt, India which were subjected to extreme crustal metamorphism at >1000°C and 8 9 kbar also carry very high density (up to 1.15 g/cm 3 ) pure CO 2 inclusions in quartz adjacent to spinel rimmed by various coronas of sillimanite, orthopyroxene and garnet. Garnets in a granulite facies rock from Salem in southern India that equilibrated at peak P T conditions of 740 800°C and 9 11 kbar carry the highest density (1.17 g/cm 3 ) pure CO 2 yet reported from continental crust. This rock also contains very high density CO 2 inclusions in plagioclase and quartz. High density (0.998 g/cm 3 ) pure CO 2 rich fluid inclusions also occur abundantly within garnets from a mafic granulite in Ampitiya, central Highland Complex, Sri Lanka. The peak P T conditions of metamorphism of the mafic granulite are around 10.6 kbar and 985°C with subsequent rapid isothermal decompression along a clock wise path down to 5.5 kbar. In most of the cases above, the representative isochores for the CO 2 inclusions either penetrate through or pass very close to the P T windows defined from mineral phase equilibria indicating that the fluid inclusions were trapped at the time of peak or near post peak metamorphism. We thus recognize a group of "ultrahigh density" (UHD) CO 2 rich fluids that characterize UHT rocks and other granulites formed under extreme crustal metamorphism. These fluids contrast sharply with the lower density (generally <1.0 g/cm 3 ) CO 2 inclusions commonly reported from normal granulite facies rocks in various terrains. The presence of "synmetamorphic" UHD CO 2 within various minerals is consistent with the low water activities predicted by the mineral assemblages in these rocks. Although the source of the CO 2 is equivocal, mantle derived mafic magmas could have provided the heat and volatiles required for crustal metamorphism at extreme conditions displayed by these rocks.

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“…The assemblages diagnostic of high temperature and low pressure are Zn‐poor spinel + quartz, sapphirine + quartz and complex Fe–Ti–Al oxide solid solution in Mg–Al granulite, and wollastonite + scapolite in calc‐silicate granulite (see Dasgupta and Sengupta, , and references therein). This phase of metamorphism in the EGP was designated as M1, with estimated peak conditions of 8–10 kbar and ~1000 °C (Dasgupta and Sengupta, , ). The retrograde path following the M1 peak is generally proposed to be one of near‐isobaric cooling, although a few studies suggest an initial phase of isothermal decompression (e.g.…”

Section: Thermal Events In the Eastern Ghats Provincementioning

confidence: 99%

Strain localization, granulite formation and geodynamic setting of ‘hot orogens’: a case study from the Eastern Ghats Province, India

Gupta

2011

Geological Journal

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The Eastern Ghats Province underwent major orogenic events in the Neoproterozoic-Cambrian period: 980-930, 900-650 and 550-500 Ma. At each time interval, deformation occurred synchronous with high-grade metamorphism. The first event was characterized by distributed strain throughout the entire province, while strain and thermal anomalies during the later orogenies were confined to the province boundaries. In the first case, pre-orogenic rifting caused ultrahigh-temperature metamorphism at the base of the crust, and was closely followed by crustal shortening related to the collision of the granulite belt with the Indian craton. The thermal anomaly persisting from the rifting event, followed by the thermal relaxation associated with crustal shortening led to prolific melt production and transfer of heat producing elements (HPE) into the middle and upper parts of the thick post-collisional crust. Heating and associated melting caused rheological weakening of the crustal section, and explains why strain was distributed across the entire thermally perturbed zone. Erosion removed a substantial portion of the HPErich upper crust, and deposited the detritus in cratonic sedimentary basins to the west. Subsequently, the rheologically stronger Eastern Ghats Province crust could effectively transmit stresses and concentrate them along pre-existing zones of weakness near the province boundaries. Progressive thrusting in these domains led to consistent loading of the footwall, even as it underwent thermal relaxation. Since both strain and heating were associated with the footwall of pre-existing discontinuities, the 'hot orogen' so formed was also spatially restricted. Copyright

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Ultrametamorphism in Precambrian granulite terranes: Evidence from Mg‐AI granulites and calc‐silicate granulites of the Eastern Ghats, India

Cited by 30 publications

References 54 publications

Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province, India

Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province, India

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

Strain localization, granulite formation and geodynamic setting of ‘hot orogens’: a case study from the Eastern Ghats Province, India

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