Timing of UHT metamorphism and cooling in south Indian granulites: New P-T-t results from a sapphirine granulite

Dev, J. Amal; Tomson, J.K.; Sorcar, Nilanjana; Francis, K. Anto

doi:10.1016/j.precamres.2022.106582

Cited by 8 publications

(18 citation statements)

References 53 publications

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“…In addition, similar crustal thickness values of 44–47 km are also noted south of Salem block into Madurai block till AKSZ, suggesting the possible continuation of the Achaean crust south of Palghat‐Cauvery Shearzone System (PCSS). This observation agrees with recent geochronological studies south of PCSS, suggesting the presence of an Archean juvenile crustal component in the western Madurai block (Dev, Tomson, et al., 2022; Dev et al., 2021). However, the timing of the inferred collision between WDC and Salem block has been revised by recent workers at 2.5 Ga, and MBCS has been designated as a late‐Archean collisional boundary assembling Dharwar Craton, Salem, and western Madurai blocks (Brandt et al., 2014).…”

Section: Discussionsupporting

confidence: 92%

Estimation of Moho Depth Beneath Southern Indian Shield by Inverting Gravity Anomalies Constrained by Seismic Data

Roy

Prasad

et al. 2023

JGR Solid Earth

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This study presents a high‐resolution 3D Moho structure beneath southern India and its surrounding regions from observed gravity anomalies. The global gravity disturbance model (XGM2019e) with a grid resolution of 0.1° is considered for this study. The extended Bott's inversion algorithm and Gauss‐Fast Fourier Transform based forward model are adopted to invert for the Moho undulations beneath the Indian peninsula. The inversion algorithm is tested for a synthetic model having a predefined density contrast and mean Moho depth. The robustness of this inversion algorithm is further tested for noise‐incorporated gravity data. The control points are required for estimating two hyper‐parameters, viz. density contrast, and reference depth, which play a crucial role in the precise estimation of Moho depth. In real case study, the inverted Moho depth of Southern India and its surrounding regions by seismic constraint receiver function‐driven control points show a very complex architecture of Moho topography. The observed average crustal thickness in the study region is 35.35 km, corroborating with the previously reported Moho depths. The maximum crustal thickness is 53.04 km beneath the southern part of Archean Western Dharwar Craton and west of Salem block, around 44–47 km Moho depth is observed at the south of Salem block into Madurai block till Achankovil Shear Zone, which suggests the possible continuation of the Achaean crust of Palghat‐Cauvery Shear Zone System. The lowest crustal thickness values are observed along the eastern margin of the Cuddapah basin, which overlaps with the Proterozoic Krishna basin of the Eastern Ghats Mobile belt.

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Section: Discussionsupporting

confidence: 92%

Estimation of Moho Depth Beneath Southern Indian Shield by Inverting Gravity Anomalies Constrained by Seismic Data

Roy

Prasad

et al. 2023

JGR Solid Earth

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“…The weighted mean 206 Pb/ 238 U ages from these domains range from 612 ± 25 Ma to 625 ± 26 Ma, which is interpreted as the timing of mafic magmatism in the area (Table 2). The high MSWD associated with these ages can be due to partial Pb loss during subsequent high-grade metamorphism (Takamura et al 2020) and is reported from the terrane by many workers (Brandt et al, 2014; Dev et al, 2022a). The planar/sector zoned rim domains show distinct low Th/U ratios (<0.5), and ages from this group represents the timing of metamorphism recorded in the mafic granulites bracketed between 573 ± 10 Ma and 540 ± 10 Ma.…”

Section: Discussionmentioning

confidence: 89%

“…Single-spot U-Pb isotope and trace element analysis of zircons was performed at the Isotope Geochemistry Facility (IGF), NCESS, using a Teledyne CETAC, Nd:YAG (solid-state laser) coupled with Agilent 7800 quadrupole ICPMS. The analytical protocol is according (Dev et al, 2022a). 91500 zircon was used as the primary standard, whereas Plesovice and BB11 zircons were monitored for quality check.…”

Section: B Zircon U-pb Geochronology Trace Element and Hf Isotope Ana...mentioning

confidence: 99%

“…Southern Granulite Terrane (SGT) is a composite of polymetamorphic terrains with prolonged crustal evolution history ranging from early Archaean to late Neoproterozoic, preserving the evidence for polyphase deformation, multiple tectonothermal and multiphase exhumation and cooling histories (Ghosh et al 2004; Plavsa et al 2012; Tomson et al 2013; Brandt et al 2014; Collins et al 2014; Kumar et al 2017; Dev et al, 2021; Dev et al, 2022b). SGT is bounded to the north by the Archaean granite–greenstone terrain of the Dharwar craton (Chadwick et al 2000; Jayananda et al 2000).…”

Section: Geological Settingmentioning

confidence: 99%

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Age and petrogenesis of mafic granulites from central Madurai block, south India: implications on regional tectonics

et al. 2023

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The Precambrian Southern Granulite Terrane (SGT) of south India is well-known for the preservation of high- to ultrahigh-temperature (HT-UHT) granulites, prominently exposed in its central part forming a linear belt referred to as the Kambam UHT belt. This belt also hosts widespread occurrences of mafic granulites that are observed in close spatial association with the HT-UHT granulites. This study presents detailed petrology, geochemistry and geochronology of representative mafic granulites from the area to understand their petrogenesis and tectonic setting. The results demonstrate that mafic granulites are low- to medium-K tholeiites, with continental arc affinity, formed by the partial melting of a subduction-modified enriched mantle source. The composition of the parent mantle source is modelled with a spinel/garnet lherzolite contribution ratio between 100/0 and 70/30, suggesting the mixing of spinel and garnet bearing melts during asthenosphere upwelling. Zircon U–Pb geochronology of mafic granulites constrains their emplacement between 612 Ma and 625 Ma, that subsequently underwent metamorphism between 581 Ma and 531 Ma. This overlaps with the timing of HT-UHT metamorphism in the Kambam UHT belt bracketed between 593 and 532 Ma. Zircon Hf isotopic studies reveal parent magma generation from reworked melting sources involving Archean and Proterozoic components. These results propose an alternative heat source for the formation of HT-UHT granulites in the Kambam UHT belt which can be designated as a major terrane boundary within the SGT.

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“…There is now mounting evidence suggesting a broader timescale of metamorphism, obtained through in situ monazite and zircon geochronology (e.g. Dev et al, 2021Dev et al, , 2022Tiwari & Sarkar, 2020). This has prompted a reconsideration of the hypothesised geodynamic scenario and the style of metamorphism in the MB.…”

Section: Introductionmentioning

confidence: 99%

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

Tiwari,

Sarkar,

Karmakar

et al. 2023

Journal Metamorphic Geology

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The Granulite Terrane of Southern India is a collage of Mesoarchean–Neoproterozoic crustal blocks that underwent high‐grade metamorphism associated with the final assembly of the Gondwana supercontinent during late Neoproterozoic–Cambrian. Here, we investigate the charnockites and associated sapphirine‐bearing semipelitic granulites from the eastern part of the Madurai Block (MB). We present new petrographic, mineral chemistry, and geochronological data to constrain the P–T–t evolution of the block and unravel the timescale and source of heat for the ultrahigh‐temperature metamorphism. Both the rock types contain coarse‐grained porphyroblastic garnet and orthopyroxene, yielding peak P–T conditions of 950 ± 30°C at 10.5 ± 0.8 kbar and 970 ± 40°C at 10 ± 0.5 kbar for semipelite and charnockite, respectively, using conventional thermobarometry. Peak ultrahigh temperatures are further supported by high Al content in the orthopyroxene (8.78 wt% Al2O3) coexisting with garnet (XMg: up to 0.57) and feldspar thermometry of the mesoperthites and antiperthites in the semipelite, yielding 950–980°C at 10 kbar. Subsequent decompression has led to the formation of coronal orthopyroxene3 + plagioclase3 in the charnockite and symplectic orthopyroxene3 + cordierite ± sapphirine ± plagioclase3 in the semipelite, yielding P–T range of 950–850°C and 9.5–6.8 kbar for semipelites and 950–820°C and 8–6.5 kbar for charnockite. Based on the obtained P–T estimates, preserved reaction textures, and phase equilibria modelling in the MnNCKFMASHTO system, a clockwise P–T evolution with isothermal decompression followed by cooling is inferred for both the rock types.Texturally constrained in situ monazite dating and rare earth element (REE) patterns show that the core of matrix monazite having low‐Th, Y, and extreme heavy rare earth element (HREE) depletion, yielding weighted mean ages of 582 ± 12 and 590 ± 22 Ma for semipelite and charnockite, respectively, dates the prograde evolution. The mantle of the matrix monazite in semipelite and comparable rim in charnockite, having relative Th‐enrichment compared to the core, yielding weighted mean ages of 552 ± 9 and 557 ± 13 Ma, respectively, dates extensive dissolution–reprecipitation from the melt at the peak stage. The relatively Th‐ and Y‐rich and moderately HREE‐depleted rim of matrix monazite in the semipelite, yielding weighted age of 516 ± 6 Ma, date initial garnet breakdown during post‐peak melt crystallization. By contrast, compositionally homogenous HREE + Y‐enriched monazite in the symplectite and retrograde monazites yielding weighted mean ages of 487 ± 47 Ma for semipelites and 508 ± 19 Ma for charnockites dates extensive garnet breakdown during final stages of melt crystallization and subsequent cooling. Our findings point to collision initiation at ~590 Ma, with the peak conditions attained at ~550 Ma followed by extensional collapse at ~510–490 Ma, resulting in rapid exhumation of lower crustal rocks to mid‐crustal levels under sustained ultrahigh‐temperature (UHT) conditions, followed by cooling to reach a stable geotherm. Our results suggest a long‐lived hot orogeny in the MB, where the UHT conditions were sustained for at least 40 MYr. The UHT conditions were most likely attained in the core of a long‐lived hot orogen by the combined effect of conductive heating through radioactive decay and mantle heat supply, with the former being the primary driver.

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Timing of UHT metamorphism and cooling in south Indian granulites: New P-T-t results from a sapphirine granulite

Cited by 8 publications

References 53 publications

Estimation of Moho Depth Beneath Southern Indian Shield by Inverting Gravity Anomalies Constrained by Seismic Data

Estimation of Moho Depth Beneath Southern Indian Shield by Inverting Gravity Anomalies Constrained by Seismic Data

Age and petrogenesis of mafic granulites from central Madurai block, south India: implications on regional tectonics

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

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