High-pressure and ultrahigh-temperature metamorphism at Komateri, northern Madurai Block, southern India

Journal of Mineralogical and Petrological Sciences

2008

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We report here the metamorphic P -T path for granulite -facies metapelites from the eastern part of the Trivandrum Granulite Block (TGB), southern India, and compare with the paths from the western part of the block as well as from other granulite blocks and shear zones in this region for understanding of exhumation history of the southern granulite terrane. The peak temperature condition of the eastern part (900 -1000 °C) is almost consistent with that from the western part, suggesting regional ultrahigh -temperature (UHT) metamorphism throughout the TGB. However, there is a slight difference in peak pressure conditions between the eastern part (12 kbar) and the western part (10 kbar) estimated from different Zn content within spinel in equilibrium with quartz. Such P ~ 12 kbar high -pressure event is consistent with that obtained from granulite -facies rocks further north in the Palghat -Cauvery Shear Zone system (PCSZ) and Madurai Granulite Block (MGB). The results therefore suggest that the TGB, MGB, and PCSZ underwent similar prograde high -pressure metamorphism followed by peak UHT event along a clockwise P -T trajectory, related to the collisional orogeny during the assembly of the Gondwana Supercontinent.

Section: Discussionsupporting

confidence: 85%

Metamorphic P-T path of the eastern Trivandrum Granulite Block, southern India: implications for regional correlation of lower crustal fragments

Tadokoro

Journal of Mineralogical and Petrological Sciences

2008

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“…The metamorphic P -T trajectories including prograde high -pressure metamorphism, peak UHT metamorphism, and subsequent isothermal decompression for the PCSZ region were confirmed robustly by the descriptions of Al -Mg granulites with moderate -Mg (Fe 0.5 Mg 0.5 ) staurolite inclusions in poikiloblastic garnets (Shimpo et al, 2006;Tsunogae and Santosh, 2006;Tsunogae et al, 2008;Sato et al, 2009;Nishimiya et al, 2010) and also an experimental study on the magnesian (Fe 0.7 Bhaskar Rao, 2006a, 2006b). The northern margin of the PCSZ system is marked by the MBSASZ.…”

Section: Introductionmentioning

confidence: 63%

Laser ablation ICP mass spectrometry for zircon U-Pb geochronology of metamorphosed granite from the Salem Block: Implication for Neoarchean crustal evolution in southern India

Sato

Journal of Mineralogical and Petrological Sciences

et al. 2011

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We report here petrological characteristics of metamorphosed granite and metagabbro from the Kanja Malai hills, the southern margin of the Salem Block in southern India. Field observations suggest that both these rock types experienced high -grade metamorphism, and exhibit strong foliation. Many of cores of zircons extracted from the granite show an internal structure suggesting magmatic crystallization. In contrast, rims of the zircons commonly display metamorphic overgrowth. We also present geochronological data utilizing laser ablation ICP mass spectrometry technique on the zircons that show the weighted means of 207 Pb/ 206 Pb age of 2647 ± 11 Ma (error: 1σ) for the timing of magmatism, and 2442 ± 20 Ma (error: 1σ) for the subsequent high -grade metamorphism. Together with a previous geochronological study on charnockites from the Salem Block, our results also provide an important constraint on the Neoarchean magmatism (2.65 -2.53 Ga) in southern India, correlating the magmatism with a major global crust formation event during the Neoarchean.

“…An alternate explanation is that, as the rock underwent significant pressure decrease during rapid exhumation along a clockwise trajectory, the fluid inclusions experienced density reversal due to sudden volume changes of the inclusion cavities (e.g., Ohyama et al, 2008). Such near isothermal decompression after the peak event is supported by the occurrence of various corona textures such as orthopyroxene + cordierite and gedrite + sapphirine + spinel symplectites around garnet, and sapphirine + spinel + cordierite symplectite between kyanite and garnet (or gedrite) in this region (e.g., Shimpo et al, 2006;Santosh and Sajeev, 2006;Tsunogae and Santosh, 2007;Tsunogae et al, 2008a;Kanazawa et al, 2008). Such density modification of fluid inclusions has been reported earlier from some of the granulites along the PCSZ Tsunogae et al, 2008b).…”

Section: Discussionmentioning

confidence: 97%

“…In this study, we present new results of petrographic and microthermometric investigations on fluid inclusions trapped in high -grade minerals in granulites from Kumiloothu, a newly discovered UHT locality near Karur in the northern MGB. Tsunogae et al (2008a) inferred prograde high -pressure (P > 12 kbar) metamorphism and subsequent peak UHT conditions of T ~ 1000 °C along a clockwise P -T trajectory from this region. The results of the present study provide important information of the nature and role of deep crustal fluids in collisional orogenic belt.…”

Section: Introductionmentioning

confidence: 91%

“…This is also regarded as the trace of the collisional suture of the Gondwana supercontinent during its final assembly in the Late Neoproterozoic to Early Cambrian (e.g., Chetty and Bhaskar Rao, 2006;Collins et al, 2007a). Recently, ultrahigh -temperature (UHT; T > 1000 °C at ~ 8 kbar) granulites have been reported from several localities in the northern MGB and PCSZ probably formed by deep subduction and subsequent continent -continent collision along this suture zone Koshimoto et al 2004;Shimpo et al, 2006;Sajeev, 2006: Collins et al, 2007b;Santosh, 2006a, 2007;Tsunogae et al, 2008a). However, only few studies on the role of fluids related to the UHT metamorphism have been carried out in this region.…”

Section: Introductionmentioning

confidence: 99%

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Carbonic fluid inclusions in ultrahigh-temperature granulite from Kumiloothu in the northern Madurai Block, southern India

Ohyama

Journal of Mineralogical and Petrological Sciences

2008

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We report fluid inclusion data on ultrahigh -temperature (UHT) granulites from Kumiloothu in the northern Madurai Block situated along the Palghat -Cauvery Shear Zone system in southern India. Three categories of fluid inclusions have been observed: primary inclusions in garnet comprising the dominant category, secondary inclusions in garnet, and rare primary inclusions in rutile and apatite enclosed within garnet. The melting temperatures of all the categories of inclusions lie in the narrow range of -57.0 to -56.6 °C, close to the triple point of pure CO 2 . Most of the fluid inclusions homogenize into the liquid phase between a temperature range of +11.3 to +30.3 °C, corresponding to low -CO 2 densities of 0.59 -0.85 g/cm 3. Slightly higher density of 0.95 g/cm 3 was obtained from a primary inclusion in rutile that homogenized at -3.6 °C. The fluid densities, when computed into isochores, indicate lower pressures (~ 6.6 kbar at 1000 °C) than the peak P -T conditions (T >1000 °C at ~ 8 kbar) estimated for this region. The results of this study, together with the primary nature of the inclusions trapped in high -grade minerals, indicates density reversal of peak metamorphic fluid, a common feature for many UHT granulites along the Gondwana suture zone as well as other UHT terranes showing clockwise P -T history.