Feldspar thermometry in ultrahigh-temperature metamorphic rocks: Evidence of crustal metamorphism attaining ~1100 °C in the Archean Napier Complex, East Antarctica

Journal of Mineralogical and Petrological Sciences

Santosh

2008

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: P-t Estimatesmentioning

confidence: 71%

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

Santosh

2008

“…Application of the ternary feldspar thermometer of Kroll et al (1993) to the lamella assemblages (Fig. 3d) following the method described in previous studies (Yoshimura et al, 2000;Hokada, 2001;Hokada and Suzuki, 2006) yields the temperatures of ~ 1000 °C suggesting high -temperature magmatic or later UHT metamorphic conditions (Fig. 4), if the pressure of 8 kbar is assumed after previous prospects (Nishimiya et al, 2008;Santosh et al, 2010) for various mafic granulites in this region.…”

Section: Petrology and Mineral Chemistrymentioning

confidence: 90%

“…1c), and also by Neoarchean charnockites in the north (e.g., Clark et al, 2009). Santosh et al (2005) performed the EPMA U -Pb dating for zircon and monazites extracted from granites, collected from the locality about 15 km west of Karur town, and they reported the late Neoproterozoic -Cambrian magmatic ages, which were different from the Rb -Sr isochron age (Nathan et al, 1994;2001).…”

Section: Geological Outline Of Sample Localitymentioning

confidence: 99%

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

Santosh

Journal of Mineralogical and Petrological Sciences

et al. 2011

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.

“…The technique involved the determination of early single phase feldspar and the application of the thermometer following the method described by Hokada (2001). Figure 5 shows a ternary An Ab Or diagram with plots of the compositions of host plagioclase and lamella K feldspar, together with early single phase feldspar inferred from host lamella volume proportions estimated from back scattered images.…”

Section: Ternary Feldspar Geothermometermentioning

confidence: 99%

“…In this study, the authors attempt to estimate the true peak metamorphic temperature of the SMZ using three geothermometric methods; (1) a ternary feldspar geothermometer using perthitic feldspar (Hokada, 2001), (2) Al solubility in orthopyroxene (Hensen and Harley, 1990;Harley, 1998), and (3) a revised garnet orthopyroxene geothermometer corrected for retrograde exchange (Pattison et al, 2003). The first two methods are regarded as being less influenced by retrograde metamorphism than conventional Fe Mg exchange geothermometers, and is therefore expected to be useful for reliably estimating peak temperatures in granulite facies terranes (e.g.…”

Section: Introductionmentioning

confidence: 99%

Ultrahigh-temperature metamorphism of the Southern Marginal Zone of the Archean Limpopo Belt, South Africa

Journal of Mineralogical and Petrological Sciences

Miyano

Reenen³

et al. 2004

We report ultrahigh temperature (T > 950°C) peak metamorphic conditions for the Southern Marginal Zone of the Archean Limpopo Belt in South Africa. Pelitic granulites of the zone have a typical mineral assemblage of garnet + biotite + orthopyroxene + cordierite + quartz + K feldspar + plagioclase ± sillimanite, to which the latest geothermobarometers are applicable. The revised P T conditions were obtained from a ternary feldspar geothermometer using antiperthitic feldspars in leucocratic granulite (920 980°C), Al solubility in orthopyroxene in pelitic granulite (970 1020°C), and a revised garnet orthopyroxene geothermometer corrected for retrograde Fe Mg exchange (920 990°C). The estimated peak temperature of metamorphism is about 100°C higher than previously estimated based on conventional Fe Mg exchange geothermometers (800 870°C), and indicates a high geothermal gradient of 35°C/km in Archean continental lower crust.