Sapphirine and corundum bearing ultrahigh temperature rocks from the Palghat-Cauvery Shear System, southern India

Abstract

We report a new occurrence of sapphirine and corundum bearing silica deficient Mg Al rocks from Paramati at the northern margin of the Palghat Cauvery Shear System which define the Archaean Proterozoic collisional boundary in southern India. Sapphirine here occurs as medium grained euhedral to subhedral crystals enclosed within plagioclase and contains inclusions of spinel and sillimanite, and is locally intergrown with corundum, suggesting the reaction Spl + Sil Spr + Crn. Temperatures estimated from sapphirine spinel equilibria lie around 930 950ºC, suggesting ultrahigh temperature peak metamorphic conditions. Gedrite is also a common rock forming mineral in these rocks, and coexists with cordierite, corundum, and sillimanite. As gedrite is totally surrounded by cordierite, we infer a prograde reaction Ged + Sil Crn + Crd + V. Lack of orthopyroxene in our samples suggests a decompressional P T history following the prograde event. Our results suggest that the whole of northern Madurai Block as well as parts of the Palghat Cauvery Shear System experienced ultrahigh temperature metamorphism followed by exhumation along a clockwise P T path.

Petrology and fluid inclusions of garnet-clinopyroxene rocks from Paramati in the Palghat-Cauvery Shear Zone System, southern India

“…1). Here, mafic to ultramafic rocks are often intercalated with corundum -, sapphirine -, and spinel -bearing Mg -Al -rich rocks (Santosh et al, 2004a;Koshimoto et al, 2004), suggesting that the package of all the lithologies underwent high -grade metamorphism. However, the field relation of the garnetclinopyroxene rock is not known as the garnet -rich layer is mostly covered by thick soil.…”

“…However, the field relation of the garnetclinopyroxene rock is not known as the garnet -rich layer is mostly covered by thick soil. Koshimoto et al (2004) estimated peak metamorphic temperature of 930 -950 °C and inferred clockwise P -T history. Mineral abbreviations discussed below are after Spear (1993).…”

Sodicgedrite in ultrahigh-temperature Mg-Al-rich rocks from the Palghat-Cauvery Shear Zone system, southern India

“…Shimpo et al (2006) and Tsunogae and Santosh (2006) reported near eclogite facies high pressure (HP) metamorphism at P>12 kbar and following UHT peak event of T = 940 990 ºC from the PCSS, which is probably related to Neoproterozoic continent continent collision orogeny from this terrane. Available petrological data from adjacent areas along the PCSS also support such HP and UHT metamorphism (Tsunogae and Santosh, 2003;Koshimoto et al, 2004;Santosh and Sajeev, 2006).…”

“…The aim of this short report is to describe new occurrence and chemistry of extremely Na rich gedrite (~ 3.1 wt% Na 2 O) in Mg Al rich rocks from the northernmost flank of the Pan African Madurai Block along the Palghat Cauvery Shear Zone system (PCSS) in southern India. Such high Na gedrite has not been reported in previous studies from this area (cf., Koshimoto et al, 2004;Shimpo et al, 2006;Santosh and Sajeev, 2006) and from other UHT terranes. Shimpo et al (2006) and Tsunogae and Santosh (2006) reported near eclogite facies high pressure (HP) metamorphism at P>12 kbar and following UHT peak event of T = 940 990 ºC from the PCSS, which is probably related to Neoproterozoic continent continent collision orogeny from this terrane.…”

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

“…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.…”