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

Abstract

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.

Subduction–accretion–collision history along the Gondwana suture in southern India: A laser ablation ICP-MS study of zircon chronology

“…2) (e.g. Koshimoto et al, 2004;Shimpo et al, 2006;Santosh et al, 2004;Tsunogae et al, 2007Tsunogae et al, , 2008aNishimiya et al, 2008Nishimiya et al, , 2010Ohyama et al, 2008;Kanazawa et al, 2009;Sato et al, 2009;Tsunogae and Santosh, 2010). For example, metamorphic P-T trajectories including prograde high-pressure metamorphism, peak UHT metamorphism, and subsequent isothermal decompression for the PCSZ system were confirmed from Al-Mg granulites with moderateMg (Fe 0.5 Mg 0.5 ) staurolite inclusions in poikiloblastic garnets (Shimpo et al, 2006;Tsunogae and Santosh, 2006;Tsunogae et al, 2008a;Sato et al, 2009;Nishimiya et al, 2010) and also from an experimental study on the magnesian (Fe 0.7 Mg 0.3 ) staurolite composition in the system FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O (Sato et al, 2010b).…”

“…The UHT metamorphism in the region also witnessed the influx of CO 2 -rich fluids, as has been suggested by the common presence of highdensity CO 2 fluid inclusions trapped during peak metamorphic conditions in various granulite-facies minerals (e.g. Ohyama et al, 2008;Santosh and Omori, 2008;Tsunogae et al, 2008b). The available geologic, petrologic, geochronologic and experimental data were synthesized in a recent plate tectonic model for southern India which proposed an early Pacific-type accretionary orogeny and a final Himalayan-style collisional orogeny (Santosh et al, 2009b;Santosh and Kusky, 2010).…”

Low-density CO2-rich fluid inclusions from charnockites of southwestern Madurai Granulite Block, southern India; implications on graphite mineralization

“…C-O-H-bearing fluids play a crucial role in the lower crustal and crust-mantle interaction processes (SatishKumar, 2005;Santosh and Omori, 2008a,b;Santosh et al, 2009a;. Recent studies on fluid inclusions focus on the integration of detailed petrography, compositional characterization by microthermometry and laser Raman spectroscopy, and chemical and isotopic analyses of fluids extracted from inclusions, and thus provide important clues on the nature and role of fluids (e.g., Satish-Kumar, 2005;Ohyama et al, 2008;. This, in turn, helps in understanding the processes of crustal evolution, which is fundamental for formulating geodynamic models.…”