Melt-fluid infiltration in Archean suprasubduction zone mantle wedge: Evidence from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes from Wynad, southern India

摘要

The southern Peninsular India preserves a number of Archean cratonic nuclei among which the Coorg Block is considered to represent a Mesoarchean microcontinent. Here we investigate the southern margin of this block where remnants of rare ultramafic rocks in association with arc magmatic rocks and accreted metasediments occur in the Wynad region. We present petrology, mineral chemistry, whole rock geochemistry and zircon U-Pb and Lu-Hf data from a suite of meta ultramafics and associated diorite, orthopyroxene-bearing felsic charnockite, and quartz-mica schist. The peak P-T conditions of metamorphism of these rocks are estimated at 720-840 degrees C and 6.5-8.7 kbar. The geochemical features of the ultramafic suite provide evidence for melting and metasomatism of lithospheric mantle in a suprasubduction zone (SSZ) setting with the involvement of both silicate melts and slab-dehydrated fluids. The parent melts were generated at varying depth levels extending from spine] to garnet stability fields. A subduction-modified, LREE replenished, metasomatically enriched mantle source endorses arc-like chemical signatures in the melts that were acquired through interaction between the depleted sub-arc lithospheric mantle and subduction components.