Laser ablation ICP mass spectrometry for zircon U-Pb geochronology of ultrahigh-temperature gneisses and A-type granites from the Achankovil Suture Zone, southern India

We report results from U-Pb analyses by laser ablation ICP mass spectrometry of zircons in ultrahigh-temperature garnet-cordierite gneisses and A-type granite intrusions within the Achankovil Shear/Suture Zone in southern India, a region considered to mark the zone of the latest Neoproterozoic-Cambrian Gondwana collision. Field evidence and geochronologic data for the gneisses and granites suggests the possibility for the multi-heating of metamorphism in earlier stage and magmatism in later stage. Zircon U-Pb dating for 138 spots on 123 grains yielded well-defined age peaks at 480-560 Ma and less prominent age peaks at approximately 600-900 Ma in compiled age data histograms. The Neoproterozoic ages of ca. 600-900 Ma correlating with the protolith history might suggest the magmatic and metamorphic processes in a subduction-accretion regime prior to the final collision during latest Neoproterozoic-Cambrian. The ages of 480-560 Ma obtained from the granites correlate with the final suturing of the Gondwana supercontinent. (C) 2010 Elsevier Ltd. All rights reserved.