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.