A continental arc tempo discovered in the Pacific-Gondwana margin mudpile?

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© 2016 Geological Society of America. The integration of detrital zircon age and trace element analyses provides a powerful tool with which to reconstruct continental arc evolution. Detrital zircons from the Ross-Delamerian orogen along the Pacific-Gondwana margin in north Victoria Land in Antarctica yield a broad 700-500 Ma U-Pb age population that shows a prominent period of activity centered at ca. 630-550 Ma. This activity is well correlated with the highest zircon Th/U and U/Yb ratios, suggesting an increase in lithospheric contribution coincident with fluid input from oceanic slab subduction, respectively. A low Yb/Gd ratio over this same period also suggests crustal thickening. Determination of zircon parent rock types using trace element proxies reveals the presence of previously unrecognized distinct pulses of granitoid activity that occur over tens of millions of years. Lulls between granitoid flare-ups overlap with increases in mafic-carbonatite-alkaline magma production, suggesting an influx of mantle or lower crustal melts during syn-subduction extension. A concomitant increase in the number of metamorphic zircons (U/Th > 10) and 40Ar/39Ar white mica cooling ages found during these extensional episodes suggest that significant thermal perturbations of the crust coincided with orogenic cooling, which was possibly influenced by uplift and exhumation.

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