Evolution of Eastern Arctic crust revealed from zircon U-Pb, O and Hf isotopic records.

Abstract:

Zircon U-Pb ages, in conjunction with O and Hf isotope geochemistry, obtained from Proterozoic to Cretaceous supracrustal metamorphic to magmatic rocks (total 30 samples) collected from Cretaceous granite-gneiss dome and magmatic arc complexes located along Arctic cost of Chukotka, Neoproterozoic basement exposures on Wrangel Island, and crustal xenoliths-bearing Neogene alkali basalts on Zhokhova Island (De Long archipelago, Russian Arctic) provide new insights about evolution of crust in Arctic Alaska-Chukotka block. The oldest magmatic zircons yield U-Pb ages ranging from 710 to 570 Ma have depleted mantle-like Hf and O isotopic signatures (d18O range predominantly from +5.3 to +6.2 ‰, whereas εHf_(i) ranges from +8 to +13), suggesting the juvenile crust formation during Cryogenian-Ediacaran, roughly correlated with Rodinia breakup. Zircons from Devonian (390-360 Ma) to Cretaceous (105-88 Ma) arc granites and rhyolites have increasingly heavier O isotopic composition (up to +6.5 to +9.0 ‰), and less radiogenic εHf_(i) (as low as to -2.5 to -10), suggesting significant anatexis of the eastern Arctic crust associated with Devonian and Cretaceous age pluton forming events.