Petrogenesis of silicic magmas in Iceland has fundamental significance for understanding the relative importance of fractional crystallization of mantle-derived basalt and partial melting of hydrothermally altered basaltic crust in formation of the earliest continental crust. First results of in situ oxygen isotope investigation of zircons in large-volume silicic eruptive products of three volcanoes in Iceland (Askja, Torfajökull, and Hekla) demonstrate isotope diversity and disequilibria and long U-Th zircon pre-eruptive residence of 10 3-10 4year. This suggests that zircons did not grow from their host melts but instead were inherited from older magma batches and leftover cumulates with generally low and variable δ 18O values. This study demonstrates that segregation of cubic kilometres of silicic magma is faster than mineral-diffusive or recrystallization time-scales (estimated at ~10 3years), and it suggests that partial melting of hydrothermally altered and oxidized oceanic crust is the mechanism that best explains silicic rocks in Iceland and early earth environments.
|Number of pages||6|
|Publication status||Published - Jun 2012|