Cenozoic crustal genesis in SW Pacific arcs and backarcs

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

ABSTRACT 0751600 (Gill) Intellectual Merit: This research examines how the mantle and crust of the Earth evolve from during one ~50 million year cycle of subduction, from initiation to demise, in the absence of pre-existing continental crust. It involves four igneous petrological projects on rocks from the Kermadec-Fiji-Tonga area of the SW Pacific. Test using the geochemical and isotopic signatures of volcanic rocks will be used to answer (1) whether subduction initiation has a characteristic magmatic signature and cause; (2) if magma genesis in the mantle wedge during back-arc rifting evolves from flux-dominated to decompression-dominated melting; and (3) whether geochemical features of primary arc magmatism get passed on to second stage" crust that is continental in character. The geochemical plan includes generation and interpretation of extensive trace element and Nd-Hf-Sr-Pb isotope data. In addition, U/Pb and Ar-Ar ages will be obtained for igneous rocks, and results compared to analogues in the northern hemisphere. The first project focuses on the oldest rocks in Fiji and Tonga. The second focuses on basalts erupted in Fiji during 3-5 Ma, and those in cross-chains and rift basins in the Havre Trough. The third uses the granitic plutons of different ages and compositions in Fiji and includes (U-Th)/He double-dating". One anticipated impact will be to assess the commonality of processes between Earth's two largest and best-studied oceanic arcs: Izu-Marianas, and Kermadec-Fiji-Tonga. Broader Impacts: All three projects directly complement the NSF-funded island arc and backarc basin research foci in RIDGE2000, MARGINS, and IODP. They also involve international collaboration with scientists in Japan and New Zealand. The project provides education/training opportunities for two graduate students and several undergraduates. Public outreach and dissemination will occur through the MARGINS Education and Outreach program and a well-documented sample collection will be provided to the Smithsonian National Museum of Natural History Islands" collection where it will be curated indefinitely.