Constraints of the Genesis of Continental Crust via Arc Magamatism: Geology, Geochemistry, Structure and Physical Properties of the Talkeetna Arc Section South Central Alaska

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

9910899 Kelemen This project is for a multi-year, interdisciplinary study of the exposed crustal section of the Talkeetna island arc (Alaska) to address the rate and mechanism of continental growth at convergent margins. The Talkeetna arc section, particularly in the Nelchina-Tonsina region, is a crustal section through an accreted, Jurassic subduction-related magmatic arc, from volcanic, volcaniclastic and sedimentary rocks at the top to residual mantle peridotites at the base. Detailed studies of exposed, island arc sections can provide a crucial link between geophysical observations and geochemical ophiolite studies have provided an ideal counterpoint to both marine geophysics and analysis of mid-ocean ridge basalts in developing a complete picture of crustal accretion at oceanic spreading ridges, studies of arc magmatism and crustal genesis over the coming decade. The project addresses a key question regarding arc processes: What is the rate and mechanism of continental growth at convergent margins? Work on the Talkeetna section can provide crucial constraints on the composition and timing of accretion of the middle and lower arc crust, which are generally not exposed in active arcs. The P.I.s will address various aspects of crustal genesis, applying a variety of analytical techniques: 1) improved geological mapping; 2) determine deformation history of lower crustal rocks, look for faults and missing sections; 3) physical properties measurements on typical rocks in the section; 4) detailed investigations of residual mantle harzburgites and igneous utlramafic rocks at base of crust; 5) delineate liquid lines of descent in the arc crustal section; 6) petrological and trace element modeling; and 7) determine the P-T-t history of the lower crust. ***