Petrological Investigation of Manus Back-Arc Basin Lavas

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This is a project to continue analyses of rocks dredged from the Manus Basin, the fastest spreading back-arc basin known. The original proposal emphasized defining the tectonic structure (SeaMARC II), and sample collection together with preliminary analyses. The field program was successful, and the preliminary petrological analyses indicate that the Manus Basin lavas form two groups--a MORB type and a calc-alkaline type (CA). Support is provided to do a number of standard geochemical analyses (glass, minerals, whole-rock XRF, a variety of isotopes, volatiles), along with petrologic modeling. The various analyses will all be done on the same samples. Hope is to address a number of questions concerning fractionation controls, range of sources, origin of transitional lavas, relation of erupted lavas to tectonic setting, etc. Many of the individual analyses are to be done by others at no cost to project. The PI is to act as overall coordinator. This project is important because it will provide new information on the origin of chemical variability of rocks from a small geographic area.