The goal of this project is to establish the existence or absence of mafic-ultramafic roots to batholiths and whether such roots can reconcile the fundamentally basaltic nature of mantle magmatism with the intermediate average composition of the crust. Two hypotheses are considered: 1) that the dense ultramafic residue founders into the mantle leaving the intermediate crustal compositions above, or 2) the residue exists below the Moho and is seismologically indistinct from mantle peridotite. The PIs will use a combination of petrology, geochemistry and geochronology on the plutons of the Central Coast Range Batholith to track changes in source, depth of origin through time and seismic and gravity data to image the present state of the lithosphere. The Central Coast Range Batholith (CCRB) in British Columbia is a very good location for this study. It is a very large batholith which is relatively young and has not had a protracted tectonic history. It's rugged topography gives access to depth profiles of 20 to 25 km.
