The Contact: Arc Plumes

This is one of my growing series about the Sierra Nevada of California. During the Farralon subduction under North America, water released from the slab melted the overlying mantle, and plumes of magma raised the crust, and ultimately crystallized as granite. Early magmas intruded the western metamorphic belt from 150–120 Ma, leaching gold from older oceanic arcs that was later reprecipitated in quartz veins injected into the surrounding rock. Farther east, younger magma pulsed through the continental crust to form the granitic plutons that dot the crest of the high Sierra today.