Regional variations in bulk chemistry, mineralogy, and the compositions of mafic and accessory minerals in the batholiths of California
We define regional variations in mafic and accessory mineral assemblages and compositions and expand the current understanding of spatial variations in whole-rock geochemistry in the batholiths of California. In so doing, we gain new insights into the nature of magmatic source rocks and mechanisms of magma generation in volcano-plutonic arcs of active continental margins. Little-studied metaluminous to strongly peraluminous granites containing Fe-rich biotite with log(X Mg /X Fe ) F/OH and Mn in biotite and amphibole increase on a regional scale from western I-WC types to eastern I-MC and I-SC types, parallel to eastward increases in incompatible elements and decreases in compatible elements in the plutons. In contrast, the belts of western I-SCR granites and eastern I-WC quartz diorites and granodiorites disrupt the regional west-to-east systematics in both mineral and whole-rock geochemistry. Spatial variations in the Al content of amphibole are regional in scale and reflect pressures of pluton crystallization. We conclude that significant, previously unrecognized complexity exists in regional geochemical systematics in the California batholiths.