Oxygen isotope relationships in plutonic igneous rocks of the Peninsular Ranges Batholith, southern and Baja California

Whole-rock δ¹⁸O values have been determined for 155 samples from approximately 140 plutons 1n the northern 600 km of the Peninsular Ranges batholith (fig. 1). Analyses of tonalites, granodiorites, gabbros and a few quartz monzonites are represented in crude proportion to the abundance of these rocks in the batholith. Host samples have been studied also for U-Pb zircon geochronology (Banks and Silver, 1968; Silver and others, 1968); K-Rb-Sr isotope and trace element systematics (Early and Silver, 1973); and rare earth element distributions (Gromet and Silver, 1977). All of these parameters display striking geographic regularities and profound transverse asymmetries related to the NNW-trending plutonic arc (Silver and others, 1975; Silver and Early, 1977).