Isotopes and ages in the northern Peninsular Ranges batholith, southern California

Abstract

Strontium, oxygen and lead isotopic and rubidium-strontium geochronologic studies have been completed on Cretaceous and Jurassic (?) granitic rock samples from the northern Peninsular Ranges batholith in southern California. Many of these samples were collected systematically and studied chemically by A. K. Baird and colleagues (Baird and others, 1979). The distribution of these granitic rocks is shown in the Santa Ana, Perris, and San Jacinto Blocks, bounded by the Malibu Coast-Cucamonga, Banning, and San Andreas fault zones, and the Pacific Ocean on the map of the Peninsular Ranges batholith and surrounding area, southern California. The granitic rock names are by Baird and Miesch (1984) who used a modal mineral classification that Bateman and others (1963) used for granitic rocks in the Sierra Nevada batholith. In this classification, granitic rocks have at least 10% quartz. Boundaries between rock types are in terms of the ratio of alkali-feldspar to total feldspar: quartz diorite, 0-10%; granodiorite, 10-35%; quartz monzonite 35-65%; granite >65%. Gabbros have 0-10% quartz. Data for samples investigated are giv in three tables: samples, longitude, latitude, specific gravity and rock type (Table 1); rubidium and strontium data for granitic rocks of the northern Peninsular Ranges batholith, southern California (Table 2); U, Th, Pb concentrations, Pb and Sr initial isotopic compositions, and δ 18 O permil values for granitic rocks of the northern Peninsular Ranges batholith (table 3).