Coupled Sr-O isotope variations as an indicator of source heterogeneity for the Northern Peninsular Ranges batholith

Primary δ^(18)O values for tonalitic rocks from the San Jacinto Intrusive Complex range from +9.0 to +10.6; initial ^(87)Sr/^(86)Sr for the same samples varies from 0.7058 to 0.7076. Rocks with low δ^(18)O tend to have higher initial ^(87)Sr/^(86)Sr. The majority of samples have a limited range of δ^(18)O values (+10.0–+10.4) that is anticorrelated with colour index; this variation is compatible with crystallization of rocks with varying mineral abundances from an homogeneous (for oxygen) reservoir. More mafic rocks show a large range of δ^(18)O values, reflecting original variations in source material compositions. The combined Sr-O isotope data demonstrate that three or more distinct components were involved in the genesis of these rocks; these three components are also seen in batholithic rocks from the Mojave Block and Sierra Nevada to the north. These data are interpreted as indicating a 0–35% (oxygen atom basis) contribution to the San Jacinto rocks from an old continental lithosphere source.