Cretaceous granite and dikes, Kehoe Beach, Point Reyes National Seashore, California


ID 2976

The crystalline basement for the Point Reyes Peninsula consists of Cretaceous granite and granodiorite of the Salinian Block. Metamorphism of the granodiorite and early dark-colored (mafic) dikes produced a vertical foliation. The light-colored granodiorite, aplite, and pegmatite dikes subsequently cut these rocks. Numerous fractures and faults also cut the basement rocks.

The mineral composition, chemistry, and age of the granitic rocks in the Salinian Block are very similar to the Sierra Nevada Batholith. These similarities suggest that the Salinian Block was separated from the Sierra Nevada Batholith in southern California and transported north by the San Andreas fault system.


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