Print this pageAbstract: Elements of Tectonism Deduced from Miocene Strata, Northern Channel Islands, California
In the southern California borderland, Miocene (Zemorrian? to Luisian) conglomerate and breccia deposits on southwestern Santa Cruz Island are similar in lithology to finer grained facies on the southwesternmost part of Santa Cruz Island, and Santa Rosa and San Miguel Islands. Recognition that lithofacies become finer grained westward clarified a confusing array of stratal nomenclature used by previous workers.
The Vaqueros Formation conglomerate and breccia on Santa Cruz Island consists primarily of locally derived diorite and greenschist debris. On Santa Rosa Island it consists mainly of quartzo-feldspathic grains probably derived from a southern source of uplifted Eocene strata, as indicated by northward paleocurrent flow.
On Santa Cruz Island, the San Onofre Breccia consists of detritus derived from a Catalina Schist source terrane, characterized by abundant glaucophane schist. The coarse-grained facies of the San Onofre Breccia interfinger with fine-grained, marine sandstone and mudstone of the Rincon Formation that has been assigned to the Saucesian Stage. Fragments of blueschist and blue amphibole continue to characterize Rincon strata on the east part of Santa Rosa Island. A source for blueschist-facies rocks is not known on any of the northern Channel Islands.
AAPG Search and Discovery Article #90976©1976 AAPG-SEPM-SEG Pacific Section Meeting, San Francisco, California