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The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG

Abstract


Aspects of the Geologic History of the California Continental Borderland, 1976
Pages 53-58

Age of Plutonic Basement Rocks, Santa Cruz Island, California

James M. Mattinson, Dawn J. Hill

Abstract

The Mesozoic basement complex of Santa Cruz Island includes two main plutonic phases: the Alamos plagiogranite and the Willows plutonic complex. Isotopic ages of zircons indicate that the Willows complex is about 162 m.y. old, whereas the Alamos plagiogranite is 141 m.y. old. The petrography and age of the Willows plutonic complex suggest close affinities with the Coast Range ophiolite. The younger Alamos plagiogranite is puzzling, however; perhaps it represents an off-ridge addition to oceanic crust (Willows) formed about 20 m.y. earlier.


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