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Kinematic evidence for extensional unroofing of the Franciscan Complex along the Coast Range Fault, Northern Diablo Range, California

December 31, 1992

Franciscan metagraywacke immediately below the Del Puerto ophiolite, an outlier of the Coast Range ophiolite in the northern Diablo Range, was sheared during top‐to‐the‐east displacement on the Coast Range fault. This represents normal faulting and extensional offset. It was accompanied by attenuation of the Coast Range ophiolite and Great Valley sequence in the hanging wall along layer‐parallel normal faults that sole into the Coast Range fault. Extension occurred as the Franciscan Complex moved relatively west, out from under North American lithosphere and across the subducting ocean plate below. This effected a lengthening and thinning in the wedge of material above the down‐going plate, presumably in response to instability brought about by subduction shallowing (Krueger and Jones, 1989) and accretion of the Franciscan Central belt in the latest Cretaceous to early Paleocene. As a result, blueschist facies terranes of the uppermost part of the Franciscan Complex are now juxtaposed directly against hanging wall units that bear only low‐grade metamorphism.

Publication Year 1992
Title Kinematic evidence for extensional unroofing of the Franciscan Complex along the Coast Range Fault, Northern Diablo Range, California
DOI 10.1029/91TC01880
Authors T.A. Harms, A. S. Jayko, M. Clark Blake
Publication Type Article
Publication Subtype Journal Article
Series Title Tectonics
Index ID 70197712
Record Source USGS Publications Warehouse
USGS Organization Geology, Minerals, Energy, and Geophysics Science Center