U-Pb zircon geochronology of rocks in the Salinas Valley region of California; a reevaluation of the crustal structure and origin of the Salinian Block

The Salinian block in the Salinas Valley region of central California consists of arc granitic and metasedimentary rocks (schist of Sierra de Salinas) sandwiched between coeval high-pressure, low-temperature melange belts. U-Pb zircon ages of three granitic plutons from this region range from 88 to...

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Bibliographic Details
Published in:Geology (Boulder) 2003-06, Vol.31 (6), p.517-520
Main Authors: Barth, Andrew P, Wooden, Joseph L, Grove, Marty, Jacobson, Carl E, Pedrick, Jane N
Format: Article
Language:English
Subjects:
absolute age
Ar/Ar
block structures
California
Cretaceous
crust
dates
faults
Geochronology
Geology
Mesozoic
metamorphic rocks
metasedimentary rocks
nesosilicates
orthosilicates
Salinas Valley
Salinian Block
schists
Sierra de Salinas
silicates
Structural geology
systems
tectonics
U/Pb
United States
Upper Cretaceous
zircon
zircon group
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Summary:The Salinian block in the Salinas Valley region of central California consists of arc granitic and metasedimentary rocks (schist of Sierra de Salinas) sandwiched between coeval high-pressure, low-temperature melange belts. U-Pb zircon ages of three granitic plutons from this region range from 88 to 82 Ma, and coexisting biotite yielded 40Ar/39Ar cooling ages of 76-75 Ma. The U-Pb ages from detrital zircons indicate derivation of the protolith of the schist from a 117-81 Ma igneous provenance. Muscovite and biotite 40Ar/39Ar cooling ages of 72-68 Ma from the nearby schist are distinctly younger than those from the granitic plutons. These data indicate that deposition and metamorphism of the schist occurred after emplacement of adjacent granitic rocks, contradicting the prevailing view that the schist comprises the local framework for the Salinian arc. We propose that the schist of Sierra de Salinas was thrust beneath the Salinian magmatic arc along a Campanian thrust fault that has not been recognized. This hypothesis implies that the Salinian arc originated as a klippe of basement rocks derived from the vicinity of the western Mojave Desert. Thrusting initiated southeastward-migrating Laramide tectonism of a style similar to that which formed the Vincent thrust and the latest Cretaceous and Paleocene Pelona and Orocopia Schists of southern California and southwestern Arizona.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(2003)031<0517:UZGORI>2.0.CO;2