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Fission-track ages of sphene and apatite of granitic rocks of the Salinian block, Coast Ranges, California

Journal of Research of the U.S. Geological Survey
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Abstract

Fission-track ages have been determined on apatite and sphene from granitic rocks of the Salinian block, California Coast Ranges. The 26 age determinations on sphene range between 68 and 93 m.y. The 24 age determinations on apatite have a greater variation, ranging from 3 to 74 m.y. None of the fission-track ages appear to reflect times of intrusion. The Pinnacles volcanic field of Miocene age apparently has thermally affected apatite ages in the central Gabilan and eastern Santa Lucia Ranges. Reduced apatite ages in the area between the Farallon Islands and the Monterey Peninsula may also be the result of Miocene volcanic activity, but the evidence is less conclusive. Fission-track ages on sphene correlate closely with previously determined potassium-argon ages on hornblende and biotite but show an unexplained "bimodal" age distribution, the ages in the Gabilan and Santa Lucia Ranges being slightly, but consistently, lower (avg 75 m.y.) than the ages for terrane to the north and south (avg 85 m.y.) The overall pattern of the sphene and apatite fission-track ages, distinctly different from that of the central Sierra Nevada, may be a "fingerprint" of correlative value in locating the parent terrane of the "ripped-off" Salinian block.

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Publication type Article
Publication Subtype Journal Article
Title Fission-track ages of sphene and apatite of granitic rocks of the Salinian block, Coast Ranges, California
Series title Journal of Research of the U.S. Geological Survey
Volume 4
Issue 4
Year Published 1976
Language English
Publisher U. S. Geological Survey
Description 6 p.
First page 415
Last page 420
Country United States
State California
Other Geospatial Coast Ranges, Salinian block, San Andreas fault
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