Geochronology, isotopic characteristics, and paleogeography of parts of the Salinian block of California

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:5967975

James, E W

Uranium-lead and Rb-Sr geochronology and isotopic characteristics clarify the geologic history and origin of the Salinian block. U-Pb zircon dates on plutons from the northern Santa Cruz Mountains fall into two age groups; an older foliated group with problematic ages greater than about 108 Ma and a younger undeformed group with ages between 103 and about 92 Ma. U-Pb dates on zircon from the San Emigdio Igneous Complex and Logan gabbro indicate that these rocks are about 161 Ma old. This substantiates earlier correlations and about 305 km of slip on the northern San Andreas fault. Correlation of clasts in the Gualala formation with the San Emigdio complex and the consequent 550 km slip estimate for the San Andreas fault appear unwarranted based on U-Pb zircon ages > 161 Ma from gabbro clasts and recognition of alternative cobble sources. Reconnaissance isotopic data from the metamorphic rocks of the Salinian block indicates Late Cretaceous metamorphism. Comparison of Rb/Sr isotopic characteristics with other Mesozoic and pre-Mesozoic rocks suggests a Mesozoic depositional age for the Sierra de Salinas schist and a possible Paleozoic or Precambrian age for Sur Series rocks. Precambrian gneisses crop out in the southeastern Salinian block suggesting an affinity between the Salinian block and rocks in the San Bernardino and San Gabriel Mountains. Salinian age and isotopic data are indistinguishable from the rest of the California batholithic belt. Similarities in geologic history between basement rocks in the Salinian block, Peninsular Ranges, southern Sierra Nevada, San Bernardino, and San Gabriel Mountains are striking and cast a shadow on hypotheses that make the Salinian block an exotic, far-traveled terrane.

• Research Organization: California Univ., Santa Barbara (USA)
• OSTI ID: 5967975
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
ACTINIDES
AGE ESTIMATION
ALKALI METALS
ALKALINE EARTH METALS
BASEMENT ROCK
CALIFORNIA
DEPOSITION
ELEMENTS
FEDERAL REGION IX
GABBROS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GNEISSES
IGNEOUS ROCKS
ISOTOPE DATING
LEAD
METALS
METAMORPHIC ROCKS
METAMORPHISM
MOUNTAINS
NORTH AMERICA
ORIGIN
PLUTONIC ROCKS
ROCKS
RUBIDIUM
SCHISTS
STRONTIUM
URANIUM
USA