Amalgamation of metamorphic terranes in the southeastern San Gabriel Mountains, California

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

OSTI ID:6784824

May, D J

Reconnaissance and locally detailed geologic mapping and U-Pb zircon geochronology have been used to establish the style, kinematics, and timing of amalgamation of metamorphic terranes in a poorly understood region in the southeastern San Gabriel Mountains. The Cucamonga, San Antonio, and Tujunga terranes were juxtaposed along subparallel east-west trending, left-lateral ductile fault zones during emplacement of late Cretaceous granitic rocks. Displacement for each of the mylonitic fault zones was approximately several tens of kilometer and was part of a broad left-lateral shear system that was active between 90 and 81 Ma ago. The Cucamonga terrane consists of early Cretaceous granulite facies gneissic rocks. These rocks were intruded by late Cretaceous granitic rocks as the Cucamonga terrane was faulted against the San Antonio terrane. Metasedimentary pendants of the San Antonio terrane were metamorphosed under upper amphibolite facies conditions during emplacement of granitic rocks between 85 and 81 Ma ago. The San Antonio terrane was concurrently juxtaposed against the Tujunga terrane (consisting of Precambrian gneiss and Precambrian and Mesozoic intrusive rocks) to the north. No lithologic, isotopic, or structural data support suggestions that any of these rocks were accreted to North America during the Tertiary. Late Cretaceous synplutonic mylonitic deformation was followed by underthrusting of the oceanic rocks of the Baldy terrane along the Vincent thrust. After palinspastic restoration of Cenozoic fault displacements, the left-lateral mylonite belts in the southeastern San Gabriel Mountains appear to represent a tear fault within a major, synplutonic, ductile thrust system. This transcurrent zone may originally have linked west-directed thrusts in the central Transverse Ranges with those along the eastern side of the Peninsular Ranges.

• Research Organization: California Univ., Santa Barbara (USA)
• OSTI ID: 6784824
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
ACTINIDES
AGE ESTIMATION
BASEMENT ROCK
CALIFORNIA
CRETACEOUS PERIOD
DEFORMATION
ELEMENTS
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
INTRUSION
LEAD
MESOZOIC ERA
METALS
METAMORPHIC ROCKS
METAMORPHISM
MINERALS
MOUNTAINS
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
URANIUM
USA
ZIRCON
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES