Petrology and provenance of the Modelo Formation, Santa Monica Mountains, southern California: Constraints on displacement along the San Gabriel fault
- Univ. of California, Los Angeles, CA (United States). Dept. of Earth and Space Sciences
The Modelo Formation of the central and eastern Santa Monica Mountains is an Upper Miocene siliceous-diatomaceous shale and sandstone submarine-fan sequence, which was deposited in the northern Los Angeles basin. The graded, poorly sorted, and angular sandstones comprise channelized mid-fan facies deposited at middle-to-upper-bathyal depths; they are arkosic (58% feldspar) with variable amounts of matrix. Published paleocurrent data yield a south-southwest flow direction. The direction of the paleocurrents constrains the timing of deposition to be after rotation of the Transverse Ranges (after 15 Ma.) Biostratigraphic data indicate that deposition commenced during the Late Mohnian (after 10.8 Ma). QFL plots indicate that the provenance was basement uplift to transitional arc (e.g. Dickinson, 1985). The meta-igneous lithic fragments and the high feldspar content of the rocks suggest an anorthositic, gneissic, tonalitic, or mylonitic source terrane. Sandstone modes and conglomerate clasts indicate that the basal section was derived locally from the Santa Monica Slate. The upper section represents a volcanic unroofing sequence, as evidenced by decreasing volcanic lithic fragments upsection. Crowell (1982) suggested 60 km of right slip on the San Gabriel fault between 12 and 5 Ma. Palinspastic restoration places the Santa Monica Mountains immediately south of the San Gabriel Mountains, which wee the likely source for Modelo sandstones. Based on plagioclase composition (95% oligoclase and albite) of Modelo sandstone, the anorthosite body in the western San Gabriel Mountains is an unlikely source. However, a source in the mylonitic, gneissic, and tonalitic bodies of the eastern San Gabriel Mountains could explain the observed petrography. This source for the Modelo is consistent with 60 km of movement on the San Gabriel fault.
- OSTI ID:
- 5098700
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALIFORNIA
GEOLOGIC FORMATIONS
DEPOSITION
PETROLOGY
TECTONICS
SANDSTONES
GEOLOGIC FAULTS
MINERALOGY
MIOCENE EPOCH
STRATIGRAPHY
CENOZOIC ERA
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
NORTH AMERICA
ROCKS
SEDIMENTARY ROCKS
TERTIARY PERIOD
USA
580000* - Geosciences