Regional Geology of Mount Diablo, California: Its Tectonic Evolution on the North America Plate Boundary

Mount Diablo and the geology of the Central California Coast Ranges are the subject of a volume celebrating the Northern California Geological Society’s 75th anniversary. The breadth of research illustrates the complex Mesozoic to Cenozoic tectonic evolution of the plate boundary. Recent faulting and folding along the eastern edge of the San Andreas system have exposed in the mountain a core of Franciscan accretionary wedge complex faulted against Cretaceous and Cenozoic forearc strata. The Memoir includes papers on structure, stratigraphy, tephrochronology, zircon provenance studies, apatite fission track analyses, and foraminifera and calcareous plankton assemblages tied to Cenozoic climate events. Chapters also address the history of geologic work in the area and the resource development of oil and gas, mercury, coal, and sand, and road aggregate.
Field and petrographic reconnaissance of Franciscan complex rocks of Mount Diablo, California: Imbricated ocean floor stratigraphy with a roof exhumation fault system Available to Purchase
-
Published:September 27, 2021
- OpenGeoSci
-
Tools
- View This Citation
- Add to Citation Manager for
CitationJohn Wakabayashi, 2021. "Field and petrographic reconnaissance of Franciscan complex rocks of Mount Diablo, California: Imbricated ocean floor stratigraphy with a roof exhumation fault system", Regional Geology of Mount Diablo, California: Its Tectonic Evolution on the North America Plate Boundary, Raymond Sullivan, Doris Sloan, Jeffrey R. Unruh, David P. Schwartz
Download citation file:
ABSTRACT
Franciscan subduction complex rocks of Mount Diablo form a 8.5 by 4.5 km tectonic window, elongated E-W and fault-bounded to the north and south by rocks of the Coast Range ophiolite and Great Valley Group, respectively, which lack the burial metamorphism and deformation displayed by the Franciscan complex. Most of the Franciscan complex consists of a stack of lawsonite-albite–facies pillow basalt overlain successively by chert and clastic sedimentary rocks, repeated by faults at hundreds of meters to <1 m spacing. Widely distributed mélange zones from 0.5 to 300 m thick containing high-grade (including amphibolite and eclogite) assemblages and other exotic blocks, up to 120 m size, form a small fraction of exposures. Nearly all clastic rocks have a foliation, parallel to faults that repeat the various lithologies, whereas chert and basalt lack foliation. Lawsonite grew parallel to foliation and as later grains across foliation. The Franciscan-bounding faults, collectively called the Coast Range fault, strike ENE to WNW and dip northward at low to moderate average angles and collectively form a south-vergent overturned anticline. Splays of the Coast Range fault also cut into the Franciscan strata and Coast Range ophiolite and locally form the Coast Range ophiolite–Great Valley Group boundary. Dip discordance between the Coast Range fault and overlying Great Valley Group strata indicates that the northern and southern Coast Range fault segments were normal faults with opposite dip directions, forming a structural dome. These relationships suggest accretion and fault stacking of the Franciscan complex, followed by exhumation along the Coast Range fault and then folding of the Coast Range fault.
- basalts
- block structures
- burial
- California
- Cenozoic
- Coast Range Ophiolite
- Coast Ranges
- Contra Costa County California
- deformation
- exhumation
- exotic terranes
- faults
- field studies
- folds
- foliation
- Franciscan Complex
- Great Valley Sequence
- igneous rocks
- imbricate tectonics
- Jurassic
- marine environment
- melange
- Mesozoic
- metamorphism
- mineral assemblages
- Neogene
- ophiolite
- Paleogene
- petrography
- plate tectonics
- stratigraphic units
- subduction
- systems
- tectonics
- terranes
- Tertiary
- thickness
- United States
- volcanic rocks
- Mount Diablo