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Tectonic implications of gravity and magnetic models along east-west seismic profiles across the Great Valley near Coalinga

Journal Article · · United States Geological Survey, Professional Paper; (USA)
OSTI ID:5599899
The authors have used gravity and magnetic data to compute east-west crustal models along a profile extending eastward from the San Andreas fault in the eastern Coast Ranges, through the town of Coalinga, and across the Great Valley of California. These models agree well with seismic refraction and reflection models, support the idea that the Franciscan assemblage near its contact with the Great Valley sequence was emplaced by tectonic wedging, and do not indicate the presence of a fossil subduction zone. The west half of the Great Valley is underlain by a thick, west-dipping slab of magnetic high-density rock that may be an ophiolite obducted from the west onto the continental margin during Jurassic time. Warping and faulting of this slab during deposition of the overlying Great Valley sequence created structures parallel to the basin's east side that later may have acted as barriers limiting the eastward intrusion of Franciscan wedges. Multiple wedging is implied by a mostly concealed magnetic slab, presumed to be Coast Range ophiolite, that is consistently present for a strike distance of 600 km along the contact of the Franciscan assemblage and the Great Valley sequence, and that has its west edge emplaced within the Franciscan assemblage.
OSTI ID:
5599899
Journal Information:
United States Geological Survey, Professional Paper; (USA), Journal Name: United States Geological Survey, Professional Paper; (USA) Vol. 1487; ISSN XGPPA
Country of Publication:
United States
Language:
English