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gabbros

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  • NCGS Smartville Complex Field Trip by Dr. Eldridge Moores Stop 5 Stop 5 - layered gabbros NORTHERN CALIFORNIA GEOLOGICAL SOCIETY FIELD TRIP - Saturday, September 18, 2010, "GEOLOGY AND TECTONICS OF THE SMARTVILLE COMPLEX, NW SIERRA NEVADA, CALIFORNIA", Leader: Dr. Eldridge M. Moores, Distinguished Professor Emeritus, University of California, Davis Abstract The Smartville Complex comprises a north-trending submarine intrusive-extrusive (ophiolitic) complex, approximately 100km long by 40km wide in the northwestern Sierra Nevada Foothills. Generally from bottom to top, rocks comprise serpentinite (a few exposures), olivine gabbro, and layered gabbro, varitextured massive pyroxene and hornblende gabbro, plagiogranite, massive diabase, sheeted diabase, pillow lava, and volcaniclastic sediments. A few massive sulfide deposits are present in the volcaniclastic sediments. Rocks range from nearly undeformed--perhaps the best-preserved sheeted dikes and pillow lavas in North America--to highly schistose. Structure is complex, but rocks describe approximately a north-trending antiform that structurally overlies mélange and associated sediments of the Central Belt of the Sierra Nevada. Dikes intrude both igneous rocks and here and there Central Belt sedimentary rocks. Dikes are mostly north-trending, but curve to NE-trending towards the N. In places (Stanfield Hill, Marysville Road) the dikes are nearly undeformed, trending NNW and dipping steeply E. In other places, eg in Auburn, Oroville Dam south abutment, and along the E. side of the complex ...