GEOLOGY OF THE CUESTA RIDGE OPHIOLITE REMNANT NEAR SAN LUISOBISPO, CALIFORNIA: EVIDENCE FOR THE TECTONIC SETTINGAND ORIGIN OF THE COAST RANGE OPHIOLITEbyCameron A. SnowA thesis submitted in partial fulfillmentof the requirements for the degreeof MASTER OF SCIENCEinGeologyApproved:_________________________ _________________________John W. Shervais Bradley D. RittsMajor Professor Committee Member_________________________ _________________________Donald W. Fiesinger Thomas KentCommittee Member Dean of Graduate StudiesUTAH STATE UNIVERSITYLogan, Utah2002

iiiABSTRACTGeology of the Cuesta Ridge Ophiolite Remnant near San Luis Obispo, California:Evidence for the Tectonic Setting and Origin of the Coast Range OphiolitebyCameron A. Snow, Master of ScienceUtah State University, 2002Major Professor: Dr. John W. ShervaisDepartment: GeologyThe Cuesta Ridge ophiolite is one of the best-preserved remnants of mid-Jurassicophiolite in California. Geologic mapping and petrologic studies show that it comprises(1) harzburgite mantle tectonite, (2) dunite-rich mantle transition zone (MTZ), (3)wehrlite and pyroxenite, (4) isotropic gabbro, (5) sheeted dike/sill complex, (6) volcanicrocks (7) late-stage dikes and flows, and (8) tuffaceous radiolarian chert.The sheeted dike/sill complex is dominated by quartz diorite, with significant modalquartz and hornblende. The volcanic section is dominated by arc tholeiite and boniniticlavas. Boninites, with high MgO, Cr, and Ni comprise 40% of the volcanic rocks. Late-stage dikes and lava flows below the overlying chert, have a MORB-like affinity.These data suggest formation in a supra-subduction zone setting with three stages of arc-related magmatism before late-stage MORB magmatism. I infer formation above the