Petrology and Geochemistry of Accreted Oceanic Crust in     Northern California
{'Code': '06030103', 'Directorate': {'Abbreviation': 'GEO', 'LongName': 'Directorate For Geosciences'}, 'Division': {'Abbreviation': 'EAR', 'LongName': 'Division Of Earth Sciences'}}
{'SignBlockName': 'Jane M. Ernst', 'PO_EMAI': None, 'PO_PHON': None}
The Coast Range ophiolite (CRO) of California comprises one                of the most extensive tracts of oceanic crust in the western                    Cordillera, and forms the basement which underlies fore-arc                     sediments of the Great Valley sequence.  Radiometric age data                   show that the CRO formed in a relatively brief time span between                155-165 million years ago, just prior to the Nevadan orogeny.                   The CRO and its correlatives form an important tectonic element                 in the western Cordillera, and understanding its evolution is                   central to unraveling the tectonic evolution of western North                   America.                                                                             Older models of ophiolite petrogenesis are commonly based on               the assumption that these bodies form during a single, long-lived               magmatic cycle, with or without the periodic influx of primitive                magma.  However, recent studies of well-exposed Tethyan                         ophiolites (Troodos, Semail) show that at least two distinct                    magmatic episodes are required to form these massifs.  These                    episodes are represented by volcanic units which are                            geochemically distinct, and by younger, commonly ultramafic                     plutonic suites that intrude older deformed gabbros.  These                     studies document the importance of multi-stage magmatic                         histories in the development of ophiolites, and imply that their                tectonic evolution must occur in a dynamic, rapidly evolving                    tectonic environment.                                                                The Elder Creek remnant of the CRO comprises the only                      complete ophiolite in northern California.  Preliminary                         geochemical data and reconnaissance field surveys suggest that                  this ophiolite had a complex magmatic history, and that at least                two and possibly three distinct magmatic suites are present.                    Evidence includes (for the plutonic rocks) gabbro pegmatite dikes               which cross-cut layered cumulates, and laminated (deformed?)                    gabbros occur as clasts in agmatite breccias and (for the                       volcanic rocks) the occurrence of volcanic studies with                         different geochemical signatures.  Relationships between these                  magmatic suites are uncertain, but one of the volcanic suites may               be related to the Stonyford complex.  The Stonyford remnant of                  the CRO lies only 35 miles farther south along strike, but it                   displays differences in its petrology, geochemistry, and                        structural relationships which require that it formed in tectonic               setting distinct from the Elder Creek ophiolite.                                     It is proposed to use field relationships, petrology, and                  geochemistry to unravel the contrasting geologic histories of                   these two ophiolite fragments, their magmatic evolution, and how                they came to be juxtaposed in the same tectonic position.  I plan               to focus in particular on the role of multi-stage magmatic                      processes in ophiolite petrogenesis.  Some of the variations                    observed probably result from tectonic juxtaposition of                         originally unrelated rocks, but others must result from changes                 in magma composition through time within a single ophiolite                     spreading center.
{'FirstName': 'John', 'LastName': 'Shervais', 'PI_MID_INIT': 'W', 'PI_SUFX_NAME': None, 'PI_FULL_NAME': 'John W Shervais', 'EmailAddress': 'john.shervais@usu.edu', 'NSF_ID': '000453809', 'StartDate': '01/01/1989', 'EndDate': None, 'RoleCode': 'Principal Investigator'}
{'Name': 'University of South Carolina at Columbia', 'CityName': 'COLUMBIA', 'ZipCode': '292083403', 'PhoneNumber': '8037777093', 'StreetAddress': '1600 HAMPTON ST', 'StreetAddress2': None, 'CountryName': 'United States', 'StateName': 'South Carolina', 'StateCode': 'SC', 'CONGRESSDISTRICT': '06', 'CONGRESS_DISTRICT_ORG': 'SC06', 'ORG_UEI_NUM': 'J22LNTMEDP73', 'ORG_LGL_BUS_NAME': 'UNIVERSITY OF SOUTH CAROLINA', 'ORG_PRNT_UEI_NUM': 'J22LNTMEDP73'}
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{'Code': '1572', 'Text': 'Tectonics'}
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