DOCSLIB.ORG

RESEARCH Subduction, Accretion, and Exhumation of Coherent

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
RESEARCH Subduction, Accretion, and Exhumation of Coherent RESEARCH Subduction, accretion, and exhumation of coherent Franciscan blueschist-facies rocks, northern Coast Ranges, California William L. Schmidt and John P. Platt UNIVERSITY OF SOUTHERN CALIFORNIA, EARTH SCIENCES DEPARTMENT, 3651 TROUSDALE PKWY, LOS ANGELES, CALIFORNIA 90089, USA ABSTRACT We present structural data and cross sections from four transects that together cover much of the Eastern Belt of the Franciscan accretion- ary complex. The westernmost, Middle Eel transect includes jadeite-lawsonite facies rocks (the Taliaferro Metamorphic Complex, TMC) intercalated with lawsonite-albite facies metagreywacke. The TMC shows subduction-related imbricate thrusting, refolded by upright folds with amplitudes of 100–1500 m, and it is cut by abundant normal faults that contributed to exhumation. East of the Coast Ranges divide, three linked transects along Thomes Creek cover the transition from lawsonite-albite facies metagreywackes to the blueschist facies South Fork Mountain Schist. The western section shows thick-bedded metagreywacke intercalated with broken formation, deformed by NW- vergent folds and associated thrusts and pressure-solution cleavage, and intensively dissected by abundant low-angle normal faults. In the central section, thin-bedded metagreywacke, broken formation, and conglomerate show an early foliation and folds overprinted by E-vergent folds and crenulation cleavage. The South Fork Mountain Schist forms the easternmost section and records the most intense deformation. The dominant foliation is a differentiated crenulation cleavage that has been refolded by NW vergent folds with amplitudes of millimeters to hundreds of meters. Structural relationships in the South Fork Mountain Schist exposed in Cottonwood Creek farther north are similar to those in Thomes Creek, indicating that our observations have regional significance. All the contractional structures and ductile deformational fabrics in these transects formed under high-P low-T metamorphic conditions during subduction and accre- tion, and the dominant deformation mechanism was pressure solution. Exhumation was achieved primarily by intensive normal faulting on the outcrop scale, and normal sense motion on the Coast Range fault. This paper provides the first documentation of syn-subduction normal faulting within the Franciscan Complex. LITHOSPHERE; v. 10; no. 2; p. 301–326 | Published online 1 March 2018 https://doi.org/10.1130/L697.1 INTRODUCTION may produce large-scale thrust-sheets (Wakabayashi, 1992) or duplexes (Kimura et al., 1996). Exhumation has variously been attributed to return The internal structure of accretionary complexes is poorly known and flow in a subduction channel (Cloos and Shreve, 1988), wedge extrusion understood: most active examples are largely or completely submerged, (Maruyama et al., 1996), normal faulting in the upper part of the accre- and ancient examples are commonly strongly modified by later events tionary wedge, or in the overlying fore-arc basin (Platt, 1986; Jayko et al., such as continent or arc collision. The problem is compounded by the fact 1987; Harms et al., 1992; Wakabayashi and Unruh, 1995; Constenius et that accretionary complexes are commonly largely composed of relatively al., 2000; Schemmann et al., 2008; Unruh et al., 2007), or erosion (Feehan monotonous greywacke sandstone and shale sequences, without well-devel- and Brandon, 1999; Ring and Brandon, 1999; Ring, 2008). oped lithostratigraphy, and with complicated and disruptive structural styles. The internal structure of the Franciscan Complex in California is This hinders field investigations of emergent examples as well as seismic particularly poorly known, in part because of the abundance of highly studies of currently active complexes in submerged fore-arcs. In spite of this, disrupted rocks generally referred to as mélange, and in part because of some excellent seismic studies have demonstrated that the frontal regions poor exposure. The aim of this paper is to present detailed field relation- of accretionary wedges are dominated by imbricate thrusting (Davey et al., ships along a transect across the relatively coherent eastern belt of the 1986; Davis and Hyndman, 1989; Moore et al., 1990; Morgan and Karig, Franciscan in well-exposed river sections in the northern Coast Ranges, 1995), and this has been confirmed by detailed studies of some well-exposed and to discuss the significance of the structure in terms of subduction, emergent examples (Moore and Karig, 1980; Wahrhaftig, 1984; Platt et al., underplating, and exhumation. 1988; Meneghini and Moore, 2007, Wakabayashi, 2017). The structure of the more deeply buried interiors of accretionary wedges is less well docu- GEOLOGIC SETTING mented, and in particular the processes driving exhumation of these rocks remain controversial. The structure in the base of the accretionary wedge is The Franciscan Complex is the archetypal accretionary complex likely to be dominated by the process of subcretion or underplating, which formed at a convergent plate boundary (Bailey et al., 1964; Ernst, 1970; LITHOSPHERE© 2018 The Authors. | Volume Gold 10Open | Number Access: 2 This | www.gsapubs.org paper is published under the terms of the CC-BY-NC license. 301 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/301/4098600/301.pdf by guest on 26 September 2021 SCHMIDT AND PLATT Wakabayashi, 1999), and reflects the subduction of tens of thousands of The Eastern Belt km of oceanic lithosphere along the western margin of North America from mid-Jurassic to mid-Tertiary time. The oceanic lithosphere carried The Eastern Belt of the Franciscan includes large tracts of lawson- with it seamounts and a pelagic sedimentary cover, and at times accumu- ite-albite facies siliciclastic rocks with a fairly coherent structure, some lated great thicknesses of clastic sediment in a trench environment, and substantial bodies of mélange, and a number of large sheets or slabs of much of this material was scraped off and accreted to form the accre- blueschist-facies metasediment and metabasalt (Suppe, 1973; Brown and tionary wedge. Some was accreted at shallow depths near the trench, but Ghent, 1983; Bröcker and Day, 1995). The largest of these thrust sheets some was carried beneath the wedge, and underplated at depths of 20–40 is the South Fork Mountain Schist (Blake et al., 1967), which is several km, where it was metamorphosed under high-pressure–low-temperature km thick and extends ~250 km along strike on the eastern margin of the (high-P/low-T) conditions (Ernst, 1971). Overall, the Franciscan comprises Franciscan. This is the largest coherent body of blueschist-facies rock in ~80% greywacke sandstone and shale, the remainder being predominantly the northern Coast Ranges, and is characterized by a very strong schistose mafic volcanic rocks and minor amounts of radiolarian chert and pelagic fabric in both metapelitic and metabasaltic rocks (Blake et al., 1967). limestone (Bailey et al., 1964). Perhaps as much as 30% of the outcrop Suppe (1973) mapped a large area of the eastern belt, encompassing area of the Franciscan shows a block-in-matrix texture, generally referred most of the area discussed in this paper. He distinguished two broad to as broken formation or mélange (Hsü, 1968). The matrix is commonly “facies” within the siliciclastic rocks: predominantly thick-bedded grey- shale, usually with a scaly fabric; the blocks, which may vary in size from wacke sandstones and shales, and scaly clay mélange or broken formation. a few mm to tens or even hundreds of m, consist mainly of greywacke He also identified a fault-bounded sheet of jadeite-bearing blueschist- sandstone in broken formation, but may include volcanic rocks, chert, facies metasediments and metabasalt, which he named the Taliaferro eclogite, garnet amphibolite, and blueschist, in which case the rock is metamorphic complex. This lies to the west of, and appears to be distinct referred to as mélange. Mélange and broken formation have variously from, the South Fork Mountain Schist, and appears to be intercalated with been interpreted as olistrostromes, mass flows, or debris flows of sedi- lower-pressure lawsonite-albite facies rocks. Suppe identified the lower mentary origin (Cowan, 1985; Wakabayashi, 2011, 2015; Platt, 2015), tectonic boundary of the South Fork Mountain Schist as a major thrust, or as a result of tectonic processes such as return flow in the subduction the Log Spring thrust, separating it from lower grade rocks beneath it. channel (Cloos, 1982). Suppe’s cross sections show the South Fork Mountain Schist and its The Franciscan Complex is bounded to the east by the mid-Jurassic basal thrust dipping steeply east beneath the Coast Range fault, but flat- Coast Range ophiolite. This represents the oceanic crust on the deformed tening westward, so that they intersect the topography near the crest of leading edge of the North American plate (Hopson et al., 2008), and is the Coast Range (Fig. 2). overlain by fore-arc basin sediments of the Great Valley Group (Dickin- Subsequent mapping (e.g., Worrall, 1981; Blake and Jayko, 1983) led son et al., 1996). Neither the Coast Range ophiolite nor the Great Valley to the distinction of a number of lithotectonic units, made up of greywacke Group shows significant metamorphism. They are separated from the sequences, mélange, or broken formation, separated by major faults, and Franciscan Complex by the Coast Range fault, which dips steeply E Jayko and Blake (1989) then subdivided the
Load more

Recommended publications
  • Unstable Slopes in the Franciscan Complex Terrane: Lessons Learned from Urban Quarry Slopes in the San Francisco Bay Area
    UNSTABLE SLOPES IN THE FRANCISCAN COMPLEX TERRANE: LESSONS LEARNED FROM URBAN QUARRY SLOPES IN THE SAN FRANCISCO BAY AREA Ted M. Sayre1 & John M. Wallace2 1Cotton, Shires & Associates, Inc., Consulting Engineers and Geologists, 330 Village Lane, Los Gatos, CA 95030 ([email protected]) 1Cotton, Shires & Associates, Inc., Consulting Engineers and Geologists, 330 Village Lane, Los Gatos, CA 95030 ([email protected]) Abstract: As the need for urban living space intensifies, an increasing number of former rock quarry sites have become prime real estate for residential living areas. This change in land use can result in inappropriate and potentially catastrophic consequences when residential structures are placed in close proximity to unstable quarry slopes that were not adequately investigated prior to development. Examples of this have occurred on the San Francisco peninsula where recent slope failures along several quarry faces serve as a testament to the variability of the Franciscan Complex terrane and the unique set of failure mechanisms associated with a given Franciscan rock type, underscoring the importance of a thorough geologic assessment prior to development. In two presented case studies, residential developments were adversely impacted by recent rock slope failures. Incomplete characterization of site geologic conditions and inadequate identification of critical slope failure mechanisms led to unsatisfactory setbacks and/or ineffective mitigation designs. The Knockash Hill development in San Francisco is underlain by thinly-bedded “ribbon” chert of the Franciscan Complex that was previously mined for roadway aggregate. The steep quarried slope, located immediately above new residential units, presented an excellent geologic exposure of bedded chert that displayed adversely oriented discontinuities and weak shale interbeds.
    [Show full text]
  • Geologic Gems of California's State Parks
    STATE OF CALIFORNIA – EDMUND G. BROWN JR., GOVERNOR NATURAL RESOURCES AGENCY – JOHN LAIRD, SECRETARY CALIFORNIA GEOLOGICAL SURVEY DEPARTMENT OF PARKS AND RECREATION – LISA MANGAT, DIRECTOR JOHN D. PARRISH, Ph.D., STATE GEOLOGIST DEPARTMENT OF CONSERVATION – DAVID BUNN, DIRECTOR PLATE 1 The rugged cliffs of Del Norte Coast Redwoods State Park are composed of some of California’s Bio-regions the most tortured, twisted, and mobile rocks of the North American continent. The California’s Geomorphic Provinces rocks are mostly buried beneath soils and covered by vigorous redwood forests, which thrive in a climate famous for summer fog and powerful winter storms. The rocks only reveal themselves in steep stream banks, along road and trail cut banks, along the precipitous coastal cliffs and offshore in the form of towering rock monuments or sea stacks. (Photograph by CalTrans staff.) Few of California’s State parks display impressive monoliths adorned like a Patrick’s Point State Park displays a snapshot of geologic processes that have castle with towering spires and few permit rock climbing. Castle Crags State shaped the face of western North America, and that continue today. The rocks Park is an exception. The scenic beauty is best enjoyed from a distant exposed in the seacliffs and offshore represent dynamic interplay between the vantage point where one can see the range of surrounding landforms. The The Klamath Mountains consist of several rugged ranges and deep canyons. Klamath/North Coast Bioregion San Joaquin Valley Colorado Desert subducting oceanic tectonic plate (Gorda Plate) and the continental North American monolith and its surroundings are a microcosm of the Klamath Mountains The mountains reach elevations of 6,000 to 8,000 feet.
    [Show full text]
  • Multi-Stage Origin of the Coast Range Ophiolite, California: Implications for the Life Cycle of Supra-Subduction Zone Ophiolites
    International Geology Review, Vol. 46, 2004, p. 289–315. Copyright © 2004 by V. H. Winston & Son, Inc. All rights reserved. Multi-Stage Origin of the Coast Range Ophiolite, California: Implications for the Life Cycle of Supra-Subduction Zone Ophiolites JOHN W. S HERVAIS,1 Department of Geology, Utah State University, 4505 Old Main Hill, Logan, Utah 84322-4505 DAVID L. KIMBROUGH, Department of Geological Sciences, San Diego State University, San Diego California 92182-1020 PAUL RENNE, Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709 and Department of Earth and Planetary Science, University of California, Berkeley, California 94720 BARRY B. HANAN, Department of Geological Sciences, San Diego State University, San Diego California 92182-1020 BENITA MURCHEY, United States Geological Survey, 345 Middlefield Road, Menlo Park California 94025 CAMERON A. SNOW, Department of Geology, Utah State University, 4505 Old Main Hill, Logan, Utah 84322-4505 and Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305 MARCHELL M. ZOGLMAN SCHUMAN,2 AND JOE BEAMAN3 Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208 Abstract The Coast Range ophiolite of California is one of the most extensive ophiolite terranes in North America, extending over 700 km from the northernmost Sacramento Valley to the southern Trans- verse Ranges in central California. This ophiolite, and other ophiolite remnants with similar mid- Jurassic ages, represent a major but short-lived episode of oceanic crust formation that affected much of western North America. The history of this ophiolite is important for models of the tectonic evolution of western North America during the Mesozoic, and a range of conflicting interpretations have arisen.
    [Show full text]
  • Polyphase Deformation in San Miguel Las Minas, Northern
    POLYPHASE DEFORMATION IN SAN MIGUEL LAS MINAS, NORTHERN ACATLAN COMPLEX, SOUTHERN MEXICO A thesis presented to the faculty of the Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Sciences Brent J. Barley August 2006 This thesis entitled POLYPHASE DEFORMATION IN SAN MIGUEL LAS MINAS, NORTHERN ACATLAN COMPLEX, SOUTHERN MEXICO by BRENT J. BARLEY has been approved for the Department of Geological Sciences and the College of Arts and Sciences by R. Damian Nance Professor of Geological Sciences Benjamin M. Ogles Dean, College of Arts and Sciences Abstract BARLEY, BRENT J., M.S., August 2006, Geological Sciences POLYPHASE DEFORMATION IN SAN MIGUEL LAS MINAS, NORTHERN ACATLAN COMPLEX, SOUTHERN MEXICO (58 pages) Director of Thesis: R. Damian Nance Mapping in the northern part of the Acatlán Complex (southern Mexico) has distinguished two lithological units: a high-grade unit assigned to the Piaxtla Suite, and a low-grade unit assigned to the Cosoltepec Formation. Two major Paleozoic tectonothermal events have been identified in these rocks. The first event produced a penetrative deformational fabric (SPS1) parallel to a compositional banding during blueschist and amphibolite facies metamorphism, which has recently been dated as ~346 Ma in a neighboring area, and a greenschist overprint during exhumation. The second event, which is recorded in both the Piaxtla Suite and Cosoltepec Formation, produced two penetrative deformational fabrics under subgreenschist metamorphic conditions. The first, high-grade tectonothermal event accompanied closure of the Rheic Ocean and tectonic juxtapositioning of the two units during exhumation of the high-grade unit in the Devono-Carboniferous.
    [Show full text]
  • Facies and Mafic
    Metamorphic Facies and Metamorphosed Mafic Rocks l V.M. Goldschmidt (1911, 1912a), contact Metamorphic Facies and metamorphosed pelitic, calcareous, and Metamorphosed Mafic Rocks psammitic hornfelses in the Oslo region l Relatively simple mineral assemblages Reading: Winter Chapter 25. (< 6 major minerals) in the inner zones of the aureoles around granitoid intrusives l Equilibrium mineral assemblage related to Xbulk Metamorphic Facies Metamorphic Facies l Pentii Eskola (1914, 1915) Orijärvi, S. l Certain mineral pairs (e.g. anorthite + hypersthene) Finland were consistently present in rocks of appropriate l Rocks with K-feldspar + cordierite at Oslo composition, whereas the compositionally contained the compositionally equivalent pair equivalent pair (diopside + andalusite) was not biotite + muscovite at Orijärvi l If two alternative assemblages are X-equivalent, l Eskola: difference must reflect differing we must be able to relate them by a reaction physical conditions l In this case the reaction is simple: l Finnish rocks (more hydrous and lower MgSiO3 + CaAl2Si2O8 = CaMgSi2O6 + Al2SiO5 volume assemblage) equilibrated at lower En An Di Als temperatures and higher pressures than the Norwegian ones Metamorphic Facies Metamorphic Facies Oslo: Ksp + Cord l Eskola (1915) developed the concept of Orijärvi: Bi + Mu metamorphic facies: Reaction: “In any rock or metamorphic formation which has 2 KMg3AlSi 3O10(OH)2 + 6 KAl2AlSi 3O10(OH)2 + 15 SiO2 arrived at a chemical equilibrium through Bt Ms Qtz metamorphism at constant temperature and =
    [Show full text]
  • Geology the Geotrail Follows Rocks Exposed on the Beaches South of Port Macquarie
    Geology The Geotrail follows rocks exposed on the beaches south of Port Macquarie. These rocks record a fascinating story involving the migration of an oceanic plate away from a mid-ocean ridge (oceanic spreading ridge) to a subduction zone about 500 million years ago (Figures 1, 2). Back then, our continent was part of a supercontinent called Gondwana which was located near the Equator (Figure 3). Since then, this supercontinent has migrated and broken up, with the Australian continent eventually reaching its current position (Figure 2S). To imagine this process of breaking up and migration, think of the way ice sheets in Antarctica crack and float across the ocean carried by ocean currents. Figure 1 shows the migration of oceanic crust away from a mid-ocean ridge exuding basalt (mid ocean ridge basalt - MORB; Shelly Beach) and down the subduction zone (Rocky Beach). Figure 2 Geological Time Scale Walking the geotrail allows you to track the migration of tectonic plates, observe how the rocks change, and learn about the setting in which they formed. At Shelly Beach (Stop 1), are dark rocks called basalt that are thought to have formed close to a spreading ridge (the boundary between two divergent tectonic plates; Figures 1S, 4) because their chemical composition is similar to mid-oceanic ridge basalts (Och 2007). The Mid-Atlantic Ridge that divides the North American plate from the African plate is an example of this type of plate border (Figure 4). Figure 3 shows the supercontinent Gondwana and the Australian continent as part of Gondwana. The Australian continent was at the Equator at this time.
    [Show full text]
  • Table of Contents. Letter of Transmittal. Officers 1910
    TWELFTH REPORT OFFICERS 1910-1911. OF President, F. G. NOVY, Ann Arbor. THE MICHIGAN ACADEMY OF SCIENCE Secretary-Treasurer, GEO. D. SHAFER, East Lansing. Librarian, A. G. RUTHVEN, Ann Arbor. CONTAINING AN ACCOUNT OF THE ANNUAL MEETING VICE-PRESIDENTS. HELD AT Agriculture, CHARLES E. MARSHALL, East Lansing. Geography and Geology, W. H. SHERZER, Ypsilanti. ANN ARBOR, MARCH 31, APRIL 1 AND 2, 1910. Zoology, A. S. PEARSE, Ann Arbor. Botany, C. H. KAUFFMAN, Ann Arbor. PREPARED UNDER THE DIRECTION OF THE Sanitary and Medical Science, GUY KIEFER, Detroit. COUNCIL Economics, H. S. SMALLEY, Ann Arbor. BY PAST-PRESIDENTS. GEO. D. SHAFER DR. W. J. BEAL, East Lansing. Professor W. H. SHERZER, Ypsilanti. BRYANT WALKER, ESQ. Detroit. BY AUTHORITY Professor V. M. SPALDING, Tucson, Arizona. LANSING, MICHIGAN DR. HENRY B. BAKER, Holland. WYNKOOP HALLENBECK CRAWFORD CO., STATE PRINTERS Professor JACOB REIGHARD, Ann Arbor. 1910 Professor CHARLES E. BARR, Albion. Professor V. C. VAUGHAN, Ann Arbor. Professor F. C. NEWCOMBE, Ann Arbor. TABLE OF CONTENTS. DR. A. C. LANE, Tuft's College, Mass. Professor W. B. BARROWS, East Lansing. DR. J. B. POLLOCK, Ann Arbor. Letter of Transmittal .......................................................... 1 Professor M. H. W. JEFFERSON, Ypsilanti. DR. CHARLES E. MARSHALL, East Lansing. Officers for 1910-1911. ..................................................... 1 Professor FRANK LEVERETT, Ann Arbor. Life of William Smith Sayer. .............................................. 1 COUNCIL. Life of Charles Fay Wheeler.............................................. 2 The Council is composed of the above named officers Papers published in this report: and all Resident Past-Presidents. President's Address—Outline of the History of the Great Lakes, Frank Leverett.......................................... 3 On the Glacial Origin of the Huronian Rocks of WILLIAM SMITH SAYER.
    [Show full text]
  • DEPARTMENT of the INTERIOR U.S. GEOLOGICAL SURVEY Review of the Great Valley Sequence, Eastern Diablo Range and Northern San
    DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Review of the Great Valley sequence, eastern Diablo Range and northern San Joaquin Valley, central California by J. Alan Bartow1 and TorH.Nilsen2 Open-File Report 90-226 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 1990 , Menlo Park, California 2Applied Earth Technologies, Inc, Redwood City, California ABSTRACT The Great Valley sequence of the eastern Diablo Range and northern San Joaquin Valley consists of a thick accumulation of marine and nonmarine clastic rocks of Jurassic to early Paleocene age deposited in a forearc basin that was situated between the Sierran magmatic arc to the east and the Franciscan subduction complex to the west. In the western part of the basin, the sequence rests conformably on the Jurassic Coast Range Ophiolite or is faulted against the structurally underlying Franciscan Complex. Beneath the eastern San Joaquin Valley, the sequence unconformably onlaps igneous and metamorphic rocks of the Sierran magmatic arc. The sequence generally thickens westward to as much as 8-9 km in the Diablo Range, where it is unconformably overlain by late Paleocene and younger strata. The stratigraphy of the Great Valley sequence has been the subject of much work, but problems, particularly nomenclatural, remain. Lithostratigraphic subdivisions of the sequence have not gained widespread acceptance because of the lenticularity of most sandstone bodies, abrupt fades changes in subsurface and outcrops, and the lack of detailed subsurface information from closely spaced or deep wells.
    [Show full text]
  • Petrologic and Textural Examination of Blueschist-Facies Micaceous Schists of Syros, Greece
    PETROLOGIC AND TEXTURAL EXAMINATION OF BLUESCHIST-FACIES MICACEOUS SCHISTS OF SYROS, GREECE. Joshua W. Otis Dept. Of Geology, Amherst College, Amherst, MA, 01002 Faculty Sponsors: John T. Cheney, Tekla Harms, Amherst College INTRODUCTION The island of Syros lies in the high pressure belt of the Attico -Cycladic crystalline massif. It is composed dominantly of metasedimentary and meta-igneous rocks with local areas of melange and serpentinite zones. These rocks preserve blueschist facies mineral assemblages, although an incomplete greenschist overprint exists locally across the island. This study focuses on the semi-pelitic and calcareous schists of Syros. The schist units are interlayered with marble across the island, and are laterally continuous parallel to the strike of the foliation, with beds generally dipping 25-45° to the NE (Hecht, 1985). The schists from the north end of the island were very consistent, laterally continuous units. Over the rest of the island, the schists tended to be much more locally variable in composition, Ideally, this project aims to integrate structural, petrographic, and compositional data to characterize the nature and timing of deformation relative to mineral growth, and to place constraints on the P/T conditions experienced by semi-pelitic rocks across the island. PETROGRAPHY The north end of the island contains calcareous schists with the relatively uniform mineral assemblages of quartz + phengite ± calcite ± minor amounts of sodic amphibole, garnet, epidote, rutile, titanite, and graphite. These rocks are divisible into two main groups based on the presence or absence of calcite, forming two fairly homogenous, mappable units (~1km scale). A greenschist overprint of albite + chlorite +/- epidote typically occurs in these rocks (Fig.
    [Show full text]
  • Major Chemical Characteristics of Mesozoic Coast Range Ophiolite in California
    JOURNAL OF OF THE U.S. GEOLOGICAL SURVEY NOVEMBER-DECEMBER 1974 VOLUME 2, NUMBER 6 Scientific notes and summaries of investigations in geology, hydrology, and related fields +r U«/ fc/ U.S. DEPARTMENT OF THE INTERIOR UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC The Journal of Research is pub­ Correspondence and inquiries concerning the Jour­ 20402. Order by SD Catalog No. lished every 2 months by the U.S. nal (other than subscription inquiries and address JRGS. Annual subscription rate Geological Survey. It contains changes) should be directed to the Journal of Re­ $15.50 (plus $3.75 for foreign mail­ papers by members of the Geologi­ search, Publications Division, U.S. Geological Survey, ing). Single copy $2.75. Make cal Survey and their professional National Center 321, Reston, VA 22092. checks or money orders payable to colleagues on geologic, hydrologic, the Superintendent of Documents. topographic, and other scientific Papers for the Journal should be submitted through Send all subscription inquiries and technical subjects. regular Division publication channels. and address changes to the Superin­ tendent of Documents at the above address. Purchase orders should not be sent to the U.S. Geological Survey The Secretary of the Interior has determined that the publication of this periodical is library. necessary in the transaction of the public business required by law of this Department. Library of Congress Catalog-card Use of funds for printing this periodical has been approved by the Director of the Office No.
    [Show full text]
  • Bigbig Sursur
    CalCal PolyPoly -- PomonaPomona GeologyGeology ClubClub SpringSpring 20032003 FFieldield TTriprip BigBig SurSur David R. Jessey Randal E. Burns Leianna L. Michalka Danielle M. Wall ACKNOWLEDGEMENT The authors of this field guide would like to express their appreciation and sincere thanks to the Peninsula Geologic Society, the California Geological Survey and Caltrans. Without their excellent publications this guide would not have been possible. We apologize for any errors made through exclusion or addition of trip field stops. For more detailed descriptions please see the following: Zatkin, Robert (ed.), 2000, Salinia/Nacimiento Amalgamated Terrane Big Sur Coast, Central California, Peninsula Geological Society Spring Field Trip 2000 Guidebook, 214 p. Wills, C.J., Manson, M.W., Brown, K.D., Davenport, C.W. and Domrose, C.J., 2001, LANDSLIDES IN THE HIGHWAY 1 CORRIDOR: GEOLOGY AND SLOPE STABILITY ALONG THE BIG SUR COAST, California Department of Conservation Division of Mines & Geology, 43 p. 0 122 0 00' 122 0 45' 121 30 Qal Peninsula Geological Society Qal G a b i Qt la Field Trip to Salina/Nacimento 1 n R S a A n L Big Sur Coast, Central California I g N qd A e S R Qt IV E Salinas R S a lin a s Qs V Qal 101 a Qs Monterey Qc lle Qt Qp y pgm Tm Qm Seaside pgm EXPLANATION Qt Chualar Qp Qt UNCONSOLIDATED Tm pgm SEDIMENTS Qp Carmel Qal sur Qs Qal Alluvium qd CARMEL RIVER Tm Qal Point sur Qs Dune Sand Tm Lobos pgm 0 S 0 36 30 ie ' r 36 30' pgm ra Qt Quaternary non-marine d CARMEL e S terrace deposits VALLEY a Qal lin a Qt Pleistocene non-marine Tm pgm s Qc 1 Tm Tula qd rcit Qp Plio-Pleistocene non-marine qd os F ault Qm Pleistocene marine Terrace sur sur deposits qd Tm COVER ROCKS pgm qd Tm Monterey Formation, mostly qm pgm qm pgm marine biogenic and sur pgm clastic sediments middle to qdp sur qd late Miocene in age.
    [Show full text]
  • A Systematic Nomenclature for Metamorphic Rocks
    A systematic nomenclature for metamorphic rocks: 1. HOW TO NAME A METAMORPHIC ROCK Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 1/4/04. Rolf Schmid1, Douglas Fettes2, Ben Harte3, Eleutheria Davis4, Jacqueline Desmons5, Hans- Joachim Meyer-Marsilius† and Jaakko Siivola6 1 Institut für Mineralogie und Petrographie, ETH-Centre, CH-8092, Zürich, Switzerland, [email protected] 2 British Geological Survey, Murchison House, West Mains Road, Edinburgh, United Kingdom, [email protected] 3 Grant Institute of Geology, Edinburgh, United Kingdom, [email protected] 4 Patission 339A, 11144 Athens, Greece 5 3, rue de Houdemont 54500, Vandoeuvre-lès-Nancy, France, [email protected] 6 Tasakalliontie 12c, 02760 Espoo, Finland ABSTRACT The usage of some common terms in metamorphic petrology has developed differently in different countries and a range of specialised rock names have been applied locally. The Subcommission on the Systematics of Metamorphic Rocks (SCMR) aims to provide systematic schemes for terminology and rock definitions that are widely acceptable and suitable for international use. This first paper explains the basic classification scheme for common metamorphic rocks proposed by the SCMR, and lays out the general principles which were used by the SCMR when defining terms for metamorphic rocks, their features, conditions of formation and processes. Subsequent papers discuss and present more detailed terminology for particular metamorphic rock groups and processes. The SCMR recognises the very wide usage of some rock names (for example, amphibolite, marble, hornfels) and the existence of many name sets related to specific types of metamorphism (for example, high P/T rocks, migmatites, impactites).
    [Show full text]