DOCSLIB.ORG

Mafic and Ultramafic Xenoliths from Volcanic Rocks of the Western United States

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mafic and Ultramafic Xenoliths from Volcanic Rocks of the Western United States Mafic and Ultramafic Xenoliths from Volcanic Rocks of the Western United States U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1443 AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the cur­ rent-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Sur­ vey publications released prior to the current year are listed in the most recent annual "Price and Availability List" Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated month­ ly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, Box 25425, Denver, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications of general in- Books of the U.S. Geological Survey are available over the terest (such as leaflets, pamphlets, booklets), single copies of Earthquakes counter at the following Geological Survey Public Inquiries Offices, all & Volcanoes, Preliminary Determination of Epicenters, and some mis- of which are authorized agents of the Superintendent of Documents: cellaneous reports, including some of the foregoing series that have gone out of print at the Superintendent of Documents, are obtainable by mail from WASHINGTON, D.C.-Main Interior Bldg., 2600 corridor, 18th and CSts.,NW. U.S. Geological Survey, Books and Open-File Reports DENVER, Colorado-Federal Bldg., Rm. 169,1961 Stout St. Federal Center, Box 25425 . LOS ANGELES, California-Federal Bldg., Rm. 7638,300 N. Denver, CO 80225 Los Angeles St. MENLO PARK, California-Bldg. 3 (Stop 533), Rm. 3128, Subscriptions to periodicals (Earthquakes & Volcanoes and 345 Middlefield Rd. Preliminary Determination of Epicenters) can be obtained ONLY from RESTON, Virginia-503 National Center, Rm. 1C402,12201 the Sunrise Valley Dr. SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105,125 Superintendent of Documents South State St. Government Printing Office SAN FRANCISCO, California-Customhouse, Rm. 504,555 Washington, D.C. 20402 Battery St. SPOKANE, Washington-U.S. Courthouse, Rm. 678, West (Check or money order must be payable to Superintendent of Docu- 920 Riverside Ave.. ments.) . ANCHORAGE, Alaska-Rm. 101,4230 University Dr. ANCHORAGE, Alaska-Federal Bldg, Rm. E-146, 701 C St. Maps For maps, address mail orders to U.S. Geological Survey, Map Distribution Maps Federal Center, Box 25286 Maps may ^ purchased over the counter at the U.S. Geologi- Denver, CO 80225 caj Survey offices where books are sold (all addresses in above list) and at the following Geological Survey offices: Residents of Alaska may order maps from ROLLA, Missouri-1400 Independence Rd. Alaska Distribution Section, U.S. Geological Survey, . DENVER Colorado-Map Distribution, Bldg. 810, Federal New Federal Building - Box 12 Center 101 Twelfth Ave., Fairbanks, AK 99701 . FAIRBANKS, Alaska-New Federal Bldg., 101 Twelfth Ave. Mafic and Ultramafic Xenoliths from Volcanic Rocks of the Western United States By H.G. WILSHIRE, C.E. MEYER, J.K. NAKATA, L.C. CALK, J.W. SHERVAIS, J.E. NIELSON, and E.G. SCHWARZMAN U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1443 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988 DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Mafic and ultramafic xenoliths from volcanic rocks of the western United States. (U.S. Geological Survey professional paper; 1443) Bibliography: p. Supt. of Docs, no.: I 19.16:1443 1. Rocks, Igneous West (U.S.) Inclusions. 2. Alkalic igneous rocks West (U.S.) 3. Rocks, Ultrabasic West (U.S.) I. Wilshire, Howard Gordon, 1926- . II. Series: Geological Survey professional paper; 1443. QE461.M234 1988 552'. 1 88-600047 For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 CONTENTS Page Abstract --------------------------- 1 Trace elements and isotopes in xenoliths and Introduction ------------------------- 2 host rocks Continued Acknowledgments --------------------- 2 Sr and Nd isotopes Continued Previous investigations ------------------- 2 Sr and Nd isotopes of megacrysts ---------- 28 Distribution and setting ------------------- 4 Problems in interpreting isotopic data -------- 28 Host rocks -------------------------- 8 Oxygen isotopes --------------------- 28 Xenoliths- -------------------------- 8 Origin and causes of variation among xenoliths ------- 28 Relations among xenolith types as indicated by composite Cognate versus accidental origin ------------- 28 xenoliths -------------------------- 12 Origin of lithologic variants within major ultramafic Proximity of mafic-ultramafic lithologies in the mantle groups ------------------------- 30 and sequence of formation --------------- 12 Salient features ------------------- 30 Systematic compositional variations in composite Physical conditions of emplacement and xenoliths ------------------------ 13 differentiation ------------------- 31 Trace elements and isotopes in xenoliths and host rocks - - - 17 Wallrock reactions and metasomatism -------- 32 Rare earth elements ------------------- 18 Origin of the main xenolith groups ------------ 35 Cr-diopside group ------------------ 18 Current concepts of mantle metasomatism: cause or effect of Composite Cr-diopside peridotite and Al-augite alkaline basaltic magmatism?- --------------- 37 pyroxenite --------------------- 20 References -------------------------- 40 Al-augite group ------------------- 20 Appendixes Mineral separates and megacrysts, all groups - - - - 22 I. Locality descriptions ----------------- 51 Problems in interpreting REE data --------- 24 II. Bulk chemical compositions and CIPW norms for host Sr and Nd isotopes- ------------------- 25 rocks ------------------------ 57 Sr isotopes of the Cr-diopside group --------- 25 III. Detailed descriptions of principal xenolith groups Sr isotopes of the Al-augite group ---------- 25 and composite xenoliths- -------------- 65 Sr isotopes of the feldspathic and bottle-green IV. Bulk chemical compositions and CIPW norms for pyroxene groups ------------------ 26 xenoliths ---------------------- 85 Sr and Nd isotopes of the Cr-diopside group ----- 26 V. Mineral analyses ------------------- 95 Sr and Nd isotopes of composite xenoliths of the VI. Systematic compositional trends of minerals in Cr-diopside and Al-augite groups ---------- 26 composite xenoliths ----------------- 131 Sr and Nd isotopes of the garnetiferous ultramafic VII. Trace element and isotope data for host rocks, group- ----------------------- 27 xenoliths, and megacrysts ------------- 167 ILLUSTRATIONS FIGURES 1-9. Maps of the Western United States showing: 1. Distribution of xenolith localities with respect to Cenozoic tectonic provinces -------------------- 3 2. Distribution of xenoliths with respect to heat-flow provinces, crustal thickness, and P-wave velocity -------- 9 3. Distribution of xenoliths in the Cr-diopside group ---------------------------------- 10 4. Distribution of xenoliths in the Al-augite group ----------------------------------- 10 5. Distribution of xenoliths with hydrous phases ------------------------------------ 11 6. Distribution of xenoliths in the feldspathic ultramafic group ---------------------------- 11 7. Distribution of xenoliths in the bottle-green pyroxene group ---------------------------- 12 8. Distribution of xenoliths in the garnetiferous ultramafic group --------------------------- 12 9. Distribution of xenoliths in the gabbroid and metagabbroid groups ------------------------- 13 in IV CONTENTS Page FIGURE 10. Alkali-silica variation of host rocks ------------------------------------------- 15 11. Chart of main xenolith groups --------------------------------------------- 16 12. Classification and nomenclature of ultramafic and gabbroic rocks --------------------------- 17 13, 14. Plots of modal compositions of xenoliths in the: 13. Cr-diopside group ------------------------------------------------- 20 14. Al-augite group -------------------------------------------------- 20 15. Photographs of Cr-diopside websterite dike in Cr-diopside Iherzolite, and Cr-diopside Iherzolite lenses in Cr-diopside websterite ------------------------------------------------------ 20 16. Schematic diagram showing sequence of emplacement of dike rocks and associated reaction zones in xenoliths - - - - 21 17-22. Photographs showing: 17. Crosscutting Cr-diopside websterite dikes in Cr-diopside Iherzolite xenolith, and crosscutting Cr-diopside websterite dikes in Cr-diopside Iherzolite, Balmuccia peridotite massif ---------------------- 22 18. Garnet pyroxenite crosscutting spinel pyroxenite layers in Cr-diopside Iherzolite, Lherz peridotite massif; Al-augite pyroxenite dikes isolating an inclusion
Load more

Recommended publications
  • Comments On'kaersutite from San Carlos, Arizona, with Comments On
    MINERALOGICAL MAGAZINE, SEPTEMBER I969, VOL. 37, NO. 287 Comments on 'Kaersutite from San Carlos, Arizona, with comments on the paragenesis of this mineral' by Brian Mason MARTIN PRINZ ~ Department of Geology, University of New Mexico, Albuquerque, New Mexico 87Io6 AND C. E. NEHRU Department of Geology, Brooklyn College, Brooklyn, New York II2~O s u MM A R Y. Electron probe analyses have been made of eight kaersutites from San Carlos, A~cizona, and one from Kakanui, New Zealand; also of olivine, clinopyroxene, ilmenite, and spinel from San Carlos. There is not as yet adequate evidence that the kaersutite is an upper mantle phase. MASON (I968a) suggests that kaersutite, as exemplified by the occurrence at San Carlos, Arizona, as well as from some other localities, may represent the amphibole phase in upper mantle rocks. The possibility of amphibole as an upper mantle phase was most clearly suggested by Oxburgh (I964) since it would help explain the alkali content of basaltic rocks, which otherwise would be derived from alkali-poor ultra- mafic mantle rocks. Since we are carrying out a detailed study of the ultramafic inclusions of the San Carlos, Arizona, locality, we would like to clarify some of the petrologic significance of the kaersutite from this area because it leads us to different conclusions from those of Mason. Hopefully, our comments will be of value to others suggesting amphibole as an upper mantle phase. San Carlos locality. The kaersutite described by Mason (I968a) in the San Carlos locality occurs as a granular aggregate of anhedral crystals, with a little inter-granular ilmenite.
    [Show full text]
  • Mantle Peridotite Xenoliths
    Earth and Planetary Science Letters 260 (2007) 37–55 www.elsevier.com/locate/epsl Mantle peridotite xenoliths in andesite lava at El Peñon, central Mexican Volcanic Belt: Isotopic and trace element evidence for melting and metasomatism in the mantle wedge beneath an active arc ⁎ Samuel B. Mukasa a, , Dawnika L. Blatter b, Alexandre V. Andronikov a a Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA b Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA Received 6 July 2006; received in revised form 3 May 2007; accepted 7 May 2007 Available online 13 May 2007 Editor: R.W. Carlson Abstract Peridotites in the mantle wedge and components added to them from the subducting slab are thought to be the source of most arc magmas. However, direct sampling of these materials, which provides a glimpse into the upper mantle beneath an active margin, is exceedingly rare. In the few arc localities where found, peridotite xenoliths are usually brought to the surface by basaltic magmas. Remarkably, the hornblende-bearing ultramafic xenoliths and clinopyroxene megaxenocrysts from El Peñon in the central Mexican Volcanic Belt were brought to the surface by a Quaternary high-Mg siliceous andesite, a rock type usually considered too evolved to be a direct product of mantle melting. The xenoliths and megaxenocrysts from El Peñon represent lithospheric mantle affected by significant subduction of oceanic lithosphere since as early as the Permian. Trace element and radiogenic isotope data we report here on these materials suggest a history of depletion by melt extraction, metasomatism involving a fluid phase, and finally, limited reaction between the ultramafic materials and the host andesite, probably during transport.
    [Show full text]
  • Depleted Spinel Harzburgite Xenoliths in Tertiary Dykes from East Greenland: Restites from High Degree Melting
    Earth and Planetary Science Letters 154Ž. 1998 221±235 Depleted spinel harzburgite xenoliths in Tertiary dykes from East Greenland: Restites from high degree melting Stefan Bernstein a,), Peter B. Kelemen b,1, C. Kent Brooks a,c,2 a Danish Lithosphere Centre, éster Voldgade 10, DK-1350 Copenhagen K, Denmark b Woods Hole Oceanographic Institution, Woods Hole, City, MA 02543, USA c Geological Institute, UniÕersity of Copenhagen, éster Voldgade 10, DK-1350 Copenhagen K, Denmark Received 28 April 1997; revised 19 September 1997; accepted 4 October 1997 Abstract A new collection of mantle xenoliths in Tertiary dykes from the Wiedemann Fjord area in Southeast Greenland shows that this part of the central Greenland craton is underlain by highly depleted peridotites. The samples are mostly spinel harzburgites with highly forsteritic olivinesŽ. Fo87± 94 , average Fo 92.7 . This, together with unusually high modal olivine contentsŽ. 70±)95% , places the Wiedemann harzburgites in a unique compositional field. Relative to depleted Kaapvaal harzburgites with comparable Fo in olivine, the Wiedemann samples have considerably lower bulk SiO2 Ž average 42.6 wt% versus 44±49 wt%. Spinel compositions are similar to those in other sub-cratonic harzburgites. Pyroxene equilibrium temperatures average 8508C, which is above an Archaean cratonic geotherm at an inferred pressure of 1±2 GPa, but low enough so that it is unlikely that the xenoliths represent residual peridotites created during Tertiary magmatism. Among mantle samples, the Wiedemann harzburgites are, in terms of their bulk composition, most similar to harzburgites from the ophiolites of Papua New GuineaŽ. PNG and New Caledonia Ž.
    [Show full text]
  • Mantle Origin and Flow Sorting of Megacryst-Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona
    Mantle Origin and Flow Sorting of Megacryst-Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1541 AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current- year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books and Maps Professional Papers, Bulletins, Water-Supply Papers, Tech­ Books and maps of the U.S. Geological Survey are available niques of Water-Resources Investigations, Circulars, publications over the counter at the following U.S. Geological Survey offices, of general interest (such as leaflets, pamphlets, booklets), single all of which are authorized agents of the Superintendent of Docu­ copies of Earthquakes & Volcanoes, Preliminary Determination of ments. Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone out of print at the Superin­ • ANCHORAGE, Alaska—4230 University Dr., Rm.
    [Show full text]
  • Kaersutite-Bearing Xenoliths and Megacrysts in Volcanic Rocks from the Funk Seamount in the Southwest Indian Ocean
    Kaersutite-bearing xenoliths and megacrysts in volcanic rocks from the Funk Seamount in the southwest Indian Ocean ARCH M. REID* AND ANTON P. LE ROEX Department of Geology, University of Cape Town, Rondebosch 7700, South Africa Abstract Eight samples (seven volcanic rocks and one quartz sandstone) have been dredged from the Funk Seamount, 60 km NW of Marion Island in the southwest Indian Ocean Oat. 46 ~ 15' S, long. 37 ~ 20' E). The volcanic rocks are fine-grained vesicular basanitoids and glass-rich volcanic breccias geochemically similar to the Marion Island lavas. Lavas and breccias contain a suite of megacryst minerals and of small polymineralic xenoliths, in both of which kaersutite is a prominent constituent. The megacryst suite comprises large unzoned single grains of kaersutite, plagioclase, pyroxene, magnetite and ilmenite, all showing textural evidence of resorption/reaction with the basanitoid host. The megacrysts have a limited range of compositions except for the plagioclase which ranges from oligoclase to labradorite. The small (2 mm to ~ 3 cm) xenoliths are mostly two-pyroxene amphibole assemblages with or without olivine, magnetite, ilmenite, plagioclase and apatite. The xenoliths show some evidence of reaction with the basanitoid host and most have undergone recrystallization and/or localised decompression melting. Xenolith and megacryst assemblages are interpreted as being associated with the formation and partial crystallization of a hydrous basanitoid melt at depth. KEYWORDS: kaersutite, amphibole, xenolith, Funk Seamount, Indian Ocean. Introduction megacrysts. Brown amphibole is a prominent con- stituent of both xenolith and megacryst suites. F U N K S E A M O U N T is a prominent seamount situa- Mantle xenoliths in abyssal lavas are rare and so ted 60 km to the NW of Marion and Prince Edward these samples are of particular interest.
    [Show full text]
  • Geology of the Saline County Xenolith and Surrounding Area
    A.G.E.S. Brochure Series 005 State of Arkansas Arkansas Geological Survey Bekki White, State Geologist Geology of the Saline County Xenolith and surrounding area By J. Michael Howard Illustrations and photos by Angela Chandler _______________________________________________________ _______________________________________________________ Xenolith – “ a foreign inclusion in an igneous rock.” Glossary of Geology American Geological Institute 1987 (from the Greek words Xenos, meaning guest or stranger, and Lithos, meaning stone.) _______________________________________________________ _______________________________________________________ Introduction Located in Saline County, Arkansas, at the south edge of the community of Bauxite, this natural outcrop of nepheline syenite contains several geologically interesting features, including a xenolith. Sloping west, the outcrop encompasses about one-quarter acre near the center of section 21, Township 2 South, Range 14 West. In early 1990, the Aluminum Company of America (ALCOA) donated the outcrop along with approximately five surrounding acres of land to the Arkansas Geological Commission so that the site can be preserved for educational purposes. Outcrop of nepheline syenite at xenolith locality. History of the site The outcrop and its geologic features were first described by J. Francis Williams in 1891 in The Igneous Rocks of Arkansas, Arkansas Geological Survey Annual Report for 1890, Volume II. Williams discussed the outcrop and xenolith in some detail and included a sketch of the xenolith (see title page). However, for many years the outcrop location remained unknown to most scientists. In the late 2 1960’s employees in the mining division of ALCOA, suspecting that the site was on their property, began a concerted search. Soon afterward the outcrop was rediscovered and was visited by a staff member of the Arkansas Geological Commission, who in turn told Dr.
    [Show full text]
  • Geochemistry of an Ultramafic-Rodingite Rock Association in the Paleoproterozoic Dixcove Greenstone Belt, Southwestern Ghana
    Journal of African Earth Sciences 45 (2006) 333–346 www.elsevier.com/locate/jafrearsci Geochemistry of an ultramafic-rodingite rock association in the Paleoproterozoic Dixcove greenstone belt, southwestern Ghana Kodjopa Attoh a,*, Matthew J. Evans a,1, M.E. Bickford b a Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853, USA b Department of Earth Sciences, Syracuse University, Syracuse, NY 13244, USA Received 11 January 2005; received in revised form 20 February 2006; accepted 2 March 2006 Available online 18 May 2006 Abstract Rodingite occurs in ultramafic rocks within the Paleoproterozoic (Birimian) Dixcove greenstone belt in southwestern Ghana. U–Pb analyses of zircons from granitoids intrusive into the greenstone belt constrain the age of the rodingite-ultramafic association to be older than 2159 Ma. The ultramafic complex consists of variably serpentinized dunite and harzburgite overlain by gabbroic rocks, which together show petrographic and geochemical characteristics consistent with their formation by fractional crystallization involving olivine and plagioclase cumulates. Major and trace element concentrations and patterns in the ultramafic–mafic cumulate rocks and associated plagiogranite are similar to rocks in ophiolitic suites. The rodingites, which occur as irregular pods and lenses, and as veins and blocks in the serpentinized zones, are characterized by high Al2O3 and CaO contents, which together with petrographic evidence indicate their formation from plagioclase-rich protoliths. The peridotites are highly depleted in REE and display flat, chondrite-normalized REE pat- terns with variable, but mostly small, positive Eu anomalies whereas the rodingites, which are also highly depleted, with overall REE contents from 0.04 to 1.2 times chondrite values, display distinct large positive Eu anomalies.
    [Show full text]
  • PRELIMINARY EVALUATION of BEDROCK POTENTIAL for NATURALLY OCCURRING ASBESTOS in ALASKA by Diana N
    Alaska Division of Geological & Geophysical Surveys MISCELLANEOUS PUBLICATION 157 PRELIMINARY EVALUATION OF BEDROCK POTENTIAL FOR NATURALLY OCCURRING ASBESTOS IN ALASKA by Diana N. Solie and Jennifer E. Athey Tremolite (UAMES 34960) displaying the soft, friable fibers of asbestiform minerals. Sample collected from the Cosmos Hills area, Kobuk District, Alaska, by Eskil Anderson. Image courtesy of the University of Alaska Museum Earth Sciences Department. June 2015 Released by STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES Division of Geological & Geophysical Surveys 3354 College Road, Fairbanks, Alaska 99709-3707 907-451-5020 dggs.alaska.gov [email protected] $2.00 (text only) $13.00 (per map sheet) TABLE OF CONTENTS Abstract ................................................................................................................................................................................................................................. 1 Introduction ........................................................................................................................................................................................................................ 1 General geology of asbestos ......................................................................................................................................................................................... 2 Naturally occurring asbestos potential in Alaska ..............................................................................................................................................
    [Show full text]
  • Sulfide Mineralization in an Ultramafic-Rock Hosted Seafloor
    Marine Geology 245 (2007) 20–39 www.elsevier.com/locate/margeo Sulfide mineralization in an ultramafic-rock hosted seafloor hydrothermal system: From serpentinization to the formation of Cu–Zn–(Co)-rich massive sulfides ⁎ Ana Filipa A. Marques a,b, , Fernando J.A.S. Barriga a, Steven D. Scott b a CREMINER (LA/ISR), Universidade de Lisboa, Faculdade de Ciências, Departamento de Geologia, Edif. C6 Piso 4. 1749-016 Campo Grande, Lisboa, Portugal b Scotiabank Marine Geology Research Laboratory, Department of Geology, University of Toronto, 22 Russell St., Toronto, Canada M5S 3B1 Received 12 December 2006; received in revised form 2 May 2007; accepted 12 May 2007 Abstract The Rainbow vent field is an ultramafic rock-hosted seafloor hydrothermal system located on the Mid-Atlantic ridge issuing high temperature, acidic, metal-rich fluids. Hydrothermal products include Cu–Zn–(Co)-rich massive sulfides with characteristics comparable to those found in mafic volcanic-hosted massive sulfide deposits. Petrography, mineralogy and geochemistry of nonmineralized and mineralized rocks sampled in the Rainbow vent field indicate that serpentinized peridotites host the hydrothermal vent system but serpentinization reactions occurred prior to and independently of the sulfide mineralization event. The onset of sulfide mineralization is reflected by extensive textural and chemical transformations in the serpentine-group minerals that show clear signs of hydrothermal corrosion. Element remobilization is a recurrent process in the Rainbow vent field rocks and, during simple peridotite serpentinization, Ni and Cr present in olivine and pyroxene are incorporated in the pseudomorphic serpentine mesh and bastite, respectively. Ni is later remobilized from pseudomorphic serpentine into the newly formed sulfides as a result of extensive hydrothermal alteration.
    [Show full text]
  • Title of Thesis
    Additions and Modifications to the Igneous Rock Classification Scheme Senior Thesis Submitted in partial fulfillment of the requirements for the Bachelor of Science Degree in Geological Sciences At The Ohio State University By Matthew R. H. Dugan The Ohio State University 2010 Approved by Anne E. Carey, Advisor School of Earth Sciences T ABLE OF C ONTENTS Abstract………………………………………………………………………....3 Acknowledgements……………………………………………………….…….4 Introduction……………………………………………………………………..5 Discussion……………….………………………………………………………5 Application……………….……………………………………………………..10 References Cited….……….……………………………………………………18 2 Abstract Igneous rocks as they are currently defined are in a sloppy state. Vague wording is throughout the whole of the definition, and there is not even any clear consensus on what it should be defined as. In this paper, I redefine igneous rocks in such a way as to remove a great deal of imprecision, and I go through some of the logical implications of the refined definition. I do not seek to change the intent of the definition, and I do not believe that I have. The most interesting implication of this change is that water, as it occurs on Earth, is an igneous rock, and I construct a basic classification scheme for it. 3 Acknowledgements I wish to thank Dr. Anne Carey for her intense support of the writing of this thesis, her wonderful edits and her dedication to keeping me on this. I also wish to acknowledge my lab group, also lead by Dr. Steve Goldsmith, for their wonderful feedback and encouragement. Dr. Fritz Graf, Professor and chair of the Department of Greek and Latin, was a great asset to me and he deserves recognition for his help in coining neologisms.
    [Show full text]
  • An Unusual Occurrence of Ultramafic and Mafic Rocks North of Mt Bischoff, Nw Tas~1Ania
    Papers and Proceedings of the Royal Society of Tasmania, Volume 117, 1983. (ms. received 18.5.1982) AN UNUSUAL OCCURRENCE OF ULTRAMAFIC AND MAFIC ROCKS NORTH OF MT BISCHOFF, NW TAS~1ANIA by P.R. Williams and A.V. Brown Geological Survey of Tasmania (with one table and one text-figure) ABSTRACT WILLIAMS, P.R. & BROWN, A.V., 1983 (31 viii): An unusual occurrence of ultramafic and mafic rocks north of Mt Bischoff, NW Tasmania. Pap. Proe. R. Soc. Tasm., 117: 53-58. ISSN 0080-4703. Department of Mines, Bligh Street, Rosny Park, Tasmania, Australia. Plagioclase-bearing harzburgite, plagioclase lherzolite, basalt and dolerite intrude a sequence of mudstone, greywacke, pillowed basalt and chert in the Arthur River valley north of Mt Bischoff. The ultramafic rocks are concordant bodies characterised by absence of internal deformation structures, abundant primary mineral assemblages and cumulate textures. The ultramafics were most probably intruded as magma. Fine- to coarse-grained dolerite were intruded in the same zone, probably as dykes. The dolerite is chemically and texturally distinct from pillowed basalt interbedded with the sedimentary sequence. INTRODUCTION Outcrops of ultramafic and mafic rocks in the Arthur River valley north of Mt Bischoff (fig. 1) were mapped during the Geological Survey of Tasmania's coverage of the St Valentine Quadrangle in northwestern Tasmania. The occurrence was previously unrecord­ ed, as was much of the sedimentary and volcanic sequence of the surrounding countryside. The ultramafic rock bodies are unusual to Tasmania, in that they are apparently undeformed, display their primary mineral compositions without extensive serpentinization and appear to intrude the surrounding sedimentary/volcanic sequence as sills.
    [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]