DOCSLIB.ORG

Komatiitic Flows of the Pioneer Ultramafic Complex of the 3.3Ga

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Komatiitic Flows of the Pioneer Ultramafic Complex of the 3.3Ga Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2008 Komatiitic flows of the pioneer ultramafic complex of the 3.3Ga Weltevreden Formation, Barberton Greenstone Belt, South Africa: stratigraphy, petrology, and geochemistry Marc Romain Cooper Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Earth Sciences Commons Recommended Citation Cooper, Marc Romain, "Komatiitic flows of the pioneer ultramafic ompc lex of the 3.3Ga Weltevreden Formation, Barberton Greenstone Belt, South Africa: stratigraphy, petrology, and geochemistry" (2008). LSU Master's Theses. 1599. https://digitalcommons.lsu.edu/gradschool_theses/1599 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. KOMATIITIC FLOWS OF THE PIONEER ULTRAMAFIC COMPLEX OF THE 3.3GA WELTEVREDEN FORMATION, BARBERTON GREENSTONE BELT, SOUTH AFRICA: STRATIGRAPHY, PETROLOGY, AND GEOCHEMISTRY A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College In partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics by Marc Romain Cooper B.S., Louisiana State University, 2003 August, 2008 ACKNOWLEDGEMENTS The author wishes to thank Dr. Gary Byerly, the author’s major advisor, for his guidance, support, and patience throughout the project, for the opportunity to carry out the field study and guidance therein, and for his unparalleled support in many other endeavors at LSU and beyond. The author also wishes to thank Dr. Darrell Henry and Dr. Huiming Bao of the Department of Geology and Geophysics at Louisiana State University for serving on his thesis committee and offering sound valuable advice and guidance. In particular, the author would also like to thank Dr. Xiaogang Xie of the microanalysis lab at LSU for technical assistance, conversation, and the opportunity to visit China on a field geology trip and Dr. Barb Dutrow for providing generous guidance, opportunities, and support throughout his time at LSU. Dr. Don Lowe and PhD candidate Melanie Thompson at Stanford University and Dr. Maud Walsh and MS graduate Judith Stoute at LSU provided memorable camaraderie during the field study in South Africa and valuable discussions on the field interpretations subsequently. The work of Dr. Gary Byerly, Dr. Don Lowe, Dr. Keena Kareem (PhD, LSU, 2005), and Melanie Thompson was integral to this study. This research was funded by an NSF Grant to Dr. Gary Byerly and the author also received scholarships from the Shreveport and Houston Geological Societies. The author wishes to commend several of his fellow graduate students for the examples they provided during his time as a graduate student at LSU. Lawrence Febo, Julie Hill, Jason Holloman, Jeff Agnew, and Jennifer Whittington made an immense impression upon the author through their contributions to the department as leaders, organizers, and community builders. Maria Pacheco, Katie Howell, Anna Belanger, Russell Willis, Matthew Hackworth, Rebecca Tedford, Mike Blevins, and Issaku Kohl were models of enthusiasm for the science and made it cool to be a geologist. The author also wishes to express gratitude to others in the Department of Geology at LSU who provided assistance: Rick Young in the rock lab, Wanda Leblanc in the ii geochemistry labs, and all the office staff whose dedication and enthusiasm did not go unnoticed. Among his friends and family, the author would like to thank Elizabeth Belton, Lisette Cooper, Grant Cooper, Kris Pottharst, Michelle Klein, Johnny Sanders, and Luke Sanders for their support. Finally, the author is grateful to the faculty of the Department of Geology at LSU with whom he had positive experiences as a student, teaching assistant, and member of the department community. The contributions of these individuals are too numerous to list. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................................................ ii ABSTRACT ................................................................................................................................... vi 1. INTRODUCTION ...................................................................................................................... 1 2. GEOLOGICAL BACKGROUND.............................................................................................. 3 BARBERTON GREENSTONE BELT ...................................................................................... 3 WELTEVREDEN FORMATION ULTRAMAFIC COMPLEXES .......................................... 8 KOMATIITES ............................................................................................................................ 9 3. FIELD OBSERVATIONS ........................................................................................................ 15 MAPPING AND STRATIGRAPHY ....................................................................................... 15 LITHOLOGIC OBSERVATIONS ........................................................................................... 20 4. METHODS ............................................................................................................................... 26 EMPA ANALYTICAL METHODS ........................................................................................ 26 XRF AND ICP-MS ANALYTICAL METHODS .................................................................... 27 MELTS MODELING PROCEDURES .................................................................................... 28 5. RESULTS ................................................................................................................................. 30 PETROGRAPHY AND ELECTRON MICROGRAPHY ....................................................... 30 Massive Cumulate Komatiites .............................................................................................. 30 Dunitic Cumulate Komatiites ............................................................................................... 38 Peridotitic Cumulate Komatiites ........................................................................................... 38 Pyroxenitic Spinifex Komatiites ........................................................................................... 41 Pyroxene Spinifex Komatiitic Basalts .................................................................................. 42 MINERAL CHEMISTRY ........................................................................................................ 42 Olivine................................................................................................................................... 43 Chromite ............................................................................................................................... 46 Pyroxene ............................................................................................................................... 49 ROCK CHEMISTRY ............................................................................................................... 57 Major Elements ..................................................................................................................... 57 Trace Elements ...................................................................................................................... 63 6. DISCUSSION ........................................................................................................................... 66 EXTRUSIVE ORIGIN AND VOLCANOLOGY .................................................................... 66 CRYSTALLIZATION MODEL .............................................................................................. 69 INTERFLOW GEOCHEMICAL VARIATIONS .................................................................... 74 PARTITION COEFFICIENTS ................................................................................................. 76 HIGH PRESSURE FRACTIONATION .................................................................................. 80 ALTERNATE PETROGENETIC MODELS ........................................................................... 83 COMPARISON TO OTHER BGB KOMATIITES ................................................................. 85 7. CONCLUSIONS....................................................................................................................... 88 iv REFERENCES ............................................................................................................................. 90 APPENDIX A: EMPA UNCERTAINTY AND RESULTS ........................................................ 95 EMPA STANDARDS .............................................................................................................. 95 EMPA UNCERTAINTY .......................................................................................................... 96 EMPA RESULTS ..................................................................................................................... 97 APPENDIX B: XRF UNCERTAINTY AND RESULTS .......................................................... 133 XRF UNCERTAINTY ..........................................................................................................
Load more

Recommended publications
  • Source and Bedrock Distribution of Gold and Platinum-Group Metals in the Slate Creek Area, Northern.Chistochina Mining District, East-Central Alaska
    Source and Bedrock Distribution of Gold and Platinum-Group Metals in the Slate Creek Area, Northern.Chistochina Mining District, East-Central Alaska By: Jeffrey Y. Foley and Cathy A. Summers Open-file report 14-90******************************************1990 UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary BUREAU OF MINES T S Arv. Director TN 23 .U44 90-14 c.3 UNITED STATES BUREAU OF MINES -~ ~ . 4,~~~~1 JAMES BOYD MEMORIAL LIBRARY CONTENTS Abstract 1 Introduction 2 Acknowledgments 2 Location, access, and land status 2 History and production 4 Previous work 8 Geology 8 Regional and structural geologic setting 8 Rock units 8 Dacite stocks, dikes, and sills 8 Limestone 9 Argillite and sandstone 9 Differentiated igneous rocks north of the Slate Creek Fault Zone 10 Granitic rocks 16 Tertiary conglomerate 16 Geochemistry and metallurgy 18 Mineralogy 36 Discussion 44 Recommendations 45 References 47 ILLUSTRATIONS 1. Map of Slate Creek and surrounding area, in the northern Chistochina Mining District 3 2. Geologic map of the Slate Creek area, showing sample localities and cross section (in pocket) 3. North-dipping slaty argillite with lighter-colored sandstone intervals in lower Miller Gulch 10 4. North-dipping differentiated mafic and ultramafic sill capping ridge and overlying slaty argillite at upper Slate Creek 11 5. Dike swarm cutting Jurassic-Cretaceous turbidites in Miller Gulch 12 6 60-ft-wide diorite porphyry and syenodiorite porphyry dike at Miller Gulch 13 7. Map showing the locations of PGM-bearing mafic and ultramafic rocks and major faults in the east-central Alaska Range 14 8. Major oxides versus Thornton-Tuttle differentiation index 17 9.
    [Show full text]
  • SPECTRAL CHARACTERIZATION of the ANCIENT SHERGOTTITES NORTHWEST AFRICA 7034 and 8159. KJ Orr1, LV Forman1, GK Benedix1
    Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6177.pdf SPECTRAL CHARACTERIZATION OF THE ANCIENT SHERGOTTITES NORTHWEST AFRICA 7034 AND 8159. K. J. Orr1, L. V. Forman1, G. K. Benedix1, M. J. Hackett2, V. E. Hamilton3, and A. R. Santos. 1Space Science and Technology Centre (SSTC), School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia ([email protected]), 2School of Molecular and Life Sciences, Curtin University, Perth, Western Australia, Australia, 3Southwest Research Institute, 1050 Walnut St. #300, Boulder, CO 80302 USA. 4USRA, 7178 Columbia Gateway Dr., Columbia, MD 21046. Introduction: Thermal infrared (TIR) spectros- Ga), the oldest confirmed shergottites recovered so far copy is a powerful remote sensing tool used to unravel [5]. As the only shergottites of Early Amazonian to No- the surface compositions of a target body. This tech- achian in age, they provide an invaluable opportunity to nique has been widely used in space missions, because understanding Mars’ early history. of its ability to detect and determine modal mineralogy Methods: Both samples (~0.5g chips) were ac- of the surface geology. It has been instrumental in de- quired from UNM and were made into epoxy mounts. veloping our understanding of Mars, as the majority of NWA 8159 was analyzed with a Tescan Integrated Min- missions sent to Mars have included an infrared spec- eral Analyzer (TIMA) to determine modal mineral trometer. These spectrometers can operate either in the abundancies and produce high-resolution mineral maps. visible (VIS) to near-infrared (NIR) or in the mid-infra- NWA 8159 was also analyzed using EBSD to charac- red (MIR).
    [Show full text]
  • Moore County Unbrecciated Cumulate Eucrite, 1.88Kg
    Moore County Unbrecciated Cumulate Eucrite, 1.88 kg Seen to fall Figure 1a: The Moore County eucrite (fusion crust on left), from the collection of the North Carolina Museum of Natural Sciences. Scale from top to bottom of sample is ~ 5 cm. Photo courtesy of Chris Tacker. Introduction: The Moore County meteorite (Figures 1a,b,c) fell at 5:00 PM on April 21, 1913, on the farm of George C. Graves, located approximately three miles east of Carthage, Moore County, North Carolina (79o23’W, 35o25’N) (Henderson and Davis, 1936). A loud “rumbling and zooming” noise “with no distinct explosions” was first observed within a five or six mile radius of the fall, followed by a sighting of a red hot ball with a 15-foot trail of blue-black smoke; the meteorite itself landed within a few feet of a farmer, in a nearly-vertical (but slightly SW-sloping) hole in a freshly-plowed field (Henderson and Davis, 1936). Only one stone was recovered (Figure 1b), weighing approximately 1.88 kg (4 lbs. 2 oz.), with maximum dimensions approximately 15 cm x 10.5 cm x 8 cm (6 in x 4 3/16 in x 3 3/16 in) (Henderson and Davis, 1936). This stone was divided between the US National Museum (Smithsonian) in Washington, D.C., and the North Carolina State Museum in Raleigh, now the North Carolina Museum of Natural Sciences (Henderson and Davis, 1936), where the main fractions of the stone are still kept (0.9 kg at the USNM and ~0.56 kg at the NC Museum: Grady, 2000; Tacker, pers.
    [Show full text]
  • The Investigated Rock Is One of the Gabbroic Bodies Which Crops out in the Surroundings of Lyngdal ( Extreme South of Norway)
    PYROXENE RELATIONS IN A HYPERITE NEAR LYNGDAL, NORWAY JOHAN J. LAVREAU Lavreau, J. J.: Pyroxene relations in a hyperite near Lyngdal, Norway. Norsk Geologisk Tidsskrift, Vol. 50, pp. 333-340. Oslo 1970. Pyroxenes from a hyperite body associated with Precambrian gneisses were studied optically, chemically, and by means of X-rays. Pyroxene relations show that crystallization takes place at a temperature higher than the inversion of pigeonite, and proceeds into the stability field of hypersthene. The composition and the mutual relations between the pyroxenes suggest a crystallization process for these minerals. Johan J. Lavreau, Laboratoire de Mineralogie et Petrologie, Universite Libre de Bruxelles, Brussels, Belgium. Introduction The investigated rock is one of the gabbroic bodies which crops out in the surroundings of Lyngdal ( extreme South of Norway). It Iies 3 km north of the town, northwest of Skoland lake, and is crossed by the E 18 road to Flekkefjord (Fig. 1). It is a well defined and homogeneous crescent-shaped unit, about 1500 m long and 500 m broad. The rock is medium grained (1-2 mm grain size), dark grey in colour, and has a gabbro-dioritic compo­ sition (Niggli 1923, p. 126). Some dioritic varieties were also recognized (Table 1). The country rock is a monzonitic phenoblastic gneiss foliated parallel to the elongation of the hyperite body. The contacts are seldom visible, for the area is covered by recent deposits except in its northern part, where the rock is unfortunately tectonized and strongly retrometa­ morphosed. Experimental techniques Plagioclase and pyroxenes were first studied with the aid of the universal stage.
    [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]
  • Pigeonite Basalt 2109 Grams
    12065 DRAFT Pigeonite Basalt 2109 grams Figure 1: Photo of 12065 showing numerous zap pits on rounded surface. Scale is in cm. NASA # S69-60591. Introduction Sample 12065 is a large rounded pigeonite basalt dated that near-surface olivine (Fo74) and some pyroxene at 3.16 ± 0.09 b.y. The outer surface is covered with settling could explain the variation in composition of micrometeorite pits on all sides (figure 1). some Apollo 12 basalts. Petrography Mineralogy 12065 is a variolitic basalt composed of pyroxene and Olivine: Olivine composition in 12065 ranges from olivine phenocrysts (figure 2) imbedded in a very fine Fo72-32 (Kushiro et al. 1971). matrix of feathery ilmenite, plagioclase and clinopyroxene (figure 3)(Reid 1971). Kushiro et al. Pyroxene: Hollister et al. (1971) and Kushiro et al. (1971) find that the fibrous pyroxene in 12065 is similar (1971) describe complex sector zoning of pyroxene to “quench pyroxenes” often found in quenching phenocrysts in 12065 (figure 4). Pigeonite cores are experiments. 12065 has a few percent void space. overgrown by subcalcic augite (Gay et al. 1971). Kushiro et al. report extreme Fe-enrichment in matrix Kushiro et al. (1971) used the bulk composition of pyroxene. Gay et al. report pyroxferroite with low Ca. 12065 to perform experiments leading to the conclusion Lunar Sample Compendium C Meyer 2005 Figure 2: Photomicrograph of thin section 12065 showing elongate pyroxene in variolitic groundmass. Scale is about 2 cm. NASA # S69-23378. Plagioclase: Plagioclase is An91 – An89 (Kushiro et al. 1971). Chemistry The chemical composition of 12065 has been reported Spinel: The Ti content of the Cr-spinel increases with by LSPET (1970), Maxwell et al.
    [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]
  • 2713^7 Contents
    MINERALS OF WASHINGTON, D.C. AND VICINITY by Lawrence R. Bernstein U. S. Geo^r^'ce.l Survey OPEN F-'::. r;.".r'0.?;r cer.-..: 2713^7 CONTENTS Introduction 1 Scope of report 4 Mineral collecting 5 Acknowledgments 6 Introduction 6a ITT3 Aclj.il1 -> ! T^______.___~^. -"» _«_____«..«_»«__.. " " .._.«__._.._*_.__._.,_.._.-. _>-.-- -_>-->.-..-. Q Triassic deposits 31 Mineral localities 38 District of Columbia : 38 IMavtrlWlCfci JT XClilUl a Tirl ~ __ ___« - - -_ -»-i-___ .__- _ __- - ________________ m~m~m~ m~ m~ «M » M* **A^J ^ Anne Arundel County 43 Baltimore County 45 Howard County - 74 Montgomery County 88 Prince Georges County 120 Virginia . 129 Arlington County 129 Fairfax County 131 Fauquier County 139 Loudoun County 143 Prince William County 149 Diabase quarries of northern Virginia 155 CAPTIONS Illustrations Plate 1. Mineral localities of Washington, B.C., and vicinity. Plate 2. Generalized geologic map of Washington. D.C. and vicinity, Plate 3. Mineral deposits and generalized geology of the Triassic rocks near Washington, D.C. List of Figures Figure 1. Index map showing region covered in this report. Stfaded area is covered in most detail. Figure 2. Block diagram of the Washington, D.C. region showing physiographic provinces and major geographic and geologic features. ITfgure -3. Coastal Plain deposits of Washington, D.C. and vicinity. Figure 4. Generalized cross section of a typical complex pegmatite of the Washington, D.C. area. Figure 5. Rhythmically.layered gabbro of the Baltimore Gabbro Com­ plex at Ilchester, Maryland. Figure 6. Triassic diabase dike forming a ridge north of Route 7 near Dranesville, Virginia.
    [Show full text]
  • Geochemical Analysis of Beaver River Diabase in Comparison to Anorthosite Inclusions and Similar Mid- Continental Rift Diabase
    GEOCHEMICAL ANALYSIS OF BEAVER RIVER DIABASE IN COMPARISON TO ANORTHOSITE INCLUSIONS AND SIMILAR MID- CONTINENTAL RIFT DIABASE Jenna Fischer NDSU Petrology Dr. Saini- Eidukat 5/3/16 BACKGROUND MID- CONTINENT RIFT SYSTEM • Also known as Keweenawan Rift • Middle Proterozoic in age: ~ 1.1 Ga • Triple- junction rift that extends into Kansas and the lower peninsula of Michigan • Outcrops from the MRS are only seen around the Lake Superior region • Generally composed of flood basalts and intrusions • Source was a mantle plume • End of MRS could be Grenvillian orogeny (debatable) Image: www.earthscope.org Miller (1997) LAKE SUPERIOR REGION • Many intrusions in comparison to volcanic rock (60%) • Types of intrusions: Troctolitic, gabbroic, anorthositic, and granitic • Duluth Complex, North Shore Volcanic Group, and Hypabyssal Intrusions • Most hypabyssal intrusions are younger than Duluth Complex • Transitional boundary between complexes • Faults Green (1972) Miller (1997) Map: Miller and Green (2002) LAKE SUPERIOR REGION Map: Miller and Green (2002) HYPABYSSAL INTRUSIONS • Definition: a sub-volcanic rock; an intrusive igneous rock that is emplaced at medium to shallow depth within the crust between volcanic and plutonic • Largest concentration of these subvolcanic intrusions forms the Beaver Bay Complex • Whole rock compositions approximate the magma compositions • Most hypabyssal intrusions do not display igneous foliation and lack signs of differentiation • But late intrusions do! Ex. Sonju Lake, Beaver River Diabase Miller and Green (2002)
    [Show full text]
  • Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington
    Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship Winter 1986 Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington Gregory Joseph Reller Western Washington University, [email protected] Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geology Commons Recommended Citation Reller, Gregory Joseph, "Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington" (1986). WWU Graduate School Collection. 726. https://cedar.wwu.edu/wwuet/726 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. STRUCTURE AMD PETROLOGY OF THE DEER PEAKS AREA iVESTERN NORTH CASCADES, WASHIMGTa^ by Gregory Joseph Re Her Accepted in Partial Completion of the Requiremerjts for the Degree Master of Science February, 1986 School Advisory Comiiattee STRUCTURE AiO PETROIDGY OF THE DEER PEAKS AREA WESTERN NORTIi CASCADES, VC'oHINGTON A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment of the requirements for the Degree Master of Science by Gregory Joseph Re Her February, 1986 ABSTRACT Dominant bedrock mits of the Deer Peaks area, nortliv/estern Washington, include the Shiaksan Metamorphic Suite, the Deer Peaks unit, the Chuckanut Fontation, the Oso volcanic rocks and the Granite Lake Stock. Rocks of the Shuksan Metainorphic Suite (SMS) exhibit a stratigraphy of meta-basalt, iron/manganese schist, and carbonaceous phyllite. Tne shear sense of stretching lineations in the SMS indicates that dioring high pressure metamorphism ttie subduction zone dipped to the northeast relative to the present position of the rocks.
    [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]
  • Papers and Proceedings of the Royal Society of Tasmania
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Tasmania Open Access Repository ON MESOZOIC DOLERITP] AND DIABASE IN TASMANIA. By W. H. Twblvetrees, F.G.S., and W. F. Petterd, C.M.Z.S. The following Notes lay no claim to be an exhaustive description of our familiar '• diabase" or "dolerite" rock, which plays such an important part in the geology and physical configuration of our Island. The present object is rather to place upon record some inferences drawn from the examination of numerous microscopical sections of speci- mens collected or received from all parts of Tasmania. It is by accumulating the results of observations that stepping stones are formed to more complete knowledge. A glance at Mr. R. M. Johnston's geological map of Tasmania, issued by the Lands Office, will show the share this rock takes in the structure of the Island. It occupies the whole upland area of the Central Tiers. On the northern face of the Tiers—the Western Tiers as they are here called—there is a tongue of the rock prolonged northwards past IMount Claude. At their north-west corner it forms or caps mountains, such as Cradle Mountain (the highest in Tas- mania), Barn Bluff, Mount Pelion West. Eldon Blufi: forms a narrow western extension. Mount Sedgwick is a western out-lier ; Mount Dundas another. In that part of the island it is also found at Mount Heemskirk Falls, and on the Magnet Range, two miles north of the Magnet Mine. Mounts Gell and Hugel are also western out-liers.
    [Show full text]