DOCSLIB.ORG

Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System AN ABSTRACT OF THE THESIS OF Brendan M. Laurs for the degree of Master of Science in Geology presented on January 17. 1995. Title: Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System. Haramosh Mountains. Northern Pakistan. Redacted for Privacy Abstract approved: John H. Di lles Emeralds form within 0.1 to 1 m thick hydrothermal veins and pegmatites which have intruded amphibolite within layered Proterozoic gneisses in the Nanga Parbat- Haramosh massif. Simply-zoned albite-rich miarolitic pegmatites and hydrothermal veins containing various proportions of massive quartz, albite, tourmaline, muscovite, and beryl are associated with a small >3 m thick heterogeneous leucogranite sill of presumed Tertiary age, which discordantly intrudes the amphibolite and is locally albitized. Emeralds form within thin <30 cm wide massive quartz veins and tourmaline- albite veins, and more rarely in pegmatites, near the contacts with altered amphibolite. Electron microprobe analyses of colorless, pale blue, and emerald green beryl indicate that coloration is due to Cr3+ ± Fe2++Fe34-. Emerald green color is produced by Cr2O3 >0.20 wt%; Fe oxide varies from 0.62 to 0.89 wt% in emerald, 0.10 to 0.63 wt% in pale blue beryl, and 0.07 to 0.28 wt% in colorless beryl. The amphibolite adjacent to the pegmatites/veins is hydrolytically altered into ca. 20 cm-wide symmetrically zoned selvages. A sporadic inner zone containing biotite + tourmaline + fluorite ± albite ± muscovite ± quartz ± beryl assemblages typically extends to ca. 3 cm from the pegmatite/vein contacts; an intermediate zone containing biotite ± plagioclase + fluorite ± quartz assemblages extends to ca. 10 cm; and an outer sparse biotite ± quartz zone grades into unaltered amphibolite. The inner alteration zones experienced gains of H+, K+, F-, B3+, Be2+, Cs+, Rb+, Ta5+, Nb5+, As3+, y3+, and Sr2+; and losses of Si4+, Mg2+, Fe2+, Fe3+, Ca2+, Cr3+, V5+, and Sc3+; Cs+, Rb+, and As3+ have also migrated into the outer alteration zone. Oxygen isotope analyses of igneous and hydrothermal minerals indicate a single fluid (8180H2o' 8%0 of magmatic origin produced the pegmatite-vein system and hydrothermal alteration. The oxygen isotopic data, along with studies of the magmatic- hydrothermal transition in other miarolitic pegmatite districts, suggest that at Khaltaro emplacement of the pegmatite-vein system and associated amphibolite alteration and emerald mineralization occurred at temperatures between ..----.550 and 400°C, and at pressures ranging from 2 to 3 kbar. The unique occurrence of emeralds at Khaltaro results from introduction of Be2+, Si4+, A13+, K+, and Na+ in HF-rich fluids of magmatic origin, which caused hydrolysis of amphibolite and diffusion of released Cr3+ into the pegmatite-vein system. There, Cr3+ was preferentially incorporated into crystallizing beryl to cause emerald green coloration. Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System, Haramosh Mountains, Northern Pakistan by Brendan M. Laurs A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed January 17, 1995 Commencement June 1995 Master of Science thesis of Brendan M. Laurs presented on January 17, 1995 APPROVED: Redacted for Privacy Major Professor, representing Geology Redacted for Privacy Chair of Department of Geosciences Redacted for Privacy Dean of Gradu chool I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Redacted for Privacy Brendan M. Laurs, Author Acknowledgments Drs. John H. Di lles, Lawrence W. Snee, and Ali H. Kazmi provided the inspiration for this project. In particular, Dr. Di lles supplied ever-helpful guidance and support throughout the course of this project, and Dr. Kazmi provided stimulating discussion and friendly accommodation in Karachi. The Geological Survey of Pakistan (GSP) provided logistical support in the field, sample preparation facilities, and XRF and XRD analyses; S. Hasan Gauhar and Allah B. Kausar coordinated logistics, and Yousef Warraich assisted with fieldwork. Dr. Nasir Ali Bhatti of the Gemstone Corporation of Pakistan (Peshawar) gave helpful advice and access to geologic reports. This study was funded by a Sigma Xi research grant, Chevron U.S.A. graduate fellowship (through Oregon State University (OSU) Department of Geosciences), National Science Foundation grant money (through Dr. Robert D. Lawrence), and the OSU Department of Geosciences Ore Deposit Research Foundation. Dr. Lawrence also provided a Khaltaro emerald sample for study, and access to his voluminous reference library. INAA analyses were made possible by the OSU Reactor Use Sharing Program (administered by Dr. Arthur G. Johnson); Martin Streck provided helpful advice, and Erwin Tome supervised sample preparation and data reduction. Dr. Roger Nielson provided instruction and advice for the electron microprobe; analyses were funded in part by the OSU College of Oceanic and Atmospheric Sciences. Dr. Reed Glasman supported XRD analyses and peak-search software at OSU Department of Geosciences, and Phong Nguyen performed computerized XRD mineral identification at OSU Department of Chemistry. David Maher carried out oxygen isotope analyses in the Dilles/Grunder lab at OSU Department of Geosciences, and Bill Rugh performed ICP-MS oxygen analyses at the OSU College of Oceanic and Atmospheric Sciences. Computer drafting of Figures 1 through 4 was performed by David Reinert. Table of Contents Introduction 1 Previous work 6 Sampling and analytical procedures 8 General geology 12 Petrology and geochemistry of host rocks 17 Garnet-mica schist 17 Amphibolite 19 Leucogranite 21 Pegmatites 26 Hydrothermal veins 28 Temporal and spatial relations of leucogranite, pegmatites, and veins 31 Emerald mineralization and beryl crystal chemistry 32 Petrology and geochemistry of amphibolite alteration 39 Biotite-tourmaline-fluorite zone 39 Biotite-plagioclase-fluorite zone 43 Sparse biotite zone 44 Whole-rock geochemistry of alteration 44 Oxygen isotopes 50 Discussion 53 Chemical exchange during amphibolite alteration 54 Relations between K- and Na-metasomatism 56 Be transport and emerald mineralization 57 Pressure and temperature conditions 58 Conclusions 60 Table of Contents References cited 61 Appendix 71 Table 1. Electron microprobe analyses of Khaltaro feldspar 72 Table 2. Electron microprobe analyses of Khaltaro garnet 83 Table 3. Electron microprobe analyses of Khaltaro amphibole 85 Table 4. Electron microprobe analyses of Khaltaro zoisite 91 Table 5. Whole-rock geochemistry of Khaltaro mica schist, amphibolite, and veins 94 Table 6. Electron microprobe analyses of Khaltaro biotite 100 Table 7. Electron microprobe analyses of Khaltaro muscovite 107 Table 8. Electron microprobe analyses of Khaltaro beryl 112 Table 9. Electron microprobe analyses of Khaltaro tourmaline 121 List of Figures 1.Regional geologic map of northern Pakistan 2 2.Geology and structure of the Khaltaro area 4 3. Map and cross section of Khaltaro Mine 1 area 15 4. Map of Khaltaro Mine 2 area 16 5.Chondrite-normalized trace element diagram of Khaltaro host rocks 18 6.Chondrite-normalized trace element diagram of Khaltaro leucogranites 24 7.Mineralogy and texture of pegmatite and veins at Khaltaro 27 8.Microprobe analyses from core to rim across a zoned beryl crystal 38 9.Representative diagram of half of a symmetrically zoned amphibolite selvage adjacent to a pegmatite or hydrothermal vein 38 10.Electron microprobe data of minerals occurring in leucogranite, pegmatite, veins, and amphibolite 42 11. Major element gains and losses in altered amphibolite 47 12.Trace element gains and losses within a single traverse of altered amphibolite 49 13.Schematic diagram showing exchange of components between pegmatites or hydrothermal veins and surrounding amphibolite, and conditions of emerald mineralization 53 List of Tables 1. Geochemistry of mica schist and amphibolite 9 2. Modal variation in unaltered amphibolite 20 3.Geochemistry of Khaltaro and Jutial leucogranites 23 4.Typical electron microprobe analyses of biotite and phlogopite from leucogranite, pegmatite, emerald, and altered amphibolite adjacent to vein 33 5.Typical electron microprobe analyses of muscovite from leucogranite, veins, and altered amphibolite adjacent to vein 34 6.Partial chemical analyses of beryl from pegmatite, veins, and altered amphibolite 36 7.Average microprobe analyses of tourmaline from pegmatite, vein, and altered amphibolite adjacent to vein 41 8.Geochemistry of altered amphibolite series adjacent to a tourmaline-albite vein 46 9.Oxygen isotope data of minerals from garnet-mica schist, amphibolite, leucogranite, pegmatite, and veins 51 Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System, Haramosh Mountains, Northern Pakistan. Introduction Emerald is a rare and valuable variety of beryl (Be3Al2Si6018) that derives its rich green color from trace amounts of Cr. Emeralds are rarely found in nature, because their formation requires the interaction of highly differentiated, Be-bearing granitic or pegmatitic fluids with mafic rocks containing Cr. Such exceptional geological conditions may take place in suture zones, granite/greenstone terranes, and metamorphosed shales (Kazmi and Snee, 1989). Suture-related
Load more

Recommended publications
  • Geology of the Vardeklettane Terrane, Heimefrontfjella (East Antarctica)
    Umbruch 79-1 04.11.2009 16:20 Uhr Seite 29 Polarforschung 79 (1), 29 – 32, 2009 Geology of the Vardeklettane Terrane, Heimefrontfjella (East Antarctica) by Wilfried Bauer1, Joachim Jacobs2, Robert J. Thomas3, Gerhard Spaeth4 and Klaus Weber5 Abstract: In the southwest of the Heimefrontfjella mountain range a granu- ly, the collected samples are extensively retrogressed with lite-facies terrane is exposed in the small Vardeklettane nunataks. The Varde- abundant chlorite and sericitised plagioclase, so granulite- klettane Terrane extends, however, at least 65 km farther WNW to the nunatak group of Mannefallknausane, where comparable granulites are exposed. The facies metamorphism was not identified. For the nunatak terrane is composed of mafic and felsic granulites, leucogranite orthogneiss group of Mannefallknausane however, JUCKES (1968) reported and metasedimentary rocks. The maximum deposition age of the latter is charnockites and granulite-facies rocks. Granulite-facies rocks constrained by detrital zircon U-Pb data ranging from 2000 to 1200 Ma whereas the leucogranite gneiss gave a late Mesoproterozoic crystallization were subsequently recognised at Vardeklettane by ARNDT et al. age of 1135 Ma. The Vardeklettane Terrane is unique as being the only part of (1987), who described charnockites as well as felsic and mafic the otherwise juvenile Late Mesoproterozoic basement of Heimefrontfjella to granulites, interpreting the latter as meta-volcanic rocks. The have a Paleoproterozoic crustal component. Structurally, the terrane is sepa- rated from the main range by the Heimefront Shear Zone. following description is based on the systematic mapping at 1:10,000 scale completed during the international Heimefront- Zusammenfassung: In den kleinen Vardeklettane Nunataks im Südwesten der fjella expedition of 1994 (BAUER et al.
    [Show full text]
  • Archaean Cratonization and Deformation in the Northern Superior Province, Canada: an Evaluation of Plate Tectonic Versus Vertical Tectonic Models Jean H
    Precambrian Research 127 (2003) 61–87 Archaean cratonization and deformation in the northern Superior Province, Canada: an evaluation of plate tectonic versus vertical tectonic models Jean H. Bédard a,∗, Pierre Brouillette a, Louis Madore b, Alain Berclaz c a Geological Survey of Canada, Division Québec, 880, ch.Ste-Foy, Quebec City, Que., Canada G1S 2L2 b Géologie Québec, Ministère des ressources naturelles du Québec, 5700, 4e Avenue Ouest, Charlesbourg, Que., Canada G1H 6R1 c Géologie Québec, Ministère des ressources naturelles du Québec, 545 Crémazie Est, bureau 1110, Montreal, Que., Canada H2M 2V1 Accepted 10 April 2003 Abstract The Archaean Minto Block, northeastern Superior Province, is dominated by tonalite–trondhjemite, enderbite (pyroxene tonalite), granodiorite and granite, with subordinate mafic rocks and supracrustal belts. The plutons have been interpreted as the batholithic roots of Andean-type plate margins and intra-oceanic arcs. Existing horizontal-tectonic models propose that penetrative recrystallization and transposition of older fabrics during terrane assembly at ∼2.77 and ∼2.69 Ga produced a N-NW tectonic grain. In the Douglas Harbour domain (northeastern Minto Block), tonalite and trondhjemite dominate the Faribault–Thury complex (2.87–2.73 Ga), and enderbite constitutes 50–100 km-scale ovoid massifs (Troie and Qimussinguat complexes, 2.74–2.73 Ga). Magmatic muscovite and epidote in tonalite–trondhjemite have corroded edges against quartz + plagioclase, suggesting resorption during ascent of crystal-charged magma. Foliation maps and air photo interpretation show the common development of 2–10 km-scale ovoid structures throughout the Douglas Harbour domain. Outcrop and thin-section scale structures imply that many plutons experienced a phase of syn-magmatic deformation, typically followed by high temperature sub-magmatic overprints.
    [Show full text]
  • The Geology of the Tama Kosi and Rolwaling Valley Region, East-Central Nepal
    The geology of the Tama Kosi and Rolwaling valley region, East-Central Nepal Kyle P. Larson* Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada ABSTRACT Tama Kosi valley in east-central Nepal (Fig. 1). which were in turn assigned to either the Hima- In order to properly evaluate the evolution of the layan gneiss group or the Midlands metasedi- The Tama Kosi/Rolwaling area of east- Himalaya and understand the processes respon- ment group (Fig. 2). The units of Ishida (1969) central Nepal is underlain by the exhumed sible for its formation, it is critical that all areas and Ishida and Ohta (1973) are quite similar in mid-crustal core of the Himalaya. The geol- along the length of the mountain chain be inves- description to the tectonostratigraphy reported ogy of the area consists of Greater Hima- tigated, at least at a reconnaissance scale. by Schelling (1992) who revisited and expanded layan sequence phyllitic schist, paragneiss, The Tama Kosi valley is situated between the the scope of their early reconnaissance work. and orthogneiss that generally increase in Cho Oyu/Everest/Makalu massifs to the east Schelling (1992) separated the geology of metamorphic grade from biotite ± garnet and the Kathmandu klippe/nappe to the west the lower and middle portion of the Tama Kosi assemblages to sillimanite-grade migmatite (Fig. 1). Recent work in these areas serves to into the more traditional Greater Himalayan up structural section. All metamorphic rocks highlight stark differences between them. In the sequence (Higher Himalayan Crystallines) and are pervasively deformed and commonly Kathmandu region, the extruded midcrustal core Lesser Himalayan sequence lithotectonic assem- record top-to-the-south sense shear.
    [Show full text]
  • Northwestern Superior Craton Margin, Manitoba: an Overview of Archean
    GS-7 Northwestern Superior craton margin, Manitoba: an overview of Archean and Proterozoic episodes of crustal growth, erosion and orogenesis (parts of NTS 54D and 64A) by R.P. Hartlaub1, C.O. Böhm, L.M. Heaman2, and A. Simonetti2 Hartlaub, R.P., Böhm, C.O., Heaman, L.M. and Simonetti, A. 2005: Northwestern Superior craton margin, Manitoba: an overview of Archean and Proterozoic episodes of crustal growth, erosion, and orogenesis (parts of NTS 54D and 64A); in Report of Activities 2005, Manitoba Industry, Economic Development and Mines, Manitoba Geological Survey, p. 54–60. Summary xenocrystic zircon, and in the The northwestern margin of the Superior Province in isotopic signature of Neoarchean Manitoba represents a dynamic boundary zone with good granite bodies (Böhm et al., 2000; potential for magmatic, sedimentary-hosted, and structur- Hartlaub et al., in press). The ALCC extends along the ally controlled mineral deposits. The region has a history Superior margin for at least 50 km, and may have a com- that commences in the early Archean with the formation mon history with other early Archean crustal fragments of the Assean Lake Crustal Complex. This fragment of in northern Quebec and Greenland (Hartlaub et al., in early to middle Archean crust was likely accreted to the press). Superior Province between 2.7 and 2.6 Ga, a major period South of the ALCC, the Split Lake Block repre- of Superior Province amalgamation. Sediments derived sents a variably retrogressed and shear zone–bounded from this amalgamation process were deposited at granulite terrain that is dominated by plutonic rocks and numerous locations along the northwestern margin of mafic granulite (Hartlaub et al., 2003, 2004).
    [Show full text]
  • The Himalayan Leucogranites: Constraints on the Nature of Their Crustal Source Region and Geodynamic Setting
    Gondwana Research 22 (2012) 360–376 Contents lists available at SciVerse ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr The Himalayan leucogranites: Constraints on the nature of their crustal source region and geodynamic setting Zhengfu Guo a,⁎, Marjorie Wilson b a Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China b School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK article info abstract Article history: Late Oligocene–Miocene leucogranites within southern Tibet form part of an extensive intrusive igneous Received 10 February 2011 province within the Himalayan orogen. The main rock types are tourmaline leucogranites (Tg) and two-mica Received in revised form 18 July 2011 87 86 leucogranites (2 mg). They have high SiO2 (70.56–75.32 wt.%), Al2O3 (13.55–15.67 wt.%) and ( Sr/ Sr)i Accepted 25 July 2011 (0.724001–0.797297), and low MgO (0.02–0.46 wt.%) and (143Nd/144Nd) (0.511693–0.511906). Chondri- Available online 11 August 2011 i te-normalized rare earth element (REE) patterns display strong negative Eu anomalies. Whole-rock major and trace element and Sr–Nd isotope data for the leucogranites suggest that their source region was a Keywords: fl Leucogranites two-component mixture between a uid derived from the Lesser Himalayan (LH) crustal sequence and the Decompression melting bulk crust of the Higher Himalayan (HH) sequence. Trace element and Sr–Nd isotope modeling indicate that Himalayan orogen the proportion of fluid derived from the LH sequence varied from 2% to 19% and the resulting metasomatised Steepening of the subducted Indian slab source experienced 7–16% melting.
    [Show full text]
  • Himalayan Leucogranites and Migmatites: Nature, Timing and Duration of Anatexis
    J. metamorphic Geol., 2016, 34, 821–843 doi:10.1111/jmg.12204 Himalayan leucogranites and migmatites: nature, timing and duration of anatexis R. F. WEINBERG School of Earth, Atmosphere and Environment, Monash University, Clayton, Vic. 3800, Australia ([email protected]) ABSTRACT Widespread anatexis was a regional response to the evolution of the Himalayan-Tibetan Orogen that occurred some 30 Ma after collision between Asia and India. This paper reviews the nature, timing, duration and conditions of anatexis and leucogranite formation in the Greater Himalayan Sequence (GHS), and compares them to contemporaneous granites in the Karakoram mountains. Himalayan leucogranites and associated migmatites generally share a number of features along the length of the mountain front, such as similar timing and duration of magmatism, common source rocks and clock- wise P–T paths. Despite commonalities, most papers emphasize deviations from this general pattern, indicating a fine-tuned local response to the dominant evolution. There are significant differences in – – P T XH2O conditions during anatexis, and timing in relation to regional decompression. Further to that, some regions underwent a second event recording melting at low pressures. Zircon and monazite ages of anatectic rocks range between c. 25 and 15 Ma, suggesting prolonged crustal melting. Typi- cally, a single sample may have ages covering most of this 10 Ma period, suggesting recycling of accessory phases from metamorphic rocks and early-formed magmas. Recent studies linking monazite and zircon ages with their composition, have determined the timing of prograde melting and retro- grade melt crystallization, thus constraining the duration of the anatectic cycle. In some areas, this cycle becomes younger down section, towards the leading front of the Himalayas, whereas the oppo- site is true in other areas.
    [Show full text]
  • Geology and Tectonic Implications of Tourmaline Bearing Leucogranite of Bastipadu, Kurnool, Andhra Pradesh, India
    J. Earth Syst. Sci. (2018) 127:87 c Indian Academy of Sciences https://doi.org/10.1007/s12040-018-0990-8 Geology and tectonic implications of tourmaline bearing leucogranite of Bastipadu, Kurnool, Andhra Pradesh, India Kiran Jyoti Mishra, Santanu Bhattacharjee* , M S Reddy, M N Praveen, A D Bhimte and N Mahanta Geological Survey of India, Southern Region, Hyderabad 500 068, India. *Corresponding author. e-mail: [email protected] MS received 17 October 2017; revised 2 January 2018; accepted 19 January 2018; published online 2 August 2018 Tourmaline bearing leucogranite occurs as a pluton with pegmatitic veins intruding the Archaean granodiorite in the Bastipadu area, Kurnool district of Andhra Pradesh. We present field and petrographic relations, mineral chemistry and geochemical data for the leucogranite. It is essentially a two-mica granite, composed of quartz, perthite, microcline, albite, tourmaline and muscovite along with minor biotite and titanite. The euhedral tourmalines are regularly distributed in the rock. The geochemical studies show that the leucogranite is calc-alkaline, peraluminous to metaluminous which formed in a syn-collisional to volcanic arc-related setting. It displays strong ‘S’ type signatures with high K/Na ratios, moderately fractionated light rare earth elements, relatively flat heavy rare earth elements with [Ce/Yb]N ≤ 27.8 and a strong negative Eu anomaly. The geochemical characteristics indicate that the leucogranite melt might have been generated from partial melting of metasediments. Electron probe microanalyser data show the presence of alkali group tourmaline in leucogranite represented by schorl and dravite. Tourmaline compositions plot in the Li-poor granitoids and associated pegmatites and aplites and metapelites/metasammites fields.
    [Show full text]
  • 40Ar/39Ar Age Constraints on Deformation and Metamorphism in the Maine Central Thrust Zone and Tibetan
    TECTONICS, VOL. 8, NO. 4, PAGES 865-880, AUGUST 1989 40Ar/39Ar AGE CONSTRAINTSON DEFORMATION AND METANDRPHISM IN THE MAIN CENTRAL THRUST ZONE AND TIBETAN SLAB, EASTERN NEPAL HIMALAYA Mary S. Hubbard1 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge T. Mark Harrison Department of Geological Sciences, State University of New York at Albany Abstract. In eastern Nepal, structural 6.4+0.8 Ma (Tc=225ñ20ø C). An adjacent and petrologic observations suggest that gneiss yields a 9.1ñ0.2 Ma biotite movement on the Main Central Thrust (MCT), isochron and a K-feldspar minimum age of the development of an inverted metamorphic 3.6_+0.2 Ma (Tc=210-+50øC). In the upper sequence, and leucogranite plutonism were Tibetan Slab, samples collected >200 m genetically related. Samples from across from visible intrusives yield a biotite the MCT zone and its hanging wall, the isochron age of 20.2!0.2 Ma and a complex Tibetan Slab, were collected from four hornblende age spectrum suggestive of locations in the Everest region for excess argon. At the fourth location an 40Ar/39Ar studies: (1) the MCT zone, (2) augen gneiss, a pegmatite, and a the lower Tibetan Slab, (3) the upper tourmaline-bearing leucogranite, all in Tibetan Slab away from intrusive rocks, mutual contact, yield indistinguishable and (4) the upper Tibetan Slab adjacent to mineral ages. The average biotite and and including leucogranitic material. muscovite isochron ages for these samples Within the MCT zone, muscovite and are 17.0_+1.4 and 16.6ñ0.2 Ma, hornblende yield cooling ages of 12.0-+0.2 respectively.
    [Show full text]
  • Petrological Description of the Leucogranite in Örsviken
    UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre Petrological description of the leucogranite in Örsviken Johanna Engelbrektsson Hannah Berg ISSN 1400-3821 B775 Bachelor of Science thesis Göteborg 2014 Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Abstract For a deeper understanding of the different processes that can create, alter and destroy magnetic minerals in rocks it is important to integrate rock magnetism with conventional petrology. Bulk composition, hydrothermal alteration, redox state, metamorphism and tectonic setting influence the magnetic properties of igneous rocks. An investigation of a part of a cape that consists of a leucogranite in Örsviken, 20 kilometres south of Gothenburg, was of interest after high susceptibility values had been discovered in the area. Five samples from the leucogranite were collected in order to do a whole rock major element analysis, find the cause of the high susceptibility, classify and interpret the origin of the leucogranite. Magnetite is the cause of the high susceptibility values across the leucogranite. The leucogranite is considered to be an A-type alkali granite with an anorogenic or a post-orogenic petrogenesis. The leucogranite shows quite similar patterns and chemistry to the Askim- and Kärra Granites, which may indicate that the leucogranite is associated with them. Keywords: Magnetic minerals, leucogranite, Örsviken, susceptibility, whole rock major element analysis, magnetite, A-type granite. Sammanfattning För att få en djupare förståelse för de olika processer som kan skapa, förändra och förstöra magnetiska mineral i berg är det viktigt att integrera bergarters magnetism och konventionell petrologi.
    [Show full text]
  • Internal Framework and Geochemistry of the Carboniferous Huaco Granite Pluton, Sierra De Velasco, NW Argentina
    Andean Geology ISSN: 0718-7092 ISSN: 0718-7106 [email protected] Servicio Nacional de Geología y Minería Chile Internal framework and geochemistry of the Carboniferous Huaco granite pluton, Sierra de Velasco, NW Argentina Sardi, Fernando; Grosse, Pablo; Murata, Mamoru; Lozano Fernández, Rafael Pablo Internal framework and geochemistry of the Carboniferous Huaco granite pluton, Sierra de Velasco, NW Argentina Andean Geology, vol. 45, no. 2, 2018 Servicio Nacional de Geología y Minería, Chile Available in: https://www.redalyc.org/articulo.oa?id=173955659006 DOI: https://doi.org/10.5027/andgeoV45n2-3015 PDF generated from XML JATS4R by Redalyc Project academic non-profit, developed under the open access initiative Fernando Sardi, et al. Internal framework and geochemistry of the Carboniferous Huaco granite plu... Artículos de Investigación Internal framework and geochemistry of the Carboniferous Huaco granite pluton, Sierra de Velasco, NW Argentina Estructura interna y geoquímica del plutón granítico carbonífero de Huaco, Sierra de Velasco, NW de Argentina Fernando Sardi DOI: https://doi.org/10.5027/andgeoV45n2-3015 INSUGEO, Argentina Redalyc: https://www.redalyc.org/articulo.oa? [email protected] id=173955659006 Pablo Grosse CONICET, Argentina [email protected] Mamoru Murata Naruto University of Education, Japón [email protected] Rafael Pablo Lozano Fernández Instituto Geológico y Minero de España, España [email protected] Received: 28 November 2016 Accepted: 11 November 2017 Abstract: e A-type Huaco granite pluton of the Velasco range (Sierras Pampeanas of northwest Argentina) is formed by three coeval granitic facies and contains subordinate coeval-to-late facies, as well as enclaves, dikes and stocks that show different temporal relations, textures and compositions.
    [Show full text]
  • Intrusive Igneous Rocks, Part 2
    GLY 4310C LAB 7 INTRUSIVE IGNEOUS ROCKS, PART 2 Granite, Alkali Feldspar Granite, Granodiorite, Quartz Monzonite, and Monzonite These intrusive (plutonic) rocks correspond to fields on diagram 2-2 of Winter. These rocks are generally richer in silica and alkali feldspar than those studied in Lab 6. More information about these rocks is included in Chapter 13 and 14 of Moorhouse. GRANITE - Intrusive igneous, plutonic. Medium to coarse-grained plutonic rock containing between 20% to 60% quartz, feldspar (the plagioclase to plagioclase plus alkali feldspar (P/A+P) ratio is between 10 to 65%), and small amounts of biotite, hornblende or other silicates. K-spar may be orthoclase and/or microcline. The plagioclase is sodic, either oligoclase or andesine. Rocks of this composition are scarce and the definition is often broadened, for example by including quartz monzonite. The alkali feldspar is commonly microcline perthite (mixture of microcline and plagioclase). In some perthites, the albite and K-feldspar are completely separated, possibly due to recrystallization. The quartz is almost always anhedral in granites. The quartz grains often contain inclusions. Biotite is usually brown or brownish green and often contains inclusions. Hornblende is dark green and pleochroitic. Biotite may form a rim around the hornblende. If pyroxene (diopside) is present, hornblende may form a rim around the pyroxene. Muscovite may occur in patches around the biotite. Many granites are foliated. The name is from the Latin granum, meaning grain. ALKALI FELDSPAR GRANITE - Intrusive igneous, plutonic. Medium to coarse-grained plutonic rock containing between 20% to 60% quartz, feldspar (the plagioclase to plagioclase plus alkali feldspar (P/A+P) ratio < 10), and small amounts of biotite, hornblende or other silicates.
    [Show full text]
  • 1 Records of the Evolution of the Himalayan Orogen from in Situ Th-Pb Ion Microprobe Dating of Monazite: Eastern Nepal and Weste
    1 Records of the evolution of the Himalayan orogen from in situ Th-Pb ion microprobe dating of monazite: Eastern Nepal and western Garhwal E.J. Catlos,1* T. Mark Harrison,1 Craig E. Manning,2 Marty Grove,2 Santa Man Rai,3 M.S. Hubbard, 4 B.N. Upreti3 1Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, 90095-1567, USA 2Department of Earth and Space Sciences, University of California, Los Angeles, California, 90095-1567, USA 3Department of Geology, Tri-Chandra Campus, Tribhuvan University, Kathmandu, Nepal 4Department of Geology, Kansas State University, Manhattan, Kansas, 66506, USA Abstract. In situ Th-Pb monazite ages from rocks collected along two transects (the Dudh Kosi-Everest, eastern Nepal and the Bhagirathi River, Garhwal Himalaya, India) perpendicular to the Main Central Thrust (MCT) suggest a striking continuity of tectonic events across the Himalaya. The youngest age reported in this study, 5.9±0.2 Ma (MSWD=0.4), from matrix monazite grains collected beneath the MCT in the Garhwal region is consistent with several age data from rocks at similar structural levels in central Nepal, providing support for widespread Late Miocene MCT activity. The lateral parallelism of orogenic events is further manifested by the 20.7±0.1 Ma age of a High Himalayan leucogranite from an injection complex that outcrops along the Dudh Kosi-Everest transect, resembling ages of these bodies reported elsewhere. The youngest monazite grain analyzed along the Dudh Kosi-Everest transect is 10.3±0.8 Ma. The absence of 7-3 Ma monazite ages in eastern Nepal may reflect a different nappe structure, which obscures the reactivated ramp equivalent exposed in the Garhwal and central Nepal.
    [Show full text]