DOCSLIB.ORG

The Coexistence of Jadeite and Omphacite in an Eclogite-Facies Metaquartz Diorite from the Southern Sesia Zone, Western Alps, Italy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Coexistence of Jadeite and Omphacite in an Eclogite-Facies Metaquartz Diorite from the Southern Sesia Zone, Western Alps, Italy Journal of Mineralogical and Petrological Sciences, Volume 100, page 70 －84, 2005 The coexistence of jadeite and omphacite in an eclogite-facies metaquartz diorite from the southern Sesia Zone, Western Alps, Italy Keisaku MATSUMOTO and Takao HIRAJIMA Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kitashirakawa Oiwakecho, Sakyo－ku, Kyoto 606－8502, Japan An association of jadeite and omphacite has been newly found in an eclogite－facies metaquartz diorite col- lected from the Orco Valley area, southern part of the Eclogitic Micaschist Complex of the Sesia Zone, Western Alps, Italy. Both the jadeite and omphacite occur as idiomorphic to subidiomorphic grains in the matrix, and some of them are in contact with each other with a sharp grain boundary. Most of the jadeite shows VI faint and irregular zoning, with a chemical variation of Xjd (Al jd /(Na + Ca)) = 0.75－0.90. Half of the omphacite grains is homogeneous, and the remainder shows various zoning patterns. Some omphacite grains exhibit pro- 3+ grade zoning with an increase in Xjd from 0.31 to 0.55 and a decrease in Xaeg (= Fe /(Na + Ca)) from 0.14 to 0.04 from the core to the rim. The rim composition of the zoned omphacite is similar to that of homogeneous omphacite (Xjd = 0.40－0.56). The average rim composition of the jadeite－omphacite pairs in direct contact shows an apparent miscibility gap between Xjd = 0.50 ± 0.06, Xaeg = 0.09 ± 0.03, and Xaug (= Ca/(Na + Ca)) = 0.41 ± 0.05 in omphacite, and Xjd = 0.79 ± 0.04, Xaeg = 0.08 ± 0.03, and Xaug = 0.13 ± 0.03 in jadeite. Application of Powell (1985) garnet－clinopyroxene geothermometer gives T = 470 ± 30°C at P = 12 kbar and application of Waters and Martin (1993) garnet－omphacite－phengite geobarometer gives P = 12.4 kbar at T = 440°C and P = 12.0 kbar at T = 500°C as peak metamorphic conditions. Composition data of the pyroxene P2/n and C2/c compositional fields obtained from both this study and the literature suggest that: (1) the shape of two miscibility gaps between jadeite and omphacite and between omphacite and augite in the jadeite－augite－ aegirine phase diagram of Carpenter (1983) is more concordant with the natural data than that of Holland (1990), (2) the miscibility gap between omphacite and augite closes at T ～ 500°C and P = 15 kbar, but the mis- cibility gap between jadeite and omphacite may still exist, and (3) the miscibility gap between jadeite and omphacite closes at T = 700－850°C and P =15－45 kbar. Keywords: Jadeite, Omphacite, Miscibility gap, Eclogite, Sesia Zone, Western Alps. INTRODUCTION Holland and Powell, 1996; Nakamura and Banno, 1997). The position of the miscibility gap has been discussed At low temperature, omphacite is regarded as an ordered with observations on natural metamorphic rocks, e.g., pyroxene with P2/n symmetry, and jadeite and augite are from omphacite－augite joins by Brown et al. (1978), regarded as a disordered C2/c structure. Two miscibility Carpenter (1980a), Enami and Tokonami (1984) and gaps between jadeite－omphacite and omphacite－augite Tsujimori (1997), and from jadeite－omphacite joins by exist in the jadeite－augite join at low temperatures. Carpenter (1979), Harlow (1994), Compagnoni et al. Several authors have considered the solid－solution prop- (1995) and D’Amico et al. (1995). However, the position erties of omphacite to construct phase diagrams, or have of the miscibility gaps has not yet been confirmed, calculated the activity of the phase components (e.g., despite many studies being conducted. Carpenter, 1980b; 1983; Banno, 1986; Davidson and We found a jadeite－omphacite association in an Burton, 1987; Holland, 1990; Carpenter et al., 1994; eclogite－facies metaquartz dioritecollected from the Orco Valley area, southern part of the Eclogitic Micaschist K. Matsumoto, keisaku@kueps.kyoto－u.ac.jp Corresponding author Complex of the Sesia Zone, Western Alps, Italy. The T. Hirajima, hirajima@kueps.kyoto－u.ac.jp specimen is poorly retrograded by a greenschist－ or The coexistence of jadeite and omphacite in an eclogite-facies metaquartz diorite 71 blueschist－facies overprint. In this paper, we will Compagnoni, 1977; Compagnoni et al., 1977; Rubie, describe the detailed petrography of the relevant rock, 1984; Oberha¨ nsli et al., 1985; Pognante, 1989; 1991; and provide an assessment of the theoretical phase dia- Droop et al., 1990; Castelli, 1991, Fig. 1). In the EMC, grams using the data obtained in this study and from two contrasting exhumation paths have been proposed for available data in the literature. the central and southern parts, respectively. Rubie (1984) reported that the central part of the EMC underwent GEOLOGICAL SETTING early－Alpine eclogite－facies metamorphism with peak P－ T conditions of T = 500－560°C and P > 14－16 kbar. The The Eclogitic Micaschist Complex (EMC) of the Sesia metamorphic conditions evolved towards lower pressure Zone is one of the best－studied quartz－eclogite－facies ter- (T ～ 470－490°C and P ～ 8 kbar in the blueschist－ ranes in the world (e.g., Compagnoni and Maffeo, 1973; facies). During the later stage of the exhumation, the Figure 1. Tectonic sketch map of the Sesia Zone (modified after Castelli et al., 1994). 1, Eclogitic Micaschist Complex (EMC); 2 , Gneiss Minuti Complex (GMC); 3, Second Diorito－Kinzigitic zone (DK), Vasario (VA); 4, Post－orogenic Oligocene intrusives of Brosso－ Traversella (BT) and Valle del Cervo (C); 5, Rocca Canavese Unit (RCT), Canavese line (CL). The star denotes the sample locality. 72 K. Matsumoto and T. Hirajima EMC was overprinted by a greenschist－facies metamor- PETROGRAPHY AND MINERAL CHEMISTRY phism (T ～ 400°C and P ～ 4－5 kbar). On the other hand, Pognante (1989) reported that the southern part of The chemical analysis of the minerals was carried out the EMC underwent early－Alpine eclogite－facies meta- using a Hitachi S550 scanning electron microscope morphism with peak P － T conditions of T = 500－550°C equipped with a Kevex energy dispersive analytical sys- and P = 13－20 kbar, and then underwent a blueschist－ tem at Kyoto University, Japan. The accelerating voltage facies metamorphism during an early stage of the exhu- and beam current were maintained at 20.0 kV and 0.5 nA, mation, which was characterized by a significant tempera- respectively. The detail of the analytical method follows ture drop at high pressures (T < 450－500°C, at pressures Mori and Kanehira (1984) and Hirajima and Banno in the jadeite－lawsonite stability field). During a later (1991). The backscattered electron images were taken by stage of the exhumation, pumpellyite and albite grew a Hitachi S3500H scanning electron microscope at Kyoto under P－T conditions around of T < 350°C and P < 5 University. The bulk rock composition was determined kbar. using X－ray fluorescence spectroscopy employing a The studied specimen was collected along a road cut Rigaku Simultix－3550 spectrometer at Kyoto University. between Alpette and Cuorgne in the Orco Valley area of The analytical procedure follows Goto and Tatsumi the EMC (Fig. 1). The sampling locality is mainly occu- (1991; 1992). Abbreviation of minerals follows those pied by glaucophanite and eclogite. Pognante (1991) con- used in Kretz (1983), except for phengite (phn). sidered that glaucophanite and eclogite were derived The Fe2+/Fe3+ estimation for clinopyroxene (jadeite from basic rocks with different CaO/Na2O. and omphacite) leads to a substantial error in the mg# (= Mg/(Mg + Fe2+)). One of the common calculation meth- ods for Fe3+ estimation in clinopyroxene is based on an ideal structural formulae and charge balance, i.e., four Table 1. The chemical composition of clinopyroxene ( *1) Total iron as FeO. * ( 2) Rim compositions of jadeite－omphacite pairs with the sharp grain boundary. The coexistence of jadeite and omphacite in an eclogite-facies metaquartz diorite 73 Table 2. The chemical compositions of glaucophane, actinolite, phengite, paragonite, garnet and clinozoisite (*1) Total iron as FeO. (*2) In contact with phengite. (*3) In contact with omphacite. cations for six oxygen atoms. However, this method propagates all analytical errors to the Fe3+ content. Table 3. Bulk rock Therefore, in this study, the Fe3+ content in the clinopy- chemistry of the 3+ VI VI study rock roxene was estimated using Fe = Na － Al jd (where Al jd total VI total IV IV = Al for Si > 2.00, or Al jd = Al － 2Al (where Al = 2 － Si) for Si < 2.00). The enstatite and ferrosilite compo- nents are very small under high－pressure conditions, and so they are ignored. In our study, we therefore treat clino- pyroxene as having three components: jadeite, aegirine and augite. The proportions of the jadeite, aegirine and VI augite components were calculated as: Xjd= Al jd /(Na + 3+ Ca), Xaeg = Fe /(Na + Ca) and Xaug = Ca/(Na + Ca). The Fe3+ content in the sodic amphibole was estimated as Fe3+ VI VI total VI = Na － Al gln (where Al gln = Al for Si > 8.00, or Algln = Altotal － 2AlIV (where AlIV = 8 － Si) for Si < 8.00). The chemical compositions of the representative minerals are shown in Tables 1 and 2, and the bulk rock (*1) Total iron as Fe O . 2 3 chemistry of the study rock is shown in Table 3. All iron of the bulk rock chemistry is assumed to be Fe2O3. 74 K. Matsumoto and T. Hirajima Figure 2. Backscattered electron images of: a) jadeite (Jd) and omphacite (Omp) in contact with sharp grain boundary, and b) Tiny omphacitic region in jadeite. The compositions of the numbered white circles are shown in Figure 3a. Grt, garnet; Phn, phengite; Czo/Zo, clinozoisite/zoisite. Figure 3. a) Chemical composition of the clinopyroxenes in the Jd－Aug－Aeg phase diagram.
Load more

Recommended publications
  • Module 7 Igneous Rocks IGNEOUS ROCKS
    Module 7 Igneous Rocks IGNEOUS ROCKS ▪ Igneous Rocks form by crystallization of molten rock material IGNEOUS ROCKS ▪ Igneous Rocks form by crystallization of molten rock material ▪ Molten rock material below Earth’s surface is called magma ▪ Molten rock material erupted above Earth’s surface is called lava ▪ The name changes because the composition of the molten material changes as it is erupted due to escape of volatile gases Rocks Cycle Consolidation Crystallization Rock Forming Minerals 1200ºC Olivine High Ca-rich Pyroxene Ca-Na-rich Amphibole Intermediate Na-Ca-rich Continuous branch Continuous Discontinuous branch Discontinuous Biotite Na-rich Plagioclase feldspar of liquid increases liquid of 2 Temperature decreases Temperature SiO Low K-feldspar Muscovite Quartz 700ºC BOWEN’S REACTION SERIES Rock Forming Minerals Olivine Ca-rich Pyroxene Ca-Na-rich Amphibole Na-Ca-rich Continuous branch Continuous Discontinuous branch Discontinuous Biotite Na-rich Plagioclase feldspar K-feldspar Muscovite Quartz BOWEN’S REACTION SERIES Rock Forming Minerals High Temperature Mineral Suite Olivine • Isolated Tetrahedra Structure • Iron, magnesium, silicon, oxygen • Bowen’s Discontinuous Series Augite • Single Chain Structure (Pyroxene) • Iron, magnesium, calcium, silicon, aluminium, oxygen • Bowen’s Discontinuos Series Calcium Feldspar • Framework Silicate Structure (Plagioclase) • Calcium, silicon, aluminium, oxygen • Bowen’s Continuous Series Rock Forming Minerals Intermediate Temperature Mineral Suite Hornblende • Double Chain Structure (Amphibole)
    [Show full text]
  • Orthopyroxene–Omphacite
    Lithos 216–217 (2015) 1–16 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Orthopyroxene–omphacite- and garnet–omphacite-bearing magmatic assemblages, Breaksea Orthogneiss, New Zealand: Oxidation state controlled by high-P oxide fractionation☆ Timothy Chapman a,⁎, Geoffrey L. Clarke a, Nathan R. Daczko b,c, Sandra Piazolo b,c, Adrianna Rajkumar a a School of Geosciences, F09, University of Sydney, Sydney, NSW 2006, Australia b ARC Centre of Excellence for Core to Crust Fluid Systems, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia c GEMOC, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia article info abstract Article history: The Breaksea Orthogneiss comprises a monzodioritic host partially recrystallised to omphacite–garnet–plagioclase– Received 19 December 2013 rutile granulite at 850 °C and 1.8 GPa, with metre to decametre-scale, cognate inclusions ranging from ultramafic Accepted 21 November 2014 through gabbroic to monzodioritic composition. Coarsely layered garnetite and diopsidic clinopyroxenite cumulate Available online 3 December 2014 preserves igneous textures, whereas garnet–omphacite cumulate shows a partial metamorphic overprint to eclogite. Garnet and omphacite in undeformed to weakly deformed rocks have similar major and rare earth element Keywords: characteristics reflecting their common igneous origin, pointing to a lack of metamorphic recrystallisation. Inclusions Omphacite–garnet granulite – – – Orthopyroxene eclogite of omphacite orthopyroxene plagioclase ulvöspinel orthogneiss have whole-rock compositions almost identical Omphacite–orthopyroxene granulite to the host monzodiorite. Reaction zones developed along contacts between the orthopyroxene-bearing inclusions REE and host contain metamorphic garnet that is microstructurally and chemically distinct from igneous garnet.
    [Show full text]
  • High-Pressure Single-Crystal Elasticity and Thermal Equation Of
    Journal of Geophysical Research: Solid Earth 10.1029/2018JB016964 2001). For example, D. Zhang et al. (2016) performed single‐crystal X‐ray diffraction (XRD) experiments on omphacite up to 47 GPa at 300 K. Pandolfo et al. (2012b) measured the thermal expansion coefficients of omphacite up to 1073 K at 1 atm. The only available in situ high P‐T EOS study for omphacite is performed on polycrystalline samples using multianvil press up to 10 GPa and thus is unable to cover the entire P stability field of omphacite in the Earth's interior (Nishihara et al., 2003). On the other hand, although the sound velocities of the Mg,Ca end member diopside have been studied at various P‐T conditions (Isaak et al., 2006; Isaak & Ohno, 2003; Levien et al., 1979; Li & Neuville, 2010; Matsui & Busing, 1984; Sang et al., 2011; Sang & Bass, 2014; Walker, 2012), the single‐crystal elastic properties of omphacite have only been measured at ambient condition (Bhagat et al., 1992) or investigated computationally at high‐P 0‐K conditions (Skelton & Walker, 2015). The lack of experimentally determined thermoelastic properties of omphacite, which is the most abundant mineral phase in eclogite, restricts our understanding of the subduction process as well as the possible seismic identification of eclogitic materials in the Earth's interior. To fill in this knowledge gap, we performed high P‐T single‐crystal XRD measurements on natural P2/n omphacite crystals up to 18 GPa 700 K at GeoSoilEnviroCARS (GSECARS), Advanced Photon Source, Argonne National Laboratory, as well as single‐crystal Brillouin spectroscopy measurements of the same crystals up to 18 GPa at 300 K at the high‐P laser spectroscopy laboratory at University of New Mexico (UNM).
    [Show full text]
  • Mid-Infrared Optical Constants of Clinopyroxene and Orthoclase Derived from Oriented Single-Crystal Reflectance Spectra
    American Mineralogist, Volume 99, pages 1942–1955, 2014 Mid-infrared optical constants of clinopyroxene and orthoclase derived from oriented single-crystal reflectance spectra JESSICA A. ARNOLD1,*, TIMOTHY D. GLOTCH1 AND ANNA M. PLONKA1 1Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, U.S.A. ABSTRACT We have determined the mid-IR optical constants of one alkali feldspar and four pyroxene compo- sitions in the range of 250–4000 cm–1. Measured reflectance spectra of oriented single crystals were iteratively fit to modeled spectra derived from classical dispersion analysis. We present the real and imaginary indices of refraction (n and k) along with the oscillator parameters with which they were modeled. While materials of orthorhombic symmetry and higher are well covered by the current literature, optical constants have been derived for only a handful of geologically relevant monoclinic materials, including gypsum and orthoclase. Two input parameters that go into radiative transfer models, the scattering phase function and the single scattering albedo, are functions of a material’s optical constants. Pyroxene is a common rock-forming mineral group in terrestrial bodies as well as meteorites and is also detected in cosmic dust. Hence, having a set of pyroxene optical constants will provide additional details about the composition of Solar System bodies and circumstellar materials. We follow the method of Mayerhöfer et al. (2010), which is based on the Berreman 4 × 4 matrix formulation. This approach provides a consistent way to calculate the reflectance coefficients in low- symmetry cases. Additionally, while many models assume normal incidence to simplify the dispersion relations, this more general model applies to reflectance spectra collected at non-normal incidence.
    [Show full text]
  • Ultra-High Pressure Aluminous Titanites in Carbonate-Bearing Eclogites at Shuanghe in Dabieshan, Central China
    Ultra-high pressure aluminous titanites in carbonate-bearing eclogites at Shuanghe in Dabieshan, central China D. A. CARSWELL Department of Earth Sciences, University of Sheffield, Sheffield $3 7HF, UK R. N. WILSON Department of Geology, University of Leicester, Leicester LE1 7RH, UK AND M. ZtIAI Institute of Geology, Academia Sinica, P.O. Box 634, Beijing 100029, China Abstract Petrographic features and compositions of titanites in eclogites within the ultra-high pressure metamorphic terrane in central Dabieshan are documented and phase equilibria and thermobarometric implications discussed. Carbonate-bearing eclogite pods in marble at Shuanghe contain primary metamorphic aluminous titanites, with up to 39 mol.% Ca(AI,Fe3+)FSiO4 component. These titanites formed as part of a coesite- bearing eclogite assemblage and thus provide the first direct petrographic evidence that AIFTi_IO_j substitution extends the stability of titanite, relative to futile plus carbonate, to pressures within the coesite stability field. However, it is emphasised that A1 and F contents of such titanites do not provide a simple thermobarometric index of P-T conditions but are constrained by the activity of fluorine, relative to CO2, in metamorphic fluids - as signalled by observations of zoning features in these titanites. These ultra-high pressure titanites show unusual breakdown features developed under more H20-rich amphibolite-facies conditions during exhumation of these rocks. In some samples aluminous titanites have been replaced by ilmenite plus amphibole symplectites, in others by symplectitic intergrowths of secondary, lower AI and F, titanite plus plagioclase. Most other coesite-bearing eclogite samples in the central Dabieshan terrane contain peak assemblage rutile often partly replaced by grain clusters of secondary titanites with customary low AI and F contents.
    [Show full text]
  • The Effect of Cation Order on the Elasticity of Omphacite from Atomistic Calculations
    This is a repository copy of The effect of cation order on the elasticity of omphacite from atomistic calculations. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/85963/ Version: Accepted Version Article: Skelton, R and Walker, AM (2015) The effect of cation order on the elasticity of omphacite from atomistic calculations. Physics and Chemistry of Minerals, 42 (8). pp. 677-691. ISSN 0342-1791 https://doi.org/10.1007/s00269-015-0754-9 Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ 1 The effect of cation order on the elasticity of omphacite from atomistic calculations 2 Richard Skeltona,* and Andrew M. Walkerb,c 3 a Research School of Earth Sciences, Australian National University,
    [Show full text]
  • Mineral Collecting Sites in North Carolina by W
    .'.' .., Mineral Collecting Sites in North Carolina By W. F. Wilson and B. J. McKenzie RUTILE GUMMITE IN GARNET RUBY CORUNDUM GOLD TORBERNITE GARNET IN MICA ANATASE RUTILE AJTUNITE AND TORBERNITE THULITE AND PYRITE MONAZITE EMERALD CUPRITE SMOKY QUARTZ ZIRCON TORBERNITE ~/ UBRAR'l USE ONLV ,~O NOT REMOVE. fROM LIBRARY N. C. GEOLOGICAL SUHVEY Information Circular 24 Mineral Collecting Sites in North Carolina By W. F. Wilson and B. J. McKenzie Raleigh 1978 Second Printing 1980. Additional copies of this publication may be obtained from: North CarOlina Department of Natural Resources and Community Development Geological Survey Section P. O. Box 27687 ~ Raleigh. N. C. 27611 1823 --~- GEOLOGICAL SURVEY SECTION The Geological Survey Section shall, by law"...make such exami­ nation, survey, and mapping of the geology, mineralogy, and topo­ graphy of the state, including their industrial and economic utilization as it may consider necessary." In carrying out its duties under this law, the section promotes the wise conservation and use of mineral resources by industry, commerce, agriculture, and other governmental agencies for the general welfare of the citizens of North Carolina. The Section conducts a number of basic and applied research projects in environmental resource planning, mineral resource explora­ tion, mineral statistics, and systematic geologic mapping. Services constitute a major portion ofthe Sections's activities and include identi­ fying rock and mineral samples submitted by the citizens of the state and providing consulting services and specially prepared reports to other agencies that require geological information. The Geological Survey Section publishes results of research in a series of Bulletins, Economic Papers, Information Circulars, Educa­ tional Series, Geologic Maps, and Special Publications.
    [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 DGGSpubs@alaska.gov $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]
  • 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]
  • Cold Subduction and the Formation of Lawsonite Eclogite – Constraints from Prograde Evolution of Eclogitized Pillow Lava from Corsica
    J. metamorphic Geol., 2010, 28, 381–395 doi:10.1111/j.1525-1314.2010.00870.x Cold subduction and the formation of lawsonite eclogite – constraints from prograde evolution of eclogitized pillow lava from Corsica E. J. K. RAVNA,1 T. B. ANDERSEN,2 L. JOLIVET3 AND C. DE CAPITANI4 1Department of Geology, University of Tromsø, N-9037 Tromsø, Norway (erling.ravna@uit.no) 2Department of Geosciences and PGP, University of Oslo, PO Box 1047, Blindern, 0316 Oslo, Norway 3ISTO, UMR 6113, Universite´ dÕOrle´ans, 1A Rue de la Fe´rollerie, 45071 Orle´ans, Cedex 2, France 4Mineralogisch-Petrographisches Institut, Universita¨t Basel, Bernoullistrasse 30, 4056 Basel, Switzerland ABSTRACT A new discovery of lawsonite eclogite is presented from the Lancoˆne glaucophanites within the Schistes Lustre´ s nappe at De´ file´ du Lancoˆne in Alpine Corsica. The fine-grained eclogitized pillow lava and inter- pillow matrix are extremely fresh, showing very little evidence of retrograde alteration. Peak assemblages in both the massive pillows and weakly foliated inter-pillow matrix consist of zoned idiomorphic Mg-poor (<0.8 wt% MgO) garnet + omphacite + lawsonite + chlorite + titanite. A local overprint by the lower grade assemblage glaucophane + albite with partial resorption of omphacite and garnet is locally observed. Garnet porphyroblasts in the massive pillows are Mn rich, and show a regular prograde growth-type zoning with a Mn-rich core. In the inter-pillow matrix garnet is less manganiferous, and shows a mutual variation in Ca and Fe with Fe enrichment toward the rim. Some garnet from this rock type shows complex zoning patterns indicating a coalescence of several smaller crystallites.
    [Show full text]
  • A Comparative Study of Jadeite, Omphacite and Kosmochlor Jades from Myanmar, and Suggestions for a Practical Nomenclature
    Feature Article A Comparative Study of Jadeite, Omphacite and Kosmochlor Jades from Myanmar, and Suggestions for a Practical Nomenclature Leander Franz, Tay Thye Sun, Henry A. Hänni, Christian de Capitani, Theerapongs Thanasuthipitak and Wilawan Atichat Jadeitite boulders from north-central Myanmar show a wide variability in texture and mineral content. This study gives an overview of the petrography of these rocks, and classiies them into ive different types: (1) jadeitites with kosmochlor and clinoamphibole, (2) jadeitites with clinoamphibole, (3) albite-bearing jadeitites, (4) almost pure jadeitites and (5) omphacitites. Their textures indicate that some of the assemblages formed syn-tectonically while those samples with decussate textures show no indication of a tectonic overprint. Backscattered electron images and electron microprobe analyses highlight the variable mineral chemistry of the samples. Their extensive chemical and textural inhomogeneity renders a classiication by common gemmological methods rather dificult. Although a deinitive classiication of such rocks is only possible using thin-section analysis, we demonstrate that a fast and non-destructive identiication as jadeite jade, kosmochlor jade or omphacite jade is possible using Raman and infrared spectroscopy, which gave results that were in accord with the microprobe analyses. Furthermore, current classiication schemes for jadeitites are reviewed. The Journal of Gemmology, 34(3), 2014, pp. 210–229, http://dx.doi.org/10.15506/JoG.2014.34.3.210 © 2014 The Gemmological Association of Great Britain Introduction simple. Jadeite jade is usually a green massive The word jade is derived from the Spanish phrase rock consisting of jadeite (NaAlSi2O6; see Ou Yang, for piedra de ijada (Foshag, 1957) or ‘loin stone’ 1999; Ou Yang and Li, 1999; Ou Yang and Qi, from its reputed use in curing ailments of the loins 2001).
    [Show full text]
  • NASA  Dr.’S Doug Stoeser & Steve Wilson, USGS  Wikipedia, 2009
    Jacqueline Graham Danielle Granlund Janet Schweizerhof Peter Rossiter Lunar Soil (regolith) is extremely-fine, dust-like material All systems that go to the Moon will interact with this material, both intentionally and unintentionally: Can it be used for construction purposes? Can it be used to grow plants? Will it affect human health? Is it detrimental to machinery, equipment, clothes, etc.? In order to colonize the Moon, it must be known how the Lunar Soil will interact with the various systems Unfortunately, the Apollo missions did not bring back enough sample to study and characterize fully Emphasis has therefore been placed on making, studying, and characterizing “simulants” such as: Minnesota Lunar Simulant (MLS-1) was developed in the 1970s and 1980s Johnson Space Center (JSC-1) in 1990’s MLS-2, JSC-1A, JSC-1F, JSC-2, JSC-3, etc. were developed later but, like the others, all were consumed in various studies International interest gains strength and a new “moon race” develops: Japan (FJS-1 and MKS-1) China (CAS-1) Previous studies were centered on using single resources of terrestrial igneous rock, predominantly from volcanic areas, with a focus on the elemental content and not necessarily the mineralogy and chemistry Most of the studies took these materials, added fluxes, heated to a molten state, allowed to solidify, and, after cooling, crushed, ground and pulverized the material Consequently, no simulant has accurately and adequately reproduced Lunar Soil Over 95% of Lunar Soil is comprised of silicates belonging
    [Show full text]