DOCSLIB.ORG

208-240 My Old Jadeite-Glaucophane

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
208-240 My Old Jadeite-Glaucophane J. Japan. Assoc. Min. Petr. Econ. Geol. 73, 300-310, 1978. 208-240 M. Y. OLD JADEITE-GLAUCOPHANE SCHISTS IN THE KUROSEGAWA TECTONIC ZONE NEAR KOCHI CITY, SHIKOKU SHIGENORI MARUYAMA Department of Earth Sciences, Faculty of Science, Nagoya University* YOSHIO UEDA Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Sendai 986 and SHOHEI BANNO Department of Earth Sciences, Faculty of Science, Kanazawa University, Kanazawa 920 A new member of the Kurosegawa tectonic zone was found in the serpentinite near Kochi city. They are high P and low T schists derived from basalt and chert. Three metamorphic events can be deciphered in the high-pressure schists, based upon the texture and mineral paragenesis: first, low P metamorphism at intermediate- to high grade, second, high P and low T metamorphism of the jadeite-glaucophane facies and the thrid, retrograde crystallization of the second stage high P schists within the stability field of lawsonite+pumpellyite+glaucophane. Further, the formation of analcime replacing jadeite took place. The second and third metamorphism can be distinguished on pyroxene mineralogy that j adeite+quartz was stable in the second, but albite+quartz+aegirinej adeite in the third stage of metamorphism. Not all of the high P and low T schists had suffered low P metamorphism before they were metamorphosed by the high P one. Some basaltic rocks directly changed to high P and low T schists. Two muscovites in the schists give K-Ar ages of 208-240 m.y., and a relic igneous biotite, being partly replaced by chlorite, gives 225 m.y. of K-Ar age. These values are different not only from those of the Sanbagawa schists, but also from the other members of the Kurosegawa zone. shaped and surrounded by serpentinite, but INTRODUCTION small blocks are xenoliths in serpentinite. A The Kurosegawa tectonic zone is a variety of rock-types have been recognized fault zone in the Chichibu terrain in south among exotic blocks: unmetamorphosed west Japan. It runs in EW direction in Silurian and Devonian, granite and gneiss the middle subbelt of the Chichibu terrain (426 m.y., Rb-Sr, Nohda, 1973), amphi (Yamashita, 1957) and accompanied by a bolite, garnet amphibolite and basic large amount of serpentinite and blocks granulite. Basic and pelitic schists of albite exotic to the neighbouring Chichibu forma epidote amphibolite facies (429 m.y., K-Ar, tion, measuring from a few meters to Maruyama and Ueda, 1975) also occur. several kilometers. Large blocks are lense Several years ago, we found that * Present address , Department of Earth Science, Faculty of Education, Toyama University, Toyama 930 (Manuscript received July 25, 1978) Fig. 1. Geological map of the Ino-Engyoji area. 208-240 m.y. old jadeite-glaucophane schists in the Kurosegawa tectonic zone 301 another type of exotic blocks occur in westwards for more than 18 kilometers is in serpentinite of the Kurosegawa zone of contact with mudstone, accompanied by a Shikoku. It includes high P and low T small amount of chert, sandstone and green schists among which are jadeite-glaucophane stone, which is probably a part of the Ino schists. In the following, we intend to formation (Katto and Kawasawa, 1958). describe the mode of occurrence , petrography The contact between the serpentinite and the and K-Ar ages of the high P and low T sedimentary sequence is concordant at some schists xenoliths in detail. places, but discordant at others. Several roof pendants of the Ino formation, one of MODE OF OCCURRENCE them measuring about 0.04km2, were A geologic map of the Kurosegawa zone mapped in the serpentinite. near Kochi city in Shikoku, is shown in Fig . I The xenoliths of the high P and low T Members constituting the tectonic zone are schists occur in the northern part of the divided into two groups on the basis of large serpentinite mass referred above. The their scale; one is called as tectonic unit and largest of the blocks measures 100m3, but is usually larger than 1.5•~0.3 square they are usually about 0.5m3 (Fig. 6). kilometer in size, and the other smaller than this size is called as tectonic block herein. PETROGRAPHY Tectonic units consist of the Triassic Kochi The high P and low T schists so far gatani, Permian Takaoka, Silurian Yoko collected are metabasites and metachert. kurayama formations, and the Ino forma Although all the schists examined contain tion of unknown age as shown in Fig. 1 . high-pressure minerals, such as jadeite, The former four are weakly metamorphosed glaucophane, chloromelanite and lawsonite, in some places, but practically unmetamor a few types of original rocks could be phosed in others. The Ino formation deciphered. They are pillow lava, hyalo suffered glaucophanitic metamorphism clastite and massive lava on the one hand, (Banno, 1964, Nakajima et al., in prepara and greenschist and amphibolite on the tion). Serpentinite is one of the major other. constitutent rock-types of the zone in this The schists derived from volcanics pre area. In some places it forms large masses, serve augite and biotite as relic minerals, but in others, it forms separate belts and hyaloclastitic texture can be seen under intruded into fault and are several meters the microscope. These metavolcanics wide, continuing for more than several suffered high P and low T metamorphism kilometers. The faults bordering tectonic without having intermediate stages of low units or large tectonic blocks are very often pressure metamorphism to be mentioned intruded by serpentinite. Small tectonic later. blocks, measuring less than 1m3 of am High P and low T metamorphics derived phibolite, albite-epidote amphibolite, basic from amphibolite is medium- to coarse granulite, garnet amphibolite, gneiss and grained and melanocratic with amphibole glaucophane schists are always enclosed by as dominant mafic phase. Fresh rock is serpentinite. commonly bluish or greenish black. A In the area north of the cities of Ino continuous series of texture is observed and Kochi, large serpentinite mass, extending between the two extreme cases: one being 302 S. Maruyama, Y. Ueda, S. Banno poor in high-pressure minerals and the (4) lawsonite+pumpellyite+glaucophane other mostly consisting of them. +jadeite+aegirinejadeite+salite+ Pale-green actinolite coexisting with chlorite+albite+quartz hornblende, green and brown, and Ca-rich (5) lawsonite+pumpellyite+crossite+ clinopyroxene are on the way being epidote+albite+quartz replaced by alkali amphibole (Fig. 2), but (6) lawsonite+pumpellyite+chloromelanite plagioclase is exclusively albite (less than +chlorite+albite+quartz XAn=0.01) that sometimes includes lawsonite, (7) lawsonite+pumpellyite+glaucophane suggesting its derivation from Ca-bearing +albite+quartz plagioclase. (8) lawsonite+glaucophane+stilpnomelane +albite+quartz (9) lawsonite+pumpellyite+glaucophane +chioromelanite+microcline+albite +quarz (10) lawsonite+glaucophane+albite (11) lawsonite+pumpellyite+glaucophane Fig. 2. Replacing texture of actinolite by alkali +albite amphiboles. Actinolite is partly replaced (12) lawsonite+pumpellyite+glaucophane by magnesioriebeckite along cleavage or +albite+aegirinejadeite crack, which in turn is thoroughly mantled by parallel-symmteric glaucophane, thereby (13) lawsonite+glaucophane+albite suggesting that magnesioriebeckite is not +aegirinejadeite equilibrated with matrix minerals. When ever magnesioriebeckite appears, it shows (14) pumpellyite+chlorite+albite nonequilibrated texture with matrix min Partial assemblages of (7) are common. erals as in this sample. Assemblages (10)-(14) are free of quartz. Sphene, apatite, white mica (phengite so far Thus, at least two stages of metamor identified), calcite and opaque minerals phic recrystallization are recognized in may be added to the above assemblages. some of the high P and low T schists. The Opaque minerals were identified for as mineral assemblagesformed by high P and semblages (4), (5), (6) and (9). Pyrite, low T metamorphismwill be describedfirst, chalcopyrite and sphalerite are present, and the relationships between these two but hematite and rutile have not been stages of metamorphism will be discussed observed. Analcime is sometimes observed later. around jadeitic pyroxene. Mineral assemblages of metabasites In the metamorphosed chert, following formed by high P and low T metamorphism assemblages were observed: are as follows: (15) lawsonite+glaucophane+graphite (1) lawsonite+glaucophane+stilpnomelane +quartz (mode 50% •})+albite +jadeite+aegirinejadeite+albite+ (16) glaucophane+graphite+quartz (mode quartz 90% •})+albite (2) lawsonite+pumpellyite+jadeite+ Aragonite was sought by staining with aegirinejadeite+albite+quartz Feigl's solution, but not detected except as (3) lawsonite+pumpellyite+glaucophane veinlet minerals in serpentinite. +aegirinejadeite+albite+quartz The assemblages listed above include 208-240 m.y. old jadeite-glaucophane schists in the Kurosegawa tectonic zone 303 some metastable ones such as (1), (2) and the list of mineral assemblages. A group (4), and it is apparent that not all of them of pyroxenes has compositions covering both are isofacial. These problems will be dis the impure jadeite and aegirinejadeite fields cussed below from the viewpoint of pyro as defined by Essene and Fyfe (1967), but xene mineralogy. they are jointly called aegirinejadeite, be There are five types of metamorphic cause they were formed by the same process, pyroxenes in the xenoliths. The first group and their majority belong to aegirinejadeite, is augite relics derived from higher
Load more

Recommended publications
  • Heat Capacity of High Pressure Minerals and Phase Equilibria of Cretan Blueschists
    Heat capacity of high pressure minerals and phase equilibria of Cretan blueschists by Matthew Rahn Manon A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology) in The University of Michigan 2008 Doctoral Committee: Professor Eric J. Essene, Chair Professor Rebecca Ann Lange Professor Youxue Zhang Associate Professor Steven M. Yalisove Matthew Rahn Manon 2008 Acknowledgments Cheers to all the grad students who have gone and come through CC-Little over the years. Zeb, Steven, Jim, Chris, Katy, Phillip, Franek, Eric, Tom, Darius, Sarah, Sara, Abir, Laura, Casey, Sam, John and anyone else I’ve been to learned something from, or argued something with. From early nights at Dominicks for subductology “seminars” through to the FWC, Michigan has been a fun place to live. Thanks to Anne Hudon, whos made sure I haven’t been able to place myself in inextricable holes. Thanks also to those from earlier in my life. College professors like Ken Hess or Barbara Nimmersheim who, in their very different ways inspired me to explore what it is I know. I’ll always remember time spent with Bob Wiebe who introduced me to the wild unknown of geology. Immeasurable thanks go to Eric Essene. The fieldtrips we took the first few years were good adventures. He’s always put aside his own issues to be there for me to talk to, especially when I didn’t deserve it. Eric’s scientific curiosity, and mental rigor are deservedly well known. His patience with me may be one of his great, unsung virtues.
    [Show full text]
  • Glaucophane Na2[(Mg; Fe )3Al2]Si8o22(OH)2 C 2001 Mineral Data Publishing, Version 1.2 ° Crystal Data: Monoclinic
    2+ Glaucophane Na2[(Mg; Fe )3Al2]Si8O22(OH)2 c 2001 Mineral Data Publishing, version 1.2 ° Crystal Data: Monoclinic. Point Group: 2=m: As prismatic crystals; columnar, ¯brous, or granular aggregates; massive. Twinning: Simple or multiple twinning 100 . k f g Physical Properties: Cleavage: Perfect on 110 , intersecting at 56± and 124±; partings on 010 , 001 . Fracture: Conchoidalfto ugneven. Tenacity:»Brittle. H»ardness = 6 D(meas.) = f3.08{g3.f22 gD(calc.) = 3.132 Optical Properties: Translucent. Color: Gray, lavender-blue, commonly zoned; lavender-blue to colorless in thin section. Streak: Blue-gray. Luster: Vitreous to pearly. Optical Class: Biaxial ({). Pleochroism: Vivid; X = yellow to colorless; Y = violet to lavender; Z = blue. Orientation: Y = b; Z c = 7± to 6±, X a 8±. Dispersion: r < v; weak. ^ ¡ ¡ ^ ' ® = 1.594{1.630 ¯ = 1.612{1.648 ° = 1.619{1.652 2V(meas.) = 0±{50± Cell Data: Space Group: C2=m: a = 9.595 b = 17.798 c = 5.307 ¯ = 103:66± Z = 2 X-ray Powder Pattern: Sebastopol quadrangle, California, USA. (ICDD 20{453). 8.26 (100), 3.06 (65), 2.693 (60), 4.45 (25), 3.38 (25), 2.937 (25), 2.523 (25) Chemistry: (1) (2) (1) (2) (1) (2) SiO2 58.04 56.28 FeO 6.12 10.34 K2O 0.02 0.11 TiO2 0.66 0.17 MnO 0.07 0.25 F 0.02 Al2O3 10.31 12.16 MgO 11.71 8.41 Cl 0.01 + Fe2O3 2.89 1.72 CaO 1.37 0.62 H2O 1.98 Cr2O3 0.11 Na2O 6.97 7.04 H2O¡ 0.00 Total 100.17 97.21 (1) Tiburon Peninsula, California, USA; corresponds to (Na1:96Ca0:04)§=2:00(Mg2:39Al1:82 2+ 3+ Fe0:61Fe0:18)§=5:00Si8O22(OH)2: (2) Kodiak Islands, Alaska, USA; by electron microprobe, 2+ 3+ 2+ 3+ Fe :Fe calculated; corresponds to (Na1:90Ca0:09K0:02)§=2:01(Al1:82Mg1:74Fe1:20Fe0:18 Mn0:03Ti0:02Cr0:01)§=5:00(Si7:83Al0:17)§=8:00O22(OH)2: Polymorphism & Series: Forms a series with ferroglaucophane.
    [Show full text]
  • 1 Revision 1 1 the High-Pressure Phase of Lawsonite
    1 Revision 1 2 The high-pressure phase of lawsonite: A single crystal study of a key mantle hydrous phase 3 4 Earl O’Bannon III,1* Christine M. Beavers1,2, Martin Kunz2, and Quentin Williams1 5 1Department of Earth and Planetary Sciences, University of California, Santa Cruz, 1156 High 6 Street, Santa Cruz, California 95064, U.S.A. 7 2Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, 8 U.S.A. 9 *Corresponding Author 10 1 11 Abstract 12 Lawsonite CaAl2Si2O7(OH)2·H2O is an important water carrier in subducting oceanic 13 crusts, and the primary hydrous phase in basalt at depths greater than ~80 km. We have 14 conducted high-pressure synchrotron single-crystal x-ray diffraction experiments on natural 15 lawsonite at room temperature up to ~10.0 GPa to study its high-pressure polymorphism. We 16 find that lawsonite remains orthorhombic with Cmcm symmetry up to ~9.3 GPa, and shows 17 nearly isotropic compression. Above ~9.3 GPa, lawsonite becomes monoclinic with P21/m 18 symmetry. Across the phase transition, the Ca polyhedron becomes markedly distorted, and 19 the average positions of the H2O molecules and hydroxyls change. The changes observed in the 20 H-atom positions under compression are different than the low temperature changes in this 21 material. We resolve for the first time the H-bonding configuration of the high-pressure 22 monoclinic phase of lawsonite. A bond valence approach is deployed to determine that the 23 phase transition from orthorhombic to monoclinic is primarily driven by the Si2O7 groups, and in 24 particular it's bridging oxygen atom (O1).
    [Show full text]
  • Author's Personal Copy
    Author's personal copy Tectonophysics 494 (2010) 201–210 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Elasticity of glaucophane, seismic velocities and anisotropy of the subducted oceanic crust L. Bezacier a,⁎, B. Reynard a, J.D. Bass b, J. Wang b, D. Mainprice c a Université de Lyon, Laboratoire de Sciences de la Terre, CNRS, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France b Department of Geology, University of Illinois, Urbana, IL, 61801, USA c Géosciences Montpellier UMR CNRS 5343, Université Montpellier 2, 34095 Montpellier Cedex 05, France article info abstract Article history: Upon subduction, the oceanic crust transforms to blueschists and eclogites, with seismic properties that Received 8 March 2010 gradually become similar to those of the surrounding mantle. In order to evaluate the anisotropy of Received in revised form 30 July 2010 blueschists and glaucophane-bearing eclogites, the elastic constants of glaucophane single-crystal plates from Accepted 9 September 2010 the Sesia–Lanzo Zone (Aosta Valley, Western Alps) were measured using Brillouin spectroscopy at ambient Available online 17 September 2010 conditions. The mean P- and S-wave velocities are 7.8 and 4.6 km s−1 respectively, and the anisotropy is high Keywords: (38.1% (AVP) and 27.3% (AVS)). Glaucophane develops strong LPO, characterized by the [001]-axes Elasticity concentrated sub-parallel to the lineation, and the {110} poles concentrated sub-perpendicular to the Glaucophane foliation in both blueschist and eclogite rocks. The measured LPO is in good agreement with viscoplastic self- Epidote consistent numerical models.
    [Show full text]
  • Metamorphic Evolution of High-Pressure, Low-Temperature Mafic Rocks Near Kini on the Island of Syros, Greece
    Metamorphic evolution of high-pressure, low-temperature mafic rocks near Kini on the island of Syros, Greece Erica DiFilippo Department of Geology, Smith College, Clark Science Center, Northampton, MA 01063-0100 Faculty sponsor: John B. Brady, Smith College INTRODUCTION The island of Syros in the Greek Cyclades exposes Eocene high-pressure, low temperature metamorphic rocks including marbles, blueschists and pelitic schists (Ridley, 1981). It has been proposed that these units have experienced two major eclogite-blueschist facies metamorphic events, the first occurring at 470-520°C and 14-18 kb and the second not exceeding 460°C and 14 kb (Lister, 1996). At approximately 20-25 Ma, these units became regionally overprinted by a medium-pressure metamorphism (Schliestedt, 1987). A well exposed sequence of metamorphosed mafic and ultra-mafic rocks outcrops along a 2.5 km long coastal cliff near Kini on the western coast of Syros. This suite consists of segments of glaucophane schist, eclogite, omphacite-epidote rock, pelitic schist, and serpentinite with blackwall reaction zones separating the serpentinite from the other rock types. This study combines petrographic and chemical evidence in order to determine whether the difference in the units exposed at Kini is due to differing bulk compositions or to differing metamorphic grades. FIELD RELATIONS Lithologies change dramatically over the 2.5 km coastal cliff of Kini. There is no distinct gradational pattern to the rock units exposed. Beginning at the southern tip of the field area and working northward, the rock units are glaucophane schist, omphacite-zoisite rock, glaucophane schist, eclogite, serpentinite and blackwall reaction zones, glaucophane schist, a greenschist facies unit and pelitic schist.
    [Show full text]
  • List of Abbreviations
    List of Abbreviations Ab albite Cbz chabazite Fa fayalite Acm acmite Cc chalcocite Fac ferroactinolite Act actinolite Ccl chrysocolla Fcp ferrocarpholite Adr andradite Ccn cancrinite Fed ferroedenite Agt aegirine-augite Ccp chalcopyrite Flt fluorite Ak akermanite Cel celadonite Fo forsterite Alm almandine Cen clinoenstatite Fpa ferropargasite Aln allanite Cfs clinoferrosilite Fs ferrosilite ( ortho) Als aluminosilicate Chl chlorite Fst fassite Am amphibole Chn chondrodite Fts ferrotscher- An anorthite Chr chromite makite And andalusite Chu clinohumite Gbs gibbsite Anh anhydrite Cld chloritoid Ged gedrite Ank ankerite Cls celestite Gh gehlenite Anl analcite Cp carpholite Gln glaucophane Ann annite Cpx Ca clinopyroxene Glt glauconite Ant anatase Crd cordierite Gn galena Ap apatite ern carnegieite Gp gypsum Apo apophyllite Crn corundum Gr graphite Apy arsenopyrite Crs cristroballite Grs grossular Arf arfvedsonite Cs coesite Grt garnet Arg aragonite Cst cassiterite Gru grunerite Atg antigorite Ctl chrysotile Gt goethite Ath anthophyllite Cum cummingtonite Hbl hornblende Aug augite Cv covellite He hercynite Ax axinite Czo clinozoisite Hd hedenbergite Bhm boehmite Dg diginite Hem hematite Bn bornite Di diopside Hl halite Brc brucite Dia diamond Hs hastingsite Brk brookite Dol dolomite Hu humite Brl beryl Drv dravite Hul heulandite Brt barite Dsp diaspore Hyn haiiyne Bst bustamite Eck eckermannite Ill illite Bt biotite Ed edenite Ilm ilmenite Cal calcite Elb elbaite Jd jadeite Cam Ca clinoamphi- En enstatite ( ortho) Jh johannsenite bole Ep epidote
    [Show full text]
  • What We Know About Subduction Zones from the Metamorphic Rock Record
    What we know about subduction zones from the metamorphic rock record Sarah Penniston-Dorland University of Maryland Subduction zones are complex We can learn a lot about processes occurring within active subduction zones by analysis of metamorphic rocks exhumed from ancient subduction zones Accreonary prism • Rocks are exhumed from a wide range of different parts of subduction zones. • Exhumed rocks from fossil subduction zones tell us about materials, conditions and processes within subduction zones • They provide complementary information to observations from active subduction systems Tatsumi, 2005 The subduction interface is more complex than we usually draw Mélange (Bebout, and Penniston-Dorland, 2015) Information from exhumed metamorphic rocks 1. Thermal structure The minerals in exhumed rocks of the subducted slab provide information about the thermal structure of subduction zones. 2. Fluids Metamorphism generates fluids. Fossil subduction zones preserve records of fluid-related processes. 3. Rheology and deformation Rocks from fossil subduction zones record deformation histories and provide information about the nature of the interface and the physical properties of rocks at the interface. 4. Geochemical cycling Metamorphism of the subducting slab plays a key role in the cycling of various elements through subduction zones. Thermal structure Equilibrium Thermodynamics provides the basis for estimating P-T conditions using mineral assemblages and compositions Systems act to minimize Gibbs Free Energy (chemical potential energy) Metamorphic facies and tectonic environment SubduconSubducon zone metamorphism zone metamorphism Regional metamorphism during collision Mid-ocean ridge metamorphism Contact metamorphism around plutons Determining P-T conditions from metamorphic rocks Assumption of chemical equilibrium Classic thermobarometry Based on equilibrium reactions for minerals in rocks, uses the compositions of those minerals and their thermodynamic properties e.g.
    [Show full text]
  • Decomposition of Kyanite and Solubility of Al2o3 in Stishovite at High Pressure and High Temperature Conditions
    Phys Chem Minerals (2006) 33:711–721 DOI 10.1007/s00269-006-0122-x ORIGINAL PAPER Decomposition of kyanite and solubility of Al2O3 in stishovite at high pressure and high temperature conditions Xi Liu Æ Norimasa Nishiyama Æ Takeshi Sanehira Æ Toru Inoue Æ Yuji Higo Æ Shizue Sakamoto Received: 9 August 2006 / Accepted: 9 October 2006 / Published online: 3 November 2006 Ó Springer-Verlag 2006 Abstract In order to constrain the high-pressure Keywords Al2O3 solubility in stishovite Á Corundum Á behavior of kyanite, multi-anvil experiments have been Kyanite Á Phase equilibrium Á Stishovite carried out from 15 to 25 GPa, and 1,350 to 2,500°C. Both forward and reversal approaches to phase equi- libria were adopted in these experiments. We find that Introduction kyanite breaks down to stishovite + corundum at pressures above ~15 GPa, and stishovite + corundum Kyanite (Ky, Al2SiO5), commonly found in peralumi- should be the stable phase assemblage at the pressure– nous eclogites and amphibolites, has been soundly temperature conditions of the transition zone and the demonstrated to be an important constituent phase for uppermost part of the lower mantle of the Earth, the materials of continental crust and pelagic sediment in agreement with previous multi-anvil experimental at pressures from ~1 to 16 GPa (Irifune et al. 1994; studies and ab initio calculation results, but in dis- Schmidt et al. 2004). Its role at higher pressures, how- agreement with some of the diamond-anvil cell ever, remains unclear. With some preliminary experi- experimental studies in the literature. The Al2O3 sol- ments in a Bridgman–anvil apparatus, Ringwood and ubility in nominally dry stishovite has been tightly Reid (1969) tentatively suggested that Ky appears sta- bracketed by forward and reversal experiments; it is ble up to 15 GPa and 1,000°C.
    [Show full text]
  • Compositional Zoning in Sodic Amphiboles from the Blueschist Facies
    MINERALOGICAL MAGAZINE, JUNE 1980, VOL. 43, PP. 741-52 Compositional zoning in sodic amphiboles from the blueschist facies ROBERT MUIR WOOD Department of Mineralogy and Petrology, Downing Place, Cambridge SUMMARY. The sodic amphiboles possess two inde- possible through solving the simultaneous equa- pendent chemical substitution series (Fe3 + -AI and Fe2 + - tions for charge balance and site occupancy. In Mg) that combine to provide a 'plane' of compositions. order to demonstrate the superiority of this tech- Yet at no single T and P are compositions covering the nique over artificial alternatives (such as that whole plane stable: (i) pure riebeckite exists under low-P of splitting the iron equally, Ernst, 1979) a partial conditions but breaks down in normal blueschists to give deerite; (ii) ferro-glaucophane is in competition at all statistical analysis of the method is presented in except the lowest blueschist temperatures with almandine Appendix I. garnet; (iii) magnesio-riebeckite is stable at high-T and The amphiboles that have formed the substance low-P but within the blueschist facies is replaced by the of this paper were collected from localities in Cali- alternative higher density aegirine-talc assemblage; and fornia, Oregon, Washington State, the Alps, and (iv) glaucophane is stable only at high-Po Greece. Further details of specific localities may be At higher T and P than those of the blueschists, com- found within the following authors' works: Layton- petition from NaCa pyroxenes, garnets, and deerite first ville Quarry exotic block, Mendocino Co., erodes, and then removes, nearly all sodic amphibole California-Chesterman (1966); Ward Creek, compositions.
    [Show full text]
  • Staurolite｜Bearing Gneiss and Re｜Examination of Metamorphic
    Staurolite－bearingJournal gneiss of Mineralogical and re－examination and Petrological of metamorphic Sciences, zonal Volume mapping 99 ,of page the Higo1─ 18, metamorphic2004 terrane 1 Staurolite－bearing gneiss and re－examination of metamorphic zonal mapping of the Higo metamorphic terrane in the Kosa area, central Kyushu, Japan * * ** Kenshi MAKI , Yoshihisa ISHIZAKA and Tadao NISHIYAMA *Graduate School of Science and Technology, Kumamoto University, 2－39－1 Kurokami, Kumamoto 860－8555, Japan **Department of Earth Sciences, Faculty of Science, Kumamoto University, 2－39－1 Kurokami, Kumamoto 860－8555, Japan This paper describes the finding of staurolite－bearing gneiss from the Higo metamorphic terrane and proposes new mineral zones in the Kosa area, Kumamoto Prefecture. Previous mineral zones of the Higo metamorphic terrane proposed by Obata et al. (1994) consist of five zones: Zone A characterized by Chl + Ms, Zone B by Bt + Ms + And, Zone C by Kfs + Sil + Bt, Zone D by Grt + Crd + Bt, and Zone E by Opx in metapelites. They identified three zones from B to D in the Kosa area. However, we found that sillimanite appears together with Grt + Crd, hence this paper shows that Zone C is absent in the Kosa area. New finding of Opx in the southern－ most part of the area made it possible to define three mineral zones; Bt zone, Grt－Crd zone, and Opx zone, in the order of increasing grade from north to south in the Kosa area. Analysis of staurolite－bearing assemblage in a KFMASH system together with textural evidence reveals that the following reactions occurred in the stauro- － lite bearing gneiss in the excess of Kfs, Qtz and H2O: [Sil] Str + Bt = Grt + Crd [Bt] Str = Grt + Crd + Sil Chemographic analysis of these reactions together with Grt－Bt geothermometers shows the metamorphic condition of P = 200 MPa and T = 600－620°C, which is much lower in pressure than that estimated by Osanai et al.
    [Show full text]
  • Electronic Supplementary Material (ESI) for Journal of Analytical Atomic Spectrometry This Journal Is © the Royal Society of Chemistry 2012
    Electronic Supplementary Material (ESI) for Journal of Analytical Atomic Spectrometry This journal is © The Royal Society of Chemistry 2012 ELECTRONIC SUPPLEMENTARY INFORMATION FOR Iron oxidation state in garnet from a subduction setting: a micro-XANES and electron microprobe (“flank method”) comparative study Elisa Borfecchia2, Lorenzo Mino2*, Diego Gianolio2, Chiara Groppo1*, Nadia Malaspina3, Gema Martinez-Criado5, Juan Angel Sans Tresserras5, Stefano Poli4, Daniele Castelli1 and Carlo Lamberti2 1 – Dept. Earth Sciences, University of Torino, via Valperga Caluso 35, I-10125 Torino (Italy) 2 – Dept. of Chemistry, University of Torino, via Giuria 7, I-10125 Torino (Italy); NIS Centre of Excellence and INSTM Centro di Riferimento, via Quarello 11, I-10135, Torino (Italy) 3 – Dept. of Geological Sciences and Geotechnology, Università degli Studi di Milano-Bicocca, Piazza della Scienza 4, I-20126 Milano (Italy) 4 – Dept. of Earth Sciences, Università degli Studi di Milano, via Botticelli 23, I-20133 Milano (Italy) 5 - European Synchrotron Radiation Facility, ID22, 6, rue Jules Horowitz, B.P. 220, F-38043 Grenoble cedex (France) Sample description The studied sample OF2727 is a fine-grained eclogitized metagabbro from the Monviso meta- ophiolite (western Alps), consisting of omphacite, garnet and rutile with minor blue amphibole and very minor lawsonite, talc and jadeite, as described by Groppo and Castelli.1 Garnet occurs as small idioblasts (up to 0.5 mm in diameter) set in a matrix mainly consisting of omphacite. Garnet cores (1a-1e in Fig. S1) are crowded of very small inclusions mostly of omphacite, whereas garnet rims (2a-2c in Fig. S1) are almost free of inclusions. Both SEM-EDS and EMP analytical techniques have been used to analyze the major element concentrations across garnet crystals.
    [Show full text]
  • Identification Tables for Common Minerals in Thin Section
    Identification Tables for Common Minerals in Thin Section These tables provide a concise summary of the properties of a range of common minerals. Within the tables, minerals are arranged by colour so as to help with identification. If a mineral commonly has a range of colours, it will appear once for each colour. To identify an unknown mineral, start by answering the following questions: (1) What colour is the mineral? (2) What is the relief of the mineral? (3) Do you think you are looking at an igneous, metamorphic or sedimentary rock? Go to the chart, and scan the properties. Within each colour group, minerals are arranged in order of increasing refractive index (which more or less corresponds to relief). This should at once limit you to only a few minerals. By looking at the chart, see which properties might help you distinguish between the possibilities. Then, look at the mineral again, and check these further details. Notes: (i) Name: names listed here may be strict mineral names (e.g., andalusite), or group names (e.g., chlorite), or distinctive variety names (e.g., titanian augite). These tables contain a personal selection of some of the more common minerals. Remember that there are nearly 4000 minerals, although 95% of these are rare or very rare. The minerals in here probably make up 95% of medium and coarse-grained rocks in the crust. (ii) IMS: this gives a simple assessment of whether the mineral is common in igneous (I), metamorphic (M) or sedimentary (S) rocks. These are not infallible guides - in particular many igneous and metamorphic minerals can occur occasionally in sediments.
    [Show full text]