DOCSLIB.ORG

Formation Process of Olivine–Clinopyroxene Cumulates Inferred from Takashima Xenoliths, Southwest Japan Arc

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Formation Process of Olivine–Clinopyroxene Cumulates Inferred from Takashima Xenoliths, Southwest Japan Arc Journal of Mineralogical and Petrological Sciences, Volume 109, page 79–84, 2014 LETTER Formation process of olivine–clinopyroxene cumulates inferred from Takashima xenoliths, Southwest Japan arc Ritsuko MUROI and Shoji ARAI Department of Earth Sciences, Kanazawa University, Kanazawa 920–1192, Japan Rocks of the dunite–clinopyroxenite series (dunite, wehrlite, olivine clinopyroxenite, and clinopyroxenite) are common as cumulates formed around Moho in arc–related environments, but their formation processes remain unclear. They are common as xenoliths of Group I from Takashima in the Southwest Japan arc, and a descrip- tion of their formation process is provided here. The rocks vary from dunite to clinopyroxenite via wehrlite and olivine clinopyroxenite, and all showing mosaic equigranular to weakly porphyroclastic textures. The rocks are completely free from plagioclase, and they contain <3 vol% chromian spinel. Some of them contain up to 3 vol% orthopyroxene; these are approximate mixtures of olivine and clinopyroxene. As the dunites change to clinopyroxenites, the Mg# [= Mg/(Mg + total Fe) atomic ratio] varies from 0.93 to 0.84 in olivine, and from 0.92 to 0.87 in clinopyroxene. The Cr# [= Cr/(Cr + Al) atomic ratio] of the chromian spinel varies from 0.8 to 0.2 with decreases in the Mg# of olivine and clinopyroxene. The Mg–Fe distribution relation between olivine and clinopyroxene suggests their subsolidus equilibration is around 800–900 °C. Initial Mg#s expected at a magmatic temperature indicate that their formation proceeded from magma in the order of Mg–rich dunites followed by clinopyroxenites and then less Mg–rich dunite–wehrlite–olivine clinopyroxenite. This suggests a zigzag liquid path, starting from a mantle–derived olivine–oversaturated magma, around the olivine–clinopy- roxene cotectic boundary. Continuous crystallization of olivine or clinopyroxene due to supersaturation could have enabled the magma to straddle the cotectic boundary to form alternately clinopyroxene– and olivine– oversaturated magmas. Keywords: Dunites, Wehrlites, Clinopyroxenites, Xenoliths, Cumulates, Takashima, Supersaturation INTRODUCTION enite series rocks (cf., Wandji et al., 2009). Igneous proc- esses for the formation of dunite–clinopyroxenite series Plutonic rocks of the dunite–clinopyroxenite series, i.e., rocks remain unclear despite their common occurrences. dunites, wehrlites, olivine clinopyroxenites, and clinopy- Crystal accumulation during the perfect fractional crys- roxenites, are commonly found in ophiolites (e.g., Ishi- tallization of a mantle–derived basaltic melt, which is oli- watari, 1985; Benn et al., 1988) and as xenoliths (e.g., vine–oversaturated at low pressures, may produce dunite Arai et al., 2000). They are especially important as the followed by olivine clinopyroxenite based on the appro- main constituents of the MTZ (Moho transition zone) of priate phase diagrams (cf., Kushiro, 1969). Wehrlite and arc–derived ophiolites (e.g., Parlak et al., 2002) as well as monomineralic clinopyroxenite cannot be, however, form- of Alaskan–type zoned complexes (e.g., Krause et al., ed by this process. 2007). Dunites and wehrlites distributed around the Moho We describe xenoliths of dunite–wehrlite–clinopy- transition zone are interpreted to be cumulates and/or re- roxenite of Group I (Frey and Prinz, 1978) from Takashima action products between the melt and harzburgite (Koga in the Southwest Japan arc (Arai et al., 2000), and discuss et al., 2001; Negishi et al., 2013). There have been many their formation process as cumulates in the sub–arc con- papers dealing with xenoliths of dunites (e.g., Sen and dition. The analyzed samples are representative of the up- Presnall, 1986) and clinopyroxenites (e.g., Neumann et permost part of the sub–arc mantle (e.g., Takahashi, 1978). al., 1988), but only a few studies on dunite–clinopyrox- doi:10.2465/jmps.131003 GEOLOGICAL BACKGROUND R. Muroi, [email protected] Corresponding author S. Arai, [email protected]–u.ac.jp Large amounts of ultramafic xenoliths from Takashima 80 R. Muroi and S. Arai are found in beach boulders of alkali olivine basalt of 3.0 a microprobe and analyzed the clinopyroxene for REE Ma (Nakamura et al., 1986) on Takashima Island, Kara- (rare earth elements) using La–ICP–MS. See the Appen- tsu City, Saga Prefecture, northern Kyushu, Japan (e.g., dix (available online from http://japanlinkcenter.org/DN/ Arai et al., 2000, 2001). Most of ultramafic xenoliths are JST.JSTAGE/jmps/131003) for analytical details. All Fe less than 30 cm across, and dominated by dunite–wehr- was assumed to be Fe2+ in silicates, and Fe2+ and Fe3+ lite–clinopyroxenite series rocks of both Group I (meta- were calculated assuming a spinel stoichiometry. Mg# morphic, green Cr–rich clinopyroxene bearing) and and Cr# represent Mg/(Mg + Fe2+) and Cr/(Cr + Al) atom- Group II (igneous, black Al–rich clinopyroxene bearing) ic ratios, respectively. Fe# is (1–Mg#). Fo is 100 × Mg# in the sense of Frey and Prinz (1978) (Arai et al., 2000). in olivine. Table 1 shows the results for the selected anal- Arai et al. (2000) presumed a thick ‘cumulus mantle’ lay- yses on the major to minor elements of olivine, clinopy- er (Takahashi, 1978) comprised of dunite–wehrlite–py- roxene, and chromian spinel, whereas results for the REE roxenites of Group I, which could be equivalent to the of clinopyroxene are shown in Table 2 (available online Moho transition zone of ophiolite (Arai and Abe, 1994), from http://japanlinkcenter.org/DN/JST.JSTAGE/jmps/ beneath Takashima. The ‘cumulus mantle’ layer has been 131003). intruded by pyroxenites of Group II (Arai et al., 2000, Olivines, clinopyroxenes, and chromian spinels are 2006). See Arai et al. (2001) for more details. homogeneous in chemistry except for rims in contact with different minerals, and homogeneous core composi- PETROGRAPHICAL DESCRIPTIONS tions were used in this study. Olivines were found to be highly Mg–rich (Fo >90) in clinopyroxene–free dunites, Rocks of the dunite–clinopyroxenite series have various and less Mg–rich (Fo >84) in clinopyroxene–rich rocks appearances on alkali olivine basalt boulders (Fig. 1). (wehrlites to clinopyroxenites) (Table 1 and Fig. 2). NiO Nearly homogeneous dunites (Fig. 1a) and olivine–bear- and MnO contents of olivine vary from 0.4 to 0.1 wt% ing clinopyroxenites (Fig. 1b) are frequent, while homo- and 0.1 to 0.2 wt%, respectively, in an approximate rela- geneous wehrlites are less frequent. Various dunite–clino- tion to decreases in Fo. The Mg# of clinopyroxene varies pyroxenite composite xenoliths are commonly found nearly with that of olivine from 0.92 (olivine–rich rocks) (Figs. 1c and 1d); it is noteworthy that the mixture of dun- to 0.86 (clinopyroxene–rich rocks) (Fig. 2). The Al2O3 ite and clinopyroxenite was more common than the homo- content of clinopyroxene varies from 1 to 4 wt% with a geneous wehrlite. For the nearly homogeneous samples, decrease in Mg# (Table 1). Clinopyroxenes are mostly dunites grade to clinopyroxenites with a gap at olivine rich in Cr2O3, containing 0.5 to 0.7 wt% irrespective of clinopyroxenites that could be due to incomplete sam- rock type (Table 1). The Cr# of chromian spinel changes pling. We could not observe fine–scale layering in these from 0.8 to 0.2 with the Fo of olivine. The TiO2 content rocks, which is in contrast to those in some ophiolites of chromian spinel varied from 0.3 wt% in dunites and up (e.g., Ishiwatari, 1985). to 0.8 wt% in clinopyroxene–rich rocks (Table 1). The The dunite–clinopyroxenite series rocks contain Fe3+/(Cr + Al + Fe3+) atomic ratio is around 0.1 (Table 1). small amounts (<3 vol%) of chromian spinel, and some The REE patterns of clinopyroxene, which was nor- of them contain orthopyroxene (<3 vol%), which is malized to the chondritic abundances (Sun and McDo- roughly in proportion to the amount of clinopyroxene. nough, 1989), are strikingly similar. The normalized val- They are completely free from plagioclase. Furthermore, ues exhibit a gentle convex upward trend from Lu to Sm, they commonly exhibit mosaic equigranular to weakly where their levels are also similar in individual samples, porphyroclastic textures. Coarse (<7 mm across) grains and roughly in sympathy with the initial igneous Mg# of olivine and clinopyroxene exhibit deformation fea- (see DISCUSSION) (Fig. 3). No zonation in terms of tures, i.e., kinking and/or undulatory extinction under REE contents was observed in the clinopyroxene grains. the microscope. Some coarse clinopyroxene grains exhib- The patterns were, however, highly variable from Sm to it exsolution lamellae, but the orthopyroxene is free from La, sometimes even in a single thin section (Fig. 3). The them. Chromian spinel is less than 0.5 mm across, and enrichment of light REEs in clinopyroxene is not corre- black to brown in color for the thin sections. Constituents lated with any petrographic or chemical features of the of composite xenoliths are similar in petrography to the host rock. equivalents occurring as discrete xenoliths. Variations of mineral chemistry are discussed below based on the initial recalculated high–temperature Mg# of MINERAL CHEMISTRY olivine and clinopyroxene. We analyzed minerals for major to minor elements using Formation process of olivine–clinopyroxene cumulates 81 2 (a) (b) 10 Wehrlite (TK-28-2, Mg#=0.898) Clinopyroxenite (TK-02, Mg#=0.883) Dunite (TK-20, Mg#=0.871) Wehrlite (TK-35, Mg#=0.856) 1 10 0 (c) (d) 10 Cpx / C1 chondrite -1 10 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 3. Chondrite–normalized REE patterns of clinopyroxene in dunite–clinopyroxenite series xenoliths from Takashima. The in- Figure 1. Xenoliths of dunite–clinopyroxenite series from Taka- itial Mg#s (discussed below) are shown in parentheses. Chon- shima, the Southwest Japan arc. (a) Dunite nearly free from drite values from Sun and McDonough (1989). Note the pat- clinopyroxene. (b) Homogeneous olivine clinopyroxenite.
Load more

Recommended publications
  • Podiform Chromite Deposits—Database and Grade and Tonnage Models
    Podiform Chromite Deposits—Database and Grade and Tonnage Models Scientific Investigations Report 2012–5157 U.S. Department of the Interior U.S. Geological Survey COVER View of the abandoned Chrome Concentrating Company mill, opened in 1917, near the No. 5 chromite mine in Del Puerto Canyon, Stanislaus County, California (USGS photograph by Dan Mosier, 1972). Insets show (upper right) specimen of massive chromite ore from the Pillikin mine, El Dorado County, California, and (lower left) specimen showing disseminated layers of chromite in dunite from the No. 5 mine, Stanislaus County, California (USGS photographs by Dan Mosier, 2012). Podiform Chromite Deposits—Database and Grade and Tonnage Models By Dan L. Mosier, Donald A. Singer, Barry C. Moring, and John P. Galloway Scientific Investigations Report 2012-5157 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 This report and any updates to it are available online at: http://pubs.usgs.gov/sir/2012/5157/ For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Suggested citation: Mosier, D.L., Singer, D.A., Moring, B.C., and Galloway, J.P., 2012, Podiform chromite deposits—database and grade and tonnage models: U.S.
    [Show full text]
  • Chromite Deposits of the North Elder Creek Area Tehama County, California
    UNITED STATES DEPARTMENT OF THE INTERIOR J. A. Krug, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director Bulletin 945-G CHROMITE DEPOSITS OF THE NORTH ELDER CREEK AREA TEHAMA COUNTY, CALIFORNIA By G. A. RYNEARSON Strategic Minerals Investigations, 1944 (Pages 191-210) UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1946 CONTENTS Page Abstract................................................... 191 Introduction............................................... 192 History and production..................................... 192 Geology.................................................... 194 Franciscan formation................................... 194 Knoxville formation.................................... 195 Argillite and metavolcanic rocks................... 195 Shale and sandstone................................ 195 Peridotite and serpentine.............................. 195 Saxonite........................................... 196 Dunite............................................. 196 Wehrlite........................................... 196 Serpentine......................................... 196 Dike rocks............................................. 197 Alteration............................................. 197 Structure.............................................. 198 Ore bodies................................................. 199 Mineralogy............................................. 199 Character of ore....................................... 200 Localization........................................... 202 Origin................................................
    [Show full text]
  • High-Temperature Ultramafic Complexes in the North Norwegian Caledonides: I - Regional Setting and Field Relationships
    High-temperature ultramafic complexes in the North Norwegian Caledonides: I - Regional setting and field relationships M.C. BENNETT, S,R. EMBLIN, B, ROBINS & W.J.A. YEO Bennett, M.C., Emblin, S.R., Robins, B. & Yeo, W.J.A. 1986: High+emperature ultramafic complexes in the North Norwegian Caledonides: I - Regional setting and field relationships. Nor. geol. unders. Bull.405, r40. Four major (25-100 km¡) ultramafìc complexes were developed in the Sørøy Nappe during the second phase of Finnmarkian deformation in the North Norwegian Caledonides. They were emplaced into layered mafic intrusions and show broadly similar emplacement histories and petrographic variations suggesting a related petrogenesis. The Nordre Bumannsford, Melkvann and Kvalford group of ulramafic complexes developed in part by emplacement ofboth replacive and dilational ne-normative ultramafic sheets and dykes which progressively fragmented the layered olivine gabbro envelope. The earliest dykes and sheets are from a few cm to l00m wide and show highly inegular, nondilational contacls. They are dominantly coarse-grained, xenolithic olivine clinopyroxenite varying locally to dunite, poikilitic wehrlite, feldspat- hic olivine clinopyroxenite and olivine melagabbro. Iater dykes are from a few cm to 20 m wide and also lack chilled margins but show regular, dilational contact relationships. They include poikilitic wehrlite (commonly spatially associated with veins and patches of secondary wehrlite and dunite), olivine clinopyroxenite, olivinehornblende clinopyroxenite, hornblende peridotite and homblende melagabbro. Some members of the dyke suite exhibit mineral lamination, modal layering and cyclic units, and others contain mosaic-porphyroclastic spinel lher¿olite nodules. Variably foliated and metamorphosed olivine gabbro, ankaramite and picrite dykes with chilled maryins were emplaced during the latest stages in the evolution ofthe complexes.
    [Show full text]
  • Occurrence of Gabbro-Wehrlite Near Lochalsh, Ontario M
    OCCURRENCE OF GABBRO-WEHRLITE NEAR LOCHALSH, ONTARIO M. H. Fnonsnnc. MacassaMi.nes. Li.mited., Toromto, Ontar'i.o, Ansrnecr Gabbro-wehrlite consisting of more than80/6 dark constituents, but in excess of 1016 plagioclase, forms the marginal facies of a mela-olivine gabbro intrusion near Lochalsh, about 150 miles north of Sault Ste. Marie, Ontario. This exceptionally fresh rock is of in- terest as a link between the gabbro and peridotite clans. In his report on the iron deposits of the Missinaibi map area, E. Thompsonl mentioned the occurrenceof peridotite at the northwest end of Dog Lake, about 1$ miles southeast of the Canadian Pacific Railway station Lochalsh. The intrusive body is roughly elliptical in outline, with its major axis striking almost due east. It is slightly over one mile long and up to 1,500 ft. wide, forming a prominent ridge rising more than 300 ft. above the level of Dog Lake. Thompson describedthis remarkably fresh basic rock as consisting essentially of pyroxene and olivine, with lesser quantities of plagioclase and biotite, and some serpentine and hornblende as secondary products. The present writer investigated the occurrencereferred to by Thomp- son, in connection with a search for war-important minerals. Micro- scopic examination of a considerablenumber of samplestaken at various points of the intrusion revealed that its plagioclase content exceedsthe amount of leucocratic constituents allowed by most petrographers in rocks classedas peridotites. Actually the mass consistsof a core bearing from 20 to 45/s plagioclase,and a more melanocratic border zone aver- aging Iessthan20/s plagioclase.In no instance was the feldspar content Iessthan t0/6 of the total constituents.
    [Show full text]
  • Igneous Petrology EOSC 321 Laboratory 1: Ultramafic Plutonic and Volcanic Rocks
    1 Igneous petrology EOSC 321 Laboratory 1: Ultramafic plutonic and volcanic rocks Material Needed: a) Microscope, b) Glossary of rock names and textures (see Pages 24- 25 and 43 of Winter); c) Lab1 Manual printed off the course website; d) tables to aid determination of mineral modes in thin sections; e) classification triangles; f) a Manual on Optical Mineralogy (i.e. Minerals in Thin Section by Perkins and Henke) Microscopes: At the start of the lab period, you will be assigned a microscope and the combination to the microscope locker by your TA. You will have access to this microscope throughout the remainder of the course. The microscope will be shared with students from the other laboratories. Please keep the microscopes in working condition and, should a problem arise, let your TA know immediately so that repairs can be made. Lab Organization: Review optical properties of common rock-forming minerals so that you’re able to identify them. There is a box with reference thin sections for igneous rock- forming minerals that can be helpful in this respect. In the next two hours of the lab period you will examine reference thin sections of ultramafic rocks. Each thin section has a brief petrographic description to assist you in the identification of minerals, textures and rock classification. Please make sure you understand the reference petrographic descriptions and can find all of the minerals mentioned. You should also be able to understand why a rock is given a particular name. For these, you should recap how to assess mineral modes under a microscope, and how to plot these on rock classification triangles.
    [Show full text]
  • Translithospheric Mantle Diapirism: Geological Evidence and Numerical Modelling of the Kondyor Zoned Ultramafic Complex (Russian Fa R-E a S T )
    JOURNAL OF PETROLOGY VOLUME 50 NUMBER 2 PAGES 289^321 2009 doi:10.1093/petrology/egn083 Translithospheric Mantle Diapirism: Geological Evidence and Numerical Modelling of the Kondyor Zoned Ultramafic Complex (Russian Fa r-E a s t ) J.-P. BURG1*,J.-L.BODINIER2,T.GERYA1, R.-M. BEDINI2, F. BOU DI ER 2,J.-M.DAUTRIA2,V.PRIKHODKO3,A.EFIMOV4, E. PUPIER2 AND J.-L. BALANEC2 1EARTH SCIENCES DEPARTMENT, ETH ZENTRUM AND UNIV. ZU« RICH, SONNEGGSTRASSE 5, ZU« RICH, 8092, SWITZERLAND 2GE¤ OSCIENCES MONTPELLIER, UNIVERSITE¤ DE MONTPELLIER 2 & CNRS, CC 60, PLACE EUGE' NE BATAILLON, 340 95 MONTPELLIER CEDEX 05, FRANCE 3INSTITUTE OF TECTONICS AND GEOPHYSICS, RUSSIAN ACADEMY OF SCIENCES, 680063 KHABAROVSK, RUSSIA 4INSTITUTE OF GEOLOGY AND GEOCHEMISTRY, RUSSIAN ACADEMY OF SCIENCES, 620151 EKATERINBURG, RUSSIA RECEIVED MARCH 10, 2008; ACCEPTED DECEMBER 30, 2008 We report new structural, microstructural, petrological, and major- core metasomatic zone, with a decreasing melt fraction from core to and trace-element data on ultramafic rocks from the Kondyor zoned rim, and also suggest that solid-state deformation induced grain-size ultramafic complex in Far-East Russia. The ultramafic rocks are reduction towards the cooling border of the Kondyor massif. Based on subdivided into three subconcentric lithologies, from core to rim: (1) their geochemistry, the dunites are interpreted as mantle rocks a metasomatic domain where generally phlogopite-rich dykes perva- strongly affected by reaction with melts similar to the Jurassic^ sively intrude dunite; (2) a main dunite core; (3) a pyroxenite rim. Cretaceous Aldan Shield lamproites. Rim pyroxenites were formed The ultramafic rocks have nearly vertical contacts with the sur- by a melt-consuming peritectic reaction, implying the existence of at rounding Archaean basement (gneisses, quartzites and marbles) least a small, conductive thermal gradient around the dunite body and hornfelsed Riphean sediments.The hornfelsed sediments show a while the latter was still at near-solidus temperature conditions.
    [Show full text]
  • Eclogite Formation and the Rheology, Buoyancy, Seismicity, and H2O
    Eclogite Formationand the Rheology,Buoyancy, Seismicity,and H20 Contentof OceanicCrust BradleyR. Hacker1 Departmentof Geologicaland EnvironmentalSciences, Stanford University, Stanford, California A broad spectrumof variably altered igneous rocks with a wide range of grain sizes are compressedand heated over a wide range of pressure-temperaturepaths in subductionzones. Although experimentalkinetic data cannotbe extrapolatedto predict the rates of blueschistand eclogite formation in nature, textural data from rocks indicate that transformationbelow temperaturesof 150øCis minimal. Completetransformation of volcanicrocks occurs by •-250øC, but incompletetransformation of gabbroicrocks heatedto 800øC has been observed.There are important consequencesto the rapid transformation of volcanic rocks and the metastable persistenceof gabbroicrocks into the blueschistand eclogite stability fields. Fast seismic velocities shouldbe evident first in the upper oceaniccrust and may be substantiallyretarded in the lower oceaniccrust. The upper oceaniccrust will be denserthan asthenospherebefore the lower oceanic crust.Early in the processof eclogiteformation, volcanic rocks will be placedin deviatorictension and the underlyingcoarser grained rocks in compression;with furtherreaction, the stateof stressin gabbroicrocks will changefrom compressiveto tensile.Earthquakes at shallowdepths should be extensional in basalt and contractionalin gabbro, changing at deeper levels to extensional throughoutthe crust. INTRODUCTION This paper summarizes the rates and
    [Show full text]
  • Characteristics and Petrogenesis of Alaskan^Type Ultranaafic-Mafic Intrusions, Southeastern Alaska
    Characteristics and Petrogenesis of Alaskan^Type«/ J: Ultranaafic-Mafic Intrusions, Southeastern Alaska U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1564 AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current- year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books and Maps Professional Papers, Bulletins, Water-Supply Papers, Tech­ Books and maps of the U.S. Geological Survey are available niques of Water-Resources Investigations, Circulars, publications over the counter at the following U.S. Geological Survey offices, of general interest (such as leaflets, pamphlets, booklets), single all of which are authorized agents of the Superintendent of Docu­ copies of Earthquakes & Volcanoes, Preliminary Determination of ments. Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone out of print at the Superin­ • ANCHORAGE, Alaska-4230 University Dr., Rm.
    [Show full text]
  • Petrological, Geochemical and Isotopic Characteristics of the Collo Ultramafic Rocks (NE Algeria)
    Journal of African Earth Sciences 125 (2017) 59e72 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci Petrological, geochemical and isotopic characteristics of the Collo ultramafic rocks (NE Algeria) * Rabah Laouar a, c, , Adel Satouh b, Sihem Salmi-Laouar a, Nachida Abdallah c, Jean-Yves Cottin d, Olivier Bruguier e, Delphine Bosch e, Aziouz Ouabadi c, Adrian J. Boyce f, Anthony E. Fallick f a Departement de geologie, FST, Universite Badji Mokhtar Annaba, B.P. 12, 23000, Annaba, Algeria b Departement de Geologie, Universite Kasdi Merbah Ouargla, Algeria c Laboratoire de Geodynamique, Geologie de l’Ingenieur et Planetologie, F.S.T.G.A.T., USTHB, BP. 32, Bab Ezzouar, 16111, Algiers, Algeria d Univ-Lyon, UJM Saint Etienne, UMR 6524 “Magmas et Volcans”, 23 rue P. Michelin, 42023, Saint Etienne Cedex, France e Geosciences Montpellier, Universite de Montpellier, CNRS-UMR 5243, Place E. Bataillon, 34095, Montpellier Cedex 5, France f Isotope Geosciences Unit, SUERC, East Kilbride, Glasgow, G75 0QU, Scotland, United Kingdom article info abstract Article history: The ultramafic rocks of the Collo region in northeastern Algeria crop out as “stratified” masses that cut Received 27 June 2016 across older metamorphic formations of the Petite Kabylie basement. Based on petrological compositions Received in revised form and mineralogical observations, these rocks are mainly peridotites and serpentinites. The peridotites are 27 September 2016 identified as lherzolites, but dunites may occur rarely. The lherzolites are composed of olivine, ortho- Accepted 25 October 2016 pyroxene, clinopyroxene and chromian spinel. Their chemical composition shows high MgO (34.4 Available online 26 October 2016 e37.5 wt%), Cr (0.14e0.27 wt%), Ni (0.14e0.26 wt%) and Co (34e133 ppm) contents and low CaO and Al2O3 concentrations (0.02e2.2 wt% and 0.5 to 2.8 wt%, respectively).
    [Show full text]
  • Pressures and Temperatures Calculated from Chromium-Rich
    American Mineralogist, Volume 6l , pages 725-731, 1976 Pressuresand temperatures calculated from chromium-rich pyroxene compositions of megacrystsand peridotitexenoliths, Black Rock Summit.Nevada JlNr E.NrrlsoN Prrr U.S. GeologicalSuruey, Menlo Park, California 94025 Abstract Olivine-rich spinel-peridotitexenoliths from basanitoidflows and pyroclastics,Black Rock Summit, Nevada, contain peculiarly Cr-rich orthopyroxenes(average lVo CrzO') and low-Ca chromian clinopyroxenes( I 5- l87oCaO). Electron probe analyses,including a scan acrossan orthopyroxenite veinlike structure in one sample,reveal that there are significantcompositional variations within megacrystsand pyroxenesof peridotite xenoliths over distancesof only a few millimeters.These variations lead to large apparent gradients in pressureand temperature when calculatedby current methodsand plotted on the widely-usedP-T diagramsof Maccregor (1974) and Boyd (1973). The chemical variations in the scannedspecimen are systematicand thus are not due to analytical error, but probably are causedby metasomaticand other reactionsin the source areas of the ultramafic rocks. The presenceof these variations brings into question the assumptionsupon which current petrogeneticgrids are based,and strongly suggeststhat the interpretationof P-T curvesas fossil geothermsis premature. Introduction to ultramafic host rocks. The megacrysts have Clinopyroxene megacrystsand spinel-faciesper- rounded shapes,are rimmed by border zonesof in- idotite xenoliths collectedfrom Black Rock Summit, cipient melting, and are usually surrounded by host Nevada(Trask, 1969)are olivine-rich.Many contain lavas of alkalic basalt. These large crystals contain a distinctive bottle-green pyroxene that resembles strain lamellae,and zonesof granulation are concen- neither the apple-green(Cr-diopside) nor the black trated along the lamellae. (Al-augite) pyroxene-bearingspinel-facies peridotite xenoliths at the same location.
    [Show full text]
  • An Unusual Tasmanian Tertiary Basalt Sequence, Near Boat Harbour, Northwest Tasmania
    AUSTRALIAN MUSEUM SCIENTIFIC PUBLICATIONS Sutherland, F. L., D. F. Hendry, B. J. Barron, W. L. Matthews and J. D. Hollis, 1996. An unusual Tasmanian Tertiary basalt sequence, near Boat Harbour, northwest Tasmania. Records of the Australian Museum 48(2): 131–161. [18 September 1996]. doi:10.3853/j.0067-1975.48.1996.285 ISSN 0067-1975 Published by the Australian Museum, Sydney naturenature cultureculture discover discover AustralianAustralian Museum Museum science science is is freely freely accessible accessible online online at at www.australianmuseum.net.au/publications/www.australianmuseum.net.au/publications/ 66 CollegeCollege Street,Street, SydneySydney NSWNSW 2010,2010, AustraliaAustralia Records of the Australian Museum (1996) Vo!. 48: 131-161. ISSN 0067-1975 An Unusual Tasmanian Tertiary Basalt Sequence, Near Boat Harbour, Northwest Tasmania RL. SUTHERLAND,! D.R HENDRY,z* B.J. BARRON,1 W.L. MATTHEWS3 AND J.D. HOLLIS! I Division of Earth and Environmental Sciences, The Australian Museum, 6 College Street, Sydney NSW 2000, Australia Internet: [email protected] 2 Department of Geology and Geophysics, The University of Sydney NSW 2006, Australia 3 Department of Mines, PO Box 56, Rosny Park TAS 7018, Australia * Present address: 16 Sunnyside Street, Gladesville NSW 2111, Australia ABSTRACT. The mineralogy and petrology of basalts near Boat Harbour, NW Tasmania, are described as this sequence is unusual for Tasmanian Tertiary basalts. The rocks are more sodic and evolved basalts carry more prolific anorthoclase and zircon megacrysts than is normal in Tasmania. Older nephelinites and melilite-nephelinites (26-27 Ma) and younger nepheline hawaiites and mugearites (14-15 Ma) are present and fission track zircon ages (l3-14 Ma and 8-9 Ma) demonstrate that zircon was erupted during and after the evolved basalts.
    [Show full text]
  • Concretes Made of Magnesium–Silicate Rocks
    minerals Article Concretes Made of Magnesium–Silicate Rocks Lyudmila I. Khudyakova 1, Evgeniy V. Kislov 2,*, Irina Yu. Kotova 1 and Pavel L. Paleev 1 1 Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, 670047 Ulan-Ude, Russia; [email protected] (L.I.K.); [email protected] (I.Y.K.); [email protected] (P.L.P.) 2 Geological Institute, Siberian Branch, Russian Academy of Sciences, 670047 Ulan-Ude, Russia * Correspondence: [email protected] Abstract: At present, there is a shortage of high-quality feedstock to produce widely used building materials—concretes. Depletion of natural resources and growing restrictions on their extraction, in connection with environmental protection, necessitate the search for an equivalent replacement for conventional raw materials. Magnesium–silicate rocks are a waste of the mining industry. We researched the possibility of using these rocks as coarse and fine aggregates in heavy concrete production. Following the requirements of the national standards, we studied the physical and mechanical characteristics of the obtained material. It was found that the strength of concrete, made of magnesium–silicate rock coarse aggregate, at the age of 28 days of hardening is within 28 MPa, while the strength of the control sample is 27.3 MPa. Replacing quartz sand with dunite sand also leads to an increase in concrete strength (~4%). Complete replacement of aggregates facilitates an increase in strength by 15–20% than the control sample. At the same time, the density of the obtained materials becomes higher. Concretes have a dense structure that affects their quality. Concrete water absorption is within 6%.
    [Show full text]