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Natural End Member Samples of Pyrope and grossular:A Cathodoluminescence-Microscopy and-Spectra Case Study

Journal of Earth Science 2018年第5期29卷 989-1004页

作者： Hans-Peter Schertl Joana Polednia Rolf D.Neuser Arne P.Willner Ruhr-University Bochum Institute of GeologyMineralogy and GeophysicsD-44780 BochumGermany College of Earth Science&Engineering Shandong University of Science and TechnologyQingdao 266590China Bayerisches Geoinstitut Universitat BayreuthD-95440 BayreuthGermany

Garnet is one of the most significant minerals in metamorphic rocks, that provides key information on prograde, peak-metamorphic and retrograde parts of the pressure-temperature （PT） path. Such results require a detailed knowledge of its different growth domains. For iron-poor compositions, the cathodoluminescence （CL） microscopy is an important and often overlooked method and allows to identify the internal structures of all garnet grains in one thin section within only a few seconds. The advantage of the CL-microscope is to deliver low magnification images in true color, not only of garnet but also, for instance, of other rock forming silicates, carbonates, sulfates, etc., of metamorphic, but also of sedimentary and magmatic origin, using polished thin sections. Internal structures of grossular from Mexico and pyrope from the Italian Alps were characterized and visualized by CL-microscopy. The different growth domains were additionally studied using CL-spectra and electron microprobe （EMP） analysis. grossular shows a patchy zonation in its core while in mantle and rim zones oscillatory zoning is observed. It contains zones of anomalous birefringence, zones of orange and bluish luminescence and zones lacking luminescence. Different but low amounts of the activator elements Mn2＋ and Eu2＋ are responsible for the orange and bluish luminescent domains. Pyrope is also characterized by oscillatory growth zones, shows a dull luminescent core with a change of crystal morphology during growth, and displays an increase of brightness from core towards rim--the outermost rim, however, is lacking luminescence. The different luminescent zones are characterized by different amounts of Dy3＋, Tb3＋, Sm3＋ and Sm2＋ as activator elements. Because of slow diffusion rates of activators such as the REEs Sm, Dy and Tb, it can be still possible to visualize possible prograde and/or peak pressure stage growth domains of garnet, even if later high temperature events may have homogenized the m

关键词： pyrope grossular cathodoluminescence (CL) oscillatory zoning REE CL-spectra.

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Pressure and Temperature Dependences of Elastic Properties of grossular Garnet up to 17 GPa and 1 650 K

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Journal of Earth Science 2010年第5期21卷 782-791页

作者： Yoshio Kono Steeve Gréaux Yuji Higo Hiroaki Ohfuji Tetsuo Irifune Geodynamics Research Center Ehime University JASRI 1-1-1 Mikazuki-cho Sayo-gun Hyogo 679-5198 Japan

Simultaneous ultrasonic elastic wave velocity and in situ synchrotron X-ray measurements on grossular garnet were carried out up to 17 GPa and 1 650 K. P- and S-wave vdoeities and bulk and shear modulus showed linear pressure and temperature dependence. These data yielded a pressure derivative of the bulk modulus of 4.42（7） and a shear modulus of 1.27（3）, which are in good agreement with those of garnets with variable chemical compositions. Temperature dependence of the bulk modulus of grossular （-1.36×10^-2 GPafK） is also similar to that of other garnets, while the temperature dependence of the shear modulus of grossular （-1.11×10^-2 GPa/K） is higher than those of magnesium end-member garnets and pyrolitic garnet.

关键词： elastic property grossular garnet high pressure high temperature.

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Mineralogy of Metacarbonate Rocks and Garnet Depositsat two Selected Areas at Asir Region, Southwestern KSA

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International Journal of Geosciences 2011年第4期2卷 657-668页

作者： Asaad Mohammed Bakor Moufti 不详

The mineralogical data materialized in the present work suggest that the previously described skarns at Ad Darb in the literature are actually marble deposits intercalated with schists and phyllites of different compositions. The marble and associated metasediments lie to the west of striking ridges of marbles that are nearly aligned in the NNW-SSE direction. Garnet at Al Madhiq occurrence often occurs in the form of bands conformable with rock foliation (gneissosity and schistosity). It is suggested that the paragenesis “quartz-gar- net-epidote” is developed due to the percolation of some Al-rich solutions along rock foliation of the horn- blende gneiss, i.e. metasomatic garnet. Careful field investigation collaborated with petrographic and SEM studies, suggest the occurrence of another garnetiferous paragenesis associating quartz, mica and feldspar in pegmatites, aplites and quartz veins, i.e. exclusively igneous garnet. Metasomatic garnet in the calc-silicates of Al Madhiq is of grossular composition. It is commonly unzoned but some distinctly to slightly zoned crystals are observed where the core is andradite-rich and the rim is grossular. Metasomatic events responseble for growth of garnet in the calc-silicates led also to formation of epidote post-dating grossular. Hand specimens, microscopic investigation and BSE images prove that this epidote post-dates and replaces gros sular, and even rims it in some instances. Igneous garnet at Al Madhiq (almandine-spessartine) is found only in pegmatites and aplites that are genetically related to alkali granitoids. Sulphides (dominated by pyrite) occur in intemate association with domains rich in grossular and hence these sulphides are more likely hydrothermal indicating reducing conditions for formation of grossular.

关键词： Asir Metacarbonate Calc-silicates grossular Almandine-Spessartine Metasomatic Igneous.

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