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GEOREF RECORD

Li-rich zincostaurolite and its decompression-related breakdown products in a diaspore-bearing metabauxite from East Samos (Greece); an EMP and SIMS study

Anne Feenstra, Ewald Ockenga, Dieter Rhede and Michael Wiedenbeck
Li-rich zincostaurolite and its decompression-related breakdown products in a diaspore-bearing metabauxite from East Samos (Greece); an EMP and SIMS study
American Mineralogist (June 2003) 88 (5-6): 789-805

Abstract

Li-H-rich zincostaurolite locally formed at a metabauxite-marble contact along the eastern coast of Samos during early Alpine high-P, low-T metamorphism. The staurolite, which probably grew from gahnite, cookeite, kaolinite/pyrophyllite, diaspore, and minor Fe-oxide, occurs as prismatic crystals (up to several mm long) in a calcite matrix. It has an unusual composition with 7.5-12.9 wt% ZnO, 1.0-4.9 wt% FeO, 0.66-0.82 wt% NiO and 0.59 wt% CoO, and < or ==0.32 wt% MgO. Calculated structural formulae point to high H (sub 2) O contents (> or =4.14 H atoms per 48 oxygen atoms). During late-Alpine uplift of the Samos rocks, the staurolite was, at greenschist-facies conditions, variably replaced by bluish cobaltoan gahnite (X (sub Zn) >0.82), white Na-Ca-Li mica, Ni-rich chlorite (X (sub Ni) = 0.42-0.59), zincohogbomite (X (sub Zn) = 0.68-0.80), diaspore, and Fe-(hydr)oxide. Detailed EMP work and determination of Li in staurolite and mica by SIMS indicates systematic Zn-Fe-Mg-Ni-Co-Li partitioning between staurolite and its decomposition products, implying local-scale chemical equilibrium. Balanced reaction equations based on mineral-chemical data indicate that the breakdown of staurolite occurred largely isochemically with only introduction of water, Na, and Ca into the reacting system. The breakdown of high-P staurolite during uplift and decompression is thought to be related to the sensitivity of its complex crystal chemistry to changes in physico-chemical conditions.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 88
Serial Issue: 5-6
Title: Li-rich zincostaurolite and its decompression-related breakdown products in a diaspore-bearing metabauxite from East Samos (Greece); an EMP and SIMS study
Affiliation: GeoForschungsZentrum Potsdam, Potsdam, Federal Republic of Germany
Pages: 789-805
Published: 200306
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 71
Accession Number: 2003-051818
Categories: General geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, sketch maps
N37°37'00" - N37°47'60", E26°34'60" - E27°04'60"
Secondary Affiliation: Technischen Universitaet Braunschweig, DEU, Federal Republic of Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200316
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