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GEOREF RECORD

Coesite-bearing eclogite in Henan Province, central China; detailed petrography, glaucophane stability and PT-path

Ru-yuan Zhang and Juhn G. Liou
Coesite-bearing eclogite in Henan Province, central China; detailed petrography, glaucophane stability and PT-path
European Journal of Mineralogy (April 1994) 6 (2): 217-233

Abstract

Coesite and polycrystalline quartz pseudomorphs after coesite are described in garnet and kyanite in eclogite in the Hongan block of the Triassic Qinling-Dabie collision zone between the Sino-Korean and Yangtze cratons in central China. The coesite-bearing eclogites occur as 4-8 m thick layers in gneiss and are rich in Al (sub 2) O (sub 3) , MgO and SiO (sub 2) compared to common basalts; they have experienced at least four stages of recrystallization. The pre-eclogite stage I assemblage is found as inclusions in garnet cores and consists of garnet + katophorite/taramite + quartz + paragonite. The peak eclogite stage II assemblage is garnet + coesite + kyanite + omphacite + phengite + rutile +- talc +- glaucophane. Decompression stage III assemblage is garnet + quartz + omphacite + kyanite + phengite + paragonite + epidote + barroisite + ilmenite. The final retrograde stage IV assemblage consists of albite + hornblende +- Ca-clinopyroxene +- taramite/pargasite + quartz +- margarite + ilmenite. Phase equilibria and geothermobarometers were used to constrain P-T conditions for the four stages; the coesite-bearing eclogite shows a clockwise P-T path with a peak P of approx 31 kbar at 620 +- 30 degrees C. The coexistence of glaucophane with kyanite and omphacite, and the existence of talc and omphacite inclusions in barroisite, provides natural evidence of relatively high-T and high-P stability for glaucophane. EPMA results are tabulated for the various silicates in these rocks. The tectonic implications for the geology of the region in central China are discussed.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 6
Serial Issue: 2
Title: Coesite-bearing eclogite in Henan Province, central China; detailed petrography, glaucophane stability and PT-path
Affiliation: Stanford University, Department of Geological & Environmental Sciences, Stanford, CA, United States
Pages: 217-233
Published: 199404
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 55
Accession Number: 1994-025770
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N31°30'00" - N36°19'60", E110°10'00" - E116°30'00"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199412
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