Original paper

Coesite-bearing granulite retrograded from eclogite in Weihai, eastern China

Qingchen, Wang; Ishiwatari, Akira; Zhοngyan, Zhao; Hirajima, Takaο; Hiramatsu, Nοbuki; Enami, Masaki; Mingguο, Zhai; Bolin, Cong

European Journal of Mineralogy Volume 5 Number 1 (1993), p. 141 - 152

32 references

published: Mar 4, 1993
manuscript accepted: Jun 30, 1992
manuscript received: Dec 17, 1991

DOI: 10.1127/ejm/5/1/0141

BibTeX file

ArtNo. ESP147050501012, Price: 29.00 €

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Abstract Coesite in a granulite host-rock is reported from Weihai City, northeastern Shandong Province, China. Coesite occurs as inclusions in garnet, which is separated from the fine-grained matrix of quartz + clinopyroxene + hornblende by a zoned corona of plagioclase + clinopyroxene + orthopyroxene + hornblende. Petrological evidence shows that the coesite-bearing granulite is retrograded from eclogite. Three stages in the metamorphic history of the granulite have been recognized, (i) Coesite-eclogite stage: The assemblage reconstructed from the inclusions in garnet is Mg-rich garnet + omphacite + coesite + rutile. (ii) During the granulite stage, these minerals reacted to form quartz + clinopyroxene + hornblende (in the matrix), clinopyroxene + albite (omphacite pseudomorphs) and plagioclase + clinopyroxene + orthopyroxene + hornblende (as corona around garnet), (iii) Amphibolite stage: Earlier minerals were replaced by biotite, epidote and hornblende. The P-T conditions estimated with various geothermobarometers show a T-increasing and P-decreasing path from the eclogite stage (T ~ 720°C, P > 28 kbar) to the granulite stage (T ~ 850°C, P ~ 10 kbar). Thus the exhumation of the ultra-high-pressure rocks in Weihai proceeded under increasing temperature, and may not have been as fast as it was thought before