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Highly magnesian olivines and green-core clinopyroxenes in ultrapotassic lavas from western Yunnan, China; evidence for a complex hybrid origin

Xu Yigang, Huang Xiaolong, Martin A. Menzies and Wang Rucheng
Highly magnesian olivines and green-core clinopyroxenes in ultrapotassic lavas from western Yunnan, China; evidence for a complex hybrid origin
European Journal of Mineralogy (December 2003) 15 (6): 965-975

Abstract

Oligocene ultrapotassic rocks from western Yunnan have abundant olivines of varying size and green-core clinopyroxenes. Olivine macrocrysts (1-5 mm) have very high forsterite contents (Fo (sub 92-94) ), and high CaO (0.15-0.30 wt%) and Cr (sub 2) O (sub 3) (up to 0.23 wt%) contents. They are believed to be magmatic rather than disintegrated crystals from the upper mantle. These magnesian olivines are not in equilibrium with melts corresponding to the whole-rock compositions of host lavas and, as such, may represent xenocrysts entrained by ultrapotassic magmas during their ascent to the surface. While komaiites, boninites and olivine lamproites are potential sources of these xenocrysts, a genetic link to the late Permian Emeishan large igneous province (LIP) is favoured, because the Emeishan flood basalt is the only known geologic event in the studied area that could have produced highly magnesian olivines. The olivine xenocrysts may have been entrained from the high velocity lower crust (Vp = 7.1-7.8 km/s), which is believed to have formed from high Mg basalts (picrites?) that underplated and intruded the crust during the Emeishan flood basalt episode. Given the presence of olivine xenocrysts and reverse-zoned clinopyroxenes, it is apparent that some magnesian ultrapotassic lavas from Yunnan have a complex hybrid origin. While the former point to ultramafic/primary melts the latter indicate interaction between evolved melts and relatively primary melts thus indicating complex magma mixing processes.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 15
Serial Issue: 6
Title: Highly magnesian olivines and green-core clinopyroxenes in ultrapotassic lavas from western Yunnan, China; evidence for a complex hybrid origin
Affiliation: Chinese Academy of Sciences, Guangzhou Institute of Geochemistry, Guangzhou, China
Pages: 965-975
Published: 200312
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 54
Accession Number: 2004-026342
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sketch map
N25°00'00" - N35°00'00", E85°00'00" - E105°00'00"
Secondary Affiliation: Royal Holloway University of London, GBR, United KingdomNanjing University, CHN, China
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200408
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