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Geochemistry of Picritic and Associated Basalt Flows of the Western Emeishan Flood Basalt Province, China |
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| Authors: | ZHANG ZHAOCHONG; MAHONEY JOHN J; MAO JINGWEN; WANG FUSHENG |
| Institution: | 1 STATE KEY LABORATORY OF GEOLOGICAL PROCESSES AND MINERAL RESOURCES, CHINA UNIVERSITY OF GEOSCIENCES BEIJING, 100083, P. R. China 2 SCHOOL OF OCEAN AND EARTH SCIENCE AND TECHNOLOGY, UNIVERSITY OF HAWAII HONOLULU, HI 96822, USA 3 INSTITUTE OF GEOLOGY, CHINESE ACADEMY OF GEOLOGICAL SCIENCES 100037, P.R. CHINA |
| Abstract: | Picritic lava flows near Lijiang in the late Permian Emeishanflood basalt province are associated with augite-phyric basalt,aphyric basalt, and basaltic pyroclastic units. The dominantphenocryst in the picritic flows is Mg-rich olivine (up to 91·6%forsterite component) with high CaO contents (to 0·42wt %) and glass inclusions, indicating that the olivine crystallizedfrom a melt. Associated chromite has a high Cr-number (73–75).The estimated MgO content of the primitive picritic liquidsis about 22 wt %, and initial melt temperature may have beenas high as 1630–1690°C. The basaltic lavas appearto be related to the picritic ones principally by olivine andclinopyroxene fractionation. Age-corrected Nd–Sr–Pbisotope ratios of the picritic and basaltic lavas are indistinguishableand cover a relatively small range e.g.  Nd(t) = –1·3to +4·0]. The higher Nd(t) lavas are isotopically similarto those of several modern oceanic hotspots, and have ocean-island-likepatterns of alteration-resistant incompatible elements. Heavyrare earth element characteristics indicate an important rolefor garnet during melting and that the lavas were formed byfairly small degrees of partial melting. Rough correlationsof isotope ratios with ratios of alteration-resistant highlyincompatible elements (e.g. Nb/La) suggest modest amounts ofcontamination involving continental material or a relativelylow-Nd component in the source. Overall, our results are consistentwith other evidence suggesting some type of plume-head originfor the Emeishan province. KEY WORDS: Emeishan; flood basalts; picrites; mantle plumes; late Permian |
| Keywords: | : Emeishan flood basalts picrites mantle plumes late Permian |
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