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Origin of high-An plagioclase in the early Permian (~280 Ma) Xiaohaizi wehrlite, Northwest China: insights from melt inclusions in clinopyroxene macrocrysts and zircon oxygen isotopes
Wei, Xun1,2; Xu, Yi-Gang2; Ren, Zhong-Yuan2; Luo, Zhen-Yu2
2016-06-10
发表期刊INTERNATIONAL GEOLOGY REVIEW
卷号58期号:8页码:1005-1019
文章类型Article
摘要The Xiaohaizi wehrlite intrusion in the early Permian Tarim Large Igneous Province, Northwest China, is characterized by unusual high-An (up to 86) plagioclases. It has been suggested that H2O may have exerted a major control on their formation, but this interpretation requires further direct evidence. Moreover, it remains unclear where the water came from. In order to unravel these questions, we present electron microprobe analyses of minerals and melt inclusions in clinopyroxene macrocrysts in the dikes crosscutting the Xiaohaizi wehrlite intrusion and in situ oxygen isotope data of zircons from the Xiaohaizi wehrlite. The homogenized melt inclusions have restricted SiO2 (45.5-48.7wt.%) and Na2O+K2O (2.4-3.8wt.%) contents, displaying sub-alkaline affinity. This is inconsistent with the alkaline characteristic of the parental magma of the clinopyroxenes, suggesting significant modification of melt inclusions by contamination of the host clinopyroxene due to overheating. Nevertheless, the Ca/Na ratios (2.9-4.7) of melt inclusions are the upper limit of the parental magma of the clinopyroxenes due to high CaO (21.5-23.0wt.%) and very low Na2O (0.22-0.34wt.%) contents in the host clinopyroxenes. Thermodynamic calculation suggests that under fixed P (2.7kbar) and T (1000 degrees C), and assumed H2O (~1.5wt.%) conditions, the Ca/Na ratio of the parental magma cannot generate high-An plagioclase in the wehrlite. The results confirm that H2O exerts a major control. Zircon delta O-18 (VSMOW) values (2.99-3.71 parts per thousand) are significantly lower than that of mantle-derived zircon (5.3 +/- 0.6 parts per thousand). Such low zircon delta O-18 values may be due to incorporation of large amounts of low-delta O-18, hydrothermally altered oceanic crust. However, geochemical and Sr-Nd-Pb isotopic data do not support recycled oceanic crust in the mantle source of the Xiaohaizi intrusion. Alternatively this can be explained by incorporation of meteoritic water in the magma chamber. This will increase the H2O content of the liquid that finally crystallize high-An plagioclases.
关键词Xiaohaizi Wehrlite Intrusion Oxygen Isotopes Zircon Tarim Large Igneous Province High-an Plagioclase Melt Inclusion
DOI10.1080/00206814.2015.1136799
收录类别SCI
语种英语
WOS记录号WOS:000373014900006
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文献类型期刊论文
版本出版稿
条目标识符http://ir.qdio.ac.cn/handle/337002/126262
专题海洋地质与环境重点实验室
作者单位1.Chinese Acad Sci, Inst Oceanol, Key Lab Marine Geol & Environm, Qingdao 266071, Peoples R China
2.Chinese Acad Sci, Guangzhou Inst Geochem, State Key Lab Isotope Geochem, Guangzhou 510640, Guangdong, Peoples R China
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Wei, Xun,Xu, Yi-Gang,Ren, Zhong-Yuan,et al. Origin of high-An plagioclase in the early Permian (~280 Ma) Xiaohaizi wehrlite, Northwest China: insights from melt inclusions in clinopyroxene macrocrysts and zircon oxygen isotopes[J]. INTERNATIONAL GEOLOGY REVIEW,2016,58(8):1005-1019.
APA Wei, Xun,Xu, Yi-Gang,Ren, Zhong-Yuan,&Luo, Zhen-Yu.(2016).Origin of high-An plagioclase in the early Permian (~280 Ma) Xiaohaizi wehrlite, Northwest China: insights from melt inclusions in clinopyroxene macrocrysts and zircon oxygen isotopes.INTERNATIONAL GEOLOGY REVIEW,58(8),1005-1019.
MLA Wei, Xun,et al."Origin of high-An plagioclase in the early Permian (~280 Ma) Xiaohaizi wehrlite, Northwest China: insights from melt inclusions in clinopyroxene macrocrysts and zircon oxygen isotopes".INTERNATIONAL GEOLOGY REVIEW 58.8(2016):1005-1019.
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