Petrology and Sr-Nd isotopic disequilibrium of the xiaohaizi intrusion, NW China: genesis of layered intrusions in thetarim large igneous province

Wei, Xun, Xu, Yi-Gang, Zhang, Chuan-Lin, Zhao, Jian-Xin and Feng, Yue-Xing (2014) Petrology and Sr-Nd isotopic disequilibrium of the xiaohaizi intrusion, NW China: genesis of layered intrusions in thetarim large igneous province. Journal of Petrology, 55 12: 2567-2597. doi:10.1093/petrology/egu067


Author Wei, Xun
Xu, Yi-Gang
Zhang, Chuan-Lin
Zhao, Jian-Xin
Feng, Yue-Xing
Title Petrology and Sr-Nd isotopic disequilibrium of the xiaohaizi intrusion, NW China: genesis of layered intrusions in thetarim large igneous province
Journal name Journal of Petrology   Check publisher's open access policy
ISSN 1460-2415
0022-3530
Publication date 2014-11-01
Year available 2014
Sub-type Article (original research)
DOI 10.1093/petrology/egu067
Volume 55
Issue 12
Start page 2567
End page 2597
Total pages 31
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Collection year 2015
Language eng
Formatted abstract
Layered mafic intrusions (LMI) are sporadically distributed in the Early Permian Tarim large igneous province (LIP), NW China, and are crosscut by numerous contemporaneous dykes. The Xiaohaizi wehrlite intrusion is composed mainly of olivine (Fo69–75), clinopyroxene (Mg# = 75–84), intercumulus plagioclase (An53–86) and Fe–Ti oxides. Both petrography and mineral compositions suggest that olivine and clinopyroxene crystallized earlier than plagioclase and Fe–Ti oxides. The dykes are of alkali basalt to trachyandesite with low Mg# (35–39). The least-contaminated dykes display strong rare earth element (REE) fractionation, enrichment of Nb and Ta, and depletion of Pb relative to other similarly incompatible elements, bearing strong similarity to ocean island basalts (OIB). This, together with their positive εNdi values (4·3–4·8), is consistent with derivation from an enriched asthenospheric mantle source. Clinopyroxenes in the wehrlites display convex-upward chondrite-normalized REE patterns. The melts in equilibrium with these clinopyroxenes have very similar trace element compositions to those of the crosscutting dykes, suggesting a similar mantle source shared by the Xiaohaizi wehrlite intrusion and dykes. The Xiaohaizi wehrlite intrusion is characterized by Sr–Nd isotopic disequilibrium between clinopyroxene and plagioclase separates: 87Sr/86Sri (0·7038–0·7041) and εNdi (1·0–1·9) of clinopyroxene are lower and higher than the respective ratios of intercumulus plagioclase (87Sr/86Sri = 0·7042–0·7043, εNdi = 0·4–1·0). The 87Sr/86Sri and εNdi of clinopyroxene separates correlate positively and negatively with Zr/Nb, respectively, implying variable degrees of crustal contamination during the formation of the Xiaohaizi wehrlite intrusion. 87Sr/86Sri increases and εNdi decreases with increasing Ca content of plagioclase, indicating that higher An plagioclases experienced higher degrees of contamination. This can be explained by assimilation of continental crust through a turbulent magma ascent (ATA) process. However, this ATA model fails to account for the positive correlation between the Mg# and εNdi of clinopyroxene separates. The isotopic disequilibrium in the Xiaohaizi LMI is more probably generated during an assimilation and fractional crystallization process involving Archean–Neoproterozoic basement and carbonates as contaminants.
Keyword Xiaohaizi intrusion
Isotopic disequilibrium
Assimilation and factional crystallization
Layered mafic intrusions
Tarim LIP
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Papers
Official 2015 Collection
 
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