Composition of the Tarim mantle plume: constraints from clinopyroxene antecrysts in the early Permian Xiaohaizi dykes, NW China

Wei, Xun, Xu, Yi-Gang, Luo, Zhen-Yu, Zhao, Jian-Xin and Feng, Yue-Xing (2015) Composition of the Tarim mantle plume: constraints from clinopyroxene antecrysts in the early Permian Xiaohaizi dykes, NW China. Lithos, 230 69-81. doi:10.1016/j.lithos.2015.05.010


Author Wei, Xun
Xu, Yi-Gang
Luo, Zhen-Yu
Zhao, Jian-Xin
Feng, Yue-Xing
Title Composition of the Tarim mantle plume: constraints from clinopyroxene antecrysts in the early Permian Xiaohaizi dykes, NW China
Journal name Lithos   Check publisher's open access policy
ISSN 1872-6143
0024-4937
Publication date 2015-08-01
Year available 2015
Sub-type Article (original research)
DOI 10.1016/j.lithos.2015.05.010
Open Access Status
Volume 230
Start page 69
End page 81
Total pages 13
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2016
Language eng
Formatted abstract
Numerous alkaline basaltic dykes crosscut the Early Permian Xiaohaizi wehrlite in drill-cores and syenite intrusion in the Tarim large igneous province, NW China. One basaltic dyke contains abundant clinopyroxene macrocrysts with strong resorption textures. Such a textural disequilibrium is consistent with their contrasting chemistry between the macrocrysts (Mg# = 80–89) and the host dyke (Mg# = 39, corresponding to Mg# = 73 of clinopyroxene in equilibrium with the dyke), indicating that they are not phenocrysts. The clinopyroxene macrocrysts are characterized by low TiO2 (0.26–1.09 wt.%), Al2O3 (1.15–3.10 wt.%) and Na2O (0.16–0.37 wt.%), unlike those in mantle peridotites but resembling those in layered mafic intrusions in the same area. The clinopyroxene macrocrysts and the clinopyroxenes from the Xiaohaizi cumulate wehrlites define a coherent compositional trend and have identical trace element patterns, pointing to a comagmatic origin for these crystals. Accordingly, the macrocrysts cannot be xenocrysts foreign to the magmatic system. Rather they are antecrysts that crystallized from progenitor magmas and have been reincorporated into the host dyke before intrusion. The 87Sr/86Sri (0.7035–0.7037) and εNdi (4.5–4.8) of the clinopyroxene macrocrysts with high Mg# (80–89) are apparently lower and higher than their respective ratios of the clinopyroxenes in the wehrlites (Mg# = 75–84, 87Sr/86Sri = 0.7038–0.7041, εNdi = 1.0–1.9). This difference in isotopes can be accounted for by assimilation and fractional crystallization (AFC) process operated during the formation of the Xiaohaizi intrusion. In this sense, the clinopyroxene macrocrysts record the composition of the uncontaminated Tarim plume-derived melts.
Keyword Clinopyroxene macrocryst
Xiaohaizi dyke
Antecryst
Tarim large igneous province
Assimilation and fractional crystallization
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 2016 Collection
 
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