Petrology and geochemistry of Permian mafic-ultramafic intrusions in the Emeishan large igneous province, SW China: Insight into the ore potential

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• 作者：Wenjuan Luo ; Zhaochong Zhang ; M. Santosh ; Tong Hou ; He Huang ; Jiang Zhu ; Xinzhe Wang ; Xiaojin Fu
• 关键词：Emeishan large igneous province ; Mafic&ndash ; ultramafic intrusions ; Fe&ndash ; Ti&ndash ; V oxide deposit ; Cu&ndash ; Ni&ndash ; (PGE) sulfide deposit ; Ore potential
• 刊名：Ore Geology Reviews
• 出版年：January, 2014
• 年：2014
• 卷：56
• 期：Complete
• 页码：258-275
• 全文大小：3583 K

文摘

Mafic-ultramafic layered intrusions constitute important components in the western part of the Emeishan large igneous province (LIP) in SW China. Here we present zircon U-Pb geochronology, geochemistry and Sr-Nd isotopic data from four representative barren mafic-ultramafic intrusions in Wupodan (WPD), Shangyi (SY), Louyi (LY) and Xiayi (XY). All these four intrusions were emplaced during the Late Permian, coeval with the formation of Emeishan flood basalts and associated mineralized intrusions. All rocks from the four intrusions exhibit mineralogical homogeneity, in the absence of any associated intermediate-felsic plutons. Chondrite-normalized REE patterns of LY, SY and WPD intrusions exhibit moderately fractionated patterns with (La/Yb)_N of 3.55-5.12, whereas the XY intrusion shows pronounced LREE enrichment with (La/Yb)_N of 11.61-12.94. Samples from the four intrusions lack any significant Eu anomalies, and have low 蔚_Nd(t) values of 鈭?#xA0;3.0 to 鈭?#xA0;1.9 and variable initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7057-0.7074, overlapping with the field defined by Permian Emeishan basalts and the related mineralized mafic-ultramafic intrusions. Clinopyroxenes from the SY, WPD and LY intrusions show relatively high equilibrium temperatures ranging from ~ 1300 掳C to ~ 1400 掳C, which can be regarded as a signature of plume-related origin. Although the clinopyroxenes from the XY intrusion exhibit a relatively lower equilibrium temperature (~ 1200 掳C), the geochemical signature resembling OIB suggests a plume-related origin. Thus, these intrusions appear to be part of the Emeishan LIP. These features, combined with moderate to pronounced depletion of HFSE (e.g. Nb, Ta and Ti) and enrichment of LILE (e.g. Rb, Ba, K), correlate the LY, SY and WPD intrusions to the interaction between mantle plume and subcontinental lithospheric mantle that had been previously modified by subduction-related materials. In contrast, the XY intrusion was derived from the plume source contaminated by subcontinental lithospheric mantle. We also attempt a comparison between the unmineralized and mineralized intrusions in terms of their parental magmas, crystallization history, nature of the mantle source, degrees of partial melting of source and the extent of crustal contamination. Some geochemical criteria that may be useful in discriminating between mineralized and unmineralized mafic-ultramafic intrusions are summarized, and insights into the ore potential of the four barren intrusions are addressed.