镁铁质
地质学
岩石成因
地球化学
长英质
火成岩大省
火成岩
玄武岩
过碱性岩
深熔
底镀
地幔柱
火成岩分异
岩石学
分步结晶(地质学)
岩浆作用
部分熔融
俯冲
古生物学
火山
岩石圈
构造学
作者
Zhiming Xue,Pengfei Lu,Ping‐Ping Liu,Lingmin Zhang
标识
DOI:10.1016/j.jseaes.2023.105893
摘要
Many Late Permian world-class Fe-Ti oxide-bearing layered intrusions in the Pan-Xi region, SW China are commonly considered to be fractionation products of the Emeishan mantle plume-related high-Ti basaltic melts. These layered intrusions coexist spatially and temporally with A-type granitoids, which consist of syenites and granites and are further classified into isotopically depleted metaluminous to peralkaline and isotopically enriched peraluminous to metaluminous groups. The petrogenesis of these mafic-felsic igneous complexes has been controversial. This study investigates geochemical correlations of the microgabbros at the margin of the Baima layered intrusions and the intruding isotopically enriched granitoids. The amphiboles at both sides of the contact zone are calcic (CaO = 10.4 to 12.5 wt.%) and display obvious mixing trends. Thermodynamical modeling using the MAGEMin program indicates that fractionation of basaltic melts compositionally similar to the Baima microgabbros seems incapable to crystallize olivine compositions comparable to those of the layered intrusions, but can be reconciled by early separation of 7.5 to 10 wt.% Fe-Ti-rich melts. Continued differentiation of the basaltic melts may lead to formation of the isotopically depleted granitoids, among which perthite accumulation in water-rich environments could result in the formation of metaluminous granitoids with high Na, K and Al contents and positive Eu anomalies. The isotopically enriched granitoids, on the other hand, can be produced by anatexis of the juvenile mafic lower crust together with the Yangtze ancient lower crust. Our study therefore provides a panoramic view on the complicated petrogenesis of the igneous complexes related to Emeishan mantle plume impingement through thermodynamic modeling.
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