黔西南下三叠统飞仙关组沉积物源分析对峨眉山大火成岩省火山剥蚀序列的重建约束

峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀，与右江盆地构成了独特的源- 汇沉积体系，相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成，具有低SiO2、高TiO2含量和低Al2O3/TiO2值的特征，具Eu的弱负异常，微弱的Nb、Ta负异常。基于Al2O3/TiO2和La/Sm物源图解分析，研究样品的主要物源由峨眉山大火成岩省的高- Ti玄武岩和少量酸性火山岩构成，这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有～260 Ma 的年龄峰值，对应锆石具有较低的Th/Nb和较高的Nb/Hf值，均支持峨眉山大火成岩省作为主要的沉积物源区，而同时存在的>400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U- Pb年龄组成和锆石化学组成对比分析表明，峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列，反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。

Provenance of the Lower Triassic Feixianguan Formation in southwestern Guizhou Province and reconstruction of volcanic denudation sequence in the Emeishan large igneous province

The Emeishan large igneous province (LIP) suffered intense weathering and denudation after its formation, and formed a unique source- sink depositional system with the Youjiang basin. The relevant clastic sedimentary records are the key to reconstruct the late volcanic sequence and reveal the Emeishan LIP magmatic evolution. In this paper, a detailed study on the provenance of the Lower Triassic Feixianguan Formation in the northern margin of the Youjiang basin in southwestern Guizhou Province was carried out. The mudstones of the Feixiaguan Formation are composed of feldspar, quartz and clay minerals. It is characterized by low SiO2, high TiO2 content and low Al2O3/TiO2 ratio. It shows weak negative Eu anomalies on the REE distribution patterns, and weak negative Nb- Ta anomalies on the primitive- mantle normalized trace element spider diagram. Based on Al2O3/TiO2 and La/Sm ratios analysis, the main provenance of the samples is composed of high- Ti basalts and a small amount of silicic volcanic rocks from the Emeishan large igneous province, which is consistent with the Late Permian clastic provenance in the Youjiang basin. Detrital zircons have a peak age of ~260 Ma, and the corresponding zircons have lower Th/Nb and higher Nb/Hf ratios, which support the Emeishan LIP as the main sediment source area. The detrital zircons with ages of>400 Ma correspond to the crustal materials captured during the ascent of the ELIP basaltic magma. Compared with the U- Pb age and geochemical composition of detrital zircons from the Upper Permian, the volcanic rocks denuded from Late Permian to Early Triassic formed a certain volcanic sequence, reflecting the magmatic evolution process from strong crustal assimilation to fractional crystallization in the late- stage of the ELIP.