四川省西昌盆地上三叠统白果湾组地球化学特征及其意义

Geochemical characteristics and their implications of Upper Triassic Baiguowan Formation in Xichang Basin,Sichuan Province

对四川省西昌盆地上三叠统白果湾组碎屑岩的主量元素、微量元素、稀土元素进行综合研究,得出其主量元素具有富SiO_2、CaO、P_2O_5,贫Al_2O_3、TFe_2O_3、MgO、Na_2O、K_2O的特征;微量元素具有富Zr、Cs、Th、U等特征;稀土元素总量相对较高,轻重稀土元素分馏明显,轻稀土较重稀土相对富集,具有中等负铕异常。白果湾组物源区为长英质岩区,属于被动大陆边缘区;白果湾期的气候经历了湿润→干旱→湿润→干旱的变化过程;成分成熟度总体偏低,呈现高→低→高→低的变化规律,与CIA变化趋势呈负相关。本次研究为该区晚三叠世环境演化研究提供了基础资料。

Through the comprehensive research on major elements,trace elements and rare earth elements of the clastic rocks in Upper Triassic Baiguowan Formation of Xichang Basin Sichuan Province,this research found that the major elements are rich in SiO2,CaO and P2O5,and lack of Al2O3,TFe2O3,MgO,Na2O and K2O.The trace elements are rich in Zr,Cs,Th and U.The capacity of rare earth elements are relatively higher.The fractionation of light and heavy rare earth elements is obvious.The light rare earth elements is richer than the heavy ones,and have medium negative europium anomaly.The provenance of Baiguowan Formation in Xichang Basin is felsic rocks and passive continental margin area.The climate period experienced the process from humid to arid and to humid and arid again.Compositional maturity of Baiguowan Formation rocks is generally low,and shows the variation from high to low,and to high and low again.The variation is negatively correlated with chemical alteration index（CIA）.This paper provides basic data for the study of environmental evolution of Late Triassic.