摘要
华北北部洪水庄组黑色页岩是中元古代的富有机质沉积,它可能记录了当时重要的地球化学信息。通过对洪水庄组页岩中的常量和微量元素特征的分析,研究了洪水庄组的物源及其风化作用。高Th/Sc、Al2O3/TiO2、La/Sc、La/Cr、La/Co、Th/Cr和Th/Co值,低Cr/Zr和TiO2/Zr比值,Euan值、Co/Y-Ti/Zr关系和La-Th-Sc组成表明洪水庄组页岩物源主要为上地壳中的长英质花岗闪长岩。洪水庄组页岩的Al、Ca、Na和K组成表明其具有较高的化学蚀变指数(CIA),同时,元素组成的化学风化作用轨迹反映了洪水庄组页岩受到钾交代作用的影响,可能导致CIA值被低估,其原始CIA值应在90以上。高的原始CIA、化学风化指数(CIW)和斜长石蚀变指数(PIA)表明洪水庄组物源区经历了强烈的化学风化作用。化学风化作用强度以及微量元素组成特征揭示了中元古代洪水庄组沉积时期可能处于温暖潮湿的气候条件,这与中元古代时期大气高CO2浓度以及华北板块古大陆当时位于低纬度地区重建的结果不谋而合。
The Hongshuizhuang Formation shales from the northern part of North China are Mesoproterozoic organic-rich sediments which may carry important information at that time. Major and trace elements contents of the Hongshuizhuang Formation shales were analyzed in order to research the provenance and source weathering. The high ratios of Th/Sc, Al2O3/TiO2, La/Sc, La/Cr, La/Co, Th/Cr and Th/Co, the low value of Cr/Zr and TiO2/Zr, and Euan, Co/Y-Ti/Zr diagram and La-Th-Sc Ternary indicate that the provenance of the Hongshuizhuang Formation shales is mainly granodiorites from the upper crust. A1, Ca, Na and K contents of the studied samples indicate they have moderate Chemical Index of Alteration （CIA）. On the ternary plot of A1203-（CaO＂ 4-NazO）-K20（A-CN-K）, the chemical weathering trend suggests that the composition of the Hongshuizhuang Formation shales was affected by the K- metasomatism which leads to underestimate the value of Chemical Index of Alteration （CIA）. The original CIA is higher than 90. The high original CIA, Chemical Index of Weathering （CIW） and Plagioclase Index of Alteration （PIA） illustrate that the provenance of the Hongshuizhuang Formation shales had experienced intense chemical weathering. Intense chemical weathering and trace element indicate the paleoclimate was warm and wet during the deposition of the Hongshuizhuang Formation, consistent with the high CO2 concentration in the atmosphere during the Mesoproterozoic and its place in Columbia supercontinent.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2013年第12期1913-1921,共9页
Acta Geologica Sinica
基金
国家科技重大专项(2011ZX05018-002)
国家自然科学基金(40472076)资助的成果
