砂岩的主量元素特征与盆地物源分析

一定的砂岩地球化学特征对应于特定的源区和构造环境,利用主量元素图解可以进行盆地物源分析。在前人大量研究的基础上,笔者选择性收集了不同构造背景的569个主量元素数据,共分为70套平均值,根据来源文献划分出克拉通内部、陆缘弧、碰撞造山带、大陆岛弧和大洋岛弧5种源区和构造环境。综合分析砂岩主量元素之间的相关性,利用整体及不同源区构造背景下元素间相关系数,得到5个主元素氧化物组合:SiO2、Al2O3 FeOT、K2O Na2O、MnO TiO2和MgO CaO;且建立了应用于5种源区判别的(Al2O3 FeOT)/(Na2O K2O)—SiO2/(MnO TiO2)/100—MgO CaO三角图解。对收集的数据进行判别方程分析得到与SiO2、CaO、MgO、FeOT、K2O、MnO、Al2O3、Na2O和TiO2相关的判别方程F1和F2,并进行F1-F2双变量物源构造环境图解判别。根据主元素对砂岩碎屑组分的反映,利用主元素摩尔含量分析石英、长石和基性岩屑矿物在砂岩中的含量,进而对源区进行约束。所建立的Qel—Fel—Lel图解既反映了主量元素对砂岩物源和构造背景的判别,也近似地表现出相应环境下砂岩的碎屑组成。

Major element characteristics of sandstones and provenance analysis of basins

Major element characteristics of sandstones from different kinds of basin are a function of particular provenance types and tectonic environments, and provenance analysis of basins may be performed using major element diagrams. Based on previous research, the authors selectively collected 569 major element data of sandstones with different tectonic environments, which are divided into 70 sets of average values. According to related references, the authors identify five kinds of provenances and tectonic environments: craton interior, continental arc, collisional orogenic belts, continental island arc and oceanic island arc. Based on an integrated analysis of the correlation between major elements in the sandstones collected, by using the correlation coefficients of the whole and major elements in sandstones derived from different provenances, the authors obtain five assemblages of major element oxides: SiO2, Al2O3 FeOT, K2O Na2O, MnO TiO2 and MgO CaO, and then a triangular discriminant diagram of (Al2O3 FeOT)/(Na2O K2O)-SiO2/(MnO TiO2)/100-MgO CaO is established. Two discriminant functions, F1 and F2, which are correlated with SiO2, CaO, MgO, FeOT, K2O, MnO, Al2O3, Na2O and TiO2, are gained by a discriminant function analysis of the collected data and a discriminant diagram of tectonic environments for two-variable (F1 and F2) provenances is established. According to the main elements in detrital grains of sandstones, the contents of quartz, feldspar and basic lithic minerals in the sandstones are analyzed using the molar percentages of the major elements to constrain the provenances. The constructed Qel-Fel-Lel diagram not only reflects the discrimination of the provenance and tectonic environments of sandstone by major elements but also approximately shows the composition of fragments in sandstones in related environments.