赣西南下寒武统杂砂岩地球化学特征和沉积环境
Geochemical characteristics and sedimentary environment of Lower Cambrian greywacke in southwestern Jiangxi Province
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摘要: 赣西南地区早寒武世发育巨厚的砂泥质复理石沉积，砂岩杂基含量普遍大于15%，以杂砂岩为主。赣州市、井冈山市和萍乡市3个地区杂砂岩的主量、微量、稀土元素含量和组合特征表明，赣西南下寒武统杂砂岩具有较高的SiO2含量，高的Al2O3/(CaO+Na2O)和K2O/Na2O比值，较低的Al2O3/SiO2、Fe2O3/MgO比值和CaO含量；微量元素含量接近中国东部上地壳值，富集大离子亲石元素；稀土元素具有LREE富集、Eu亏损明显的特征。综合分析推测，物源剥蚀区为华夏陆块，其北缘显示为被动大陆边缘的地球化学特征，赣西南地区海水较深，且自南向北略微加深。Abstract: In Lower Cambrian, thick sandy and muddy flysch deposits were distributed in southwestern Jiangxi Province. The matrix of the sand possesses more than 15%, and hence most of the sand is greywacke. This paper is focused on the compositions and assemblages of major, trace and rare earth elements of greywacke in Ganzhou, Jinggangshan and Pingxiang. Studies show that the greywacke has relatively high SiO2 content, high Al2O3/(CaO+Na2O)ratios and K2O/Na2O ratios, and comparatively low Al2O3/SiO2 ratios and Fe2O3/MgO ratios as well as lower CaO content. The trace earth elements are similar to those in the upper crust of eastern China, with the enrichment of the large ion radius elements. The rare earth elements are characterized by rich LREE and obvious negative Eu anomaly. It is held that the provenance was from Cathaysia Block. Geochemical characteristics indicate that the northern edge of this area belonged to a passive continental-margin tectonic environment. The sea water somewhat got deeper from south to north.
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