摘要
通过对松潘—甘孜地块与龙门山区的前寒武纪—三叠纪碎屑沉积岩的主量与微量元素地球化学及Sm-Nd同位素地球化学的系统研究,确定这些碎屑岩应属于杂砂岩与长石砂岩,其物质来源上应是镁铁质与长英质及石英+碳酸盐的混合物。从前寒武纪到三叠纪稀土总量增高、铕负异常更为明显,反映了壳内深熔作用的不断加强。晚古生代处于相对稳定的构造环境,而出现铈负异常。Nd模式年龄在1.6~2.4Ga之间,分布特征类似于扬子克拉通、南秦岭、北秦岭,而完全不同于华北克拉通,从而证明物质来源主要是扬子克拉通,是在扬子克拉通的基础上发展而成的构造单元。源区对比分析表明新元古代构造层应是沉积盆地的主要物源,其次是太古宙与古元古代,三叠纪的碎屑沉积岩中应含有晚古生代的幔源物质。三叠纪碎屑沉积岩的Nd同位素组成的空间分布特征说明北、东是剥蚀区,西、南为深水沉积区。
Based on systematic studies of major and trace element and Sm-Nd isotopic geochemistry, the Precambrian to Triassic clastic sedimentary rocks in the Garze-Songpan block and Longmen Mountains have been finished. The rocks are determined to be graywacke and arkose and their material source should be a mixture of mafic and felsic materials and quartz+carbonate. The total REE contents of the rocks increase gradually and negative Eu anomalies become more evident from Precambrian to Triassic rocks, which may imply intensifying crustal anatexis. The tectonic setting was relatively stable during the Late Paleozoic;therefore there appear pronounced negative Ce anomalies. The Nd model ages range between 1.6 and 2.4 Ga;this age range is similar to that of the Yangtze craton, South Qinling and North Qinling and quite different from that of the North China craton. Therefore, the provenance of the sedimentary rocks in the Garze-Songpan block and Longmen Mountains is the western margin of the Yangtze craton, and the block is a tectonic unit that developed on the basis of the Yangtze craton. The correlation between provenances of the western Yangtze craton shows that the source materials of the sedimentary basin should mainly be the Neoproterozoic tectonic layer and secondarily the Archean and Paleoproterozoic tectonic layers. Triassic clastic sedimentary rocks may contain Late Paleozoic mafic mande-derived, and the spatial distribution of the Nd isotopic composition indicates that there occurred denudating areas in the east and north and deep-water depositional areas in the west and south in the Garze-Songpan basin during the Triassic.
出处
《中国地质》
CAS
CSCD
2006年第1期109-118,共10页
Geology in China
基金
国家自然科学基金项目(40234052
40173007)
教育部重点科研项目(重点03032)共同资助。