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大兴安岭北部的兴华渡口群和扎兰屯群长期以来一直被认为是古元古代变质岩,代表兴安和额尔古纳地块的前寒武纪基底,但这种认识缺乏可信的同位素年代学及古生物资料的支持.采用高精度离子探针(SHRIMPⅡ)对黑龙江新林-韩家园子地区出露的兴华渡口群中变质火成岩和变质碎屑岩和内蒙古扎兰屯地区的扎兰屯群变火山岩进行了锆石U-Pb定年研究.结果表明:兴华渡口群中的变火成岩类形成于(506±10)~(547±46)Ma,属早寒武世-中寒武世,变碎屑岩中碎屑锆石年龄谱中出现大量的1.0~1.2,1.6~1.8和2.5~2.6Ga的年龄,说明其成岩时代至少<1.0Ga;扎兰屯群绿泥片岩(变基性火山岩类)形成年龄为(506±3)Ma.这些资料说明兴华渡口群和扎兰屯群均形成于寒武纪或晚元古代,而不是先前认识的古元古代.变火成岩中古老继承或捕获锆石和变碎屑岩中大量前寒武纪碎屑锆石的存在,暗示这些岩石可能形成于古大陆边缘.结合岩性及其组合特征,认为兴华渡口群及扎兰屯群代表寒武纪或晚元古界活动大陆边缘的火山-沉积建造,但具体的陆缘类型还有待进一步研究.
The Hing Wah DuKou Group and the Zalantun Group in the northern part of the Daxinganling Mountains have long been considered to be Paleoproterozoic metamorphic rocks that represented the Precambrian basement of the Xing’an and Erguna massifs but lacked a credible isotopic age Science and palaeontology data.According to SHRIMP Ⅱ, metamorphic igneous rocks and metamorphic clastic rocks in Xinghua Duankou Group in Xinlin-Hanjiayuanzi area of Heilongjiang Province and Zhalantun in Zhalantun area of Inner Mongolia The results show that the altered igneous rocks in the Hinghua DuKou Formation are (506 ± 10) ~ (547 ± 46) Ma and belong to the Early Cambrian-Middle Cambrian , Ages of 1.0 ~ 1.2,1.6 ~ 1.8 and 2.5 ~ 2.6Ga appear in the detrital zircon detrital zircons ages, indicating that the diagenetic age is at least <1.0Ga; zhalantun group greenschist (506 ± 3) Ma.These data indicate that both Xinghuaduankou and Zalantun formations were formed in the Cambrian or Late Proterozoic, rather than the previously recognized Paleoproterozoic.The ancient volcanic rocks The succession or capture of a large number of Precambrian detrital zircons in zircon and metamorphic rocks suggests that these rocks Which may be formed on the margin of the ancient continent.Combining with lithology and its assemblage characteristics, it is considered that the Xinghuaduankou Group and the Zhalantun Group represent the volcanic-sedimentary formation of the active continental margin of the Cambrian or Late Proterozoic. However, For further study.