摘要:秦岭造山带早古生代发育一套完整的“沟—弧—盆”体系，其中二郎坪群作为弧后盆地的代表。为了查明二郎坪弧后盆地俯冲消减的构造演化时限，本文以二郎坪群及其相关侵入岩体为研究对象，进行了锆石U-Pb年代学研究。结果表明，火神庙组斜长角闪片岩测得锆石U-Pb加权平均年龄为495.2±6.9 Ma，属于原岩的结晶年龄；侵入二郎坪群内部的变形岩体主要代表板山坪岩体、张家庄岩体、郭家幔岩体，测得其结晶年龄分别为：479.9±5.6 Ma、461.5±5.4 Ma和456.5±6.3 Ma。板山坪岩体的变形特征与二郎坪群北部岩片向北俯冲消减特征相同，张家庄岩体、郭家幔岩体的变形特征与二郎坪群南部岩片向南俯冲消减特征相同。另外，在二郎坪群南部岩片内部发现顺面理面侵入的未变形岩脉，其结晶年龄为427.8±5.4 Ma，以及切穿二郎坪群南部岩片面理的未变形岩脉，给出一颗锆石结晶年龄为388 Ma。综合上述以及前人研究成果，认为二郎坪弧后盆地可能于460 Ma闭合，其俯冲消减方式为双向式俯冲，并且两侧岩片俯冲变形可能持续至427 Ma，最终岩石俯冲变形结束时间上限为388 Ma。
关键词: 北秦岭/
二郎坪弧后盆地/
双向式俯冲/
锆石U-Pb年代学/
构造演化
Abstract:A complete "trench-arc-basin" system was developed in the Early Paleozoic in the Qinling orogenic belt, in which the Erlangping Group is the representative of the back-arc basin. In order to find out the tectonic evolution time limit of subduction in Erlangping back-arc basin, the zircon U-Pb chronology of Erlangping Group and its intrusive bodies is studied in this paper. The results show that the U-Pb weighted average age of zircons from amphibolite schist of Huoshenmiao formation is 495.2±6.9 Ma, which represents its crystallization age. The deformed rock bodies intruded into the Erlangping Group are mainly represented by Banshanping pluton, Zhangjiazhuang pluton and Guojiaman pluton, and their crystallization ages are 479.9±5.6 Ma, 461.5 ±5.4 Ma and 456.5±6.3 Ma, respectively. The deformation characteristics of the Banshanping pluton are the same as those of the northward subduction of the northern part of Erlangping Group, and the deformation characteristics of the Zhangjiazhuang pluton and the Guojiaman pluton are the same as the southward subduction of the southern part of Erlangping Group. In addition, undeformed dikes intruded along the foliation plane are found in the southern part of the Erlangping Group, with a crystallization age of 427.8±5.4 Ma, and the undeformed dikes cut through the southern part of the Erlangping Group, and a zircon gives a crystallization age of 388 Ma. Based on the above and previous research results, it is considered that the Erlangping back-arc basin may have been closed at 460 Ma, its subduction mode is bidirectional subduction, and the subduction deformation on both sides may last up to 427 Ma, and the final end time of rock subduction deformation is 388 Ma.
Key words:North Qinling/
Erlangping back-arc basin/
Bidirectional subduction/
Zircon U-Pb chronological/
Tectonic evolution
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