摘要:黑龙江杂岩带作为佳木斯地块与松嫩地块间缝合带的组成部分，对于探究佳木斯地块晚古生代—中生代构造演化具有重要意义。本文选取牡丹江地区黑龙江杂岩带中云母片岩进行碎屑锆石LA-ICP-MS U-Pb年代学分析，从而限定黑龙江杂岩的形成时代。结果显示，云母片岩中最年轻的碎屑锆石年龄分布为176～172 Ma，平均年龄为174±1 Ma，该组锆石发育明显的岩浆振荡环带结构，并且Th/U比值大于0.3，具有岩浆锆石的典型特征，限定了云母片岩原岩的沉积时间下限，表明黑龙江杂岩的形成时代可能在早侏罗世晚期至中侏罗世之后。本文对黑龙江杂岩中云母片岩的碎屑锆石年龄谱进行物源分析，结合前人的研究成果，发现其碎屑锆石年龄分布介于1 339～172 Ma之间，主要集中在1 339～741 Ma、553～497 Ma和267～172 Ma的3个区间，分别与佳木斯地块和松嫩—张广才岭地块上的多期岩浆事件相对应，说明其源区主要是佳木斯地块和松嫩—张广才岭地块。通过对黑龙江杂岩和小兴安岭—张广才岭岩浆岩带所报道的研究结果进行归纳总结，对佳木斯地块晚古生代—中生代的构造演化提出了新的认识：在早二叠世，佳木斯地块为牡丹江洋中的陆块；晚三叠世—早-中侏罗世期间，牡丹江洋向松嫩地块进行俯冲，形成黑龙江杂岩。
关键词: 碎屑锆石/
云母片岩/
黑龙江杂岩/
佳木斯地块/
俯冲碰撞
Abstract:The Heilongjiang complex, as a part of the suture belt between the Jiamusi and Songnen blocks, plays an important role in exploring the Late Paleozoic to Mesozoic tectonic evolution of the Jiamusi block. In this paper, the mica schist from the Heilongjiang complex in Mudanjiang area was selected for detrital zircon U-Pb dating. Among these, fifteen analyses with close ages of 176～172 Ma yield a youngest weighted mean age of 174±1 Ma, in which the corresponding zircons have apparent oscillatory zoning and high Th/U ratios（＞0.3）, indicating a magmatic origin. This youngest concordant age of the detrital zircons constrains the maximum sedimentation age of the protolith of the mica schist and suggests that the Heilongjiang complex might form after the late Early Jurassic to Middle Jurassic. In this paper, we compile a detrital zircon age spectrum for the Heilongjiang complex, and combined with the previous studies, it shows U-Pb ages spanning from 1 339～172 Ma with three age populations：267～172 Ma, 553～497 Ma and 1 339～741 Ma, which match those of multi-phase magmatism in the Jiamusi block and the Songnen-Zhangguangcai block, indicating that these two blocks are likely the source for the detrital zircons from the Heilongjiang complex. Integrating all the results obtained from the Heilongjiang complex and the Lesser Xing′an-Zhangguangcai Range, we conclude that in the Early Permian, the Jiamusi block was probably a micro-continent in Mudanjiang Ocean; during the Late Triassic to Early-Middle Jurassic, the Mudanjiang Ocean kept subduction towards the Songnen block, resulting in the Heilongjiang complex.
Key words:Detrital zircons/
Mica schist/
Heilongjiang complex/
Jiamusi block/
Subduction and collision
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