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本文对完达山大顶子山蛇绿混杂岩开展了岩相学、锆石U-Pb年代学和岩石地球化学研究，厘定了蛇绿混杂岩的岩石组成及其形成时代，探讨了岩石形成构造环境和就位机制。大顶子山蛇绿岩位于完达山地体东部大顶子山至坨瑶山的南北向蛇绿混杂岩条带内，呈构造透镜体分布于晚三叠-早侏罗世大岭桥组(泥质碎屑岩)中，呈北北东向带状展布，由东侧超镁铁质堆积杂岩(以橄榄岩为主)和西侧为镁铁质堆积杂岩(以辉长岩为主)组成，其锆石U-Pb年龄显示为159.61±0.44 Ma和138.4±0.72 Ma,属中侏罗世晚期-早白垩世早期。岩石地球化学研究显示其主量元素特征为低铝、低钙、富碱；稀土元素显示为稀土元素总量较高，介于17.65-105.16×10-6,LREE与HREE含量稳定，LREE富集型，HREE相对亏损，(La/Yb)N介于2.32-5.55,轻重稀土分异明显，分馏程度较大；高场强元素Th、Nb、Ta和大离子亲石头元素Pb、Ba明显富集，Sr较亏损。蛇绿岩形成于洋岛环境，属地幔柱型蛇绿岩，随着太平洋板块向大陆的俯冲，在佳木斯陆块东缘形成规模较大的增生楔。
Abstract：This study presents a comprehensive investigation of the Dadingzishan ophiolitic mélange in the Wanda Mountains, focusing on its petrology, zircon U-Pb geochronology, and whole-rock geochemistry.The aim is to constrain its lithological assemblage, formation age, tectonic setting, and emplacement mechanism.The Dadingzishan ophiolitic mélange is situated within a north-south-trending belt extending from Dadingzishan to Tuoyaoshan in the eastern Wanda terrane.It occurs as tectonic lenses hosted within the Late Triassic-Early Jurassic Dalingqiao Formation(mudstone-dominated clastic rocks) and is distributed in a NNE-trending zone.The ophiolite consists of ultramafic accumulates dominated by peridotite in the east and mafic accumulates dominated by gabbro in the west.Zircon U-Pb dating yields crystallization ages of 159.61±0.44Ma and 138.40±0.72Ma, corresponding to the Late Middle Jurassic to Early Cretaceous.Geochemical data show low Al and Ca contents and high alkali concentrations in major elements.The rocks exhibit moderately high total rare earth element(REE) contents(∑REE=17.65-105.16ppm),with relatively consistent concentrations of both LREEs and HREEs.Chondrite-normalized REE patterns exhibit LREE enrichment and HREE depletion, with(La/Yb)n ratios ranging from 2.32 to 5.55,indicating significant LREE-HREE fractionation.Trace elements show enrichment in high field strength elements(Th, Nb, Ta) and large ion lithophile elements(Pb, Ba),along with relative depletion in Sr.These geochemical signatures suggest formation in an ocean island setting, characteristic of plume-type ophiolites.It is proposed that with the subduction of the Pacific Plate beneath the continent, a large-scale accretionary wedge developed along the eastern margin of the Jiamusi Block.
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基本信息:
中图分类号:P548;P587
引用信息:
[1]孙刚,杨云宝,孙健,等.完达山大顶子山蛇绿岩地球化学及其构造意义[J].黑龙江国土资源,2025,23(08):106-114.
2025-08-18
2025-08-18