北山造山带黑鹰山晚三叠世逆冲推覆构造特征及其对造山带演化的制约

    Characteristics of Heiyingshan Late Triassic thrust nappe structure in the Beishan orogenic belt and its constraint on the evolution of the orogenic belt

    • 摘要: 北山造山带位于中亚构造带南缘,是塔里木板块、华北板块及西伯利亚板块的交汇部位,是全球显生宙陆壳增生与改造最显著的地区,成为研究古亚洲洋俯冲消减到最终拼贴闭合和陆内改造过程的关键地区,其陆内改造过程涵盖了晚古生代以来,特别是中、新生代时期的陆内变形、盆山耦合与再调整的复杂过程。前人对北山造山带的研究多以早期俯冲、碰撞过程为主,而对陆内阶段,尤其是印支期构造作用的研究相对薄弱。在北山造山带北部黑鹰山地区开展野外地质调查时发现,早古生代变质砂岩−火山岩向南逆冲至石炭纪安山质火山凝灰岩与三叠纪酸性熔结凝灰岩、变质砂岩之上。通过对该推覆构造系统的构造特征和推覆系统上、下盘不同时代火山岩的锆石U-Pb测年,提出了该逆冲推覆构造具有由北向南的推覆,且呈现出“立交桥”式叠置构造的特征,新的年龄数据指示,该逆冲推覆系统是晚三叠世(晚印支期)北山造山带陆内挤压构造作用的结果。黑鹰山逆冲推覆构造的识别及时代厘定对于深入认识北山造山带陆内构造演化过程等具有重要的借鉴意义。

       

      Abstract: Beishan orogenic belt is located in the southern margin of the Central Asian tectonic belt, where the Tarim Plate, North China Plate and Siberia Plate meet, which is the most significant area of the Phanerozoic continental crust accretion and transformation in the world, has become the key area for studying the process from subduction to final collage closure and intracontinental transformation of the Paleo−Asian Ocean, and the process of intracontinental transformation covers the complex process of intracontinental deformation, basin-mountain coupling and readjusting since Late Paleozoic, especially during the Mesozoic and Cenozoic. Previous studies on the Beishan orogenic belt mainly focus on the early subduction and collision process, but the study on the intracontinental stage, especially the Indosinian tectonic process is relatively weak. In the field geological survey of the Heiyingshan area in the northern of the Beishan orogenic belt, we found the Early Paleozoic metamorphic sandstone-volcanic rocks thrust southward onto the carboniferous andesitic volcanic tuff and Triassic acid fused tuff, metamorphic sandstone. By studying the structural characteristics of the thrust system and the zircon U−Pb ages of the upper and lower strata volcanic rocks, it is proposed that the thrust system has nappe from north to south and shows the characteristics of the ‘flyover type’ superimposed structure. The new geochronological data indicate that the thrust nappe system is the result of intracontinental compression in Beishan orogenic belt during the Late Triassic (Late Indosinian). The identification and age determination of the Heiyingshan thrust nappe structure have important significance for a further understanding of the intracontinental tectonic evolution of the Beishan orogenic belt.

       

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