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    龙门山冲断带中—新生代隆升及扩展的热年代学证据

    Thermochronology of Meso-Cenozoic uplift and tectonic growth of the Longmenshan Thrust Belt

    • 摘要:研究目的】为探讨龙门山冲断带中—新生代垂向构造隆升与横向构造扩展之间的关系,本文开展了低温热年代学测试及分析工作。【研究方法】通过磷灰石和锆石裂变径迹测定及结果分析,剖析构造变形演化特征。【研究结果】磷灰石裂变径迹长度介于11.4±2.6~12.2±2.2μm,有效反映本地构造隆升史;热史模拟结果表明本地区样品经历了―构造快速隆升期—构造稳定期—构造快速隆升期‖三个阶段,且构造隆升具有北早南晚的特征;研究区内各岩石样品冷却速率介于1.211~6.053℃/Myr,自南东向北西构造隆升速率逐渐增加,构造隆升时间逐渐变晚。【结论】龙门山冲断带在中—新生代(150 Ma)以来表现出后展式扩展,此后分别在晚白垩世—始新世(70~50Ma)和渐新世以来(尤其约20Ma),又再次表现为后展式特征,龙门山冲断带中西部地区具有多期构造隆升叠加的特征。

       

      Abstract: This paper is the result of geological survey engineering. Objective In order to discuss the relationship between the vertical tectonic uplift and the lateral tectonic expansion happened in Meso-Cenozoic in the Longmenshan thrust belt, this paper carries out low-temperature thermal chronology testing and analysis. Methods Through the determination and analysis of apatite and zircon fission track age, the characteristics of tectonic evolution are studied. Results The study shows that the lengths of apatite fission tracks are within the range of 11.4±2.6~12.2±2.2μm, which can effectively reflect the local tectonic uplift history; the results of thermal history simulation show that the apatite samples have experienced three critical stages, including the rapid tectonic uplift, the stable tectonic stage and the rapid tectonic uplift. Besides, the uplifting events happened in the northern area were earlier than those in the southern area. The cooling rate of each rock sample is within the range of 1.211~6.053℃/Myr. The tectonic uplift rate gradually increases from southeast to northwest, and the time of uplifting gradually becomes late in the same direction. Conclusions The tectonic deformation of Longmenshan thrust belt has had the characteristics of piggyback propagation from northwest to southeast since Meso-Cenozoic (150Ma), and it has showed these characteristics again from late Cretaceous to Eocene (70~50Ma), even Oligocene (about 20Ma). The central and western regions of the Longmenshan thrust belt are characterized by multi-stage tectonic uplift and superposition.

       

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