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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 the 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,剖析构造隆升演化特征。
      研究结果 磷灰石裂变径迹长度介于(11.4±2.6)~(12.2±2.2) μm,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 ℃/Ma,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(70~50 Ma)和渐新世以来(约20 Ma),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 This study focuses on the relationship between the vertical tectonic uplift and the lateral tectonic expansion that occurred during the Meso-Cenozoic in the Longmenshan thrust belt. To examine this relationship, low-temperature thermal chronology testing and analysis were conducted.
      Methods The characteristics of tectonic evolution were examined by determining and analyzing apatite and zircon fission track ages.
      Results The lengths of apatite fission tracks are within the range of (11.4 ± 2.6)–(12.2 ± 2.2) μm. This range effectively reflects the local tectonic uplift history. The thermal history simulation results show that the apatite samples experienced three critical stages: a rapid tectonic uplift, a stable tectonic stage, and a rapid tectonic uplift. The uplifting events occurred earlier in the northern area than in the southern area. The cooling rate of each rock sample was in the range of 1.211–6.053 °C/Ma. From the southeast to the northwest, the tectonic uplift rate increased gradually, while the time of uplifting was gradually delayed.
      Conclusions The Longmenshan thrust belt has undergone tectonic deformation characterized by piggyback propagation from northwest to southeast since the Meso−Cenozoic (150 Ma). This deformation continued from the Late Cretaceous to the Eocene (70–50 Ma) and persisted into the Oligocene (approximately 20 Ma). The central and western regions of the Longmenshan thrust belt are characterized by multi-stage tectonic uplift and superposition.

       

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