冈底斯构造带西段帮布勒铅锌铜矿床的剥露和保存:来自裂变径迹热年代学的证据

    Exhumation and preservation of Bangbule Pb-Zn-Cu deposit in West Gangdese Tectonic Belt: evidence from fission track thermochronology

    • 摘要: 帮布勒铅锌铜矿床是近年在冈底斯构造带西段新发现的大型矽卡岩型矿床。采用低温热年代学方法,揭示帮布勒矿区的冷却和剥露历史,评估矿床保存情况,完善冈底斯构造带西段隆升剥露记录。结果显示,石英斑岩磷灰石裂变径迹年龄为24±2~32±3 Ma(1σ),记录了矿区在渐新世时的冷却和剥露时间。热演化历史模拟表明,帮布勒矿区存在3期冷却事件:Ⅰ始新世—渐新世晚期(48~24 Ma),冷却速率为4.56~10.64℃/Ma,与印度-欧亚大陆碰撞及碰撞后的地壳增厚有关;Ⅱ渐新世晚期—中新世中期(24~14 Ma),冷却速率为0.38~1.9℃/Ma,与印度俯冲板块折返、断离有关;Ⅲ中新世中期至今(14 Ma至今),冷却速率为2.28~9.88℃/Ma,与冈底斯构造带发育的南北向裂谷有关;其中5 Ma时,与冈底斯构造带普遍隆升有关。帮布勒矿区自始新世以来的剥露厚度为1.5~2.5 km,典中组火山岩的覆盖为矿床保存至今起到了保护作用。

       

      Abstract: The Bangbule Pb-Zn-Cu deposit is a newly discovered large-scale skarn deposit in the western part of the Gangdese Tectonic Belt in recent years. In this study, the low-temperature thermochronology method was used to reveal the cooling and exhumation history of the Bangbule deposit, evaluate the preservation of the deposit, and improve the uplift and exhumation records of the western Gangdese Tectonic Belt. Apatite fission track age in quartz porphyry is 24±2 ~ 32±3 Ma (1σ), which indicates the rapid cooling and exhumation of Bangbule deposit during the Oligocene. The simulation of thermal evolution history shows that there are three stages of cooling events in the Bangbule deposit. (Ⅰ) From the Eocene to the Late Oligocene (48~24 Ma), the cooling rate was between 4.56℃/Ma and 10.64℃/Ma and the cooling event was related to the tectonic background of India-Eurasia collision and the post-collision crustal thickening; (Ⅱ) From Late Oligocene to Middle Miocene (24~14 Ma), the cooling rate ranges from 0.38℃/Ma to 1.9℃/Ma, which is related to the tectonic background of break-off of the Indian subducted plate.(Ⅲ) From the Middle Miocene to the present (14 Ma to present), the cooling rate is between 2.28℃/Ma and 9.88℃/Ma, which is related to tectonic background of the north-south rift developed in the Gangdese Tectonic Belt.The cooling event was related to the general uplift of the Gangdese Tectonic Belt since 5 Ma ago. The exhumation thickness of the Bangbule deposit since the Eocene is between 1.5~2.5 km. The cover of the volcanic rocks of the Dianzhong Formation has played a protective role in the preservation of the deposit.

       

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