东昆仑东段那日马拉黑南地区构造活动的磷灰石裂变径迹新证据

  • 摘要: 那日马拉黑南铜矿床地处东昆仑东段,其成矿区带属于祁漫塔格都兰华力西期多金属成矿带,对其构造活动进行研究可为后续矿产勘查及矿床的保存变化提供科学数据。本文应用磷灰石裂变径迹年代学方法探讨了区内不同阶段构造活动热年代学制约,定量计算了隆升速率和隆升量。从那日马拉黑南地区自北西向展布的Ⅳ、Ⅴ、Ⅵ号矿体获得了6件磷灰石样品,磷灰石裂变径迹结果显示其年龄分别为(64±4)、(59±3)、(54±4)、(57±4)、(51±4)、(57±4) Ma,样品单颗粒年龄及频率曲线呈单峰式分布,P(χ2)>5%,表明年龄数据是单一热事件反应。磷灰石样品年龄与高程呈正相关,表明研究区受构造活动整体抬升。磷灰石样品裂变径迹长度为(10.6±1.9)~(12.3±1.7) μm,变化幅度窄,径迹长度大,峰值在11.5 μm左右,样品年龄值与径迹长度呈正相关,表明年龄大的样品在退火带停留时间较短,受后期热事件影响较小。基于Ketcham退火模型,应用罗特卡罗逼近法模型,采用HeFTy软件进行模拟,结果显示,6件样品的演化趋势具有一致性。分析结果表明,那日玛拉黑南地区整体上经历了快速冷却、缓慢降温、快速冷却3阶段演化过程。第1阶段:温度从130 ℃降至80 ℃,时间从80 Ma持续到65 Ma,平均冷却速率为3.33 ℃/Ma,表现为快速冷却过程。第2阶段:温度从80 ℃降到65 ℃,时间从65 Ma持续到15 Ma,平均冷却速率为0.30 ℃/Ma,表现为缓慢降温过程。第3阶段:温度从65 ℃降至地表温度15 ℃,时间从15 Ma持续至今,平均冷却速率为3.3 ℃/Ma,表现为快速冷却过程。冷却曲线模拟结果显示,研究区的演化经历了快速隆升、平稳抬升、快速隆升3个阶段,对应的隆升量分别为1 429、285、1 571 m。应用HeFTy软件对区内进行了热历史模拟,结果显示,白垩纪期间雅鲁藏布洋开始闭合,印度亚洲大陆开始碰撞,致使那日马拉黑南地区白垩纪以来的构造演化分为3个阶段:白垩纪—古新世、古新世—中新世、中新世至今。第1阶段为白垩纪—古新世构造活动,80—65 Ma隆升速率为0.095 mm/a、隆升量为1 429 m,发生快速隆升事件,记录了雅鲁藏布洋开始闭合,印度亚洲大陆开始碰撞,东昆仑地区80—65 Ma受欧亚地块碰撞的远程响应发生快速隆升事件;第2阶段为古新世—中新世构造活动,65—15 Ma隆升速率为0.006 mm/a、隆升量为285 m,发生缓慢抬升作用,记录了印度板块和欧亚板块同碰撞,致使那日玛拉黑矿区发生平缓抬升;第3阶段为中新世至今的构造活动,15 Ma至今,隆升速率为0.105 mm/a、隆升量为1 571 m,记录了印度板块和欧亚板块后碰撞作用,致使东昆仑在15 Ma发生快速隆升,直接动力来源于东昆仑逆冲推覆构造和左行走滑运动。

     

    Abstract: Narimalaheinan copper deposit is located in the east section of East Kunlun. Its ore forming belt belongs to Qimantage Dulan Variscan polymetallic metallogenic belt. The study of its tectonic activity provides scientific data for subsequent mineral exploration and the preservation and change of the deposit. Apatite fission track chronology method was used to explore the thermal chronological constraints of tectonic activities in different stages in the area, and the uplift rate and amount were quantitatively calculated. The ages of six apatite samples obtained in this study were (64±4), (59±3), (54±4), (57±4), (51±4), (57±4) Ma, P(χ2)>5%, indicating a single thermal event reaction. The age of apatite samples is positively correlated with the elevation, indicating that the study area is uplifted as a whole by tectonic activities. The fission track length of apatite sample is (10.6±1.9)(12.3±1.7) μm. The track length is large, and the sample age value has a positive correlation with the track length, indicating that the older samples have a shorter residence time in the return zone and are less affected by later thermal events. The cooling curve simulation results show that the study area has experienced three stages of evolution: rapid uplift, stable uplift and rapid uplift, and the corresponding uplift amounts are 1 429, 285 and 1 571 m respectively. The thermal history in the area was simulated by HeFTy software, the results show that the thermal evolution in the region is divided into three stages. In the first stage (8065 Ma), the uplift rate is 0.095 mm/a and the uplift amount is 1 429 m. There is a rapid uplift event, which records the beginning of the closure of the Yarlung Zangbo ocean and the beginning of the collision between India and Asia. In the second stage (6515 Ma) the uplift rate is 0.006 mm/a and the uplift volume is 285 m, which occurrs slow uplift and records the collision event between the Indian plate and the Eurasian plate. In the third stage (15 Ma to now), the uplift rate is 0.105 mm/a and the uplift volume is 1 571 m, which records the post collision between the Indian plate and the Eurasian plate, resulting in the rapid uplift of the study area at 15 Ma.

     

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