Fission track constrain on mineralization time and tectonic events in Ganzi-Litang gold belt, Tibet Plateau
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摘要:
通过对甘孜-理塘金矿带内6个金矿区的11个磷灰石和锆石的裂变径迹数据分析，并对磷灰石数据进行热历史模拟，分析讨论了甘孜-理塘金矿带的成矿时代、构造热历史和构造事件。锆石裂变径迹结果显示金成矿时代主要为82~140Ma，属早白垩世成矿，并由南往北成矿时代具有变小的趋势，其中南段为124~140Ma，中段107Ma，北段约82Ma。磷灰石年龄亦具有同样趋势，矿石年龄为14~27Ma，围岩为88~95Ma。金矿带自燕山期以来，主要经历3个演化阶段，200~140Ma处于退火带中，为缓慢降温期，140~30Ma为相对平缓降温阶段，30Ma以来为快速降温期。从南到北降温速率依次加快，从锆石封闭温度250℃降至磷灰石封闭温度100℃的平均速率分别为1.46℃/Ma、1.67℃/Ma和2.21℃/Ma，对应的隆升速率为48.7m/Ma、55.7m/Ma和73.7m/Ma；从100℃降至地表温度的速率为3.15℃/Ma、5℃/Ma和6.07℃/Ma, 对应的隆升速率为104.9m/Ma、166.7m/Ma和202.4m/Ma。甘孜-理塘带的大规模陆内隆升主要在3Ma内，平均20℃/Ma, 667m/Ma，属于快速隆升，隆升量约2km。
Abstract:This paper applies fission track thermochronology to probe mineralization age for six gold deposits and reveal the evolution of geological thermal history and tectonic events in the last 200Ma in Ganzi-Litang gold belt, Tibet Plateau. The results of zircon fission track analysis suggest the main mineralization ages are about 82~140Ma, decreasing from south section to north section. The mineralization ages are 124~140Ma, 107Ma and 82Ma in the south section, the middle section and the north section respectively. The apatite fission track analysis shows the similar trend from south section to north section, in which the ore ages are about 14~27Ma and the wallrock ages are 88~95Ma. Thermal history modeling results show that three cooling stages since Yanshannian. The first stage occurred before 200~140Ma and the third stage after 30Ma. The cooling rates were fast from south section to north section. From zircon closure temperature 250℃ to apatite closure temperature 100℃, the three ages had different cooling rates of 1.46℃/Ma, 1.67℃/Ma and 2.21℃/Ma, and uplifting rates were 48.7m/Ma, 55.7m/Ma and 73.7m/Ma respectively. From 100℃ to surface temperature, the three stages have average cooling rates of 3.15℃/Ma, 5℃/Ma and 6.07℃/Ma, and uplifting rates of 104.9m/Ma, 166.7m/Ma and 202.4m/Ma respectively. Thermal history modeling results reveal that uplifting rates were very fast in the last 3Ma. The cooling rate, uplifting rate and uplifting amount averaged 20℃/Ma, 667m/Ma, and 2km, indicating rapid uplifting.
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图 2
磷灰石样品裂变径迹单颗粒年龄直方图(下图)及其频率曲线(上图)
Figure 2.
Histograms of apatite single grain ages for each sample (lower) and their frequency curves (upper)
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