钦-杭成矿带南段庞西垌断裂带热年代学证据

Thermochronology of Pangxidong Fault Zone in Southern Section of Qin-Hang Metallogenic Belt

庞西垌断裂带是钦-杭成矿带南段众多NE向韧性剪切带的其中一条,控制着一系列韧性剪切带型银金矿床的分布.对其进行热年代学研究有助于了解钦-杭成矿带南段NE向韧性剪切带的构造演化及其对伴生矿床的控制作用.获得的庞西垌断裂带内糜棱岩中两件白云母40 Ar/39 Ar总气体年龄分别为221.98±1.16Ma和223.77±1.16Ma.据此认为庞西垌断裂带在印支期发生韧性剪切活动,为伴生矿床的形成提供了有利空间;在同一糜棱岩样品中获得的磷灰石、锆石裂变径迹年龄分别为64.83±4.13Ma和75.69±2.88Ma,结合热史模拟结果可以得出,庞西垌断裂带在75~60Ma期间发生了快速冷却作用(6.2℃/Ma),与区域整体缓慢冷却过程(1.5℃/Ma)差别显著,据此推测庞西垌断裂带可能在约75~60Ma期间再次发生活动,而庞西垌银金矿床可能形成于晚白垩世.

The Pangxidong fault zone is one of many NE-strength ductile shear zones in the southern section of the Qin-Hang metallogenic belt and controls the distribution of a series of ductile shear zones related Ag-Au deposits.Study on its thermochronology is helpful to understand the tectonic evolution of the NE-trending ductile shear zone in the southern part of the QinHang metallogenic belt and its effect on the associated mineral deposits.A set of muscovite 40 Ar/39 Ar and fission track analysis were carried out in this paper.Two muscovite samples from the mylonite yielded 40 Ar/39 Ar isotopic total gas ages of 221.98±1.16 Ma and 223.77±1.16 Ma,respectively.It is interpreted that the ductile shearing happened in Pangxidong fault zone during the Indosinian period,which is believed to have provided favorable space for the formation of associated mineral deposits.Apatite and zircon fission track ages from the same mylonite sample yield 64.83±4.13 Ma and 75.69±2.88 Ma,respectively.Combined with the thermal history modeling results,it is shown that the fault zone had experienced a rapid cooling process during^75-60 Ma（6.2℃/Ma）,which is much different from the slow cooling process of the Yunkai region（1.5℃/Ma）.The results suggest that the Pangxidong fault zone was active again during^75-60 Ma and the Pangxidong Ag-Au deposits possibly formed in the Late Cretaceous.