大别山东缘郯庐断裂带早期韧性剪切带的形成温度

Determination of the formation temperature of the earlier ductile shear zone in the Tan-Lu fault zone,eastern Dabie Mountains

年龄的解释强烈依靠于构造热事件的发生温度和矿物的封闭温度,在缺少构造热事件的温度资料的情况下,很难对年龄数据做出正确合理的解释.利用白云母-绿泥石地质温度计,计算了大别山东缘郯庐早期左旋走滑韧性剪切带的形成温度,获得了350～450℃的温度区间,并且多数温度值位于430～450℃之间.该温度值大于40Ar/39Ar法中自云母的封闭温度,从而由主要以残斑形式存在的白云母获得的年龄值记录了郯庐断裂带的活动时间,190 Ma左右的白云母年龄值为接近于韧性剪切带变形年龄的冷却年龄.并由此年龄和温度数据得出郯庐断裂带形成于大别造山带造山作用后期.该韧性剪切带形成温度明显低于所叠加的造山带高角闪岩相变质岩,也指示为造山后期走滑运动的结果.

The explanation of age data depends on the happening temperature of thermo-tectonic events and the closure temperature of minerals,and the age data is not easy to be interpreted if the temperature data of thermo-tectonic events are lacking. In this paper,the muscovite-chlorite geothermometer is used to calculate the formation temperature of the earlier ductile shear zone in the Tan-Lu fault zone,eastern Dabie Mountains. The formation temperature of the ductile shear zone is found to be between 350 ℃ and 450 ℃, and mainly between 430 ℃ and 450 ℃,which is beyond the closure temperature of muscovite in the way of ^(40)Ar/^(39)Ar. So the age data mostly from porphyroid muscovite record the action time of the Tan-Lu fault zone. And 190 Ma,the ^(40)Ar/^(39)Ar age of muscovite, is the cooling age close to the deformation age of the ductile shear zone. The formation temperature of the ductile shear zone,which is lower than that of the metamorphic rocks of high amphibolite phases,also suggests that the Tan-Lu fault zone was developed in the late phase of orogeny in Dabie Mountains.