金沙江—哀牢山断裂带几个富碱斑岩体的锆石U-Pb定年及地质意义

Zircon U-Pb Dating of Several Selected Alkali-rich Porphyries from the Jinshajiang-Ailaoshan Fault Zone and Geological Significance

运用LA-ICP-MS锆石U-Pb同位素定年方法测定了金沙江—哀牢山断裂带内4个富碱斑岩的年龄。结果表明:剑川地区角闪正长斑岩形成时间为(37.6±2.2)Ma,姚安地区黑云母二长斑岩具有2组锆石U-Pb年龄数据,较年轻的一组为(36.86±0.63)Ma,较老的一组为(40.41±0.24)Ma,姚安黑云母角闪正长斑岩的形成时间为(31.8±2.6)Ma,大理九顶山斑状黑云母二长花岗岩的形成时间为(37.93±0.82)Ma。这些富碱斑岩的形成时间与整个滇西地区新生代富碱斑岩岩浆作用高峰期一致,属于青藏高原后碰撞岩浆作用的时间范围,富碱斑岩岩浆活动是对印度—欧亚大陆巨大碰撞的一种响应。

By using LA-ICP-MS zircon U Pb dating,the ages of four alkali rich porphyries from the Jinshajiang Ailaoshan fault zone have been determined.The results show that the age of the Jianchuan hornblende syenite porphyry is（37.6±2.2） Ma,the age of Yaoan biotite hornblende syenite porphyry is（31.8±2.6）Ma and that of Jiudingshan porphyritic biotite adamellite is（37.93±0.82） Ma.There are,however,two ages for Yaoan biotite monzonitic porphyry,（36.86±0.63）Ma and（40.41±0.24）Ma,respectively.The formation ages of these four porphyries are consistent with the peak timing of formation of the Cenozoic alkali rich prophyries in western Yunnan,and all in the time frame of the post collision magmatism of the Tibetan Plateau.It is believed that the emplacement of the porphyries was a magmatic response to India Eurasia collision.