摘要
滇西腾冲—梁河地区发育古近纪二长花岗岩和钾长花岗岩,记录了印度-欧亚大陆碰撞的岩浆活动信息。二长花岗岩的锆石U-Pb年龄为51.4±0.4 Ma,其176 Hf/177 Hf值为0.282554~0.282592,εHf(t)=-6.65~-5.30,其二阶段模式年龄为1.46~1.55Ga。腾冲—梁河古近纪花岗岩以高SiO2(68.96%~78.68%)、高K2O(4.56%~6.29%)和高Al2O3(12.40%~16.42%)为特征,K2O/Na2O值为0.93~7.24,Al2O3>(K2O+Na2O),A/CNK值为0.99~2.31,属于富钾钙碱性偏铝—强过铝质花岗岩;绝大多数样品具有强烈的负Eu异常(Eu/Eu*为0.19~0.51),富集Cs、Rb,亏损Sr、P、Ti、Ba、Nb、Ta,具有Pb的正异常。元素地球化学特征指示,其主要源于区域上地壳变质杂砂岩的部分熔融;结合区域地质,认为腾梁地区62~51Ma的花岗岩是对印度-欧亚大陆碰撞高峰期的岩浆响应。
Paleogene adamellite and feldspar granite developed in the Tengchong-Lianghe area,Western Yunnan,records magmatism information during the collision between Indian and Asian continents.The LA-ICP-MS zircon U-Pb age of typical adamellite is 51.4±0.4Ma,with 176 Hf/177 Hf ratio of 0.282554~ 0.282592andεHf(t)values of-6.65to-5.30,and Hf modal ages are 1.46~1.55Ga.Major elements of Paleogene granite from the Tengchong-Lianghe area are characterized by high SiO2(68.96%~78.68%), K2 O(4.56%~6.29%)and Al2 O3(12.40%~16.42%),and have K2 O/Na2 O ratios of 0.93~7.24,A/ CNK values of 0.99to 2.31with Al2 O3 >(K2 O+Na2 O).These features suggest that the granite belongs to metaluminous-strongly peraluminous high K calc-alkaline granite.Most samples show strong negative Eu anomalies with Eu/Eu*values of 0.19to 0.51,enrichment of Cs,Rb,Pb and depletion of Sr,P,Ti, Ba,Nb and Ta.Elements geochemical features signify that the granites might be generated from upper crust by partial melting of metagraywacke.Basing on the regional geology,we suggest the Tengliang granites(62~51Ma)might respond to the magmatic events at the peak period of India-Asia collision.
引文
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