【摘要】 为探讨滇西丽江地区新生代岩浆侵位时代、起源及构造环境,对丽江地区小桥头岩体开展了岩相学、LA-ICP-MS锆石年代学及锆石微量元素分析。结果表明,小桥头岩体由石英二长斑岩和二长花岗斑岩组成,其中锆石U-Pb的年龄分别为35.47±0.48 Ma（MSWD=0.49,n=11）和34.70±0.54 Ma（MSWD=0.1,n=10）,形成于始新世晚期;两者岩浆锆石具有一致的稀土微量元素特征, HREE强烈富集（Ce_N/Yb_N=0.00～0.55）,强Ce正异常（δCe=1.2～179.4）和较弱Eu负异常（δEu=0.38～0.88）,高Nb（1.26～51.07）×10^-6、 Ta（0.19～1.52）×10^-6、 Hf（0.98%～1.39%）含量,是演化程度高的岩浆产物。根据锆石Ti温度计,得出岩浆锆石结晶温度小于800℃。结合前人研究成果,认为小桥头岩体的形成除了下地壳岩石的部分熔融外,还有幔源物质的混入,是印度-亚洲大陆晚碰撞阶段的岩浆事件记录。更多还原

【Abstract】 In order to investigate the geochronology, magma generation and structural setting of the Cenozoic igneous in Lijiang, western Yunnan, we have concentrated on the petrography, LA-ICP-MS U-Pb dating and trace element analysis of zircon of the Xiaoqiaotou porphyry. The results show that the Xiaoqiaotou porphyry consisted of masanophyre and monzonitic granite porphyry, their respective ages are 35.47 Ma±0.48 Ma and 34.70 Ma±0.54 Ma, in agreement with that of Cenozoic alkali-rich porphyry in western Yunnan. Their magmatic zircons had consistent REE and trace element characteristics, with enriched HREE（Ce_N/Yb_N=0.00-0.55）, slight or none Eu negative（δEu=0.38-0.88） and Ce positive anomaly（δCe=1.2-179.4）, high Nb（1.26-51.07）×10^-6, Ta（0.19-1.52）×10^-6, Hf（0.98%-1.39%）, and they might be the products of highly evolved magma. All the zircons yield different Ti-in zircon temperatures, but all below 800 ℃. Combined with previous studies, it’s strongly shown that in addition to partial melting of the thickened lower crust base, the magma of the Xiaoqiaotou porphyry located in underplating of mantle-derived magmas. It was formed from the structure transition phase of late-collisional between Indian and Asian continents,the magmatic event response to syn-collisional processes in the structural transform zone.更多还原