滇西高黎贡山南段奥陶纪花岗岩SHRIMP锆石U-Pb测年和地球化学特征

在1∶5万马厂幅、道街坝幅区域地质调查工作的基础上,对高黎贡山南段的2个二长花岗质糜棱片麻岩样品所作的SHRIMP锆石U-Pb测年结果分别为（473.5±2.9）Ma和（461.5±7.3）Ma,属于中奥陶世侵入岩。岩石地球化学分析结果表明,岩石的SiO2、Al2O3、K2O含量高（SiO2=71.06%~73.88%,Al2O3=13.03%~14.27%,K2O=2.81%~5.53%）,CaO含量低（CaO=0.67%~1.71%）,属于过铝质（AL/CNK=1.4~1.8）钙碱性岩;稀土元素Eu明显亏损（δEu=0.19~0.47）;微量元素中Rb、Th相对富集,Ba相对亏损;Sm、Nd同位素分析结果：143Nd/144Nd为0.512022、0.512056。结合野外地质调查所作的综合研究认为该期花岗岩为壳源岩石,反映了泛非运动晚期冈瓦纳大陆北部陆-陆碰撞环境的岩浆活动。

SHRIMP zircon U-Pb dating and petrogeochemistry of Ordovician granite bodies in the south- ern segment of Gaoligong Mountain, western Yunnan Province

SHRIMP U-Pb dating of zircons from two representative samples of the batholith shows that the crystallization age is 473.5±2.9Ma and 461.5±7.3Ma respectively. Petrochemical and geochemical analyses show that the granite is high-silica （SiO2= 71.06%-73.88%）, high-aluminous （A1203=13.03%-14.27%）, high-K （K2O=2.81%-5.53%）, low-Ca （CAO=0.67%-1.71%） and pera- luminous （ASI=1.4-1.8）. There is an evident negative Eu anomaly（δEu=0.19-0.47） in its REE patterns. In the diagrams of trace ele- ment patterns, there are very high peaks of Rb and Th and strong depletion of Ba. As for the Sm and Nd isotopes, ^143Nd/^144Nd ratio is 0.512022 and 0.512056 respectively. The above data show that the magma of the granite was derived mainly from the melting of the upper crest. The authors have come to the conclusion that the emplacement and crystallization of the granite batholith had a close re- lationship with the collisional orogeny and crustal thickening and were also closely related to the crustal partial melting in the late period of the Pan-African orogeny.