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康滇地区是我国南方元古宇地层集中出露的地区,元古宙岩浆活动频繁,是研究扬子陆块早期地质构造演化的窗口,也是最近研究的热点。近年本项目组在南北走向的元谋-绿汁江深大断裂北部、云南元谋县黄瓜园地区识别出了中元古代晚期的片麻状花岗岩。花岗岩锆石的LA-ICP-MS U-Pb年龄为1069.4±6.9Ma(MSWD=0.47,n=18)。岩石化学表现为较高的SiO_2(平均值高达72.79%)和中等Na_2O+K_2O(平均为6.62%),低TiO_2(平均0.26%)、低CaO(平均0.79%)、低MgO(平均0.52%,Mg#平均值22.13)和高Al_2O_3(平均12.84%,A/CNK平均值为1.33)含量,总体表现为亚碱性花岗岩的特征。微量元素分析显示稀土元素总量(∑REE)为132.96×10~(-6)~278.72×10~(-6),平均237.00×10~(-6),稀土配分曲线明显呈轻稀土富集、重稀土亏损的特点;δEu在0.38~0.49之间;微量元素配模式明显亏损Ba、Ta、Nb、Sr、P和Ti,相对富集Rb、Th、U、K等大离子亲石元素和La、Zr、Hf、Y等元素。岩石地球化学特征显示本区花岗岩属于A2亚类,可能源于下地壳基性岩部分熔融,为板块碰撞后伸展构造背景下的产物。花岗岩锆石U-Pb定年和地球化学特征表明在中元古代末期,康滇地区除了发生过南北向的块体汇聚外,可能还可能发生过较大规模东西向的汇聚过程,为全球性格林威尔造山运动的组成部分。此外,该区花岗岩的时代与邻近拉拉IOCG矿床中辉钼矿的Re-0s年龄高度一致,表明拉拉铜铁矿床成矿物质的最终定位富集与中元古代晚期康滇地区微陆块东西方向汇聚后的伸展运动密切相关。
The Kang-Dian area is a region where the southern Proterozoic-Jura strata are concentrated in southern China. The Paleo-Proterozoic magmatic activity is frequent and is a window to study the early geotectonic evolution of the Yangtze block. It is also a hot spot of recent research. In recent years, the project team identified the late Mesoproterozoic gneissic granite in the north-south Yuanmou-Lvjingjiang deep fault north and the Cucumber Garden in Yuanmou County, Yunnan Province. The LA-ICP-MS U-Pb ages of granite zircons were 1069.4 ± 6.9Ma (MSWD = 0.47, n = 18). The rock chemistry is characterized by higher SiO 2 (average 72.79%) and medium Na 2 O + K 2 O (average 6.62%), low TiO 2 (average 0.26%), low CaO (average 0.79%) and low MgO Mg # average 22.13) and high Al 2 O 3 (average 12.84%, average A / CNK of 1.33), which are generally characterized by sub-alkaline granites. Trace element analysis showed that the total REE content (ΣREE) ranged from 132.96 × 10 -6 to 278.72 × 10 -6 with an average of 237.00 × 10 -6, , Heavy rare earth loss characteristics; δEu between 0.38 ~ 0.49; Trace elements with obvious loss of Ba, Ta, Nb, Sr, P and Ti, relatively enrichment of Rb, Th, U, K and other large ion lithophile elements and La, Zr, Hf, Y and other elements. The geochemical characteristics of the rocks show that the granites in this area belong to the A2 subtype, which may be due to the partial melting of the underlying lithostratigraphic rocks, which is the product of the extensional tectonic setting after the plate collision. The zircon U-Pb dating and geochemical characteristics of granite suggest that besides the north-south block agglomeration occurred in Kang-Dian area during the late Mesoproterozoic, a larger-scale east-west convergence process may also occur, Part of the Will orogeny. In addition, the age of the granite in this area is highly consistent with the Re-0s age of the molybdenite in the nearby Lala IOCG deposit, indicating that the final localization and enrichment of the ore-forming materials in the Lala-Cu-Fe deposit is consistent with that of the later Proterozoic Kang-Dian area Block east-west direction after the convergence of stretching are closely related.