- 责任者：Chen Yongqing (School of Earth Sciences and Resources ; China University of Geosciences ; Beijing 100083 ; China) ; Lu Yingxiang
- 刊名：Earth Science Frontiers
- 出版年：2013
- 卷期：20(5
- 关键词：铀—铅计时 ; U-Pb dating ; 地球化学 ; geochemistry ; 花岗岩型矿床 ; granite type deposit ; 钼矿 ; molybdenum ores ; 云南 ; Yunnan Province
- 页码：p.1-14
- 图表：9 illus., 3 tables, 50 refs.
- 分类号：1001
- issnNo：ISSN1005-2321
- isbnNo：CN11-3370/P
The Tengchong Block is tectonically located on the south side of the eastern tectonic syntaxis of Himalaya, lying to the east of East Burma Block bounded by the Myitkyina suture zone and lying to the west of Baoshan Block bounded by the Nujiang River-Ruili fault zone. Due to the subduction of Meso-Tethyan oceanic crust and the evolution of the Neo-Tethys and the Himalaya orogen, a series of granites and related tin, lead- zinc polymetallic mineralization associated with plate convergence, subduction, and collision had been developed in this block since Triassic time. The disseminated molybdenum mineralization associated with granites was discovered as a new mineralization type in this area. Based on the studies on the zircon SHRIMP U-Pb geochronology, geochemistry and Sr-Nd-Pb isotope system of the Xiaochang granite, some conclusions can be drawn as follows： （1） Xiaochang granite is medium to coarse-grained biotite-hearing monzonitic granite with porphyritic like texture, which is characteristic of high SiO2 （73. 96%-75. 70%） and K2O （4. 42%- 5.13%） contents. Total alkali （K2O＋Na2O） ranges from 5.44% to 8.03%, and the K2O/Na2O ratios vary from 1.37 to 2.00. Total content of the rare earth elements （∑REE） of the granite ranges from 155.12 to 191.75 μg/g, and LREE/HREE ratio shifts from 5.67-7.78, exhibiting medium negative Eu anomalies. On the mantle-normalized trace element distribution patterns, all the samples show pronounced negative anomalies in Ba, Sr, P, Ti and Nb but with significant positive anomalies in K, Rb, U, Th and Pb, indicating the features of silicarich high potassium calc-alkaline S-type granite. （2） The zircon SHRIMP U-Pb dating results of the two granite-samples are 121. 2O4-0. 90 Ma and 121.60-0.70 Ma, respectively, which suggests that the rock forming age of this granite belongs to the late period of the Early Cretaceous. The Re-Os dating results of three molybdenum samples from the granite are 120. 1± 2. 1 Ma, 124. 5± 2. 6 Ma and 125. 4±2. 1 Ma respectively, showing that the ore-forming age approaches the rock forming age of this granite. （3） The contents of Sr-Nd-Pb isotopes, major and trace elements imply that the granitic magma may have been formed from partial melting of graywacke-rich crustal materials under a probable crystallization temperature of 732-769 ℃ as calculated by saturated Zr concentration. （4） On both of the Hf-Rb-Ta and R1-R2 diagrams, almost all the samples fall within the field of syn collision tectonic setting. （5） It is inferred that the granite and the related porphyry molybdenum mineralization may have been formed in a syn-collision tectonic setting during the westward subduction of the Nujiang oceanic plate beneath Tengchong block and continent-continent conver- gence and collision between Tengchong block and Baoshan block in the late period of the Early Cretaceous.