跨越中甸弧到扬子地块西缘的～80Ma中酸性火成岩成因及其对碰撞后成矿的意义

Petrogenesis of the ca. 80Ma felsic-intermediate magmatism in the Zhongdian arc terrane and western Yangtze block: Implications for post-collisional metallogenesis

热林钼铜矿床和铜厂沟钼多金属矿床位于西南三江特提斯构造域义敦弧南部的中甸弧。热林含矿二长花岗岩和铜厂沟含矿花岗闪长斑岩,锆石U-Pb年龄分别为79.0±1.4Ma和81.3±1.1Ma。岩石地球化学显示热林岩体和铜厂沟岩体具有高的SiO_2(>65%)、Al_2O_3(13.74%~14.91%)和低的MgO(0.86%~1.49%)含量和Mg~#值(36.3~47.3),同时也具有高的Sr(326×10^(-6)~1174×10^(-6))、低的Yb(1.00×10^(-6)~1.51×10^(-6))和Y(10.2×10^(-6)~15.6×10^(-6))含量以及较高的Sr/Y(22~86)、La/Yb(30~70)比值,并富集大离子亲石元素和亏损高场强元素。这些特征表明热林和铜厂沟岩体具有明显的埃达克质岩特征,很可能是以石榴石为稳定相的加厚下地壳部分熔融的结果。位于扬子西缘的大理花岗岩,锆石U-Pb年龄为76.4±2.3Ma,首次在扬子西缘证实有晚白垩世岩浆活动,表明晚白垩世中酸性岩浆侵入活动已经跨越了中甸弧进入了扬子地块西缘。对比中甸弧及保山地块发育于晚白垩世的岩浆作用及其构造背景,初步认为在燕山晚期,扬子西缘很可能处于与中甸弧类似的伸展构造背景。

The Relin Mo-Cu deposit and Tongchanggou Mo polymetallic deposit located in the Zhongdian arc which is the southern part of the Yidun arc of Sanjiang Tethys Region. Mineralization is closely associated with the Relin monzonitic granites and Tongchanggou granodiorite-porphyry,which were formed at 79. 0 ± 1. 4 Ma and 81. 3 ± 1. 1 Ma,respectively,according to LA-ICPMS zircon U-Pb dating. Geochemically,the Relin and Tongchanggou rocks have high SiO2（ 〉65%） and Al2 O3（13. 74% - 14. 91%）,low MgO（0. 86% - 1. 49%） and Mg-#（36. 3 - 47. 3）,and affinity of adakitic rocks given their high Sr（326 × 10-（-6）- 1174 × 10-（-6））,Sr/Y（22 - 86） and La/Yb（30 - 70） ratios,and low Y（10. 2 × 10^-6- 15. 6 × 10^-6） and Yb（1. 00 × 10^-6- 1. 51 × 10^-6）. These geochemical characters indicate that the Relin and Tongchanggou rocks were derived from partial melting of the thickened lower continental crust within garnet as residual minerals. Additionally,our zircon U-Pb dating reveals that the Dali granites in the western Yangtze block were formed at 76. 4 ± 2. 3 Ma,indicating that the Late Cretaceous magmatism are also developed in the western Yangtze block. We suggest that the western Yangtze block probably have the similar tectonic environment with the Zhongdian arc in the Late Cretaceous.