东天山觉罗塔格带黄山地区角闪辉长岩岩体的年代学、地球化学特征及岩石成因

Geochronology,Geochemistry and Petrogenesis of Hornblende Gabbro in Huangshan Area of Jueluotage Belt,Eastern Tianshan

为了确定东天山觉罗塔格带黄山地区单一的角闪辉长岩岩体的形成时代、源区性质及其构造属性,本文对东天山觉罗塔格带黄山地区早二叠世角闪辉长岩岩体进行了系统的LA-ICP-MS锆石U-Pb定年与地球化学分析。结果表明:2个岩体中的锆石在CL图像上主要呈条痕状吸收,Th/U值较高(0.23~0.58),指示其岩浆成因,成岩年龄为早二叠世(281.1~282.3 Ma)。这些岩体均由单一的角闪辉长岩构成,w(SiO_2)为46.45%~52.76%,w(MgO)为5.15%~8.42%,w(Al2O3)为14.52%~16.84%,Mg#主要为0.55~0.63;稀土元素配分模式呈右倾型,LREE/HREE=3.36~5.11,(La/Yb)N=2.64~4.41,δEu值多为1.06~1.98;在微量元素蛛网图上,Rb、Ba、K、Sr等大离子亲石元素相对富集,高场强元素Nb、Ta及Zr、P、Hf相对亏损;εNd(t)=10.66~12.54(t=282 Ma),平均为11.60。综上所述,东天山觉罗塔格带黄山地区早二叠世角闪辉长岩的岩浆源区主要为受俯冲流体交代的亏损地幔楔。结合同时代火成岩的组合特征、沉积作用以及区域构造演化历史,认为东天山觉罗塔格带黄山地区早二叠世角闪辉长岩体形成于吐哈地块与中天山地块碰撞后的伸展背景。

Many ore-bearing complexes in Huangshan area of Jueluotage belt in eastern Tianshan become hot spots in recent years. This study focused on the hornblende-gabbro plutons in the area to obtain the formation age, source region of the magma and tectonic implications of the hornblende-gabbro plutons. The research result showed that the selected zircons of two plutons exhibit striped absorption in cathodoluminescence （CL） images, and have high Th/U ratios （0.23-0.58）, implying a magmatic origin. The zircon U-Pb dates indicated that they formed in the Early Permian （281.1-282.3 Ma）, representing the emplacement age of these plutons. These plutons are composed of the single hornblende gabbro, with w（SiO2）=46.45%-52.76%, w（MgO）=5.15%-8.42%, w（Al2O3）=14.52%-16.84%, and Mg#=0.55-0.63. The rare earth element distribution patterns display as right-leaning, with LREE/HREE=3.36-5.11, （La/Yb）N=2.64-4.41, δEu=1.06-1.98, and the trace element spider diagrams showed that they are enriched in LILE （Rb, Ba, K and Sr）, moderately depleted of HFSE （Nb, Ta, Zr, P and Hf）, and εNd（t）=10.66-12.54（t=282 Ma）,at average of 11.60. The results suggest that the Early Permian hornblende-gabbro in the area was from the partial melting of a depleted mantle wedge metasomatized by the fluid released from a subducted slab. Combining with the composition features, sedimentation and tectonic implications of the volcanic rocks, the Early Permian hornblende-gabbro was formed in post-collisional crust extension setting of the Tuha and central Tianshan blocks.