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引用本文:江拓,邱啸飞,卢山松,杨红梅,邓新,彭练红. 桐柏—大别造山带南缘七尖峰花岗岩成因:来自地球化学、锆石U-Pb年代学和Hf同位素的制约[J]. 中国地质, 2020, 47(4): 1109-1126.
JIANG Tuo,QIU Xiaofei,LU Shansong,YANG Hongmei,DENG Xin,PENG Lianhong. Petrogenesis of the Qijianfeng granite in southern Tongbai-Dabie orogenic belt:Constraints from geochemistry, zircon U-Pb age and Hf isotope[J]. Geology in China, 2020, 47(4): 1109-1126(in Chinese with English abstract).
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桐柏—大别造山带南缘七尖峰花岗岩成因:来自地球化学、锆石U-Pb年代学和Hf同位素的制约
江拓1,2,3, 邱啸飞1,2,3, 卢山松1,2,3, 杨红梅1,2,3, 邓新1,2, 彭练红1,2
1.中国地质调查局武汉地质调查中心, 湖北 武汉 430205;2.中南地质科技创新中心, 湖北 武汉 430205;3.中国地质调查局花岗岩成岩成矿地质研究中心, 湖北 武汉 430205
摘要:
以桐柏—大别造山带南缘七尖峰花岗岩体为研究对象,进行了详细的同位素年代学和元素-同位素地球化学研究,对其岩石成因和桐柏—大别造山带南缘早白垩世构造背景与钼成矿作用进行了探讨。锆石LA-ICP-MS U-Pb定年结果表明,七尖峰花岗岩形成年龄为(140±1)Ma,说明其为早白垩世岩浆活动的产物。地球化学研究表明,七尖峰花岗岩具有高SiO2(72.88%~73.60%)、低MgO(0.33%~0.36%),高Sr(620×10-6~642×10-6)、Sr/Y(107~111)比值,低Y(5.65×10-6~5.95×10-6)、Yb(0.52×10-6~0.59×10-6)、无Eu负异常的地球化学特征,是典型的埃达克岩。岩体富K2O、贫Cr和Ni,具有富集的Sr-Nd同位素组成(ISr=0.7075~0.7078,εNdt)=-15.5~-15.1),锆石εHft)值在-19.9~-13.2变化,对应的两阶段Nd和Hf模式年龄分别介于2.15~2.19 Ga和2.00~2.43 Ga,暗示七尖峰花岗岩是由古老的加厚下地壳含石榴石角闪岩部分熔融形成。结合前人的研究成果,认为桐柏—大别造山带白垩纪存在两期与钼成矿密切相关的岩浆事件,早期(>130 Ma)与加厚下地壳部分熔融有关,晚期(<130 Ma)则形成于非加厚地壳部分熔融,证明桐柏—大别造山带南缘早白垩世(约130 Ma)经历了从碰撞挤压地壳加厚到碰撞后伸展地壳减薄的构造垮塌演化过程。
关键词:  桐柏-大别造山带  七尖峰花岗岩  锆石U-Pb年龄  Hf同位素  埃达克岩  地质调查工程  矿产勘查工程
DOI:10.12029/gc20200414
分类号:P541
基金项目:国家自然科学基金项目(41902232、41303026)和中国地质调查局地质调查项目(DD20190291、DD20190050)联合资助。
Petrogenesis of the Qijianfeng granite in southern Tongbai-Dabie orogenic belt:Constraints from geochemistry, zircon U-Pb age and Hf isotope
JIANG Tuo1,2,3, QIU Xiaofei1,2,3, LU Shansong1,2,3, YANG Hongmei1,2,3, DENG Xin1,2, PENG Lianhong1,2
1.Wuhan Center of China Geological Survey, Wuhan 430205, Hubei, China;2.Central South China Innovation Center for Geosciences, Wuhan 430205, Hubei, China;3.Research Center of Petrogenesis and Mineralization of Granitoid Rock, China Geological Survey, Wuhan 430205, Hubei, China
Abstract:
Based on comprehensive geochronological, elemental and isotopic geochemical studies of the Qijianfeng granite in southern Tongbai-Dabie orogenic belt, the authors investigated the petrogenesis as well as the geodynamic settings and Mo mineralization of southern Tongbai-Dabie orogenic belt during Early Cretaceous. LA-ICP-MS zircon U-Pb dating yielded an age of (140±1) Ma for the Qijianfeng granite. The rocks exhibit adakitic characteristics, such as high SiO2 (72.88%-73.60%), low MgO (0.33%-0.36%), high Sr (620×10-6-642×10-6) content and high Sr/Y(107-111) ratios, low Y (5.65×10-6-5.95×10-6) and Yb (0.52×10-6-0.59×10-6) content, with negligible Eu anomalies. The rocks are enriched in K2O and depleted in Cr and Ni, and show enriched Sr-Nd isotopic compositions with initial 87Sr/86Sr and epsilon Nd(t) ranging from 0.7075 to 0.7078 and from -15.5 to -15.1, respectively. The rocks have zircon εHf(t) values of -19.9--13.2 with corresponding two-stage Nd and Hf model ages from 2.15 to 2.19 Ga and from 2.00 to 2.43 Ga respectively, suggesting that the magmas were derived from partial melting of ancient garnet-bearing amphibolites from the thickened lower crust. Combined with the previous studies, the authors propose two-stage magmatic activities and accompanying Mo mineralization during Early Cretaceous in southern Tongbai-Dabie orogenic belt. The first stage Mo-related rocks (>130 Ma) were derived from the partial melting of the thickened lower crust, while the second stage Mo-related rocks (<130 Ma) were generated in a normal crustal environment. It is suggested that the southern Tongbai-Dabie orogenic belt experienced a tectonic transition from collisional compression to post-collisional extension, i.e., collapse, delamination and thinning of over-thickened orogenic crust and lithosphere during early Cretaceous (ca. 130 Ma).
Key words:  Tongbai-Dabie orogenic belt  Qijianfeng granite  zircon U-Pb age  Hf isotope  adakite  geological survey engineering  mineral exploration engineering