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作 者:夏群科[1] 郑永飞[1] 葛宁洁[1] Etienne DELOULE
机构地区:[1]中国科技大学地球和空间科学学院 [2]法国国家科研中心岩石学和地球化学研究中心
出 处:《岩石学报》2003年第3期506-512,共7页Acta Petrologica Sinica
基 金:国家自然科学基金(40033010);中国科学院知识创新重点项目(KZCX2-107);国家重点基础研究发展规划(G1999075503)联合资助
摘 要:利用阴极发光和离子探针技术,对大别山北部黄土岭片麻岩的锆石进行了内部结构、U-Pb年龄和氧同位素组成的系统分析。黄土岭片麻岩的锆石具有核-幔-边三层结构,核部是原岩的岩浆锆石,形成时代为~2800Ma;幔部是变质重结晶的产物,变质作用的时代为~2000Ma;边部则是在~110Ma从部分熔融体里结晶出来的增生锆石,是受大别山燕山期构造-岩浆事件影响的反映。黄土岭片麻岩和麻粒岩中~2800Ma和~2000Ma的年龄,以及麻粒岩中约3400Ma的残留锆石年龄均可以与扬子崆岭群变质岩对比。由此可以推断,北大别在构造属性上属于扬子板块,扬子与华北板块的缝合线应在北大别以北。锆石的核-幔-边具有不同的氧同位素组成,氧同位素数据表明黄土岭片麻岩的原岩是S型花岗岩,在~2000Ma和~110Ma的事件中都有外来物质(流体或熔体)的加入。The internal structure of zircons from gneiss of Huangtuling, Northern Dabie has been investigated by cathodoluminescence imaging, and their U-Pb ages and oxygen isotope compositions have been determined by SIMS (Cameca 1270). Zircons display core-mantle-rim structure, the core is the magmatic domain which preserves oscillatory zoning, the mantle is the metamorphic zone induced by recrystallization, and the rim is the overgrowth domain which was precipitated from partial melt. These three domains have different ages: similar to2800 Ma for the core is the protolith age, similar to2000 Ma for the mantle is the metamorphic age, and similar to110 Ma age for the rim reflects the influence of Cretaceous thermal event. similar to2800 Ma and similar to2000 Ma ages for Huangtuling gneiss and its included granulite and similar to3400 Ma age for relict zircon from Huangtuling granulite are comparable with the ages for Kongling group of Yangtze block, so it is inferred that Northern Dabie was a part of Yangtze block and the suture between Yangtze and North China blocks should be north of Northern Dabie. Oxygen isotope composition of the core, mantle and rim of zircons are different, delta(18)O values of the core are similar to11.7parts per thousand, 11.1parts per thousand similar to18.7parts per thousand for the mantle and 5.5parts per thousand similar to8.2parts per thousand for the rim. From these oxygen isotope data we suggest that the protolith of Huangtuling gneiss was S-type granite and exotic fluid/melt involved in the system during both similar to2000 Ma and similar to110 Ma events.
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