北大别混合岩类型及其成因

发布时间：2018-03-25 11:31

  本文选题：混合岩　切入点：岩石类型　出处：《矿物岩石》2017年02期

【摘要】：大别造山带北大别超高压变质构造单元中广泛发育混合岩。基于对罗田和岳西穹隆中混合岩的野外观察、岩相学、矿物化学和锆石LA-ICP-MS U-Pb定年系统工作,发现北大别混合岩主要分为中等深熔混合岩和高度深熔混合岩两种类型。中等深熔混合岩为叠层状混合岩和膨胀结构混合岩;高度深熔混合岩为眼球状混合岩和析离体状混合岩。锆石U-Pb同位素定年结果表明,混合岩中新生锆石年龄范围为125 Ma~138 Ma,加权平均年龄为130.7 Ma±1.8 Ma;两个继承锆石的年龄分别为602.8 Ma±16.8 Ma和667.3 Ma±17.6 Ma;混合岩叠层状暗色体中锆石年龄连续且分布集中,加权平均年龄为703 Ma±10 Ma,代表原岩的形成年龄。北大别混合岩的原岩为新元古代的岩石,其混合岩化作用发生在140 Ma至125 Ma期间。不同浅色体中斜长石的含量和牌号差异显著,反映了浅色体形成于不同演化程度的熔体结晶。斜长石-角闪石温压计估算结果显示,混合岩形成的温压条件为723℃~768℃和370 MPa~520 MPa,对应于中上地壳环境。混合岩的成因机制以长英质片麻岩水饱和条件下的富水熔融为主。其反应为:黑云母+石英+斜长石+水=角闪石+斜长石(残留)+花岗质熔体。少数混合岩的成因机制为角闪片麻岩中角闪石的脱水熔融。其反应为:角闪石+斜长石+石英=单斜辉石+富水熔体。
[Abstract]:The migmatite is widely developed in the Dabie ultrahigh pressure metamorphic tectonic unit of the Dabie orogenic belt. Based on the field observation of the migmatite in the Luotian and Yuexi dome, lithofacies, mineralogical chemistry and zircon LA-ICP-MS U-Pb dating system, It is found that the Northern Dabie migmatite is mainly divided into two types: medium deep melt migmatite and high deep melt migmatite. The medium deep melt migmatite is composed of laminated migmatite and expansive structure migmatite. The highly submersible migmatite is an eyeball migmatite and an isolated migmatite. The zircon U-Pb isotopic dating results show that, The age range of new zircon in the migmatite is 125 Ma~138 Ma, the weighted mean age is 130.7 Ma 卤1.8 Ma, the ages of two inherited zircons are 602.8 Ma 卤16.8Ma and 667.3 Ma 卤17.6Ma.The zircon ages in the laminated dark bodies of the migmatite are continuous and concentrated. The weighted mean age is 703 Ma 卤10 Ma, which represents the age of formation of the original rocks. The protolith of the Beidabie migmatite is a Neoproterozoic rock, and its migmatization occurred between 140 Ma and 125 Ma. The contents and grades of plagioclase in different light-colored bodies vary significantly. The results of temperature and pressure estimation of plagioclase and hornblende indicate that, The temperature and pressure conditions of the migmatite formation are 723 鈩，

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