胶-辽-吉造山带北辽河变基性岩的成因、地球化学属性及其构造意义

发布时间：2018-04-17 11:25

本文选题：华北克拉通 + 胶-辽-吉造山带　；参考：《岩石学报》2017年09期

【摘要】：大规模出露于胶-辽-吉造山带的北辽河变基性岩(NLHmetabasicrocks)是恢复造山带构造演化的关键之一,然而,研究者们对这些变基性岩的成因和构造环境有很大争议,制约了对胶-辽-吉造山带早期构造演化的深入研究。基于详细的野外地质调查,本文对北辽河变基性岩进行了系统的岩石学研究并提供了新的全岩地球化学数据,结合前人的测试结果,我们对这些变基性岩的成因和构造环境进行了相关探讨。变基性岩侵入于北辽河群的大理岩和碎屑岩中,经历了一定程度的蚀变以及绿片岩相-角闪岩相变质。岩石类型包括变质辉长岩、变质辉绿岩、斜长角闪岩以及石榴斜长角闪岩;前两者具有明显的变余辉长或者辉绿结构,可见自形斜长石,少见原生矿物单斜辉石的残留;后两者主要由斜长石和角闪石组成,部分含有石榴子石变斑晶;此外,岩石中出现大量Fe-Ti氧化物(磁铁矿和钛铁矿)。地球化学研究表明,北辽河变基性岩均属于拉斑玄武岩系列(SiO_2=44.55%~54.11%,Nb/Y=0.16~0.31),以低TiO_2(0.69%~1.99%)和低MgO(多数5.47%~7.97%)为特征,轻稀土轻微富集((La/Sm)_N=1.22~2.66;(La/Yb)_N=1.66~4.56),并具有明显的Nb、Ta、P以及轻微的Zr、Ti亏损,岩石经历了橄榄石、单斜辉石和斜长石等矿物的三相结晶分异以及Fe-Ti氧化物(磁铁矿和钛铁矿)的堆晶;它们的微量元素配分型式类似于E-MORB和地壳岩石,并且地球化学组成与MORB相近,而不同于弧玄武岩和板内玄武岩;这些变基性岩的Ce/Pb(3.07~26.58)、(Ta/La)PM(0.47~1.45)以及(Hf/Sm)PM(0.91~1.15)显示出有限的俯冲相关流体的交代作用;此外,大多数不相容元素比值(例如Th/Nb、La/Nb及Th/La等)的变化趋势则表明北辽河变基性岩的岩浆源区不可能是大陆岩石圈地幔,并且在形成过程中经历了明显的地壳物质混染。基于这些野外地质调查和地球化学研究,我们认为北辽河变基性岩应形成于相对成熟的弧后盆地,这样一个形成环境也表明胶-辽-吉造山带在早期存在~2.1Ga的洋壳俯冲过程,该构造带应该是~1.9Ga岛弧与大陆碰撞形成的一条古元古代造山带。
[Abstract]:The North Liaohe metamorphic rocks (NL Hmetababasicrocks), which emerged in large scale in the Jiao-Liaojia-Jiaoshan orogenic belt, is one of the key factors to restore the tectonic evolution of the orogenic belt. However, the origin and tectonic environment of these altered basic rocks have been greatly disputed by researchers.It restricts the deep study of the early tectonic evolution of the Jiao-Liao-Ji orogenic belt.Based on the detailed field geological survey, a systematic petrological study of the North Liaohe metamorphic rocks has been carried out in this paper, and new geochemistry data of the whole rock have been provided.The genesis and tectonic environment of these metamorphic rocks are discussed.The metamorphic rocks intruded into the marble and clastic rocks of the North Liaohe Group and underwent a certain degree of alteration and greenschist facies-amphibolite facies metamorphism.The rock types include metamorphic gabbro, metamorphic diabase, amphibolite and pomegranate amphibolite.The latter two are mainly composed of plagioclase and hornblende, some of which contain garnet changed into porphyry, in addition, a large number of Fe-Ti oxides (magnetite and ilmenite) are found in the rocks.Geochemical studies show that the northern Liaohe metamorphic rocks belong to the tholeiite series SiO44.5554.1111, characterized by low TiO20.69I 0.99I and low MgO (most 5.477.97m). LREE are slightly enriched in La / Sm / N1.22 / 2.66 / 2.664.56T, and have a significant loss of NB / Ta-P and a slight loss of Zr-Ti, and the rocks have experienced olivine loss.The three-phase crystallization differentiation of clinopyroxene and plagioclase and the stacking of Fe-Ti oxides (magnetite and ilmenite) are similar to those of E-MORB and crustal rocks, and their geochemical composition is similar to that of MORB.In contrast to arc basalt and intraplate basalt, the ce / Pb ~ (3.07) ~ (26.58 ~ (0.47) ~ 1.45) and Hf / SmPM _ (0.91) ~ 1.15) of these basaltic rocks show a limited metasomatism of subduction-related fluids.The variation trend of most incompatible element ratios (such as Th/ NB / La / NB and Th/La etc.) indicates that the magmatic source of the North Liaohe metamorphic rocks cannot be the continental lithospheric mantle and experienced obvious crustal material mixing during the formation process.Based on these field geological and geochemical studies, we believe that the basic rocks of the North Liaohe River should be formed in the relatively mature back-arc basin. Such a forming environment also indicates that there was an oceanic crust subduction process of 2.1Ga in the early stage of the Jiao-Liaoji orogenic belt.The tectonic belt should be an ancient Gu Yuan orogenic belt formed by the collision of 1.9Ga island arc with the continent.
【作者单位】：中国地质科学院地质研究所;
【基金】：国家自然科学基金重点项目(41430210) 中国地质科学院基本科研业务费专项经费资助(YYWF201703) 中国地质调查局地质调查项目(DD20160121)联合资助
【分类号】：P542;P588.124

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