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华北克拉通胶—辽—吉带内发育大量古元古代条痕状花岗岩,岩性主要为含角闪石或磁铁矿的二长花岗岩,以暗色矿物定向排列为显著识别特征。基于系统的野外调查、岩石学、地质年代学和地球化学研究,对条痕状花岗岩成因和其形成的构造环境提出了不同的模式。LA-ICP-MS锆石U-Pb年龄显示这些条痕状花岗岩形成于2 173~2 205 Ma,基性岩脉侵位于2 159 Ma,后期的角闪岩相变质发生于约1 907Ma。条痕状花岗岩中发育基性暗色微粒包体,也发育钙质角闪石和镁铁质角闪石,副矿物为锆石、榍石和磁铁矿。主量和微量元素分析结果显示:条痕状花岗岩属于钙碱性岩浆系列,A/CNK值为0.9~1.2(多数小于1.1),A/NK值为0.9~1.4,SiO2质量分数为68.3%~76.9%,岩石具有低TiO2质量分数(小于0.3%);岩石富集大离子亲石元素(如K、Rb、Sr、Cs),亏损部分高场强元素(如Nb和Ti)。这些特征都指示条痕状花岗岩可能是形成于俯冲带环境下的I型花岗岩。部分岩体(如大房身岩体)具有类似A型花岗岩的特征,这是岩浆体系富硼而引起的高分异所致的,岩体高SiO2质量分数(76.7%~77.1%)也是高分异的表现。硼的加入会导致岩浆体系固相线温度降低,使得岩浆具有更为充分的时间进行演化。全岩εNd(t)值(-8.6~1.5)和锆石εHf(t)值(-1.3~5.6)都具有非常宽的变化范围,结合基性暗色微粒包体的岩相学特征以及斜长石的环带,说明条痕状花岗岩形成于下地壳熔融的酸性岩浆和富集地幔熔融的基性岩浆的混合。花岗岩的弧岩浆属性及其老于2 500Ma的太古代继承锆石指示胶—辽—吉带在古元古代可能发生了北向俯冲。
A large number of Paleoproterozoic feldspathic granites were developed in the North China Craton Glue-Liao-Kyrgyzstan belt. The lithologies are mainly of monzonitic granites containing hornblendite or magnetite, and are characterized by the directional arrangement of dark-colored minerals. Based on the systematic field investigation, petrology, geochronology and geochemistry, different models are proposed for the genesis and tectonic setting of feldspathic granites. The LA-ICP-MS zircon U-Pb age shows that these streak-shaped granites formed at 2 173-2 205 Ma, the basic dikes invaded at 2 159 Ma, and the late amphibolite facies metamorphism occurred at about 1 907 Ma. Striated granite in the development of the basic dark-particle inclusions, also developed calcium hornblendit amphibole and mafic amphibole, side minerals zircon, sclerite and magnetite. The main trace elements and trace elements analysis show that the streak-like granites belong to calc-alkaline magma series with A / CNK of 0.9-1.2 (mostly less than 1.1), A / NK of 0.9-1.4 and SiO2 of 68.3% 76.9%. The rocks have low TiO2 mass fraction (less than 0.3%). The rocks are enriched in large ion lithophile elements such as K, Rb, Sr and Cs and depleted in some high field strength elements such as Nb and Ti. These characteristics indicate that the feldspathic granites may be Type I granites formed in the subduction zone. Part of the rock mass (such as the Dachen rock mass) has similar A-type granite characteristics, which is caused by boron enrichment caused by magmatic system. The high SiO2 mass fraction (76.7% ~ 77.1%) of the rock mass is also high Differentiated performance. The addition of boron leads to a decrease in the solidus temperature of the magmatic system, allowing the magma to evolve more adequately. The values of εNd (t) of whole rock (-8.6 ~ 1.5) and εHf (t) of zircon (-1.3 ~ 5.6) all have a very wide range of variation. Combined with the lithofacies characteristics of basal dark- Stone ring zone, indicating the formation of felled granite in the lower crust melting acidic magma and rich mantle melting basic magma mixture. The arc magma attribute of granite and its zircon bearing gel, the Liao-Kyrgyzstan, which was older than 2 500 Ma, may have been subjected to northward subduction in the Paleoproterozoic.