阴山陆块武川石榴基性麻粒岩P-T条件及其变质时代:来自相平衡模拟与锆石U-Pb定年的约束     

刘平华  刘福来  蔡佳  杨红  王舫  刘超辉  刘建辉  施建荣 《岩石学报》2016,32(7):1949-1979

武川高级片麻岩地体中石榴基性麻粒岩的变质用与同位素年代学研究对于揭示阴山陆块新太古代构造演化过程具有十分重要的研究意义。它们主要以不规则透镜体或变形岩墙/岩脉群的形式赋存于新太古代晚期英云闪长质片麻岩或变质表壳岩系之中,并切割近南-北向的区域性片麻理。岩相学观察、矿物相转变分析与矿物化学研究表明,武川石榴基性麻粒岩保留了十分典型的高压麻粒岩相矿物:石榴石+单斜辉石+斜长石+角闪石+石英+铁-钛氧化物。其中,粗粒石榴石边部常发育微弱的扩散环带,表现为从幔部至边部,镁铝榴石组分不断减少,相应地铁铝榴石组分不断增加,而钙铝榴石与锰铝榴石组分基本不变,指示晚期冷却降温作用对石榴石成分产生一定影响。斜长石具有细粒包体型与粗粒基质型两种不同的类型,它们具有十分相似化学成分,均为An=35~45的中长石。在NCFMASHTO(Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3)体系下,利用THERM OCA LC 3.33软件,对两件石榴基性麻粒岩样品进行了相平衡模拟,模拟的峰期矿物组合为:石榴石+单斜辉石+斜长石+角闪石+石英+铁-钛氧化物,与岩相学观察十分一致。采用石榴石中最小x(g)Fe~(2 +)/(Fe~(2 +)+Mg))与斜长石是中最小ca(pl)(Ca/(Ca+Na))等值线,将本区石榴基性麻粒岩峰期高压麻粒岩相的温压条件限定在P=1.31~1.40GPa,T=770~840℃的范围内。LA-ICP-MS锆石U-Pb定年结果表明,两件石榴基性麻粒岩麻粒岩中发育的变质锆石分别记录了2517±6Ma(BT58-1,MSWD=0.66,n=21)与2512±16Ma(LH66-1,MSWD=0.26,n=42)的加权平均年龄,与阴山陆块其它新太古代岩石记录的约2500Ma变质年龄一致,被解释为本区石榴基性麻粒岩遭受高压麻粒岩相变质时代。结合本区其它新的研究资料,本文认为武川石榴基性麻粒岩形成可能与区内新太古代晚期造山作用有关。  相似文献   

东昆仑东段巴隆地区朝火鹿陶勒盖花岗闪长岩体锆石U-Pb年龄、地球化学及其地质意义     

陈功  裴先治  李佐臣  李瑞保  陈有炘  刘成军  陈国超  王旭斌  桑继镇  杨森  邓文兵 《地质通报》2016,35(12):1990-2005

东昆仑造山带晚古生代—早中生代由于布青山-阿尼玛卿洋的俯冲发育有大量岛弧型花岗岩类。选取东昆北巴隆地区朝火鹿陶勒盖花岗闪长岩体寄主岩和闪长质暗色微粒包体进行了岩相学、LA-ICP-MS锆石U-Pb年代学及地球化学研究。结果表明,岩体寄主岩的结晶年龄为242.3±1.3Ma,暗色微粒包体结晶年龄为241.2±0.8Ma,显示其形成于中三叠世;寄主岩和暗色微粒包体A/CNK值介于0.86~1.06之间,为准铝质-弱过铝质;稀土元素总量分别为119×10~(-6)~170×10~(-6)、189×10~(-6),稀土元素配分模式显示右倾型,具有负Eu异常;岩石富集Rb、Ba、Th等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,具有弧岩浆岩特征。野外及岩相学特征均显示包体为基性岩浆进入酸性岩浆快速冷凝形成的,为俯冲板片断离导致幔源岩浆上侵形成的岩浆混合作用的产物,是布青山-阿尼玛卿洋俯冲晚期的岩浆记录。  相似文献   

内蒙古解放营子花岗闪长岩岩浆混合机制——来自斜长石和角闪石的矿物化学证据     

吕前露  刘建峰  赵硕  郭春丽  车亚文 《岩石矿物学杂志》2022,41(2):322-338

为揭示华北克拉通北缘中晚三叠世解放营子花岗闪长岩的岩浆混合机制,对寄主岩石和镁铁质包体中斜长石和角闪石开展了电子探针分析.分析结果显示,多斑和少斑包体边部的斜长石斑晶发育An值增加的突变环带,环带的An值为32～46,明显高于核部和边部斜长石的An值(18～31),而核部的An值与寄主岩石中斜长石的An值一致,该特征指...  相似文献   

Radiating 1.0 Ga Mafic Dyke Swarms of Eastern Brazil and Western Africa: Evidence of Post-Assembly Extension in the Rodinia Supercontinent?     

L.C. Correa-Gomes  E.P. Oliveira 《Gondwana Research》2000,3(3)

Several mafic dyke swarms of similar composition and age (tholeiite- ca.1.0 Ga) occur on both sides of the Atlantic Ocean in eastern South America and western Africa. When assembled to their pre-drift position in the Mesozoic, the Brazilian coastal dyke province of Bahia, and the African dykes in Cameroun (Ebolowa suite) and Congo (Comba and Sembe-Ouesso provinces) define a giant radiating pattern (1200 km × 800 km) similar to other dyke swarms elsewhere associated with large-scale continental rifting. Magma flow indicators of the Brazilian dykes and branching propagation styles of their African counterparts indicate that the dyke conduits were fed with magmas diverging from a source beneath the long axis of the Meso-Neoproterozoic West-Congolian Basin in Africa. There, MORB-like metabasalts have been described in the La Bikossi Group of the Mayombian Supergroup. Whether the rifting event and intrusion of dyke swarms were triggered or not by a mantle plume beneath part of the Rodinia subcontinental lithosphere remain to be confirmed.  相似文献   

华北克拉通中生代以来基性岩墙群的分布及研究意义   总被引：2，自引：0，他引：2  

刘燊  胡瑞忠  冯光英  杨毓红  冯彩霞  齐有强  王涛 《地质通报》2010,29(203):259-267

围绕岩石圈破坏和减薄这个主题,华北克拉通成为近10年来国内外研究的热点地区。华北克拉通中生代以来基性岩墙群分布广泛,然而对此仍缺乏系统的研究。通过对基性岩墙群的系统总结,在详尽的资料收集和已有研究的基础上,重点对华北克拉通中生代基性岩墙群的研究现状、分布和意义进行了汇总和讨论。随后,结合近年来的研究经验,提出了基性岩墙群定年中应注意的问题。  相似文献   

华北克拉通南缘中条山-嵩山地区1.78Ga基性岩墙群的地球化学特征及构造环境   总被引：8，自引：6，他引：2  

胡国辉  胡俊良  陈伟  赵太平 《岩石学报》2010,26(5):1563-1576

幔源岩浆侵位产生的基性岩墙群是地壳伸展裂解的重要标志。华北克拉通南缘中条山-嵩山地区出露有大量的中元古代基性岩墙群,对其研究将有助于深入了解华北克拉通中元古代构造演化特征。其岩石类型以辉绿岩为主,少量辉长辉绿岩和辉绿玢岩;主要造岩矿物为斜长石和单斜辉石,其它矿物包括角闪石、Fe-Ti氧化物、磷灰石、黑云母、碱性长石和石英。锆石SHRIMPU-Pb年龄为1785±18Ma,代表岩墙的结晶年龄。岩石K2O+Na2O含量为3.63%～6.18%,K2O/Na2O比值为0.73～1.38,FeOT含量较高(10.03%～13.59%),属于拉斑玄武岩系列。岩石的稀土元素含量高(142×10-6～381×10-6),亏损Nb、Ta、Zr、Hf等高场强元素,富集Rb、Ba、La等大离子亲石元素,全岩εNd(t)值为-6.2～-8.1。岩墙的固结指数(SI)和MgO含量呈明显的正相关关系,说明幔源岩浆发生过明显的结晶分异作用。地球化学分析表明,研究区基性岩墙属于板内拉斑玄武岩系列,与熊耳群火山岩有相似的地球化学特征;基于两者紧密的产出关系,我们认为该区岩墙可能是熊耳群火山岩的通道岩墙,共同代表了华北克拉通东、西陆块碰撞后伸展事件。  相似文献   

Complex geometry of the Cenozoic magma plumbing system in the central Sahara,NW Africa     

《International Geology Review》2012,54(14):1576-1592

Topographic uplifts in the central Sahara occur in the Hoggar-Aïr and Tibesti-Gharyan swells that consist of Precambrian rocks overlain by Cenozoic volcanic rocks. The swells and associated Cenozoic volcanism have been related either to mantle plumes or to asthenospheric upwelling and to partial melting due to rift-related delamination along pre-existing Pan-African mega-shears during the collision between Africa and Europe. The Cenozoic volcanic rocks in the Hoggar generally range from Oligocene tholeiitic/transitional plateau basalts, which occur in the centre of the dome, to Neogene alkali basalts characterized by a decrease in their degree of silica undersaturation and an increase in their La/Yb ratios. The alkali basaltic rocks occur mainly along the margins of the dome and typically have less radiogenic Nd and Sr isotopic ratios than the tholeiitic/transitional basalts. The geochemistry of the most primitive basaltic rocks resembles oceanic island basalt (OIB) tholeiitic – in particular high-U/Pb mantle (HIMU)-type – and is also similar to those of the Circum-Mediterranean Anorogenic Cenozoic Igneous (CiMACI) province. These characteristics are consistent with, but do not require, a mantle plume origin. Geophysical data suggest a combination of the two mechanisms resulting in a complex plumbing system consisting of (a) at depths of 250–200 km, an upper mantle plume (presently under the Aïr massif); (b) between 200 and 150 km, approximately 700 km northeastward deflection of plume-derived magma by drag at the base of the African Plate and by mantle convection; (c) at approximately 150 km, the magma continues upwards to the surface in the Tibesti swell; (d) at approximately 100 km depth, part of the magma is diverted into a low S-wave velocity corridor under the Sahara Basin; and (e) at approximately 80 km depth, the corridor is tapped by Cenozoic volcanism in the Hoggar and Aïr massifs that flowed southwards along reactivated Precambrian faults.  相似文献   

Timing of granitic magma mixing in the southeastern Gyeongsang Basin,Korea: SHRIMP-RG zircon data     

《International Geology Review》2012,54(10):1150-1162

Late Cretaceous calc-alkaline granites in the Gyeongsang Basin evolved through the mixing of mafic and felsic magmas. The host granites contain numerous mafic magmatic/microgranular enclaves of various shapes and sizes. New SHRIMP-RG zircon U–Pb ages of both granite and mafic magmatic/microgranular enclaves are 75.0?±?0.5 Ma and 74.9?±?0.6 Ma, respectively, suggesting that they crystallized contemporaneously after magma mixing. The time of injection of mafic melt into the felsic magma chamber can be recognized as approximately 75 Ma by field relations, petrographic features, geochemical evolution, and SHRIMP-RG zircon dating. This Late Cretaceous magma mixing event in the Korean Peninsula was probably related to the onset of subduction of the Izanagi (Kula)–Pacific ridge.  相似文献   

Geochronologic-petrochemical studies of the Hongshishan mafic–ultramafic intrusion,Beishan area,Xinjiang (NW China): petrogenesis and tectonic implications     

《International Geology Review》2012,54(3):270-289

The Hongshishan mafic–ultramafic intrusion (SIMS zircon U–Pb age 286.4 ± 2.8 Ma) consists of dunite, clinopyroxene peridotite, troctolite, and gabbro. Major elements display systematic correlations. Trace elements have identical distribution patterns, including flat rare-earth element (REE) patterns with positive Eu anomalies and enrichments in large ion lithophile elements (LILE) but depletions in Nb and Ta, indicating fractional crystallization as a key factor in magmatic evolution. Petrologic and geochemical variations in drill core samples demonstrate that minor assimilation and progressive magma injections were closely associated with Ni–Cu mineralization. Mass balance estimates and Sr–Nd isotopes reveal that the Hongshishan parental magmas were high-Mg and low-Ti tholeiitic basalts and were derived from a lithospheric mantle source that had been modified by subducted slab metasomatism before partial melting.

Southward subduction of the Palaeo-Tianshan–Junggar Ocean is further constrained by a compilation of inferred, subduction-induced modifications of mantle sources in mafic–ultramafic intrusions distributed in the eastern Tianshan–Beishan area. Integrating the regional positive ?_Nd(t) granites, high-Mg and low-Ti basaltic magmas (mafic–ultramafic intrusions), and slightly later high-Ti basalts in NW China suggests that their petrogenesis could be attributed to Permian mantle plume activities.  相似文献   

Petrochemistry of Mesozoic mafic intrusions related to the Paraná Magmatic Province,Uruguay     

《International Geology Review》2012,54(7):844-860

The Cuaró Formation is part of the sequence of Mesozoic mafic intrusions related to the Early Cretaceous break-up of Gondwana and represents the southernmost occurrences within the Paraná Magmatic Province in Uruguay. We present field data, petrography and lithogeochemical results regarding these dike swarms and sills that crop out in the southern extreme of the Paraná Basin. Dolerites and sills mainly exhibit glomeroporphyritic textures; the phenocrysts consist of plagioclase, clinopyroxene, relicts of olivine and titaniferous magnetite. Bulk-rock geochemical analyses allowed their classification as low-Ti subalkaline tholeiitic basalts and andesitic basalts. Trace element data indicated that the protoliths of these intrusions include the subcontinental lithospheric mantle, as is generally recognized for other Gondwana-related continental flood basalt provinces.  相似文献