Geochronologic Constraints on the Magmatic Underplating of the Gangdisê Belt in the India-Eurasia Collision: Evidence of SHRIMP II Zircon U-Pb Dating     

DONG Guochen  MO Xuanxue  ZHAO Zhidan  GUO Tieying  WANG Liangliang  CHEN Tao 《《地质学报》英文版》2005,(6)

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Episodic granite accumulation and extraction from the mid‐crust          下载免费PDF全文

D. Hall  A. Kisters 《Journal of Metamorphic Geology》2016,34(5):483-500

The processes of long‐range granitic magma transfer from mid‐ and lower crustal anatectic zones to upper crustal pluton emplacement sites remain controversial in the literature. This is partly because feeder networks that could have accommodated this large‐scale magma transport remain elusive in the field. Existing granite ascent models are based largely on numerical and theoretical studies that seek to demonstrate the viability of fracture‐controlled magma transport through dykes or self‐propagating hydrofractures. In most cases, the models present very little supporting field evidence, such as sufficiently voluminous near‐ or within‐source magma accumulations, to support their basic premises. We document large (deca‐ to hectometre‐scale), steeply dipping and largely homogeneous granite lenses in suprasolidus (~5 kbar, ~750 °C) mid‐crustal rocks in the Damara Belt in Namibia. The lenses are surrounded by and connected to shallowly dipping networks of stromatic leucogranites in the well‐layered gneisses of the deeply incised Husab Gorge. The outcrops define a four‐stage process from (i) the initial formation and growth of large, subvertical magma‐filled lenses as extension fractures developed at high angles to the subhorizontal regional extension in relatively competent wall‐rock layers. This stage is followed by (ii) the simultaneous lateral inflation and (iii) subcritical vertical growth of the lenses to a critical length that (iv) promotes fracture destabilization, buoyancy‐driven upward fracture mobilization and, consequently, vertical magma transport. These field observations are compared with existing numerical models and are used to constrain, by referring to the dimensions of the largest preserved inflated leucogranite lens, an estimate of the minimum fracture length (~100 m) and volume (~2.4 × 10⁵ m³) required to initiate buoyancy‐driven brittle fracture propagation in this particular mid‐crustal section. The critical values and field relationships compare favourably with theoretical models of magma ascent along vertical self‐propagating hydrofractures which close at their tails during propagation. This process leaves behind subtle wake‐like structures and thin leucogranite trails that mark the path of magma ascent. Reutilization of such conduits by repeated inflation and drainage is consistent with the episodic accumulation and removal of magma from the mid‐crust and is reflected in the sheeted nature of many upper crustal granitoid plutons.  相似文献   

东南印度洋中脊澳大利亚-南极洲不整合带地区岩浆供应与构造作用沿洋脊的变化     

刘守金  林间  周志远  张帆 《海洋学报(英文版)》2020,39(1):118-129

We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge(SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differences of the Australian-Antarctic Discordance(AAD) from adjacent ridge segments with the residual mantle Bouguer gravity anomaly(RMBA) being more positive, seafloor being deeper, morphology being more chaotic, M factors being smaller at the AAD. These systematic anomalies, as well as the observed Na_(8.0) being greater and Fe_(8.0) being smaller at AAD, suggest relatively starved magma supply and relatively thin crust within the AAD.Comparing to the adjacent ridges segments, the calculated average map-view M factors are relatively small for the AAD, where several Oceanic Core Complexes(OCCs) develop. Close to 30 OCCs were found to be distributed asymmetrically along the SEIR with 60% of OCCs at the northern flank. The OCCs are concentrated mainly in Segments B3 and B4 within the AAD at ～124°–126°E, as well as at the eastern end of Zone C at ～115°E. The relatively small map-view M factors within the AAD indicate stronger tectonism than the adjacent SEIR segments.The interaction between the westward migrating Pacific mantle and the relatively cold mantle beneath the AAD may have caused a reduction in magma supply, leading to the development of abundant OCCs.  相似文献   

PETROLOGY 1.IGNEOUS PETROLOGY     

《Abstract of Chinese Geological Literature》2014,(2)

正20140707Bai Yunshan(Wuhan Center,China Geological Survey,Wuhan 430205,China);Duan Qifa Geological Characteristics and Tectonic Significance of Volcanic Rocks from Kenan Formation of the Upper Triassic in Zhahe Area,Southern Qinghai Province(Geology and Mineral Resources of South China,ISSN1007-3701,CN42-1417/P,29(2),  相似文献   

东天山哈密地区早二叠世花岗岩体及镁铁质包体的年代学, 岩石地球化学特征及其构造意义   总被引：2，自引：0，他引：2  

陈希节  张奎华  周健 《地质学报》2016,90(9):2334-2354

花岗岩中包体是区域构造与深部过程研究结合的良好窗口,对研究花岗岩的成因和壳-幔相互作用有非常重要的意义。东天山南山口黑云母二长花岗岩中广泛发育镁铁质包体。主量元素组成上,寄主花岗岩岩具有中酸性、准铝质、富碱、富钾等特征;镁铁质包体则偏基性、贫钾。微量和稀土元素组成上,富集Rb、K、Th、U,贫Sr、P、Nb、Ta、Ti,且Zr、Hf含量相对较高,具中-强的铕负异常(0.46~0.57)。镁铁质包体与寄主岩具有相似的微量元素特征,但相对富集Sr、P,贫Zr、Hf,铕负异常中等或不明显(0.80~0.93)。闪长质包体属于同源包体,为寄主花岗岩同源母岩浆经结晶分异形成的早期产物。运用LA-ICP-MS锆石U-Pb定年技术,该南山口岩体暗色镁铁质微粒包体与寄主黑云母二长花岗岩的锆石U-Pb年龄分别为298.2±2.0Ma和294.0±2.7Ma,包体与寄主岩样品具有相似的Hf同位素组成,暗示其母岩浆来自新元古代晚期和早古生代亏损地幔中分离的新生地壳。该高钾钙碱性的花岗岩及其包体可能形成于东天山后碰撞背景下的板片断离后引起软流圈上涌,底侵体带来的热能使得新元古代晚期和早古生代的新生地壳发生部分熔融。  相似文献   

东昆北成矿带冰沟南铜镍矿辉长岩地球化学特征   总被引：2，自引：0，他引：2  

闫佳铭  孙丰月  陈广俊  钱烨  李良  王超  何书跃 《世界地质》2016,35(3):729-737

通过对东昆北成矿带冰沟南铜镍矿辉长岩的全岩地球化学进行分析,以确定该岩体的岩石成因及其形成的构造环境。冰沟南辉长岩SiO_2的含量为49.72%~51.58%,岩石系列为钙碱性。稀土元素球粒陨石分配模式为轻稀土略富集型,δEu为1.26~1.54,轻微正Eu异常。岩石富集大离子亲石元素(LILE)Rb、Ba、K,相对亏损P。岩体中的La/Sm、Th/La和Nb/U比值显示在就位过程中经历了一定程度的地壳混染。研究认为,岩体的岩浆源区为亏损地幔。结合区域演化,认为岩体形成于碰撞后伸展的背景。  相似文献   

腾冲火山构造区马站岩浆囊地球物理特征的再探讨          下载免费PDF全文

姜枚  谭捍东  彭淼  钱荣毅  张聿文  李庆庆  张立树  许乐红  郭帅 《中国地质》2016,(5):1688-1696

云南腾冲火山盆地深部存在岩浆囊是人们关注的问题,多方面进行了大量的研究且存在不同意见。作者此前依据低电阻异常推断出位于小空山、大空山、黑空山等火山口的下部,深13~30 km范围内东西向25 km,南北向30km的低电阻率的岩浆囊,其东侧为大盈江断裂。文章利用反射地震、重力、航空磁测资料进一步探讨了岩浆囊的其他地球物理特征。由于火山喷发,不仅在火山口附近形成了局部物质亏损,而且,岩浆囊本身也亏损了岩浆物质,在重力上延图中滤去了表层的火山局部负重力异常后,呈现出大空山北侧的与低阻体相对应的负重力异常,这与岩浆囊高温熔融状态含水低密度物质有密切关系。整体的重力负异常印证了低阻岩浆囊的存在。腾冲马站岩浆囊的温度为397~651°C,平均温度为524°C,其主体中心部位不可能存在磁性体。对航磁资料的处理,消除表层火山岩影响后,仍然发现有较强磁异常,其平面投影范围与低阻体相近,推断磁异常是岩浆囊顶层,在15 km深度以上范围内,随着岩浆囊体温度逐步下降,当低于480°C以后会形成新的铁磁性矿物,因此,在囊体上层出现了范围与囊体相近的较强的磁性体。反射地震仅仅在浅部较清楚地观测到较连续的反射波界面,是浅部火山岩、含水层、以及花岗岩顶界面的反映。向深部反射界面很不连续推测是由于多次岩浆上涌,其喷发时间有先后,成分有差异,故岩浆囊物质的不均匀性,虽然由于含水、矿化、熔融体构成了低电阻的共性,可温度的不均匀,却又显示了不同期次岩浆成分有变化,由岩浆囊向地表的通道上,东部花岗岩下为高速,相对于较低温度的物质,在小空山、大空山和黑空山深部沿大盈江断裂带有东西两个大的隐伏花岗岩体之间是最新的火山喷发通道,具有相对低速的通道。  相似文献   

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   

斑岩型钼矿床研究进展与问题   总被引：1，自引：0，他引：1  

曹冲  申萍 《地质论评》2018,64(2):477-497

本文在简要介绍全球重要成矿带斑岩型钼矿床品位、储量、时空分布以及构造背景的基础上,着重归纳了斑岩型钼矿床中Mo在岩浆—热液演化过程中的地球化学行为特征以及Mo在成矿流体中的迁移与沉淀机制两个方面的研究进展。取得了以下认识:形成斑岩型钼矿床成矿岩浆氧逸度(f_(O2))变化范围较大,但一般大于铁橄榄石—磁铁矿—石英(FMQ)缓冲体系。斑岩钼矿床形成的主要受岩浆房的大小,大体积的岩浆流体能否高效聚集到浅部岩株或岩脉,岩浆中的挥发分(例如F)含量等因素的控制,但与成矿花岗岩和出溶流体中Mo的含量高低无直接关系。成矿流体的氧逸度与p H降低对辉钼矿沉淀具有关键作用。除此之外,温度与盐度降低对辉钼矿沉淀也有重要作用。流体的多阶段沸腾可能对提高Mo品位具有重要意义。此外,应加强岩浆结晶分异过程、岩浆热液转化过程Mo的地球化学行为研究。  相似文献