锡林浩特东部早白垩世白音高老组岩石地球化学特征、LA-MC-ICP-MS锆石U-Pb年龄及地质意义   总被引：6，自引：0，他引：6  

张学斌 《地质与勘探》2015,51(2):290-302

锡林浩特东部白音高老组火山岩主要由石泡流纹岩、珍珠岩、碎斑熔岩、流纹质熔结凝灰岩等组成。LA-MC-ICP-MS锆石U-Pb定年显示,火山岩形成于134 Ma~139 Ma之间的早白垩世。岩石地球化学研究表明:该组火山岩具有高硅、高钾、高Fe OT/Mg O比值(4.88~19.09),贫镁、钙特征,属高钾钙-碱性岩系;稀土元素表现为稀土总量较高(∑REE=82.02~436.61)、轻重稀土分馏明显(LaN/YbN=2.23~20.74)、属轻稀土富集型(LRE/HRE=2.71~11.87)、Eu负异常显著(δEu=0.06~0.42);微量元素特征表现为大离子亲石元素(LILE)Rb、Th、U、K相对较为富集,高场强元素(HFSE)Nb、Ta相对亏损,而Ba、Sr、Zr、Ti强烈亏损,与A2型花岗岩特征相似。其岩浆来源为典型的壳源岩浆系列,是陆壳岩石部分熔融的产物,形成于造山后的张性构造环境。  相似文献   

通化大川地区稀有稀土矿找矿方向研究     

赵来社  杨复顶  张勇 《吉林地质》2015,(2)

通化大川地区在1:200 000水系沉积物测量中圈出了"通通-84-Hs-23"号组合异常,异常内出露的岩体为燕山期碱性花岗岩。通过对花岗岩特征研究,岩体有明显的分异特征,具备了产出稀有稀土矿产的地质条件。在异常区内开展了1:50 000水系沉积物地球化学测量工作,在碱性花岗岩分布区进一步圈出了稀有稀土异常套合区。综合了区域物化遥特征信息,圈出了重要的找矿远景区,在库仓围子远景区开展1:10 000地质填图和土壤测量工作,发现了多处矿化体,显示出该地区巨大的稀有稀土找矿前景。  相似文献   

浙中后山店花岗斑岩体的LA-ICP-MS锆石U-Pb定年、锆石Hf同位素及其地质意义     

王对兴  李春麟  高万里  王宗秀  朱骥 《矿物岩石》2015,35(1)

针对浙中地区后山店花岗斑岩体进行高精度LA-ICP-MS锆石U-Pb测年和锆石Lu-Hf同位素的测定。测年结果显示其加权平均年龄值为148.5 Ma±1.2 Ma(MSWD=1.4),说明浙中地区有晚侏罗世侵入岩的存在,属于燕山早期晚阶段岩浆活动的产物,其成岩时代可能代表了古太平洋构造域下的板内岩浆活动和陆缘弧间的过渡阶段。锆石的εHf(t)值为-10.3~-3.5,均为负值,二阶段模式年龄tHf2(Ma)变化范围主要集中于1 400 Ma~1 829 Ma之间,反映其物质来源可能为中元古代下地壳基底物质,并在成岩过程中有幔源组分的参与。  相似文献   

秦岭造山带光头山岩体群黑云母地球化学特征及成岩意义   总被引：1，自引：0，他引：1  

张有军  梁文天  罗先熔  董云鹏  张国伟 《矿物岩石》2015,35(1)

针对南秦岭光头山岩体群的岩相学和黑云母地球化学分析,进而对秦岭造山带晚三叠世花岗岩形成的温度、压力和氧逸度等物理化学条件进行专门的研究。其中岩相学观察表明,光头山岩体群主要由黑云母二长花岗岩和花岗闪长岩组成。电子探针分析结果表明黑云母二长岗岩中的黑云母是铁质黑云母,花岗闪长岩中的黑云母是镁质黑云母,所测黑云母的Fe2+/(Fe2++Mg)比值变化范围较小,表明其未受到后期改造,为原生黑云母,可以用来估算岩体的成岩物理化学条件。根据黑云母地球化学成分计算的成岩温度为(645~710)℃,压力为(126~309)MPa,logfo2为-12~-15,岩体侵位于中上地壳层次(约8.6km)。黑云母地球化学分析还表明,光头山岩体群主要为过铝质-造山带钙碱性花岗岩,岩浆以壳源为主兼具壳幔混源的特征。  相似文献   

Muscovite dehydration melting: Reaction mechanisms,microstructures, and implications for anatexis     

Brendan Dyck  David J. Waters  Marc R. St-Onge  Mike P. Searle 《Journal of Metamorphic Geology》2020,38(1):29-52

Dehydration melting of muscovite in metasedimentary sequences is the initially dominant mechanism of granitic melt generation in orogenic hinterlands. In dry (vapour-absent) crust, muscovite reacts with quartz to produce K-feldspar, sillimanite, and monzogranitic melt. When water vapour is present in excess, sillimanite and melt are the primary products of muscovite breakdown, and any K-feldspar produced is due to melt crystallization. Here we document the reaction mechanisms that control nucleation and growth of K-feldspar, sillimanite, and silicate melt in the metamorphic core of the Himalaya, and outline the microstructural criteria used to distinguish peritectic K-feldspar from K-feldspar grains formed during melt crystallization. We have characterized four stages of microstructural evolution in selected psammitic and pelitic samples from the Langtang and Everest regions: (a) K-feldspar nucleates epitaxially on plagioclase while intergrowths of fibrolitic sillimanite and the remaining hydrous melt components replace muscovite. (b) In quartzofeldspathic domains, K-feldspar replaces plagioclase by K⁺–Na⁺ cation exchange, while melt and intergrowths of sillimanite+quartz form in the aluminous domains. (c) At 7–8 vol.% melt generation, the system evolves from a closed to open system and all phases coarsen by up to two orders of magnitude, resulting in large K-feldspar porphyroblasts. (d) Preferential crystallization of residual melt on K-feldspar porphyroblasts and coarsened quartz forms an augen gneiss texture with a monzogranitic-tonalitic matrix that contains intergrowths of sillimanite+tourmaline+muscovite+apatite. Initial poikiloblasts of peritectic K-feldspar trap fine-grained inclusions of quartz and biotite by replacement growth of matrix plagioclase. During subsequent coarsening, peritectic K-feldspar grains overgrow and trap fabric-aligned biotite, resulting in a core to rim coarsening of inclusion size. These microstructural criteria enable a mass balance of peritectic K-feldspar and sillimanite to constrain the amount of free H₂O present during muscovite dehydration. The resulting modal proportion of K-feldspar in the Himalayan metamorphic core requires vapour-absent conditions during muscovite dehydration melting and leucogranite formation, indicating that the generation of large volumes of granitic melts in orogenic belts is not necessarily contingent on an external source of fluids.  相似文献   

小兴安岭-张广才岭地区晚古生代至中生代花岗岩的成因及其地质意义     

葛茂卉  张进江  刘恺  王盟  李壮 《岩石矿物学杂志》2020,39(4):385-405

中国东北地区显生宙花岗岩的成因一直是中亚造山带东段研究的热点之一,尤其是小兴安岭-张广才岭地区的花岗岩其成因及形成的大地构造背景一直存在较大争议。本文新获得小兴安岭-张广才岭铁力和依兰地区的二长花岗岩LA-ICP-MS锆石U-Pb年龄分别为188±1 Ma和257±3 Ma。地球化学数据显示,两地区的二长花岗岩均为Ⅰ型花岗岩并且富集大离子亲石元素(Th和U等)和轻稀土元素,亏损高场强元素(Nb和Ta等)和重稀土元素具有弧岩浆岩的地球化学特征。锆石Hf同位素数据显示,铁力地区二长花岗岩的岩浆源区可能来自于中新元古代的下地壳部分熔融。综合前人在小兴安岭-张广才岭地区已发表的花岗岩类岩石的地质年代学和地球化学数据,初步推测小兴安岭-张广才岭地区在晚古生代至中生代期间处于活动大陆边缘环境。同时,小兴安岭-张广才岭地区晚古生代至中生代的岩浆岩具有自东向西形成时代逐渐变年轻的趋势,这可能是由于东侧的牡丹江洋在晚古生代至中生代期间俯冲角度逐渐变缓造成的。  相似文献   

内蒙古沙麦钨矿区高分异花岗岩独居石U-Pb定年及成矿意义     

宓奎峰  杨艳  颜廷杰  吕志成  柳振江 《现代地质》2020,34(3):504-513

兴蒙造山带是中国北方重要的多金属成矿带,产出有一系列的钨多金属矿床。沙麦钨矿位于内蒙古二连浩特—东乌旗成矿带东侧,是兴蒙造山带发育的典型石英脉型钨矿床之一。通过对沙麦矿区出露的花岗岩开展独居石U-Pb测年,总结区域钨矿化的成矿年龄与矿化特征,探讨区域钨矿成矿时序及构造动力学背景。测年结果显示,沙麦矿区中细粒黑云母二长花岗岩、似斑状黑云母二长花岗岩LA-ICP-MS独居石U-Pb谐和年龄分别为(141.6±1.1) Ma 和(141.4±0.3) Ma,进一步确认沙麦钨矿形成于早白垩世。而二连浩特—东乌旗成矿带及其邻区钨矿化存在晚石炭世—早二叠世、早白垩世两期,成矿时代分别发生于约300 Ma和140~130 Ma。300 Ma成矿期钨成矿作用受古亚洲洋的影响;140~130 Ma成矿期为区域钨矿成矿作用高峰期,成矿作用受到古太平洋和蒙古—鄂霍次克洋构造体系叠加作用的影响。  相似文献   

浙南花岗岩残积土物质结构及工程地质特性研究     

孙强  张泰丽  伍剑波  王赫生 《地质论评》2020,66(S1):163-166

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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   

Fluid generation and evolution during exhumation of deeply subducted UHP continental crust: Petrogenesis of composite granite–quartz veins in the Sulu belt,China          下载免费PDF全文

S.‐J. Wang  L. Wang  M. Brown  P. M. Piccoli  T. E. Johnson  P. Feng  H. Deng  K. Kitajima  Y. Huang 《Journal of Metamorphic Geology》2017,35(6):601-629

Composite granite–quartz veins occur in retrogressed ultrahigh pressure (UHP) eclogite enclosed in gneiss at General's Hill in the central Sulu belt, eastern China. The granite in the veins has a high‐pressure (HP) mineral assemblage of dominantly quartz+phengite+allanite/epidote+garnet that yields pressures of 2.5–2.1 GPa (Si‐in‐phengite barometry) and temperatures of 850–780°C (Ti‐in‐zircon thermometry) at 2.5 GPa (~20°C lower at 2.1 GPa). Zircon overgrowths on inherited cores and new grains of zircon from both components of the composite veins crystallized at c. 221 Ma. This age overlaps the timing of HP retrograde recrystallization dated at 225–215 Ma from multiple localities in the Sulu belt, consistent with the HP conditions retrieved from the granite. The ε_Hf(t) values of new zircon from both components of the composite veins and the Sr–Nd isotope compositions of the granite consistently lie between values for gneiss and eclogite, whereas δ¹⁸O values of new zircon are similar in the veins and the crustal rocks. These data are consistent with zircon growth from a blended fluid generated internally within the gneiss and the eclogite, without any ingress of fluid from an external source. However, at the peak metamorphic pressure, which could have reached 7 GPa, the rocks were likely fluid absent. During initial exhumation under UHP conditions, exsolution of H₂O from nominally anhydrous minerals generated a grain boundary supercritical fluid in both gneiss and eclogite. As exhumation progressed, the volume of fluid increased allowing it to migrate by diffusing porous flow from grain boundaries into channels and drain from the dominant gneiss through the subordinate eclogite. This produced a blended fluid intermediate in its isotope composition between the two end‐members, as recorded by the composite veins. During exhumation from UHP (coesite) eclogite to HP (quartz) eclogite facies conditions, the supercritical fluid evolved by dissolution of the silicate mineral matrix, becoming increasingly solute‐rich, more ‘granitic’ and more viscous until it became trapped. As crystallization began by diffusive loss of H₂O to the host eclogite concomitant with ongoing exhumation of the crust, the trapped supercritical fluid intersected the solvus for the granite–H₂O system, allowing phase separation and formation of the composite granite–quartz veins. Subsequently, during the transition from HP eclogite to amphibolite facies conditions, minor phengite breakdown melting is recorded in both the granite and the gneiss by K‐feldspar+plagioclase+biotite aggregates located around phengite and by K‐feldspar veinlets along grain boundaries. Phase equilibria modelling of the granite indicates that this late‐stage melting records P–T conditions towards the end of the exhumation, with the subsolidus assemblage yielding 0.7–1.1 GPa at <670°C. Thus, the composite granite–quartz veins represent a rare example of a natural system recording how the fluid phase evolved during exhumation of continental crust. The successive availability of different fluid phases attending retrograde metamorphism from UHP eclogite to amphibolite facies conditions will affect the transport of trace elements through the continental crust and the role of these fluids as metasomatic agents interacting with the mantle wedge in the subduction channel.  相似文献