内蒙古乌拉特中旗色尔腾山岩群东五分子岩组锆石SHRIMP定年及其地质意义     

王挽琼  刘正宏  徐仲元  白新会 《吉林大学学报(地球科学版)》2019,49(4):1053-1062

色尔腾山岩群是华北克拉通中西部早前寒武纪变质结晶基底的主要组成部分，对研究华北克拉通基底演化具有十分重要的意义。色尔腾山岩群的形成时代是目前研究的热点之一，本文通过岩石学和锆石SHRIMP U-Pb定年研究，查明了内蒙古乌拉特中旗乌兰乡查干哈达地区色尔腾山岩群东五分子岩组的岩石组成和年代学特征。东五分子岩组遭受了后期岩浆和构造作用的强烈破坏，未见顶底，主要由中细粒斜长角闪岩、细粒黑云斜长片麻岩、眼球状细粒黑云斜长片麻岩、条带状细粒黑云斜长片麻岩和细粒黑云角闪片岩组成，矿物组合特征指示岩石经历了低绿片岩相-低角闪岩相变质。其中，眼球状细粒黑云斜长片麻岩出露相对较厚，与细粒黑云斜长片麻岩多呈互层状产出，局部偶夹细粒黑云斜长片麻岩。本次研究选取其中新鲜的细粒黑云斜长片麻岩进行了锆石SHRIMP U-Pb测年分析，其锆石多呈自形-半自形，发育震荡环带，主体为岩浆成因，锆石SHRIMP U-Pb定年结果为（1 930.7±9.6）Ma，代表原岩（中酸性火山岩）冷凝结晶年龄，表明东五分子岩组经历变质作用的时代应晚于1 930 Ma。  相似文献   

Characterization of partial melting events in garnet-cordierite gneiss from the Kerala Khondalite Belt,India     

Nilanjana Sorcar  Kumar Batuk Joshi  Elson POliveira  JKTomson  VNandakumar 《地学前缘(英文版)》2020,(2):597-611

Phase equilibria modelling coupled with U–Pb zircon and monazite ages of garnet–cordierite gneiss from Vallikodu Kottayam in the Kerala Khondalite Belt,southern India are presented here.The results suggest that the area attained peak P–T conditions of^900
C at 7.5–8 kbar,followed by decompression to 3.5–5 kbar and cooling to 450–480
C,preserving signatures of the partial melting event in the field of high to ultra-high temperature metamorphism.Melt reintegration models suggest that up to 35%granitic melt could have been produced during metamorphism at^950
C.The U–Pb age data from zircons(~1.0–~0.7 Ga)and chemical ages from monazites(~540 Ma and^941 Ma)reflect a complex tectonometamorphic evolution of the terrain.The^941 Ma age reported from these monazites indicate a Tonian ultra-high temperature event,linked to juvenile magmatism/deformation episodes reported from the Southern Granulite Terrane and associated fragments in Rodinia,which were subsequently overprinted by the Cambrian(~540 Ma)tectonothermal episode.  相似文献   

High to ultrahigh temperature contact metamorphism and dry partial melting of the Tasiuyak paragneiss,Northern Labrador     

R. K. Mitchell  A. Indares  B. Ryan 《Journal of Metamorphic Geology》2014,32(6):535-555

Contact aureoles of the anorthositic to granitic plutons of the Mesoproterozoic Nain Plutonic Suite (NPS), Labrador, are particularly well developed in the Palaeoproterozoic granulite facies, metasedimentary, Tasiuyak gneiss. Granulite facies regional metamorphism (M_R), c. 1860 Ma, led to biotite dehydration melting of the paragneiss and melt migration, leaving behind biotite‐poor, garnet–sillimanite‐bearing quartzofeldspathic rocks. Subsequently, Tasiuyak gneiss within a c. 1320 Ma contact aureole of the NPS was statically subjected to lower pressure, but higher temperature conditions (M_C), leading to a second partial melting event, and the generation of complex mineral assemblages and microstructures, which were controlled to a large extent by the textures of the M_R assemblage. This control is clearly seen in scanning electron microscopic images of thin sections and is further supported by phase equilibria modelling. Samples collected within the contact aureole near Anaktalik Brook, west of Nain, Labrador, mainly consist of spinel–cordierite and orthopyroxene–cordierite (or plagioclase) pseudomorphs after M_R sillimanite and garnet, respectively, within a quartzofeldspathic matrix. In addition, some samples contain fine‐grained intergrowths of K‐feldspar–quartz–cordierite–orthopyroxene inferred to be pseudomorphs after osumulite. Microstructural evidence of the former melt includes (i) coarse‐grained K‐feldspar–quartz–cordierite–orthopyroxene domains that locally cut the rock fabric and are inferred to represent neosome; (ii) very fine‐ to medium‐grained cordierite–quartz intergrowths interpreted to have formed by a reaction involving dissolution of biotite and feldspar in melt; and (iii) fine‐scale interstitial pools or micro‐cracks filled by feldspar interpreted to have crystallized from melt. Ultrahigh temperature (UHT) conditions during contact metamorphism are supported by (i) solidus temperatures >900 °C estimated for all samples, coupled with extensive textural evidence for contact‐related partial melting; (ii) the inferred (former) presence of osumilite; and (iii) titanium‐in‐quartz thermometry indicating temperatures within error of 900 °C. The UHT environment in which these unusual textures and minerals were developed was likely a consequence of the superposition of more than one contact metamorphic event upon the already relatively anhydrous Tasiuyak gneiss.  相似文献   

安徽滁州地区闪长质岩锆石U-Pb年龄与地球化学:岩石成因和动力学意义     

朱强  胡召齐  施珂  吴礼彬  江来利 《地质通报》2018,37(6):1101-1112

用LA-ICP-MS测得安徽滁州2个闪长玢岩样品中锆石~(206)Pb/~(238)U年龄为126.19±0.44Ma和126.4±0.7Ma,结合前人研究,得出滁州地区岩体的侵位时代应为120~130Ma之间,为早白垩世。岩石地球化学研究显示,Si O_2含量变化范围为56.75%~60.90%,具有高Al_2O_3(14.82%~15.77%)、Mg O(4%)、Sr(750×10~(-6))、Sr/Y(62~110)、La/Yb(20~36),低Y、Yb的特征,同时富集轻稀土元素和大离子亲石元素,亏损高场强元素,Eu异常不明显,属于典型的埃达克质岩。Mg~#值为39~45,K_2O/Na_2O值为0.57~0.96,平均值为0.75,明显低于大别造山带加厚下地壳埃达克岩,Ce/Pb值较低,大多集中在3~5之间,类似于陆壳而明显低于洋壳。研究认为,安徽滁州地区埃达克质岩由拆沉下地壳部分熔融形成,埃达克质岩浆在上升过程中与地幔橄榄岩发生反应,导致熔体Mg O、Cr、Ni等含量增加。早白垩世中国东部地壳伸展减薄导致下地壳拆沉,地幔物质的参与带来铜、金等成矿物质,埃达克质岩可作为该地区重要的找矿标志。  相似文献   

中阿尔金南缘志留纪高压泥质片麻岩的发现及其构造地质意义     

马拓  刘良  盖永升  杨文强  王超  康磊  廖小莹  PAK SangWan 《岩石学报》2019,35(6):1800-1818

在中阿尔金南缘西段尤努斯萨依北部原划长城系巴什库尔干岩群中首次发现一套高压泥质片麻岩。根据岩相学观察和矿物化学成分可识别出其四期矿物共生组合:早期为石榴子石+多硅白云母+单斜辉石(?)+斜长石+黑云母+石英+金红石+钛铁矿;第二期为石榴子石+蓝晶石+钾长石+斜长石+黑云母+石英+金红石+钛铁矿;第三期为石榴子石+夕线石+钾长石+斜长石+黑云母+石英+金红石+钛铁矿;晚期为石榴子石+夕线石+斜长石+黑云母+石英+钛铁矿。依据矿物内部一致性热力学数据,基于THERMOCALC 3. 40程序平台,计算出P-T视剖面图,并结合矿物等值线、矿物对温压计等计算,依次确定四期变质温压条件为15. 8～18. 3kbar/646～729℃、10. 30～12. 30kbar/781～821℃、8. 50～9. 60kbar/812～838℃和4. 65～5. 70kbar/698～725℃。上述四期变质阶段共同构成一个早期降压升温后降压降温的顺时针型演化的P-T轨迹,指示出与陆壳俯冲-折返相关的变质地质事件。利用LA-ICP-MS进行的锆石原位微区U-Pb定年和微量元素分析结果表明,该岩石记录了432. 0±2. 7Ma、401. 4±2. 5Ma和381. 1±2. 4Ma三期变质年龄,可能分别代表了该岩石早期高压、中期高压麻粒岩相-麻粒岩相和后期角闪岩相变质阶段的时代。该高压岩石出露于中阿尔金地块西段南缘长城系巴什库尔干岩群之中,与南侧以断裂带分隔的赋存于阿尔金岩群之中的南阿尔金高压-超高压岩石出露的构造位置明显不同,其峰期变质时代(～432Ma)亦明显不同于南阿尔金高压-超高压岩石的峰期变质时代(～500Ma)。因此,该高压岩石与南阿尔金高压-超高压岩石显然不能构成同一条变质岩带。结合区域地质背景和前人关于柴北缘陆壳属性高压-超高压岩石峰期变质时代(～430Ma)的研究成果综合分析,本文初步认为该高压岩石可能是柴北缘高压-超高压变质岩带的西延或是被中新生代以来阿尔金复杂多期次走滑断裂系迁移而就位于中阿尔金南缘的部分柴北缘高压-超高压变质岩片/岩块。  相似文献   

海南公爱地区抱板群花岗片麻岩的年代学、地球化学及其构造意义     

张立敏  王岳军  李庶波  张玉芝 《大地构造与成矿学》2017,41(2):396-411

海南岛地处华南陆块南缘,紧邻印支陆块,大地构造位置独特,其地质特征一直备受关注。厘定该地区中元古代岩石的成因对恢复华南中元古代构造演化具有重要意义。海南岛西部公爱地区花岗质岩石与围岩抱板群变沉积岩呈侵入接触关系,绝大部分岩石片麻状构造发育、韧性剪切标志明显。这些岩石高SiO_2、K_2O、Al_2O_3、Rb、U,贫CaO、MgO、FeO~T、TiO_2,铝饱和指数A/CNK1.1,具S型花岗岩特点,稀土元素配分模式类似于抱板群变沉积岩,全岩ε_(Nd)(t)=-2.02~-2.38,Nd同位素二阶段亏损模式年龄(t_(DM2)~(Nd))为2.2~2.3 Ga,锆石Hf同位素ε_(Hf)(t)=-5.4~4.0,Hf同位素二阶段亏损模式年龄t_(DM2)~(Hf)=1.71~2.53 Ga。对四个代表性花岗片麻岩样品进行LA-ICP-MS锆石U-Pb定年,其~(207)Pb/~(206)Pb加权平均年龄为1444±15 Ma、1439±19 Ma、1433±31 Ma和1450±23 Ma,属中元古代。综合区域研究资料认为,海南岛西部公爱地区中元古代花岗质岩石的熔融源区为类似抱板群变沉积岩组分,推测其产出于大陆边缘构造背景,是哥伦比亚超大陆边缘的增生产物。  相似文献   

The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)          下载免费PDF全文

M. P. Doublier  S. Potel  K. Wemmer 《Journal of Metamorphic Geology》2015,33(1):71-89

The Montagne Noire in the southernmost French Massif Central is made of an ENE‐elongated gneiss dome flanked by Palaeozoic sedimentary rocks. The tectonic evolution of the gneiss dome has generated controversy for more than half a century. As a result, a multitude of models have been proposed that invoke various tectonic regimes and exhumation mechanisms. Most of these models are based on data from the gneiss dome itself. Here, new constraints on the dome evolution are provided based on a combination of very low‐grade petrology, K–Ar geochronology, field mapping and structural analysis of the Palaeozoic western Mont Peyroux and Faugères units, which constitute part of the southern hangingwall of the dome. It is shown that southward‐directed Variscan nappe‐thrusting (D₁) and a related medium‐P metamorphism (M₁) are only preserved in the area furthest away from the gneiss dome. The regionally dominant pervasive tectono‐metamorphic event D₂/M₂ largely transposes D₁ structures, comprises a higher metamorphic thermal gradient than M₁ (transition low‐P and medium‐P metamorphic facies series) and affected the rocks between c. 309 and 300 Ma, post‐dating D₁/M₁ by more than 20 Ma. D₂‐related fabrics are refolded by D₃, which in its turn, is followed by dextral‐normal shearing along the basal shear zone of both units at c. 297 Ma. In the western Mont Peyroux and Faugères units, D₂/M₂ is largely synchronous with shearing along the southern dome margin between c. 311 and 303 Ma, facilitating the emplacement of the gneiss dome into the upper crust. D₂/M₂ also overlaps in time with granitic magmatism and migmatization in the Zone Axiale between c. 314 and 306 Ma, and a related low‐P/high‐T metamorphism at c. 308 Ma. The shearing that accompanied the exhumation of the dome therefore was synchronous with a peak in temperature expressed by migmatization and intrusion of melts within the dome, and also with the peak of metamorphism in the hangingwall. Both, the intensity of D₂ fabrics and the M₂ metamorphic grade within the hangingwall, decrease away from the gneiss dome, with grades ranging from the anchizone–epizone boundary to the diagenetic zone. The related zonation of the pre‐D₃ metamorphic field gradients paralleled the dome. These observations indicate that D₂/M₂ is controlled by the exhumation of the Zone Axiale, and suggest a coherent kinematic between the different crustal levels at some time during D₂/M₂. Based on integration of these findings with regional geological constraints, a two‐stage exhumation of the gneiss dome is proposed: during a first stage between c. 316 and 300 Ma dome emplacement into the upper crust was controlled by dextral shear zones arranged in a pull‐apart‐like geometry. The second stage from 300 Ma onwards was characterized by northeast to northward extension, with exhumation accommodated by north‐dipping detachments and hangingwall basin formation along the northeastern dome margin.  相似文献   

Stable staurolite–cordierite assemblages in K‐poor metapelitic schists in Aston and Hospitalet gneiss domes of the central Pyrenees (France,Andorra)          下载免费PDF全文

J. E. Mezger  J‐L. Régnier 《Journal of Metamorphic Geology》2016,34(2):167-190

Staurolite–cordierite assemblages are common in mica schists of the Aston and Hospitalet gneiss domes of the central Axial Zone, Pyrenees (France, Andorra). Within a 200 m wide zone, staurolite, cordierite and andalusite porphyroblasts contain inclusion trails that preserve the same stage of development of a crenulation cleavage, strongly suggesting that all three phases are contemporaneous. Their syntectonic growth occurred during a short period at the beginning of the formation of the dominant schistosity (S₂) of the domes. Staurolite and cordierite touching each other further indicates an equilibrium relationship. Whole‐rock analyses show that some staurolite–cordierite schists are depleted in K₂O compared to post‐Archean shales (PAAS) and amphibolite facies pelites. Analysis of the st‐crd paragenesis in K‐poor schists without muscovite using KFMASH and MnNCKFMASH petrogentic grids, pseudosections and AFM compatibility diagrams predicts stable conditions at pressures of ~3.5 kbar at 575 °C. For metapelites with intermediate X_Mg values (0.7 >  X_Mg >0.48) a ‘muscovite‐out window’ exists from 550–650 °C at 3.5 kbar in the KFMASH system. Conventional thermobarometry (GB‐GASP, AvT‐AvP) and petrogenetic grids show an isobaric P–T path to peak temperatures of ~650 °C, supported by the presence of sillimanite‐K‐feldspar gneiss and migmatites. LP‐HT metamorphism in the Aston dome is related to early Carboniferous (c. 339 Ma) granitic intrusions into the dome core. As metamorphism is directly linked with the formation of the main S₂ schistosity, the temporal relations demonstrated in this study conflict with previous studies which constrained LP‐HT metamorphism and the development of flat‐lying schistosity to the late Carboniferous (315–305 Ma) – at least in the eastern Axial Zone.  相似文献   

Re–Os and U–Pb Geochronology of the Erlihe Pb–Zn Deposit, Qinling Orogenic Belt, Central China, and Constraints on Its Deposit Genesis     

ZHANG Fan  LIU Shuwen  LI Qiugen  SUN Yali  WANG Zongqi  YAN Quanren  YAN Zhen 《《地质学报》英文版》2011,85(3):673-682

The Erlihe Pb–Zn deposit is an important mine of the Pb–Zn metallogenic zone in the South Qinling Orogen. It has been considered a sedimentary exhalative deposit in previous investigations because the ore body occurs concordantly at the transitional location of an upright fold. Re and Os isotopic analyses for paragenetic pyrites with sphalerite and galena from the ore body have been used to determine the timing of mineralization and to trace the source of metallogenic materials. The Re–Os isotopic data of four pyrite samples construct an isochron, yielding a weighted average age of 226±17 Ma (mean square weighted deviation=1.7), which is considered the main mineralization age. A dioritic porphyrite vein sample, showing weaker mineralization, was also dated using the SHRIMP zircon U–Pb isotopic method to constrain the youngest metallogenic age of the ore deposit, because it distributes along a group of tensional joints cutting not only the upright fold in the deposit field, but also the main ore bodies. The dioritic porphyrite sample yields a weighted mean 206Pb/238U age of 221±3 Ma, which is slightly younger than the Re–Os isotopic isochron age of the pyrites, considered as the upper age limit of the mineralization, namely the ending age of the mineralization. The Os isotopic compositions of sulfide minerals distribute within a range between Os isotopic compositions of the crust and the mantle, indicating that the ore deposit can be derived from magma-related fluid, and the metallogenic materials are most likely derived from the mixing source of the crust and the mantle. The Erlihe Pb–Zn deposit and associated dioritic porphyrite vein, important records of Qinling tectonic–magmatism–mineralization activities, were formed during the Triassic collisional orogeny processes.  相似文献   

内蒙古大青山地区古元古代早期榴云片麻岩(大青山表壳岩)深熔作用:地质、锆石年代学和地球化学研究   总被引：8，自引：5，他引：3  

马铭株  董春艳  徐仲元  谢士稳  刘敦一  万渝生 《岩石学报》2015,31(6):1535-1548

大青山位于华北克拉通西部孔兹岩带中段,古元古代晚期孔兹岩系(上乌拉山岩群)十分发育。近年来,在上乌拉山岩群中分辨出一套古元古代早期变质碎屑沉积岩(大青山表壳岩,榴云片麻岩),它们遭受强烈变质变形和深熔作用改造,形成古元古代早期石榴石花岗岩。包头哈德门沟是古元古代早期榴云片麻岩典型出露区,并有古元古代早期石榴石花岗岩(哈德门沟石榴石花岗岩)形成。由榴云片麻岩经深熔榴云片麻岩再到石榴石花岗岩,浅色体增多,石榴石增多且颗粒增大,黑云母减少,石榴石包裹黑云母、石英、斜长石等矿物。石榴石岩的锆石呈浑圆状,普遍具核-幔-边或核-边结构,碎屑锆石年龄为~2.5Ga,变质锆石年龄为~2.45Ga和~1.90Ga。锆石形态、内部结构和年龄与榴云片麻岩、深熔榴云片麻岩和石榴石花岗岩中的锆石类似,但记录了古元古代晚期变质事件年龄。石榴石花岗岩与榴云片麻岩和深熔榴云片麻岩的地球化学组成特征总体上类似,高Al2O3含量和FeO T/MgO比值,CaO含量和K2O/Na2O比值存在较大变化,富集轻稀土和大离子亲石元素,亏损Nb、Ta、P和Ti。研究表明:1)浅色体和石榴石花岗岩中的石榴石是黑云母转熔的产物,并非岩浆结晶形成的;2)石榴石岩是在石榴石花岗岩岩浆形成之后进一步演化过程中石榴石不断地发生运移、分异和聚集的结果;3)尽管哈德门沟石榴石花岗岩具有一定或较大的规模,但具有深熔岩浆的性质;4)石榴石花岗岩地球化学组成变化与熔融母岩组成变化和深熔及岩浆演化过程中残余矿物相石榴石、锆石局部变化有关。  相似文献