Metamorphic charnockite in contact aureoles around intrusive enderbite from Natal, South Africa     

Alfons M. van den Kerkhof  Geoffrey H. Grantham 《Contributions to Mineralogy and Petrology》1999,137(1-2):115-132

In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10 m in width in the normally garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration reaction Bt + Qtz → Opx + Kfs + H₂O and the reaction of Grt + Qtz → Opx + Pl were responsible for the charnockitization. The compositions of fluid inclusions show systematic variation with: (1) the Port Edward Enderbite being dominated by CO₂ and N₂ fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18–23 EqWt% NaCl; (3) the charnockitic aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity with minor CO₂. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range (up to 390 °C) compared to the fluid inclusions in granite (mostly <250 °C). Contrary to fluid-controlled charnockitization (brines, CO₂) which may have taken place along shear zones away from the intrusive body, the present “proximal” charnockitized granite formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of “dry” enderbitic magma into “wet” granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the Port Edward Enderbite suggests intrusion at temperatures of ∼1000–1050 °C into country rock with temperature of <700 °C. The temperature of aureole formation must have been between ∼700 °C (breakdown of pyrite to form pyrrhotite) and ∼1000 °C. Charnockitization was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred. Received: 8 November 1998 / Accepted: 21 June 1999  相似文献   

西藏雄村斑岩型铜(金)矿床Ⅰ、Ⅱ号矿体热液黑云母特征及地质意义     

肖鸿天  谢富伟  郎兴海  冉凤琴 《岩石矿物学杂志》2020,39(4):469-480

雄村铜(金)矿区位于西藏冈底斯成矿带中段南缘,由Ⅰ、Ⅱ、Ⅲ号矿体和多个矿化体组成。本文以Ⅰ、Ⅱ号矿体钾硅酸盐化蚀变带内的热液黑云母为研究对象,采用光薄片镜下鉴定、电子探针等分析方法,系统研究了热液黑云母的产状和成分特征。结果显示,雄村矿区Ⅰ号矿体黑云母类型主要为金云母和镁质黑云母;Ⅱ号矿体黑云母类型为镁质黑云母。两个矿体黑云母都具有低Ti(TiO_2 3%)、高Al(Al_2O_315%)的特点,且具有较高的MgO含量,Mg/Fe0.5,K/Na10,显示了与矿化良好的相关性。Ⅰ号矿体热液黑云母平均结晶温度470℃,氧逸度位于镍-氧化镍缓冲剂与磁铁矿-钛铁矿缓冲剂之间(NNO—HM);Ⅱ号矿体热液黑云母平均结晶温度234℃,氧逸度位于镍-氧化镍缓冲剂与铁橄榄石-石英-磁铁矿缓冲剂之间(NNO—FQM),说明Ⅰ号矿体形成于较高温、高氧逸度的热液系统,Ⅱ号矿体形成于相对较低温、低氧逸度的热液系统。此外,Ⅰ号矿体热液黑云母Ⅳ(F)值介于0.61～2.72之间,平均值1.26,Ⅳ(Cl)值介于-5.49～-4.53之间,平均值-5.03,Ⅳ(F/Cl)值介于5.63～7.89之间,平均值6.29;Ⅱ号矿体热液黑云母Ⅳ(F)值介于1.83～3.32之间,平均值2.66,Ⅳ(Cl)值介于-5.64～-4.89之间,平均值-5.31,Ⅳ(F/Cl)值介于7.14～8.68之间,平均值7.97,说明Ⅰ、Ⅱ号矿体都形成于富Cl的热液系统,且Ⅱ号矿体热液较Ⅰ号矿体更富Cl,贫F。富Cl流体易萃取流体中的Cu和Au等金属元素并以Cl的络合物形式运移,在沿构造裂隙向上运移的过程中,物理化学条件发生改变,使得流体中金属元素络合物溶解度降低,促使硫化物沉淀成矿。  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   

张宣地区大白阳金矿床包裹体特征及矿床剥蚀保存     

徐渴鑫  申俊峰  李胜荣  黄绍峰  张士全  王业晗 《矿床地质》2020,39(6):1030-1048

华北克拉通破坏及其成矿事件已引起地学界的广泛关注,其中张宣地区是华北克拉通的重要金矿集中区之一,通过对张宣地区大白阳金矿成矿类型、成矿深度及剥蚀保存的探讨,为区内深部找矿提供了重要的参考依据。文章通过流体包裹体研究对大白阳金矿成矿温度及成矿深度进行计算,利用矿物压力计对矿区周边岩体侵位深度进行估算。流体包裹体研究结果显示大白阳金矿成矿温度160~220℃、盐度w（NaCl_eq）=9%~15%,密度0.78~0.97 g/cm³、压力46.3~104.6 MPa,成矿流体主要属于NaCl-H₂O体系,成矿过程中流体温度和盐度都呈现明显的降低趋势。采用黑云母压力计,针对大白阳金矿周边谷嘴子、杨家营以及前坝口花岗质岩体的侵位深度进行估算,并对大白阳金矿自形成以来的剥蚀保存情况进行了探讨,估算结果显示,谷嘴子岩体（236.0 Ma）成岩深度7.02 km、杨家营岩体（138.6 Ma）成岩深度2.66 km、前坝口岩体（140.2 Ma）成岩深度3.13 km。结合前人的裂变径迹结果,认为张宣地区自中生代以来剥蚀速率为0.022~0.029 km/Ma,剥蚀量为3 km。按照前述成矿压力46.3~104.6 MPa换算,大白阳金矿成矿深度6.93 km,剥蚀量小于矿床成矿深度,说明该矿深部仍具有良好的找矿前景。  相似文献   

Biotite Reference Materials for Secondary Ion Mass Spectrometry 18O/16O Measurements          下载免费PDF全文

Guillaume Siron  Lukas Baumgartner  Anne‐Sophie Bouvier  Benita Putlitz  Torsten Vennemann 《Geostandards and Geoanalytical Research》2017,41(2):243-253

Five new biotite reference materials were calibrated at the SwissSIMS laboratory (University of Lausanne) for oxygen isotope determination by secondary ion mass spectrometry (SIMS) and are available to the scientific community. The oxygen isotope composition of the biotites, UNIL_B1 to B5, was determined by laser‐heating fluorination to be 11.4 ± 0.11‰, 8.6 ± 0.15‰, 6.1 ± 0.04‰, 7.1 ± 0.05‰ and 7.6 ± 0.04‰, respectively. SIMS analyses on spots smaller than 20 μm gave a measurement repeatability of 0.3‰ (2 standard deviation, 2s). The matrix effect due to solid solution in natural biotite could be expressed as a linear function of X_Mg and X_F for biotite. No effect was found for different crystallographic orientations. SIMS analysis allows the oxygen isotope composition of biotite to be measured with a measurement uncertainty of 0.3–0.4‰ (2s) for biotites with similar major element compositions. A measurement uncertainty of 0.5‰ (2s) is realistic when F poor biotites (lower than 0.2% m/m oxides) within the compositional range of X_Mg of 0.3–0.9 were compared from different sessions. The linear correlation with F content offers a reasonable working curve for F‐rich biotites, but additional reference materials are needed to confirm the model.  相似文献   

阿尔金南缘新元古代盖里克片麻岩年代学、地球化学特征及其构造意义     

李琦  曾忠诚  陈宁  赵江林  张若愚  易鹏飞  高海峰  毕政家 《现代地质》2015,29(6):1271-1283

盖里克片麻岩分布于阿中地块亚干布阳-帕夏拉依档一带,岩体主要岩性由眼球状黑云斜长片麻岩、二云二长片麻岩组成。LA-ICP-MS锆石U-Pb定年得到²⁰⁶Pb/²³⁸U加权平均年龄值为(886.5±5)Ma,说明盖里克片麻岩原岩形成于新元古代早期青白口纪;地球化学结果显示：主量元素具有高SiO₂、Al₂O₃、K₂O+Na₂O含量,低Na₂O、MgO、CaO和TiO₂含量的特征,A/CNK值介于1.03~1.17之间,属于高钾钙碱性系列的过铝质花岗岩。岩石富集Rb、Th、K等大离子亲石元素,亏损Nb、Ta、Sr、P、Hf、Ti等高场强元素,具有典型的大陆碰撞型花岗岩相应的元素丰度特征;岩石轻稀土富集而重稀土亏损,具有明显的负Eu异常,总体呈右倾的“V”型稀土分配模式,显示了典型的地壳重熔型花岗岩特征。盖里克片麻岩的源岩为地壳中角闪岩相基性岩类(变玄武岩),形成于同碰撞构造环境。综上说明本区存在新元古代早期的构造岩浆事件,可能对应于新元古代的罗迪尼亚(Rodinia)超大陆汇聚事件,说明塔里木和柴达木板块之间在新元古代早期曾经存在板块的汇聚碰撞。  相似文献   

阿尔泰造山带南缘昆格依特岩体LA-ICP-MS锆石U-Pb年代学、岩石成因及其地质意义   总被引：1，自引：0，他引：1  

张亚峰  蔺新望  王星  郭岐明  赵端昌  吕军利  王旭 《现代地质》2014,28(1):16-28

昆格依特岩体出露于阿尔泰造山带南缘青河县大青格里河昆格依特一带,主要为角闪黑云英云闪长岩。LA-ICP-MS锆石U-Pb定年结果显示,锆石的²⁰⁶Pb/²³⁸U年龄加权平均值为(403.4±7.4)Ma,表明该岩体形成于早泥盆世。岩体的SiO₂含量介于52.39%~71.89%之间,里特曼指数为0.68~1.53,A/CNK 值为0.76~1.06,属中钾、钙碱性、准铝质-弱过铝质岩石。具有富集Cs、Rb、Th、U等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Hf、Ti等高场强元素和重稀土元素,弱的负Eu异常(δEu=0.56~0.86)的岛弧岩浆岩特征。结合区域地质资料,认为阿尔泰造山带南缘早泥盆世昆格依特岩体形成于活动大陆边缘的陆缘弧构造环境,是古亚洲洋俯冲过程中幔源的基性岩浆底侵下地壳使之熔融,并发生了岩浆混合和分异作用的产物。  相似文献   

内蒙古化德县沙拉哈达石英脉型钨矿床成矿地质特征     

王佳新  张雪旎  张赋 《地质与资源》2014,23(2):154-157

沙拉哈达钨矿区处于内蒙地轴北缘和大兴安岭地槽褶皱系的交接处.矿化主要分布在安山玢岩内,矿体主要由含矿石英脉组成,矿脉中普遍含黑钨矿、白钨矿、黄铁矿及多金属硫化物.与钨矿有关的侵人岩体主要是燕山期黑云母花岗岩及花岗斑岩.围岩蚀变以硅化、云英岩化、绢云母化为主.该矿床属高温热液成因类型.  相似文献   

胶东艾山岩体二长花岗岩地球化学、锆石U-Pb年代学及Lu-Hf同位素特征研究     

李秀章  王立功  李衣鑫  王英鹏  于晓卫  张文  郭瑞朋  刘汉栋 《现代地质》2022,36(1):333-346

胶东地区大规模金成矿作用发生于125～110 Ma,与金成矿作用同期的早白垩世晚期艾山岩体出露于华北克拉通东缘,由深成相的石英闪长岩-似斑状二长花岗岩类及浅成相的闪长玢岩、花岗斑岩等组成,岩体发育岩浆暗色包体.对艾山二长花岗岩开展了岩相学、岩石地球化学、锆石LA-ICP-MS年代学和Lu-Hf同位素测试和研究,探讨了该...  相似文献   

鲁西地区新太古代早期的岩浆活动——泰山岩套英云闪长质片麻岩锆石SHRIMP UPb年龄的证据          下载免费PDF全文

王世进  万渝生  宋志勇  杨恩秀  王伟  董春艳 《山东国土资源》2013,29(4):1-7

泰山岩套主要岩性为英云闪长质片麻岩和条带状英云闪长质片麻岩,出露于鲁西地区泰山—化马湾—蒙山一带。根据新测的锆石SHRIMP U-Pb年龄结果,其岩浆结晶年龄2 729～2 700Ma,变质年龄2 600Ma,其形成时代确定为新太古代早期。该岩套组成古老陆核,是地幔岩浆侵入混入地壳物质形成的。  相似文献