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1.
The Valentine wollastonite skarn in the north-west Adirondack Mountains, New York, is a seven million ton deposit which resulted from channellized infiltration of H2O-rich, silica-bearing fluids. The wollastonite formed by reaction of these fluids with non-siliceous calcite marble. The skarn formed at the contact of the syenitic Diana Complex and was subsequently overprinted by Grenville-age granulite facies metamorphism and retrograde hydrothermal alteration during uplift. Calcite marbles adjacent to the deposit have generally high δ18O values (c. 21‰), typical of Grenville marbles which have not exchanged extensively with externally derived fluids. Carbon isotopic fractiona-tions between coexisting calcite and graphite in the marbles indicate equilibration at 675d? C, consistent with the conditions of regional metamorphism. Oxygen isotopic ratios from wollastonite skarn are lower than in the marbles and show a 14‰ variation (-1‰ to 13‰). Some isotopic heterogeneity is preserved from skarn formation, and some represents localized exchange with low-δ18O retrograde fluids. Detailed millimetre- to centimetre-scale isotopic profiles taken across skarn/marble contacts reveal steep δ18O gradients in the skarn, with values increasing towards the marble. The gradients reflect isotopic evolution of the fluid as it reacted with high δ18O calcite to form wollastonite. Calcite in the marble preserves high δ18O values to within <5 mm of the skarn contact. The preservation of high δ18O values in marbles at skarn contacts and the disequilibrium fractionation between wollastonite skarn and calcite marble across these contacts indicate that the marbles were not infiltrated with significant quantities of the fluid. Thus, the marbles were relatively impermeable during both the skarn formation and retrograde alteration. Skarn formation may have been episodic and fluid flow was either chaotic or dominantly parallel to lithological contacts. Although these steep isotope gradients resemble fluid infiltration fronts, they actually represent the sides of the major flow system. Because chromatographic infiltration models of mass transport require the assumption of pervasive fluid flow through a permeable rock, such models are not applicable to this hydrothermal system and, by extension, to many other metamorphic systems where low-permeability rocks restrict fluid migration pathways. Minimum time-integrated fluid fluxes have been calculated at the Valentine deposit using oxygen isotopic mass balance, reaction progress of fluid buffering reactions, and silica mass balance. All three approaches show that large volumes of fluid were necessary to produce the skarn, but silica mass balance calculations yield the largest minimum flux and are hence the most realistic.  相似文献   

2.
The Middle-Lower Yangtze (Changjiang) River Valley metallogenic belt is located on the northern margin of the Yangtze Craton of eastern China. Most polymetallic deposits in the Changjiang metallogenic belt are clustered in seven districts where magmatism of Mesozoic age (Yanshanian tectono-thermal event) is particularly extensive. From west to east these districts are: E-dong, Jiu-Rui, Anqing-Guichi, Lu-Zong, Tong-Ling, Ning-Wu and Ning-Zhen. World-class iron ore deposits occur in the Lu-Zong and Ning-Wu ore clusters, which are mainly located in continental fault-bound volcanic-sedimentary basins. One of these deposits is the Longqiao iron deposit, discovered in the northern part of the Lu-Zong Basin in 1985. This deposit consists of a single stratabound and stratiform orebody, hosted in sedimentary carbonate rocks of the Triassic Dongma'anshan Formation. A syenite pluton (Longqiao intrusion) is situated below the deposit. The iron ore is massive and disseminated and the ore minerals are mainly magnetite and minor pyrite. Wall rock alteration mostly consists of skarn minerals, such as diopside, garnet, potassic feldspar, quartz, chlorite, phlogopite and anhydrite. Thin sedimentary siderite beds of Triassic age occur as relict laminated ore at the top and the margin of the magnetite orebody. These sideritic laminae are part of Triassic evaporite-bearing carbonate deposits (Dongma'anshan Formation).Sulfur isotopic compositions show that the sulfur in the deposit was derived from a mixture of magmatic hydrothermal fluids and carbonate–evaporite host rocks. Similarly, the C and O isotopic compositions of limestones from the Dongma'anshan Formation indicate that these rocks interacted with magmatic hydrothermal fluids. The O isotopic compositions of the syenitic rocks and minerals from the deposit show that the hydrothermal magnetite and skarn minerals were formed from magmatic fluids. The Pb isotopic compositions of sulfides are similar to those of the Longqiao syenite. Phlogopite coexisting with magnetite in the magnetite ores yielded a plateau age of 130.5 ± 1.1 Ma (2σ), whereas the LA-ICP MS age of the syenite intrusion is 131.1 ± 1.5 Ma, which is slightly older than the age of phlogopite.The Longqiao syenite intrusion may have crystallized from a parental alkaline magma, generated by partial melting of lithospheric mantle, during extensional tectonics. The ore fluids were probably first derived from magma at depth, later emplaced in the sedimentary rocks of the Dongma'anshan Formation, where it interacted with siderite and evaporite-bearing carbonate strata, resulting in the formation of magnetite and skarn minerals. The Longqiao iron deposit is a skarn-type stratabound and stratiform mineral system, genetically and temporally related to the Longqiao syenite intrusion. The Longqiao syenite is part of the widespread Mesozoic intracontinental magmatism (Yanshanian event) in eastern China, which has been linked to lithospheric delamination and asthenospheric upwelling.  相似文献   

3.
安徽铜陵凤凰山铜矿是铜陵矿集区内最典型的矽卡岩型铜矿床之一,也是凤凰山矿田内规模最大的铜矿床。矿区内新屋里岩体属于高钾钙碱性系列,主要岩性为石英二长闪长岩和花岗闪长岩。岩石地球化学特征表明凤凰山中酸性侵入岩岩浆属于壳幔混合型,原始岩浆来源于上地幔碱性玄武岩区并有地壳物质混染,在岩浆不断演化过程中有外来物质的加入,成岩过程以混合作用为主。凤凰山铜矿体分布于岩体与大理岩的内矽卡岩带上,岩体中铜含量较高。铜矿体是岩浆期后热液交代碳酸盐地层形成的。矿体的空间分布受构造变形-岩浆侵入高温高压作用的双重控制。矿化经历了从高温矽卡岩阶段到中低温热液阶段的多期次复合成矿作用。  相似文献   

4.
The Sausfjellet pluton is made up of two intrusive units emplaced into high-grade metamorphic rocks of the Helgeland Nappe Complex of the Uppermost Allochthon in the Norwegian Caledonides. The eastern part of the pluton intruded marble and less voluminous calc-silicate and pelitic rocks. The western half is hosted predominantly by semi-pelitic migmatite with intercalated marble. Remelting of the migmatite during pluton emplacement occurred in a thermal aureole as much as 1000 m wide. The early gabbroic unit forms the southeastern part of the body; it consists of hornblende-bearing to hornblende-rich gabbro and diorite which is thought to have crystallized from an H2O-rich andesitic parental magma. The younger dioritic unit underlies the central and western parts of the pluton, as well as a zone as much as 200 m wide that separates the rest of the pluton from its host rocks (herein the “annular zone”). The interior or central zone of the dioritic unit is pyroxene diorite that is locally interlayered with anorthosite. The western and annular zones are, by comparison, mineralogically heterogeneous. They range from diorite to quartz monzonite and from biotite-bearing two- and three-pyroxene assemblages to biotite–hornblende assemblages. Neither rock type nor mafic assemblage is correlated with position in the pluton or proximity to a contact. Stoped blocks of a distinctive coarse-grained diorite, as well as pyroxene-rich calc-silicates, are present in the gabbroic unit and the central zone of the dioritic unit. The few stoped blocks observed in the western zone of the dioritic unit are predominantly quartz-rich gneiss. Chemical variation in the central zone of the dioritic unit is interpreted to result from accumulation of pyroxenes+plagioclase from an H2O-poor andesitic parent. These rocks have approximately constant δ18O of +6.6±0.2‰ and lack evidence of in situ assimilation. Heterogeneities in the western and annular zones of the dioritic unit are reflected in variable, anomalously enriched incompatible element contents and in δ18O, which ranges from +6.7‰ to +8.6‰. Petrologic models indicate that the magma parental to the central zone could also be parental to the western and annular zones. If so, evolution of the western and annular zone magma was by crystal accumulation and assimilation of metapelitic host rocks. As much as 20% of the mass of the western and annular zones can be ascribed to assimilated material, which apparently entered the magma by stoping. Therefore, the asymmetrical zoning of the pluton is due to differences in host rock compositions and the relative ability of the magma to assimilate its host rocks.  相似文献   

5.
陈兵  熊富浩  马昌前  陈越  黄虎 《地球科学》2021,46(6):2057-2072
壳-幔岩浆相互作用如何影响长英质火成岩的岩石学多样性是当前岩石学研究的焦点问题之一.以岩石类型丰富的东昆仑白日其利长英质岩体和暗色微粒包体为研究对象,开展系统的锆石U-Pb年代学、矿物学、全岩元素地球化学和Sr-Nd-Hf同位素研究,探讨和解析这一重要科学问题.LA-ICPMS锆石U-Pb年代学研究表明,暗色微粒包体（247.8±2.0 Ma）与二长花岗岩（247.5±1.4 Ma）、花岗闪长岩（248.8±2.1 Ma）和石英闪长岩（248.8±1.5 Ma）均侵位结晶于早三叠世.岩相学和矿物学研究表明,白日其利长英质岩石与包体的成因机制与壳-幔岩浆的机械或化学混合作用密切相关.元素地球化学和Sr-Nd-Hf同位素组成研究揭示,幔源镁铁质岩浆端元起源于受俯冲板片流体交代的富集地幔熔融,而壳源长英质岩浆端元则起源于东昆仑古老的变质杂砂岩基底.岩石成因分析揭示,幔源镁铁质岩浆侵入长英质晶粥岩浆房,促使长英质晶粥发生活化,随后壳-幔岩浆端元以不同比例和不同方式发生机械和化学混合等相互作用,从而形成镁铁质岩墙、包体、石英闪长岩和花岗闪长岩等多种岩石类型.晶粥状态下壳-幔岩浆相互作用是控制东昆仑长英质火成岩多样性和大陆地壳生长演化的重要方式.   相似文献   

6.
西藏甲玛铜多金属矿床为冈底斯成矿带的超大型矿床之一,其矽卡岩型主矿体受林布宗组砂板岩、角岩(硅铝质岩石)和多底沟组大理岩(钙质岩石)的岩性界面所控制。基于岩、矿心地质编录,开展矽卡岩岩石、矿物分带及矽卡岩地球化学、矿物化学研究,探讨硅钙岩性界面对矽卡岩及多金属矿体形成的影响。从顶板至底板由石榴子石矽卡岩、硅灰石石榴子石矽卡岩至硅灰石矽卡岩表现出Si O2、Ca O逐渐增加和Al2O3、Fe2O3+Fe O逐渐减少的趋势,石榴子石矽卡岩、硅灰石矽卡岩的稀土元素和微量元素特征对顶板、底板岩石表现出明显的继承性。靠近顶板的矽卡岩中石榴子石属于钙铝-钙铁过渡系列,由石榴石核部向外环带具有Al含量减少、Fe含量增加的特点;靠近底板矽卡岩相对于靠近顶板具有钙铁榴石比例增加、钙铝榴石比例减少特征,由核部向外围未见明显的环带成分演变特征。矽卡岩是流体与硅铝质、钙质岩石水岩反应的产物,沿硅钙界面流体减压沸腾、地下水混合作用和界面内垂向的流体地球化学障是主要的致矿机制。硅、铝质岩石化学性质、物理性质差异是界面控矿的主要因素,硅钙面复合张性构造带、岩浆热事件增加界面渗透率差异有利于矿体规模的增加和品位提高。  相似文献   

7.
通过野外地质、光学显微镜以及背散射(BSE)电子图像的观察,南泥湖—三道庄钼(钨)矿床中矽卡岩的形成过程为:第一期流体首先与靠近岩体的大理岩发生反应生成硅灰石、钙铁榴石、钙铝榴石、钙铁辉石和透辉石,当流体继续向外运移遇到灰岩时,直接将其交代形成透辉石矽卡岩或曲卷纹层状透辉石矽卡岩;第二期流体则沿裂隙向围岩中呈面型分布,叠加交代第一期矽卡岩化过程。据此,石榴子石和辉石可以划分为两个世代,第一世代石榴子石(Gro_(3-82)And_(15-96))呈斑点状,第一世代辉石(Di_(18-86)Hd_(13-70)Jo_(0-13))可与斑点状石榴子石共生,也可与斜长石(Ab_(55-70)An_(30-44))共生;第二世代石榴子石(Gro_(23-58)And_(37-74))呈面型分布,第二世代辉石(Di_(0-68)Hd_(28-84)Jo_(3-16))沿裂隙呈面型向围岩中展布。第一世代石榴子石和辉石在空间上分布范围较第二世代广。钼钨矿化在矽卡岩的最早阶段即已开始,贯穿整个矽卡岩的形成过程,引起钼钨沉淀的原因可能是具有较高钼钨含量的流体与围岩发生反应时引起的局部还原性环境。  相似文献   

8.
The late Cretaceous A-type Karaçay?r pluton in Central Anatolia, Turkey, intrudes and entrains xenoliths of Palaeozoic limestone. Carbonatitic magmatic rocks within the syenite have been previously interpreted (Schuiling in Nature, 192:1280, 1961) to result from metasomatic alteration and syntectic melting of marble. Carbonatites and associated calcite-syenites exhibit mineralogical characteristics (Ab-rich plagioclase, Ba-rich K-feldspar, low-Mg# biotite) that are petrogenetically more evolved than the host syenitic suite. Geochemically, carbonate-rich magmatic rocks are greatly enriched in Sr, Ba, Th, and REE and have higher LREE/HREE ratios than either syenites or marbles. In terms of O-C-Sr-Pb isotope ratios, the carbonatite/calcite-syenite suite form a consistent and geochemically coherent group that is distinct from the marble country rock and xenolith population, but similar to some of the syenitic, and particularly the nepheline syenite components of the Karaçay?r pluton. Other silicate magmatic rocks are geochemically, isotopically, and geochronologically different, suggesting the pluton is composite. Overall, the mineralogical and geochemical characteristics of the carbonatites are incompatible with binary mixing of syenite and marble but are consistent with derivation of carbonatite from petrogenetically evolved foid syenite. Carbonate–silicate rock types have modal variations compatible with an origin by fractional crystallisation, rather than by liquid immiscibility.  相似文献   

9.
青海省兴海县赛什塘铜矿床矽卡岩矿物学特征及地质意义   总被引：1，自引：0，他引：1  
赛什塘铜矿位于东昆仑造山带东端的鄂拉山地区,是中国西部重要的矽卡岩型铜矿之一。矽卡岩形成于印支期石英闪长岩与中—下三叠统地层Tb2 1-2岩性段的接触带,矿体主要呈似层状、透镜状产于外接触带矽卡岩中。Tb2 1-2岩性段由中性火山岩、大理岩及变质粉砂岩构成,其中变安山质凝灰岩及安山岩与铜矿化有着密切的空间关系。岩相学研究表明,含铜矽卡岩的形成经历了矽卡岩阶段、退化蚀变阶段、石英-硫化物阶段及石英-碳酸盐阶段。矽卡岩阶段形成石榴子石、辉石及硅灰石,退化蚀变阶段则形成绿帘石、角闪石及磁铁矿,石英-硫化物阶段大量金属硫化物发生沉淀。电子探针分析表明,石榴子石与辉石矿物组分分别为Gro0.00~91.00And7.02~100.00(Pyr+Alm+Spe)0.00~4.27与Di12.80~98.08Hd2.41~79.80(Jo+Jd+Opx)0.00~13.47,表明其属于典型的钙矽卡岩类。空间上,靠近石英闪长岩与安山岩接触带处,钙铝榴石和绿帘石更富集,而向大理岩的一侧以钙铁榴石为主,并常见硅灰石及含Mn的钙铁辉石。矿物学特征及矿物成分的变化显示:从矽卡岩阶段到石英-硫化物阶段,流体性质呈幕式的变化,成矿流体至少经历了2次氧化还原性质的转变,这种变化可能与成矿流体中大气降水的不断加入有关。赛什塘铜矿属于矽卡岩型矿床,以石英闪长岩为主的岩浆活动携带了大量的热量及流体,侵入到中—下三叠统地层中,与围岩地层发生物质交换的同时,引起了大理岩、变质粉砂岩与中性火山岩之间的双交代作用,是导致矽卡岩和矿体形成的重要机制。  相似文献   

10.
The Mazraeh Cu–Fe skarn deposit, NW Iran is the result of the intrusion of an Oligocene–Miocene granitic pluton into Cretaceous calcareous rocks. The pluton ranges in composition from monzonite to quartz monzonite, monzogranite, tonalite and granodiorite with I-type, calc-alkaline, and weakly peraluminous characteristics. The Mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of ~8 km. Pyroxene skarn, garnet skarn, and epidote skarn zones were formed during the intrusive phase. The garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton, respectively, prior to mineralization. Garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies. Mass balance calculation of garnet skarn in the endoskarn zone indicates that hydrothermal fluids originating from the cooling magma introduced Si, Fe, Mn, Ca, Mg, P, Ag, Cu, Zn, La, Pb, Cd, Mo, and Y. The main mass loss in the garnet skarn was due to destruction of feldspars in the Mazraeh plutonic rocks and leaching of K2O and Na2O. Released Ca has been fixed in the andraditic garnet. Garnetization of the Mazraeh pluton was accompanied by mass and volume increase. The magnitude of these changes depends mainly on the degree of alteration and composition of the precursor. The brittle behavior of the endoskarn zone was increased due to formation of massive garnet which subsequently fractured. These fractures not only facilitated movement of hydrothermal fluids but also provided new locations for Cu mineralization. Therefore locating strongly garnetized zones may be a vector to ore in skarn deposits.  相似文献   

11.
哈勒尕提-木祖克铁铜铅锌矿床是近年来在新疆西天山博罗科努成矿带内发现的一处典型的矽卡岩型铜多金属矿床,目前为中型规模,有达到大型矿床的潜力。矿体赋存于大瓦布拉克岩体与上奥陶统呼独克达坂组(O3h)大理岩、大理岩化灰岩的接触带。成矿受岩浆岩、地层岩性和接触带构造"三位一体"联合控制。大瓦布拉克岩体主要岩性为二长花岗岩和花岗闪长岩,岩石地球化学显示高硅、准铝、低镁、富碱、富钾,为I型花岗岩,富集大离子亲石元素,相对亏损高场强元素,具俯冲带岩浆岩的地球化学特点。呼独克达坂组(O3h)碳酸盐岩地球化学性质活泼且富含铜、锌,有利于含矿热液交代成矿,是区域找矿的优势层位。接触带构造既是成矿地球化学障,又是良好的成矿热液运移通道,直接控制着矿体的产出。  相似文献   

12.
龙新岩体和夏郢岩体位于扬子地块与华夏地块拼合带的西南端,岩体中的Ⅰ型花岗岩成因研究对揭示桂东南地区早古生代的地球动力学背景及其构造演化具有重要的地质意义.对龙新岩体的寄主岩和其暗色微粒包体,以及夏郢岩体岩石进行了LA-ICP-MS锆石U-Pb定年、Lu-Hf同位素和全岩地球化学研究.锆石U-Pb定年结果显示,龙新岩体的寄主岩（花岗闪长岩）的年龄为440±2 Ma;龙新岩体的暗色包体（闪长岩）的年龄为441±1 Ma,寄主岩与暗色包体为同期岩浆作用的产物.夏郢岩体花岗闪长岩和二长花岗岩年龄分别为447±3 Ma和436±3 Ma,说明夏郢岩体至少发生了2期岩浆侵入事件.Hf同位素研究表明,龙新岩体寄主岩和暗色微粒包体的锆石εHf（t）值分别为-3.32~-5.83和-17.89~-1.82,二阶段模式年龄（TDM2）分别为1.62~1.76 Ga和1.57~2.54 Ga;夏郢岩体早期花岗岩闪长岩和晚期二长花岗岩的锆石εHf（t）值分别为-15.43~3.03和-4.79~6.82,TDM2分别为1.59~1.99 Ga和0.97~1.70 Ga,指示物源主要来自古-中元古代的地壳物质.地球化学特征表明龙新岩体寄主岩为准铝质高钾钙碱性Ⅰ型花岗岩,寄主岩和暗色微粒包体均富集轻稀土元素和大离子亲石元素,亏损重稀土元素及高场强元素;夏郢岩体早期的花岗闪长岩为弱过铝质高钾钙碱性Ⅰ型花岗岩,晚期的二长花岗岩则为强过铝质高钾钙碱性Ⅰ型花岗岩,主微量元素特征均与龙新岩体寄主岩相似.根据研究区花岗岩和镁铁质包体的岩相学、年代学、地球化学及Hf同位素组成特征,表明龙新岩体的暗色包体（闪长岩）为岩浆混合成因,而龙新岩体寄主岩（花岗闪长岩）和夏郢岩体（早期花岗岩闪长岩和晚期二长花岗岩）具有一致的岩石源区和岩石成因,但在后期的成岩过程中存在岩浆混合和结晶分异程度的差异.综合以往对华南地区构造背景的研究,认为龙新和夏郢岩体是在扬子地块和华夏地块陆内造山期后,岩石圈伸展减薄,热的幔源岩浆上涌底侵,中-下地壳受到地幔热影响发生部分熔融,形成的酸性岩浆在源区和基性岩浆经历了不均一且不强烈的壳-幔混合作用形成的.   相似文献   

13.
Sm-Nd isotopic compositions were determined for the peralkaline Ilímaussaq Complex of the Gardar Province of southern Greenland. The majority of the samples in the agpaitic and augite syenitic units have near chondritic initial Nd(≈ 0), whereas a few samples trend towards Nd values as low as − 6 at the time of intrusion (1143 Ma). This latter value, from a sample taken from the margin of the complex, lying on the evolutionary trend for Ketilidian country-rock granitoids, suggests that large-scale contamination took place only at the margins of the complex. The similarity of the Nd isotopic compositions of the augite syenite and agpaitic units suggests that their parental magmas were derived from the same reservoir. A comparison of the Nd with existing Sr and Hf isotopic data for the complex suggests an origin by combined assimilation fractionation processes. Assimilation-fractional crystallization modeling of the isotopic compositions indicates that the Ilímaussaq magmas could have formed through fractional crystallization of a basaltic melt while assimilating granitic crust. The model requires initially higher assimilation rates from basalt to augite syenite composition with subsequent decreasing assimilation rates from augite syenite to agpaitic compositions. Alkali granites, which formed after the intrusion of the augite syenites, have isotopic compositions intermediate between those of the augite syenites and the surrounding Ketilidian basement. This implies even greater amounts of assimilation and is interpreted as evidence for an origin through fractionation of a basaltic or augite syenite magma with concurrent assimilation of Ketilidian crust.  相似文献   

14.
Abstract  Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Qüxü batholith is the most typical MME‐bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U‐Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions. Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge‐scale magma mixing in the Gangdisê belt took place 15–20 million years after the initiation of the India‐Asia continental collision, genetically related to the underplating of subduction‐collision‐induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass‐energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.  相似文献   

15.
内蒙古朝不楞铁铜锌铋矿床位于二连浩特-东乌旗多金属成矿带的东段,其矿化蚀变沿着花岗岩体与围岩的接触带分布。在外接触带,大理岩热液蚀变形成了进化矽卡岩,由石榴子石、辉石、硅灰石和方解石组成,泥质砂岩蚀变成角岩,由角闪石、黑云母、长石和石英组成。矽卡岩或角岩经退化蚀变形成了铁氧化物矿化,由磁铁矿、磁赤铁矿和镜铁矿组成,伴随有绿帘石、方解石、萤石和黑云母蚀变;晚期热液退化蚀变形成了硫化物,由黄铜矿、白铁矿、黄铁矿、辉钼矿、闪锌矿、辉铋矿和自然铋组成,伴随有透闪石、绿泥石、萤石、石英和方解石蚀变。在内接触带,花岗岩的热液蚀变形成了钾化,由钾长石、黑云母和少量石榴子石组成,随后被退化绿帘石、方解石和少量磁铁矿交代;晚期退化蚀变形成了硫化物脉,伴随有黑云母、方解石、石英和萤石蚀变。流体包裹体爆裂温度结果表明,该矿床形成于浅成（1.7~3.5 km）、高温环境,成矿热液具有从高温向低温多阶段演化的冷却史。矿床的地质、矿物组合特征及成矿物理化学条件显示出该矿床属于浅成、高温、近端的矽卡岩型矿床。  相似文献   

16.
邱检生  李真  刘亮  赵姣龙 《地质学报》2012,86(4):561-576
漳浦复式花岗岩体位于福建东南沿海,为一由多期岩浆作用形成的大岩基,出露面积大于1500km2。按岩性特征,该复式岩体可肢解为长桥黑云母花岗岩、程溪碱长花岗岩和湖西花岗闪长岩3个单元。锆石LA-ICP-MS U-Pb定年结果表明,3个单元岩石的成岩年龄分别为119Ma、101Ma和96Ma。化学组成上,各单元岩石均具有亚碱、准铝或弱过铝、贫磷特征,它们的A/NKC值均在1.10以下,P2O5含量均低于0.20%,均可归为钙碱性的I型花岗岩。各单元岩石均富Cs、Rb、Th、U、Pb和轻稀土,贫Ba、Sr、P、Ti,但长桥和程溪单元较之湖西单元岩石Rb/Sr、Rb/Ba比值高,K/Rb比值低,并表现出更显著的铕负异常,指示各单元岩石的分异演化程度各不相同。3单元岩石具有较均一的Nd同位素组成,εNd(t)=-2.43～-3.24,tDM2=1.11～1.16Ga,但锆石Hf同位素组成普遍具有较大的变化范围,长桥、程溪和湖西3单元岩石的εHf(t)值分别为-8.3～+3.0、+1.7～+10.2和-2.5～+3.5,变化幅度均在6个εHf单位以上,反映岩体的形成存在不同来源物质的贡献。综合分析表明,各单元岩石的形成均经历了幔源岩浆与其诱发地壳物质熔融产生的长英质岩浆在地壳深部混合,随后又经不同程度结晶分异的二阶段成岩过程。各单元岩石之间显著的成岩时差及成分变异趋势指示复式岩体不可能为同一原始岩浆分异演化的产物,而最可能为演化程度各异的壳幔混源岩浆叠次侵位复合的结果。  相似文献   

17.
江西朱溪铜钨矿床成因:来自矿物学和年代学的启示   总被引：1，自引：0，他引：1  
江西景德镇朱溪铜钨矿床是近年来发现的一个世界级超大型铜钨矿床。矿床地质特征、矽卡岩矿物学和成矿岩体年代学的研究表明,矿体赋存于上石炭统黄龙组大理岩与新元古界双桥山群变质岩之间的不整合界面之上,空间上具有明显的矿物组合分带特征。根据矽卡岩产状、矿物共生组合和相互关系,把成矿作用划分为矽卡岩阶段、退化蚀变阶段、石英-硫化物阶段、碳酸盐-萤石阶段。代表性的矽卡岩矿物组合有石榴子石、透辉石、透闪石、硅灰石、符山石、蛇纹石、绿泥石等。电子探针分析表明,石榴子石为钙铝榴石—钙铁榴石系列,辉石为透辉石—钙铁辉石系列。同位素年代学及岩浆与成矿关系的研究表明：花岗闪长岩与早期矽卡岩型矿化相关,矿化范围较小,矿石品位较低;黑云母花岗岩与云英岩型和晚期矽卡岩型的矿化相关,矿化范围较广,矿石品位较高,并获得黑云母花岗岩LA-ICP-MS锆石U-Pb年龄为（147.7±2.2）Ma。综合分析指出,朱溪铜钨矿床为晚侏罗世花岗岩浆有关的热液与晚古生代碳酸盐岩发生多阶段交代作用而形成,成矿作用以矽卡岩型和云英岩型为主。  相似文献   

18.
为研究西藏甲玛铜多金属矿床中矽卡岩的矿物学特征,进一步确定矿床成因类型,利用电子探针测试和镜下鉴定手段对矽卡岩矿物中的石榴子石、辉石、硅灰石等矿物成分进行了分析。测试结果表明,矽卡岩中石榴子石以钙铁榴石-钙铝榴石为主,辉石以透辉石为主,甲玛矿床矽卡岩属于交代矽卡岩中典型的钙矽卡岩。结合前人对矿区矽卡岩、围岩和花岗岩类的岩石地球化学、矿床成矿年代学等的研究,进一步证实甲玛铜多金属矿床系矿区花岗岩类岩浆交代大理岩形成的典型矽卡岩型矿床。  相似文献   

19.
西藏山南努日铜钼钨矿床矽卡岩地球化学特征及成因   总被引：5，自引：0，他引：5  
陈雷 《地质与勘探》2011,47(1):78-88
西藏山南地区努日Cu-W-Mo多金属矿床位于冈底斯火山-岩浆弧构造带东段南缘,属于冈底斯铜钼成矿带的南亚带,是新近探明的一个大型矽卡岩型的铜钨钼矿床,也是西藏冈底斯带首例钨矿床.对矿区内出露的矽卡岩、大理岩和灰岩的地球化学组成研究表明:在主量元素方面,Ca、Ti、Al、Mg、Mn、Fe及Si等元素在灰岩、大理岩和矽卡岩...  相似文献   

20.
Interaction of magma with wall rock is an important process in igneous petrology, but the mechanisms by which interactions occur are poorly known. The western outer granodiorite of the Cretaceous Tuolumne Intrusive Suite of Yosemite National Park, California, intruded a variety of metasedimentary and igneous wall rocks at 93.1 Ma. The May Lake metamorphic screen is a metasedimentary remnant whose contact zone exhibits a variety of interaction phenomena including xenolith incorporation, disaggregation, and partial melting. The chemical contrast of these metasedimentary rocks with the invading pluton provides an excellent measure of pluton/wall rock interactions. Wall rock xenoliths (mostly pelitic quartzite) are predominantly located in an elongate horizon surrounded by a hybridized fine-grained granodiorite. Initial Sr and Nd isotopic ratios of the hybridized granodiorite indicate significant local incorporation of crustal material. Major- and trace-element geochemical data indicate that contamination of the granodiorite occurred via selective assimilation of both high-K and low-K, high-silica partial melts derived from pelitic quartzite. Although the hybridized granodiorite shows significant amounts of contamination, adjacent to xenoliths the proportion of contamination is undetectable more than a meter away. These results indicate that the chemical and isotopic variability of the Tuolumne Intrusive Suite is not caused by magma contamination via in situ wall rock assimilation.  相似文献   

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