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1.
不纯碳酸盐岩的变质作用 总被引：1，自引：0，他引：1
不纯碳酸盐岩中的矿物共生组合与变质时的总压和二氧化碳分压密切相关。总压增高促使透闪石、透辉石和橄榄石等矿物生成温度增高。变质过程中岩石中流体成分的变化有两种极端情况,即渗滤作用和缓冲作用。渗滤作用下变质反应,变质矿物界线和变质矿物特征等均与缓冲作用下有所差异,以此可以区别它们。湖北宿松群和河北红旗营子群不纯大理岩是在渗滤作用下变质的。山西五台群板峪口组不纯大理岩是在缓冲加渗滤作用下变质的。 相似文献
2.
根据矿物成分及其结构演变,将大别山榴辉岩的退变质过程分为三个阶段:贫流体阶段、弱流体阶段和富流体阶段。贫流体阶段发生于榴辉岩相环境中,其主要作用是柯石英-石英和文石- 方解石等同质多象转变、石榴子石和绿辉石等的重结晶,以及绿辉石中硬玉和钠长石的固溶体出溶等。弱流体阶段发生于榴辉岩相退变质的晚期,含水矿物闪石、绿帘石和云母,以及钠长石等低压矿物大量形成之前,其标志是蓝晶石变斑晶和金红石脉的形成,以及浸染状金红石的富集成矿。富流体阶段始于低级角闪岩相退变质环境,并可能一直持续到近地表处。该阶段以出现大量含水和挥发份的矿物(如闪石、绿帘石、多硅白云母、钠云母、黑云母、磷灰石和碳酸盐等)为特征。围绕石榴子石和绿辉石的闪石次变边、闪 相似文献
3.
湘东北杨山庄金矿床流体成矿机制 总被引：3，自引：3，他引：0
杨山庄金矿床位于江南造山带中部,矿体严格受NW-NWW向断裂控制,赋存于新元古代浅变质的绢云母板岩和粉砂质板岩中,成矿期分为三个阶段:石英-毒砂-黄铁矿(少量)-自然金-白钨矿-白云石-白云母(阶段Ⅰ)、石英-毒砂-黄铁矿-自然金-黄铜矿-方铅矿-闪锌矿-绢云母(阶段Ⅱ)和石英-方解石(阶段Ⅲ)。成矿Ⅰ、Ⅱ阶段流体包裹体以两相水溶液包裹体为主,含有少量的气相包裹体和含CO_2的三相包裹体,气相包裹体成分为CH_4-N_2-CO_2、N_2-CO_2和N_2。成矿温度集中在240~320℃,盐度集中在7%~9%Na Cleqv,成矿流体为中-低温、中低盐度H_2O-Na Cl-CO_2体系。在成矿Ⅰ、Ⅱ阶段,成矿流体与围岩发生交代反应,流体发生相分离,使液相CO_2含量降低,引起Au(HS)~(2-)溶解度降低,导致金发生沉淀。 相似文献
4.
南召县老庄透辉石–透闪石矿是河南省唯一的透辉石–透闪石矿床。矿区位于区域性栾川–明港大断裂的北侧，大地构造位置处于华北陆块南缘。矿区有2个透辉石–透闪石矿体，呈似层状赋存于青白口系栾川群南泥湖组上段中，矿体形态简单。围岩蚀变为透闪石化和透辉石化，次为钾长石化和金云母化等。矿石自然类型主要为金云母透辉石透闪石矽卡岩型、金云母透闪石透辉石矽卡岩型和金云母透闪石矽卡岩型。矿物成分主要为透闪石和透辉石，次为钾长石和金云母，方解石少量。矿石化学成分主要为SiO2、CaO、MgO和Al2O3，其次是FeO、K2O、Na2O和CO2等。透闪石+透辉石(Tl+Di)品位较高、较稳定，矿床平均品位(Tl+Di)为68.25%。透辉石–透闪石原矿代替硅灰石用于生产釉面砖。初步试验表明，制品性能稳定，节能效果明显。矿床属矽卡岩型矿床，成矿时代为早白垩世。矿床形成受早白垩世竹园石英正长斑岩体与南泥湖组上段中的白云石大理岩及层间破碎带的多重控制。矽卡岩期为主成矿期，干矽卡岩阶段形成... 相似文献
5.
超高压岩石-脉体体系是认识俯冲带流体性质和行为的天然实验室.通过总结大别超高压变质带3个榴辉岩（角闪岩）-脉体体系的研究成果,探讨了大陆俯冲带变质流体的溶解-结晶过程和氧逸度变化规律以及流体对轻元素硼的迁移过程.对榴辉岩-复合高压脉体的研究发现超高压流体通过溶解矿物富集溶质组分,流体随后经历3期结晶过程,分别形成绿辉石-绿帘石脉、绿帘石-石英脉和蓝晶石-绿帘石-石英脉.绿帘石La、Cr和δEu值是判断结晶次序的关键指标.对榴辉岩-角闪岩-低压脉体研究表明大陆俯冲带低压变质流体的氧逸度明显高于高压-超高压变质流体.高氧逸度条件也导致一些反常矿物（如退变金红石）的生长.对含电气石榴辉岩-脉体研究揭示变质碳酸盐岩是大陆俯冲板片中重硼同位素的重要储库,其在汇聚板块边界的脱硼作用显著影响深部硼循环.上述研究成果为理解俯冲带变质流体演化和物质循环提供重要科学依据. 相似文献
6.
胶东乳山脉状金矿床成矿流体性质与演化 总被引：10，自引：12，他引：10
位于胶东牟平-乳山金矿带中部的乳山金矿(原称金青顶金矿)是目前我国单脉金储量最大的矿床,金主要产于黄铁矿和多金属硫化物石英脉/细脉中。流体包裹体研究表明,乳山金矿不同蚀变带岩石和各成矿阶段金矿石中的流体包裹体有两种类型:CO_2～H_2O 包裹体和水溶液包裹体。钾长石化蚀变岩、黄铁绢英岩和弱蚀变花岗岩的石英中含有丰富的 CO_2-H_2O 包裹体,而黄铁矿石英脉和多金属硫化物石英脉中 CO_2-H_2O 包裹体数量逐渐减少,以富水的 CO_2-H_2O 两相包裹体和水溶液包裹体为主。显微测温结果显示,弱蚀变花岗岩、钾长石化岩石和黄铁绢英岩石英中的 CO_2-H_2O 包裹体的均一温度范围为236～377℃;而黄铁矿和多金属硫化物石英包裹体的均一温度为170～324℃。成矿早期流体为富含挥发份(X_(CO_2)高达0.53)、中低盐度(3.33～10.48 wt% NaCl)的流体,到主成矿期逐渐演化为以含较低的 CO_2的富水流体(X_(CO_2)为0.01～0.05) 和水溶液流体,盐度为1.23～12.55Wt% NaCl。金和硫化物(尤其是黄铁矿)紧密共生,说明金主要以金硫络合物形式被搬运,CO_2包裹体的广泛存在则表明其对成矿流体的 pH 变化起着重要的抑制作用。水/岩反应、温度下降和压力降低引起的流体不混溶可能是乳山金矿金沉淀成矿的主要原因。 相似文献
7.
在Sierra Nevada变质带,中生代后生含金石英脉群中的层控浸染状黄铁矿型金矿体由围岩与贯流(Through—flowing)流体之间的反应而形成的.含Fe碳酸盐和硫化物的相平衡关系对于确定什么样的围岩最有利于在不整合矿脉中形成浸染状矿化是极为重要的。在美国加里福尼亚州Alleghany金矿田中,热液蚀变围岩中交代成因的碳酸盐矿物的成份在很大程度上取决于未蚀变岩石中Fe、Mg和Ca的相对比例。这样,不同围岩中共存的菱镁矿—菱铁矿和白云石—铁白云石固溶体系列就可以用来确立在交代作用温度条件下(325±50℃)大部分CaCO_3-MgCO_3-FeCO_3体系的经验相图,因为Fe、Mg硅酸盐矿物在近矿脉的蚀变中是不稳定的,围岩中的Fe在碳酸盐矿物和硫化物中重新分配.黄铁矿化和浸染金矿化可出现一系列作为围岩的岩浆岩和变沉积岩之中,这些岩石的Fe/(Fe Mg)初始摩尔比值≥0.5.当蚀变岩石中Fe/(Fe Mg)摩尔比值≤0.5时,Fe差不多全部地被分配在富镁的碳酸盐矿物之中(在菱镁矿一菱铁矿固溶体中XFeCO_3<0.6)。本文提出当与蚀变和矿化有关的富CO_2的含矿流体,流经中性火山岩和沉积岩并使其蚀变时,H_2S/CO_2/H_2比值由于黄铁矿和Mg_(0.4)Fe_(0.6)CO_3( 百墨?)之间的平衡而被部分地缓冲.含矿流体在局部与低Fe/(Fe Mg)比值的岩石反应,形成含铁的白云石十菱镁矿组合;与高Fe/(Fe Mg)比值的岩石反应形成铁白云石 黄铁矿组合.金之所以能从双硫络合物饱和溶液中沉淀下来,部分是由于黄铁矿化所引起的流体脱硫化和还原作用所导致的。在以变中性火山岩和变沉积岩为主的地块中,对这种类型金矿化的有利围岩并不需要含铁量高,但却必须具备高的Fe/(Fe Mg)比值,和长英质火山岩相深成岩,富铁的拉斑玄武岩质分异物,条带状铁建造以及许多硅质和泥质沉积岩.由于超镁铁质和镁铁质岩浆岩以及一些泥质沉积岩中的初始Fe/(Fe Mg)比值低,所以它们的硫化程度也较低.上述规律所揭示的勘探方向,如果修改后能够反映流体流动过程中起缓冲作用的主要岩石类型,那么对于在Sierra Nevada和其它类似非均一性的变质地块中指导找矿将具有重大的意义.碳酸盐一硫化物相平衡大致能缓冲富CO_2含矿流体中的碳酸盐一硫化物比值(325℃时fCO_2≥10~(2.8),200MPa).假定石墨饱和,Alleghany金矿田中含矿流体(fCO_2≈10~(3.2),或10mol％CO_2)的CO_2/H_2S摩尔比值大致为10~3.在较低的CO_2活度条件下,含铁的硅酸盐矿物也会起到缓冲作用.碳酸盐化可以潜在地使一些围岩脱硫化,使硫(包括有关的金属?)释放到流体中.这种情形最可能出在现含黄铁矿的镁铁质和超镁铁质岩石及一些泥质岩石中. 相似文献
8.
西秦岭阳山金矿带安坝金矿床流体包裹体特征及矿床成因 总被引：1，自引：0，他引：1
安坝金矿是近年来在西秦岭地区阳山金矿带探明的一超大型矿床,大地构造位置处于勉略缝合带内,其产出主要受区域逆冲挤压断裂带控制。矿石类型可划分为蚀变岩型和石英脉型,以前者为主,主要矿石矿物为黄铁矿、毒砂、辉锑矿、自然金、银金矿等,围岩蚀变以硅化、绢云母化、绿泥石化、碳酸盐化为主。成矿过程可划分为黄铁矿-绢云母阶段(Ⅰ)、黄铁矿-毒砂-石英阶段(Ⅱ)、毒砂-黄铁矿-石英阶段(Ⅲ)、自然金-辉锑矿-石英阶段(Ⅳ)、方解石-石英阶段(Ⅴ)等5个阶段。不同阶段石英中均含有大量的流体包裹体,多数直径3~10μm,以富CO_2、含CO_2和水溶液3种类型为主,总体为中低温(110~330℃)、低盐度(0.62~9.34%Na Cl.eq)的流体。单个流体包裹体激光拉曼分析表明,流体以CO_2、H_2O为主,不同阶段含金石英脉石英δD变化范围为-83‰~-107‰,δ~(18)O变化范围为-0.31‰~11.95‰。从成矿早阶段到晚阶段,流体包裹体大小、CO_2含量、温度逐渐降低,盐度先升高后降低。成矿早阶段以下地壳的变质流体为主,而后经历了减压沸腾作用,压力降低,盐度增高,导致金大量沉淀。稳定同位素特征反映主成矿阶段以变质流体为主,成矿晚期发生低温流体的注入。总之,阳山金矿成矿流体经历了长期的演化过程,亦揭示金成矿作用的复杂性。 相似文献
9.
鲁东南岚山头含柯石英榴辉岩主要产于花岗质片麻岩内,是苏鲁超高压变质带主要榴辉岩体密集分布区之一。流体包裹体研究表明,榴辉岩矿物及细脉石英中捕获有四种类型包裹体:在超高压-高压榴辉岩相条件下捕获的 N_2±CO_2包裹体;在高压榴辉宕重结晶阶段被捕获的 CO_2-H_2O 包裹体和含子矿物高盐度 H_2O 溶液包裹体:在超高压岩石折返过程中的最晚(角闪岩相退变质甚至更晚)阶段捕获的低盐度 H_2O 溶液包裹体。利用榴辉岩矿物及脉体石英中捕获的流体包裹体相互期次关系,可以对本区超高压变质作用板片折返过程中的流体演化史进行重建。 相似文献
10.
茂租铅锌矿床位于扬子地台西南缘,是滇东北矿集区内的一个大型矿床,矿体主要呈似层状产于震旦系灯影组白云岩中;矿石矿物以闪锌矿为主,次为方铅矿;脉石矿物主要为白云石、方解石和萤石。本文对该矿床中与铅锌矿密切共生的团块状白云石、方解石和萤石以及围岩灯影组白云岩的REE地球化学特征和C、O、Sr同位素进行了对比研究。结果表明:团块状白云石和方解石的稀土配分模式、C同位素和Sr同位素比值与围岩灯影组白云岩比较接近,表明形成团块状白云石和方解石的成矿流体主要来源于围岩灯影组白云岩的溶解;但这两种矿物的稀土总量ΣREE高于灯影组白云岩,说明成矿流体除了主要由围岩提供REE外,还有部分其他富含REE流体的加入。萤石则具有LREE亏损和分配曲线相对平缓的稀土配分模式特征,表明萤石形成于成矿的晚阶段,有更多的外部流体的加入。团块状白云石、方解石和萤石表现出明显的Eu正异常,且团块状白云石和方解石的O同位素低于灯影组白云岩,反映了存在较高温度的流体活动,这3种脉石矿物是由高温热液流体形成的。灯影组白云岩和3种脉石矿物都具有明显的Ce负异常,说明成矿流体可能主要来源于地层循环水,继承了围岩的Ce负异常特征。方解石和萤石的Sr同位素比值高于围岩震旦系灯影组白云岩和峨眉山玄武岩,但小于基底岩石昆阳群和会理群,说明成矿流体主要由赋矿围岩等沉积地层中的循环流体与流经了基底岩石的深部流体混合形成。 相似文献
11.
Marbles from the Pohorje area in Slovenia are investigated by mineralogical-petrographical analyses of thin sections as well as by cathodoluminescence in order to detect their local variability in texture and mineral assemblages. The CL colours observed in a cold cathode device are related to the manganese contents. An attempt is made to relate the textures seen under CL to mineral reactions during the process of metamorphism. The predominantly calcite marbles from Pohorje exhibit orange luminescence with some dolomite lenses with red luminescence. The typical mineral assemblages are calcite+tremolite+phlogopite or calcite+dolomite+tremolite+phlogopite. Therefore, the estimated temperature from the stability of mineral assemblage is assumed at approximately 500 °C. 相似文献
12.
Ultra-high-pressure (UHP) marble and eclogite in the Su-Lu UHP terrane, eastern China 总被引：22，自引：0，他引：22
A large mass of dolomitic marble including many eclogite blocks occurs in orthogneisses of the Rongcheng area of the Su-Lu province, eastern China. The marble consists mainly of dolomite, calcite (formerly aragonite), graphite, forsterite, diopside, talc, tremolite and phlogopite. Aggregates of talc and calcite occur at the boundary between dolomite and diopside. Tremolite is a reaction product between talc and calcite. Eclogite blocks are rimmed by dark green amphibolite. The primary mineral assemblage in the core of eclogite is Na-bearing garnet (up to 0.2 wt% Na2 O), omphacitic pyroxene, clintonite and rutile. Secondary minerals are pargasitic/edenitic amphibole, plagioclase, sodic diopside, chlorite, zoisite and titanite. The peak metamorphic conditions, based on stability of the dolomite+forsterite+aragonite (now calcite)+graphite assemblage, under conditions where tremolite is unstable, are estimated at T =610–660 °C and P =2.5–3.5 GPa (for X CO=0.001). A reaction between dolomite and diopside to form talc under tremolite-unstable conditions indicates a temperature decrease under ultra-high-pressure conditions ( P >2.4 GPa, X CO<0.0013). The formation of secondary tremolite is consistent with a nearly adiabatic pressure decrease post-dating the ultra-high-pressure metamorphism. The temperature decrease under ultra-high-pressure conditions preceding decompression may reflect the underplating of a cold slab, and the rapid decompression probably corresponds to the upwelling stage promoted by the delamination of a downwelling lithospheric root. The P – T conditions of the amphibolitization stage are estimated at <0.9 GPa and <460 °C, and are similar to conditions recorded by the surrounding orthogneisses. 相似文献
13.
D. Puhan 《Contributions to Mineralogy and Petrology》1995,120(2):180-185
Magnesian calcite temperatures of calcites formed during metamorphic reactions and fluorine distribution between OH-bearing minerals have been measured for the assemblage {ie180-1} within a sample of siliceous dolomite from the southern Damara Orogen. Two groups of temperatures were found: A group with higher temperatures in the range 583 to 545°C for reaction sites where tremolite was formed, and a second group with lower temperatures from 522 to 476°C for reaction sites where talc has grown. From special reaction textures it is evident that the reaction sites of the higher temperature group related with temolite is older, whereas talc has grown after the formation of tremolite with decreasing temperature. The transition from the tremolite stability field to the talc stability field occurred at a temperature between the two temperature groups. Each measured magnesian calcite temperature can be assigned to a microscopic fluid vein which connects single reaction sites either with tremolite or with talc. Single microveins developed at different times, because the prevailing temperature during the formation of individual fluid veins and the connected reaction sites are different. The mineral associations and the reaction textures of the sample were formed within a period of time necessary for cooling the rock at least from about 580 to 480°C. The textural relations after the successive reaction processes appear to be the result of a single univariant reaction. Distribution of fluorine between tremolite-phlogopite pairs and tremolite-talc pairs show that the fluorine content of the tremolite may be inherited in the latter case. A plausible P-T path is outlined explaining the evolution of assemblages in dolomites and metapelites of the same area which contain staurolite and kyanite. The first appearance of staurolite and kyanite in the field is situated on the lower grade side of the zone containing assemblage (I). The conversation of the present field occurrence of assemblage (I) is due to the fading of fluid infiltration into the dolomites. 相似文献
14.
Tremolite–calcite veins in the footwall of the Simplon Fault,Antigorio Valley,Lepontine Alps (Italy)
Vito Meggiolaro Michele Sapigni Anna Maria Fioretti 《Swiss Journal of Geoscience》2011,104(3):355-365
The lowermost units of the nappe pile of the Lepontine Alps crop out in the Antigorio valley in the footwall of the Simplon
Fault. The whole orthogneiss section of the Antigorio Unit is exposed on both sides of the valley, sandwiched between the
Mesozoic metasedimentary sequences of the Baceno unit below and the Tèggiolo unit above. The petrography and mineral composition
of tremolite–calcite veins occurring in dolomite marble in both metasedimentary sequences were investigated. Tremolite–calcite
(with lesser talc and minor phlogopite) veins have rhythmic banded texture. Banding is due to cyclic differences in modal
abundances and fabric of tremolite and calcite. These veins are very similar to those occurring in dolomite rafts within the
Bergell granite and it is inferred that they formed by the same “fracture-reaction-seal” mechanism. Veins formed by reaction
of a silica-rich aqueous fluid with the host dolomite marble along fractures. According to thermo-barometric calculations,
based on electron microprobe analyses, reaction occurred at temperatures between 450 and 490°C and minimum pressure of 2–3 kbar.
Such temperature conditions occurred in this footwall region of the Simplon Fault Zone around 15 Ma, during exhumation and
cooling of the nappe pile and a transition to brittle behaviour. Aqueous, silica-rich fluids concentrated along fractures,
forming tremolite–calcite veins in the dolomite marbles and quartz veins in the orthogneiss. 相似文献
15.
16.
Jack M. Rice 《Contributions to Mineralogy and Petrology》1977,59(3):237-259
Progressive metamorphism of impure dolomitic limestone in the 1.5 to 2.5 km wide contact aureole surrounding the northernmost portion of the boulder batholith has resulted in a consistent sequence of uniformly distributed zones of low-variance mineral parageneses separated by abrupt and distinctive isograds. In silica-undersaturated, aluminous marbles, the following mineral assemblages occur, in order of increasing grade: calcite-dolomite-calcic amphibole-chlorite, calcite-dolomite-calcic amphibole-chlorite-spinel, calcite-dolomite-calcic amphibole-chlorite-olivine-spinel, calcite-dolomite-chlorite-olivine-spinel, calcite-dolomite-olivine-spinel. The spatial distribution of parageneses and the occurrence of low-variance parageneses indicate buffering of the pore fluid composition by the local mineral assemblages. The observed sequence of mineral reactions and the spacing of isograds is in good agreement with experimental and calculated equilibria in terms of P-T-X
CO
2and temperatures of equilibration inferred from calcite-dolomite geothermometry, which range from 435 to 607 °C across the aureole.Microprobe analyses of coexisting minerals indicate attainment of exchange equilibrium. Calcic amphibole and chlorite coexisting with calcite and dolomite become progressively more aluminous with increasing grade; calcic amphibole changes rapidly from Al-poor tremolite to pargasite, while AlIV in Cte increases from 2.0 to 2.3 atoms per 8 tetrahedral sites. Observed low-variance assemblages fix the activities of calcic amphibole and chlorite end-member components as a function of P and T, and hence the systematic compositional variation in these phases is not an independent variable, but is controlled by the local mineral assemblage. 相似文献
17.
在野外地质调查的基础上,通过显微薄片观察、电子探针分析、X射线衍射分析、红外光谱分析、X射线荧光光谱分析、微量元素分析、稀土元素分析等现代测试方法对河北小寺沟蛇纹石玉的矿物成分、化学成分进行了研究。结果表明,小寺沟蛇纹石玉为富镁碳酸盐岩蚀变形成的蛇纹岩,其主要矿物成分为利蛇纹石,次要矿物成分有方解石、白云石、透辉石、金云母、磁铁矿、黄铁矿等。蛇纹石玉的稀土元素来源于围岩大理岩,其稀土元素球粒陨石标准化配分图与其围岩大理岩的稀土配分图非常相似,为陡右倾型,具有稀土元素总量较低、富集轻稀土、具δEu负异常的特点。 相似文献
18.
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
19.
X射线粉晶衍射仪在山东蒙阴金伯利岩蚀变矿物鉴定中的应用 总被引：5，自引：4，他引：1
山东蒙阴金伯利岩组成矿物以蚀变矿物为主,X射线粉晶衍射仪鉴定结果显示无矿金伯利岩矿物组分为方解石、白云石、石英、钙锆钛矿,标志性矿物为白云石和钙锆钛矿;贫矿金伯利岩矿物组分为蛇纹石、方解石、钙铝榴石、磁铁矿和金云母,标志性矿物为钙铝榴石;富矿金伯利岩矿物组分为蛇纹石、方解石、绿泥石、磷灰石、磁铁矿和金云母,标志性矿物为绿泥石和磷灰石。采用X射线粉晶衍射仪鉴定金伯利岩蚀变矿物组合,寻找蚀变矿物组分变化与金伯利岩含矿性的关系,利用标志性的蚀变矿物判断金伯利岩无矿、贫矿还是富矿,是非常有意义的。 相似文献
20.
H. MIZUOCHI M. SATISH‐KUMAR Y. MOTOYOSHI K. MICHIBAYASHI 《Journal of Metamorphic Geology》2010,28(5):509-526
Calcite–dolomite solvus geothermometry is a versatile method for the estimation of metamorphic temperature because of its simplicity. However, in medium‐ to high‐grade metamorphic rocks the accuracy of estimating temperature by the integration of unmixed dolomite and calcite is hampered by the heterogeneous distribution of unmixed dolomite, difficulties in distinguishing between preexisting and exsolved dolomite and demarcating grain boundaries. In this study, it is shown that calcite–dolomite solvus thermometry can be applied to calcite inclusions in forsterite and spinel for the estimation of peak metamorphic temperature in granulite facies marbles from Skallevikshalsen, East Antarctica. The marbles are comprised of a granoblastic mineral assemblage of calcite + dolomite + forsterite + diopside + spinel + phlogopite ± apatite, characteristic of granulite facies metamorphic conditions. Forsterite, spinel and apatite frequently contain ‘negative crystal’ inclusions of carbonates that display homogeneously distributed dolomite lamellae. On the basis of narrow ranges of temperature (850–870 °C) recorded from carbonate inclusions compared with the range from matrix carbonate it is regarded that the inclusion carbonates represent a closed system. Furthermore, this estimate is consistent with dolomite–graphite carbon isotope geothermometry, and is considered to be the best estimate of peak metamorphic temperature for this region. Matrix calcite records different stages of retrograde metamorphism and re‐equilibration of calcite that continued until Mg diffusion ceased at ～460 °C. Electron backscattered diffraction (EBSD) results together with morphological features of unmixed coarse tabular dolomite suggest anisotropic diffusion and mineral growth are influenced by crystallographic orientation. Identification of sub‐grain boundaries and formation of fine‐grained unmixing in calcite rims suggest the presence of grain boundary fluids in the late retrograde stages of metamorphic evolution. These results, thus, demonstrate the usefulness of carbonate inclusion geothermometry in estimating the peak metamorphic temperatures of high‐grade terranes and the application of EBSD in understanding the unmixing behaviour of minerals with solid solutions. 相似文献