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1.
Seven pyroxene varieties were identified in nepheline syenites and foidolites of the Khibiny pluton: enstatite, ferrosilite, diopside, hedenbergite, augite, aegirine-augite, and aegirine. Enstatite and augite are typical of alkaline and ultramafic rocks of dike series. Ferrosilite was found in country quartzitic hornfels. Diopside is a rock-forming mineral in alkaline and ultramafic rocks, alkali gabbroids, hornfels in xenoliths of volcanic and sedimentary rocks and foyaite, melteigite-urtite that assimilate them, and certain hydrothermal pegmatite veins. Hedenbergite was noted in hornfels from xenoliths of volcanic and sedimentary rocks and in a hydrothermal pegmatite vein at Mount Eveslogchorr. Aegirine-augite is the predominant pyroxene in all types of nepheline syenites, phonolites and tinguaites, foidolites, alkaline and ultramafic rocks of dike series, fenitized wall rocks surrounding the pluton, and xenoliths of Devonian volcanic and sedimentary rocks. Aegirine is an abundant primary or, more often, secondary mineral in nepheline syenites, foidolites, and hydrothermal pegmatite veins. It occurs as separate crystals, outer zones of diopside and aegirine-augite crystals, and homoaxial pseudomorphs after Na-Ca amphiboles. Microprobe analyses of 265 pyroxenes samples allowed us to distinguish ten principal trends of isomorphic replacement and corresponding typomorphic features of pyroxenes. Compositional variations in clinopyroxenes along the sampled 35-km profile from the margin of the Khibiny pluton to its center confirm the symmetric zoning of the foyaite pluton relative to semicircular faults of the Minor Arc and the Main (Central) Ring marked by Devonian volcanic and sedimentary rocks, foidolites, and related metasomatic rocks (rischorrite, albitite, and aegirinite). Changes in the composition of pyroxenes are explained mainly by the redistribution of elements between coexisting minerals of foyaites in the process of their intense differentiation under the effect of foidolite melts that have intruded into the circular fault zones.  相似文献   

2.
This paper describes the structural-compositional zoning of the well-known Khibiny pluton in regard to rock-forming feldspars. The content of K-Na-feldspars increases inward and outward from the Main foidolite ring. The degree of coorientation of tabular K-Na-feldspar crystals sharply increases in the Main ring zone, and microcline-dominant foyaite turns into orthoclase-dominant foyaite. The composition of K-Na-feldspars in the center of the pluton and the Main ring zone is characterized by an enrichment in Al. This shift is compensated by a substitution of some K and Na with Ba (the Main ring zone) or by an addition of K and Na cations to the initially cation-deficient microcline (the central part of the pluton). Feldspars of volcanosedimentary rocks occurring as xenoliths in foyaite primarily corresponded to plagioclase An15–40, but high-temperature fenitization and formation of hornfels in the Main ring zone gave rise to the crystallization of anorthoclase subsequently transformed into orthoclase and albite due to cooling and further fenitization. Such a zoning is the result of filling the Main ring fault zone within the homogeneous foyaite pluton with a foidolite melt, which provided the heating and potassium metasomatism of foyaite and xenoliths of volcanosedimentary rocks therein. The process eventually led to the transformation of foyaite into rischorrite-lyavochorrite, while xenoliths were transformed into aluminum hornfels with anorthoclase, annite, andalusite, topaz, and sekaninaite.  相似文献   

3.
Five minerals of the corundum group have been identified in the Khibiny pluton with certainty. Corundum proper and karelianite occur only in hornfels after volcanic and sedimentary rocks. Xenoliths of hornfels mark the ring faults that bound foidalite within the field of foyaite. Hematite occurs in hydrothermally altered nepheline syenite and crosscutting hydrothermal veins related to the ring faults. Minerals of the ilmenite-pyrophanite series are present in all rocks of the pluton, including veins. Accessory ilmenite in foyaite varies from the manganese variety and pyrophanite in the inner and outer parts of the pluton to manganese-free ilmenite in zone of the Main Ring Fault. In xenoliths of volcanic rocks and alkaline ultramafic rocks, ilmenite is enriched in magnesium. The zoning in distribution of the above-mentioned minerals and the character of variation in their compositions from margins of the pluton to its center are consistent with the petrochemical zoning formed as a result of foyaite alteration of near ring faults.  相似文献   

4.
The occurrence, morphology, and composition of rinkite are considered against the background of zoning in the Khibiny pluton. Accessory rinkite is mostly characteristic of foyaite in the outer part of pluton, occurs somewhat less frequently in foyaite and rischorrite in the central part of pluton, even more sparsely in foidolites and apatite–nepheline rocks, and sporadically in fenitized xenoliths of the Lovozero Formation. The largest, up to economic, accumulations of rinkite are related to the pegmatite and hydrothermal veins, which occur in nepheline syenite on both sides of the Main foidolite ring. The composition of rinkite varies throughout the pluton. The Ca, Na, and F contents in accessory rinkite and amorphous products of its alteration progressively increase from foyaite and fenitized basalt of the Lovozero Formation to foidolite, rischorrite, apatite–nepheline rocks, and pegmatite–hydrothermal veins.  相似文献   

5.
Seven spinel-group minerals in various geological settings have been revealed in the rocks of the Khibiny pluton. Hercynite, gahnite, and vuorelainenite occur only in xenoliths of hornfels after volcanic and sedimentary rocks, whereas spinel and magnesiochromite occur in alkaline ultramafic rocks of dike series. Franklinite has been discovered in a low-temperature hydrothermal vein. Ubiquitous magnetite is abundant in foyaite, foidolites, alkaline ultrabasic rocks, and pegmatite and hydrothermal veins and may even be the main mineral in some foidolite varieties. The spinel-group minerals are characterized by various chemical compositions due to the fractionation of nepheline syenites resulting in formation of the Main ring of foidolites and apatite-nepheline ore. Like most other minerals found throughout the pluton, magnetite is characterized by variation in the chemical composition along the radial line from the contact with country Proterozoic volcanic rocks to the geometric center of the pluton. Toward the center, the total Ti and Mn contents in magnetite increase from 5–15 up to 40 at %.  相似文献   

6.
中国夕卡岩矿床中的角闪石   总被引：6，自引：3，他引：6       下载免费PDF全文
赵一鸣  李大新 《矿床地质》2003,22(4):345-359
文章综合分析研究了中国21个夕卡岩矿床中的130个角闪石的成分分析数据。根据夕卡岩类型及其伴生金属矿化的不同，把角闪石分为4大类：钙夕卡岩中的角闪石多属钙角闪石，包括绿钙闪石、铁角闪石、镁绿钙闪石、铁浅闪石、阳起石、铁阳起石、铁镁钙闪石和铁韭闪石等；镁夕卡岩中的角闪石以透闪石为主，局部有浅闪石或韭闪石；锰质夕卡岩中的角闪石有锰质阳起石、锰质透闪石、锰直闪石和锰镁闪石；碱质夕卡岩中的角闪石属钠-钙角闪石或钠角闪石类，包括钠透闪石、镁亚铁钠闪石、亚铁钠闪石、镁铝钠闪石和镁钠闪石。碳酸盐围岩和有关侵入岩的成分对角闪石的类型、成分及其伴生金属矿化起重要的作用。  相似文献   

7.
超高压闪石的发现及其成因矿物学意义   总被引：1，自引：0，他引：1  
在缅甸硬玉岩区发现了 6种相对罕见的钠质、钠钙质角闪石 (蓝闪石、灰闪石、铝钠闪石、镁红闪石、镁钠钙闪石和蓝透闪石 ) ,其中蓝透闪石、灰闪石和镁红闪石的发现属首次。灰闪石和镁红闪石只产于挪威、中国大别和阿尔卑斯超高压带 ,或在超高压实验岩石学的实验中被合成。同时还研究了这些闪石的化学组成、种属间的关系及形成条件 ,这些闪石形成时压力不低于 2 .2× 1 0 6 k Pa,因此缅甸硬玉岩区可能是世界上又一个超高压区。  相似文献   

8.
Data on the occurrence, morphology, anatomy, composition, and formation conditions of loparite-(Ce) in the Khibiny alkaline pluton are given. Loparite-(Ce), (Na,Ce,Sr)(Ce,Th)(Ti,Nb)2O6, resulted from metasomatic alteration and assimilation of metamorphic host rocks at the contact with foyaite as well as foyaite on the contact with foidolite. This alteration was the highest in pegmatite, and albitite developed there. A decrease in temperature resulted in enrichment of the perovskite and tausonite endmembers in loparite-(Ce) owing to a decrease in the loparite and lueshite endmembers. La and Ce sharply predominate among rare earth elements in the composition of loparite-(Ce).  相似文献   

9.
Based on the results of microprobe analyses, six groups of calcium amphiboles were distinguished for the Tyrnyauz deposit. Group I (mainly edenite) includes amphiboles of hornfels and periskarn rocks. Groups II-VI (actinolite-hastingsite series) are related to post-skarn metasomatic rocks of the productive stage after hornfels (II), the tonalite and plagiogranite complex (III), ultrabasic rocks (IV), pyroxene-plagioclase periskarn rocks (V), and skarn (VI). Group IV is represented by actinolite; group VI, by hastingsite; groups II, III, and V, by hornblende varieties.  相似文献   

10.
Re-mapping of the Alnö complex has radically reduced the area identified as fenite, in comparison with the classic work of Eckermann (1948). A marginal fenite zone, generally 500–600 m wide, is present around the complex, and the petrography and mineralogy of six selected key areas have been investigated in detail. Fenitization of the country rock migmatitic gneiss led to replacement of quartz, feldspars, biotite and chlorite by alkali pyroxene and amphibole, new generations of feldspars, calcite, titanite, fluorite and apatite. In some areas, however, a distinctive narrow band of fenitization, referred to as contact fenite, adjacent to large sövite dykes, contains mineral assemblages that include phlogopite, nepheline, melanite and wollastonite. Amphiboles in the fenites are richterite, katophorite, arfvedsonite and eckermannite. There is a very wide variation in the composition of pyroxenes which vary between diopside, aergirine-augite and aergirine. Although trends from aergirine to aegirine-augite and aegirine-augite to diopside have been defined, which are similar to those of other fenite localities, distinctive trends for the eastern part of the aureole have been identified that converge on aegirine, and approximate trends in some series of alkaline igneous rocks. Analyses of mica, garnet, wollastonite and feldspar are also presented and discussed. The mineralogical data are used to estimate the conditions of temperature, oxidation state, and activity of CO2, H2O and silica pertaining during the fenitization process. The fluids with which the fenites equilibrated were apparently different in composition in different parts of the aureole, and varied with time, implying more than one magmatic source. The various evolutionary trends identified in the pyroxenes and amphiboles, in particular, are explained in terms of two main fluid types, which emanated from ijolitic and carbonatitic magma sources.  相似文献   

11.
大别山典型燕山期侵入体中矿物成分特征及其地质意义   总被引：4，自引：0，他引：4  
分析了大别造山带核部典型燕山期侵入体中的斜长石、黑云母和角闪石的化学成分和成因特点,并从矿物平衡角度讨论了典型侵入体岩石成因。结果表明：（１）石鼓尖侵入岩中,斜长石成分较稳定,共生角闪石和黑云母为岩浆平衡结晶的矿物;（２）天堂寨和九资河侵入岩中,部分斜长石和黑云母可能为深蚀残留矿物,角闪石属于火成岩区的新生矿物,可能为斜长石和黑云母发生融反应所形成;（３）三个侵入体的岩石均为岩浆成因。  相似文献   

12.
Investigation of an eclogite xenolith, discovered in a Cretaceous granite from the Central Domain of the Dabieshan massif in eastern China, yields new petrological insights into the high to ultrahigh-pressure metamorphism, experienced by the Qinling-Dabie orogen. Prior to inclusion as a xenolith in the granite during the Early Cretaceous, this eclogite xenolith had recorded a complex metamorphic evolution that complies with subduction and exhumation processes experienced by the continental crust of the South China Block. Well-preserved mineral parageneses substantiate the prograde and retrograde stages revealed by inclusions in porphyroblastic garnet and zoned minerals such as garnet, omphacite and amphibole in the matrix. The relatively low P/T re-equilibration during a late metamorphic stage was textually inferred by the presence of aluminous and calcic-subcalcic amphiboles such as katophorite, edenite, taramite and pargasite as main matrix phases. According to our U/Pb, Rb/Sr and new 40Ar/39Ar geochronological results, namely109 ± 1 and 112 ± 2 Ma plateau ages for muscovite and amphiboles, respectively, two successive but distinct cooling stages account for the thermal history of the granite–migmatite gneiss dome that forms the Central Dabieshan Domain. We argue that prior to the Cretaceous doming, the Central Dabieshan Domain experienced a tectono-metamorphic evolution similar to that observed in the high-pressure to ultra high-pressure units developed in the Southern Dabieshan Domain and Hong’an massif.  相似文献   

13.
Calcic amphiboles are ubiquitous in the East Bull Lake anorthosite-gabbro complex, northeastern Ontario. The mode of occurrence suggests the amphiboles replaced clinopyroxene throughout the stratigraphic levels of the pluton, but they are also prolific in the top younger units. Three types of amphiboles, namely (1) tremolite-actinolite, (2) actinolitic hornblende and (3) hornblende, were identified. The composition of the amphiboles shows that they define a continuous series without any obvious compositional-miscibility gap. The analyses further indicated that the amphiboles evolved from actinolite to hornblende through coupled substitution involving edenite and tschermakite end members. Among the three coexisting amphiboles, chlorine is concentrated in hornblende. This is due to preferential location of hornblende along grain boundaries and/or its favourable structure.The compositional variability of amphiboles is controlled by (1) bulk rock composition and (2) faulting and fracturing. The most Fe- and Al-rich hornblendes are confined generally to top units in the gabbro. These units are rich in Si and Fe, but relatively poor in Mg. The Mg-rich tremolite is restricted to a Si-poor, Mg-rich troctolite unit. Amphiboles in gabbro samples from fault zones also contain relatively Mg-rich calcic amphibole. The fault gabbro is highly oxidized.  相似文献   

14.
The geological position and probable origin of nepheline-bearing alkaline syenite (pulaskite) found within foyaite of the Khibina pluton, Kola Peninsula, Russia, are discussed. A large body of pulaskite (4.5 km2) was identified under the Quaternary deposits in the eastern part of the pluton as a result of gravimetric surveying and drilling. Genetic relations between pulaskite and the host foyaite were examined by whole-rock chemistry, including major and trace elements, the composition of the rock-forming clinopyroxenes and the diagram of phase equilibria in the system NaAlSiO4–KAlSiO4–SiO2–H2O. The results regarding mafic silicates show that pulaskite may constitute the less evolved member of a pulaskite-foyaite series, which suggests that it was formed by feldspar fractionation from an almost eutectic phonolitic melt, the parental one for both foyaite and pulaskite. The geochemical data, however, also enable us to assume the probability of additional petrogenetic mechanisms. The trace element abundance patterns may provide preliminary evidence for a process of crustal contamination of a mantle-derived phonolite magma. This process may have contributed to the genesis of the pulaskite.  相似文献   

15.
徐州-宿州地区中生代闪长质岩石中存在丰富的榴辉岩类捕虏体。对该类捕虏体的岩相学和矿物化学研究表明,其中的角闪石具有4种产状：1）位于石榴石中的早期角闪石包裹体,为镁质普通角闪石;2）与榴辉岩中矿物平衡存在的原生角闪石,为韭闪石或韭闪石质普通角闪石;3）位于石榴石和单斜辉石周边的退变角闪石,主要为浅闪石质和阳起石质普通角闪石;4）沿单斜辉石解理分布的出溶角闪石,主要为浅闪石、浅闪石质角闪石和含亚铁韭闪石质普通角闪石。不同产状角闪石矿物化学成分的差异和温压估算结果显示,榴辉岩类捕虏体经历了一个顺时针的P—T演化轨迹,进而反映了中生代早期华北克拉通东部造山作用的存在。  相似文献   

16.
河北平泉光头山碱性花岗岩中的钠铁非石   总被引：1，自引：0，他引：1       下载免费PDF全文
韩宝福  洪大卫 《地质科学》1994,29(2):159-164
碱性花岗岩一般以含钠质镁铁硅酸盐矿物为特征,但光头山碱性花岗岩中除钠铁闪石和霓辉石外,还有钢铁非石。钠铁非石是一种三斜晶系的富钛、铁、铀的单链非辉石类硅酸盐矿物,通常和钠质辉石共生。和钠质角门石、钠质辉石一样,钠铁非石也是一种碱性指示矿物,只是比较少见。过碱性岩浆岩中是否出现钢铁非石,主要受岩浆的温度、氧逸度和成分的控制。钠铁非石形成于过碱性岩浆演化的晚期阶段。  相似文献   

17.
孙凯  周肃  赵志丹  张琳琳  刘栋 《岩石学报》2011,27(12):3718-3726
出露于雅鲁藏布江缝合带北侧尼木县的变质岩主要由石榴黑云片麻岩和黑云斜长角闪角岩组成.研究表明岩石变质程度达到角闪角岩相-辉石角岩相;石榴子石变斑晶具有生长环带,角闪石均为钙质角闪石,黑云母大多为铁质黑云母和铁叶云母,长石多为更长石和中长石,少量为正长石.利用石榴子石-黑云母温度计、石榴子石-黑云母-斜长石-石英压力计和角闪石-斜长石温度及压力计计算获得石榴黑云片麻岩和黑云斜长角闪角岩的变质温度分别为619 ～661℃,695 ～ 702℃,压力范围分别为1.86～1.94kbar和3.69～4.56kbar.野外和室内研究认为岩石原岩为冈底斯带南缘叶巴组火山岩及其上部沉积岩,岩石经历了高温低压的接触变质作用.结合已有冈底斯带陆缘岩浆活动特征,对变质岩的形成环境和过程进行了反演.  相似文献   

18.
The Mendejin pluton is located in the Mianeh area, NW Iran, 550 km from Tehran. This pluton is probably of Oligo-Miocene age and is the result of extensive magmatism which occurred during and after the Alpine Orogeny. Similar plutons are common in the Alborz–Azarbaijan structural zone of Iran, and it is likely that there are concealed plutons related to this extensive Cenozoic magmatism, but due to their youth and low rates of erosion they have not yet been exposed. The Mendejin pluton is a composite body made up of four types of plutonic rocks: pink tonalite, grey tonalite, diorite and aplite. The pink tonalite is porphyritic and contains phenocrysts of plagioclase, K-feldspar and hornblende in a groundmass consisting of quartz, plagioclase, K-feldspar, hornblende, zircon, monazite, leucoxene, apatite and hematite. The grey porphyritic tonalite has more biotite, pyroxene and pyrite and less accessory phases compared with the pink tonalite. The diorite has a microporphyritic texture with phenocrysts of plagioclase, hornblende and augite. This rock also occurs as xenoliths in the Mendejin pluton. The aplitic dykes are the youngest magmatic products at Mendejin. The Mendejin tonalite contains more Cl, As, S, Cu, Ni and Zn than the global granite. These rocks are of I-type, peraluminous and calc-alkaline, with medium to high potassium, and were formed as part of a volcanic arc. The Mendejin pluton contains up to 8 ppb gold and could potentially have been the source of an economic gold deposit by leaching of Au from wall rocks and deposition in extensive hydrothermally altered marginal zones.  相似文献   

19.
During alkali metasomatism of the country-rock associated with ijolite-carbonatite complexes the development of sodic amphibole and/or pyroxene is characteristic. In this paper, some new chemical analyses of these minerals, together with published analyses from fenites of Kenya, Uganda and Tanzania, include those of co-existing pairs of amphibole and pyroxene. The common amphiboles of the fenites are magnesioarfvedsonites with 100 Mg: Mg+Fe+Mn ranging from 67 to 36. They co-exist with aegirines having 0.75 to 0.89 ions Fe+3. Most of these minerals are poor in Ca; co-existing pairs tend to show corresponding increases in Ca and in Fe+2. In the syenitic fenites of Tororo and Budeda, considered to have formed at higher temperatures, the stable mineral is aegirine-augite. New analyses of richterite, magnesioarfvedsonite and aegirine from carbonate-rich rocks are also presented, and the relation between fenites and carbonatites is discussed.  相似文献   

20.
The Purulia carbonatite of West Bengal, India is a dyke occurring within the 100 km long South Purulia Shear Zone (SPSZ), which marks the boundary between the Singhbhum Group of Rocks and the Chhotanagpur Granite Gneissic Complex (CGGC). It is composed essentially of calcite with apatite, amphibole, phlogopite, biotite, magnetite and ilmenite as common accessories. Based on optical properties and mineral chemistry two varieties of the amphibole are recognized: magnesiokatophorite and richterite. The latter is characterized by a relatively high content of Si and Na, while the former is enriched in Al and Ca. Such a composition of the amphibole is characteristic for the intermediate to the late stage carbonatite development. These two co-existing amphiboles reflect a sudden variation in total pressure within the magma chamber during the intrusion of the carbonatite dyke. It is inferred that the magnesiokatophorite started crystallizing first along with calcite and apatite. Subsequently, the ascent of carbonatitic magma to a more shallow depth (hypabyssal) resulted in the formation of the richterite. The difference in amphibole composition reflects a variation in the total pressure within the magma chamber that took place during the formation of the Purulia carbonatite. However, an alternative explanation, such as wallrock contamination, or liquid immiscibility, followed by carbonate magma segregation or magma mixing, may also be possible. There is, however, no evidence corroborating such an interpretation.  相似文献   

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