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1.
镁铁- 超镁铁岩是揭示地幔物质组成和壳幔相互作用的重要窗口，也是Ni- Cu- PGE- Cr等金属矿产资源的重要载体。不同的镁铁- 超镁铁岩体赋矿特征明显不同：蛇绿岩以产出铬铁矿床为特征，阿拉斯加型岩体主要赋含铂族元素(PGE)矿床，大型层状岩体则可同时产出铬铁矿床、PGE矿床和Cu- Ni硫化物矿床。这种成矿差异显然与赋矿岩体形成的构造背景、母岩浆经历的岩浆演化过程有关，但缺少关键控制因素的研究。前人对上述不同种类矿床的研究工作主要集中于地幔源区的部分熔融、上升过程中或岩浆房内的围岩混染和结晶分异等岩浆过程，而极少关注流体作用。近年来，实验岩石学和岩石地球化学的研究均表明幔源岩浆演化过程中的流体活动可能对成矿元素的富集迁移起到至关重要的作用，同时这些成矿元素的赋存状态和分配系数也在不断更新。厘清Cr和PGE在熔体演化——尤其是流体出溶过程中的地球化学行为，刻画并揭示其迁移富集、分离和再富集的成矿过程及控制因素，已成为当前岩浆矿床研究的热点。本文围绕富水流体与铬铁矿和PGE成矿关系的科学问题，总结了不同镁铁- 超镁铁岩体的成矿差异以及铬铁矿和PGE矿床成矿过程中的流体活动记录，提出流体性质和组分对铬铁矿和PGE迁移富集的控制作用，强调有必要开展蛇绿岩、大型层状镁铁- 超镁铁岩体和阿拉斯加型岩体的对比研究。 相似文献
2.
Sulphides, tellurides and sulpharsenides, with special reference to the platinum-group minerals (PGM), have been studied from a subeconomic Cu-Ni-PGE mineralization encountered within the Syöte section of the Lower Proterozoic (2.44 Ga) Koillismaa layered igneous complex (KLIC) in northern Finland using electron microprobe and ore-microscopical methods. The ore minerals occur partly as strata-bound patches and spots associated with spots of light-coloured secondary low-temperature silicates in the gabbronorite IV of the general igneous stratigraphic column of the complex and partly as a fine-grained impregnation in the penecontemporaneous basic sills and dykes. Among the PGM sperrylite, michenerite and a palladian bismuthian melonite have been encountered. The chemical composition is reported for these minerals as well as for the rest of the ore minerals (chalcopyrite, pentlandite, pyrrhotite, pyrite, sphalerite, cobaltite and hessite). It is concluded that volatile components played a significant role in the solution, transport and the final deposition of the sulphides and the PGM. 相似文献
3.
A series of layered basic and ultrabasic intrusions in Central Australia is similar to other folded basic complexes. The Australian examples were emplaced after a period of highgrade metamorphism and have subsequently been rotated. Chemical investigation of several of the intrusions shows that cryptic variation is present, and in at least two cases intrusions were initially of different bulk composition. It is suggested that the parent magma was partially fractionated prior to final emplacement. The relative deficiency of ultrabasic rocks in this complex (less than 10%) when compared with other complexes is attributed to this process. 相似文献
4.
A. V. Stepanova V. S. Stepanov A. N. Larionov P. Ya. Azimov S. V. Egorova Yu. O. Larionova 《Petrology》2017,25(6):566-591
The Vorochistoozersky, Nizhnepopovsky, and Severo-Pezhostrovsky gabbro-anorthosite massifs have been studied in the central part of the Belomorian Province, Fennoscandian Shield. The similarity of geological setting and rock composition of these massifs suggests their affiliation to a single complex. The age of the gabbro-anorthosites was determined by U-Pb (SHRIMP II) zircon dating of gabbro-pegmatites from the Vorochistoozersky massif at 2505 ± 8 Ma. The studied massifs were overprinted by the high-pressure amphibolite facies metamorphism. Relicts of magmatic layering and primary magmatic assemblages preserved in the largest bodies. The massifs consist mainly of leucocratic gabbros but also contain rocks of the layered series varying in composition from olivinite to anorthosite. The presence of troctolites in the layered series indicates the stability of the olivine–plagioclase liquidus assemblage and, respectively, shallow depths of melt crystallization. Despite the composition differences between gabbro-anorthosites of the Belomorian and peridotite–gabbronorite intrusions Kola provinces, these simultaneously formed massifs presumably mark a single great igneous event. It also includes the gabbronorite dikes in the Vodlozero terrane of the Karelian province, the Mistassini swarm in the Superior province, and the Kaminak swarm in the Hearne Craton, Canadian Shield. The large igneous province of age ~2500 Ma reflects the oldest stage of within-plate magmatism after a consolidation of the Neoarchean crust of the Kenorland Supercontinent (Superia supercraton). 相似文献
5.
The Early Paleoproterozoic Burakovsky complex contains Europe’s largest layered mafic-ultramafic pluton and giant Avdeevo gabbronorite dike. The pluton consists of two independent bodies of different age (the Aganozero and Shalozero-Burakovsky bodies), each having its own internal structure and contacting each other in their apical parts. Both bodies have a similar rock sequence including five differentiated zones (from bottom upward, based on the predominant cumulus assemblages): ultrabasic, pyroxenite, gabbronorite, pigeonite gabbronorite, and magnetite gabbronorite-diorite. Being generally similar to each other owing to a common differentiation trend of similar melts, these bodies differ notably in the character of their cumulus stratigraphy and, to a lesser extent, in mineral and geochemical composition. The pluton is distinguished by the presence of marker horizons—singular interlayers of high-temperature mafic cumulates emplaced in the sequence of lower-temperature gabbroid. Their origin is believed to have been associated with the influxes of fresh magma portions into the crystallizing magma chambers. Based on petrological, geochemical, and mineralogical data, the Aganozero and Shalozero-Burakovsky bodies, as well as additional intrusive phases, were derived from the compositionally similar but not identical melts of siliceous high-Mg (boninite like) series. The Avdeevo dike (2436 ± 46 Ma at ?Nd(T) = ?1.5) extends along the southeastern contact of the Shalozero-Burakovsky body and was formed almost simultaneously with it. The dike is made up of pigeonite gabbronorites, which are almost identical to the rocks of the Pigeonite gabbronorite zone of the Burakovsky pluton in geochemistry and mineral composition. It was concluded that the Burakovsky Complex was a long-lived igneous center, whose origin was related to the activity of an Early Paleoproterozoic mantle superplume. 相似文献
6.
The Petrogenesis of the Niquelandia Layered Basic-Ultrabasic Complex, Central Goias, Brazil 总被引：1，自引：0，他引：1
The Niquelandia igneous layered complex is made up of a lowersequence (LS), consisting of a basal layered zone (gabbros,peridotites, and pyroxenites), followed by an ultramafic zone(peridotites and pyroxenites), followed in turn by layered gabbros,and an upper sequence (US), composed of coronitic gabbros andanorthosites and upper amphibolites. Its stratigraphy and theproportion between ultramafic and gabbroic units resemble thoseof other layered complexes of the world, e.g. Stillwater andBushveld. The LS and US have different fractionation trendsrelated to the different liquidus phases, viz. ol (?sp), cpxand opx in the LS and ol, pl, and cpx in the US. Differentiatesappear at the top of both the LS and US. The possibility thatthe Niquelandia complex is formed by two unrelated intrusionsis rejected and a model accounting for the fractionation patternis presented. This model implies that, during crystallization,water caused a decrease in the temperature of the liquidus ofthe magma in the upper portion of the chamber. Taking into account the shape of the geotherm and its intersectionswith the liquidus temperature gradient, a point was reachedat which crystallization may have occurred simultaneously inthe lower and upper portions of the magma chamber, leaving differentiatedresidua both at the roof and in the middle of the complex. The inferred composition of the parent magma is that of a low-Tipicritic basalt of possibly transitional character, poor inincompatible elements and rich in Cr and Ni. These characteristicsimply a derivation by extensive partial melting of a relativelydepleted source in a tensional environment. The compositionof the liquid and the occurrence of metamorphic xenoliths ofthe country-rock in the uppermost gabbros suggest that the complexintruded the continental crust during a rifting episode. Theabnormal thickness of the complex (14 500 m) implies a continentalcrust comparable in thickness to the present one. 相似文献
7.
The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt, NW China. The strongly layered complex comprising garnet-bearing dunite, garnet-harzburgite, garnet-lherzolite and garnet-pyroxenite and garnet-free dunite, occurs together with eclogite embedded in various continental gneisses. The geological setting, the internal structure, bulk-composition, rare earth elements, isotopic and mineral composition data show that the garnet peridotite derives from a middle Ordovician Alaskan-type layered sub-arc cumulate intrusion of ascending mantle wedge melts. An abyssal peridotite protolith can be excluded. During the Ordovician-Silurian continental collision, thickening and foundering, the Luliangshan peridotite complex was exposed to ultrahigh pressures (UHP) reaching 5.5 GPa possibly >6 GPa at temperatures of 900 °C (perhaps up to 1000 °C) corresponding to a depth of ∼200 km. The extreme pressure conditions have been derived from thermobarometry using mineral compositions of the garnet peridotite assemblages, but they are supported by a wealth of decompression-induced mineral exsolutions in UHP minerals and by diamond inclusion in zircon. The Luliangshan garnet peridotite has experienced four stages of retrograde overprint during exhumation that lasted into the Devonian: (i) decompression-induced unmixing of the UHP minerals; (ii) garnet kelyphitisation; (iii) amphibole overprinting and (iv) serpentinization. Hydrous minerals occurring within peak metamorphic assemblage represent pseudo-inclusions, that is reaction products of reactions related to various stages of decompression and cooling rather than prograde inclusions during porphyroblast growth. 相似文献
8.
In the ophiolite series of N. Oman numerous small and large elongated podiform chromite deposits occur within the peridotite complex at a certain level of 100–200 meters below the layered zone, which grades into the overlying gabbro complex. The chromite grains were corroded after their deposition; their composition shows a large variation in Cr/Al ratio and a small variation in Cr/Fe ratio. The chromium is thought to have been liberated from clino-pyroxenes during partial melting of lherzolitic upper mantle material. Precipitation of large quantities of chromite at the specific level below the gabbro complex is related to the plagioclase- /spinel-lherzolite transition, but the influence of a change in oxygen fugacity is also considered. 相似文献
9.
The basic-ultrabasic Treknattan intrusion is an important example of a late intrusion in a solidified, evolved, layered complex and sheds light on possible mechanisms by which such associations may develop. The Treknattan intrusion, emplaced into the basic Fongen-Hyllingen intrusion shortly after the latter had solidified, consists mainly of massive or weakly layered peridotite (olivine ± Cr-spinel cumulate) and troctolite (plagioclase + olivine ± Cr-spinel cumulate). The mineral compositional range partially overlaps the most primitive end of the much larger variation-interval in the Fongen-Hyllingen intrusion. The margin of the Treknattan intrusion is sometimes outlined by massive feldspathic websterite which appears to have formed by reaction between magma and melts of gabbroic country rock. The parental magma appears to have been a relatively water-rich picritic basalt with a possible genetic relationship to the magma parental to the enveloping Fongen-Hyllingen intrusion, both displaying tholeiitic relationship between olivine and Ca-poor pyroxene, and having crystallized from relatively water-rich magmas with an early crystallization order of olivine ± Cr-spinel-plagioclase-Ca-rich pyroxene. The recognition of the Treknattan intrusion as a separate body suggests that the bulk composition of the Fongen-Hyllingen intrusion is dioritic rather than gabbroic as previously thought. 相似文献
10.
11.
Three iron, titanium-rich layered basic-ultrabasic intrusives have been described. They occur in an approximately south-north striking belt of tectonic-magmatic complex within an anteklise. Iron and titanium were concentrated in the lower or middle-lower parts of these intrusives at the early and the middle stages of differentiation, during which FeO may have played an important role. Intimate spacial and temporal association as well as common petrochemical features (i.e., high iron and titanium contents) have been found between these layered intrusives and the syenite and alkali-syenite plutons. All of these rocks are considered as hypogene products of the differentiation of the Omeishan basaltic magma. In other words, the hypogene differentiation of the iron (titanium)-rich, sub-alkali Omeishan basltic magma under the same structural-geological conditions resulted in the formation of the rock series of layered intrusives (peridotite → iron, titanium-rich ultramafic rocks → iron-, titanium-rich gabbro, plagioclasite) → syenite, alkali-syenite. 相似文献
12.
The age ranges of Upper Cretaceous lithotectonic complexes of Western Kamchatka—terrigenous Kikhchik, volcanic Irunei, and terrigenous Omgon—are analyzed to reveal their almost simultaneous deposition. The pre-Cenozoic settings of these complexes are reconstructed. Based on analysis of the composition and structural features of Late Cretaceous lithotectonic complexes and on correlation of events, the Late Cretaceous paleogeography is reconstructed. It is found that the formation of the contemporary structure of the studied region would have required significant displacement of the volcanic Irunei complex from west to east and the terrigenous Omgon complex from north to south. It is concluded that the Western Kamchatka continental block (minor lithospheric plate) was independent in the Late Cretaceous. 相似文献
13.
The Asama igneous complex, central Japan: An ultramafic-mafic layered intrusion in the Mikabu greenstone belt, Sambagawa metamorphic terrain 总被引：1，自引：0，他引：1
The Asama igneous complex comprises layered mafic and ultramafic plutonic rocks exposed over about 500×6000 m in the Mikabu greenstone belt, Sambagawa metamorphic terrain of Mie Prefecture; its margins terminate by faults, and there is no trace of chilled rocks. The exposed layered sequence is about 460 m thick, and includes dunite, plagioclase wehrlite, olivine gabbro and two-pyroxene gabbro. The crystallization sequence of essential cumulus minerals is olivine, followed by plagioclase and clinopyroxene together, and finally the appearance of orthopyroxene. Olivine systematically varies in composition from Fo89 to Fo78 with stratigraphic height in the lower to middle portion of the layered sequence. The composition of clinopyroxene changes from Ca49Mg46Fe5 to Ca40Mg47Fe13 upward in the layered sequence; cumulus orthopyroxene, which occurs at the top of the exposed layered sequence, has a composition of Ca2Mg74Fe24. Cumulus chromite occurs as disseminated grains in peridotitic rocks, and tends to increase its Fe3+/(Cr+Al+Fe3+) ratio with stratigraphic height. The most aluminous chromite [Cr/(Cr+Al) = 0.48] occurs in dunite that crystallized shortly before plagioclase began to separate as an essential phase. The Cr/(Cr+Al) ratio of the most aluminous chromite, coupled with the crystallization order of essential minerals, suggests that the Asama parental magma was moderately enriched in plagioclase and clinopyroxene components in the normative mineral diagram plagioclase-clinopyroxene-orthopyroxene. It was similar to a Hawaiian tholeiite and different from the Bushveld and Great “Dyke” parental magmas that were more enriched in orthopyroxene component; it also differed from mid-oceanic ridge basalts that are more depleted in the orthopyroxene component. The Asama clinopyroxene and chromite show characteristically high TiO2 contents and are also similar to those in Hawaiian tholeiites. The Asama igneous complex probably resulted from the crystallization of a magma of a Hawaiian (oceanic-island) tholeiite composition and formed in an oceanic island regime. 相似文献
14.
The petrogenesis of the Fiskenaesset anorthosite body has been investigated using major and trace element data for a large range of rock types from each zone of the complex. The chemistry of these ultramafic to anorthositic cumulates is interpreted in terms of crystal fractionation of a parental, trace element impoverished, tholeiitic magma, involving crystallisation of the cumulus phases olivine, orthopyroxene, clinopyroxene and (dominant) plagioclase feldspar. Amphibole appears not to have been a significant cumulus phase at any stage of crystallisation of the body, the abundant amphibole found in the rocks of the complex being produced by primary intercumulus crystallisation, supplemented by secondary metamorphic recrystallisation. Similarly, magnetite is unlikely to have been a significant early cumulus phase, although, together with chromite, it crystallised as a cumulus phase at high stratigraphic levels in the complex. The metamorphism appears to be largely isochemical, although sub-solidus metamorphic re-equilibration of the REE can be demonstrated on a grain-size scale.The spatial and temporal association between the anorthosite complex and the bordering metavolcanic amphibolites is matched by a strong similarity between the observed trace element chemistry of the amphibolites and the trace element chemistry of calculated successive liquids for the complex. This is taken to suggest a genetic relationship between the evolution of the anorthosite complex and enclosing amphibolites. The presence of trace element impoverished amphibolites (which are not cumulates) with trace element abundances comparable to those of the suggested parental liquid to the anorthosite complex, is used to derive a major element composition for the primary Fiskenasset magma. This composition approximates a moderately aluminous tholeiitic basalt, which may have been generated by hydrous fusion of previously depleted mantle. This primary magma underwent crystal fractionation under low pressure conditions, allowing the development of extensive plagioclase cumulates.The Fiskenaesset anorthosite, and similar bodies, cannot represent a cumulate residue complementary to the enclosing voluminous tonalitic gneisses, which have a calc-alkaline chemistry controlled by high pressure crystal liquid fractionation. Rather, the association between the cumulate layered complex and bordering supracrustal sequence may imply an ancient ocean crust analogue for the development of this component of Archaean high-grade terrains. It is suggested that slices of such Archaean ocean floor may be emplaced laterally into the base of the continental crust during subduction of oceanic lithosphere at Cordilleran type continental margins. 相似文献
15.
汉南镁铁层状杂岩是出露于扬子板块北缘的一个大岩体，据测同位素年代为1121-748Ma，属中元古侵位于西乡群变质岩系的岩体。杂岩体按岩石类型分为由辉长岩类组成的上部带和由辉石-橄榄岩组成的下部岩带构成。岩石化学、矿物化学和微量元素地球化学的演变与层状岩序变化相当一致。韵律层发育部位，矿物组分多次重复出现。层状岩序的稀土总量（La/Yb）N值完全符合随着层序增高、分馏趋势增加一般规律。本文系统阐述了杂岩体各为岩石的铂族元素分配特征，初步确定了铂矿化与铜镍矿化产出部位。在分析了杂岩体产出构造环境的基础上，探讨了杂岩体原始岩浆性质，估算了部分熔融程度。 相似文献
16.
《International Geology Review》2012,54(5):570-577
New data collected since 1955 on the geology of the Lovozero massif, considerably detailing and supplementing existing ideas as to its structure and geochemistry, are presented. As a result of these investigations the thickness of the ore-bearing stratified rock complex has been traced to a depth of 1700 m. Laws governing the vertical alteration of rock composition of individual series have been established as well as the fact that the amount of titanium-bearing minerals increases with depth.—Auth. English summ. 相似文献
17.
本文报道了浙江省21个中生代火成岩的Nd-Sr同位素组成,其中火山岩的εNd值为-12.6——4.9,ISr值为0.70613-0.71079,tDM年龄为1945-1296Ma;花岗岩类的εNd值为-12.9——5.8,ISr值为0.70533-0.71208,tDM年龄为1900-1230Ma,表明两者具有相似的同位素组成。这种相似性在同一火山-侵入杂岩体中表现更为明显,意味着两者在时、空、源方面具有同一性。与扬子地块的相比,华夏地块的中生代火成岩具有较低的εNd值,较高的ISr值和较古老的Nd模式年龄,这种差异可能主要同这两个区域内基底变质岩在形成时代和成分上的差异有关。通过Sm-Nd同位素组成的对比研究,笔者认为,浙江境内的中生代火成岩可能主要是由基底变质沉积岩衍生的。原始岩浆的形成可能同中、下地壳岩石的熔融有关。 相似文献
18.
汉南金水-青泥坑镁铁层状杂岩体位于扬子板块北缘汉南地体东北部,岩体侵位于中元古代西乡群。岩体出露面积大于500km~2。杂岩体主要由镁铁质辉长岩和部分超镁铁质辉石岩和橄榄岩组成。按层状岩序和岩石类型可以划分为上、下两个岩带,即由辉长岩类组成的上部带和由辉石岩-橄榄岩-粗粒蚀变辉长岩组成的下部岩带。研究表明,岩体的岩石化学、矿物化学和微量元素地球化学与层状岩序的演变相一致。韵律层发育部位,矿物组分多次重复出现,反映了形成杂岩体的岩浆有过多次侵位活动。还表明,层状岩序稀土总量和(La/Yb)_N值随层序增高而增加分馏趋势的一般规律。系统阐述了杂岩体各类岩石铂族元素分配特征。初步确定了铂矿化与铜镍矿化产出部位,讨论了铂族元素成矿作用问题。报告在分析了杂岩体产出的地质构造环境的基础上,探讨了杂岩体原始岩浆源的性质,同时估算了部分熔融程度。 相似文献
19.
In the Wealden beds of the Dalum oil pool (NW-Germany), cycles of the following composition have been deposited especially on synsedimentary uplifts: Bituminous shales (at the base) — shales with cyrena layers — cyrena coquinas (at the top). The cyrena and gastropod shells are preserved in aragonite, if they are embedded in shale or surrounded by oil, which stopped the diagenesis. Water saturated coquinae, poor in clay, are always calcitisated. As a consequence, the transformation aragonite → calcite should have been performed by solution and recrystallisation. Only in aragonitic shells, organic structures are visible by fluorescence microscopy. In the bituminous shales, admixtures of Mg-calcite have been preserved sporadically. 相似文献
20.
《International Geology Review》2012,54(2):137-142
Chemical thermodynamic data and mineralogical-geochemical observations help to define the conditions of precipitation of uranium arid its satellites from infiltration waters in the thinning-out area of zones of layered limonitization. Localization of mineralisation, morphology of the ore segregations, and mineral composition of the ores are dependent on the grade of uranium content of the oxygenated formation solutions and their amounts of carbonate ion. It has been shown that ore bodies with narrow “saccate” particles, sometimes disintegrating into a series of lensoid segregations and often consisting of finely dispersed coffinite, develop where the ore-forming waters have low concentrations of dissolved uranium - less than 5. 10-5 g/liter (with ΣaCO on the order of 10-2 g/kg of H2O). The scheme of infiltration ore formation in thermodynamic respects is of little use in explaining the origin of the black-pitchblende ores superimposed on ihe limonitized rocks.—Author. 相似文献