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1.
New geochemical data are discussed on the magmatic complexes of the Koksharovka alkaline ultrabasic massif of Late Jurassic age obtained by the ICP-MS method. Based on the first results on rare earth geochemistry of carbonatites and associating pyroxenites and geological observations, the magmatic origin of the Koksharovka carbonatites was substantiated, and the problems of formation of accompanying igneous rocks were considered.  相似文献   

2.
The magmatic heritage of carbonatites can be identified on the basis of a combination of geological criteria such as, their mode of occurrence, the nature of associated igneous rocks, the presence of minerals of igneous origin, fenitization, characteristic trace element contents and isotopic composition. Late Proterozoic Samalpatti carbonatites were studied in view of these criteria, and were found to contain metamorphic minerals that normally form under thermal metamorphic conditions and which have unusual chemical compositions. A combination of criteria points clearly to a magmatic origin for these carbonatites. Field relations indicate that the dominant modes of intrusion of carbonatite into the encompassing pyroxenites and syenites include small dykes, veins, or lenses. The igneous nature of these carbonatites has been described elsewhere and chemically they are classified as calico-carbonatites. Currently, very little is known about the metamorphic textures and mineralogy observed in the Samalpatti carbonatites. In this study, several metamorphic minerals are reported including diopside, grossularite, vesuvianite, K-feldspar and wollastonite, and a hornfelsic texture is described. These mineral phases and texture characterize thermal metamorphism under low pressure and high temperature (LP-HT) metamorphic conditions (650°_750°C) or metasomatism aided by hot-fluid advection. The metamorphic nature of minerals reported is also confirmed by electron microprobe study. The Samalpatti carbonatite samples show much lower values of characteristic trace elements (P, Sr, Ba, Zr, Nb, Th, Y and REEs) than average concentrations for magmatic carbonatite. Stable isotopic (d13C and d18O) compositions of Samalpatti carbonatites do not fall in the primary igneous carbonatite (PIC) domain. The petrological and chemical signatures of these carbonatites suggest metasomatism in conjunction with fluid advection. Such a metasomatic process may drastically change the chemistry of the rocks in addition to enrichment of heavier stable isotopes. During this metasomatic process, characteristic elements would be dissolved in the high d18O fluid, and together with Rayleigh fractionation would contribute to enhanced concentrations of 13C and 18O in Samalpatti carbonatites.  相似文献   

3.
岩浆(型)碳酸岩研究进展   总被引：19，自引：0，他引：19  
主要从岩石学，矿物学，岩石分类，C，O，Sr同位素，碳酸岩与矿化的关系等各方面对（碱性）碳酸岩的研究进行了较为全面的总结，并结合近20年来实验岩石等，流体包裹体研究，CO2^- H2O－NaCl流体体系的性质的研究，对碳酸岩岩浆的来源及成因，岩浆－热液的演化进行了分析和探讨，碳酸岩形成至少经历了三个阶段，即岩浆阶段，岩浆期后阶段（气相碳酸岩／岩浆热液阶段），交代碳酸岩阶段，而作为与碳酸岩在空间和成因上有密切联系的基性，超基性岩，碱性岩杂岩体，则经历了碳酸岩成岩阶段以前的岩浆不混熔作用，结晶分异作用，岩浆结晶作用以及碳酸岩形成之后的围岩蚀变（霓长岩化）作用。  相似文献   

4.
Zircons from a nepheline-syenite of the Fuerteventura Basal Complex were dated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The age obtained from a total of 21 U–Th–Pb analyses is 25.4 ± 0.3 Ma (2σ) indicating a late Oligocene–early Miocene crystallization. This age is consistent with new K–Ar ages on nepheline-syenites and pyroxenites, and contradicts previously published 39Ar–40Ar (feldspar) ages that were interpreted to represent a late Cretaceous–early Paleocene, pyroxenitic–syenitic magmatic episode. These new geochronological data are consistent with both field observations and most of the previously published ages on alkaline silicate rocks and associated carbonatites of Fuerteventura. Therefore, they strongly support the existence of a single, late Oligocene–early Miocene event of alkaline–carbonatitic magmatism in the Basal Complex of Fuerteventura, taking place at approximately 25 Ma and comprising: alkaline-pyroxenites, melteigites-ijolites, nepheline-syenites and carbonatites, as well as their volcanic equivalents and associated dykes.

These new data provide an estimate for the length of time that it took the island to grow, thus eliminating one of the major problems in explaining its development by a hot-spot model.  相似文献   


5.
Associated syenitic rocks and carbonatites from Ihouhaouene, Algeria, have been investigated for their Sr and Nd isotope and trace element geochemistry. A zircon U-Pb emplacement age (1994 +22 -17 Ma) has been obtained from the carbonatites. The REE characteristics, among which the significant and approximately constant negative Eu anomaly and the evolution of (La/Ce)N and (Yb/Lu)N ratios which increase sympathetically with total REE abundances, are considered to be of purely magmatic origin. They are used to constrain the genetic links between syenites and carbonatites. Sr and Nd isotopes suggest a similar source for carbonatites and syenites, which is enriched compared to a chondritic reference: Nd(T)=-6.4 to -8.6 and ISr(T)=0.7097. These features are interpreted as evidence of contamination of a mantle-derived magmatic precursor by continental crust, occurring in a magmatic chamber.  相似文献   

6.
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7.
Large igneous provinces (LIPs) and carbonatites   总被引：4，自引：0，他引：4  
There is increasing evidence that many carbonatites are linked both spatially and temporally with large igneous provinces (LIPs), i.e. high volume, short duration, intraplate-type, magmatic events consisting mainly of flood basalts and their plumbing systems (of dykes, sills and layered intrusions). Examples of LIP-carbonatite associations include: i. the 66 Ma Deccan flood basalt province associated with the Amba Dongar, Sarnu-Dandali (Barmer), and Mundwara carbonatites and associated alkali rocks, ii. the 130 Ma Paraná-Etendeka (e.g. Jacupiranga, Messum); iii. the 250 Ma Siberian LIP that includes a major alkaline province, Maimecha-Kotui with numerous carbonatites, iv. the ca. 370 Ma Kola Alkaline Province coeval with basaltic magmatism widespread in parts of the East European craton, and v. the 615–555 Ma CIMP (Central Iapetus Magmatic Province) of eastern Laurentia and western Baltica. In the Superior craton, Canada, a number of carbonatites are associated with the 1114–1085 Ma Keweenawan LIP and some are coeval with the pan-Superior 1880 Ma mafic-ultramafic magmatism. In addition, the Phalaborwa and Shiel carbonatites are associated with the 2055 Ma Bushveld event of the Kaapvaal craton. The frequency of this LIP-carbonatite association suggests that LIPs and carbonatites might be considered as different evolutionary ‘pathways’ in a single magmatic process/system. The isotopic mantle components FOZO, HIMU, EM1 but not DMM, along with primitive noble gas signatures in some carbonatites, suggest a sub-lithospheric mantle source for carbonatites, consistent with a plume/asthenospheric upwelling origin proposed for many LIPs.  相似文献   

8.
The Newania carbonatite complex of Rajasthan, India is one of the few dolomite carbonatites of the world, and oddly, does not contain alkaline silicate rocks thus providing a unique opportunity to study the origin and evolution of a primary carbonatite magma. In an attempt to characterize the mantle source, the source of carbon, and the magmatic and post-magmatic evolution of Newania carbonatites, we have carried out a detailed stable carbon and oxygen isotopic study of the complex. Our results reveal that, in spite of being located in a metamorphic terrain, these rocks remarkably have preserved their magmatic signatures in stable C and O isotopic compositions. The δ13C and δ18O variations in the complex are found to be results of fractional crystallization and low temperature post-magmatic alteration suggesting that like other carbonatites, dolomite carbonatites too fractionate isotopes of both elements in a similar fashion. The major difference is that the fractional crystallization of dolomite carbonatites fractionates oxygen isotopes to a larger extent. The modes of δ13C and δ18O variations in the complex, ?4.5?±?1‰ and 7?±?1‰, respectively, clearly indicate its mantle origin. Application of a multi-component Rayleigh isotopic fractionation model to the correlated δ13C versus δ18O variations in unaltered carbonatites suggests that these rocks have crystallized from a CO2 + H2O fluid rich magma, and that the primary magma comes from a mantle source that had isotopic compositions of δ13C ~ ?4.6‰ and δ18O ~ 6.3‰. Such a mantle source appears to be a common peridotite mantle (δ13C = ?5.0?±?1‰) whose carbon reservoir has insignificant contribution from recycled crustal carbon. Other Indian carbonatites, except for Amba Dongar and Sung Valley that are genetically linked to Reunion and Kerguelen plumes respectively, also appear to have been derived from similar mantle sources. Through this study we establish that dolomite carbonatites are generated from similar mantle source like other carbonatites, have comparable evolutionary history irrespective of their association with alkaline silicate rocks, and may remain resistant to metamorphism.  相似文献   

9.
The Turiy Massif, lying within the Kandalaksha Graben, and onthe southern coast of the Kola Peninsula, contains carbonatites,phoscorites, melilitolites, ijolites and pyroxenites withinone central and four surrounding satellite complexes. Sr–Ndisotopic data from the central complex phoscorites and carbonatites,and the nearby Terskii Coast kimberlites, combined with otherrecently published data on the Devonian Kola Alkaline Province,allow us to redefine the position of the Kola Carbonatite Line(KCL) of Kramm (European Journal of Mineralogy 5, 985–989,1993). We propose that the revised-KCL mantle sources includea lower-mantle plume, and a second enriched source, which alsocontributed to the Terskii Coast and Archangelsk kimberlites.The Turiy Massif silicate rocks and northern complex carbonatiteshave more enriched isotopic signatures than the distinct, anddepleted signatures of the central complex phoscorites and carbonatites,particularly with respect to  相似文献   

10.
碳酸岩Sr、Nd、Pb 同位素地球化学研究评述   总被引：3，自引：0，他引：3  
碳酸岩是出露相对较少的幔源岩石，其中Sr与Nd是研究地幔物质组成的主要对象之一。本文统计了世界上主要碳酸岩的锶、钕、铅同位素组成特征；研究显示，碳酸岩源区主要是洋岛玄武岩高U／Pb的HIMU端员和富集端员(EM1或EM2)的混合作用；此外大部分碳酸岩的锶、钕同位素落在大洋玄武岩范围内；这些均表明其成因与地慢柱有密切联系。碳酸岩及与之共生的硅酸岩的同源或独立源区模式部很难充分解释两者同位素组成特征，逭反映碳酸岩的演化模式涉及更复杂的过程。可能是俯冲作用使碳酸岩源区经历不同时间和程度的富集、亏损过程导致地幔源区成分不均一。  相似文献   

11.
In most alkaline-ultrabasic-carbonatite ring complexes, the distribution of trace elements in the successive derivatives of mantle magmas is usually controlled by the Rayleigh equation of fractional crystallization in accordance with their partition coefficients, whereas, that of late derivatives, nepheline syenites and carbonatites, is usually consistent with trends characteristic of silicate-carbonate liquid immiscibility. In contrast to the carbonatites of ring complexes, carbonatites from deep-seated linear zones have no genetic relation with alkaline-ultrabasic magmatism, and the associated alkaline rocks are represented only by the nepheline syenite eutectic association. The geochemical study of magmatic rocks from the Vishnevye Gory nepheline syenite-carbonatite complex (Urals), which is assigned to the association of deep-seated linear zones, showed that neither differentiation of a parental melt nor liquid immiscibility could produce the observed trace element distribution (Sr, Rb, REE, and Nb) in miaskites and carbonatites. Judging from the available fragmentary experimental data, the distribution patterns can be regarded as possible indicators of element fractionation between alkaline carbonate fluid and alkaline melt. Such trace element distribution is presumably controlled by a fluid-melt interaction; it was also observed in carbonatites and alkaline rocks of some ring complexes, and its scarcity can be explained by the lower density of aqueous fluid released from magma at shallower depths.  相似文献   

12.
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   

13.
Most carbonatites occur in relatively stable, intra\|plate areas but some are found to occur in near to plate margins and may be linked with plate separation (Woolley, 1989). Although many carbonatites have been discovered to occur in the orogenic belts in recent years, most of these rocks are related to post\|orogenic magmatism, that is, the rocks occur in the specially extensional setting. Therefore it is unusual that such magmatic rocks occur in the typical convergent environment. Here we report carbonatites and associated ultramafic and mafic rocks in the core of the eastern Himalayan syntaxis. The eastern Himalayan syntaxis consists of three tectonic units: the Gangdise, the Yarlung Zangbo, and the Himalayan units, each of which is bounded by faults (Liu & Zhong, 1997). The Himalayan unit, the northernmost exposed part of the Indian plate, is divided into two complexes, the amphibolite facies complex in the south and the granulite facies complex in the north. The granulite facies complex in the Himalayan unit have been argued to experience high\|pressure metamorphism and represent materials buried to upper\|mantle depths (Liu & Zhong, 1997). The carbonatites and associated ultramafic and mafic rocks only occur in the granulite facies rocks and are divided into two belts: northern and southern belts.The northern belt extends at least 30km, and is about 20km in width. The southern belt extends several kilometers, and is 3km or so in width. Each belt consists mainly of differently compositional dykes, extending parallel to gneissosity of granulite facies gneiss. Carbonatitic agglomerates are observed in the northern belt. From the center of carbonatite dykes to country rocks, five types of rock are observed: the center parts of carbonatites, the rim parts of carbonatites, ultramafic and mafic rocks, altered rocks and country rocks. The gneissosity of country rock was deformed by intrusion of dykes.  相似文献   

14.
LA-ICP MS data are presented for ilmenites from different rocks of the alkaline complexes of the Ukrainian Shield (Chernigovka carbonatite, Oktyabr’skii, Malaya Tersa, and Southern Kal’chinskii gabbrosyenite massifs). Ilmenites from the early intrusive phases (alkaline pyroxenites, gabbroids, and ultramafic rocks) have the elevated contents of Cr, Co, Ni, and V, while ilmenites from later alkaline and nepheline syenites, monzonites, and carbonatites are significantly enriched in Nb and Ta, which is caused by change in the alkalinity of the mineral-forming medium. Zr shows the more intrinsic behavior: its content is higher in the ilmenites from basic and ultrabasic rocks than in those from the nepheline syenites and carbonatites. This is mainly caused by temperature conditions of the formation of differentiated alkaline complexes. The carbonatites contain magnesian ilmenite (up to 22 mol % MgTiO3). Variations of Mg contents in ilmentes are correlated with Mg number of mafic minerals and depend also on the iron oxidation state (amount of magnetite) in the carbonatites. In the alkaline massifs of the Ukrainian Shield, ilmenites usually have the low contents of hematite end member (3–7 mol %). Ilmenite serves as a sensitive indicator of temperature, oxygen fugacity, and alkalinity of the mineral-forming medium during crystallization.  相似文献   

15.
霓长岩岩石学特征及其地质意义评述   总被引：9，自引：2，他引：7  
杨学明  范宏瑞 《地质论评》2000,46(5):480-490
本文以几个典型实例,综合评述了与碱性岩和碳酸岩有关的碱质交代蚀变岩－霓长岩的岩石学特征。按照在霓长岩化作用过程中形成的新生矿物组合、结构构造、化学成分、空间分布及物质来源等特征,霓长岩可以分为低级、中级、高级、接触和脉状等５种类型。控制霓长岩化作用５的主要因素包括：（１）碳酸岩或者碱性岩的岩石学特征和侵位条件;（２）流体的来源、性质和成分;（３）围岩的矿物组合、结构构造和化学成分;（４）霓长岩化作  相似文献   

16.
Summary ?A new occurrence of carbonatites associated with intrusive ijolite and syenite has been discovered within the Hawasina Complex underlying the Semail Ophiolite Complex at the southern part of the Rawda-Masfut ridge, Northern Oman Mountains. The carbonatites occur as dikes and sills with lengths of several hundreds of meters and range in composition from calciocarbonatites to ferruginous calciocarbonatites. The carbonatites intruded the ijolite and the associated radiolarian cherts of the Early Cretaceous Sid’r Formation. The close spatial association of carbonatite, ijolite, syenite and radiolarian cherts along with geological, petrographical and geochemical data indicates that these rocks are of intra-oceanic origin. Petrological and field relationships between the carbonatite and associated alkaline silicate intrusives from the Masfut area are consistent with the carbonatites being generated as derivative magmas through liquid immiscibility. They appear to represent magmas related to the volcanism associated with regional crustal extension that preceded the genesis of the Semail Ophiolite. Received April 19, 2001; revised version accepted February 18, 2002  相似文献   

17.
The Siluro-Ordovician Loch Borralan (c. 430 Ma) and Loch Ailsh Complexes (c. 439 Ma) comprise a suite of intrusive rocks ranging in composition from clinopyroxenites, through potassic melasyenites to quartz syenites. The rock suite at Loch Borralan also includes nepheline syenite. Geochemical data in the literature indicate that the intrusions are alkaline, with pronounced enrichments in LILE and LREE relative to contemporaneous calc-alkaline magmatic centres further to the south-east, although they share similar high LILE/Nb, subduction-related characteristics. The Loch Borralan Complex is associated with marginal gravity and magnetic anomalies which can be interpreted in terms of a shallow body less than 400 m thick. Analysis of rocks and drill core revealed widespread elevated Pt and Pd values in pyroxenites and syenites in both complexes. The highest concentrations, up to about 900 ppb Pt+Pd, occur in pyroxenites in the Loch Borralan Complex. Extensive archived drill core provides an excellent section through the marginal pyroxenites, which host the PGE at Loch Borralan. The pyroxenites show unusual petrological features; early clinopyroxene is followed by biotite, apatite, magnetite, sphene and plagioclase with later garnet, which might be metasomatic in origin. Sulphides occur in minor amounts. High-temperature shearing produced local granulation and mylonitisation. Later brittle deformation caused extensive micro-fracturing and the introduction of minor carbonate veining. Platinum-group minerals (PGM) were located in a number of samples with high PGE assay values. These occur as clusters of grains around 1–2 m in diameter, and are difficult to identify uniquely. A few grains appear to be magmatic; these are Pt and PtPd sulphides that occur enclosed in clinopyroxene or garnet. All other grains occur in late fractures or along grain boundaries. These include sperrylite (PtAs2), Pd antimonides and PdBi tellurides, along with hessite (Ag2Te). They occur in microfractures accompanied by carbonate and barite and fine-grained sulphides and are probably of secondary origin. The PGE in the pyroxenites may have been introduced during the magmatic phase of the intrusion but the observed distribution of PGM results from low-temperature, hydrothermal remobilisation following brittle deformation and introduction of fluids.
Michael T. StylesEmail: Phone: +44-115-9363414Fax: +44-115-9363352
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18.
The results of a Sr isotopic study of coexisting alkaline silicate rocks and carbonatites of two Cretaceous alkaline complexes of India, Amba Dongar (Deccan Flood Basalt Province) and Sung Valley (Rajmahal–Bengal–Sylhet Flood Basalt Province) are reported. The overlapping nature of initial Sr isotopic ratios of alkaline rocks and carbonatites of both the complexes is consistent with a magmatic differentiation model. Modelling of initial 87Sr/86Sr variation in alkaline rocks of Amba Dongar is consistent with a process of crustal assimilation by the parent magma undergoing simultaneous fractional crystallization of silicate rocks and silicate–carbonate melt immiscibility. A maximum of ∼5% crustal contamination has been estimated for the parent magma of Amba Dongar, the effect of which is not seen in the Sr isotope ratio of carbonatites generated by liquid immiscibility. A two point Rb–Sr isochron of the Sung Valley carbonatites, pyoxenite and a phlogopite from a carbonatite yielded an age of 106±11 Ma, which is identical to the 40Ar–39Ar age of this complex. The same age for the carbonatites and the alkaline silicate rocks, similar initial Sr ratios and the higher Sr concentration in the former than the latter favour the hypothesis of liquid immiscibility for the generation of the Sung Valley. The higher initial 87Sr/86Sr ratio for these complexes than that of the Bulk Earth indicates their derivation from long-lived Rb/Sr-enriched sources.  相似文献   

19.
A great deal of data is available on the geochemistry of the carbonatite family as well as diverse sedimentary, metamorphic and endogenic carbonate rocks. The distinctive geochemical features of carbonatites are expressed first of all in their simultaneous enrichment in Sr, Ba, ree and V. Since the carbonatite family is related both to alkaline petrogenesis and a mantle origin, these associations allow distinction of carbonatites from the large variety of other carbonate rocks. At the same time, carbonatites associated with different types of alkaline rocks under different geologic-tectonic settings differ in contents of a number of elements (Sr, Ba, Nb, ree, Pb, Zn, P). These differences permit the geochemical classification of various rock associations of carbonatites. This geochemical classification is of practical interest because the ore productivity of the various associations is different.  相似文献   

20.
The present study introduces the carbonatite in the northern part of the Korean Peninsula for the first time.Recent exploration and development of the phosphorus-bearing carbonate rocks in the area have accumulated new geological data which gave us an opportunity to study origin of the carbonate rocks.We conducted geological survey,geochemical analyses of trace elements and rare earth elements,and carbon and oxygen isotope analyses for the carbonatites from Ssangryong,Pungnyon,Yongyu and Puhung districts of the northern part of the Korean Peninsula.This research confirms that the phosphorus-bearing carbonate rocks are carbonatite originating from the mantle.The studied carbonatites are distributed at the junctions of ring and linear structures or around their margins and contain a greater amount of REEs,Y,and Sr than carbonate rocks.The carbonatites in Yongyu and Puhung area show evidence that they were formed from mantle plume generated at the lower mantle and display similar fractionation characteristics to carbonatites in Barrado Itapirapua in Brazil and Kalkfeld and Ondurakorume in Namibia.REE patterns of the carbonatites are typical of carbonatites and the carbon and oxygen isotope analyses demonstrate that the carbonatites were originated from mantle.The carbonatites from the northern part of the Korean Peninsula have a great potential for sources of REE,Y,PGE(platinum group elements),copper,and gold.  相似文献   

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