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1.
V.D. Kozlov 《Russian Geology and Geophysics》2009,50(1):29-42
The meteoritic-material-normalized REE patterns of rare-metal granite intrusions of the ore-bearing Kukul'bei complex (J2–J3), eastern Transbaikalia, were studied. It is shown that the intrusions were initially enriched in granitophile volatiles and trace elements (rare metals), i.e., this phenomenon is not related to the differentiation of their parental magma chambers. On the differentiation of the Kukul'bei rare-metal intrusions, the REE contents decrease in passing from granites of the main intrusive phase (MP) to late leucocratic differentiates (muscovite and amazonite granites), the differentiates become more enriched in granitophile elements, and their rare-metal contents drastically increase as compared with the MP granites. The ore-bearing bodies of muscovite and amazonite granites have extremely low REE contents and the highest contents of granitophile (including ore-forming) elements.The REE patterns of the Kukul'bei intrusive differentiates are not universal among rare-metal intrusions. By the example of highly ore-bearing rare-metal granite intrusions of the Erzgebirge, Central Europe, it has been established that their late deep-seated differentiates (ultrarare-metal lithionite-zinnwaldite Li-F-granites) accompanied by highly productive Sn-W mineralization concentrate both granitophile elements and REE (particularly HREE). Among the studied Transbaikalian rare-metal intrusions of the Kukul'bei complex, only the differentiates of the most ore-bearing Sherlovaya Gora intrusive system belong to the above type. The analysis of the REE patterns of the Kukul'bei granites confirmed the earlier conclusions on the low ore potential of the rare-metal mineralization of the studied intrusive complex. 相似文献
2.
E. V. Badanina L. F. Syritso V. S. Abushkevich R. Thomas R. B. Trumbull 《Petrology》2008,16(3):299-311
Dikes, stocks and/or sheet flows of felsic volcanic and subvolcanic rocks are typically observed in the vicinity of rare-metal Li-F granite massifs. Their ubiquitous spatial association to rare-metal granites and, often, geochemical affinity to them suggest their certain petrological relation. Compositionally unique ultrapotassic trachydacites enriched in many rare elements were found among these rocks within the Khangilay complex of ore deposits in Eastern Transbaikalia. Melt inclusions in rock-forming quartz were studied to reconstruct the composition and evolution of parent melt. The obtained data demonstrated the existence of a super-potassic peraluminous melt (K2O = 6.12 wt %, Na2O = 1.08 wt %) having elevated contents of rare lithophile elements (730 ppm Rb2O and 900 ppm BaO). The ion-microprobe content of Li is 354.23 ppm at a relatively low F content (up to 0.5 wt %). The residual melt is characterized by the most unusual composition: extremely low contents of mafic components and basicity (< 0.5 wt % femic oxides), a high Al index (A/CNK = 1.53) at comparatively low SiO2 (60 wt %), and high total sodic alkalinity (more than 10 wt % K2O + Na2O; 6.11 wt % Na2O). Such a composition corresponds to ongonite magma. However, the melt contains no F but has a high Cl content (0.34 wt %), which corresponds to the limit Cl saturation of haplogranite melt. SHRIMP-II U-Pb zircon dating showed significant difference between rare metal granites and trachyrhyodacites of the Khangilay complex of ore deposits: 139.9 ± 1.9 Ma and 253.4 ± 2.4 Ma, respectively. The geochemical similarity of these rocks, primarily in terms of abundance of refractory elements, REE distribution patterns, and initial Sr ratio, indicates their derivation from similar protolith. 相似文献
3.
This paper focuses on reasons for the appearance of tetrad effects in chondrite-normalized REE distribution patterns of granitoids
(Li-F granites, peralklaine granites, ongonites, fluorine-rich rhyolites, and granitic pegmatites). The analysis of published
data showed that the alteration of such rocks by high- and/or low-temperature metasomatic processes does not result in most
cases in the appearance or enhancement of M-type tetrad effects in REE patterns. These processes are accompanied by the removal
or addition of lanthanides, a W-type sag appears between Gd and Ho, and negative or positive Ce anomalies develop sometimes
in REE patterns. The formation conditions of peculiar rocks enriched in Ca and F from the Ary Bulak ongonite massif (eastern
Transbaikalia) and the character of REE distribution in these rocks and melt inclusion glasses were discussed. Based on the
obtained data and the analysis of numerous publications, it was concluded that REE tetrad effects in rare-metal granitoids
are caused by fluoride-silicate liquid immiscibility and extensive melt differentiation in the accumulation chambers of fluorine-rich
magmas. A considerable increase in fluorine content in a homogeneous granitoid melt can cause its heterogenization (liquation)
and formation of fluoride melts of various compositions. The redistribution of lanthanides between the immiscible liquid phases
of granitoid magma will result in the formation of M-type tetrad effects in the silicate melts, because the REE patterns of
fluoride melts exhibit pronounced W-type tetrad effects. The maximum M-type tetrad effect between La and Nd, which is observed
in many rare-metal granitoids, is related to the character of REE partitioning between fluoride and silicate melts and F-
and Cl-rich magmatic fluids. The low non-chondritic Y/Ho ratio (<15) of many rare-metal granitoids may be indicative of a
contribution of fluoride melts to the differentiation of F-rich silicic magmas, from which these rocks were formed. The influence
of high-temperature F-Cl-bearing fluids on melts and/or granitoid rocks results in an increase in Y/Ho ratio owing to the
elevated solubility of Ho in such fluids. 相似文献
4.
G. P. Zaraisky A. M. Aksyuk V. N. Devyatova O. V. Udoratina V. Yu. Chevychelov 《Petrology》2009,17(1):25-45
The Zr-Hf geochemical indicator, i.e., the Zr/Hf ratio (in wt %) in granitic rocks is proposed to be used as the most reliable indicator of the fractionation and ore potential of rare-metal granites. It was empirically determined that the fractional crystallization of granitic magma according to the scheme granodiorite → biotite granite → leucogranite → Li-F granite is associated with a decrease in the Zr/Hf ratio of the granites. The reason for this is the stronger affinity of Hf than Zr to granitic melt. This was confirmed by experiments on Zr and Hf distribution between granitic melt and crystals of Hf-bearing zircon (T = 800°C, P= 1 kbar). The application of the Zr/Hf indicator was tested at three classic territories of rare-metal granites: eastern Transbaikalia, central Kazakhstan, and the Erzgebirge in the Czech Republic and Germany. The reference Kukul’bei complex of rare-metal granites in eastern Transbaikalia (J3) is characterized by a uniquely high degree of fractionation of the parental granitic melt, with the granites and their vein derivatives forming three intrusive phases. The biotite granites of phase 1 are barren, the leucogranites of phase 2 are accompanied by greisen Sn-W mineral deposits (Spokoininskoe and others), and the final dome-shaped stocks of amazonite Li-F granites of phase 3 host (in their upper parts) Ta deposits of the “apogranite” type: Orlovka, Etyka, and Achikan. The Kukul’bei Complex includes also dikes of ongonites, elvanes, amazonite granites, and miarolitic pegmatites. All granitic rocks of the complex are roughly coeval and have an age of 142±0.6 Ma. The Zr/Hf ratio of the rocks systematically decreases from intrusive phase 1 (40–25) to phases 2 (20–30) and 3 (10–2). Compared to other granite series, the granites of the Kukul’bei Complex are enriched in Rb, Li, Cs, Be, Sn, W, Mo, Ta, Nb, Bi, and F but are depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From earlier to later intrusive phases, the rocks become progressively more strongly enriched or depleted in these elements, and their Zr/Hf ratio systematically decreases from 40 to 2. This ratio serves as a reliable indicator of genetic links, degree of fractionation, and rare-metal potential of granites. Greisen Sn, W, Mo, and Be deposits are expected to accompany granites with Zr/Hf < 25, whereas granites related to Ta deposits should have Zr/Hf < 5. 相似文献
5.
T.V. Donskaya D.P. Gladkochub A.M. Mazukabzov B. De Waele S.L. Presnyakov 《Russian Geology and Geophysics》2012,53(1):22-36
The Kataev volcanoplutonic association has been recognized in western Transbaikalia. It unites the volcanosedimentary rocks of the Kataev Formation and associated granites localized within the lower plates of the Buteel-Nuur and Zagan metamorphic-core complexes. The rocks of the Kataev association are dynamometamorphosed to different degrees, which is due to the tectonic exposure of metamorphic-core complexes in the Early Cretaceous. The U-Pb zircon dating of the Kataev Formation rhyolites yielded an age of 226 ± 3 Ma. The U-Pb zircon age of the granites intruding the Kataev Formation rocks is 223.4 ± 5.0 Ma. The volcanics of the Kataev Formation belong to the subalkalic basalt-andesite-dacite-rhyolite series. The trachybasalts and trachyandesite-basalts of the Kataev Formation have geochemical characteristics of igneous rocks formed as a result of subduction, e.g., they show distinct negative Nb and Ti and positive Ba and Sr anomalies on multielemental patterns. The specific composition of mafic volcanics points to their formation through the melting of a mantle source resulted from the mixing of depleted mantle and subduction components. Trachyandesites have higher Th and U contents than basaltoids. They can result from the contamination of a mantle source, similar in composition to the Kataev Formation basaltoids, with crustal material. The felsic volcanics of the Kataev Formation and granites intruding them show nearly identical geochemical characteristics corresponding to both A-and I-type granites. These rocks might have formed through the melting of a moderately water-saturated magmatic source of diorite-tonalite composition at 742–833°C. We have established that the rocks of the Kataev volcanoplutonic association in western Transbaikalia and Northern Mongolia formed in the Late Triassic synchronously with the calc-alkaline granitoids of the Henteyn–Daurian batholith and the alkali granites and bimodal volcanic associations of the Kharitonovo and Tsagaan-Hurtey volcanoplutonic associations. The synchronous formation of volcanoplutonic associations of normal and high alkalinity agrees with the geodynamic setting of the Andean-type active continental margin existing in the area of present-day western Transbaikalia and Northern Mongolia in the Early Mesozoic. This setting was the result of the subduction of the Mongol-Okhotsk oceanic plate beneath the Siberian continent. 相似文献
6.
浙西开化地区皖浙边界断裂带西侧浅变质岩系中发育了一套以流纹岩为主的酸性火山岩。两个流纹岩样品的锆石LA-ICP-MS U-Pb定年分别给出了785±5 Ma和781±10 Ma的结果,显示为南华裂谷期的产物。岩石地球化学分析显示:该流纹岩富硅偏碱,铝饱和指数A/CNK大于1.11,显示过铝质特点;稀土元素总量高,相对富集轻稀土元素,具中等Eu负异常;相对富集Rb、Th、U、Pb等强不相容元素,而相对亏损亲石元素Ba、Sr、Nb、Ta,Zr含量较高。与壳源花岗质岩浆的地球化学特征相似。在微量元素构造判别图中显示为板内火山岩。结合地质背景分析,认为其形成于大陆裂谷环境,可能与华南地幔柱活动有关。 相似文献
7.
本文对嫩江地区中生代双峰式火山岩进行了锆石LA-ICP-MSU-Pb年代学和岩石地球化学研究。测年结果显示嫩江地区中生代双峰式火山岩形成于127.5Ma的早白垩世晚期。岩石地球化学研究表明,早白垩世晚期火山岩具有双峰式组合特点,基性端员富碱,富含轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素（Nb、Ta、Ti、Y）,形成于富集的岩石圈地幔的部分熔融和分离结晶作用,形成的过程可能含有少量的陆壳混染。酸性端员显示A型流纹岩的特征,为幔源岩浆底侵,使中下地壳岩石发生部分熔融的成因。双峰式火山岩组合的存在暗示其形成于陆内拉张的构造环境。结合区域上中生代火山岩的空间展布特征,嫩江地区早白垩世晚期双峰式火山岩的形成应与太平洋板块向欧亚大陆的俯冲作用有关。 相似文献
8.
A genetic model for magmatic rocks of the Ary-Bulak Massif is discussed based on a detailed geological map of the massif (prepared
by the authors) and on original data of the authors on the petrography of the massif, its compositional zoning, trace-element
geochemistry, physicochemical parameters of its crystallization, and melt inclusions in its minerals. The Ary-Bulak Massif
was determined to be zonal, with the predominance (approximately 70% by area) of porphyritic topaz ongonites (central facies),
which grade toward contacts into weakly porphyritic ongonites bearing topaz and, occasionally, fluorite (margin facies). Aphyric
rocks with fluorite (inner-contact facies) occur as a stripe 50–80 m wide at the southwestern inner contact of the massif.
Analysis of petrographic and geochemical data indicates that subvolcanic rocks of the Ary-Bulak Massif differ from typical
elvanes (as they occur in the Cornwall province) but are similar to classic ongonites in the central and marginal facies of
the massif. Rocks in the southwestern inner-contact zone are unusual high-F and high-Ca varieties, whose analogues have never
been found in any rare-metal provinces with ongonites and which provide evidence of a complicated evolutionary history of
the Ary-Bulak Massif. The geochemical evolution of this massif was determined to be characterized by the enrichment of the
older inner-contact facies rocks in CaO, K2O, F, and Rb, Cs, B, Ba, Sr, Sn, and Ta, whose concentrations decrease in the ongonites of the central facies. The central-facies
ongonites thereby have much higher Na2O and Li concentrations than those in the inner-contact facies rocks. It is demonstrated that the intense heating and melting
of crustal material in this region at the Jurassic-Cretaceous boundary could have been induced by subalkaline basaltic magma.
The chemical composition of the rocks, which is unusual for typical ongonites in, for example, high Ca and Sr concentrations,
could be caused by the possible assimilation by the magma of limestones, which occur in the territory at a certain depth in
the Ust’-Borzya Formation that hosts the Ary-Bulak Massif. The genesis of most rocks in the massif was controlled by the magmatic
differentiation of crustal granitic magma, with the residual melts forming Li-F granites enriched in several trace elements
(Li, Rb, Cs, B, Ba, Sr, etc.) and ongonites as their subvolcanic analogues. 相似文献
9.
G. P. Zaraisky A. M. Aksyuk V. N. Devyatova O. V. Udoratina V. Yu. Chevychelov 《Petrology》2008,16(7):710-736
The concept of granitic melt fractionation as the main process in the concentration of rare elements in granites calls for
the development of a reliable method to determine the evolutionary sequences of granite series. We propose to use for this
purpose a zirconium-hafnium indicator, the Zr/Hf weight ratio in granitic rocks (Zaraisky et al., 1999, 2000). By the example
of three classic regions of rare-metal deposits, eastern Transbaikalia, central Kazakhstan, and Erzgebirge (Czech Republic
and Germany), it was empirically shown that the Zr/Hf ratio of granites decreases during the fractional crystallization of
granite magmas in the sequence granodiorite → biotite granite → leucogranite → lithium-fluorine granite. The reason is the
higher affinity of Hf compared with Zr to a granite melt. This implies that the crystallization and settling of accessory
zircon will cause the progressive enrichment of Hf relative to Zr in the residual melt. As a result, the Zr/Hf ratio decreases
regularly in the series of sequential phases of granite intrusion related to a single magma chamber from granodiorite to biotite
granite, leucogranite, and Li-F granite (from 45-30 to 10-2). Our experimental investigations supported the preferential enrichment
of haplogranite melt in Hf and zircon crystals in equilibrium with melt in Zr (T= 800°C and P = 1 kbar). The Zr/Hf indicator was tested by the example of the wellknown Kukulbei rare-metal granite complex of eastern
Transbaikalia (J3), which is unique in the degree of fractionation of initial granite melt with the formation of three phases
of granite emplacement and vein derivatives. An important feature of the complex is its “short” differentiation trend. It
was supposed that the granite magma of the first phase is parental, and the later phases forming small intrusive bodies in
large massifs of biotite granites of the first phase are sequential products of its crystallization differentiation in a magma
chamber. The biotite granites of the first phase are barren. The leucocratic granites of the second phase are accompanied
by tin-tungsten greisen deposits (e.g., Spokoininskoe), and the upper part of cupola-like stocks of Li-F amazonite granites
of the third phase host apogranite-type tantalum deposits (Orlovka, Etyka, and Achikan). In addition to three granite phases,
the Kukulbei complex includes dikes of ongonites, elvans, amazonite granites, and chamber miarolitic pegmatites. All of the
granitic rocks of the complex have similar isotopic ages of 142± 0.6 Ma. The Zr/Hf ratio decreases systematically from phase
1 (40–25), to phase 2 (20–10), and phase 3 (10–2). The ongonites, elvans, and pegmatites have similar Zr/Hf ratios (15-5),
falling between the ranges of leucocratic muscovite granites and Li-F granites. Compared with other granite series, the granitic
rocks of the Kukulbei complex show specific petrographic and geochemical features: they are strongly enriched in Rb, Li, Cs,
Be, Sn, W, Mo, Ta, Nb, Bi, and F but depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From the early
to late intrusion phases, the degree of enrichment and depletion in these element groups increases regularly. This is accompanied
by a significant decrease (from 40 to 2) in Zr/Hf, which can be used as a reliable indicator of genetic relations, degree
of fractionation, and rare-metal potential of granites. Granites with Zr/Hf values lower than 25 are promising for prospecting
for Sn, W, Mo, and Be greisen deposits, whereas the formation of Ta deposits requires Zr/Hf values lower than 10. 相似文献
10.
The tungsten distribution in rocks of the Kukulbei Complex in eastern Transbaikal region results in a high potential of rare-metal peraluminous granites (RPG) for W mineralization and displays a different behavior of W in Li–F and “standard” RPG. These subtypes differ in the behavior of W in melt, spatial localization of mineralization, and the timing of wolframite crystallization relative to the age of the parental granitic rocks. The significant of W concentration is assumed to be due to fractionation of the Li–F melt; however, wolframite mineralization in Li–F enriched granite is not typical in nature. The results of experiments and our calculations of W solubility in granitic melt show that wolframite hardly ever crystallizes directly from melt; it likely migrates in the fluid phase and is then removes from the magma chamber to the host rocks, where secondary concentration takes place in exocontact greisens and quartz–cassiterite–wolframite veins. At the same time, the isotopic age of accessory wolframite (139.5 ± 2.1 Ma) within the Orlovka massif of Li–F granite is close to the formation age of the massif (140.6 ± 2.9 Ma). A different W behavior is recorded in the RPG subtype with a low lithium and fluorine concentration, exemplified by the Spokoininsky massif. There is no significant W gain in the melt. All varieties of wolframite mineralization in the Spokoininsky massif are derived from greisens, veins, and pegmatoids yielding the same crystallization ages (139.5 ± 1.1 Ma), which are 0.9–1.8 Ma later (taking into account the mean-square weighted deviation) than the Spokoininsky granite formation (144.5 ± 1.4 Ma). Perhaps this period corresponds to the time of transition from the magmatic stage to hydrothermal alteration. Comparison of the isotope characteristics (Rb–Sr and Sm–Nd isotope systems) of rocks and the associated ore minerals (wolframite, cassiterite) from all examined deposits shows a depletion in εNd values for ore minerals relative to the rock and the opposite behavior for the intial Sr isotope ratios. This may indicate the specific nature of ore matter, where the effect of the juvenile component is definitely expressed. Our geochronological results show that tantalum and tungsten mineralization took place within a narrow age interval, almost synchronously with the crystallization of associated granites. The coeval development of peraluminous magmatism enriched in lithophile rare elements and volatiles with ore complexes located in different structural settings and separated by a considerable distance from each other (up to 500 km) suggests a regional and deep-seated magma source. Rifting and increased thermal flux from the mantle, manifestations of which have been recorded during this period in the territory, may be a deep-seated process. 相似文献
11.
The Late Paleozoic intraplate magmatism of the Selenga-Vitim structural zone of the Baikal region (Khamar-Daban Range) produced
granitoids of different geochemical types: palingenic calc-alkaline granitoids, subalkaline monzogranites, and rare-metal
Li-F granitoids and their subvolcanic analogues. Subalkaline and rare-metal granitoids occur in the periphery of the Late
Paleozoic magmatic zone. Rare metal granite magmatism is manifested in this region as nearly N-S trending intrusive-dike belts
comprising multiphase intrusions (Kharagul, Urugudei, and Bitu-Dzhida massifs) with an exposed area of ∼10 km2 and an age of formation from 311 to 321 Ma and series of accompanying dikes. The early phases of the intrusions are made
up of biotite granites usually with fluorite, which are changed during the late stage by typical topazbearing rare-metal amazonite-albite
granites. In the subvolcanic facies, thicker subalkaline dikes of monzonite porphyry, granite porphyry, and elvan are changed
by ongonites, topaz rhyolites, and topazites, which occasionally serve as cement in eruptive and fluid-explosive breccias.
The development of multiphase intrusions from early biotite granites to late amazonite-albite granites with Li-F mica was
accompanied by an increase in SiO2 and, especially, Na2O contents, whereas the level of (FeO + Fe2O3), CaO, and K2O declined. Geochemical evolution includes an increase in the same direction in the contents of F, Li, Rb, Cs, Sn, Be, Ta,
and Pb and a decrease in Ba, Sr, Zn, Zr, Th, and U. Similar evolution is also characteristic of the subvolcanic rocks, which
emphasizes the genetic relation of the whole intrusive-dike complex of the Khamar-Daban province. Significant differences
were detected in the distribution of K, Ba, Sr, and Zr between the calc-alkaline granitoids and rare-metal Li-F granites.
The continental crust-normalized patterns of the raremetal granites show positive anomalies for Li, Rb, Nb, and Pb. The rare-metal
Li-F granites could not be produced by palingenesis only, and their formation required specific conditions causing extensive
accumulation of characteristic trace elements. During the evolution of granite melts, Li, Rb, Ta, Nb, Sn, W, and F are extensively
accumulated in late intrusive phases, which indicates an important role of the processes of magmatic and fluid-magmatic differentiation
during their formation. The composition and isotope geochemical characteristics of the supposed magma source material correspond
to the ancient Precambrian continental crust with a mean model age of more than 1200 Ma. 相似文献
12.
W.U. Reimold 《Geochimica et cosmochimica acta》1982,46(7):1203-1225
Impact melt lithologies of the 77 m.y. old Finnish meteorite crater Lappajärvi as well as the Precambrian target rocks have been studied in detail, to identify and characterize different impact melt types (clast-poor, clast-rich, suevitic melt) and to study their chemical (major and trace elements) and isotopic (Rb-Sr) compositions in comparison to the composition of the target rocks.The Rb-Sr system of the whole melt body—including the suevitic melt—is shown to have been reequilibrated by the impact by extensive turbulent mixing of the various melted or vaporized target rocks. Chemical interactions (exchange of alkali elements, 87Sr-redistribution) between feldspar clasts and impact melt surrounding them are the result of thermal metamorphism following the incorporation of target rock fragments of various degrees of shock metamorphism into the superheated melt. Exchange reactions between clasts and melt are determined by thermal activation, but the degree of shock metamorphism in the clasts plays an important role, too.Major and trace element distributions in impact melt and basement rocks indicate that the Lappajärvi melt body chemically is extremely homogeneous. Even volatile elements (such as Zn and Cu) were not strongly fractionated. Comparison of the abundances of siderophile elements in the impact melt (e.g., 118–177 ppm Cr, 195–340 ppm Ni, 6–12 ppb Ir) and calculated target rock mixture (79% mica schist, 11% granite-pegmatite, 10% amphibolite) (e.g., 85.6 ppm Cr, 54.8 ppm Ni, 0.5 ppb Ir) revealed the chondritic nature (C or H chondritic) of the meteoritic projectile. Less than 2% of the meteorite can be detected in the coherent melt, whereas the suevitic melt is uncontaminated by the projectile. 相似文献
13.
E. V. Sklyarov D. P. Gladkochub A. B. Kotov A. E. Starikova V. V. Sharygin S. D. Velikoslavinsky A. M. Larin A. M. Mazukabzov E. V. Tolmacheva E. A. Khromova 《Russian Journal of Pacific Geology》2016,10(3):155-167
Arguments in favor of magmatic or metasomatic genesis of the Katugin rare-metal ore deposit are discussed. The geological and mineralogical features of the deposit confirm its magmatic origin: (1) the shape of the ore-bearing massif and location of various types of granites (biotite, biotite–amphibole, amphibole, and amphibole–aegirine); (2) the geochemical properties of the massif rocks corresponding to A type granite (high alkali content (up to 12.3% Na2O + K2O), extremely high FeO/MgO ratio (f = 0.96–1.00), very high content of the most incoherent elements (Rb, Li, Y, Zr, Hf, Ta, Nb, Th, U, Zn, Ga, and REE) and F, and low concentrations of Ca, Mg, Al, P, Ba, and Sr); (3) Fe–F-rich rock-forming minerals; (4) no previously proposed metasomatic zoning and regular replacement of rock-forming minerals corresponding to infiltration fronts of metasomatism. The similar ages of the barren (2066 ± 6 Ma) and ore-bearing (2055 ± 7 Ma) granites along with the features of the ore mineralization speak in favor of the origin of the ore at the magmatic stage of the massif’s evolution. The nature of the ore occurrence and the relationships between the ore minerals support their crystallization from F-rich aluminosilicate melt and also under melt liquation into aluminosilicate and fluoride (and/or aluminofluoride) fractions. 相似文献
14.
《International Geology Review》2012,54(8):1029-1048
We have undertaken major and trace element analyses of volcanic rocks in Northeast China, as well as U–Pb dating and Hf isotopic analysis of their zircons, in order to determine the petrogenesis and tectonic setting of the volcanics. Mesozoic volcanism in the southern Manzhouli area occurred in two stages: Middle to Late Jurassic (164–147 Ma) and Early Cretaceous (142–123 Ma). The first stage is represented by the Tamulangou, Jixiangfeng, and Qiyimuchang formations. The Jixiangfeng Formation (162–156 Ma) is a rhyolite–trachyte dominated unit that lies between two basalt units, namely the underlying Tamulangou (164–160 Ma) and overlying Qiyimuchang (151–147 Ma) formations. The second igneous stage is dominated by rhyolitic lavas and tuffs of the Shangkuli Formation and basaltic rocks of the Yiliekede Formation, and they yield zircon U–Pb ages of 142–125 and 135–123 Ma, respectively. Basaltic rocks of the Tamulangou and Yiliekede formations have a wide range of MgO contents (1.64–9.59 wt%), but are consistently depleted of Nb and Ta and enriched with incompatible trace elements such as large ion lithophile elements (LILEs) and light rare earth elements (LREEs). Trachytes and rhyolites of the Jixiangfeng and Shangkuli formations are characterized by enrichment in LILEs and LREEs relative to HFSEs and HREEs, and with negative Nb, Ta, P, and Ti anomalies and positive ? Hf(t) values (3.49–9.98). These data suggest that basaltic volcanic rocks in southern Manzhouli were generated by fractional crystallization of a common parental magma, which was derived by partial melting of metasomatized (enriched) lithospheric mantle, whereas the trachytic and rhyolitic magmas were produced by the melting of lower crustal mafic and felsic granulites, respectively. Geochronological data indicate that Mesozoic volcanism in southern Manzhouli was initiated in the Middle to Late Jurassic and continued into the Early Cretaceous. It was mainly induced by lithospheric extension after the closure of the Mongol–Okhotsk Ocean. 相似文献
15.
The dike belt and separate intrusive bodies of the Abdar–Khoshutula series were formed in the NE-trending linear zone, southwest of the Daurian–Khentei batholith, in the peripheral part of the Early Mesozoic magmatic area, on the western termination of the Mongol–Okhotsk belt. The granitoids of this series are subdivided into following geochemical types: anatectic granitoids of the calc-alkaline and subalkaline series, alkaline rocks, and plumasite rare-metal leucogranites (Li–F granites). The entire series was formed within approximately 12–15 Ma. Its geochemical evolution follows two trends, which correspond to two stages of the granitoid magmatism. The early stage was responsible for the formation of granitoids of two phases of the Khoshutulinsky Pluton and alkaline syenites with similar trace element distribution patterns. However, syenites, as agpaitic rocks, are significantly enriched in Ba, Zr, and Hf. The late stage of the intrusive- dike series resulted in the formation of the dike belt and Abdar Massif of rare-metal granites. These rocks show enrichment in Li, Rb, Cs, Nb, Ta, Sn, and Y, and deep negative anomalies of Ba, Sr, La, and Ce, which are best expressed in the late amazonite–albite granites of the Abdar intrusion and ongonites of the dike belt. The intrusive-dike series in the magmatic areas of different age of Mongolia and Baikal region are characterized by the wide compositional variations, serve as important indicators of mantle-crustal interaction and differentiation of granitoid magmas, and could highlight the nature of zonal areas within the Central Asian Fold Belt. Obtained geochemical data indicate a potential opportunity to concentrate trace and ore components during long-term evolution of the intrusive-subvolcanic complexes, which could be indicators of the evolution of the ore-magmatic systems bearing rare-metal mineralization. 相似文献
16.
下扬子区二叠纪主要岩石类型成因的地球化学信息 总被引：5，自引：0，他引：5
作者在全面了解陆相层序地层学研究现状的基础上,认为陆相层序及体系域发育仍受控于湖平面相对变化。构造、气候及沉积物供给的控制作用最终通过湖平面变化表现出来。而湖平面变化可分完整旋回与不完整旋回两种情况,进而提出了所形成的层序及体系域模式：在完整旋回中形成了湖泊充填、湖泊扩张、湖泛和湖泊萎缩四个体系域,对应层序为Ⅰ型层序;在不完整旋回中形成了湖泊充填、湖泊扩张、湖泛三个体系域,或者湖泊扩张、湖泛、湖泊萎缩三个体系域,对应层序为Ⅱ型层序。以松辽盆地西部斜坡实际工作为例,提出了中生代层序及体系域划分方案,较前人研究有新认识。 相似文献
17.
Stefanie S. Schmidberger Ernst Hegner 《Contributions to Mineralogy and Petrology》1999,135(4):373-385
Late Carboniferous (300–290 Ma) calc-alkaline basalts, andesites, and rhyolites typical of volcanic arc settings occur in
the intermontane Saar-Nahe basin (SW Germany) within the Variscan orogenic belt. The volcanic rock suite was emplaced under
a regime of tensional tectonics during orogenic collapse and its origin has been explained by melting of mantle and crust
in the course of limited lithospheric rifting. We report major, trace and rare-earth-element data (REE), and Nd-Pb-Sr-O isotope
ratios for a representative sample suite, which are fully consistent with an origin closely related to plate subduction. Major
and trace element data define continuous melt differentiation trends from a precursor basaltic magma involving fractional
crystallization of olivine, pyroxene, plagioclase, and magnetite typical of magma evolution in a volcanic arc. This finding
precludes an origin of the andesitic compositions by mixing of mafic and felsic melts as can be expected in anorogenic settings.
The mafic samples have high Mg numbers (Mg# = 65–73), and high Cr (up to 330 ppm) and Ni (up to 200 ppm) contents indicating
derivation from a primitive parental melt that was formed in equilibrium with mantle peridotite. We interpret the geochemical
characteristics of the near-primary basalts as reflecting their mantle source. The volcanic rocks are characterized by enrichment
in the large ion lithophile elements (LILE), negative Nb and Ti, and positive Pb anomalies relative to the neighboring REE,
suggesting melting of a subduction-modified mantle. Initial Nd values of −0.7 to −4.6, Pb, and 87Sr/86Sr(t) isotope ratios for mafic and felsic volcanics are similar and indicate partial melting of an isotopically heterogeneous and
enriched mantle reservoir. The enrichment in incompatible trace elements and radiogenic isotopes of a precursor depleted mantle
may be attributed to addition of an old sedimentary component. The geochemical characteristics of the Saar-Nahe volcanic rocks
are distinct from typical post-collisional rock suites and they may be interpreted as geochemical evidence for ongoing plate
subduction at the margin of the Variscan orogenic belt not obvious from the regional geologic context.
Received: 3 August 1998 / Accepted: 2 January 1999 相似文献
18.
通过对辽北平岗盆地中德仁组火山岩的岩石学、地球化学和年代学的研究,探讨了其岩石成因、形成时代、构造环境,以及华北克拉通东部岩石圈减薄时间和减薄机制。用LA-ICP-MS技术测定了平岗盆地中德仁组中部英安质角砾晶屑岩屑凝灰岩和上部流纹岩中的锆石U-Th-Pb同位素组成。获得前者的锆石~(206)Pb/~(238)U年龄为246.8±3.5Ma和169.6±4.6Ma,代表了2期岩浆活动的年龄,是平岗盆地基底早三叠世和中侏罗世岩浆活动的表现;后者的锆石~(206)Pb/~(238)U年龄为117.0±0.9Ma,表明流纹岩形成于早白垩世。德仁组火山岩富集大离子亲石元素K、Rb、Ba,亏损高场强元素Nb、Ta、Zr、Hf、Y、Yb;富集轻稀土元素,亏损重稀土元素,稀土元素配分曲线呈右倾型,表现出壳源特征。德仁组火山岩形成于活动大陆边缘火山弧环境,原始岩浆来源于盆地基底岩浆岩重熔。研究区在117~135Ma期间,发生了由正地形向负地形的重大转变,区域上发育伸展盆地和变质核杂岩,并在基底岩石重熔过程中受到地幔混染作用,表明研究区在早白垩世发生了岩石圈减薄,且减薄的起始时间早于117.0±0.9Ma,减薄机制为拆沉作用。 相似文献
19.
This paper presents a study of ongonites from the Chechek and Akhmirovo dike belts located within the Kalba—Narym batholith in Eastern Kazakhstan. The obtained conclusions are based on the investigations of melt and fluid inclusion in quartz phenocrysts, supplemented by mineralogical and geochemical data. It was established that the dike rocks were formed by crystallization of volatile-rich rare-metal melts in the presence of an aqueous fluid phase with subordinate amounts of carbon dioxide and methane. The ongonites crystallized from three geochemically different melts. Porphyritic phenocrysts in the ongonites of the Chechek and Akhmirovo dike belts crystallized at close temperatures 560–605°C and pressure of 3.6–5.3 kbar. Ongonite magmas that formed the Chechek and Akhmirovo dike belts had a high ore potential. However, degassing dynamics was not favorable for the development of metasomatism and formation of hydrothermal mineralization at the level of dike emplacement. The area of the rare-metal magmatism represented by ongonite dikes and rare-metal granite pegmatites has been distinguished in the northern part of the Kalba—Narym zone. The formation of rare-metal magmas was related to the differentiation in large granitoid chambers under the effect of juvenile fluids derived from the Tarim mantle plume. 相似文献
20.
The paper presents detailed geochemical data on the rocks of the Zashikhinsky Massif and mineralogical–geochemical characteristics of the ores of the eponymous deposit. The rare-metal granites are divided into three facies varieties on the basis of the degree of differentiation and ore potential: early facies represented by microcline–albite granites with arfvedsonite, middle facies represented by leucocratic albite–microcline granites, and late (most ore-bearing) facies represented by quartz–albite granites grading into albitites. Microprobe data were obtained on major minerals accumulating trace elements in the rocks and ores. All facies of the rare-metal granites, including the rocks of the fluorite–rare-metal vein, define single compositional trends in the plots of paired correlations of rock-forming and trace elements. In addition, they also show similar REE patterns and spidergrams. The latter, however, differ in the depth of anomalies of some elements. Obtained geological, petrographic, and geochemical data suggest a magmatic genesis of the rocks of different composition and their derivation from a single magma during its differentiation. On the basis of all characteristics, the Zashikhinskoe deposit is estimated as one of the largest tantalum rare-metal deposits of alkaline-granite type in Russia. 相似文献