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1.
Crystalline and melt inclusions were studied in large (up to 2 cm across) dipyramidal quartz phenocrysts from Miocene dacites in the area of the Rosia Montana Au-Ag deposit in Romania. Data were obtained on the homogenization of fluid inclusions and the composition of crystalline inclusions and glasses in more than 40 melt inclusions, which were analyzed on a electron microprobe. The minerals identified in the crystalline inclusions are plagioclase (An 51–62), orthoclase, micas (biotite and phengite), zircon, magnetite (TiO2 = 2.8 wt %), and Fe sulfide. Two types of the melts were distinguished when studying the glasses of the melt inclusions. Type 1 of the melts is unusual in composition. The average composition of 20 inclusions is as follows (wt %): 76.1 SiO2, 0.39 TiO2, 6.23 Al2O3, 4.61 FeO, 0.09 MnO, 1.64 MgO, 3.04 CaO, 2.79 Na2O, 3.79 K2O (Na2O/K2O = 0.74), 0.07 P2O5, 0.02 Cl. The composition of type 2 of the melts is typical of acid magmas. The average of 23 inclusion analyses is (wt %) 79.3 SiO2, 0.16 TiO2, 10.27 Al2O3, 0.63 FeO, 0.08 MnO, 0.29 MgO, 1.83 CaO, 3.56 Na2O, 2.79 K2O (Na2O/K2O = 1.28), 0.08 P2O5, 0.05 Cl. The compositions of these melts significantly differ in concentrations of Ti, Al, Fe, Mg, Ca, Na, and K. The high analytical totals of the analyses (close to 100 wt %, more specifically 98.9 and 99.0 wt %, respectively) testify that the melts were generally poor in water. Two inclusions of type 1 and two inclusions of type 2 were analyzed on an ion probe, and their analyses show remarkable differences in the concentrations of certain trace elements. These concentrations (in ppm) are for the melts of types 1 and 2, respectively, as follows: 10.0 and 0.69 for Be, 29.3 and 5.7 for B, 6.4 and 1.4 for Cr, 146 and 6.9 for V, 74 and 18 for Cu, 92 and 29 for Rb, 45 and 15 for Zr, 1.7 and 0.6 for Hf, 10.3 and 2.3 for Pb, and 52 and 1.3 for U. The Th/U ratio of these two melt types are also notably different: 0.04 and 0.19 for type 1 and 2.0 and 2.9 for type 2. These data led us to conclude that the magmatic melts were derived from two different sources. Our data on the melts of type 1 testify that the magmatic chamber was contaminated with compositionally unusual crustal rocks (perhaps, sedimentary, metamorphic, or hydrothermal rocks enriched in Si, Fe, Mg, U, and some other components). This can explain the ore-forming specifics of magmatic chambers in the area.  相似文献   

2.
Melt inclusions were examined in phenocrysts in basalt, andesite, dacite, and rhyodacite from the Karymskii volcanic center in Kamchatka and dacite form Golovnina volcano in Kunashir Island, Kuriles. The inclusions were examined by homogenization and by analyzing glasses in more than 80 inclusions on an electron microscope and ion microprobe. The SiO2 concentrations in the melt inclusions in plagioclase phenocrysts from basalts from the Karymskii volcanic center vary from 47.4 to 57.1 wt %, these values for inclusions in plagioclase phenocrysts from andesites are 55.7–67.1 wt %, in plagioclase phenocrysts from the dacites and rhyodacites are 65.9–73.1 wt %, and those in quartz in the rhyodacites are 72.2–75.7 wt %. The SiO2 concentrations in melt inclusions in quartz from dacites from Golovnina volcano range from 70.2 to 77.0 wt %. The basaltic melts are characterized by usual concentrations of major components (wt %): TiO2 = 0.7–1.3, FeO = 6.8–11.4, MgO = 2.3–6.1, CaO = 6.7–10.8, and K2O = 0.4–1.7; but these rocks are notably enriched in Na2O (2.9–7.4 wt % at an average of 5.1 wt %, with the highest Na2O concentration detected in the most basic melts: SiO2 = 47.4–52.0 wt %. The concentrations of volatiles in the basic melts are 1.6 wt % for H2O, 0.14 wt % for S, 0.09 wt % for Cl, and 50 ppm for F. The andesite melts are characterized by high concentrations (wt %) of FeO (6.5 on average), CaO (5.2), and Cl (0.26) at usual concentrations of Na2O (4.5), K2O (2.1), and S (0.07). High water concentrations were determined in the dacite and rhyodacite melts: from 0.9 to 7.3 wt % (average of 15 analyses equals 4.5 wt %). The Cl concentration in these melts is 0.15 wt %, and those of F and S are 0.06 and 0.01 wt %, respectively. Melt inclusions in quartz from the dacites of Golovnina volcano are also rich in water: they contain from 5.0 to 6.7 wt % (average 5.6 wt %). The comparison of melt compositions from the Karymskii volcanic center and previously studied melts from Bezymyannyi and Shiveluch volcanoes revealed their significant differences. The former are more basic, are enriched in Ti, Fe, Mg, Ca, Na, and P but significantly depleted in K. The melts of the Karymskii volcanic center are most probably less differentiated than the melts of Bezymyannyi and Shiveluch volcanoes. The concentrations of water and 20 trace elements were measured in the glasses of 22 melt inclusions in plagioclase and quartz from our samples. Unusually high values were obtained for Li concentrations (along with high Na concentrations) in the basaltic melts from the Karymskii volcanic center: from 118 to 1750 ppm, whereas the dacite and rhyolite melts contain 25 ppm Li on average. The rhyolite melts of Golovnina volcano are much poorer in Li: 1.4 ppm on average. The melts of the Karymskii volcanic center are characterized by relative minima at Nb and Ti and maxima at B and K, as is typical of arc magmas.  相似文献   

3.
Using various methods of melt inclusion investigation, including electron and ion microprobe techniques, we estimated the composition, evolution, and formation conditions of melts producing the trachydacites and pantellerites of the Late Paleozoic bimodal volcanic association of Dzarta-Khuduk, Central Mongolia. Primary crystalline and melt inclusions were detected in anorthoclase from trachydacites and quartz from pantellerites and pantelleritic tuffs. Among the crystalline inclusions, we identified hedenbergite, fluorapatite, and pyrrhotite in the trachydacites and F-arfvedsonite, fluorite, ilmenite, and the rare REE diorthosilicate chevkinite in the pantellerites. Melt inclusions in anorthoclase from the trachydacites are composed of glass, a gas phase, and daughter minerals (F-arfvedsonite, fluorite, villiaumite, and anorthoclase rim on the inclusion wall). Melt inclusions in quartz from the pantellerites are composed of glass, a gas phase, and a fine-grained salt aggregate consisting of Li, Na, and Ca fluorides (griceite, villiaumite, and fluorite). Melt inclusions in quartz crystalloclasts from the pantelleritic tuffs are composed of homogeneous silicate glasses. The phenocrysts of the trachydacites and pantellerites crystallized at temperatures of 1060–1000°C. During thermometric experiments with quartz-hosted melt inclusions from the pantellerites, the formation of immiscible silicate and salt (fluoride) melts was observed at a temperature of 800°C. Homogeneous melt inclusions in anorthoclase from the trachydacites have both trachydacite and rhyolite compositions (wt %): 68–70 SiO2, 12–13 Al2O3, 0.34–0.74 TiO2, 5–7 FeO, 0.4–0.9 CaO, and 9–12 Na2O + K2O. The agpaitic index ranges from 0.92 to 1.24. The glasses of homogenized melt inclusions in quartz from the pantellerites and pantelleritic tuffs have rhyolitic compositions. Compared with the homogeneous glasses trapped in anorthoclase of the trachydacites, quartz-hosted inclusions from the pantellerites show higher SiO2 (72–78 wt %) and lower Al2O3 contents (7.8–10.0 wt %). They also contain 0.14–0.26 wt % TiO2, 2.5–4.9 wt % FeO, 9–11 wt % Na2O + K2O, and 0.9–0.15 wt % CaO and show an agpaitic index of 1.2–2.05. Homogeneous melt inclusions in quartz from the pantelleritic tuffs contain 69–72 wt % SiO2. The contents of other major components, including TiO2, Al2O3, FeO, and CaO, are close to those in the homogeneous glasses of quartzhosted melt inclusions in the pantellerites. The contents of Na2O + K2O are 4–10 wt %, and the agpaitic index is 1.0–1.6. The glasses of melt inclusions from each rock group show distinctive volatile compositions. The H2O content is up to 0.08 wt % in anorthoclase of the trachydacites, 0.4–1.4 wt % in quartz of the pantellerites, and up to 5 wt % in quartz of the pantelleritic tuffs. The content of F in the glasses of melt inclusions in the phenocrysts of the trachydacites is no higher than 0.67 wt %, and up to 1.4–2.8 wt % in quartz from the pantellerites. The Cl content is up to 0.2 wt % in the glasses of melt inclusions in the minerals of the trachydacites and up to 0.5 wt % in the glasses of quartz-hosted melt inclusions from the pantellerites. The investigation of trace elements in the homogenized glasses of melt inclusions in minerals showed that the trachydacites and pantellerites were formed from strongly evolved rare-metal alkaline silicate melts with high contents of Li, Zr, Rb, Y, Hf, Th, U, and REE. The analysis of the composition of homogeneous melt inclusions in the minerals of the above rocks allowed us to distinguish magmatic processes resulting in the enrichment of these rocks in trace and rare earth elements. The most important processes are the crystallization differentiation and immiscible separation of silicate and fluoride salt melts. It was also shown that all the melts studied evolved in spatially separated magma chambers. This caused the differences in the character of melt evolution between the trachydacites and pantellerites. During the final stages of differentiation, when the magmatic system was saturated with respect to ore elements, Na-Ca fluoride melts were separated and extracted considerable amounts of Li.  相似文献   

4.
Inclusions of mineral-forming environments in apatite-containing ijolites and magnetite–phlogopite–apatite ores in carbonatites were studied to elucidate the genesis of apatite mineralization in the Guli alkaline ultramafic carbonatite massif. Primary inclusions of carbonate–salt and carbonate melts have been discovered and studied. The carbonate–salt melt inclusions are of alkaline high-Ca composition and are enriched in P, Sr, SO3, and F (wt.%): CaO—30–40, Na2O—5–12, K2O—2–4, P2O5—1–3, SO3—1.5–3, and SrO—1–3. They also contain minor MgO, FeO, BaO, and SiO2 (tenths and hundredths of percent). The homogenization temperature of these inclusions is 850–970 °C. The carbonate inclusions contain predominant CaO (54–67 wt.%) and minor MgO, FeO, SrO, Na2O, and P2O5 (tenths of percent). Their homogenization temperature is 840–860 °C. Similar primary carbonate–salt and carbonate inclusions were found in garnet, and secondary ones were detected in silicate minerals (clinopyroxene and nepheline) of ijolites. Clinopyroxenes of ijolites also contain primary inclusions of alkaline ultramafic high-Ca melts similar in composition to melilitite-melanephelinites highly enriched in P, SO3, and CO2 (wt.%): SiO2—41–46, Al2O3—8–16, FeO—2–8, MgO—3–6, CaO—12–20, Na2O—2–9, K2O—1–6, P2O5—0.4–2.1, SO3—0.2–2.3, and Cl—0.02–0.35. According to the obtained data, apatite of the magnetite–phlogopite–apatite ores and ijolites of the Guli pluton crystallized from phosphorus-rich alkaline carbonate–salt melts at 850–970 °C. The generation of these melts was, most likely, due to the silicate–salt immiscibility in melilitite-melanephelinite melts highly enriched in salts, which occurred either at the final stages of clinopyroxene crystallization or during the formation of melilite. The presence of alkalies, S, F, and CO2 in spatially separated carbonate–salt melts contributed to the concentration and preservation of phosphorus in them at low temperatures, which led to the formation of apatite mineralization in ijolites and ore deposit in carbonatites.© 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.  相似文献   

5.
Two natural, low K2O/Na2O, TTG tonalitic gneisses (one hornblende-bearing and the other biotite-bearing) were partially melted at 0.8–1.2 GPa (fluid-absent). The chief melting reactions involve the breakdown of the biotite and hornblende. The hornblende tonalite is slightly less fertile than the biotite tonalite, but melt volumes reach around 30% at 1,000°C. This contrasts with results of most previous work on more potassic TTGs, which generally showed much lower fertility, though commonly producing more potassic melts. Garnet is formed in biotite-bearing tonalitic protoliths at P > 0.8 GPa and at > 1.0 GPa in hornblende-bearing tonalitic protoliths. All fluid-absent experiments produced peraluminous granitic to granodioritic melts, typically with SiO2 > 70 wt.%. For the biotite tonalite, increasing T formed progressively more melt with progressively lower K2O/Na2O. However, the compositions of melts from the hornblende tonalite do not vary significantly with T. With increasing P, melts from the biotite tonalite become less potassic, due to the increasing thermal stability of biotite. For the hornblende tonalite, again there is no consistent trend. Fluid-absent melting of sodic TTGs produces melts with insufficient K2O to model the magmas that formed the voluminous, late, potassic granites that are common in Archaean terranes. Reconnaissance fluid-present experiments at 0.6 GPa imply that H2O-saturated partial melting of TTGs is also not a viable process for producing magmas that formed these granites. The protoliths for these must have been more potassic and less silicic. Nevertheless, at granulite-facies conditions, sodic TTGs will produce significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths. Upward abstraction of this melt would result in some LILE depletion of the terrane. Younger K-rich magmatism is unlikely to represent recycling of TTG crust on its own, and it seems most likely that evolved crustal rocks and/or highly enriched mantle must be involved. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

6.
The compositions of approximately 70 naturally quenched melt inclusions in olivine, clinopyroxene, orthopyroxene, and plagioclase phenocrysts from tephra of the soil–pyroclastic cover of Simushir Island (Central Kuril Islands) were studied. The concentrations of the major rock-forming components, H2O, S, and Cl were analyzed in inclusions. The reconstructed melts contain 48.6–78.4 wt % SiO2, 0.3–8.26 wt % MgO, and 0.12–1.72 wt % K2O. The concentration of S and Cl in the melts changes regularly with increasing SiO2 content: from 0.14 to ~0.02 wt % S and from ~0.05 to ~0.28 wt % Cl. The content of H2O in parental melts is 4.2–4.5 wt %.  相似文献   

7.
Melt inclusions in kimberlitic and metamorphic diamonds worldwide range in composition from potassic aluminosilicate to alkali-rich carbonatitic and their low-temperature derivative, a saline high-density fluid (HDF). The discovery of CO2 inclusions in diamonds containing eclogitic minerals are also essential. These melts and HDFs may be responsible for diamond formation and metasomatic alteration of mantle rocks since the late Archean to Phanerozoic. Although a genetic link between these melts and fluids was suggested, their origin is still highly uncertain. Here we present experimental results on melting phase relations in a carbonated pelite at 6 GPa and 900–1500 °C. We found that just below solidus K2O enters potassium feldspar or K2TiSi3O9 wadeite coexisting with clinopyroxene, garnet, kyanite, coesite, and dolomite. The potassium phases react with dolomite to produce garnet, kyanite, coesite, and potassic dolomitic melt, 40(K0.90Na0.10)2CO3·60Ca0.55Mg0.24Fe0.21CO3 + 1.9 mol% SiO2 + 0.7 mol% TiO2 + 1.4 mol% Al2O3 at the solidus established near 1000 °C. Molecular CO2 liberates at 1100 °C. Potassic aluminosilicate melt appears in addition to carbonatite melt at 1200 °C. This melt contains (mol/wt%): SiO2 = 57.0/52.4, TiO2 = 1.8/2.3, Al2O3 = 8.5/13.0, FeO = 1.4/1.6, MgO = 1.9/1.2, CaO = 3.8/3.2, Na2O = 3.2/3.0, K2O = 10.5/15.2, CO2 = 12.0/8.0, while carbonatite melt can be approximated as 24(K0.81Na0.19)2CO3·76Ca0.59Mg0.21Fe0.20CO3 + 3.0 mol% SiO2 + 1.6 mol% TiO2 + 1.4 mol% Al2O3. Both melts remain stable to at least 1500 °C coexisting with CO2 fluid and residual eclogite assemblage consisting of K-rich omphacite (0.4–1.5 wt% K2O), almandine-pyrope-grossular garnet, kyanite, and coesite. The obtained immiscible alkali‑carbonatitic and potassic aluminosilicate melts resemble compositions of melt inclusions in diamonds worldwide. Thus, these melts entrapped by diamonds could be derived by partial melting of the carbonated material of the continental crust subducted down to 180–200 km depths. Given the high solubility of chlorides and water in both carbonate and aluminosilicate melts inferred in previous experiments, the saline end-member, brine, could evolve from potassic carbonatitic and/or silicic melts by fractionation of Ca-Mg carbonates/eclogitic minerals and accumulation of alkalis, chlorine and water in the residual low-temperature supercritical fluid. Direct extraction from the hydrated marine sediments under conditions of cold subduction would be another possibility for the brine formation.  相似文献   

8.
The Losevka pluton of rare-metal albite granite, which was explored as a possible source of columbite-zircon-malacon ore, is composed of quartz, sodic plagioclase, potassium feldspar, annite, protolithionite, lepidomelane, and Li-muscovite. The average chemical composition of this rock is as follows, wt %: 74.14 SiO2, 0.04 TiO2, 14.07 Al2O3, 1.05 Fe2O3, 0.78 FeO, 0.15 MnO, 0.09 MgO, 0.47 CaO, 4.65 Na2O, 4.11 K2O, and 0.03 P2O5. The accessory minerals are zircon, malacon, and cyrtolite (874 ppm); apatite (18 ppm); ilmenite (114 ppm); xenotime and monazite (119 ppm); and Nb-columbite (463 ppm). The black inclusions up to 15 cm in size, which are observed in this granite and called “birthmarks” by local geologists, consist of the same rock-forming minerals as the surrounding granite, but are enriched in MnO, MgO, CaO, TiO2, and F and depleted in SiO2 relative to the light granite. The black granite is also distinguished by much higher Sr and Ba contents and lower La, Rb, Y, Nb, REE, Cs, Ta, Th, and U contents. The black color is caused by enrichment in manganese oxides, manganoilmenite, and Mn-annite. All rock-forming minerals are pervaded by thin veinlets of Mn-oxides. In addition, bastnaesite, Y-and Th-fluorides, zircon, and malacon have been identified. Aggregates of black-colored minerals are not the products of the fractionation of the initial magma or immiscibility effects, because the structure of the albite-potassium feldspar-quartz-mica matrix is the same both in black and light granites. The percolation of a deep-sourced fluid enriched in Mn and F into a granitic melt might be a more probable origin.  相似文献   

9.
The Oroscocha Quaternary volcano, in the Inner Arc Domain of the Andean Cordillera (southern Peru), emitted peraluminous rhyolites and trachydacites that entrained decimetric to millimetric lamprophyric blobs. These latter show kersantite modal compositions (equal proportion of groundmass plagioclase and K-feldspar) and potassic bulk-rock compositions (1<K2O/Na2O<2; 6.7–7.2 wt.% CaO). Kersantite blobs have shapes and microstructures consistent with an origin from a mixing process between mafic potassic melts and rhyolitic melts. Both melts did exchange their phenocrysts during the mixing process. In addition to index minerals of lamprophyres (Ba–Ti–phlogopite, F-rich apatite, andesine and Ca-rich sanidine), the groundmass of kersantite blobs displays essenite-rich diopside (up to 22 mol%), Ti-poor magnetite microlites, Ti-poor hematite microlites and a series of Ca–Ti–Zr- and REE-rich accessory minerals that have never been reported from lamprophyres. Titanite [up to 5.3 wt.% ZrO2 and 5.2 wt.% (Y2O3 + REE2O3)] and Zr- and Ca-rich perrierite (up to 7.2 wt.% ZrO2 and 10.8 wt.% CaO) predate LREE- and iron-rich zirconolite and Fe-, Ti-, Hf-, Nb- and Ce-rich baddeleyite (up to 5.3 wt.% Fe2O3, 3.2 wt.% TiO2, 1.5 wt.% HfO2, 1.2 wt.% Nb2O5, 0.25 wt.% CeO2) in the crystallization order of the groundmass. Isomorphic substitutions suggest iron to occur as Fe3+ in all the accessory phases. This feature, the essenitic substitution in the clinopyroxene and the occurrence of hematite microlites, all indicate a drastic increase of the oxygen fugacity (from FMQ − 1 to FMQ + 5 log units) well above the HM synthetic buffer within a narrow temperature range (1100–1000 °C). Such a late-magmatic oxidation is ascribed to assimilation of water from the felsic melts during magma mixing, followed by rapid degassing and water dissociation during eruption of host felsic lavas. Thus, magma mixing involving felsic melt end-members provides a mechanism for mafic potassic melts to be oxidized beyond the HM synthetic buffer curve.  相似文献   

10.
Electron microprobe analyses sensitive to 20ppmw (2σ) were made for Na, P, K and Ti in garnet, pyroxenes and olivine from peridotite and eclogite xenoliths from African kimberlites and volcanic rocks in Tanzania. Average concentrations (ppmw) in peridotite (mostly garnet lherzolite) are: Na2O gt 340 ol 90 opx 1070 cpx 2.1 (wt.%); P2O5 gt 460 ol 130 opx 50 cpx 350; K2O gt <20 ol <20 opx 30 cpx 170; TiO2 gt 1470 ol 130 opx 480 cpx 1630. For eclogites and a cpx megacryst with gt inclusions: Na2O gt 610 cpx 4.3 (wt.%); P2O5 gt 530 cpx 300; K2O gt <20 cpx 370; TiO2 gt 1990 cpx 1980.In garnet, Na can be explained by coupled substitution with P and Ti, and there is no need to invoke six-coordinated silicon. The Na distribution between garnet and clinopyroxene correlates with the Fe/Mg distribution for both eclogites and peridotites, and for the peridotites correlates with estimates of pressure and temperature from pyroxene composition. When calibrated experimentally, the Na distribution may be a useful indicator of physical conditions at depths for which the Fe/Mg distribution is insensitive; furthermore the Na distribution may be less sensitive to oxidation state.  相似文献   

11.
Manganese oxides, which are widespread and of great practical importance, are formed and transformed by the active role of microorganisms. Manganese aggregates occur as both crystallized varieties and disordered fine-grained phases with significant ore grade and up to 50–60 vol % of X-ray amorphous components. X-ray amorphous nanosized Mn oxides in Fe-Mn nodules from the Pacific Ocean floor were examined from the standpoint of their biogenic origin. SEM examination showed abundant mineralized biofilms on the studied samples. The chemical composition of bacterial mass is as follows (wt %): 28.34 MnO, 17.14 Fe2O3, 7.11 SiO2, 2.41 CaO, 17.90 TiO2, 1.74 Na2O, 1.73 Al2O3, 1.30 MgO, 1.25 P2O5, 1.25 SO3, 0.68 CoO, 0.54 CuO, 0.53 NiO, and 0.50 K2O. The chemical composition of fossilized cyanobacterial mats within the interlayer space of nodulesis as follows (wt %): 48.35 MnO, 6.23 Fe2O3, 8.76 MgO, 5.05 Al2O3, 4.45 SiO2, 3.63 NiO, 2.30 Na2O, 2.19 CuO, 1.31 CaO, and 0.68 K2O is direct evidence for participation of bacteria in Mn oxide formation. This phase consists of mineralized glycocalix consisting of nanosized flakes of todorokite. Native metals (Cu, Fe, and Zn) as inclusions 10–20 μm in size were identified in ferromanganese nodules as well. The formation of nativemetals can be explained by their crystallization at highly reducing conditions maintained by organic matter.  相似文献   

12.
Melt and fluid inclusions were investigated in six quartz phenocryst samples from the igneous rocks of the extrusive (ignimbrites and rhyolites) and subvolcanic (granite porphyries) facies of the Lashkerek Depression in the Kurama mining district, Middle Tien Shan. The method of inclusion homogenization was used, and glasses from more than 40 inclusions were analyzed on electron and ion microprobes. The chemical characteristics of these inclusions are typical of silicic magmatic melts. The average composition is the following (wt %): 72.4 SiO2, 0.06 TiO2, 13.3 Al2O3, 0.95 FeO, 0.03 MnO, 0.01 MgO, 0.46 CaO, 3.33 Na2O, 5.16K2O, 0.32 F, and 0.21 Cl. Potassium strongly prevails over sodium in all of the inclusions (K2O/Na2O averages 1.60). The average total of components in melt inclusions from five samples is 95.3 wt %, which indicates a possible average water content in the melt of no less than 3–4 wt %. Water contents of 2.0 wt % and 6.6 wt % were determined in melt inclusions from two samples using an ion microprobe. The analyses of ore elements in the melt inclusions revealed high contents of Sn (up to 970 ppm), Th (19–62 ppm, 47 ppm on average), and U (9–26 ppm, 18 ppm on average), but very low Eu contents (0.01 ppm). Melt inclusions of two different compositions were detected in quartz from a granite porphyry sample: silicate and chloride, the latter being more abundant. In addition to Na and K chlorides, the salt inclusions usually contain one or several anisotropic crystals and an opaque phase. The homogenization temperatures of the salt inclusions are rather high, from 680 to 820°C. In addition to silicate inclusions with homogenization temperatures of 820–850°C, a primary fluid inclusion of aqueous solution with a concentration of 3.7 wt % NaCl eq. and a very high density of 0.93 g/cm3 was found in quartz from the ignimbrite. High fluid pressure values of 6.5–8.3 kbar were calculated for the temperature of quartz formation. These estimates are comparable with values obtained by us previously for other regions of the world: 2.6–4.3 kbar for Italy, 3.7 kbar for Mongolia, 3.3–8.7 kbar for central Slovakia, and 3.3–9.6 kbar for eastern Slovakia. Unusual melt inclusions were investigated in quartz from another ignimbrite sample. In addition to a gas phase and transparent glass, they contain spherical Feoxide globules (81.2 wt % FeO) with high content of SiO2 (9.9 wt %). The globules were dissolved in the silicate melt within a narrow temperature range of 1050–1100°C, and the complete homogenization of the inclusions was observed at temperatures of 1140°C or higher. The combined analysis of the results of the investigation of these inclusions allowed us to conclude that immiscible liquids were formed in the high-temperature silicic magma with the separation of iron oxide-dominated droplets.  相似文献   

13.
Melt and fluid inclusions have been studied in olivine phenocrysts (Fo 81–79) from trachybasalts of the Southern Baikal volcanic area, Dzhida field. The melt inclusions were homogenized, quenched, and analyzed on an electron and ion microprobe. The study of homogenized glasses of nine inclusions showed that basaltic melts (SiO2 = 47.1–50.3 wt %, MgO = 5.0–7.7 wt %, CaO = 7.1–11.1 wt %) have high contents of Al2O3 (17.1–19.6 wt %), Na2O (4.1–6.2 wt %), K2O (2.2–3.3 wt %), and P2O5 (0.6–1.1 wt %). The volatile contents are low (in wt %): 0.24–0.31 H2O, 0.08 F, 0.03 Cl, and 0.02 S. Primary fluid inclusions in olivines from four trachybasalt samples contain high-density CO2 (0.73–0.87 g/cm3), indicating a CO2 fluid pressure of 4.3–6.6 kbar at 1200–1300°C and olivine crystallization depths of 16–24 km. Ion microprobe analyses of 20 glasses from melt inclusions for trace elements showed that the magmas of the Baikal rift were enriched in incompatible elements, thus differing from oceanic rift basalts and resembling oceanic island basalts. A comparison of our data on melt and fluid inclusions in olivine from trachybasalts of the Dzhida field with preexisting data on the Eastern Tuva volcanic highland in the Southern Baikal volcanic area showed that they had similar contents of volatiles, major, and trace elements.  相似文献   

14.
A dike–vein complex of potassic type of alkalinity recently discovered in the Baikal ledge, western Baikal area, southern Siberian craton, includes calcite and dolomite–ankerite carbonatites, silicate-bearing carbonatite, phlogopite metapicrite, and phoscorite. The most reliable 40Ar–39Ar dating of the rocks on magnesioriebeckite from alkaline metasomatite at contact with carbonatite yields a statistically significant plateau age of 1017.4 ± 3.2 Ma. The carbonatite is characterized by elevated SiO2 concentrations and is rich in K2O (K2O/Na2O ratio is 21 on average for the calcite carbonatite and 2.5 for the dolomite–ankerite carbonatite), TiO2, P2O5 (up to 9 wt %), REE (up to 3300 ppm), Nb (up to 400 ppm), Zr (up to 800 ppm), Fe, Cr, V, Ni, and Co at relatively low Sr concentrations. Both the metapicrite and the carbonatite are hundreds of times or even more enriched in Ta, Nb, K, and LREE relative to the mantle and are tens of times richer in Rb, Ba, Zr, Hf, and Ti. The high (Gd/Yb)CN ratios of the metapicrite (4.5–11) and carbonatite (4.5–17) testify that their source contained residual garnet, and the high K2O/Na2O ratios of the metapicrite (9–15) and carbonatite suggest that the source also contained phlogopite. The Nd isotopic ratios of the carbonatite suggest that the mantle source of the carbonatite was mildly depleted and similar to an average OIB source. The carbonatites of various mineral composition are believed to be formed via the crystallization differentiation of ferrocarbonatite melt, which segregated from ultramafic alkaline melt.  相似文献   

15.
I. A. Andreeva 《Petrology》2016,24(5):462-476
Melt inclusions were studied by various methods, including electron and ion microprobe analysis, to determine the compositions of melts and mechanisms of formation of rare-metal peralkaline granites of the Khaldzan Buregtey massif in Mongolia. Primary crystalline and coexisting melt inclusions were found in quartz from the rare-metal granites of intrusive phase V. Among the crystalline inclusions, we identified potassium feldspar, albite, tuhualite, titanite, fluorite, and diverse rare-metal phases, including minerals of zirconium (zircon and gittinsite), niobium (pyrochlore), and rare earth elements (parisite). The observed crystalline inclusions reproduce almost the whole suite of major and accessory minerals of the rare-metal granites, which supports the possibility of their crystallization from a magmatic melt. Melt inclusions in quartz from these rocks are completely crystallized. Their daughter mineral assemblage includes quartz, microcline, aegirine, arfvedsonite, polylithionite, a zirconosilicate, pyrochlore, and a rare-earth fluorocarbonate. The melt inclusions were homogenized in an internally heated gas vessel at a temperature of 850°C and a pressure of 3 kbar. After the experiments, many inclusions were homogeneous and consisted of silicate glass. In addition to silicate glass, some inclusions contained tiny quench zircon crystals confined to the boundary of inclusions, which indicates that the melts were saturated in zircon. In a few inclusions, glass coexisted with a CO2 phase. This allowed us to estimate the content of CO2 in the inclusion as 1.5 wt %. The composition of glasses from the homogeneous melt inclusions is similar to the composition of the rare-metal granites, in particular, with respect to SiO2 (68–74 wt %), TiO2 (0.5–0.9 wt %), FeO (2.2–4.6 wt %), MgO (0.02 wt %), and Na2O + K2O (up to 8.5 wt %). On the other hand, the glasses of melt inclusions appeared to be strongly depleted compared with the rocks in CaO (0.22 and 4 wt %, respectively) and Al2O3 (5.5–7.0 and 9.6 wt %, respectively). The agpaitic index is 1.1–1.7. The melts contain up to 3 wt % H2O and 2–4 wt % F. The trace element analysis of glasses from homogenized melt inclusions in quartz showed that the rare-metal granites were formed from extensively evolved rare-metal alkaline melts with high contents of Zr, Nb, Th, U, Ta, Hf, Rb, Pb, Y, and REE, which reflects the metallogenic signature of the Khaldzan Buregtey deposit. The development of unique rare metal Zr–Nb–REE mineralization in these rocks is related to the prolonged crystallization differentiation of melts and assimilation of enclosing carbonate rocks.  相似文献   

16.
The Llano uplift exposes rocks of approximately 1000 m.y. age. The weighted average composition of the exposed crust is: 70.7% SiO2; 0.35% TiO2; 13.6% A12O3; 3.4% total Fe as Fe2O3; 1.1% MgO; 2.6% CaO; 3.3% Na2O; and 4.4% K2O. This composition is similar to, but more potassic, than equivalent estimates for the Canadian shield.  相似文献   

17.
Melt inclusions were studied in chrome diopside from the Inagli deposit of gemstones in the Inagli massif of alkaline ultrabasic rocks of potassic affinity in the northwestern Aldan shield, Yakutia, Russia. The chrome diopside is highly transparent and has an intense green color. Its Cr2O3 content varies from 0.13 to 0.75 wt %. Primary and primary-secondary polyphase inclusions in chrome diopside are dominated by crystal phases (80–90 vol %) and contain aqueous solution and a gas phase. Using electron microprobe analysis and Raman spectroscopy, the following crystalline phases were identified. Silicate minerals are represented by potassium feldspar, pectolite [NaCa2Si3O8(OH)], and phlogopite. The most abundant minerals in the majority of inclusions are sulfates: glaserite (aphthitalite) [K3Na(SO4)2], glauberite [Na2Ca(SO4)2], aluminum sulfate, anhydrite (CaSO4), gypsum (CaSO4 × 2H2O), barite (BaSO4), bloedite [Na2Mg(SO4)2 × 4H2O], thenardite (NaSO4), polyhalite [K2Ca2Mg(SO4)4 × 2H2O], arcanite (K2SO4), and celestite (SrSO4). In addition, apatite was detected in some inclusions. Chlorides are probably present among small crystalline phases, because some analyses of aggregates of silicate and sulfate minerals showed up to 0.19–10.3 wt % Cl. Hydrogen was identified in the gas phase of polyphase inclusions by Raman spectroscopy. The composition of melt from which the chrome diopside crystallized was calculated on the basis of the investigation of silicate melt inclusions. This melt contains 53.5 wt % SiO2, considerable amounts of CaO (16.3 wt %), K2O (7.9 wt %), Na2O (3.5 wt %), and SO3 (1.4 wt %) and moderate amounts of Al2O3 (7.5 wt %), MgO (5.8 wt %), FeO (1.1 wt %), and H2O (0.75 wt %). The content of Cr2O3 in the melt was 0.13 wt %. Many inclusions were homogenized at 770–850°C, when all of the crystals and the gas phase were dissolved. The material of inclusions heated up to the homogenization temperature became heterogeneous even during very fast quenching (two seconds) producing numerous small crystals. This fact implies that most of the inclusions contained a salt (rather than silicate) melt of sulfate-dominated composition. Such inclusions were formed from salt globules (with a density of about 2.5 g/cm3) occurring as an emulsion in the denser (2.6 g/cm3) silicate melt from which the chrome diopside crystallized.  相似文献   

18.
The paper presents data on inclusions in minerals of the least modified potassic lamprophyres in a series of strongly carbonatized potassic alkaline ultramafic porphyritic rocks. The rocks consist of diopside, kaersutite, analcime, apatite, and rare phlogopite and titanite phenocrysts and a groundmass, which is made up, along with these minerals, of potassic feldspar and calcite. The diopside and kaersutite phenocrysts display unsystematic multiple zoning. Chemically and mineralogically, the rock is ultramafic foidite and most likely corresponds to monchiquite. Primary and secondary melt inclusions were found in diopside, kaersutite, apatite, and titanite phenocrysts and are classified into three types: sodic silicate inclusions with analcime, potassic silicate inclusions with potassic feldspar, and carbonate inclusions, which are dominated by calcite. Heating and homogenization of the inclusions show that the potassic lamprophyres crystallized from a heterogeneous magma, with consisted of mixing mafic sodic and potassic alkaline magmas enriched in a carbonatite component. The composition of the magmas was close to nepheline and leucite melanephelinite. The minerals crystallized at 1150–1090°C from the sodic melts and at 1200–1250°C from the potassic ones. The sodic mafic melts were richer in Fe than the potassic ones, were the richest in Al, Mn, SO3, Cl, and H2O and poorer in Ti and P. The potassic mafic melts were not lamproitic, as follows from the presence of albite in the crystallized primary potassic melt inclusions. The diopside, the first mineral to crystallize in the rock, started to crystallize in the magmatic chamber from sodic mafic melt and ended to crystallize from mixed sodic–potassic melts. The potassic mafic melts were multiply replenished in the chamber in relation to tectonic motions. The ascent of the melts to the surface and rapidly varying P–T parameters of the magma were favorable for multiple separations of carbonatite melts from the alkaline mafic ones and their mixing and mingling.  相似文献   

19.
Hydrothermal experiments were carried out at 2 kbar water pressure, 700 °–800 ° C, with the objective of determining the level of dissolved Zr required for precipitation of zircon from melts in the system SiO2-Al2O3-Na2O-K2O. The saturation level depends strongly upon molar (Na2O + K2O)/Al2O3 of the melts, with remarkably little sensitivity to temperature, SiO2 concentration, or melt Na2O/ K2O. For peraluminous melts and melts lying in the quartz-orthoclase-albite composition plane, less than 100 ppm Zr is required for zircon saturation. In peralkaline melts, however, zircon solubility shows pronounced, apparently linear, dependence upon (Na2O + K2O)/Al2O3, with the amount of dissolvable Zr ranging up to 3.9 wt.% at (Na2O + K2O)/Al2O3 = 2.0. Small amounts (1 wt.% each) of dissolved CaO and Fe2O3 cause a 25% relative reduction of zircon solubility in peralkaline melts.The main conclusion regarding zirconium/zircon behavior in nature is that any felsic, non-peralkaline magma is likely to contain zircon crystals, because the saturation level is so low for these compositions. Zircon fractionation, and its consequences to REE, Th, and Ta abundances must, therefore, be considered in modelling the evolution of these magmas. Partial melting in any region of the Earth's crust that contains more than 100 ppm Zr will produce granitic magmas whose Zr contents are buffered at constant low (< 100 ppm) values; unmelted zircon in the residual rock of such a melting event will impart to the residue a characteristic U- or V-shaped REE abundance pattern. In peralkaline, felsic magmas such as those that form pantellerites and comendites, extreme Zr (and REE, Ta) enrichment is possible because the feldspar fractionation that produces these magmas from non-peralkaline predecessors does not drive the melt toward saturation in zircon.Zircon solubility in felsic melts appears to be controlled by the formation of alkali-zirconosilicate complexes of simple (2:1) alkali oxide: ZrO2 stoichiometry.  相似文献   

20.
The data obtained on melt and fluid inclusions in minerals of granites, metasomatic rocks, and veins with tin ore mineralization at the Industrial’noe deposit in the southern part of the Omsukchan trough, northeastern Russia, indicate that the melt from which the quartz of the granites crystallized contained globules of salt melts. Silicate melt inclusions were used to determine the principal parameters of the magmatic melts that formed the granites, which had temperatures at 760–1020°C, were under pressures of 0.3–3.6 kbar, and had densities of 2.11–2.60 g/cm3 and water concentrations of 1.7–7.0 wt %. The results obtained on the fluid inclusions testify that the parameters of the mineral-forming fluids broadly varied and corresponded to temperatures at 920–275°C, pressures 0.1–3.1 kbar, densities of 0.70–1.90 g/cm3, and salinities of 4.0–75.0 wt % equiv. NaCl. Electron microprobe analyses of the glasses of twelve homogenized inclusions show concentrations of major components typical of an acid magmatic melt (wt %, average): 73.2% SiO2, 15.3% Al2O3, 1.3% FeO, 0.6% CaO, 3.1% Na2O, and 4.5% K2O at elevated concentrations of Cl (up to 0.51 wt %, average 0.31 wt %). The concentrations and distribution of some elements (Cl, K, Ca, Mn, Fe, Cu, Zn, Pb, As, Br, Rb, Sr, and Sn) in polyphase salt globules in quartz from both the granites and a mineralized miarolitic cavity in granite were assayed by micro-PIXE (proton-induced X-ray emission). Analyses of eight salt globules in quartz from the granites point to high concentrations (average, wt %) of Cl (27.5), Fe (9.7), Cu (7.2), Mn (1.1), Zn (0.66), Pb (0.37) and (average, ppm) As (2020), Rb (1850), Sr (1090), and Br (990). The salt globules in the miarolitic quartz are rich in (average of 29 globules, wt %) Cl (25.0), Fe (5.4), Mn (1.0), Zn (0.50), Pb (0.24) and (ppm) Rb (810), Sn (540), and Br (470). The synthesis of all data obtained on melt and fluid inclusions in minerals from the Industrial’noe deposit suggest that the genesis of the tin ore mineralization was related to the crystallization of acid magmatic melts. Original Russian Text@ V.B. Naumov, V.S. Kamenetsky, 2006, published in Geokhimiya, 2006, No. 12, pp. 1279–1289.  相似文献   

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