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1.
Aplite dikes intruding the Proterozoic 1.42(±?3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P2O5, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride?+?phosphate (+?S?+?CO2) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride?+?phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(±?25) and 1.442(±?8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, εNd1.42Ga values for the granites and related granitic pegmatites range from ??3.3 to ??4.7 (average ??3.9), and differ from the values for both the aplites and REE-rich segregations, which range from ??1.0 to ??2.2 (average ??1.6). Furthermore, the granites and pegmatites have (La/Yb)N <50 with significant negative Eu anomalies, which contrast with higher (La/Yb)N >100 and absence of an Eu anomaly in both the aplites and segregations. These data are consistent with the aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher εNd1.42Ga values for the aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite. 相似文献
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3.
Spinel-hosted hydrous silicate mineral inclusions are often observed in dunite and troctolite as well as chromitite. Their origin has been expected as products associated with melt–peridotite reaction, based on the host rock origin. However, the systematics in mineralogical and geochemical features are not yet investigated totally. In this study, we report geochemical variations of the spinel-hosted pargasite inclusions in reacted harzburgite and olivine-rich troctolite collected from Atlantis Massif, an oceanic core complex, in the Mid-Atlantic Ridge. The studied samples are a good example to examine geochemical variations in the inclusions because the origin and geological background of the host rocks have been well constrained, such as the reaction between MORB melt and depleted residual harzburgite beneath the mid-ocean ridge spreading center. The trace-element compositions of the pargasite inclusions are characterized by not only high abundance of incompatible elements but also the LREE and HFSE enrichments. Distinctive trace-element partitioning between the pargasite inclusion and the host-rock clinopyroxene supports that the secondary melt instantaneously formed by the reaction is trapped in spinel and produces inclusion minerals. While the pargasite geochemical features can be interpreted by modal change reaction of residual harzburgite, such as combination of orthopyroxene decomposition and olivine precipitation, degree of the LREE enrichment as well as variation of HREE abundance is controlled by melt/rock ratio in the reaction. The spinel-hosted hydrous inclusion could be embedded evidence indicating melt–peridotite reaction even if reaction signatures in the host rock were hidden by other consequent reactions. 相似文献
4.
Data are presented on the equilibrium compositions of olivine and melts in the products of 101 experiments performed at 1300–1600°C, atmospheric pressure, and controlled oxygen fugacity by means of new equipment at the Vernadsky Institute. It was shown that the available models of the olivine–melt equilibrium describe with insufficient adequacy the natural systems at temperatures over 1400°C. The most adequate is the model by Ford et al. (1983). However, this model overestimates systematically the equilibrium temperature with underestimating by 20–40°C at 1450–1600°C. These data point to the need for developing a new, improved quantitative model of the olivine–melt equilibrium for high-temperature magnesian melts, as well as to the possibility of these studies on the basis of the equipment presented. 相似文献
5.
Compositional dependence of REE partitioning between diopside and melt at 1 atmosphere 总被引：1，自引：1，他引：0
The effects of composition on pyroxene-melt partitioning of several REE (rare earth elements), Y, and Sr were experimentally
evaluated. Using the synthetic model systems anorthite–diopside, diopside–titanite and anorthite–diopside–titanite different
diopsides were grown at atmospheric conditions in a double-ellipsoid mirror furnace. The single samples were melted and crystallised
in a Pt/Au crucible with compositions corresponding to the invariant points of these systems. Rotational motion with approximately
25 rpm around the longitudinal axis of the crucible increases the prevailing convection flows. By this means, the exclusively
diffusional transport of assembly groups onto the growing crystals is avoided. Quenching is achieved by dropping the crucible
into water. Crystals up to 2 mm were obtained and analysed by electron microprobe. No inhomogeneities or compositional zonation,
either in the diopsides or in the coexisting melts, were observed within the analytical uncertainty of the electron microprobe.
The crystallised diopsides occur as both euhedral single crystals and large symplectitic lamellar intergrowths with anorthite
or titanite. The chemical homogeneity and the texture indicate near-equilibrium conditions. The analyses show strong positive
correlations between DREE and tetrahedrally coordinated Al in diopside but are not affected by octahedral Al or Ti-concentration. By means of correlations
and mass balances the incorporation of REE can be described by 2 different coupled substitutions:
The Al-coupled incorporation of REE3+ (1) dominates the D-values. The Na-coupled substitution (2) is of minor importance. Depending on the compositions investigated
the D-values vary by up to a factor of 10. This range overlaps most of the published pyroxene-melt partition coefficients.
Because we conducted isothermal and isobaric experiments, this overlap indicates that a wide range of D-values is a function
of composition. For the coupled substitutions (1) and (2) this indicates that the DREE strongly depends on the amount of tetrahedrally coordinated Al3+ in clinopyroxenes.
Received: 5 January 1998 / Accepted: 11 June 1998 相似文献
6.
E. I. Zhimulev V. M. Sonin V. P. Afanasiev A. I. Chepurov N. P. Pokhilenko 《Doklady Earth Sciences》2016,471(2):1277-1279
The first results of experimental study of diamond dissolution in a S-bearing Fe melt at high P–T parameters are reported and the morphology of partially dissolved crystals is compared with that of natural diamonds. Our results show that under the experimental conditions (4 GPa, 1400°C), flat-faced octahedral diamond crystals are transformed into curve-faced octahedroids with morphological features similar to those of natural diamonds. 相似文献
7.
To test a recently developed oxybarometer for silicic magmas based on partitioning of vanadium between magnetite and silicate melt, a comprehensive oxybarometry and thermometry study on 22 natural rhyolites to dacites was conducted. Investigated samples were either vitrophyres or holocrystalline rocks in which part of the mineral and melt assemblage was preserved only as inclusions within phenocrysts. Utilized methods include vanadium magnetite–melt oxybarometry, Fe–Ti oxide thermometry and -oxybarometry, zircon saturation thermometry, and two-feldspar thermometry, with all analyses conducted by laser-ablation ICP–MS. Based on the number of analyses, the reproducibility of the results and the certainty of contemporaneity of the analyzed minerals and silicate melts the samples were grouped into three classes of reliability. In the most reliable (n = 5) and medium reliable (n = 10) samples, all fO2 values determined via vanadium magnetite–melt oxybarometry agree within 0.5 log units with the fO2 values determined via Fe–Ti oxide oxybarometry, except for two samples of the medium reliable group. In the least reliable samples (n = 7), most of which show evidence for magma mixing, calculated fO2 values agree within 0.75 log units. Comparison of three different thermometers reveals that temperatures obtained via zircon saturation thermometry agree within the limits of uncertainty with those obtained via two-feldspar thermometry in most cases, whereas temperatures obtained via Fe–Ti oxide thermometry commonly deviate by ≥50 °C due to large uncertainties associated with the Fe–Ti oxide model at T-fO2 conditions typical of most silicic magmas. Another outcome of this study is that magma mixing is a common but easily overlooked phenomenon in silicic volcanic rocks, which means that great care has to be taken in the application and interpretation of thermometers and oxybarometers. 相似文献
8.
J. J. Hanley J. E. Mungall T. Pettke E. T. C. Spooner C. J. Bray 《Mineralium Deposita》2005,40(3):237-256
We report methane-dominant hydrocarbon (fluid) inclusions (CH4±C2H6–C2H2, C3H8) coexisting with primary brine inclusions and secondary halide melt (solid NaCl) inclusions in Au–Pt-rich quartz-sulfide-epidote
alteration veins associated with the footwall-style Cu–PGE (platinum-group element)–Au deposits at the Fraser Mine (North
Range of the Sudbury Igneous Complex). Evidence for coentrapment of immiscible hydrocarbon–brine, and hydrocarbon–halide melt
mixtures is demonstrated. A primary CH4–brine assemblage was trapped during quartz growth at relatively low T (min. T
trapping∼145–315°C) and P (max. P
trapping∼500 bar), prior to the crystallization of sulfide minerals in the veins. Secondary inclusions contain solid halite and a
mixture of CH4, C2H6–C2H2 and C3H8 and were trapped at a minimum T of ∼710°C. The halite inclusions may represent halide melt that exsolved from crystallizing sulfide ores that texturally
postdate (by replacement) early alteration quartz hosting the primary, lower T brine–CH4 assemblage. Laser ablation ICP-MS analyses show that the brine, hydrocarbon and halide melt inclusions contain significant
concentrations of Cu (0.1–1 wt% range), Au, Bi, Ag and Pt (all 0.1–10 ppm range). Cu:Pt and Cu:Au ratios in the inclusions
are significantly (up to 4 log units) lower than in the host alteration veins and adjacent massive sulfide ore veins, suggesting
either (1) early Cu loss from the volatiles by chalcopyrite precipitation or (2) enhanced Au and Pt solubilities relative
to Cu at the temperatures of entrapment. Concentration ratios between coexisting brine and CH4 inclusions
are lower for Cu, Au, Bi and Ag than for other elements (Na, Ca, Fe, Mn, Zn, Pb) indicating that during interaction with
the brine, the hydrocarbon phase was enriched in ore metals. The high concentrations of ore metals in hydrocarbon, brine and
halide melt phases confirm that both aqueous and non-aqueous volatiles were carriers of precious metals in the Sudbury environment
over a wide range of temperatures. Volatile evolution and magmatic sulfide differentiation were clearly part of a single,
continuous process in the Sudbury footwall. The exsolution of H2O-poor volatiles from fractionated sulfide liquid may have been a principal mechanism controlling the final distribution of
PGE and Au in the footwall ore systems. The study reports the first measurements of precious metal concentrations in fluid
inclusions from a magmatic Ni–Cu–PGE environment (the Sudbury district).
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
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This study reports a geochemical investigation of two thick basalt sequences, exposed in the Bracco–Levanto ophiolite (northern Apennine, Italy) and in the Balagne ophiolite (central-northern Corsica, France). These ophiolites are considered to represent an oceanward and a continent-near paleogeographic domain of the Jurassic Liguria–Piedmont basin. Trace elements and Nd isotopic compositions were examined to obtain information about: (1) mantle source and melting process and (2) melt–rock reactions during basalt ascent. Whole-rock analyses revealed that the Balagne basalts are slightly enriched in LREE, Nb, and Ta with respect to the Bracco–Levanto counterparts. These variations are paralleled by clinopyroxene chemistry. In particular, clinopyroxene from the Balagne basalts has higher CeN/SmN (0.4–0.3 vs. 0.2) and ZrN/YN (0.9–0.6 vs. 0.4–0.3) than that from the Bracco–Levanto basalts. The basalts from the two ophiolites have homogeneous initial Nd isotopic compositions (initial εNd from +?8.8 to +?8.6), within typical depleted mantle values, thereby excluding an origin from a lithospheric mantle source. These data also reject the involvement of contaminant crustal material, as associated continent-derived clastic sediments and radiolarian cherts have a highly radiogenic Nd isotopic fingerprint (εNd at the time of basalt formation?=???5.5 and ??5.2, respectively). We propose that the Bracco–Levanto and the Balagne basalts formed by partial melts of a depleted mantle source, most likely containing a garnet-bearing enriched component. The decoupling between incompatible elements and Nd isotopic signature can be explained either by different degrees of partial melting of a similar asthenospheric source or by reaction of the ascending melts with a lower crustal crystal mush. Both hypotheses are reconcilable with the formation of these two basalt sequences in different domains of a nascent oceanic basin. 相似文献
11.
Geoff Kilgour Jon Blundy Kathy Cashman Heidy M. Mader 《Contributions to Mineralogy and Petrology》2013,166(2):371-392
Historical eruptions from Mt. Ruapehu (New Zealand) have been small (<0.001 km3 of juvenile magma) and have often occurred without significant warning. Developing better modelling tools requires an improved understanding of the magma storage and transport system beneath the volcano. Towards that end, we have analysed the volatile content and major element chemistry of groundmass glass and phenocryst-hosted melt inclusions in erupted samples from 1945 to 1996. We find that during this time period, magma has been stored at depths of ~2–9 km, consistent with inferences from geophysical data. Our data also show that Ruapehu magmas are relatively H2O-poor (<2 wt%) and CO2-rich (≤1,000 ppm) compared to typical arc andesites. Surprisingly, we find that melt inclusions are often more evolved than their transporting melt (as inferred from groundmass glass compositions). Furthermore, even eruptions that are separated by less than 2 years exhibit distinct major element chemistry, which suggests that each eruption involved magma with a unique ascent history. From these data, we infer that individual melt batches rise through, and interact with, crystal mush zones formed by antecedent magmas. From this perspective, we envision the magmatic system at Ruapehu as frequently recharged by small magma inputs that, in turn, cool and crystallise to varying degrees. Melts that are able to erupt through this network of crystal mush entrain (to a greater or lesser extent) exotic crystals. In the extreme case (such as the 1996 eruption), the resulting scoria contain melt inclusion-bearing crystals that are exotic to the transporting magma. Finally, we suggest that complex interactions between recharge and antecedent magmas are probably common, but that the small volumes and short time scales of recharge at Ruapehu provide a unique window into these processes. 相似文献
12.
《中国地球化学学报》2006,25(B08):117-117
13.
Diffusive reequilibration of quartz-hosted silicate melt and fluid inclusions: Are all metal concentrations unmodified? 总被引：1，自引：0，他引：1
Zoltan Zajacz Jacob J. Hanley Werner E. Halter 《Geochimica et cosmochimica acta》2009,73(10):3013-2827
Experiments were conducted to determine the extent and mechanism by which the composition of quartz-hosted silicate melt inclusions (SMI) and aqueous fluid inclusions (FI) can undergo post-entrapment modification via diffusion. Quartz slabs containing assemblages of SMI and FI were reacted with synthetic HCl bearing and metalliferous aqueous fluids at T = 500-720 °C and P = 150-200 MPa. SMI from the single inclusion assemblages were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and electron probe microanalysis (EPMA) before and after the experiments. Analyses revealed that rapid diffusion of the univalent cations Na+, Li+, Ag+, Cu+ and H+ occurred through the quartz from the surroundings, resulting in significant changes in the concentrations of these elements in the inclusions. Concentrations of other elements with an effective ionic radius larger than that of Ag+, or multiple valence states were not modified in the inclusions during the experiments. Our results warn inclusion‘‘ researchers that the interpretation of Na, Li, Cu and Ag concentrations from quartz-hosted SMI and FI should be treated critically. 相似文献
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T. F. Shcherbakova 《Geochemistry International》2017,55(9):833-839
Zircon hosted in granite, which crystallized from local pools of anatectic melt among migmatites, in the Rikolatvi structure, Belomorian Mobile Belt, contains minute inclusions of various minerals, biotite and garnet among others. The compositions of the biotite and garnet in the microinclusions differ from those of the same minerals in the granite containing the zircon. The crystallization temperature of the anatectic melt was estimated by the biotite–garnet geothermometer and the composition of the biotite and garnet inclusions at ~800°C. 相似文献
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In nature selenate reduction and nitrate denitrification both follow a similar biogeo-chemical mechanism.It has been proved that abiotic stresses such as alternative drying and wetting can exert an important influence on nitrate denitrification as well as on selenate reduction.Our experimental results lend great support to the above conclusion. 相似文献
19.
《Chemical Geology》2002,182(2-4):139-178
The Kohistan–Ladakh Terrane in the NW Himalaya is a remnant of a Cretaceous arc sequence obducted onto the Indian margin. This paper presents a geochemical study (major and trace elements and Sr, Nd, Pb isotopes) of the Mid-Cretaceous lavas of the Ladakh side of the arc sequence, which were erupted in response to northward subduction of Neo-Tethys oceanic crust.Lavas from the western Ladakh in Pakistan can be divided into three groups which, from north to south, are: (1) the Northern Group of back-arc tholeiites [0.5<(La/Yb)N<1.4; 0.3<(Nb/La)N<1.4; 4<εNd<8; 38.66<208Pb/204Pb<38.80], (2) the Southern Group of arc tholeiites [1.8<(La/Yb)N<3.9; 0.1<(Nb/La)N<0.6; 5<εNd<6; 38.40<208Pb/204Pb<38.66], and (3) the Katzarah Formation of tholeiitic Nb-rich lavas [3.4<(La/Yb)N<9.8; 1.4<(Nb/La)N<2.1; 3<εNd<5], including radiogenic Pb lavas [39.31<208Pb/204Pb<39.51] and less radiogenic lavas [38.31<208Pb/204Pb<38.55]. Magmas from the eastern Ladakh in India show a simple series of more evolved arc volcanics from basalts to rhyolites [basalts and basaltic andesites: 2.5<(La/Yb)N<5.7; 0.4<(Nb/La)N<0.5; 1.8<εNd<5.5; 38.70<208Pb/204Pb<38.80]. Isotope and trace element data of western Ladakh lavas are compatible with high-degree melting (14–21%) of a fertile MORB-mantle source. An adakitic lava [(La/Yb)N=55.8; (Nb/La)N=0.3; εNd=1.7; 208Pb/204Pb=39.00] and a Mg-poor Nb-rich basalt [(La/Yb)N=4.6; (Nb/La)N=1.3; εNd=−2; 208Pb/204Pb=39.07] are spatially associated with the tholeiitic arc lavas. Isotope compositions of all the lavas, and in particular the radiogenic Nb-rich and adakitic lavas suggest three-component mixing between depleted mantle similar to the Indian MORB mantle, and enriched components similar to the volcanogenic or pelagic sediments. The geochemical diversity of magma types is attributed to contribution of melts from the subducted crust and associated sediments, and their subsequent interaction with the mantle. Such melt–mantle interactions can also be inferred from relicts of sub-arc mantle found in Indian Ladakh. These results lead to a geodynamic reconstruction of the Kohistan–Ladakh arc as a single entity in the Mid-Cretaceous, emplaced south of the Asian margin. Slab melting imply subduction of young oceanic crust, as already proposed for the Oman ophiolite farther west. The fast northward drift of the Indian Plate could have triggered wide-scale inversion of the divergent tectonic regime responsible for the opening of the Neo-Tethys Ocean. Our results suggest breaking of the young oceanic crust initiated at the ridge rather than at passive plate boundaries. 相似文献