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21.
A. A. Ariskin E. G. Konnikov L. V. Danyushevsky E. V. Kislov G. S. Nikolaev D. A. Orsoev G. S. Barmina K. A. Bychkov 《Geochemistry International》2009,47(5):425-453
This paper presents a review of petrological-geochemical studies at the Yoko-Dovyren Massif with an emphasis on relations between parameters of the parental magma, a model for the genesis of the lower contact zone, and the nature of Ni sulfide ore mineralization, including the evaluation of the possible ore potential. Arguments are presented in support of the conclusion that the Dovyren magma brought much intratelluric olivine of the composition Fo 85–87 into the chamber, and the composition of the initial melt corresponded to gabbronorite or moderately magnesian basite with no more than 10 wt % MgO. The probable temperature of the parental magma was approximately 1200–1250°C, and the sulfur solubility did not exceed 0.10–0.12 wt % (P = 1 kbar, WM buffer). The comparison of this estimate with the average S contents in the bottom plagioperidotites (0.12±0.06 wt %) indicates that the initial magma was saturated with a sulfide phase. For the first time the problem of the composition of contaminated dunites was formulated (these rocks occur in the Layered Series and contain more magnesian olivine Fo 87–92). The reason for the increase in the mg# of olivine is thought to be the partial melting and compaction of the original cumulates due to the infiltration of intercumulus melt enriched in volatile components. The volatiles were presumably provided by the thermal decomposition of carbonate xenoliths, a process that resulted in an increase in the CO2 pressure and the transfer of calcite-magnesite components of carbonates into the melt. This follows from (1) the occurrence of magnesian skarn developing after carbonates, (2) high CaO contents in olivine form the contaminated dunite, (3) the appearance of olivine-bearing pyroxenites and wehrlites in the upper part of the dunite zone, (4) correlation between the olivine and chromite composition in the contaminated and uncontaminated dunites, (5) broad variations in the oxygen isotopic composition of olivine and plagioclase from rocks of the Layered Series, (6) experimental data on the dissolution of carbonates in alkali basalt melts, and (7) analogies with isotopic-geochemical characteristics of rocks from the Jinchuan ultramafic complex. Petrological implications of the interpretation of the Dovyren chamber are discussed with reference to closed and flow-through (during an initial stage) magmatic systems. A petrological-geological model is proposed for the genesis of the Synnyr-Dovyren volcanic-plutonic complex and related Ni sulfide ore mineralization. The potential resources of Cu-Ni sulfide ores in the plagioperidotites are evaluated with regard to the still-unexposed part of the massif. 相似文献
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24.
Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications 总被引:4,自引:1,他引:3
L. V. Danyushevsky F. N. Della-Pasqua S. Sokolov 《Contributions to Mineralogy and Petrology》2000,138(1):68-83
We describe and model a potential re-equilibration process that can affect compositions of melt inclusions in magnesian olivine
phenocrysts. This process, referred to as “Fe-loss”, can operate during natural pre-eruptive cooling of host magma and results
in lower FeOt and higher MgO contents within the initially trapped volume of inclusion. The extent of Fe-loss is enhanced by large temperature
intervals of magma cooling before eruption. The compositions of homogenised melt inclusions in olivine phenocrysts from several
subduction-related suites demonstrate that (1) Fe-loss is a common process, (2) the maximum observed degree of re-equilibration
varies between suites, and (3) within a single sample, variable degrees of re-equilibration can be recorded by melt inclusions
trapped in olivine phenocrysts of identical composition. Our modelling also demonstrates that the re-equilibration process
is fast going to completion, in the largest inclusions in the most magnesian phenocrysts it is completed within 2 years. The
results we obtained indicate that the possibility of Fe-loss must be considered when estimating compositions of parental subduction-related
magmas from naturally quenched glassy melt inclusions in magnesian olivine phenocrysts. Compositions calculated from glassy
inclusions affected by Fe-loss will inherit not only erroneously low FeOt contents, but also low MgO due to the inherited higher Mg##of the residual melt in re-equilibrated inclusions. We also demonstrate
that due to the higher MgO contents of homogenised melt inclusions affected by Fe-loss, homogenisation temperatures achieved
in heating experiments will be higher than original trapping temperatures. The extent of overheating will increase depending
on the degree of re-equilibration, and can reach up to 50 °C in cases where complete re-equilibration occurs over a cooling
interval of 200 °C.
Received: 2 November 1998 / Accepted: 27 September 1999 相似文献
25.
M. V. Portnyagin L. V. Danyushevsky V. S. Kamenetsky 《Contributions to Mineralogy and Petrology》1997,128(2-3):287-301
We present a detailed mineralogical, petrological and melt inclusion study of unusually fresh, primitive olivine + clinopyroxene
phyric Lower Pillow Lavas (LPL) found near Analiondas village in the northeastern part of the Troodos ophiolite (Cyprus).
Olivine phenocrysts in these primitive LPL show a wide compositional range (Fo82–92) and have higher CaO contents than those from the Upper Pillow Lavas (UPL). Cr-spinel inclusions in olivine are significantly
less Cr-rich (Cr/Cr + Al = 28–67 mol%) compared to those from the UPL (Cr# = 70–80). These features reflect differences in
melt compositions between primitive LPL and the UPL, namely higher CaO and Al2O3 and lower FeO* compared to the UPL at a given MgO. LPL parental melts (in equilibrium with Fo92) had ∼10.5 wt% MgO and crystallization temperatures ∼1210 °C, which are significantly lower than those previously published
for the UPL (14–15 wt% MgO and ∼1300 °C for Fo92). The fractionation path of LPL parental melts is also different from that of the UPL. It is characterized initially by olivine + clinopyroxene
cotectic crystallization joined by plagioclase at ∼9 wt% MgO, whereas UPL parental melts experienced a substantial interval
of olivine-only crystallization. Primitive LPL melts were formed from a mantle source which was more fertile than that of
tholeiites from well-developed intra-oceanic arcs, but broadly similar in its fertility to that of Mid-Ocean Ridge Basalt
(MORB) and Back Arc Basin Basalts (BABB). The higher degrees of melting during formation of the LPL primary melts compared
to average MORB were caused by the presence of subduction-related components (H2O). Our new data on the LPL coupled with existing data for the UPL support the existing idea that the LPL and UPL primary
melts originated from distinct mantle sources, which cannot be related by progressive source depletion. Temperature differences
between these sources (∼150 °C), their position in the mantle (∼10 kbar for the colder LPL source vs 15–18 kbar for the UPL
source), and temporal succession of Troodos volcanism, all cannot be reconciled in the framework of existing models of mantle
wedge processes, thermal structure and evolution, if a single mantle source is invoked. Possible tectonic settings for the
origin of the Troodos ophiolite (forearc regions of intra-oceanic island arc, propagation of backarc spreading into arc lithosphere)
are discussed.
Received: 20 May 1996 / Accepted: 25 March 1997 相似文献
26.
S. A. Silantyev L. V. Danyushevsky A. A. Plechova L. Dosso B. A. Bazylev V. E. Bel’tenev 《Petrology》2008,16(1):36-62
Data presented in the paper suggest significant differences between the thermodynamic conditions under which magmatic complexes were formed in MAR at 29°–34° N and 12°–18° N. The melts occurring at 29°–34° N were derived by the melting of a mantle source with a homogeneous distribution of volatile components and arrived at the surface without significant fractionation, likely, due to their rapid ascent. The MAR segments between 12° and 18° N combine contrasting geodynamic environments of magmatism, which predetermined the development of a large plume region with the widespread mixing of the melting products of geochemically distinct mantle sources. At the same time, this region is characterized by conditions favorable for the origin of localized zones of anomalous plume magmatism. These sporadic magmatic sources were spatially restricted to MAR fragments with the Hess crust, whose compositional and mechanical properties were, perhaps, favorable for the focusing and localization of plume magmatism. The plume source between 12° and 18°N beneath MAR may be geochemically heterogeneous. 相似文献
27.
Summary Several experimentally-based, empirical calibrations of the fO2 of natural silicate melts at atmospheric pressure as a function of melt composition, melt Fe2+/Fe3+, and crystallization temperature have been developed (e.g.Sack et al., 1980;Kilinc et al., 1983;Kress andCarmichael, 1988;Borisov andShapkin, 1990). Cr-Al spinel is a liquidus phase of primitive mantle-derived melts, and is commonly found as inclusions in near-liquidus phenocrysts (mainly olivine). The established atmospheric pressure correlation between Fe2+/Fe3+ values in spinel and coexisting melts over a broad range of basaltic compositions (Maurel andMaurel, 1982) can be used to calculate the Fe2+/Fe3+ value of a melt if the composition of the equilibrium spinel is known. Compositions and crystallization temperatures of primitive melts can be determined by experimental studies of melt inclusions trapped by early-formed refractory phenocrysts. Thus, the association of spinel and melt inclusions in early liquidus phenocrysts can be used to estimate fO2 conditions at the time of their crystallization.In this paper, we present a calibration of this method and discuss its applications. We conclude that combination of the equations ofMaurel andMaurel (1982) andBorisov andShapkin (1990) can be used to calculate fO2 with an accuracy of ±0.71og units, when liquidus spinels have TiO2 <2.5 wt% and Cr2O3 > 13 wt.%, and melt compositions are in the range from basaltic to picritic with H2O contents <6 wt.%.Using this technique we find NNO fO2 values of –0.8 to –1.4 for MORB dredged at the VEMA Fracture Zone in the Atlantic, and 0 to + 1 for Tongan high-Ca boninites.
With 7 Figures 相似文献
Die Berechnung von Fe2+/Fe3+ und der Sauerstoff-Fugazitäten für primitive Mantelschmelzen: Kalibration einer empirischen Methode
Zusammenfassung Empirische, auf Experimenten basierende, Kalibrationen zur Berechnung von fO2 natürlicher Silikatschmelzen bei atmosphärischem Druck in Abhängigkeit von der Schmelzzusammensetzung, des Fe2+/Fe3+ Verhältnisses und der Kristallisationstemperatur wurden z.B. vonSack et al. (1980),Kilinc et al. (1983),Kress undCarmichael (1988) undBorisov undShapkin (1980) entwickelt. Cr-Al-Spinell ist eine Liquidusphase primitiver Mantelschmelzen und kommt üblicherweise als Einschluß in near-liquidus Phänokristallen (hauptsächlich in Olivin) vor. Die Korrelation des Atmosphärendruckes zwischen Fe2+/Fe3+ in Spinell und koexistierender Schmelze kann dazu verwendet werden, das Verhältnis von Fe2+/Fe3+ der Schmelze für einen weiten Bereich basaltischer Zusammensetzungen zu berechnen, wenn die Zusammensetzung des im Gleichgewicht gebildeten Spinells bekannt ist (Maurel undMaurel, 1982). Die Zusammensetzungen und Kristallisationstemperaturen primitiver Schmelzen können durch experimentelle Studien von Schmelzeinschlüssen, die in früh gebildeten refraktären Phänokristallen eingeschlossen wurden, ermittelt werden. Daher lassen sich Spinelle und assoziierte Schmelzeinschlüsse in frühen Liquidus-Phänokristallen dazu benützen, die fO2-Bedingungen während der Kristallisation abzuschätzen.In dieser Arbeit präsentieren wir eine neue Kalibration dieser Methode und diskutieren ihre Anwendungen. Wir schlußfolgern, daß unter Kombination der verwendeten Gleichungen vonMaurel undMaurel (1982) sowie vonBorisov undShapkin (1990) fO2 mit einer Genauigkeit von ±0.7 log Einheiten berechnet werden kann, soferne die Liquidus-Spinelle < 2.5 Gew.% TiO2 und > 13 Gew.% Cr2O3 haben und die Schmelzzusammensetzungen von basaltisch bis pikritisch, mit maximal 6 Gew.% H2O, reichen.Unter Verwendung dieser Technik wurden die NNO fO2 Werte für die von der VEMA Fracture Zone im Atlantik stammenden MORB Proben mit 0.8 bis - 1.4, die der der High-Ca Boninite von Tonga mit 0 bis + 1 bestimmt.
With 7 Figures 相似文献
28.
N. R. Ayupova V. V. Maslennikov V. A. Kotlyarov S. P. Maslennikova L. V. Danyushevsky R. Large 《Doklady Earth Sciences》2017,473(1):318-322
For the first time, extremely high Se and In contents were determined for the pinches of massive sulfide orebodies that are composed of small-clastic layered sulfide sediments transformed during submarine supergenesis. Se (clausthalite and naumannite) and In (roquesite) minerals were found. Hydrothermal chalcopyrite, a significant amount of which is present in the clasts of paleohydrothermal black smoker chimneys, was the source of Se. Most of the amount of In was contributed during dissolution of clasts of hydrothermal sphalerite, which is unstable in the submarine oxidation zone in the presence of oxidized pyrite. 相似文献
29.
Melekestseva I. Yu. Maslennikov V. V. Ayupova N. R. Belogub E. V. Maslennikova S. P. Bel’tenev V. E. Danyushevsky L. Large R. 《Geology of Ore Deposits》2020,62(3):254-259
Geology of Ore Deposits - The formation of present-day seafloor sulfide deposits is accompanied by their continuous oxidation and crystallization of insoluble Fe oxyhydroxides, which absorb metals... 相似文献
30.
Falloon Trevor J.; Green David H.; Danyushevsky Leonid V.; McNeill Andrew W. 《Journal of Petrology》2008,49(4):591-613
We have determined the near-solidus melt compositions for peridotiteMM-3, a suitable composition for the production of mid-oceanridge basalt (MORB) by decompression partial melting, at 1 and1·5 GPa. At 1 GPa the MM-3 composition has a subsolidusplagioclase-bearing spinel lherzolite assemblage, and a solidusat 1270°C. At only 5°C above the solidus, 4% meltis present as a result of almost complete melting of plagioclase.This melting behaviour in plagioclase lherzolite is predictedfrom simple systems and previous experimental work. The persistenceof plagioclase to > 0·8 GPa is strongly dependenton bulk-rock CaO/Na2O and normative plagioclase content in theperidotite. At 1·5 GPa the MM-3 composition has a subsolidusspinel lherzolite assemblage, and a solidus at 1350°C.We have determined a near-solidus melt composition at 2% meltingwithin 10°C of the solidus. Near-solidus melts at both 1and 1·5 GPa are nepheline normative, and have low normativediopside contents; also they have the highest TiO2, Al2O3 andNa2O, and the lowest FeO and Cr2O3 contents compared with higherdegree partial melts. Comparison of these near-solidus meltswith primitive MORB glasses, which lie in the olivine-only fieldof crystallization at low pressure, indicate that petrogeneticmodels involving aggregation of near-fractional melts formedduring melting at pressures of 1·5 GPa or less are unlikelyto be correct. In this study we use an experimental approachthat utilizes sintered oxide mix starting materials and peridotitereaction experiments. We also examine some recent studies usingan alternative approach of melt migration into, and entrapmentwithin melt traps (olivine, diamond, vitreouscarbon) and discuss optimal procedures for this method. KEY WORDS: experimental petrology; mantle melting; near-solidus; fertile peridotite; MORB 相似文献