排序方式： 共有9条查询结果，搜索用时 31 毫秒
1
1.
The purpose of GPS-satellite-to-satellite tracking (GPS-SST) is to determine the gravitational potential at the earth's surface from measured ranges (geometrical distances) between a low-flying satellite and the high-flying satellites of the Global Positioning System (GPS). In this paper, GPS-satellite-to-satellite tracking is reformulated as the problem of determining the gravitational potential of the earth from given gradients at satellite altitude. The uniqueness and stability of the solution are investigated. The essential tool is to split the gradient field into a normal part (i.e. the first-order radial derivative) and a tangential part (i.e. the surface gradient). Uniqueness is proved for polar, circular orbits corresponding to both types of data (first radial derivative and/or surface gradient). In both cases gravity recovery based on satellite-to-satellite tracking turns out to be an exponentially ill-posed problem. Regularization in terms of spherical wavelets is proposed as an appropriate solution method, based on the knowledge of the singular system. Finally, the extension of this method is generalized to a nonspherical earth and a non-spherical orbital surface, based on combined terrestrial and satellite data. 相似文献
2.
R. J. Baumgartner F. Zaccarini G. Garuti O. A. R. Thalhammer 《Contributions to Mineralogy and Petrology》2013,165(3):477-493
The Bracco–Gabbro Complex (Internal Liguride ophiolite), that intruded subcontinental mantle peridotite, contains layers of chromitite that are associated with ultramafic differentiates. The chromitites and disseminated chromites in the ultramafics have Al contents similar to the Al-rich podiform chromitites [0.40 < Cr# = Cr/(Cr + Al) < 0.55]. TiO2 contents of the chromitites are unusually high and range up to 0.82 wt%. The calculated Al2O3 and TiO2 content of the parental melt suggest that the melt was a MORB type. Geothermobarometrical calculations on few preserved silicate inclusions revealed formation temperatures between 970 and 820 °C under a relatively high oxygen fugacity (ΔlogfO2 at +2.0–2.4). Chromitites were altered during the post-magmatic tectono-metamorphic uplift and the final exposure at the seafloor, as evidenced by the formation of ferrian chromite. The PGE contents of the chromitites and associated ultramafics are unusually low (PGEmax 83 ppb). The chondrite-normalized PGE spidergrams show positive PGE patterns and to some extent similarities with the typical trend of stratiform chromitites. No specific PGM have been found but low concentrations of PPGE (Rh, Pt, and Pd) have been detected in the sulphides that occur interstitially to or enclosed in chromite. Recently, it has been shown that the Internal Liguride gabbroic intrusions have formed by relatively low degrees of partial melting of the asthenospheric mantle. We conclude that the low degree of partial melting might be the main factor to control the unusual low PGE contents and the rather unique PGE distribution in the Bracco chromitites. 相似文献
3.
4.
Kreshimir N. Malitch Oskar A. Thalhammer Vladimir V. Knauf Frank Melcher 《Mineralium Deposita》2003,38(3):282-297
We report highly unusual platinum-group mineral (PGM) assemblages from geologically distinct chromitites (banded and podiform) of the Kraubath massif, the largest dismembered mantle relict in the Eastern Alps. The banded chromitite has a pronounced enrichment of Pt and Pd relative to the more refractory platinum-group elements (PGEs) of the IPGE group (Os, Ir, Ru), similar to crustal sections of ophiolites. On the contrary, the podiform chromitite displays a negatively sloping chondrite-normalised PGE pattern typical of ophiolitic podiform chromitite. The chemical composition of chromite varies from Cr# 73-77 in the banded type to 81-86 in the podiform chromitite. Thirteen different PGMs and one gold-rich mineral are first observed in the banded chromitite. The dominant PGM is sperrylite (53% of all PGMs), which occurs in polyphase assemblages with an unnamed Pt-base metal (BM) alloy and Pd-rich minerals such as stibiopalladinite, mayakite, mertieite II, unnamed Pd-Rh-As and Pd(Pt)-(As,Sb) minerals. This banded type also contains PGE sulphides (about 7%) represented by a wide compositional range of the laurite-erlichmanite series and irarsite (8%). Os-Ir alloy, geversite, an unnamed Pt-Pd-Bi-Cu phase and tetrauricupride are present in minor amounts. By contrast, the podiform chromitite, which yielded 21 different PGMs, is dominated by laurite (43% of all PGMs) which occurs in complex polyphase assemblages with PGE alloys (Ir-Os, Os-Ir, Pt-Fe), PGE sulphides (kashinite, bowieite, cuproiridsite, cuprorhodsite, unnamed (Fe,Cu)(Ir,Rh)2S4, braggite, unnamed BM-Ir and BM-Rh sulphides) and Pd telluride (keithconnite). A variety of PGE sulpharsenides (33%) including irarsite, hollingworthite, platarsite, ruarsite and a number of intermediate species have been identified, whereas sperrylite and stibiopalladinite are subordinate (2%). The occurrence of such a wide variety of PGMs from only two, 2.5-kg chromitite samples is highly unusual for an ophiolitic environment. Our novel sample treatment allowed to identify primary PGM assemblages containing all six PGEs in both laurite-dominated podiform chromitite as well as in uncommon sperrylite-dominated banded chromitite. We suggest that the geologically, geochemically and mineralogically distinct banded chromitite from Kraubath characterises the transition zone of an ophiolite, closely above the mantle section hosting podiform chromitite, rather than being representative of the crustal cumulate pile. 相似文献
5.
Dr. O. Thalhammer 《Mineralogy and Petrology》1987,37(3-4):221-242
Summary The eastern part (Ostfeld) of the Mittersill stratabound scheelite deposit, located in the central Hohe Tauern (Salzburg Province, Austria) was investigated in detail. New geochemical data from the mineralized sequence reveal the presence of a succession of volcanic rocks with subalkaline to talc-alkaline characteristics. Hornblendites and coarse-grained amphibolites with acid intercalations are the main constituents of the mineralized sequence. The entire rock sequence has been emplaced at a converging plate margin in the early history of a lower Paleozoic island are. Hornblendites and coarse-grained amphibolites exhibit boninite-type parentage; geochemical evidence points towards derivation from an upper mantle peridotite which has been depleted in certain incompatible elements by previous melting episodes.As a tentative model, compositional zonation in the magma is presented to explain a) the close spatial association of basic and acid rocks and b) the primary enrichment of tungsten and niobium as integral primary constituents of the host rocks. Tungsten enrichment during magmatic evolution thus provided the basis for local concentrations of tungsten in gneisses and quartz veins during two phases of metamorphism and tectonic deformation. The Mittersill scheelite deposit is interpreted as the product of metamorphic concentration of primary metal contents in boninites.
With 12 Figures 相似文献
Boninite als Ausgangsgesteine für die Wolframmineralisation in Mittersill, Österreich?
Zusammenfassung Geochemische Untersuchungen im Ostfeld der Scheelitlagerstätte Mittersill in den mittleren Hohen Tauern (Salzburg, Österreich) zeigen, daß eine kontinuierliche vulkanische Abfolge mit subalkalischem bis kalk-alkalischem Charakter vorliegt. Die erzführenden Abfolgen sind im wesentlichen aus Hornblenditen und Grobkornamphiboliten mit Einschaltung von Gneisen aufgebaut. Sie stellen eine an einem destruktiven Plattenrand im Anfangsstadium eines altpaläozoischen Inselbogens gebildete Abfolge dar. Die Hornblendite und Grobkornamphibolite repräsentieren boninitähnliche Gesteine. Sie können von einem Peridotit des Oberen Mantels hergeleitet werden, der durch frühere Aufschmelzungsvorgänge an einzelnen inkompatiblen Elementen verarmt ist.Die Anceicherung besummter Elemente (Nb, W) und die räumlich und zeitlich enge Assoziation von Gesteinsfolgen unlerschiedlicher Zusammensetzung gehören zu den auffälligsten Charakteristiken der vererzlen Abfolge. Diese lassen sich am Model einer stofflichen Zonierung innerhalb eines Magmas erklären.Eine primär, magmatische Anreicherung des Wolframs stellt die Grundlage für die heute vorliegenden Wolframkonzentrationen in gneisen und Quarzgängen dar, die im Zuge von zwei Metamorphosen und Deformationen entstanden sind. Die Scheelitlagersfälle Mittersill ist damit als eime metamorphe Lagerstätte mit einer primär magmatischen Anlage zu sehen.
With 12 Figures 相似文献
6.
Solid inclusions in chrome-spinels and platinum group element concentrations from the hochgrössen and kraubath ultramafic massifs (Austria) 总被引：1，自引：0，他引：1
O. A. R. Thalhammer W. Prochaska H. W. Mühlhans 《Contributions to Mineralogy and Petrology》1990,105(1):66-80
A great variety of platinum group mineral, sulfide and silicate inclusions in chrome spinel from Hochgrössen and Kraubath ultramafic massifs, and platinum group element contents of three different rock types have been investigated. Both ultramafic massifs are tectonically isolated bodies, variably serpentinized and metamorphosed (greenschist to lower amphibolite facies), and show ophiolitic geochemical affinities. The chromite from massive chromitites and disseminated in serpentinized dunites and serpentinites, exhibits compositional zonation as the result of alteration during serpentinization and metamorphism. Three distinctive alteration stages are indicated in the chrome-spinels from the Hochgrössen, whereas alteration is less significant in chromites from Kraubath: The core of chrome spinel represents the least altered part, surrounded by an inner rim characterized by slight compositional differences in Cr, Mn, Fe2+ and Al with respect to the core. The outer rim is formed by ferritchromite with a sharp boundary to the inner rim and shows a significant decrease of Al, Mg, Cr and increase of Fe2+, Fe3+ and Ni compared to the core. Two different groups of inclusions in chrome-spinel are present: the first group occurs within the chromite core, and comprises olivine, orthopyroxene, amphibole, sulfides and platinum-group minerals, i.e. dominated by Ru-Os-Ir-sulfides. The second group is formed by chlorite, serpentine, galena, pyrite, arsenopyrite, Pt-Pd-Rh-dominated sulfarsenides and sperrylite. In particular the abundance of Pt-Pd-Rh-sulfarsenides and arsenides is typical of both ultramafic massifs and is very unusual for chromitites from ophiolites. Morphology, paragenesis and chemical composition indicate a different origin for these two groups of inclusions. The first group is intimately related to the crystallisation of the chromite host. The second group of inclusions clearly displays a secondary formation during serpentinization and metamorphism, closely related to the alteration of chrome-spinel and the development of ferritchromite. The distribution patterns of the platinum group elements from massive chromitites, disseminated chrome-spinel bearing serpentinites and serpentinites exhibit variable enrichment of Rh, Pt and Pd, Rh, Pt for the Hochgrössen and Kraubath massifs, respectively. These results are in accordance with the occurrence and distribution of platinum-group mineral phases. A remobilisation of Pt, Pd, and Rh, together with Ni, Cu and possibly Fe as bisulfide and/or hydroxide complexes and deposition of metals by the reaction of the metal bearing hydrothermal fluid with chromite is proposed. 相似文献
7.
Summary The distribution of platinum group elements (PGE) within individual lithological units of the dismembered ophiolite of the Great Serpentinite Belt in New South Wales displays distinctive patterns. Within the ophiolite the PGE are mainly magmatic in origin, although the whole sequence has been extensively metamorphosed and deformed. The PGE in this ophiolite demonstrate fractionation resulting from magmatic processes.Harzburgite is characterised by a flat normalised PGE pattern, with only a slight depletion in PPGE. The minor PGE differentiation in the residual mantle rocks is probably due to the control on the PGE distribution by residual alloys and sulfides. This implies that the primary magma, generated from partial melting, was S-saturated.Cumulates of the overlying magmatic sequence show a positively sloped PGE pattern, favouring PPGE enrichment. PGE distribution in the cumulate sequence was controlled by immiscible sulfides, resulting in a similar PGE pattern for individual members of the cumulates. The highest PGE content in the magmatic section is recorded in the banded chromitite where the PGE enrichment probably results from upward-migrating magmatic fluids.Podiform chromitite is the earliest fractionated product from ascending partial melts within narrow magma conduits that channeled melts from the mantle source up to the overlying magma chamber. Such a process operated at high temperatures, hence the high melting-point IPGE was preferentially crystallised along with the chromites so that podiform chromitite displays a negatively sloped PGE pattern. Normally, sulfide saturation in the ascending melt does not take place until the melt enters the crustal magma chamber. However, immiscible sulfide liquids might have been present temporarily in some high-level podiform chromitite to generate a Pt- and Pd-enriched pod. Chromite in this pod is less in both Cr/(Al + Cr) and Mg/(Mg + F2+) than in those of other podiform chromitites that are dominated by IPGE and, therefore, the composition of chromite is of significance in identifying the potential Pt- and Pd-rich chromitites in this ophiolite belt.
With 9 Figures 相似文献
Verteilung der Platingruppen-Elemente im Great Serpentinite Belt von New South Wales, Ost-Australien
Zusammenfassung Die Verteilung der Platingruppen-Elemente (PGE) innerhalb der einzelnen lithologischen Einheiten des zerbrochenen Ophiolites des Great Serpentinite Belt in New South Wales zeigt charakteristische Verteilungsmuster. Die PGE sind überwiegend magmatischen Ursprungs, obwohl der gesamte Komplex intensiv metamorphosiert und deformiert worden ist. Innerhalb des Ophiolites zeigen die PGE Fraktionierung, die das Resultat magmatischer Prozesse ist.Der Harzburgit ist durch flache, normierte PGE Verteilungskurven charakterisiert, die lediglich eine schwache Verarmung an PPGE zeigen. Die geringe PGE Differenzierung in den residualen Mantelgesteinen wird durch die Steuerung der PGE Verteilung durch residuale Legierungen und Sulfide kontrolliert. Dies bedeutet, daß das durch Teilaufschmelzung entstandene Magma S-gesättigt gewesen ist.Die Kumulate der hangenden, magmatischen Abfolge zeigen positive PGE Verteilungskurven, die auf eine Anreicherung der PPGE hinweisen. Die PGE Verteilung in der Kumulat-Sequenz wurde durch entmischte Sulfide kontrolliert, weshalb die einzelnen Schichtglieder der Kumulat-Abfolge ähnliche PGE Verteilungsmuster aufweisen. Die gebänderten Chromitite zeigen die höchsten PGE Gehalte der magmatischen Abfolge, die Anreicherung der PGE ist vermutlich auf aufsteigende, magmatische Fluida zurückzuführen.Der podiforme Chromitit ist das früheste Fraktionierungsprodukt der vom Mantel durch enge Kanäle in die Magmakammer aufsteigenden Teilschmelzen. Ein derartiger Prozeß findet bei hohen Temperaturen statt, weshalb die IPGE, die hohe Schmelzpunkte aufweisen, zusammen mit dem Chromit zur Kristallisation gelangten, podiforme Chromitite zeigen daher negative PGE Verteilungskurven. Normalerweise findet eine Schwefel-Sättigung der aufsteigenden Schmelze nicht vor dem Eintritt in die krustale Magmenkammer statt. Temporär könnte jedoch eine entmischte Schwefel-Schmelze bereits in einigen high level podiformen Chromititen existiert haben, sodaß ein Pt- und Pd-angereicherter Pod entsteht. Der Chromit in diesem Pod zeigt niedere Cr/(Al + Cr) und Mg/(Mg + Fe2+) Verhältnisse als jene in anderen podiformen Chromititen, die von IPGE dominiert sind. Die Zusammensetzung des Chromites ist daher signifikant, um Pt-und Pd-reiche Chromitite innerhalb dieses Ophiolit-Gürtels zu identifizieren.
With 9 Figures 相似文献
8.
The Ni-Co-Cu ores of Pevkos and Lakxia tou Mavrou, Limassol Forest, Cyprus, have been investigated microscopically and by electron microprobe analysis. At Pevkos, the mineral association consists of pyrrhotite, pentlandite, maucherite, chalcopyrite, cubanite, magnetite, chromite and valleriite with minor amounts of westerveldite, bornite, neodigenite, covellite and cobaltite. The mineralization at Lakxia tou Mavrou comprises pyrrhotite, pentlandite, löllingite, chalcopyrite, cubanite and chromite with traces of magnetite, pyrite, maucherite and valleriite. Paragenetic, compositional and textural features suggest a nonmagmatic origin for the sulfides and arsenides; they were deposited during serpentinization of the ultramafic host rocks. A conceptual model for mineralization linked to decreasing temperatures in a hydrothermal system is presented. 相似文献
9.
The giant chromite deposits at Kempirsai, Urals: constraints from trace element (PGE, REE) and isotope data 总被引：6，自引：0，他引：6
The investigation of stable and radiogenic isotopes and of platinum-group (PGE) and rare earth elements (REE) in chromitites
and associated ultramafic rocks of the Kempirsai Massif, southern Urals, gives strong evidence for a multistage formation
of giant ophiolitic-podiform chromite deposits present in the southeastern part of the massif. The Kempirsai ophiolite massif
is divided by a shear zone into two parts: in the northwestern area, small bodies of Al-rich chromite formed from basaltic
melts between 420 to 400 Ma, according to Sm-Nd mineral isochrons of harzburgite, pyroxenite, websterite and gabbro. Harzburgites
and pyroxenites in this area are enriched in light REE and have ɛNd(400) > +6 and ɛSr(400) ∼ +5. Chromitites have scattered PGE distributions (Pd/Ir, 0.4–7.0), being partly enriched in Pd and Pt. γOs(400) of one chromitite is −4.4. The southeastern part of the Kempirsai Massif, well-known for its world-class deposits of
podiform low-Al magnesiochromite, is characterized by harzburgite and dunite enriched in light REE with very low ɛNd(400) (+4.3 to –17.1) and positive ɛSr(400) (>+10) values. Chromitites are strongly enriched in Ir, Os and Ru and depleted in Pd and Pt. γOs(400) of three chromitites is uniform and approaches C1 and DMM compositions. In veins and pods postdating crystallization
of massive chromite, pargasitic amphibole formed in equilibrium with fluid-inclusion-bearing chromite at temperatures close
to 1000 °C. These amphiboles give 40Ar/39Ar stepwise heating ages of 365 to 385 Ma and are characterized by low ɛNd(400) (+0.6 to −4.6) and general enrichment in REE. The cooling ages correspond to a 379.3 ± 1.6 Ma Rb-Sr mineral isochron
produced from amphibole and phlogopite of a pyroxenite vein in the western part of the massif. From these data it is concluded
that parts of the Kempirsai Massif have been pervasively metasomatized by large amounts of fluids and melts derived from a
subducted slab composed of oceanic crust and sediments. Subduction occurred at least 15–35 Ma after a melting event that produced
a typical ophiolitic sequence in the Paleozoic Sakmara Zone. We conclude that large chromite orebodies formed from second-stage
high-Mg melts that interacted with depleted mantle and fluids on their way upward in a suprasubduction zone regime, and in
a fore-arc position to the Magnitogorsk island arc.
Received: 21 January 1998 / Accepted: 24 August 1998 相似文献
1