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Osman Parlak - One of the best experts on this subject based on the ideXlab platform.
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petrology of ultramafic to mafic Cumulate rocks from the goksun kahramanmaras ophiolite southeast turkey
Geoscience frontiers, 2020Co-Authors: Tamer Rizaoglu, Utku Bagci, Osman Parlak, Volker Hock, C Ionescu, Guzide Onal, Huseyin KozluAbstract:Abstract The Goksun (Kahramanmaras) ophiolite (GKO), cropping out in a tectonic window bounded by the Malatya metamorphic unit on both the north and south, is located in the EW-trending lower nappe zone of the southeast Anatolian orogenic belt (Turkey). It exhibits a complete oceanic lithospheric section and overlies the Middle Eocene Maden Group/Complex with a tectonic contact at its base. The ophiolitic rocks and the tectonically overlying Malatya metamorphic (continental) unit were intruded by I-type calc-alkaline Late Cretaceous granitoid (∼81–84 Ma). The ultramafic to Cumulates in the GKO are represented by wehrlite, plagioclase wehrlite, olivine gabbro and gabbro. The crystallization order for the Cumulate rocks is as follows: olivine ± chromian spinel→clinopyroxene→plagioclase. The major and trace element geochemistry as well as the mineral chemistry of the ultramafic to mafic Cumulate rocks suggest that the primary magma generating the GKO is compositionally similar to that observed in the modern island-arc tholeiitic sequences. The mineral chemistry of the ultramafic to mafic Cumulates indicates that they were derived from a mantle source that was previously depleted by earlier partial melting events. The highly magnesian olivine (Fo77–83), clinopyroxene (Mg# of 82–90) and the highly Ca-plagioclase (An81–89) exhibit a close similarity to those, which formed in a supra-subduction zone (SSZ) setting. The field and the geochemical evidence suggest that the GKO formed as part of a much larger sheet of oceanic lithosphere, which accreted to the base of the Tauride active continental margin, including the Ispendere, Komurhan and the Guleman ophiolites. The latter were contemporaneous and genetically/tectonically related within the same SSZ setting during the closure of the Neotethyan oceanic basin (Berit Ocean) between the Taurides to the north and the Bitlis-Puturge massif to the south during the Late Cretaceous.
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geochemical character and tectonic environment of ultramafic to mafic Cumulate rocks from the tekirova antalya ophiolite southern turkey
Geological Journal, 2006Co-Authors: Utku Bagci, Osman Parlak, Volker HockAbstract:The Upper Cretaceous Tekirova (Antalya) ophiolite derived from the southern branch of the Neotethys is located at the southwestern part of the Antalya Complex along the Tauride belt in southern Turkey. It comprises harzburgitic tectonites, ultramafic to mafic Cumulates, isotropic gabbro, sheeted dykes, volcanics and associated sedimentary rocks. The Cumulate rocks are located mainly along the Cirali–Tekirova section to the south and at Doyran to the north. Several isolated blocks of Cumulate rocks are also observed in the north–south-trending Godene zone of the Antalya Complex. The ultramafic and mafic Cumulate rocks are represented by wehrlite, lherzolite, olivine clinopyroxenite, olivine gabbronorite, olivine gabbro, gabbronorite and gabbro. The order of crystallization in the Cumulates is olivine (Fo88–76) ± chromian spinel clinopyroxene (Mg#92–76) orthopyroxene (Mg#86–70) plagioclase (An97–84). The major and trace element geochemistry of the plutonic rocks suggests that the primary magma generating the Tekirova (Antalya) ophiolite is compositionally similar to those observed in modern island arc tholeiitic sequences. The presence of highly magnesian clino- and orthopyroxenes along with the absence of plagioclase in the ultramafic Cumulates suggest their formation as a result of high-pressure crystal fractionation (c. 10 kbar). In contrast, the mafic Cumulates in the upper crustal level show evidence of a lower-pressure (2–2.5 kbar) environment within the same tectonic setting. Therefore, it is suggested that the Cumulate ultramafic rocks were probably precipitated as a result of in situ crystallization processes along the walls of a conduit system extending downward from a crustal level magma chamber to mantle depths of approximately 30 km. After their formation, the ultramafic Cumulates were transported to a shallow-level magma chamber where the remainder of the plutonic section (mafic Cumulates) was formed at a lower pressure environment. Copyright © 2006 John Wiley & Sons, Ltd.
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whole rock and mineral chemistry of Cumulates from the kizildag hatay ophiolite turkey clues for multiple magma generation during crustal accretion in the southern neotethyan ocean
Mineralogical Magazine, 2005Co-Authors: Utku Bagci, Osman Parlak, Volker HockAbstract:The late Cretaceous Kizildag ophiolite forms one of the best exposures of oceanic lithospheric remnants of southern Neotethys to the north of the Arabian promontory in Turkey. The ultramafic to mafic Cumulate rocks, displaying variable thickness (ranging from 165 to 700 m), are ductiley deformed, possibly in response to syn-magmatic extension during seafloor spreading and characterized by wehrlite, olivine gabbro, olivine gabbronorite and gabbro. The gabbroic Cumulates have an intrusive contact with the wehrlitic Cumulates in some places. The crystallization order of the cumulus and intercumulus phases is olivine (Fo86–77)±chromian spinel, clinopyroxene (Mg#92–76), plagioclase(An95–83), orthopyroxene(Mg#87–79). The olivine, clinopyroxene, orthopyroxene and plagioclase in ultramafic and mafic Cumulate rocks seem to have similar compositional range. This suggests that these rocks cannot represent a simple crystal line of descent. Instead the overlapping ranges in mineral compositions in different rock types suggest multiple magma generation during crustal accretion for the Kizildag ophiolite. The presence of high Mg# of olivine, clinopyroxene, orthopyroxene, and the absence of Ca-rich plagioclase as an early fractionating phase co-precipitating with forsteritic olivine, suggest that the Kizildag plutonic suite is not likely to have originated in a mid-ocean ridge environment. Instead the whole-rock and mineral chemistry of the Cumulates indicates their derivation from an island arc tholeiitic (IAT) magma. All the evidence indicates that the Kizildag ophiolite formed along a slow-spreading centre in a fore-arc region of a suprasubduction zone tectonic setting.
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mineral chemistry of ultramafic and mafic Cumulates as an indicator of the arc related origin of the mersin ophiolite southern turkey
International Journal of Earth Sciences, 1996Co-Authors: Osman Parlak, Michel Delaloye, Erguzer BingolAbstract:The Mersin ophiolite, represented by approximately 6-km-thick oceanic lithospheric section on the southern flank of the Taurus calcareous axis, formed in the Mesozoic Neo-Tethyan ocean some time during Late Cretaceous in southern Turkey. The ultramafic and mafic Cumulates having over 3 km thickness consist of dunite ± chromite, wehrlite, clinopyroxenite at the bottom and pass into gabbroic Cumulates in which leucogabbro, olivine-gabbro and anorthosite are seen. Crystallization order is olivine (Fo91−80) ± chromian spinel (Cr# 60-80), clinopyroxene (Mg#95−77), plagioclase (An95.6−91.6) and orthopyroxene (Mg#68−77). Mineral chemistry of ultramafic and mafic Cumulates suggest that highly magnesian olivines, clinopyroxenes and absence of plagioclase in the basal ultramafic Cumulates are in good agreement with products of high-pressure crystal fractionation of primary basaltic melts beneath an island-arc environment. Major, trace element geochemistry of the cumulative rocks also indicate that Mersin ophiolite was formed in an arc environment. Coexisting Ca-rich plagioclase and Forich olivine in the gabbroic Cumulates show arc Cumulate gabbro characteristics. Field relations as well as the geochemical data support that Mersin ophiolite formed in a supra-subduction zone tectonic setting in the southern branch of the Neo-Tethys in southern Turkey.
Paul C Hess - One of the best experts on this subject based on the ideXlab platform.
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an experimental study of trace element partitioning between augite and fe rich basalts
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nick Dygert, Yan Liang, Chenguang Sun, Paul C HessAbstract:Abstract Aluminous titanium-rich hedenbergite and Fe-rich augite were experimentally produced at 1050–1220 °C and 0.8–2.2 GPa. Major element compositions are analogous to clinopyroxene from layered intrusions, angrites, nakhlites, and late-stage lunar magma ocean Cumulates. Trace element concentrations in pyroxene and coexisting melt were measured by laser ablation inductively coupled plasma mass spectrometry for rare earth elements (REE), high field strength elements (HFSE), transition metals, and large-ion lithophile elements. REE, HFSE, and transition metal partition coefficients (Ds) are tightly correlated with the cation abundance of Fe on the pyroxene M1 site ( X Fe M1 ), and also correlated with Al on the tetrahedral site ( X Al T ). Parameterized lattice-strain models were developed to predict REE and HFSE partition coefficients as functions of temperature and pyroxene composition ( X Al T or X Fe M1 ). The parameterized models can be used to calculate REE and HFSE partition coefficients for Fe-rich high-Ca pyroxene. We calculated partition coefficients for clinopyroxene derived from modeled end-stage lunar magma ocean Cumulate compositions and observe a factor of 3 variation in clinopyroxene-melt REE partition coefficients. Using representative nakhlite clinopyroxene core and rim compositions we calculated partition coefficients and observed a factor of 4 variability in clinopyroxene-melt REE partition coefficients. HFSE partition coefficients are even more sensitive to composition, showing variations of a factor of 4 for lunar late Cumulates and an order of magnitude for nakhlites. The strong dependence of REE and HFSE partitioning on composition necessitates careful selection of appropriate partition coefficients for Fe-rich systems.
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the stability and major element partitioning of ilmenite and armalcolite during lunar Cumulate mantle overturn
Geochimica et Cosmochimica Acta, 2009Co-Authors: Carla Thacker, Yan Liang, Qinglan Peng, Paul C HessAbstract:Abstract Ilmenite has played an important role in the petrogenesis of lunar high-Ti picritic magmas, and armalcolite is another high-Ti oxide that was first discovered on the moon. In this study, we examined the thermodynamic stability of ilmenite and armalcolite in the context of lunar Cumulate mantle overturn. Two starting compositions were explored, an ilmenite-bearing dunite (olivine + ilmenite) and an ilmenite-bearing harzburgite (olivine + orthopyroxene + ilmenite). Experiments were conducted using a 19.05 mm piston-cylinder apparatus at temperatures of 1235–1475 °C and pressures of 1–2 GPa. In runs with the ilmenite-bearing dunite mixture, ilmenite is stable in the subsolidus assemblage at least up to 1450 °C and 2 GPa. In runs with the ilmenite-bearing harzburgite starting mixture, ilmenite is stable at pressures greater than 1.4 GPa, and armalcolite is stable at lower pressures. Solidi for both starting compositions were determined, and the phase boundary between ilmenite- and armalcolite-bearing harzburgite was shown to have little dependence on temperature. During lunar Cumulate overturn, sinking ilmenite formed near the end of lunar magma ocean solidification transforms into armalcolite when in contact with harzburgite Cumulates at depths of less than 280 km in the lunar mantle. Inefficient overturn could leave isolated, inhomogeneously distributed pockets of armalcolite-bearing harzburgite in the upper lunar mantle, underlain by an ilmenite-bearing lower lunar mantle. These high-Ti oxide-bearing harzburgitic pockets can serve as potential sources for the generation of high-Ti magmas through partial melting or through assimilation of high-Ti minerals during transport of low-Ti picritic magmas in the lunar mantle. FeO–MgO exchange between olivine and either ilmenite or armalcolite was also examined in this study. We found the FeO–MgO distribution coefficient to be effectively independent of temperature for the pressures, temperatures, and compositions explored, with an average value of 0.179 ± 0.008 for olivine/ilmenite and 0.319 ± 0.021 for olivine/armalcolite. Given the bulk composition of an overturned lunar Cumulate mantle, our measured FeO–MgO distribution coefficients can be used to estimate the Mg# of coexisting minerals in armalcolite- or ilmenite-bearing harzburgite and dunite in the overturned lunar mantle. Finally, the transformation from ilmenite-bearing harzburgite to armalcolite-bearing harzburgite results in a density increase of up to 2%. Large armalcolite-bearing Cumulate bodies in the upper lunar mantle may be detectable in future lunar geophysical experiments.
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early magnetic field and magmatic activity on mars from magma ocean Cumulate overturn
Earth and Planetary Science Letters, 2005Co-Authors: Linda T Elkinstanton, E M Parmentier, Sarah E Zaranek, Paul C HessAbstract:Abstract Significant and perhaps complete melting of the young terrestrial planets is expected from their heat of accretion and core formation. The process of subsequent magma ocean fractional solidification creates a Cumulate mantle unstable to gravitational overturn. Overturn should be fast (≤ 1 to 10 Ma) and result in increasing mantle density with depth. This stable stratification inhibits later thermal convection, preserving geochemical heterogeneities. Overturn places cold Cumulates against the core–mantle boundary, which creates sufficient heat flux to drive a core dynamo, producing a brief, strong magnetic field. During overturn, hot Cumulates rise from depth and melt adiabatically, creating an early crust to record this field and leaving behind mantle reservoirs with isotopic fractionations dating from the early evolution of the planet.
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magma ocean fractional crystallization and Cumulate overturn in terrestrial planets implications for mars
Meteoritics & Planetary Science, 2003Co-Authors: Linda T Elkinstanton, E M Parmentier, Paul C HessAbstract:Crystallization of a magma ocean on a large terrestrial planet that is significantly melted by the energy of accretion may lead to an unstable Cumulate density stratification, which may overturn to a stable configuration. Overturn of the initially unstable stratification may produce an early basaltic crust and differentiated mantle reservoirs. Such a stable compositional stratification can have important implications for the planet's subsequent evolution by delaying or suppressing thermal convection and by influencing the distribution of radiogenic heat sources. We use simple models for fractional crystallization of a martian magma ocean, and calculate the densities of the resulting Cumulates. While the simple models presented do not include all relevant physical processes, they are able to describe to first order a number of aspects of martian evolution. The models describe the creation of magma source regions that differentiated early in the history of Mars, and present the possibility of an early, brief magnetic field initiated by cold overturned Cumulates falling to the core- mantle boundary. In a model that includes the density inversion at about 7.5 GPa, where olivine and pyroxene float in the remaining magma ocean liquids while garnet sinks, Cumulate overturn sequesters alumina in the deep martian interior. The ages and compositions of source regions are consistent with SNC meteorite data.
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a model for the thermal and chemical evolution of the moon s interior implications for the onset of mare volcanism
Earth and Planetary Science Letters, 1995Co-Authors: Paul C Hess, E M ParmentierAbstract:Crystallization of the lunar magma ocean creates a chemically stratified Moon consisting of an anorthositic crust and magma ocean Cumulates overlying the primitive lunar interior. Within the magma ocean Cumulates the last liquids to crystallize form dense, ilmenite-rich Cumulates that contain high concentrations of incompatible radioactive elements. The underlying olivine-orthopyroxene Cumulates are also stratified with later crystallized, denser, more Fe-rich compositions at the top. This paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy. Rayleigh-Taylor instability causes the dense ilmenite-rich Cumulate layer and underlying Fe-rich Cumulates to sink toward the center of the Moon, forming a dense lunar core. After this overturn, radioactive heating within the ilmenite-rich Cumulate core heats the overlying mantle, causing it to melt. In this model, the source region for high-TiO2 mare basalts is a convectively mixed layer above the core-mantle boundary which would contain small and variable amounts of admixed ilmenite and KREEP. This deep high-pressure melting, as required for the generation of mare basalts, occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the Moon. Regardless of details implied by particular model parameters, gravitational overturn driven by the high density of magma ocean Fe-rich Cumulates should concentrate high-TiO2 mare basalt sources, and probably a significant fraction of radioactive heating, toward the center of the Moon. This will have important implications for both the thermal evolution of the Moon and for mare basalt genesis.
Volker Hock - One of the best experts on this subject based on the ideXlab platform.
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petrology of ultramafic to mafic Cumulate rocks from the goksun kahramanmaras ophiolite southeast turkey
Geoscience frontiers, 2020Co-Authors: Tamer Rizaoglu, Utku Bagci, Osman Parlak, Volker Hock, C Ionescu, Guzide Onal, Huseyin KozluAbstract:Abstract The Goksun (Kahramanmaras) ophiolite (GKO), cropping out in a tectonic window bounded by the Malatya metamorphic unit on both the north and south, is located in the EW-trending lower nappe zone of the southeast Anatolian orogenic belt (Turkey). It exhibits a complete oceanic lithospheric section and overlies the Middle Eocene Maden Group/Complex with a tectonic contact at its base. The ophiolitic rocks and the tectonically overlying Malatya metamorphic (continental) unit were intruded by I-type calc-alkaline Late Cretaceous granitoid (∼81–84 Ma). The ultramafic to Cumulates in the GKO are represented by wehrlite, plagioclase wehrlite, olivine gabbro and gabbro. The crystallization order for the Cumulate rocks is as follows: olivine ± chromian spinel→clinopyroxene→plagioclase. The major and trace element geochemistry as well as the mineral chemistry of the ultramafic to mafic Cumulate rocks suggest that the primary magma generating the GKO is compositionally similar to that observed in the modern island-arc tholeiitic sequences. The mineral chemistry of the ultramafic to mafic Cumulates indicates that they were derived from a mantle source that was previously depleted by earlier partial melting events. The highly magnesian olivine (Fo77–83), clinopyroxene (Mg# of 82–90) and the highly Ca-plagioclase (An81–89) exhibit a close similarity to those, which formed in a supra-subduction zone (SSZ) setting. The field and the geochemical evidence suggest that the GKO formed as part of a much larger sheet of oceanic lithosphere, which accreted to the base of the Tauride active continental margin, including the Ispendere, Komurhan and the Guleman ophiolites. The latter were contemporaneous and genetically/tectonically related within the same SSZ setting during the closure of the Neotethyan oceanic basin (Berit Ocean) between the Taurides to the north and the Bitlis-Puturge massif to the south during the Late Cretaceous.
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geochemical character and tectonic environment of ultramafic to mafic Cumulate rocks from the tekirova antalya ophiolite southern turkey
Geological Journal, 2006Co-Authors: Utku Bagci, Osman Parlak, Volker HockAbstract:The Upper Cretaceous Tekirova (Antalya) ophiolite derived from the southern branch of the Neotethys is located at the southwestern part of the Antalya Complex along the Tauride belt in southern Turkey. It comprises harzburgitic tectonites, ultramafic to mafic Cumulates, isotropic gabbro, sheeted dykes, volcanics and associated sedimentary rocks. The Cumulate rocks are located mainly along the Cirali–Tekirova section to the south and at Doyran to the north. Several isolated blocks of Cumulate rocks are also observed in the north–south-trending Godene zone of the Antalya Complex. The ultramafic and mafic Cumulate rocks are represented by wehrlite, lherzolite, olivine clinopyroxenite, olivine gabbronorite, olivine gabbro, gabbronorite and gabbro. The order of crystallization in the Cumulates is olivine (Fo88–76) ± chromian spinel clinopyroxene (Mg#92–76) orthopyroxene (Mg#86–70) plagioclase (An97–84). The major and trace element geochemistry of the plutonic rocks suggests that the primary magma generating the Tekirova (Antalya) ophiolite is compositionally similar to those observed in modern island arc tholeiitic sequences. The presence of highly magnesian clino- and orthopyroxenes along with the absence of plagioclase in the ultramafic Cumulates suggest their formation as a result of high-pressure crystal fractionation (c. 10 kbar). In contrast, the mafic Cumulates in the upper crustal level show evidence of a lower-pressure (2–2.5 kbar) environment within the same tectonic setting. Therefore, it is suggested that the Cumulate ultramafic rocks were probably precipitated as a result of in situ crystallization processes along the walls of a conduit system extending downward from a crustal level magma chamber to mantle depths of approximately 30 km. After their formation, the ultramafic Cumulates were transported to a shallow-level magma chamber where the remainder of the plutonic section (mafic Cumulates) was formed at a lower pressure environment. Copyright © 2006 John Wiley & Sons, Ltd.
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whole rock and mineral chemistry of Cumulates from the kizildag hatay ophiolite turkey clues for multiple magma generation during crustal accretion in the southern neotethyan ocean
Mineralogical Magazine, 2005Co-Authors: Utku Bagci, Osman Parlak, Volker HockAbstract:The late Cretaceous Kizildag ophiolite forms one of the best exposures of oceanic lithospheric remnants of southern Neotethys to the north of the Arabian promontory in Turkey. The ultramafic to mafic Cumulate rocks, displaying variable thickness (ranging from 165 to 700 m), are ductiley deformed, possibly in response to syn-magmatic extension during seafloor spreading and characterized by wehrlite, olivine gabbro, olivine gabbronorite and gabbro. The gabbroic Cumulates have an intrusive contact with the wehrlitic Cumulates in some places. The crystallization order of the cumulus and intercumulus phases is olivine (Fo86–77)±chromian spinel, clinopyroxene (Mg#92–76), plagioclase(An95–83), orthopyroxene(Mg#87–79). The olivine, clinopyroxene, orthopyroxene and plagioclase in ultramafic and mafic Cumulate rocks seem to have similar compositional range. This suggests that these rocks cannot represent a simple crystal line of descent. Instead the overlapping ranges in mineral compositions in different rock types suggest multiple magma generation during crustal accretion for the Kizildag ophiolite. The presence of high Mg# of olivine, clinopyroxene, orthopyroxene, and the absence of Ca-rich plagioclase as an early fractionating phase co-precipitating with forsteritic olivine, suggest that the Kizildag plutonic suite is not likely to have originated in a mid-ocean ridge environment. Instead the whole-rock and mineral chemistry of the Cumulates indicates their derivation from an island arc tholeiitic (IAT) magma. All the evidence indicates that the Kizildag ophiolite formed along a slow-spreading centre in a fore-arc region of a suprasubduction zone tectonic setting.
Nick Dygert - One of the best experts on this subject based on the ideXlab platform.
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the effect of ilmenite viscosity on the dynamics and evolution of an overturned lunar Cumulate mantle
Geophysical Research Letters, 2017Co-Authors: Nick Dygert, Yan Liang, Nan Zhang, E M ParmentierAbstract:Lunar Cumulate mantle overturn and the subsequent upwelling of overturned mantle Cumulates provides a potential framework for understanding the first-order thermochemical evolution of the Moon. Upwelling of ilmenite-bearing Cumulates (IBC) after the overturn has a dominant influence on the dynamics and long-term thermal evolution of the lunar mantle. An important parameter determining the stability and convective behaviour of the IBC is its viscosity, which was recently constrained through rock-deformation experiments. To examine the effect of IBC viscosity on the upwelling of overturned lunar Cumulate mantle, here we conduct three-dimensional mantle convection models with an evolving core superposed by an IBC-rich layer, which resulted from mantle overturn after magma ocean solidification. Our modelling shows that a reduction of mantle viscosity by one order of magnitude, due to the presence of ilmenite, can dramatically change convective planform and long-term lunar mantle evolution. Our model results suggest a relatively stable partially molten IBC layer that has surrounded the lunar core to the present day.
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A flow law for ilmenite in dislocation creep: Implications for lunar Cumulate mantle overturn
Geophysical Research Letters, 2016Co-Authors: Nick Dygert, Greg Hirth, Yan LiangAbstract:We present results from new deformation experiments and a dislocation creep flow law for synthetic ilmenite. The flow law predicts an effective viscosity more than 3 orders of magnitude lower than dry olivine at mantle stresses and temperatures. Using the flow law, we predict that lunar ilmenite-bearing Cumulates (IBC) will be weakened by the presence of low-viscosity ilmenite. Dense, low-viscosity IBC are expected to flow into the lunar interior by a process known as Cumulate mantle overturn. Low-viscosity IBC that sink to the core-mantle boundary may be dynamically stable with respect to upwelling. A hot, stable layer of IBC surrounding the lunar core would suppress the development of a core dynamo. A layer of partially molten IBC can also explain the inferred zone of seismic attenuation around the lunar core, as well as a low-viscosity layer suggested by tidal dissipation.
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an experimental study of trace element partitioning between augite and fe rich basalts
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nick Dygert, Yan Liang, Chenguang Sun, Paul C HessAbstract:Abstract Aluminous titanium-rich hedenbergite and Fe-rich augite were experimentally produced at 1050–1220 °C and 0.8–2.2 GPa. Major element compositions are analogous to clinopyroxene from layered intrusions, angrites, nakhlites, and late-stage lunar magma ocean Cumulates. Trace element concentrations in pyroxene and coexisting melt were measured by laser ablation inductively coupled plasma mass spectrometry for rare earth elements (REE), high field strength elements (HFSE), transition metals, and large-ion lithophile elements. REE, HFSE, and transition metal partition coefficients (Ds) are tightly correlated with the cation abundance of Fe on the pyroxene M1 site ( X Fe M1 ), and also correlated with Al on the tetrahedral site ( X Al T ). Parameterized lattice-strain models were developed to predict REE and HFSE partition coefficients as functions of temperature and pyroxene composition ( X Al T or X Fe M1 ). The parameterized models can be used to calculate REE and HFSE partition coefficients for Fe-rich high-Ca pyroxene. We calculated partition coefficients for clinopyroxene derived from modeled end-stage lunar magma ocean Cumulate compositions and observe a factor of 3 variation in clinopyroxene-melt REE partition coefficients. Using representative nakhlite clinopyroxene core and rim compositions we calculated partition coefficients and observed a factor of 4 variability in clinopyroxene-melt REE partition coefficients. HFSE partition coefficients are even more sensitive to composition, showing variations of a factor of 4 for lunar late Cumulates and an order of magnitude for nakhlites. The strong dependence of REE and HFSE partitioning on composition necessitates careful selection of appropriate partition coefficients for Fe-rich systems.
Yan Liang - One of the best experts on this subject based on the ideXlab platform.
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the effect of ilmenite viscosity on the dynamics and evolution of an overturned lunar Cumulate mantle
Geophysical Research Letters, 2017Co-Authors: Nick Dygert, Yan Liang, Nan Zhang, E M ParmentierAbstract:Lunar Cumulate mantle overturn and the subsequent upwelling of overturned mantle Cumulates provides a potential framework for understanding the first-order thermochemical evolution of the Moon. Upwelling of ilmenite-bearing Cumulates (IBC) after the overturn has a dominant influence on the dynamics and long-term thermal evolution of the lunar mantle. An important parameter determining the stability and convective behaviour of the IBC is its viscosity, which was recently constrained through rock-deformation experiments. To examine the effect of IBC viscosity on the upwelling of overturned lunar Cumulate mantle, here we conduct three-dimensional mantle convection models with an evolving core superposed by an IBC-rich layer, which resulted from mantle overturn after magma ocean solidification. Our modelling shows that a reduction of mantle viscosity by one order of magnitude, due to the presence of ilmenite, can dramatically change convective planform and long-term lunar mantle evolution. Our model results suggest a relatively stable partially molten IBC layer that has surrounded the lunar core to the present day.
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A flow law for ilmenite in dislocation creep: Implications for lunar Cumulate mantle overturn
Geophysical Research Letters, 2016Co-Authors: Nick Dygert, Greg Hirth, Yan LiangAbstract:We present results from new deformation experiments and a dislocation creep flow law for synthetic ilmenite. The flow law predicts an effective viscosity more than 3 orders of magnitude lower than dry olivine at mantle stresses and temperatures. Using the flow law, we predict that lunar ilmenite-bearing Cumulates (IBC) will be weakened by the presence of low-viscosity ilmenite. Dense, low-viscosity IBC are expected to flow into the lunar interior by a process known as Cumulate mantle overturn. Low-viscosity IBC that sink to the core-mantle boundary may be dynamically stable with respect to upwelling. A hot, stable layer of IBC surrounding the lunar core would suppress the development of a core dynamo. A layer of partially molten IBC can also explain the inferred zone of seismic attenuation around the lunar core, as well as a low-viscosity layer suggested by tidal dissipation.
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an experimental study of trace element partitioning between augite and fe rich basalts
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nick Dygert, Yan Liang, Chenguang Sun, Paul C HessAbstract:Abstract Aluminous titanium-rich hedenbergite and Fe-rich augite were experimentally produced at 1050–1220 °C and 0.8–2.2 GPa. Major element compositions are analogous to clinopyroxene from layered intrusions, angrites, nakhlites, and late-stage lunar magma ocean Cumulates. Trace element concentrations in pyroxene and coexisting melt were measured by laser ablation inductively coupled plasma mass spectrometry for rare earth elements (REE), high field strength elements (HFSE), transition metals, and large-ion lithophile elements. REE, HFSE, and transition metal partition coefficients (Ds) are tightly correlated with the cation abundance of Fe on the pyroxene M1 site ( X Fe M1 ), and also correlated with Al on the tetrahedral site ( X Al T ). Parameterized lattice-strain models were developed to predict REE and HFSE partition coefficients as functions of temperature and pyroxene composition ( X Al T or X Fe M1 ). The parameterized models can be used to calculate REE and HFSE partition coefficients for Fe-rich high-Ca pyroxene. We calculated partition coefficients for clinopyroxene derived from modeled end-stage lunar magma ocean Cumulate compositions and observe a factor of 3 variation in clinopyroxene-melt REE partition coefficients. Using representative nakhlite clinopyroxene core and rim compositions we calculated partition coefficients and observed a factor of 4 variability in clinopyroxene-melt REE partition coefficients. HFSE partition coefficients are even more sensitive to composition, showing variations of a factor of 4 for lunar late Cumulates and an order of magnitude for nakhlites. The strong dependence of REE and HFSE partitioning on composition necessitates careful selection of appropriate partition coefficients for Fe-rich systems.
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the stability and major element partitioning of ilmenite and armalcolite during lunar Cumulate mantle overturn
Geochimica et Cosmochimica Acta, 2009Co-Authors: Carla Thacker, Yan Liang, Qinglan Peng, Paul C HessAbstract:Abstract Ilmenite has played an important role in the petrogenesis of lunar high-Ti picritic magmas, and armalcolite is another high-Ti oxide that was first discovered on the moon. In this study, we examined the thermodynamic stability of ilmenite and armalcolite in the context of lunar Cumulate mantle overturn. Two starting compositions were explored, an ilmenite-bearing dunite (olivine + ilmenite) and an ilmenite-bearing harzburgite (olivine + orthopyroxene + ilmenite). Experiments were conducted using a 19.05 mm piston-cylinder apparatus at temperatures of 1235–1475 °C and pressures of 1–2 GPa. In runs with the ilmenite-bearing dunite mixture, ilmenite is stable in the subsolidus assemblage at least up to 1450 °C and 2 GPa. In runs with the ilmenite-bearing harzburgite starting mixture, ilmenite is stable at pressures greater than 1.4 GPa, and armalcolite is stable at lower pressures. Solidi for both starting compositions were determined, and the phase boundary between ilmenite- and armalcolite-bearing harzburgite was shown to have little dependence on temperature. During lunar Cumulate overturn, sinking ilmenite formed near the end of lunar magma ocean solidification transforms into armalcolite when in contact with harzburgite Cumulates at depths of less than 280 km in the lunar mantle. Inefficient overturn could leave isolated, inhomogeneously distributed pockets of armalcolite-bearing harzburgite in the upper lunar mantle, underlain by an ilmenite-bearing lower lunar mantle. These high-Ti oxide-bearing harzburgitic pockets can serve as potential sources for the generation of high-Ti magmas through partial melting or through assimilation of high-Ti minerals during transport of low-Ti picritic magmas in the lunar mantle. FeO–MgO exchange between olivine and either ilmenite or armalcolite was also examined in this study. We found the FeO–MgO distribution coefficient to be effectively independent of temperature for the pressures, temperatures, and compositions explored, with an average value of 0.179 ± 0.008 for olivine/ilmenite and 0.319 ± 0.021 for olivine/armalcolite. Given the bulk composition of an overturned lunar Cumulate mantle, our measured FeO–MgO distribution coefficients can be used to estimate the Mg# of coexisting minerals in armalcolite- or ilmenite-bearing harzburgite and dunite in the overturned lunar mantle. Finally, the transformation from ilmenite-bearing harzburgite to armalcolite-bearing harzburgite results in a density increase of up to 2%. Large armalcolite-bearing Cumulate bodies in the upper lunar mantle may be detectable in future lunar geophysical experiments.
