Papers by Gordana Garapic
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Ofioliti, Jan 3, 2011
Abstract Ophiolite mélanges of Mts. Kalnik and Ivanšcica form the northern sector of the Kalnik U... more Abstract Ophiolite mélanges of Mts. Kalnik and Ivanšcica form the northern sector of the Kalnik Unit and represent the northeasternmost exposed tip of the Sava-Vardar Suture Zone. Petrological; geochemical and isotopic characteristics of extrusive rock blocks ...
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American Mineralogist, 2015
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Lithos, 2015
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Geophysical Journal International, 2016
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Rapid Prototyping Journal
Purpose The purpose of this paper is to empirically determine general models and methods for yiel... more Purpose The purpose of this paper is to empirically determine general models and methods for yield strength and modulus at different print orientations adequate for design purposes associated with typical fused deposition modeled (FDM) components/parts. Emphasis was placed on characterizing the impacts of anisotropy and resulting trends independent of material toward developing a method that matched the level of engineering required for current limited structural capabilities of FDM. Design/methodology/approach Tensile tests were performed with a range of unidirectional filament orientations of three different materials allowing for determination of the generalized models, which are then compared to previous findings of others. Findings Though anisotropic trends were similar to previous findings, minimum yield strength was found to be associated with filaments 75° from the loading direction resulting in a sinusoidal generalization. Modulus was found to be best approximated with an e...
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Geochimica et Cosmochimica Acta
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Lithos, 2014
ABSTRACT The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of th... more ABSTRACT The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of the Alps to the Albanian and Greek ophiolites. Detailed sampling of the Krivaja-Konjuh massif, one of the largest massifs in the Dinaride belt, reveals fertile compositions and an extensive record of deformation at spinel peridotite facies conditions. High Na2O clinopyroxene and spinel-orthopyroxene symplectites after garnet indicate a relatively high pressure, subcontinental origin of the southern and western part of Krivaja, similar to orogenic massifs such as Lherz, Ronda and the Eastern Central Alpine peridotites. Clinopyroxene and spinel compositions from Konjuh show similarities with fertile abyssal peridotite. In the central parts of the massif the spinel lherzolites contain locally abundant patches of plagioclase, indicating impregnation by melt. The migrating melt was orthopyroxene undersaturated, locally converting the peridotites to massive olivine-rich troctolites. Massive gabbros and more evolved gabbro veins cross-cutting peridotites indicate continued melt production at depth. Overall we infer that the massif represents the onset of rifting and early stages of formation of a new ocean basin. In the south of Krivaja very localized chromitite occurrences indicate that much more depleted melts with supra-subduction affinity traversed the massif that have no genetic relationship with the peridotites. This indicates that volcanics with supra-subduction affinity at the margins of the Krivaja-Konjuh massif record separate processes during closure of the ocean basin. Comparison with published compositional data from other Balkan massifs shows that the range of compositions within the Krivaja-Konjuh massif is similar to the compositionalrange of the western massifs of the Dinarides. The compositions of the Balkan massifs show a west to east gradient, ranging from subcontinental on the western side of the Dinarides to depleted mid-ocean ridge/arc compositions in the Vardar zone in the east. This is consistent with the hypothesis that both ophiolite belts originate in a single ocean, rather than from two separate basins. A distinct decrease in fertility occurs in the south of the Dinarides toward the Albanian ophiolites with supra-subduction affinity.
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Geochemistry, Geophysics, Geosystems, 2013
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Geochemistry, Geophysics, Geosystems, 2013
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The currently existing model of grain-scale melt geometry in the Earth's upper mantle is deri... more The currently existing model of grain-scale melt geometry in the Earth's upper mantle is derived from theoretical considerations that stem from material science research, combined with relatively low-resolution observations of polished two-dimensional surfaces. This model predicts a simple, interconnected network of melt along three-grain edges in static surface energy equilibrium. However, due to a continuous rearrangements of neighboring grains caused by grain growth, melt forms complex shapes among the grains. As a result, it is impossible to construct a 3D image of the pore space from 2D surfaces, which makes it particularly challenging to resolve the current controversy on whether all two-grain boundaries are wetted or melt-free. We present a new method for reconstruction of the 3D pore space in partially molten rocks. The method consists of serial sectioning and high resolution imaging (Field Emission SEM) of polished surfaces, followed by image alignment and rendering. Th...
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The grain scale melt distribution in the Earth's upper mantle affects the physical properties... more The grain scale melt distribution in the Earth's upper mantle affects the physical properties of partially molten rock, such as seismic properties, rheology, electrical conductivity and permeability. To investigate the impact of the melt geometry on these properties we constructed a 3-D model of the grain scale melt distribution. The model was obtained from serial sectioning, high-resolution imaging and image rendering of an experimentally produced sample of partially molten dunite. This sample consists of Fo90 olivine with a mean grain size of 33 microns and 4% melt equilibrated in a piston cylinder at 1350°C and 1 GPa for 432 hours. The 3-D model shows that the grain scale melt distribution is complex and deviates significantly from simple analytical models. The principal reasons for the complexity are the broad range in grain sizes and the tendency of olivine to develop facets; both driven by surface energy reduction. As a consequence a significant portion of the melt resides...
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Helium isotopes are used as a tracer for primitive reservoirs that have persisted in the Earth’s ... more Helium isotopes are used as a tracer for primitive reservoirs that have persisted in the Earth’s mantle. Basalts erupted at several intraplate oceanic islands, including Hawaii, Iceland, Galapagos, and Samoa, have hosted the highest 3He/4He ratios (>30 Ra, where Ra is atmospheric 3He/4He ratio) globally that are far in excess of the 3He/4He typical of the upper mantle sampled at mid-ocean ridges (8 Ra). These lavas have been suggested to be melts of a primitive, or possibly slightly depleted, mantle reservoir, i.e., either fertile or a depleted peridotite. Here we report evidence for geochemical enrich- ment in the high-3He/4He mantle sampled by lavas with the highest 3He/4He from Hawaii, Samoa, and possibly Galapagos. The titanium concentrations in high-3He/4He lavas from Samoa are too high to be explained by melts of a mantle peridotite, even at infinitesimally small degrees of melting, and the elevated Ti corresponds to elevated Pb-isotopic ratios. The highest 3He/4He lavas from Loihi, Hawaii, also have Ti concentrations that are too high to be melts of primitive mantle peridotite at the degrees of melt extraction proposed for this ocean island. Thus, Ti-rich material must have been added to the high-3He/4He mantle reservoir, and this material is likely to be recycled mafic crust similar to MORB- like eclogite, which is consistent with the elevated Pb-isotopic ratios. We show that fractionation corrected, major element compositions of high-3He/4He alkalic lavas can be satisfactorily modeled by melting and melt-rock interaction scenario in a fertile peridotite-MORB-eclogite hybrid system. Primitive peridotitic and recycled eclogitic reservoirs are suggested to be intimately associated in the deepest mantle and high-3He/4He lavas from several localities may sample a mantle source that hosts a component of recycled oceanic crust.
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We present new He-Sr-Nd-Pb-Os isotopic compositions and major and trace-element concentrations fo... more We present new He-Sr-Nd-Pb-Os isotopic compositions and major and trace-element concentrations for ten subaerially-erupted lavas and one seamount lava associated with the Pitcairn hotspot. The most geochemically- enriched lavas at the Pitcairn hotspot have signatures that are consistent with recycled sediments derived from upper continental crust. Pitcairn lavas have elevated Ti, which also supports the presence of a mafic protolith in the Pitcairn mantle. A subset of Pitcairn seamount samples, including the seamount sample presented here, are tholeiitic. Tholeiitic lavas are uncommon at ocean hotspots located far from mid-ocean ridges. Like tholeiites that erupted in Hawaii, the presence of tholeiites in the Pitcairn magmatic suite can be explained by melting a silica- saturated recycled mafic component in the Pitcairn mantle source. We also present the highest 3He/4He ratio (12.6 Ra, ratio to atmosphere) from the Pitcairn hotspot. This sample anchors the high 206Pb/204Pb portion of the Pitcairn array and provides evidence for a plume component in the Pitcairn mantle. In contrast, Pitcairn lavas that have the lowest 206Pb/204Pb are the most geochemically enriched, and have the highest 87Sr/86Sr and lowest 143Nd/144Nd in the Pitcairn suite; these EM-1 end-member lavas have MORB-like 3He/4He (~ 8 Ra, ratio to atmosphere). Recycled oceanic crust and sediment suggested to be in the Pitcairn EM-1 mantle are expected to have low 3He/4He (b 0.1 Ra). Therefore, the higher, MORB-like 3He/4He in Pitcairn EM-1 lavas is paradoxical, but might be explained by diffusive exchange of helium, but not the heavy radiogenic isotopes, with the ambient mantle over billion-year timescales.
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The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of the Alps to... more The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of the Alps to the Albanian and Greek ophiolites. Detailed sampling of the Krivaja–Konjuh massif, one of the largest massifs in the Dinaride belt, reveals fertile compositions and an extensive record of deformation at spinel peridotite facies conditions. High Na2O clinopyroxene and spinel–orthopyroxene symplectites after garnet indicate a relatively high pressure, subcontinental origin of the southern and western part of Krivaja, similar to orogenic massifs such as Lherz, Ronda and the Eastern Central Alpine peridotites. Clinopyroxene and spinel compositions from Konjuh show similarities with fertile abyssal peridotite. In the central parts of the massif the spinel lherzolites contain locally abundant patches of plagioclase, indicating impregnation by melt. The migrating melt was orthopyroxene under- saturated, locally converting the peridotites to massive olivine-rich troctolites. Massive gabbros and more evolved gabbro veins cross-cutting peridotites indicate continued melt production at depth. Overall we infer that the massif represents the onset of rifting and early stages of formation of a new ocean basin. In the south of Krivaja very localized chromitite occurrences indicate that much more depleted melts with supra- subduction affinity traversed the massif that have no genetic relationship with the peridotites. This indicates that volcanics with supra-subduction affinity at the margins of the Krivaja–Konjuh massif record separate pro- cesses during closure of the ocean basin. Comparison with published compositional data from other Balkan mas- sifs shows that the range of compositions within the Krivaja–Konjuh massif is similar to the compositional range of the western massifs of the Dinarides. The compositions of the Balkan massifs show a west to east gradient, ranging from subcontinental on the western side of the Dinarides to depleted mid-ocean ridge/arc compositions in the Vardar zone in the east. This is consistent with the hypothesis that both ophiolite belts originate in a single ocean, rather than from two separate basins. A distinct decrease in fertility occurs in the south of the Dinarides towards the Albanian ophiolites with supra-subduction affinity.
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We determine the 3-D melt geometry of partially molten samples of olivine containing 1.6 and 3.6v... more We determine the 3-D melt geometry of partially molten samples of olivine containing 1.6 and 3.6vol.% of basaltic melt that were held in a piston cylinder apparatus at upper mantle conditions for 430 h. Our approach involves serial sectioning and high-resolution field emission SEM imaging. Resolution is such that melt pockets approaching ~30 nm in size were resolved while covering an area of ~300 by 230 mm. The principal result of this study is to show that thin layers (typically 100 nm or less in thickness) between adjacent grains observed in 2-D images persist with depth and are therefore wetted two-grain boundaries. Melt geometries most closely resembling triple junction tubules of the isotropic equilibrium model occur at all three-grain edges but are small compared to larger pockets. The wetted grain boundaries at a dihedral angle >0 for this system are inferred to be due to slow expulsion of melt from dynamically reorganizing grain boundaries during steady state grain growth. The attenuation peak observed in forced torsional oscillation experiments on similar samples is likely related to the wetted grain boundaries. Grain growth, driven by surface energy reduction, occurs also at the larger grain sizes expected for the mantle. This suggests the presence of wetted grain boundaries and significant velocity reduction and attenuation in partially molten upper mantle, as observed for example in back-arc basins.
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Papers by Gordana Garapic