The Experts below are selected from a list of 33 Experts worldwide ranked by ideXlab platform
Melinda Hutson - One of the best experts on this subject based on the ideXlab platform.
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differentiation and evolution of the iva Meteorite parent body clues from pyroxene geochemistry in the steinbach stony iron Meteorite
Meteoritics & Planetary Science, 2006Co-Authors: A Ruzicka, Melinda HutsonAbstract:We analyzed the Steinbach IVA Stony-Iron Meteorite using scanning electron microscopy (SEM), electron microprobe analysis (EMPA), laser ablation inductively-coupled-plasma mass spectroscopy (LA-ICP-MS), and modeling techniques. Different and sometimes adjacent low-Ca pyroxene grains have distinct compositions and evidently crystallized at different stages in a chemically evolving system prior to the solidification of metal and troilite. Early crystallizing pyroxene shows evidence for disequilibrium and formation under conditions of rapid cooling, producing clinobronzite and type 1 pyroxene rich in troilite and other inclusions. Subsequently, type 2 pyroxene crystallized over an extensive fractionation interval. Steinbach probably formed as a cumulate produced by extensive crystal fractionation (~6070% fractional crystallization) from a high-temperature (~1450-1490 °C) silicate-metallic magma. The inferred composition of the precursor magma is best modeled as having formed by ≥30-50% silicate partial melting of a chondritic protolith. If this protolith was similar to an LL chondrite (as implied by O-isotopic data), then olivine must have separated from the partial melt, and a substantial amount (~53-56%) of FeO must have been reduced in the silicate magma. A model of simultaneous endogenic heating and collisional disruption appears best able to explain the data for Steinbach and other IVA Meteorites. Impact disruption occurred while the parent body was substantially molten, causing liquids to separate from solids and oxygen-bearing gas to vent to space, leading to a molten metal-rich body that was smaller than the original parent body and that solidified from the outside in. This model can simultaneously explain the characteristics of both Stony-Iron and iron IVA Meteorites, including the apparent correlation between metal composition and metallographic cooling rate observed for metal.
R Hutchison - One of the best experts on this subject based on the ideXlab platform.
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the bencubbin stony iron Meteorite breccia electron petrography shock history and affinities of a carbonaceous chondrite clast
Meteoritics, 1991Co-Authors: D J Barber, R HutchisonAbstract:— A “carbonaceous chondrite” clast from Bencubbin was studied by analytical transmission electron microscopy and other electron beam techniques. In section, the clast consists of oval augen, with a preferred orientation, set in fine-grained matrix. The augen comprise olivine microphenocrysts in fine-grained to glassy mesostases. The olivines are heavily deformed, giving rise to mosaicism. Many sub-grains have high densities of dislocations with [001] Burgers vectors. In some regions the dislocation configurations are recovered, causing a reduced dislocation density; recrystallization is rarer. Severe cataclasis is absent; there are few open fractures and little intergranular porosity except where a second phase occurs. Such porosity in olivine mainly occurs as finescale negative crystals, which appear to be healed cracks. Some mesostases consist of small amounts of microporous oxides and feldspathic glass but glassy veins are absent. Pyrhottite and Fe/Ni sulfides are major mesostasis constituents that rarely form tongues between the olivines, which commonly include smaller sulfide blebs. The matrix of the clast has abundant sulfides and fine-grained, poorly crystalline Fe- and Fe/Ni-oxides, with more sparse ferrihydrite. The oxides mostly occur in contact with, or within, aluminous and siliceous glassy material in which crystals of melilite, spinel, Ca-pyroxene, feldspar, and other minor silicate phases have grown. Small patches of fibrous and/or sheet-like Mg/Fe silicates with layer morphologies also occur. They are microporous, poorly crystalline and lack the layer spacings of phyllosilicates, of which they may be relics. Grains of anhydrite and calcite are interlaced with fibrous silicates. There is evidence that one, or more, intense shock-heating event(s) produced local melting. A later shock event(s) involved less severe shock-heating, to about 900 °C. The mineralogy indicates that the clast may have originated from a CM2 precursor or from material like Allan Hills 85085, although it is just possible that terrestrial weathering produced some of the diagnostic minerals.
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The Bencubbin Stony-Iron Meteorite breccia: Electron petrography, shock-history and affinities of a “carbonaceous chondrite” clast
Meteoritics, 1991Co-Authors: D J Barber, R HutchisonAbstract:— A “carbonaceous chondrite” clast from Bencubbin was studied by analytical transmission electron microscopy and other electron beam techniques. In section, the clast consists of oval augen, with a preferred orientation, set in fine-grained matrix. The augen comprise olivine microphenocrysts in fine-grained to glassy mesostases. The olivines are heavily deformed, giving rise to mosaicism. Many sub-grains have high densities of dislocations with [001] Burgers vectors. In some regions the dislocation configurations are recovered, causing a reduced dislocation density; recrystallization is rarer. Severe cataclasis is absent; there are few open fractures and little intergranular porosity except where a second phase occurs. Such porosity in olivine mainly occurs as finescale negative crystals, which appear to be healed cracks. Some mesostases consist of small amounts of microporous oxides and feldspathic glass but glassy veins are absent. Pyrhottite and Fe/Ni sulfides are major mesostasis constituents that rarely form tongues between the olivines, which commonly include smaller sulfide blebs. The matrix of the clast has abundant sulfides and fine-grained, poorly crystalline Fe- and Fe/Ni-oxides, with more sparse ferrihydrite. The oxides mostly occur in contact with, or within, aluminous and siliceous glassy material in which crystals of melilite, spinel, Ca-pyroxene, feldspar, and other minor silicate phases have grown. Small patches of fibrous and/or sheet-like Mg/Fe silicates with layer morphologies also occur. They are microporous, poorly crystalline and lack the layer spacings of phyllosilicates, of which they may be relics. Grains of anhydrite and calcite are interlaced with fibrous silicates. There is evidence that one, or more, intense shock-heating event(s) produced local melting. A later shock event(s) involved less severe shock-heating, to about 900 °C. The mineralogy indicates that the clast may have originated from a CM2 precursor or from material like Allan Hills 85085, although it is just possible that terrestrial weathering produced some of the diagnostic minerals.
A Ruzicka - One of the best experts on this subject based on the ideXlab platform.
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differentiation and evolution of the iva Meteorite parent body clues from pyroxene geochemistry in the steinbach stony iron Meteorite
Meteoritics & Planetary Science, 2006Co-Authors: A Ruzicka, Melinda HutsonAbstract:We analyzed the Steinbach IVA Stony-Iron Meteorite using scanning electron microscopy (SEM), electron microprobe analysis (EMPA), laser ablation inductively-coupled-plasma mass spectroscopy (LA-ICP-MS), and modeling techniques. Different and sometimes adjacent low-Ca pyroxene grains have distinct compositions and evidently crystallized at different stages in a chemically evolving system prior to the solidification of metal and troilite. Early crystallizing pyroxene shows evidence for disequilibrium and formation under conditions of rapid cooling, producing clinobronzite and type 1 pyroxene rich in troilite and other inclusions. Subsequently, type 2 pyroxene crystallized over an extensive fractionation interval. Steinbach probably formed as a cumulate produced by extensive crystal fractionation (~6070% fractional crystallization) from a high-temperature (~1450-1490 °C) silicate-metallic magma. The inferred composition of the precursor magma is best modeled as having formed by ≥30-50% silicate partial melting of a chondritic protolith. If this protolith was similar to an LL chondrite (as implied by O-isotopic data), then olivine must have separated from the partial melt, and a substantial amount (~53-56%) of FeO must have been reduced in the silicate magma. A model of simultaneous endogenic heating and collisional disruption appears best able to explain the data for Steinbach and other IVA Meteorites. Impact disruption occurred while the parent body was substantially molten, causing liquids to separate from solids and oxygen-bearing gas to vent to space, leading to a molten metal-rich body that was smaller than the original parent body and that solidified from the outside in. This model can simultaneously explain the characteristics of both Stony-Iron and iron IVA Meteorites, including the apparent correlation between metal composition and metallographic cooling rate observed for metal.
D J Barber - One of the best experts on this subject based on the ideXlab platform.
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the bencubbin stony iron Meteorite breccia electron petrography shock history and affinities of a carbonaceous chondrite clast
Meteoritics, 1991Co-Authors: D J Barber, R HutchisonAbstract:— A “carbonaceous chondrite” clast from Bencubbin was studied by analytical transmission electron microscopy and other electron beam techniques. In section, the clast consists of oval augen, with a preferred orientation, set in fine-grained matrix. The augen comprise olivine microphenocrysts in fine-grained to glassy mesostases. The olivines are heavily deformed, giving rise to mosaicism. Many sub-grains have high densities of dislocations with [001] Burgers vectors. In some regions the dislocation configurations are recovered, causing a reduced dislocation density; recrystallization is rarer. Severe cataclasis is absent; there are few open fractures and little intergranular porosity except where a second phase occurs. Such porosity in olivine mainly occurs as finescale negative crystals, which appear to be healed cracks. Some mesostases consist of small amounts of microporous oxides and feldspathic glass but glassy veins are absent. Pyrhottite and Fe/Ni sulfides are major mesostasis constituents that rarely form tongues between the olivines, which commonly include smaller sulfide blebs. The matrix of the clast has abundant sulfides and fine-grained, poorly crystalline Fe- and Fe/Ni-oxides, with more sparse ferrihydrite. The oxides mostly occur in contact with, or within, aluminous and siliceous glassy material in which crystals of melilite, spinel, Ca-pyroxene, feldspar, and other minor silicate phases have grown. Small patches of fibrous and/or sheet-like Mg/Fe silicates with layer morphologies also occur. They are microporous, poorly crystalline and lack the layer spacings of phyllosilicates, of which they may be relics. Grains of anhydrite and calcite are interlaced with fibrous silicates. There is evidence that one, or more, intense shock-heating event(s) produced local melting. A later shock event(s) involved less severe shock-heating, to about 900 °C. The mineralogy indicates that the clast may have originated from a CM2 precursor or from material like Allan Hills 85085, although it is just possible that terrestrial weathering produced some of the diagnostic minerals.
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The Bencubbin Stony-Iron Meteorite breccia: Electron petrography, shock-history and affinities of a “carbonaceous chondrite” clast
Meteoritics, 1991Co-Authors: D J Barber, R HutchisonAbstract:— A “carbonaceous chondrite” clast from Bencubbin was studied by analytical transmission electron microscopy and other electron beam techniques. In section, the clast consists of oval augen, with a preferred orientation, set in fine-grained matrix. The augen comprise olivine microphenocrysts in fine-grained to glassy mesostases. The olivines are heavily deformed, giving rise to mosaicism. Many sub-grains have high densities of dislocations with [001] Burgers vectors. In some regions the dislocation configurations are recovered, causing a reduced dislocation density; recrystallization is rarer. Severe cataclasis is absent; there are few open fractures and little intergranular porosity except where a second phase occurs. Such porosity in olivine mainly occurs as finescale negative crystals, which appear to be healed cracks. Some mesostases consist of small amounts of microporous oxides and feldspathic glass but glassy veins are absent. Pyrhottite and Fe/Ni sulfides are major mesostasis constituents that rarely form tongues between the olivines, which commonly include smaller sulfide blebs. The matrix of the clast has abundant sulfides and fine-grained, poorly crystalline Fe- and Fe/Ni-oxides, with more sparse ferrihydrite. The oxides mostly occur in contact with, or within, aluminous and siliceous glassy material in which crystals of melilite, spinel, Ca-pyroxene, feldspar, and other minor silicate phases have grown. Small patches of fibrous and/or sheet-like Mg/Fe silicates with layer morphologies also occur. They are microporous, poorly crystalline and lack the layer spacings of phyllosilicates, of which they may be relics. Grains of anhydrite and calcite are interlaced with fibrous silicates. There is evidence that one, or more, intense shock-heating event(s) produced local melting. A later shock event(s) involved less severe shock-heating, to about 900 °C. The mineralogy indicates that the clast may have originated from a CM2 precursor or from material like Allan Hills 85085, although it is just possible that terrestrial weathering produced some of the diagnostic minerals.
A. R. Basu - One of the best experts on this subject based on the ideXlab platform.
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Trace Element-Isotope Geochemistry of Impact Breccia, Target Basalts and Laser Raman Spectroscopy of Shocked Plagioclase from Lonar Crater, India
2020Co-Authors: R. Chakrabarti, A. R. BasuAbstract:Lonar impact Crater, approximately 50 Kyr old, is the best known terrestrial impact crater in basalts and is located within the ~65Ma old Deccan Traps in India (1958’N, 7631’E). It is an almost circular depression and is 1830m across. The impact origin of the Lonar Crater has been well established by the presence of shatter cones and maskelynite-bearing microbreccia from the crater floor (Fredriksson et al., 1973). A smaller circular depression, called the little Lonar, 300m in diameter and about 700m north of the Lonar Crater is a second crater, probably formed after the throwout from the main crater landed. The target Deccan basalts show much lower concentrations of Rb, Ba, Th, U and Pb compared to the impact breccia. These basalts show characteristic Rb, Ba and Pb depletion with respect to Th, U, Nb, Ta, La, Ce etc. when normalized to the primitive mantle abundances for these elements. In contrast, the breccia rocks are strikingly enriched in these three elements as well as Th and U (Fig 1a). The impact breccia rocks have more fractionated chondrite normalized light rare earth element (LREE) (LaN/SmN = 1.58-1.81) patterns compared to the target basalts (LaN/SmN = 1.26-1.39). Nd-Sr isotopic composition (Fig 1b) of the Lonar host basalts (eNd = + 0.4 -2.8; Sr/Sr =0.70552-0.70624) is similar to the Poladpur suite, one of the mid-section volcano-stratigraphic units of the Deccan traps. The Pb-isotopic composition (Fig 1c) of the target basalts in the crater (PbPb = 18.86-19.34; PbPb = 15.64-15.71; PbPb = 39.20-39.57) is also similar to the Poladpur suite of Deccan basalts. In contrast, the impact breccia rocks have more radiogenic Sr (Sr/Sr = 0.70729-0.70824), less radiogenic Nd (eNd = -3.8 to –0.9), higher Rb/Sr and lower Sm/Nd ratios, indicating an additional component, other than the target basalt, that is derived from the local continental crust beneath the basaltic target rocks. The Pb-isotopic composition of the breccia rocks (PbPb = 17.67-18.69; PbPb = 15.63-15.80; PbPb = 37.6739.02), especially the high PbPb ratios at low PbPb, further indicates this crustal component to be of Archean age. The Deccan traps in western India are underlain by Archean to mid-Proterozoic crust, composed of amphibolites and granulites including sediments derived from them. Collectively, the data presented here on the trace element compositions, negative eNd values and radiogenic Sr isotopic composition of the impact breccia rocks indicate that a major component of the Lonar impact breccia was derived from melting of Archean basement rocks, similar to the Dharwar craton of peninsular India. Using Pi-group scaling relations, the observed crater diameter, and density of the basaltic target rocks, we have estimated with reasonable approximation the diameter of the Lonar impactor to be either 70m, 86m or 120m, assuming the bolide to be an iron Meteorite, Stony-Iron Meteorite, or an ordinary chondrite, respectively. Raman scattering measurements were performed on Lonar maskelynites in the impact breccia and compared with maskelynites from the Manicouagan crater using the 514.5 nm line of an argon ion laser at an intensity of 40 kW/cm . An inverted microscope (Nikon TE3000) with 50x objective (NA 0.55) was used for confocal imaging. A holographic notch filter removed residual laser scatter and the Raman scattering was detected by a silicon CCD at -90 C (Princeton Instruments Spec10-400R). 2
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Trace element and isotopic evidence for Archean basement in the Lonar crater impact breccia, Deccan Volcanic Province
Earth and Planetary Science Letters, 2006Co-Authors: R. Chakrabarti, A. R. BasuAbstract:Abstract The Lonar impact crater in the Deccan Traps of the Indian peninsula provides unique opportunities to study physical and chemical processes of impact cratering on basaltic targets, because terrestrial impact craters on basalts are extremely rare. Such studies are needed for determining provenance and other parameters of the excavated rocks and the cratering phenomenon that may have implications for similar crater formations in Lunar, Martian and other basaltic targets in the solar system. Considering some of these objectives, we analyzed trace elements and Nd, Sr, Pb-isotopes of impact breccia rocks and target basalts collected from the Lonar crater. Chondrite-normalized Rare Earth Element (REE) patterns in the target basalts and breccia rocks show similar light REE-enriched patterns, although in detail, the impact breccia are more fractionated in La/Sm compared to the target basalts. The target basalts also show much lower concentrations of Rb, Ba, Th, U and Pb compared to the breccia and are characterized by Rb, Ba and Pb depletions with respect to the primitive mantle-normalized Th, U, Nb, Ta and the REE contents. The breccia rocks are significantly enriched in Rb, Ba and Pb, and to a lesser extent in Th and U, compared to the target rocks. The Nd, Sr and Pb-isotopic compositions of the Lonar target basalts can be correlated with those of the Poladpur suite, one of the mid-section volcano-stratigraphic units of the Deccan traps. In contrast to the host basalts, the impact breccia rocks show more radiogenic Sr, less radiogenic Nd and higher Rb/Sr and lower Sm/Nd ratios, indicating an additional component, other than the target basalt, that must have been derived from beneath the basaltic target rocks at the impact site. The Deccan traps in western India are underlain by Archean to mid-Proterozoic cratonic rocks. The overall geochemical signatures of the impact breccia rocks, specifically, the trace element concentrations, negative eNd values, radiogenic Sr isotopic composition as well as the high 207Pb/204Pb at low 206Pb/204Pb indicate that a major component of the Lonar impact breccia was derived from melting of Archean basement rocks. We argue that the Archean component in the breccia cannot be from the incorporation of paleosols that are weathering products of the target basalts, or from the inter-trappean sediments that are most commonly cherts and limestones of Mesozoic age. Similarly, the possible role of eolian sediments in causing the Archean Pb-isotopic signature, identical to those of the Deccan basement, in the breccia rocks can be excluded. The basement beneath the Lonar region is believed to be similar to the Dharwar craton of peninsular India. Based on their similar Pb-isotopic compositions with the breccia rocks, we suggest the Archean Chitradurga Group of rocks of this craton to be present in the basement beneath the Deccan lavas of the Lonar region. The thickness of the basaltic target rocks at the crater-site (∼ 400 m) and the inferred crater depth (350 m–610 m), based on depth to diameter ratios in simple planetary craters (0.2–0.33), are consistent with our conclusion regarding melting and incorporation of these ancient basement rocks in the impact breccia of the Lonar crater. Using Pi-group scaling relations, the observed crater diameter, and density of the basaltic target rocks, we have estimated with reasonable approximation the diameter of the Lonar impactor to be either 70 m, 86 m or 120 m, assuming the bolide to be an iron Meteorite, Stony-Iron Meteorite, or an ordinary chondrite, respectively.