No evidence is found for the reduction of Fe from the Lamont silicates; the Fe/Mg ratios of the s... more No evidence is found for the reduction of Fe from the Lamont silicates; the Fe/Mg ratios of the silicates therefore reflect their igneous history rather than a later mesosiderite history. The system from which the Lamont silicates formed is nevertheless more magnesian than that of most other mesosiderites, and may represent deeper insights into their evolution.
Kapoeta lithologies sampled as clasts are being systematically documented petrographically, chron... more Kapoeta lithologies sampled as clasts are being systematically documented petrographically, chronologically, and isotopically by microsampling protocols to constrain in detail the history of the source regolith.
Most achondritic meteorites have Fe/Mn ratios that are lower than those of carbonaceous chondrite... more Most achondritic meteorites have Fe/Mn ratios that are lower than those of carbonaceous chondrites and of course are lower than the solar system abundance ratio of these elements. Models of the origin of achondritic assemblages must, therefore, account for these ratios. Fe/Mn ratios are suggested to be distinctive for samples from each achondrite parent body and for the Earth and
Ten glass cosmic spherules (CS) from the South Pole water well collection were analyzed by electr... more Ten glass cosmic spherules (CS) from the South Pole water well collection were analyzed by electron microprobe. Nine of them have Fe/Mn and Fe/Mg ratios in the range typical of chondrites. One of them (SP37-3), along with up to six other previously analyzed CS, have nonchondritic Fe/Mn and Fe/Mg ratios that agree well with values typical of either (basaltic) howardite,
Synchrotron micro-XANES spectroscopy (SmX) is used to examine the amount and distribution of Fe 2... more Synchrotron micro-XANES spectroscopy (SmX) is used to examine the amount and distribution of Fe 2+ and Fe 3+ in five samples of fayalite previously studied by Mössbauer spectroscopy. Rockport fayalite is homogeneous and the Fe in it is completely reduced. Olivine from Qianan is almost completely oxidized, and probably contains finely intergrown silica, laihunite, and hematite with hematite predominating. Pantelleria
In order to assess the extent of X-ray anisotropy in biaxial minerals, Fe XANES spectra were acqu... more In order to assess the extent of X-ray anisotropy in biaxial minerals, Fe XANES spectra were acquired on single crystals of pyroxenes, amphiboles, and micas with the X-ray beam polarized along the X, Y, and Z optical orientations. Specifically, single crystals of enstatite (En), augite (Aug), aegirine (Ae), kaersutite (Krs; three different compositions), dioctahedral (Ms and Ill), and trioctahedral (Ann
... in Archean greenstone-granitoid terranes have been shown to be useful in providing significan... more ... in Archean greenstone-granitoid terranes have been shown to be useful in providing significant new insights concerning the geodynamic origin of Archean greenstone belts and the evolution of the Archean mantle-crustal system (Sylvester et al., 1997a; Condie, 1994, 1998 ...
The basaltic achondrites, eucrites, diogenites, and howardites have compositions on a common oxyg... more The basaltic achondrites, eucrites, diogenites, and howardites have compositions on a common oxygen isotope mass fractionation line and probably formed from a chondritic precursor also lying on that same line. No chondritic meteorite group has the same isotopic signature as the basaltic achondrites, so the oxygen isotope ratios of several known chondritic groups were used to construct a two component mixing model for the composition of the precursor. This model does not provide a unique solution, as several mixtures of ordinary and carbonaceous precursors will satisfy the isotopic constraints. The FeMnMg abundances of the precursors and of the eucrites were used to provide an additional constraint. The precursor composition selected for study is a mixture of 70% (wt) H-chondrite with 30% (wt) CM-chondrtte. This mixture generates a slightly FeO-rich silicate precursor that, after reduction and separation of an iron + sulfide core, is compatible with the mantle of the basaltic achondrite planetoid (BAP) having a similar composition to that modeled by Dreibus and Wänke (1980). Partial melting experiments of this H-CM precursor composition suggest that eucritic magmas could be formed in such a mantle. These experiments also suggest that the mantle must have experienced metal loss to constrain the Fe/Mn ratios and probably significant olivine fractionation as well. Diogenite precursors may also be generated in this mantle composition as FeO reduction and olivine fractionation lead to the formation of SiO2 enriched compositions from which diogenite source magmas may be extracted. If mixing of material from two very distinct chondritic reservoirs (H and CM-chondrites) is realistic, then an asteroid scale mixing process is needed to generate the achondrite precursor. Large impact events would provide a plausible method for mixing material from reservoirs with quite different oxygen isotope characteristics to assemble the basaltic achondrite planetoid.
Fe-rich mica crystals have been studied using microbeam XANES spectroscopy of the Fe K edges in o... more Fe-rich mica crystals have been studied using microbeam XANES spectroscopy of the Fe K edges in order to evaluate the dependence of XANES features and resultant Fe 3+ / Fe values on the orientation of the crystals with respect to the polarization of the synchrotron beam. ...
... Richard A. Volkert a , * , Mark D. Feigenson b , Lina C. Patino 1 , b , Jeremy S. Delaney b a... more ... Richard A. Volkert a , * , Mark D. Feigenson b , Lina C. Patino 1 , b , Jeremy S. Delaney b andAvery Ala Drake Jr ... Table 8. Abbreviations of 7.5-minute quadrangles are: WAY, Wawayanda; GLK, Greenwood Lake; NFD, Newfoundland; WQ, Wanaque; RAM, Ramsey; ST, Stanhope ...
No evidence is found for the reduction of Fe from the Lamont silicates; the Fe/Mg ratios of the s... more No evidence is found for the reduction of Fe from the Lamont silicates; the Fe/Mg ratios of the silicates therefore reflect their igneous history rather than a later mesosiderite history. The system from which the Lamont silicates formed is nevertheless more magnesian than that of most other mesosiderites, and may represent deeper insights into their evolution.
Kapoeta lithologies sampled as clasts are being systematically documented petrographically, chron... more Kapoeta lithologies sampled as clasts are being systematically documented petrographically, chronologically, and isotopically by microsampling protocols to constrain in detail the history of the source regolith.
Most achondritic meteorites have Fe/Mn ratios that are lower than those of carbonaceous chondrite... more Most achondritic meteorites have Fe/Mn ratios that are lower than those of carbonaceous chondrites and of course are lower than the solar system abundance ratio of these elements. Models of the origin of achondritic assemblages must, therefore, account for these ratios. Fe/Mn ratios are suggested to be distinctive for samples from each achondrite parent body and for the Earth and
Ten glass cosmic spherules (CS) from the South Pole water well collection were analyzed by electr... more Ten glass cosmic spherules (CS) from the South Pole water well collection were analyzed by electron microprobe. Nine of them have Fe/Mn and Fe/Mg ratios in the range typical of chondrites. One of them (SP37-3), along with up to six other previously analyzed CS, have nonchondritic Fe/Mn and Fe/Mg ratios that agree well with values typical of either (basaltic) howardite,
Synchrotron micro-XANES spectroscopy (SmX) is used to examine the amount and distribution of Fe 2... more Synchrotron micro-XANES spectroscopy (SmX) is used to examine the amount and distribution of Fe 2+ and Fe 3+ in five samples of fayalite previously studied by Mössbauer spectroscopy. Rockport fayalite is homogeneous and the Fe in it is completely reduced. Olivine from Qianan is almost completely oxidized, and probably contains finely intergrown silica, laihunite, and hematite with hematite predominating. Pantelleria
In order to assess the extent of X-ray anisotropy in biaxial minerals, Fe XANES spectra were acqu... more In order to assess the extent of X-ray anisotropy in biaxial minerals, Fe XANES spectra were acquired on single crystals of pyroxenes, amphiboles, and micas with the X-ray beam polarized along the X, Y, and Z optical orientations. Specifically, single crystals of enstatite (En), augite (Aug), aegirine (Ae), kaersutite (Krs; three different compositions), dioctahedral (Ms and Ill), and trioctahedral (Ann
... in Archean greenstone-granitoid terranes have been shown to be useful in providing significan... more ... in Archean greenstone-granitoid terranes have been shown to be useful in providing significant new insights concerning the geodynamic origin of Archean greenstone belts and the evolution of the Archean mantle-crustal system (Sylvester et al., 1997a; Condie, 1994, 1998 ...
The basaltic achondrites, eucrites, diogenites, and howardites have compositions on a common oxyg... more The basaltic achondrites, eucrites, diogenites, and howardites have compositions on a common oxygen isotope mass fractionation line and probably formed from a chondritic precursor also lying on that same line. No chondritic meteorite group has the same isotopic signature as the basaltic achondrites, so the oxygen isotope ratios of several known chondritic groups were used to construct a two component mixing model for the composition of the precursor. This model does not provide a unique solution, as several mixtures of ordinary and carbonaceous precursors will satisfy the isotopic constraints. The FeMnMg abundances of the precursors and of the eucrites were used to provide an additional constraint. The precursor composition selected for study is a mixture of 70% (wt) H-chondrite with 30% (wt) CM-chondrtte. This mixture generates a slightly FeO-rich silicate precursor that, after reduction and separation of an iron + sulfide core, is compatible with the mantle of the basaltic achondrite planetoid (BAP) having a similar composition to that modeled by Dreibus and Wänke (1980). Partial melting experiments of this H-CM precursor composition suggest that eucritic magmas could be formed in such a mantle. These experiments also suggest that the mantle must have experienced metal loss to constrain the Fe/Mn ratios and probably significant olivine fractionation as well. Diogenite precursors may also be generated in this mantle composition as FeO reduction and olivine fractionation lead to the formation of SiO2 enriched compositions from which diogenite source magmas may be extracted. If mixing of material from two very distinct chondritic reservoirs (H and CM-chondrites) is realistic, then an asteroid scale mixing process is needed to generate the achondrite precursor. Large impact events would provide a plausible method for mixing material from reservoirs with quite different oxygen isotope characteristics to assemble the basaltic achondrite planetoid.
Fe-rich mica crystals have been studied using microbeam XANES spectroscopy of the Fe K edges in o... more Fe-rich mica crystals have been studied using microbeam XANES spectroscopy of the Fe K edges in order to evaluate the dependence of XANES features and resultant Fe 3+ / Fe values on the orientation of the crystals with respect to the polarization of the synchrotron beam. ...
... Richard A. Volkert a , * , Mark D. Feigenson b , Lina C. Patino 1 , b , Jeremy S. Delaney b a... more ... Richard A. Volkert a , * , Mark D. Feigenson b , Lina C. Patino 1 , b , Jeremy S. Delaney b andAvery Ala Drake Jr ... Table 8. Abbreviations of 7.5-minute quadrangles are: WAY, Wawayanda; GLK, Greenwood Lake; NFD, Newfoundland; WQ, Wanaque; RAM, Ramsey; ST, Stanhope ...
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