Jeremy Delaney - Academia.edu (original) (raw)

Papers by Jeremy Delaney

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 and Phl) micas were selected. Each crystal was oriented morphologically and with the aid of EXCALIBR using a spindle stage equipped polarized light microscope, and their XANES spectra were acquired at beamline X26a, NSLS, using a special geometry of the beam to accommodate the goniometer head and a 20 ϫ 30 m X-ray beam. As would be expected from visible and IR spectra of these minerals, the intensity of both pre-edge and main edge peaks is variable as a function of orientation. Structural similarities among these mineral groups result in similarities among their XANES spectra. Spectra acquired along the length of the chains (c for pyroxene, c for amphibole, and a for sheet silicates) are similar, with corresponding changes in the optical directions, such that Y dioct ≈ Z trioct ≈ Z Krs ≈ Z En ≈ X Ae (clinopyroxene is intermediate). Spectra taken along the b crystallographic axes (along the layer of octahedra, across the I-beam) are similar for all groups (Z dioct ≈ Y trioct ≈ Y Krs ≈ X En ≈ Y Aug), and more similar for the amphiboles and micas. Lastly, spectra acquired along the stacking direction, which is the a crystallographic direction for pyroxene and amphiboles and the c crystallographic direction in sheet silicates, are analogous. From these relationships, assignment of specific transitions to individual features in XANES spectra are facilitated. Furthermore, errors on use of pre-edge positions for determination of Fe 3+ /⌺Fe in minerals can be better constrained.

The formation of achondrites is typically associated with temperatures that cause magmatic, or ne... more The formation of achondrites is typically associated with temperatures that cause magmatic, or near-magmatic reprocessing of chondritic precursors. This view is incomplete. The formation of planetesimals (and the process of aggregation that must occur to form the planets, planetoids and asteroids of the solar system) can initially produce cold objects as well as the hot bodies implied by evidence of magmatism. Objects that form sufficiently early in the evolution of the Solar System, will have a significant budget of short-lived isotopes that decay producing internal heating of the body. (Other heating mechanisms may also apply.) Heating of these bodies from nebular ambient temperatures to silicate melting temperatures occurs. The presence of fully differentiated bodies requires this. The initial heating step in planetary differentiation subjects the interior of the body to steadily rising temperatures and has predictable consequences. Consider the gradual heating of a mass of CI co...

CONSTRAINTS OF SMALL SAMPLES ON X-RAY AND OTHER SPECTROSCOPIES. J.S. Delaney, M.D. Dyar, M.E. Gun... more CONSTRAINTS OF SMALL SAMPLES ON X-RAY AND OTHER SPECTROSCOPIES. J.S. Delaney, M.D. Dyar, M.E. Gunter, S.R. Sutton, and A. Lanzarotti. Dept. Geol. Sci., Rutgers University, Piscataway, NJ 08854, jsd@rci.rutgers.edu; Mount Holyoke College, Dept. Earth and Environment, Mount Holyoke College, South Hadley, MA, 01075; Dept. Geological Sciences, Univ. of Idaho, Moscow, ID 83844; GSECARS and Dept. of Geophysics, Univ. of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637.

Introduction: The oxidation state of Fe in Martian meteorites is a parameter of great interest an... more Introduction: The oxidation state of Fe in Martian meteorites is a parameter of great interest and the ability to determine this value in micrometer scale samples is important [1]. Intense, tunable x-ray sources at large synchrotron storage rings are being exploited to examine the Fe K-absorption edge with energy resolution of ~1-1.5eV in spots of 10x15 μm on thin sections of a wide variety of materials including several Martian meteorites [2-5]. Synchrotron microXANES (SmX) spectroscopy is the technique that provides the most flexible capability for investigating Fe/ΣFe. Variation of Fe/ΣFe is manifested as a function of the energy of the pre-edge to the Fe absorption edge produced by the sample. SmX is at present the only technique that can be used with conventional polished thin sections [6]. Data for a broad spectrum of minerals have been produced and indicate that SmX can be used with a large variety of samples types [1]. Results for the Martian meteorites have been available s...

Shock modification of feldspar has been documented and experimentally reproduced in many studies ... more Shock modification of feldspar has been documented and experimentally reproduced in many studies since the recognition of maskelynite in Shergotty. Experimentally shocked feldspar samples have been well studied using chemical and crystallographic techniques. The crystallographic, site-specific characterization of major and minor elements is less well documented. We present early x-ray absorption (XAS) spectral data for a suite of albitite samples that were experimentally shocked at pressures between 17 and 50 Gpa.

Introduction: How do HED meteorites constrain the data to be returned from 4 Vesta by the Dawn Di... more Introduction: How do HED meteorites constrain the data to be returned from 4 Vesta by the Dawn Discovery Mission? Vesta has long been equated with the " eucrite parent body " in its various iterations and the spectroscopic similarities between Vesta and HED meteorites are compelling. The assumption is made that Vesta is a fully differentiated body. In common with other terrestrial planets, the surface of the 'asteroid' Vesta (more realistically a planetoid) has provinces with distinct spectral characteristics. On the Earth, Moon, Mars and Venus, dichotomies between highlands and lowlands provinces are clearly delineated in existing planetary maps. On Vesta, the presence of a dichotomy is manifested as the huge elevation difference between the south polar region and the northern hemisphere when compared to an ideal spherical body. Petrologically, the uplands and lowlands provinces of Vesta have variable spectral signatures. These lithologies are assumed to correspon...

Introduction: The Kapoeta howardite is of particular interest as it contains a spectrum of minera... more Introduction: The Kapoeta howardite is of particular interest as it contains a spectrum of mineral and lithic fragments that cover the known range of the HED planetoid Vesta with Fe/(Fe+Mg) ratios between 0.10 and 0.95 with a mode intermediate to eucrites and diogenites. The lithic clasts have been studied by a variety of techniques, but were generally limited by the inability to characterize very small samples. The char­ acterization of the relationship among the different samples is generally limited to the observation that they are located in the same meteorite. We have begun a campaign to sample petrographically distinct objects from two parallel slabs (Fig. 1) of Kapoeta (AMNH4788) with the purpose of generating correlated isotop­ ic, compositional, mineralogical and textural data that are strongly constrained by location both within the sample and relative to each other. These objects are currently being prepared for laser Ar-Ar dating of bulk clasts and of mineral separates f...

Introduction: The influence of the intense and variable radiation fields associated with the grow... more Introduction: The influence of the intense and variable radiation fields associated with the growht of the early sun are being recognized as a major control on isotopic systems (Theimens, 1994, 1999). The magnitude of these isotopic effects in oxygen and sulfur are large and provide a framework that suggests that several thermal/photochemical regimes existed within the early nebula. The effectiveness of photochemical processes that modify mineral and rock chemistry, in addition to the isotopic composition, needs to be assessed critically. Photochemistry in the Solar Nebula: Correlations between mass independent fractionation signatures in oxygen and Fe/Mn/Mg ratios in chondrules and among some meteorite groups are known, but have not been explored in depth. Selective photochemical excitation of gaseous elements such as H2 and O2 as well as gaseous compounds such as CO, CO2, H2O, CH4, CH3OH, SO2, SOx and others, provides mechanisms that account for the observed isotopic signatures. H...

Introduction: Mixing of oxygen reservoirs to explain variations of oxygen isotope signatures amon... more Introduction: Mixing of oxygen reservoirs to explain variations of oxygen isotope signatures among different meteorite classes has been long recognized(2). The majority of samples measured are solid planetary, or meteoritic components. Gas and liquid samples are rare. The known range of values in all solar system materials including atmospheres(3) is ∆17O > +150 to ∆17O ≈-50 is large (Figure 1a) whereas most planetary and meteoritic samples plot close to the terrestrial fractionation line (TFL), ∆17O = 0+/-2, in the Clayton-Mayeda diagram (Fig 1). If the solar nebula was radially stratified with respect to volatile components, ices dominated the cold outermost solar system (>5-10AU). The ices of the solar system are the major oxygen reservoir other than the Sun and the rocky portions of the planets. Perhaps 10-20 M⊕ of ices exist today in the Kuiper Belt-Oort cloud region. Abundant H2O in the early nebula presumably migrated outward from the protosun, nucleating ice crystals a...

Introduction: Appreciable numbers of micrometeorites (MM) may form when larger (>1 cm) bodies ... more Introduction: Appreciable numbers of micrometeorites (MM) may form when larger (>1 cm) bodies fragment in the Earth’s atmosphere [1]. If fragmentation affects all incoming bodies similarly, then MM collections should resemble meteorite collections. Compositional and isotopic data support this inference in the broad sense that most MM appear to be “chondritic” [2-5]. Relative to conventional meteorites, however, micrometeorites comprise a larger fraction of carbonaceous material [3,5,6], few or no irons [7], and, to date, no achondrites. Several factors probably account for these differences. First, some MM may arrive as small bodies dust rather than as parts of larger bodies. The principal sources for dust are not necessarily the same as those for conventional meteoroids [8]. Second, the varying toughness of meteoroids and asteroids may influence their susceptibility to break-up. Third, our ability to search for achondritic MM is limited absolutely by the relatively small numbers...

Contrib Mineral Petrol, 1978

Meteoritics and Planetary Science Supplement, Sep 1, 2009

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 and Phl) micas were selected. Each crystal was oriented morphologically and with the aid of EXCALIBR using a spindle stage equipped polarized light microscope, and their XANES spectra were acquired at beamline X26a, NSLS, using a special geometry of the beam to accommodate the goniometer head and a 20 ϫ 30 m X-ray beam. As would be expected from visible and IR spectra of these minerals, the intensity of both pre-edge and main edge peaks is variable as a function of orientation. Structural similarities among these mineral groups result in similarities among their XANES spectra. Spectra acquired along the length of the chains (c for pyroxene, c for amphibole, and a for sheet silicates) are similar, with corresponding changes in the optical directions, such that Y dioct ≈ Z trioct ≈ Z Krs ≈ Z En ≈ X Ae (clinopyroxene is intermediate). Spectra taken along the b crystallographic axes (along the layer of octahedra, across the I-beam) are similar for all groups (Z dioct ≈ Y trioct ≈ Y Krs ≈ X En ≈ Y Aug), and more similar for the amphiboles and micas. Lastly, spectra acquired along the stacking direction, which is the a crystallographic direction for pyroxene and amphiboles and the c crystallographic direction in sheet silicates, are analogous. From these relationships, assignment of specific transitions to individual features in XANES spectra are facilitated. Furthermore, errors on use of pre-edge positions for determination of Fe 3+ /⌺Fe in minerals can be better constrained.

The formation of achondrites is typically associated with temperatures that cause magmatic, or ne... more The formation of achondrites is typically associated with temperatures that cause magmatic, or near-magmatic reprocessing of chondritic precursors. This view is incomplete. The formation of planetesimals (and the process of aggregation that must occur to form the planets, planetoids and asteroids of the solar system) can initially produce cold objects as well as the hot bodies implied by evidence of magmatism. Objects that form sufficiently early in the evolution of the Solar System, will have a significant budget of short-lived isotopes that decay producing internal heating of the body. (Other heating mechanisms may also apply.) Heating of these bodies from nebular ambient temperatures to silicate melting temperatures occurs. The presence of fully differentiated bodies requires this. The initial heating step in planetary differentiation subjects the interior of the body to steadily rising temperatures and has predictable consequences. Consider the gradual heating of a mass of CI co...

CONSTRAINTS OF SMALL SAMPLES ON X-RAY AND OTHER SPECTROSCOPIES. J.S. Delaney, M.D. Dyar, M.E. Gun... more CONSTRAINTS OF SMALL SAMPLES ON X-RAY AND OTHER SPECTROSCOPIES. J.S. Delaney, M.D. Dyar, M.E. Gunter, S.R. Sutton, and A. Lanzarotti. Dept. Geol. Sci., Rutgers University, Piscataway, NJ 08854, jsd@rci.rutgers.edu; Mount Holyoke College, Dept. Earth and Environment, Mount Holyoke College, South Hadley, MA, 01075; Dept. Geological Sciences, Univ. of Idaho, Moscow, ID 83844; GSECARS and Dept. of Geophysics, Univ. of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637.

Introduction: The oxidation state of Fe in Martian meteorites is a parameter of great interest an... more Introduction: The oxidation state of Fe in Martian meteorites is a parameter of great interest and the ability to determine this value in micrometer scale samples is important [1]. Intense, tunable x-ray sources at large synchrotron storage rings are being exploited to examine the Fe K-absorption edge with energy resolution of ~1-1.5eV in spots of 10x15 μm on thin sections of a wide variety of materials including several Martian meteorites [2-5]. Synchrotron microXANES (SmX) spectroscopy is the technique that provides the most flexible capability for investigating Fe/ΣFe. Variation of Fe/ΣFe is manifested as a function of the energy of the pre-edge to the Fe absorption edge produced by the sample. SmX is at present the only technique that can be used with conventional polished thin sections [6]. Data for a broad spectrum of minerals have been produced and indicate that SmX can be used with a large variety of samples types [1]. Results for the Martian meteorites have been available s...

Shock modification of feldspar has been documented and experimentally reproduced in many studies ... more Shock modification of feldspar has been documented and experimentally reproduced in many studies since the recognition of maskelynite in Shergotty. Experimentally shocked feldspar samples have been well studied using chemical and crystallographic techniques. The crystallographic, site-specific characterization of major and minor elements is less well documented. We present early x-ray absorption (XAS) spectral data for a suite of albitite samples that were experimentally shocked at pressures between 17 and 50 Gpa.

Introduction: How do HED meteorites constrain the data to be returned from 4 Vesta by the Dawn Di... more Introduction: How do HED meteorites constrain the data to be returned from 4 Vesta by the Dawn Discovery Mission? Vesta has long been equated with the " eucrite parent body " in its various iterations and the spectroscopic similarities between Vesta and HED meteorites are compelling. The assumption is made that Vesta is a fully differentiated body. In common with other terrestrial planets, the surface of the 'asteroid' Vesta (more realistically a planetoid) has provinces with distinct spectral characteristics. On the Earth, Moon, Mars and Venus, dichotomies between highlands and lowlands provinces are clearly delineated in existing planetary maps. On Vesta, the presence of a dichotomy is manifested as the huge elevation difference between the south polar region and the northern hemisphere when compared to an ideal spherical body. Petrologically, the uplands and lowlands provinces of Vesta have variable spectral signatures. These lithologies are assumed to correspon...

Introduction: The Kapoeta howardite is of particular interest as it contains a spectrum of minera... more Introduction: The Kapoeta howardite is of particular interest as it contains a spectrum of mineral and lithic fragments that cover the known range of the HED planetoid Vesta with Fe/(Fe+Mg) ratios between 0.10 and 0.95 with a mode intermediate to eucrites and diogenites. The lithic clasts have been studied by a variety of techniques, but were generally limited by the inability to characterize very small samples. The char­ acterization of the relationship among the different samples is generally limited to the observation that they are located in the same meteorite. We have begun a campaign to sample petrographically distinct objects from two parallel slabs (Fig. 1) of Kapoeta (AMNH4788) with the purpose of generating correlated isotop­ ic, compositional, mineralogical and textural data that are strongly constrained by location both within the sample and relative to each other. These objects are currently being prepared for laser Ar-Ar dating of bulk clasts and of mineral separates f...

Introduction: The influence of the intense and variable radiation fields associated with the grow... more Introduction: The influence of the intense and variable radiation fields associated with the growht of the early sun are being recognized as a major control on isotopic systems (Theimens, 1994, 1999). The magnitude of these isotopic effects in oxygen and sulfur are large and provide a framework that suggests that several thermal/photochemical regimes existed within the early nebula. The effectiveness of photochemical processes that modify mineral and rock chemistry, in addition to the isotopic composition, needs to be assessed critically. Photochemistry in the Solar Nebula: Correlations between mass independent fractionation signatures in oxygen and Fe/Mn/Mg ratios in chondrules and among some meteorite groups are known, but have not been explored in depth. Selective photochemical excitation of gaseous elements such as H2 and O2 as well as gaseous compounds such as CO, CO2, H2O, CH4, CH3OH, SO2, SOx and others, provides mechanisms that account for the observed isotopic signatures. H...

Introduction: Mixing of oxygen reservoirs to explain variations of oxygen isotope signatures amon... more Introduction: Mixing of oxygen reservoirs to explain variations of oxygen isotope signatures among different meteorite classes has been long recognized(2). The majority of samples measured are solid planetary, or meteoritic components. Gas and liquid samples are rare. The known range of values in all solar system materials including atmospheres(3) is ∆17O > +150 to ∆17O ≈-50 is large (Figure 1a) whereas most planetary and meteoritic samples plot close to the terrestrial fractionation line (TFL), ∆17O = 0+/-2, in the Clayton-Mayeda diagram (Fig 1). If the solar nebula was radially stratified with respect to volatile components, ices dominated the cold outermost solar system (>5-10AU). The ices of the solar system are the major oxygen reservoir other than the Sun and the rocky portions of the planets. Perhaps 10-20 M⊕ of ices exist today in the Kuiper Belt-Oort cloud region. Abundant H2O in the early nebula presumably migrated outward from the protosun, nucleating ice crystals a...

Introduction: Appreciable numbers of micrometeorites (MM) may form when larger (>1 cm) bodies ... more Introduction: Appreciable numbers of micrometeorites (MM) may form when larger (>1 cm) bodies fragment in the Earth’s atmosphere [1]. If fragmentation affects all incoming bodies similarly, then MM collections should resemble meteorite collections. Compositional and isotopic data support this inference in the broad sense that most MM appear to be “chondritic” [2-5]. Relative to conventional meteorites, however, micrometeorites comprise a larger fraction of carbonaceous material [3,5,6], few or no irons [7], and, to date, no achondrites. Several factors probably account for these differences. First, some MM may arrive as small bodies dust rather than as parts of larger bodies. The principal sources for dust are not necessarily the same as those for conventional meteoroids [8]. Second, the varying toughness of meteoroids and asteroids may influence their susceptibility to break-up. Third, our ability to search for achondritic MM is limited absolutely by the relatively small numbers...

Contrib Mineral Petrol, 1978

Meteoritics and Planetary Science Supplement, Sep 1, 2009