Dorrit Jacob | The Australian National University (original) (raw)
Papers by Dorrit Jacob
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Chemical Geology 261, 346-369, 2009
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First-principles Raman spectra have been computed for several new vaterite structural models tha... more First-principles Raman spectra have been computed for several new vaterite structural models
that have been recently proposed, and compared with spectra recorded on a set of biogenic,
geological and synthetic samples. This set includes new measurements collected on Herdamania
momus spicules (Great Barrier Reef, Queensland, Australia), which are known to have purity and
crystallinity that are higher than for other biogenic samples. Overall, due to the close structural
connection between the various models, the computed Raman spectra are found to be broadly
similar. However, the spectra obtained for the two most stable models (monoclinic C2 and
trigonal P3221, corresponding to two different polytypes of vaterite) exhibit features that are in
excellent agreement with the experimental spectra, whereas the other theoretical structures show
minor peaks that are not observed experimentally. When comparing the spectra for the two
lowest energy structural models (C2 and P3221), the differences are too small to discriminate
between these candidates. The Raman spectrum of Herdamania momus is of higher quality with
respect to spectra obtained in previous studies on other biogenic samples. However, there is no
significant and systematic difference with respect to samples of geological and synthetic origin.
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Gayana (Concepción), Jan 1, 2010
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Abstracts & Program of …, Jan 1, 2006
正In addition to the well-known mantle peridotite xenoliths, the Kimberley kimberlites in South Af... more 正In addition to the well-known mantle peridotite xenoliths, the Kimberley kimberlites in South Africa carry rare, fine-grained, Fe-rich dunite xenoliths that are not well studied. Distinct textural, major and trace element, as well as Re-Os isotope characteristics enable the dunites to be ...
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The Canadian …, Jan 1, 2011
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Fuel, Jan 1, 2011
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… Assembly 2010, held 2-7 May, …, Jan 1, 2010
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Lithos, Jan 1, 2009
Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with ... more Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5–0.63 wt.% H2O and 2.0–3.2 wt.% CO2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K2O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress gradually from carbonate-rich to carbonated silicate in composition: near-solidus melts have Ca/(Ca + Mg) of 0.46–0.53, which fall to < 0.40 more than 50 °C above the solidus. With increasing temperature for the K-enriched peridotite HPK at 50 kbar, melts are characterised by strong increases in SiO2 (< 3 to > 30 wt.%) and Al2O3 (< 1 to > 9 wt.%) and concomitant decrease in CaO (> 20 to < 3 wt.%), with little change in MgO. K2O and TiO2 exhibit maxima at intermediate temperatures, reflecting the stability of phlogopite and ilmenite above the solidus, indicating the presence of up to 13 wt.% K2O and 2.6 wt.% TiO2 in carbonate-rich melts with only 13 wt.% SiO2. Of 30 trace elements, only Cr, Mn, Ni, and Zn are compatible in the residue, whereas U, Rb, Ba and the LREE are most enriched in the melts. Low melt fractions exhibit troughs in trace element patterns for Hf, Nb, Ta and Cs that are diminished or eliminated at higher degrees of melting. Apart from these features and larger LREE/HREE ratios, trace element compositions are similar to silicate melts of peridotite in CO2-free conditions.Partial melts of peridotite with CO2 and H2O are too low in MgO to resemble kimberlites, but will act as effective metasomatic agents enriching the lithosphere in K and carbonates, of relevance for ultramafic lamprophyres and kamafugites. Higher-degree melts (15–35%) have > 20 wt.% SiO2, are only mildly enriched in trace elements, and will not cause large time-integrated isotopic in-growth except over long geological time intervals. The temperature interval over which melts are carbonatitic with SiO2 contents < 10 wt.% narrows with increasing pressure from 30– 60 kbar, meaning that the metasomatic effects of carbonatitic melts may be greatest at 20–30 kbar.
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Journal of …, Jan 1, 2011
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Chemical Geology, Jan 1, 2012
The high spatial resolution of laser ablation inductively coupled plasma mass spectrometry (LA-IC... more The high spatial resolution of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) microanalysis of speleothems and biogenic calcium carbonates makes it possible to improve our understanding of past climatic conditions. However, there are analytical problems associated with this method, such as molecular interferences, elemental fractionation, and mass-load-dependent matrix effects, when using NIST silicate reference glasses for calibration.
Our study with a sector-field ICP-MS shows that many masses are affected by interferences, such as 24Mg+ by 48Ca++ or 31P+ by 15N16O+. Elemental fractionation and mass-load-dependent matrix effects have been detected for both 213 and 193 nm Nd:YAG lasers. They are small for refractory lithophile elements, in particular for the 193 nm laser (< 5%). For chalcophile/siderophile trace elements with low boiling points, however, these effects are large (up to 40% and 20% for the 213 and 193 nm lasers, respectively), and variable for the NIST glasses and carbonates.
In this paper, a protocol for precise and accurate LA-ICP-MS analysis of calcium carbonates is established. Isotopes for interference-free measurements at low (M/ΔM ~ 300) and medium (M/ΔM ~ 4000) mass resolution have been identified. The NIST glasses are suitable for calibration of refractory lithophile element concentrations. However, matrix-matched calibration with carbonate reference materials, such as USGS MACS-1 or MACS-3, is necessary for accurate analysis of chalcophile/siderophile elements with low boiling points. Analytical reproducibility (RSD) is a factor of ~ 2 better using the 193 nm laser than the 213 nm laser. As shown by the analysis of MACS-1 and MACS-3, LA-ICP-MS analyses yield results that agree with the reference values within relative uncertainties of ca. 5–10% at the 95% confidence level.
We have applied LA-ICP-MS for the determination of trace element concentrations in calcite and aragonite layers of a stalagmite and found large variations for Mg, Zn, Sr, and U. In ostracod shells, the concentrations of some trace elements (e.g., Sr and Ba) vary significantly, indicating the potential for paleoclimate research.
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Gems & …, Jan 1, 2012
ABSTRACT In 2006, emeralds were discovered in the Fazenda Bonfim region of northeastern Brazil. E... more ABSTRACT In 2006, emeralds were discovered in the Fazenda Bonfim region of northeastern Brazil. Emerald mineralization occurs in association with small recrystallized pegmatitic bodies hosted by metamorphosed ultramafic rocks within the Santa Monica Shear Zone. Prospecting and exploration have been carried out in a few small pits and tunnels, producing emerald crystals with transparent areas that typically range between 2 and 5 mm. Polished samples typically show a saturated bluish green color with a medium-light to medium tone. The most common internal features are partially healed fissures with two-phase (liquid-gas) fluid inclusions and a variety of fine, parallel-oriented growth tubes. The emeralds contain moderate amounts of the chromophore elements Cr and Fe, and traces of V; they also show relatively high K and low Li. FTIR spectroscopic features are consistent with alkali-bearing emeralds that contain considerable CO 2 and a small amount of deuterated water. Emeralds from Fazenda Bonfim can be distinguished from those of other schist-and pegmatite-related commercial deposits.
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2008 Joint Meeting of …, Jan 1, 2008
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Contributions to Mineralogy and …, Jan 1, 2011
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Chemical Geology 261, 346-369, 2009
Bookmarks Related papers MentionsView impact
First-principles Raman spectra have been computed for several new vaterite structural models tha... more First-principles Raman spectra have been computed for several new vaterite structural models
that have been recently proposed, and compared with spectra recorded on a set of biogenic,
geological and synthetic samples. This set includes new measurements collected on Herdamania
momus spicules (Great Barrier Reef, Queensland, Australia), which are known to have purity and
crystallinity that are higher than for other biogenic samples. Overall, due to the close structural
connection between the various models, the computed Raman spectra are found to be broadly
similar. However, the spectra obtained for the two most stable models (monoclinic C2 and
trigonal P3221, corresponding to two different polytypes of vaterite) exhibit features that are in
excellent agreement with the experimental spectra, whereas the other theoretical structures show
minor peaks that are not observed experimentally. When comparing the spectra for the two
lowest energy structural models (C2 and P3221), the differences are too small to discriminate
between these candidates. The Raman spectrum of Herdamania momus is of higher quality with
respect to spectra obtained in previous studies on other biogenic samples. However, there is no
significant and systematic difference with respect to samples of geological and synthetic origin.
Bookmarks Related papers MentionsView impact
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Gayana (Concepción), Jan 1, 2010
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Bookmarks Related papers MentionsView impact
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Abstracts & Program of …, Jan 1, 2006
正In addition to the well-known mantle peridotite xenoliths, the Kimberley kimberlites in South Af... more 正In addition to the well-known mantle peridotite xenoliths, the Kimberley kimberlites in South Africa carry rare, fine-grained, Fe-rich dunite xenoliths that are not well studied. Distinct textural, major and trace element, as well as Re-Os isotope characteristics enable the dunites to be ...
Bookmarks Related papers MentionsView impact
The Canadian …, Jan 1, 2011
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Fuel, Jan 1, 2011
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… Assembly 2010, held 2-7 May, …, Jan 1, 2010
Bookmarks Related papers MentionsView impact
Lithos, Jan 1, 2009
Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with ... more Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5–0.63 wt.% H2O and 2.0–3.2 wt.% CO2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K2O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress gradually from carbonate-rich to carbonated silicate in composition: near-solidus melts have Ca/(Ca + Mg) of 0.46–0.53, which fall to < 0.40 more than 50 °C above the solidus. With increasing temperature for the K-enriched peridotite HPK at 50 kbar, melts are characterised by strong increases in SiO2 (< 3 to > 30 wt.%) and Al2O3 (< 1 to > 9 wt.%) and concomitant decrease in CaO (> 20 to < 3 wt.%), with little change in MgO. K2O and TiO2 exhibit maxima at intermediate temperatures, reflecting the stability of phlogopite and ilmenite above the solidus, indicating the presence of up to 13 wt.% K2O and 2.6 wt.% TiO2 in carbonate-rich melts with only 13 wt.% SiO2. Of 30 trace elements, only Cr, Mn, Ni, and Zn are compatible in the residue, whereas U, Rb, Ba and the LREE are most enriched in the melts. Low melt fractions exhibit troughs in trace element patterns for Hf, Nb, Ta and Cs that are diminished or eliminated at higher degrees of melting. Apart from these features and larger LREE/HREE ratios, trace element compositions are similar to silicate melts of peridotite in CO2-free conditions.Partial melts of peridotite with CO2 and H2O are too low in MgO to resemble kimberlites, but will act as effective metasomatic agents enriching the lithosphere in K and carbonates, of relevance for ultramafic lamprophyres and kamafugites. Higher-degree melts (15–35%) have > 20 wt.% SiO2, are only mildly enriched in trace elements, and will not cause large time-integrated isotopic in-growth except over long geological time intervals. The temperature interval over which melts are carbonatitic with SiO2 contents < 10 wt.% narrows with increasing pressure from 30– 60 kbar, meaning that the metasomatic effects of carbonatitic melts may be greatest at 20–30 kbar.
Bookmarks Related papers MentionsView impact
Journal of …, Jan 1, 2011
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Chemical Geology, Jan 1, 2012
The high spatial resolution of laser ablation inductively coupled plasma mass spectrometry (LA-IC... more The high spatial resolution of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) microanalysis of speleothems and biogenic calcium carbonates makes it possible to improve our understanding of past climatic conditions. However, there are analytical problems associated with this method, such as molecular interferences, elemental fractionation, and mass-load-dependent matrix effects, when using NIST silicate reference glasses for calibration.
Our study with a sector-field ICP-MS shows that many masses are affected by interferences, such as 24Mg+ by 48Ca++ or 31P+ by 15N16O+. Elemental fractionation and mass-load-dependent matrix effects have been detected for both 213 and 193 nm Nd:YAG lasers. They are small for refractory lithophile elements, in particular for the 193 nm laser (< 5%). For chalcophile/siderophile trace elements with low boiling points, however, these effects are large (up to 40% and 20% for the 213 and 193 nm lasers, respectively), and variable for the NIST glasses and carbonates.
In this paper, a protocol for precise and accurate LA-ICP-MS analysis of calcium carbonates is established. Isotopes for interference-free measurements at low (M/ΔM ~ 300) and medium (M/ΔM ~ 4000) mass resolution have been identified. The NIST glasses are suitable for calibration of refractory lithophile element concentrations. However, matrix-matched calibration with carbonate reference materials, such as USGS MACS-1 or MACS-3, is necessary for accurate analysis of chalcophile/siderophile elements with low boiling points. Analytical reproducibility (RSD) is a factor of ~ 2 better using the 193 nm laser than the 213 nm laser. As shown by the analysis of MACS-1 and MACS-3, LA-ICP-MS analyses yield results that agree with the reference values within relative uncertainties of ca. 5–10% at the 95% confidence level.
We have applied LA-ICP-MS for the determination of trace element concentrations in calcite and aragonite layers of a stalagmite and found large variations for Mg, Zn, Sr, and U. In ostracod shells, the concentrations of some trace elements (e.g., Sr and Ba) vary significantly, indicating the potential for paleoclimate research.
Bookmarks Related papers MentionsView impact
Gems & …, Jan 1, 2012
ABSTRACT In 2006, emeralds were discovered in the Fazenda Bonfim region of northeastern Brazil. E... more ABSTRACT In 2006, emeralds were discovered in the Fazenda Bonfim region of northeastern Brazil. Emerald mineralization occurs in association with small recrystallized pegmatitic bodies hosted by metamorphosed ultramafic rocks within the Santa Monica Shear Zone. Prospecting and exploration have been carried out in a few small pits and tunnels, producing emerald crystals with transparent areas that typically range between 2 and 5 mm. Polished samples typically show a saturated bluish green color with a medium-light to medium tone. The most common internal features are partially healed fissures with two-phase (liquid-gas) fluid inclusions and a variety of fine, parallel-oriented growth tubes. The emeralds contain moderate amounts of the chromophore elements Cr and Fe, and traces of V; they also show relatively high K and low Li. FTIR spectroscopic features are consistent with alkali-bearing emeralds that contain considerable CO 2 and a small amount of deuterated water. Emeralds from Fazenda Bonfim can be distinguished from those of other schist-and pegmatite-related commercial deposits.
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2008 Joint Meeting of …, Jan 1, 2008
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Contributions to Mineralogy and …, Jan 1, 2011
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