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John C Tipper - One of the best experts on this subject based on the ideXlab platform.
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minlith an experience based algorithm for estimating the likely mineralogical compositions of sedimentary rocks from Bulk Chemical analyses
Computers & Geosciences, 2004Co-Authors: O M Rosen, Ali A Abbyasov, John C TipperAbstract:The MINLITH algorithm is a tool for estimating the likely mineralogical compositions of sedimentary rocks, using information from Bulk Chemical analyses. It is an experience-based algorithm that represents compositions in terms of a simplified set of normative minerals. MINLITH has been designed to be applied principally to mature sedimentary rocks, but it can (with care) be applied also to immature sediments and to metasedimentary rocks; the compositions that MINLITH gives for metasedimentary rocks are approximations to the original (i.e. pre-metamorphic) mineralogical compositions. The experience base on which MINLITH is built is a collection of 600 reference samples of sedimentary rocks. The compositional regularities found in these samples have allowed empirical rules to be developed to predict how the oxides reported in a Bulk Chemical analysis should be partitioned among the minerals most likely to be present. The discrepancies between MINLITH-estimated compositions and physically determined modal compositions are relatively small for the most widespread types of mature sedimentary rocks; they are comparable in their magnitude to the discrepancies associated with other methods for estimating mineralogical compositions from Bulk Chemical analyses, and to the discrepancies associated with quantitative X-ray diffractometry. The MINLITH algorithm is of particular value: (1) for providing preliminary estimates of mineralogical composition, prior to precise modal analysis; (2) for identifying systematic compositional variation within suites of samples; (3) in generalised sample classification; (4) in the sedimentological interpretation of metasedimentary rocks.
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MINLITH—an experience-based algorithm for estimating the likely mineralogical compositions of sedimentary rocks from Bulk Chemical analyses
Computers & Geosciences, 2004Co-Authors: O M Rosen, Ali A Abbyasov, John C TipperAbstract:The MINLITH algorithm is a tool for estimating the likely mineralogical compositions of sedimentary rocks, using information from Bulk Chemical analyses. It is an experience-based algorithm that represents compositions in terms of a simplified set of normative minerals. MINLITH has been designed to be applied principally to mature sedimentary rocks, but it can (with care) be applied also to immature sediments and to metasedimentary rocks; the compositions that MINLITH gives for metasedimentary rocks are approximations to the original (i.e. pre-metamorphic) mineralogical compositions. The experience base on which MINLITH is built is a collection of 600 reference samples of sedimentary rocks. The compositional regularities found in these samples have allowed empirical rules to be developed to predict how the oxides reported in a Bulk Chemical analysis should be partitioned among the minerals most likely to be present. The discrepancies between MINLITH-estimated compositions and physically determined modal compositions are relatively small for the most widespread types of mature sedimentary rocks; they are comparable in their magnitude to the discrepancies associated with other methods for estimating mineralogical compositions from Bulk Chemical analyses, and to the discrepancies associated with quantitative X-ray diffractometry. The MINLITH algorithm is of particular value: (1) for providing preliminary estimates of mineralogical composition, prior to precise modal analysis; (2) for identifying systematic compositional variation within suites of samples; (3) in generalised sample classification; (4) in the sedimentological interpretation of metasedimentary rocks.
Vasileios Mavromatis - One of the best experts on this subject based on the ideXlab platform.
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the rapid resetting of the ca isotopic signatures of calcite at ambient temperature during its congruent dissolution precipitation and at equilibrium
Chemical Geology, 2019Co-Authors: Eric H Oelkers, Philip Pogge A E Von Strandmann, Vasileios MavromatisAbstract:Abstract This study provides direct experimental evidence of the resetting of the calcium (Ca) isotope signatures of calcite in the presence of an aqueous fluid during its congruent dissolution, precipitation, and at equilibrium at ambient temperatures over week-long timescales. Batch reactor experiments were performed at 25 °C in aqueous NaCl solutions; air or CO2-gas mixtures were bubbled through this fluid to fix pH. During congruent calcite dissolution, the fluid became enriched in isotopically heavy Ca, and the Ca isotope composition continued to become heavier after the fluid attained Bulk Chemical equilibrium with the mineral; the δ44/42Ca composition of the fluid was up to 0.8‰ higher than the dissolving calcite at the end of the dissolution experiments. Calcite precipitation was provoked by increasing the reactor fluid pH after Chemical equilibrium had been attained via dissolution. Rayleigh isotope fractionation effects were observed immediately after the pH was increased and rapid calcite precipitation occurred. However, isotopic exchange continued after the system Chemically equilibrated, eradicating this Rayleigh signal. Taken together, these observations 1) confirm dynamic mineral-fluid equilibrium (i.e. dissolution and precipitation occur at equal, non-zero rates at equilibrium), and 2) indicate that isotopic compositions of calcite can readily equilibrate even when this mineral is in Bulk Chemical equilibrium with its coexisting fluid. This latter observation suggests the preservation of paleo-environmental isotopic signatures in calcite may require a combination of the isolation of the fluid-mineral system from external Chemical input and/or the existence of a yet to be defined calcite dissolution/precipitation inhibition mechanism.
A. J. R. Prentice - One of the best experts on this subject based on the ideXlab platform.
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Titan at the time of the Cassini spacecraft first flyby: a prediction for its origin, Bulk Chemical composition and internal physical structure
Astroparticle Physics, 2020Co-Authors: A. J. R. PrenticeAbstract:I report the results of a new set of calculations for the gravitational contraction of the protosolar cloud to quantify the idea that Titan may be a captured moon of Saturn (Prentice 1981, 1984). It is proposed that Titan initially condensed as a secondary embryo in the same protosolar gas ring from which Saturn’s central solid core and gaseous envelope were acquired. The new model for the protosolar cloud (hereafter PSC) includes the influence of very strong superadiabaticity in its outer layers that is observed in an exact numerical simulation of supersonic turbulent convection (Prentice & Dyt 2003). I adopt the protosolar elemental abundances recommended by Lodders (2003). At Saturn’s orbit, the Bulk Chemical constituents of the condensate are rock (mass fraction 0.494), water ice (0.474), and graphite (0.032). The mean density is 1523 kg m. Structural models for a frozen Titan yield a mean density of 2095 kg m 3 (Chemically homogeneous case) and 1904 kg m (fully differentiated 2-zone case). The agreement to one percent of the latter value with the observed mean density suggests that Titan is indeed a fully differentiated satellite. The value of C/MR for this model is 0.316. It is predicted that Titan has no internal ocean or induced magnetic field but it may possess a small native dipole field of magnitude 2×10 11 Tesla m due to thermoremanent magnetization fed by Saturn’s ancient magnetic field. Capture of Titan was achieved by gas drag at the edge of the proto-Saturnian envelope at a time when that cloud had a radius close to Titan’s present orbital size. Collisional drag was also probably an important agent in securing Titan’s capture. Perhaps Hyperion is the shattered remnant of a pre-existing native moon of Saturn that was destroyed on Titan’s arrival. Titan should thus have much the same appearance as Triton, being nearly smooth, crater-free and streaked with elemental carbon (Prentice 2004a).
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Ultima Thule: a Prediction for the Origin, Bulk Chemical Composition, and Physical Structure, submitted prior to the New Horizons Spacecraft 100 Pixel LORRI Data Return
arXiv: Earth and Planetary Astrophysics, 2019Co-Authors: A. J. R. PrenticeAbstract:The 2019 January 01 flypast of Ultima Thule by the New Horizons spacecraft has provided the author with a new opportunity to test his gas ring model of planetary origin (Prentice, 1978, Moon Planets 19 341). The model proposes that Ultima Thule condensed from the first gas ring shed by the gravitationally contracting protosolar cloud. I use the fully quantified gas ring model to compute the thermal properties of the gas ring in which Ultima condensed and thence to predict the initial Bulk Chemical composition of the condensate. It is predicted that all KBOs initially contained large stores of CO2 ice and CH4 ices. These make up fractions 0.2210 and 0.0513 of the condensate mass, respectively. Water ice makes up a mass fraction 0.1845, nearly-dry rock has fraction 0.5269 and graphite has 0.0163. Next, I compute the thermal evolution of Ultima, taking into account the radiogenic heat released by the decay of 26Al. Stellar occultation data suggest that Ultima Thule may consist of 2 lobes of radius about 10 km and 7.5 km. The thermal evolution model shows that within 0.2 Myr, the peak internal temperatures are sufficient for a fraction ~0.7 of the CH4 ice in the larger lobe to melt and for a fraction ~0.4 of the CO2 ice to sublime. For the smaller lobe, these fractions are less. Liquid CH4 quickly migrates upwards to the surface and refreezes to form a thick outer shell of CH4 ice. The sublimation of CO2 takes place after the melting of CH4. The possibility now exists for rising CO2 vapour to become trapped beneath the CH4 shell. This may lead to explosive eruptions of the outer shell and destruction of the primordial surface of Ultima and loss of the CO2. If 60% of CO2 is lost, the lobe radii each shrinks by ~5%. Even so, the intensity of 26Al radiogenic heating may not be sufficient to render the surface of Ultima Thule globally smooth, unless the lobe sizes are of order ~15 km.
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Origin and Bulk Chemical Composition of Mercury
Highlights of Astronomy, 2016Co-Authors: A. J. R. Prentice, Daniel Jontof-hutterAbstract:AbstractThe origin of Mercury’s high metal content is examined within a gas ring model for the condensation of the planetary system. Mercury’s axial moment-of-inertia factor is predicted to be 0.325 ± 0.002.
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Saturn's Icy Moon Rhea: A Prediction for its Bulk Chemical Composition and Physical Structure at the Time of the Cassini Spacecraft First Flyby
Publications of the Astronomical Society of Australia, 2006Co-Authors: A. J. R. PrenticeAbstract:I report a model for the formation of Saturn’s family of mid-sized icy moons to coincide with the first flypast of Rhea by the Cassini spacecraft on 2005 November 26. It is proposed that the moons had condensed from a concentric family of orbiting gas rings that were shed some 4.6 × 109 yr ago by the proto-Saturnian (hereafter p-Sat) cloud. The p-Sat cloud is made up of gas and residual grains of the gas ring that was shed by the proto-Solar cloud (hereafter PSC) at Saturn’s orbit. The Bulk of the condensate within this proto-Solar ring accumulates to form Saturn’s central core of mass ~10–20 M ⊕ (M ⊕ = Earth mass). The process of formation of Saturn’s solid core thus provides an opportunity for the p-Sat cloud to become depleted in rock and water ice relative to the usual solar abundances of these materials. Nitrogen, which exists as uncondensing N2 in the PSC and as NH3 in the p-Sat cloud, retains its solar abundance relative to H2. If the depletion factor of solids relative to gas is ζ dep = 0.25, as suggested by the low mass of Rhea relative to solar abundance expectations, the mass-percent ratio of NH3 to H2O in the dense p-Sat cloud is 36:64. Numerical and structural models for Rhea are constructed on the basis of a ‘cosmogonic’ Bulk Chemical composition of hydrated rock (mass fraction 0.385), H2O ice (0.395), and NH3 ice (0.220). It is difficult to construct a Chemically differentiated model of Rhea whose mean density matches the observed value ρ Rhea = 1.23 ± 0.02 g cm–3 for reasonable bounds of the controlling parameters. Chemically homogeneous models can, however, be constrained to match the observed Rhea density provided that the mass fraction of NH3 is permitted to exceed the cosmogonic value by a factor ζ NH3 ζNH3--> = 1.20–1.35. A large proportion of NH3 in the ice mass inhibits the formation of the dense crystalline phase II of H2O ice at high pressure. This may explain the lack of compressional features on the surface of the satellite that are expected as a result of ice II formation in the cooling core. The favoured model of Rhea is Chemically uniform and has mass proportions of rock (0.369), H2O ice (0.378), and NH3 ice (0.253). The enhancement factor of NH3 lies within the measured uncertainties of the solar abundance of nitrogen. The satellite is very cold and nearly isodense. The predicted axial moment-of-inertia coefficient is [C/MR 2]Rhea = 0.399 ± 0.004.
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Titan at the time of the Cassini spacecraft first flyby: a prediction for its origin, Bulk Chemical composition and internal physical structure
arXiv: Astrophysics, 2006Co-Authors: A. J. R. PrenticeAbstract:I report the results of a new set of calculations for the gravitational contraction of the proto-solar cloud to quantify the idea that Titan may be a captured moon of Saturn (Prentice 1981, 1984). It is proposed that Titan initially condensed as a secondary embryo in the same proto-solar gas ring from which the central solid core and gaseous envelope of Saturn were acquired. At the orbit of Saturn, the Bulk Chemical constituents of the condensate are rock (mass fraction 0.494), water ice (0.474), and graphite (0.032). The mean density is 1523 kg/m^3. Structural models for a frozen Titan yield a mean density of 2095 kg/m^3 (Chemically homogeneous case) and 1904 kg/m^3 (fully differentiated 2-zone case). The agreement to one percent of the latter value with the observed mean density suggests that Titan is indeed a fully differentiated satellite. The value of C/MR^2 for this model is 0.316. It is predicted that Titan has no internal ocean or induced magnetic field but it may possess a small native dipole field of magnitude 2 x 10^11 Tesla m^3 due to thermoremanent magnetization fed by the ancient magnetic field of Saturn. Capture of Titan was achieved by gas drag at the edge of the proto-Saturnian envelope at a time when that cloud had a radius close to the present orbital size of Titan. Collisional drag was also probably an important agent in securing the capture of Titan. Perhaps Hyperion is the shattered remnant of a pre-existing native moon of Saturn that was destroyed on the arrival of Titan. Titan should thus have much the same appearance as Triton, being nearly smooth, crater-free and streaked with elemental carbon (Prentice 2004a).
O M Rosen - One of the best experts on this subject based on the ideXlab platform.
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minlith an experience based algorithm for estimating the likely mineralogical compositions of sedimentary rocks from Bulk Chemical analyses
Computers & Geosciences, 2004Co-Authors: O M Rosen, Ali A Abbyasov, John C TipperAbstract:The MINLITH algorithm is a tool for estimating the likely mineralogical compositions of sedimentary rocks, using information from Bulk Chemical analyses. It is an experience-based algorithm that represents compositions in terms of a simplified set of normative minerals. MINLITH has been designed to be applied principally to mature sedimentary rocks, but it can (with care) be applied also to immature sediments and to metasedimentary rocks; the compositions that MINLITH gives for metasedimentary rocks are approximations to the original (i.e. pre-metamorphic) mineralogical compositions. The experience base on which MINLITH is built is a collection of 600 reference samples of sedimentary rocks. The compositional regularities found in these samples have allowed empirical rules to be developed to predict how the oxides reported in a Bulk Chemical analysis should be partitioned among the minerals most likely to be present. The discrepancies between MINLITH-estimated compositions and physically determined modal compositions are relatively small for the most widespread types of mature sedimentary rocks; they are comparable in their magnitude to the discrepancies associated with other methods for estimating mineralogical compositions from Bulk Chemical analyses, and to the discrepancies associated with quantitative X-ray diffractometry. The MINLITH algorithm is of particular value: (1) for providing preliminary estimates of mineralogical composition, prior to precise modal analysis; (2) for identifying systematic compositional variation within suites of samples; (3) in generalised sample classification; (4) in the sedimentological interpretation of metasedimentary rocks.
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MINLITH—an experience-based algorithm for estimating the likely mineralogical compositions of sedimentary rocks from Bulk Chemical analyses
Computers & Geosciences, 2004Co-Authors: O M Rosen, Ali A Abbyasov, John C TipperAbstract:The MINLITH algorithm is a tool for estimating the likely mineralogical compositions of sedimentary rocks, using information from Bulk Chemical analyses. It is an experience-based algorithm that represents compositions in terms of a simplified set of normative minerals. MINLITH has been designed to be applied principally to mature sedimentary rocks, but it can (with care) be applied also to immature sediments and to metasedimentary rocks; the compositions that MINLITH gives for metasedimentary rocks are approximations to the original (i.e. pre-metamorphic) mineralogical compositions. The experience base on which MINLITH is built is a collection of 600 reference samples of sedimentary rocks. The compositional regularities found in these samples have allowed empirical rules to be developed to predict how the oxides reported in a Bulk Chemical analysis should be partitioned among the minerals most likely to be present. The discrepancies between MINLITH-estimated compositions and physically determined modal compositions are relatively small for the most widespread types of mature sedimentary rocks; they are comparable in their magnitude to the discrepancies associated with other methods for estimating mineralogical compositions from Bulk Chemical analyses, and to the discrepancies associated with quantitative X-ray diffractometry. The MINLITH algorithm is of particular value: (1) for providing preliminary estimates of mineralogical composition, prior to precise modal analysis; (2) for identifying systematic compositional variation within suites of samples; (3) in generalised sample classification; (4) in the sedimentological interpretation of metasedimentary rocks.
D.l. Evans - One of the best experts on this subject based on the ideXlab platform.
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Microwave dielectric properties of dry rocks
IEEE Transactions on Geoscience and Remote Sensing, 1990Co-Authors: F.t. Ulaby, T.h. Bengal, M.c. Dobson, J.r. East, J.b. Garvin, D.l. EvansAbstract:The use of a combination of several measurement techniques to investigate the dielectric properties of 80 rock samples in the microwave region is discussed. The real part of the relative dielectric constant epsilon ' was measured in 0.1-GHz steps from 0.5 to 18 GHz, and the imaginary part epsilon " was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the Bulk density was measured for all the samples and the Bulk Chemical composition was determined for 56 of the samples. This study shows that epsilon ' is frequency-independent over the range of 0.5-18 GHz for all rock samples, and that the Bulk density rho /sub b/ accounts for about 50% of the observed variance of epsilon '. For silicate rocks, as much as 78% of the observed variance of epsilon ' may be explained by the combination of density and the fractional contents of various oxides determined by X-ray fluorescence when the silicates are subgrouped by genesis. In contrast, the loss factor epsilon " decrease with increasing frequency for most rock samples. It was not possible to establish statistically significant relationships between epsilon " and the measured density of the rock samples. However, in the case of silicate rocks, 60% of the variance in epsilon " generally can be explained by the Bulk Chemical composition when the silicates are subgrouped by genesis.
