21 research outputs found
Outgassing history of Venus and the absence of water on Venus
Similarities in the size and mean density of Earth and Venus encourage the use of Earth-analogue models for the evolution of Venus. However, the amount of water in the present Venus atmosphere is miniscule compared to Earth's oceans. The 'missing' water is thus one of the most significant problems related to the origin and evolution of Venus. Other researchers proposed that Venus accreted with less water, but this was challenged. The high D/H ratio in Venus' atmosphere is consistent with an earlier water mass more than 100 times higher than at present conditions and is often cited to support a 'wet' Venus, but this amounts to only 0.01 to 0.1 percent of the water in terrestrial oceans and the high D/H ratio on Venus could easily reflect cometary injection. Nevertheless, many authors begin with the premise that Venus once had an oceanlike water mass on its surface, and investigate the many possible mechanisms that might account for its loss. In this paper we propose that Venus degassed to lower degree than the Earth and never had an oceanlike surface water mass
Geochemical processes in the earth's mantle and the nature of crust-mantle interactions : evidence from studies of Nd and Sr isotope ratios in mantle-derived igneous rocks and lherzolite nodules
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980.Microfiche copy available in Archives and Science.Bibliography: leaves 212-231.by Alan Zindler.Ph.D
Oxygen Isotope Variations in Recent Magnesian Lavas from Iceland’s Northern Neovolcanic Zone
Geochemical variations of Icelandic lavas reflect both differences
in the compositions and conditions and extents of melting
of their sources (e.g., Thirlwall, 1994) and magmatic differentiation
and crustal contamination (e.g., Gee et al., 1996).
Discriminating between these two processes is key to
constructing models of the composition and dynamics of the
Iceland plume. Recent efforts to do so have focused on relatively
magnesian lavas from the northern and western neovolcanic
zones; Theistareykir volcano has been of particular importance
for this work because of its abundance of magnesian lavas, the
absence of a well-developed central volcanic complex, and the
fact that it's lavas include the 'depleted' extreme to the array of
compositional variations in Icelandic lavas generally (e.g.,
Elliott et al., 1991). We report here a study of oxygen-isotope
variations in phenocrysts from recent Theistareykir lavas,
conducted to search for evidence for both crustal contamination
and oxygen isotope variations in the sub-Icelandic mantle
Fe-Al-rich tridymite-hercynite xenoliths with positive cerium anomalies: preserved lateritic paleosols and implications for Miocene climate
Abstract We report isotopic and chemical compositions of unusual tridymite -hercynite xenoliths in middle Miocene Niutoushan tholeiites from the southeast coastal area of China. These xenoliths are characterized by positive cerium (Ce) anomalies and extremely high Al 2 O 3 (32 -34 wt.%) and total iron oxide (20 -22%). . Their chemical and isotopic compositions suggest that these xenoliths represent preserved aluminous lateritic paleosols that are not genetically related to host tholeiites. These lateritic paleosols with strongly desilicated minerals were formed by intense chemical weathering under warm and humid tropical conditions (with annual average temperature of >19 jC and the annual rainfall of >165 cm) in SE China during the interval from 17 to 15 Ma. The formation age of the paleosols corresponds to a period characterized by slow uplift of the Himalayan -Tibetan Plateau region (and thus less consumption of CO 2 ) after 17 Ma, and eruptions of 17 -15 Ma Columbia River flood basalts, the Vogelsberg basalts, and eastern China basalts (and thus more input of CO 2 into the atmosphere). The tridymite -hercynite xenoliths in the Niutoushan basalts thus preserve evidence of extraordinary climatic greenhouse conditions in the middle Miocene that would otherwise have been lost by the erosion of paleosols.
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Electronic data publication in geochemistry
Many disciplines of geochemistry have no data reporting standards, and their use of metadata is inadequately developed. This presents problems to the quality of the published science, and it limits the utility of computers in data analysis and the exploitation of Information Technology (IT). We discuss problems of data and metadata publication, in particular for geochemistry, and offer solutions to these problems in the form of consistent data publication formats and a proposal for publication of metadata in geochemistry. Metadata are grouped according to types (location, sampling, characterization), and this grouping allows for the transfer of these formats to other Earth science disciplines. In a companion paper [Helly et al., 2003], we illustrate how these metadata groupings can be used in an IT context. Formats presented here are comprehensive and allow for modification and expansion. It is the hope of the authors that this paper initiates a constructive discussion of data formats and metadata in geochemistry. The most recent contributions to this discussion may be found at http:\\earthref.org\metadata\GERM\.Keywords: sample characterization, database, geochemistry, information technology, Metadata, cyberinfrastructur
Calibration of the 14C timescale over the past 30,000 years using mass spectrometric U–Th ages from Barbados corals
International audienc
234U/238U mass spectrometry of corals: How accurate is the UTh age of the last interglacial period?
International audienc
Comparison of one- and two-color ionization schemes for the analysis for osmium and rhenium isotopic ratios by sputter-induced resonance ionization mass spectrometry
Sputter-Induced resonance Ionization mass spectrometry Is a technique In which atoms sputtered from a sample are Ionized using a pulsed laser beam. To maximize sample utilization, a pulsed Ion beam Is used to atomize the sample so there is a high temporal and spatial overlap between the atom plume and laser beam. The frequency of the laser Is tuned to resonantly excite electrons In the atoms Into an excited state and then nonresonantly Into the continuum. A two-color scheme which uses a portion of the excimer pump laser to excite the Ionization step was Investigated as a method of Increasing the ionization signal. Ionization Intensity enhancements In many transitions In Re and Os were measured. Isotope ratio measurements of Re filaments showed more sample to sample variations due to varying conditions of the laser beams and a higher bias than corresponding analyses of loaded samples