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Dustin Trail Ilya N. Bindeman E. Bruce Watson Axel K. Schmitt 《Geochimica et cosmochimica acta》2009,73(23):7110-7126
We report the results of an experimental calibration of oxygen isotope fractionation between quartz and zircon. Data were collected from 700 to 1000 °C, 10–20 kbar, and in some experiments the oxygen fugacity was buffered at the fayalite–magnetite–quartz equilibrium. Oxygen isotope fractionation shows no clear dependence on oxygen fugacity or pressure. Unexpectedly, some high-temperature data (900–1000 °C) show evidence for disequilibrium oxygen isotope partitioning. This is based in part on ion microprobe data from these samples that indicate some high-temperature quartz grains may be isotopically zoned. Excluding data that probably represent non-equilibrium conditions, our preferred calibration for oxygen isotope fractionation between quartz and zircon can be described by: This relationship can be used to calculate fractionation factors between zircon and other minerals. In addition, results have been used to calculate WR/melt–zircon fractionations during magma differentiation. Modeling demonstrates that silicic magmas show relatively small changes in δ18O values during differentiation, though late-stage mafic residuals capable of zircon saturation contain elevated δ18O values. However, residuals also have larger predicted melt–zircon fractionations meaning zircons will not record enriched δ18O values generally attributed to a granitic protolith. These results agree with data from natural samples if the zircon fractionation factor presented here or from natural studies is applied. 相似文献
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Mineralogy and Petrology - Apatite is widely distributed in terrestrial and extraterrestrial environments and may therefore crystallize in relatively oxidized environments found here on Earth, and... 相似文献
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Dustin Trail E. Bruce Watson Nicholas D. Tailby 《Journal of the Geological Society of India》2013,81(5):605-636
Geologists investigate the evolution of the atmosphere, crust, and mantle through time by direct study of the rock record. However, the Hadean eon (>3.85 Ga) has been traditionally viewed as inaccessible due to the absence of preserved rocks. The discovery of >4.0 Ga detrital zircons from Western Australia in the 1980s — coupled with the development of new micro-analytical capabilities — made possible new avenues of early Earth research. The prevailing view that emerged is that the early Earth may have contained a stable hydrosphere, water-saturated or (near watersaturated) granitic magmas, and volcanic emanations dominated by neutral gas species (e.g., CO2, H2O, and SO2). The Hadean Earth may have been capable of supporting life ～200 Ma after accretion and perhaps earlier. Many of these models are formulated — or have been subsequently supported — by laboratory experiments of zircon. Important petrological variables such as temperature, pressure, oxygen fugacity, and component activities (e.g., SiO2/TiO2-activities) can be controlled. These experiments are fundamental for extrapolation to ‘deep time’ because they provide a means to understand primary chemistry preserved in ancient zircons. This review paper specifically focuses on zircon experimental studies (oxygen isotope fractionations, Ti-thermometry, and redox sensitive element incorporation into zircon), which have influenced our view of the very early Earth. 相似文献
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We report the first U-Th-Pb ion microprobe depth profiles of four Hadean zircons from the Jack Hills and Mount Narryer supracrustal belts of the Narryer Gneiss Complex (NGC), Western Australia. This ultra-high spatial resolution technique probes the age and origin of sub-micron features in individual crystals that can record episodes of zircon growth. Near-surface grain dates of 2700 Ma or older are coincident with post-depositional growth/modification. Some ages may coincide with documented pre-deposition metamorphic events for the NGC and igneous emplacement at ca. 3700 Ma. Separate events that do not correlate in time with known geologic episodes prior to the preserved rock record are also present on pre-4000 Ma zircons. We find evidence for a ∼3.9 Ga event, which is coterminous within age uncertainty with one or several large basin-forming impacts (e.g. Nectaris) on the Moon attributed to the late heavy bombardment of the inner solar system. 相似文献
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