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Christine Floss Larry A. Taylor Prinya Promprated Douglas Rumble 《Meteoritics & planetary science》2005,40(3):343-360
Abstract— We have carried out a detailed petrographic, mineralogical, and trace element study of Northwest Africa (NWA) 011. This meteorite bears many similarities to the eucrites it was initially identified with, although oxygen isotopic compositions rule out a genetic relationship. Like many eucrites, NWA 011 crystallized from a source with approximately chondritic proportions of REE, although a slightly LREE‐enriched bulk composition with a small positive Eu anomaly, as well as highly fractionated Fe/Mg ratios and depleted Sc abundances (Korotchantseva et al. 2003), suggest that the NWA 011 source experienced some pyroxene and/or olivine fractionation. Thermal metamorphism resulted in homogenization of REE abundances within grains, but NWA 011 did not experience the intergrain REE redistribution seen in some highly metamorphosed eucrites. Despite a similarity in oxygen isotopic compositions, NWA 011 does not represent a basaltic partial melt from the acapulcoite/lodranite parent body. The material from which NWA 011 originated may have been like some CH or CB chondrites, members of the CR chondrite clan, which are all related through oxygen isotopic compositions. The NWA 011 parent body is probably of asteroidal origin, possibly the basaltic asteroid 1459 Magnya. 相似文献
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Prinya Promprated Lawrence A. Taylor Mahesh Anand Christine Floss Nikolai V. Sobolev Nikolai P. Pokhilenko 《Lithos》2004,77(1-4):69-81
Multiple inclusions of minerals in diamonds from the Snap Lake/King Lake kimberlites of the southeastern Slave craton in Canada have been analyzed for trace elements to elucidate the petrogenetic history of these inclusions, and of their host diamonds. As observed worldwide, the harzburgitic-garnet diamond inclusions (DIs) possess sinusoidal REE patterns that indicate an early depletion event, followed by metasomatism by LREE-enriched, HREE-depleted fluids. Furthermore, these fluids appear to contain appreciable concentrations of LILE and HFSE, based on the increasing abundances of these elements in the olivine inclusion that occurs at the outer portion of a diamond compared to that near the core. The compositions of these fluids are probably a mixture of hydrous-silicic melt, carbonatitic melt, and brine, similar to the compositions of micro-inclusions in diamonds reported by Navon et al. (2003). Comparison between the compositions of majoritic and normal harzburgitic garnets shows that the former are more depleted in terms of major/minor elements (higher Cr#) but significantly more enriched in the REE (up to 10×). This characteristic may indicate the higher susceptibility for metasomatic enrichment of previously more depleted garnets. Garnets of eclogitic paragenesis show strong LREE-depleted patterns, whereas the coexisting omphacite inclusion has relatively flat light- and middle-REE but depleted HREE. Whole-rock reconstruction from coexisting garnet and omphacite inclusions indicates that the protolith of these inclusions was probably the extrusive section of an oceanic crust, subducted beneath the Slave craton. 相似文献
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Abstract— We have analyzed the size, shape, composition, and spatial distribution of 6 kg of layered tektite fragments excavated from a 3 m × 3 m area near the town of Ban Huai Sai in northeast Thailand. Our analysis suggests that these fragments represent a single homogeneous mass that underwent fragmentation far in the past and has undergone little disturbance since its deposition. We have also studied the stratigraphic occurrence of layered tektites exposed in situ near the town of Ban Huai Om. Tektites were found along a disconformable paleo-erosion surface covered by recent aeolian sand, similar to other occurrences throughout Southeast Asia. This stratigraphic relationship provides little chronostratigraphic information and, thus, does not support a stratigraphic “age paradox” for the Australasian tektites. The present-day surface density of layered tektites in this area is 2 to 20 g/m2. 相似文献
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