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Natural Partial Melting of Spinel Lherzolite 总被引：3，自引：1，他引：3
Spinel lherzolite nodules from Dreiser Weiher, Germany, containsmall glass bearing microcrystalline blebs that were formedfrom a partial melt. The partial melting occurred during contactanatexis of lherzolite surrounding a deep seated magma chamberin the mantle. The blebs formed from melt drops that were isolatedfrom each other and not from an intergranular film. The resultssuggest that primary magma originates as small melt drops ina lherzolitic matrix. This evidence indicates a limited mobilityof traces of partial melt in the mantle, and suggests that theaccumulation of primary magmas formed at very small degreesof partial melting is unlikely. 相似文献
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The alkalic suite of Jan Mayen is of the trachybasaltic typewith a K2O/Na2O ratio of about 1·64. The suite includesall intermediate types of lavas between ankaramite and trachyte,with ankaramites being particularly prevalent. The major andtrace element trends are well defined. A new method allows distinctionbetween fractionated and accumulative ankaramites, and it isshown that the most primitive ankaramite contains 13–14per cent MgO. Experimentally determined P-T phase relationsof this composition suggest that it might be a primary composition,formed by partial melting of a spinel lherzolitic source at19·5kb and 1415°C. The fractionation from ankaramiteto trachybasalt occurred at low pressure, and was controlledby delayed gravitative settling of phenocrysts, while the fractionationfrom trachybasalt to trachyte is explained by crystallizationon the walls of the magma chambers. 相似文献
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The statistical probability of a connected network of randomlyoriented melt veins in partially molten mantle suggests thatthe critical melting model can account for observed (226Ra/230Th)isotope activity ratios. Similarly, if the reactive percolationmodel also includes such veins, then this modified model isalso relevant. Critical melting models for the isotope activityratios imply that material exchange between the melt and theresiduum must be negligible. Hence, any diffusive exchange betweenthe melt in the veins and the residuum must be limited. Thiscondition suggests that the veins form a rooted system whereseveral smaller veins supply larger veins. Further, the veinsshould be situated at least some decimetres apart, and the permeabilityconstant of the residuum should be larger than 相似文献
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