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Age, Geochemistry and Petrogenesis of the Ultramafic Pipes in the Ivrea Zone, NW Italy 总被引：3，自引：0，他引：3
Pipe-like ultramafic bodies, hosting Ni–Cu–PGE sulphidedeposits, intrude the Main Gabbro and the roof metasedimentsof the Ivrea Zone, NW Italy. These bodies were emplaced at 287± 3 Ma and represent the last mantle-derived melts associatedwith an underplating event that largely drove the crustal evolutionof this area during the late Carboniferous ( 相似文献
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Residence of REE, Y, Th and U in Granites and Crustal Protoliths; Implications for the Chemistry of Crustal Melts 总被引：36，自引：8，他引：28
A systematic study with laser ablation—ICP-MS, scanningelectron microscopy and electron microprobe revealed that 70–95wt% of REE (except Eu), Y, Th and U in granite rocks and crustalprotoliths reside within REEYThU-rich accessories whose nature,composition and associations change with the rock aluminosity.The accessory assemblage of peraluminous granites, migmatitesand high-grade rocks is composed of monazite, xenotime (in low-Cavarieties), apatite, zircon, Thorthosilicate, uraninite andbetafite-pyrochlore. Metaluminous granites have allanite, sphene,apatite, zircon, monazite and Thorthosilicaie. Peralkaline graniteshave aeschinite, fergusonite, samarskite, bastnaesite, fluocerite,allanite, sphene, zircon, monazite, xenotime and Th-orthosilicate.Granulite-grade garnets are enriched in Nd and Sm by no lessthan one order of magnitude with respect to amphibolite-gradegarnets. Granulitegrade feldspars are also enriched in LREEwith respect to amphibolite-grade feldspars. Accessories causenon-Henrian behaviour of REE, Y, Th and U during melt—solidpartitioning. Because elevated fractions of monazite, xenotimeand zircon in common migmatites are included within major minerals,their behaviour during anatexis is controlled by that of theirhost. Settling curves calculated for a convecting magma showthat accessories are too small to settle appreciably, beingseparated from the melt as inclusions within larger minerals.Biotite has the greatest tendency to include accessories, therebyindirectly controlling the geochemistry of REE, Y, Th and U.We conclude that REE, Y, Th and U are unsuitable for petrogeneticalmodelling of granitoids through equilibrium-based trace-elementfractionation equations. KEY WORDS: accessory minerals; geochemical modelling; granitoids; REE, Y, Th, U 相似文献
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A method for modelling mass balance in partial melting and anatectic leucosome segregation 总被引：1，自引：0，他引：1
F. BEA 《Journal of Metamorphic Geology》1989,7(6):619-628
A method is proposed for adjusting the mass balance to characterize quantitatively the behaviour of minerals in anatexis. The method is based on an unconstrained simple mixing model that can be expressed as: where B , A 0, and A 1-n, are compositional vectors of segregate, source rock and source minerals, respectively. The most important concepts are: (1) degree of partial fusion: FMM= 1/a0; (2) mineral fractionation index: and (3) plagioclase differentiation index: . For a given mineral, the MFI values have the following meaning: (a) MFI <0: residual phase originated, at least partly, as a product of incongruent melting; (b) 0 > MFI <1: preferential retention in the residue; (c) MFI= 1: identical modal fraction in source and melt; (d) a0 > MFI > 1: preferential incorporation into the segregate, and (e) MFI > a0: external contribution to the anatectic system defined by a0 A 0. To test the method and illustrate its use, it was applied to two real problems of partial melting in the Peña Negra Anatectic Complex (Central Spain). The first is a very simple case of segregation of a diktyonitic neosome from an orthogneiss through partial melting located in vertical shear zones. This process is characterized by: (1) FMM= 0.51; (2) active incorporation of K-feldspar, plagioclase and biotite into the segregate; (3) disequilibrium melting of plagioclase; (4) residual behaviour of quartz and ilmenite. The second case concerns the formation of a cordierite-bearing granite from granodioritoid diatexites through an anatectic process, whose most salient characteristics are: (1) FMM= 0.45; (2) incongruent melting of biotite; (3) residual behaviour of plagioclase, which melted with a PDI of 1.22; (4) preferential incorporation of quartz into the segregate; (5) total extraction of K-feldspar from the residue. 相似文献
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