The Pan-African high-K calc-alkaline peraluminous Elat granite from southern Israel: geology, geochemistry and petrogenesis
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Petrogenesis
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Abstract The studied granitic bodies belong to the south Eastern Desert of Egypt. They extend in a NNW–SSE trend along the same strike of the Nugrus weakness zone by which they are structurally controlled. These rocks are composed of biotite and biotite‐muscovite monzogranites to syenogranites. Geochemically, a higher abundance of Ba and Rb in biotite granites with a relatively low abundance in biotite‐muscovite granites as well as the diversity of Th, U, Nb, Ta, Zr, and REE reflects their origin from different sources and geodynamic settings. The biotite granites are predominantly metaluminous to low peraluminous whereas the biotite‐muscovite granites have a peraluminous nature. Potassium enrichment at the expense of calcium in these rocks reflects a derivation from crustal sources by partial melting in the presence of a volatile system. Radiometric investigation showed high abundances of U (up to 38 ppm) and Th (up to 26 ppm) in biotite‐muscovite granites relative to biotite granites (up to 5 ppm U and 18 ppm Th). Radioactive anomalies furthermore have been recorded in parts of biotite‐muscovite granites that were affected by the faults (up to 116 ppm eU and 97 ppm eTh). Consequently, biotite‐muscovite granites form a potentially fertile source for uranium mineralization.
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An intergrowth of muscovite and biotite from Mitchell Creek Mine, Upson County, Georgia, was studied with a high resolution transmission electron microscope. Atomic arrangements of the interface between muscovite and biotite have been derived, revealing far more complexity for the interface structure than that proposed previously based on optical and X-ray analysis (Gresens and Stensrud, 1971). It was found that the muscovite has an almost perfectly ordered 2M 1 structure, while the biotite is highly disordered. Despite such disorder in biotite, both octahedral layers and K ion interlayers of the two minerals are connected perfectly at the interface, while about 60% of the tetrahedral sheets are discontinued across the interface. Occasional occurrences of coherent intergrowths of chlorite-like structure in biotite were recognized in the vicinity of the interface.--Journal abstract.
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Based on a compilation and comprehensive analysis of recent published geochronological and geochemical data of the Early Yanshanian(Jurassic)granites in the Nanling area,SE China,it is pointed out that there exit at least two genetic types for the biotite granites,which are mostly exposed in the Nanling area,i.e.S-and(Caledonian)I-type in the sense of Pitcher(1982,1997);meanwhile,there some biotite belong to the transitional granite between I-and S-type.However,there is not petrogenetic relation between the two-mica and muscovite-bearing leucogranites and the biotite in the Nanling area.The two-mica and muscovite-bearing leucogranites are not the ends of biotite granites,but the products of crustal melting.Therefore,the two-mica and muscovite-bearing leucogranites are not the fractionated I-type granites as argued by Li Xianhua and co-workers(2007).
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Radiogenic nuclide
Isotopes of argon
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Isotopes of argon
Closure temperature
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Selected analyses from the Moine of the northwestern Highlands of Scotland have been considered in relation to the recently questioned (Weiss, 1955, p. 225-236) interpretation of non-coaxial girdles of quartz and mica having resulted from two distinct movements and with respect to the relative ease of reorientation of muscovite, biotite, and quartz. It is concluded that quartz can acquire a pronounced preferred orientation in response to stress conditions which fail to modify or only incompletely modify a pre-existing mica fabric; that quartz acquires a new preferred orientation more rapidly than biotite, and biotite more rapidly than muscovite.
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