Author： Ruiz Cruz María Dolores Novák Jirí K.
Publisher： E. Schweizerbart'sche Verlagsbuchhandlung
ISSN： 0935-1221
Source： European Journal of Mineralogy, Vol.15, Iss.1, 2003-02, pp. : 67-80
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Abstract
Low-grade metamorphic mineral associations present in mafic dikes from the Maláguide Complex were examined by X-ray diffraction (XRD) analysis, electron microprobe analysis (EMPA) and transmission-analytical electron microscopy (TEM/AEM). The low-grade phyllosilicates occur both as pseudomorphs after pyroxene and as matrix phases of the rock. The metamorphic phyllosilicate assemblage is formed either by chlorite + muscovite or by the association chlorite + randomly ordered chlorite/vermiculite mixed-layers + 1:1 regular chlorite/vermiculite mixed-layers + vermiculite (or Na-biotite). Chemical changes observed from chlorite to vermiculitic phases include: 1) increase of the Si/Al ratio; 2) decrease of Mg+Fe; and 3) presence of variable amounts of Ca+alkali. Later alteration of the second assemblage originates Al-smectite, which forms from chlorite-, mixed-layers- and low-charge biotite (vermiculite) packets. Excluding the alteration products, the mineral associations observed in dikes are similar, as studied by XRD, to those observed in metaclastites from this Complex, suggesting a common metamorphic event. Nevertheless, both EMPA and TEM/AEM analyses reveal chemical differences, which are probably related to differences in bulk-chemistry between metaclastites and dikes.
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