Original paper
Metamorphic chlorite and "vermiculitic" phases in mafic dikes from the Malaguide Complex (Betic Cordillera, Spain)
Ruiz Cruz, Marí a Dolores; Nová k, Jirí K.
European Journal of Mineralogy Volume 15 Number 1 (2003), p. 67 - 80
published: Feb 18, 2003
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.
Keywords
betic cordillera • chlorite • low-grade metamorphism • mixed-layer minerals • vermiculite • tem/aem