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Neocrystallization of clay minerals in the Alhama de Murcia Fault (southeast Spain): implications for fault mechanics

Abad, I; Jimenez-Millan, J; Sanchez-Roa, C; Nieto, F; Velilla, N; (2019) Neocrystallization of clay minerals in the Alhama de Murcia Fault (southeast Spain): implications for fault mechanics. Clay Minerals , 54 (1) pp. 1-13. 10.1180/clm.2019.2. Green open access

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Abstract

Two preferred textures were observed in the Alhama de Murcia Fault rocks: (a) foliated bands (>100 µm thick) rich in well-crystallized dioctahedral micas, quartz, hematite and dolomite; and (b) ultrafine-grained bands (<100 µm thick) made of patches composed of small mica crystals (<15 µm) and dispersed Fe-oxides. In both textures, kaolinite forms intergrowths or patches of randomly oriented crystals filling gaps or opening layers of presumably inherited detrital mica crystals, which is interpreted as an epitaxial growth from fluids. The Na/K ratio of mica crystals in the thin ultrafine-grained bands shows a wider range than the micas from the foliated bands including muscovitic, intermediate Na/K and paragonitic compositions. The absence of the 0.98 nm intermediate peak in the diffractograms indicates that the small micas are submicroscopically paragonite and phengite intergrowths. The d001 values of the K-dioctahedral micas in the <2 µm and whole fractions are clearly different from each other. The d001 values of micas of the <2 µm fraction are larger, indicating a higher K and lower Na content in the small micas. Their composition corresponds to lower temperatures, suggesting their growth during a genetic episode in the fault. The textural relationships indicate a late growth of kaolinite, probably due to the fluid–rock interaction along fault planes and fractures. The neoformed clay minerals might alter the stability of the fault plane. The absence of expandable clay minerals and the relatively high frictional strength of kaolinite under wet conditions might explain the observed velocity-neutral behaviour of this gouge and earthquake propagation towards the surface.

Type: Article
Title: Neocrystallization of clay minerals in the Alhama de Murcia Fault (southeast Spain): implications for fault mechanics
Location: Granada, SPAIN
Open access status: An open access version is available from UCL Discovery
DOI: 10.1180/clm.2019.2
Publisher version: http://dx.doi.org/10.1180/clm.2019.2
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10093008
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