Triassic redbeds in the Malaguide Complex (Betic Cordillera — Spain): petrography, geochemistry and geodynamic implications

Sandstone petrography and mudstone mineralogy and geochemistry of Triassic mudstones and sandstones from continental redbeds of the Malaguide Complex (Betic Cordillera, southern Spain) provide useful information on provenance, palaeoclimate and geodynamics during the early stages of the Pangea break-up, and on their diagenetic evolution. The sandstones are quartzarenites to sub-litharenites, with minor lithic fragments and rare feldspars. The mudstone samples show a PAAS like elemental distribution. The samples likely record recycling processes from their metasedimentary basement rocks that significantly affected the weathering indices, and monitors cumulative effects, including a first cycle of weathering at the source rocks. Sandstone composition and chemical–mineralogical features of mudstones record a provenance derived from continental block and recycled orogen that were weathered under warm and episodically wet climate. Source areas were located towards the east of the present-day Malaguide outcrops, and were formed by fairly silicic rock types, made up mainly of Palaezoic metasedimentary rocks, similar to those of the Paleozoic underlying series, with subordinate contributions from magmatic–metamorphic sources, and a rare supply from mafic metavolcanic rocks. Clay-mineral distribution of mudstones is dominated by illite and illite/smectite mixed-layer that result from differences in provenance, weathering, and burial/temperature history. Illite crystallinity values, illitization of kaolinite, occurrence of typical authigenic minerals and apatite fission-track studies, coupled with a subsidence analysis of the whole Malaguide succession suggest burial depths of at least 4–6 km with temperatures of 140–160 °C, typical of the burial diagenetic stage, and confirm the Middle Miocene exhumation of the Betic Internal Domain tectonic stack topped by the Malaguide Complex.

This research has been carried out within the MIUR-COFIN Project 2001.04.5835 “Age and characteristics of the Verrucano-type deposits from the Northern Apennines to the Betic Cordilleras: consequences for the palaeogeographic and structural evolution of the central-western Mediterranean Alpine Chains” (support to V. Perrone), MIUR-ex60% Projects (Palaeogeographic and Palaeotectonic Evolution of the Circum-Mediterranean Orogenic Belts, 2001–2005; and Relationships between Tectonic Accretion, Volcanism and Clastic Sedimentation within the Circum-Mediterranean Orogenic Belts, 2006; support to S. Critelli), and the 2006–2008 MIUR-PRIN Project 2006.04.8397 “The Cenozoic clastic sedimentation within the circum-Mediterranean orogenic belts: implications for palaeogeographic and palaeotectonic evolution” (support to S. Critelli). Financial support from the Projects CGL2009-09249 and CGL2011-30153-CO2-02 (MCI, Spain) and from the RNM-208 and P08-RNM-03715 Research Groups of the Junta de Andalucia is also acknowledged.