Tectonics, structural analysis and geodynamic evolution of the Maghrebian Flysch Basin and Ligurian Accretionary Complex Units: Examples in the Western Mediterranean Area

• Main Author: Tramparulo, Francesco D'Assisi
• Format: Text
• Language: unknown
• Published: Università degli Studi di Napoli Federico II 2015
• Subjects: Diamante; Dorsale; Rif; Terranova
• Online Access: https://dx.doi.org/10.6092/unina/fedoa/10187; http://www.fedoa.unina.it/10187

This work provides a structural study on some successions of the Ligurian Accretionary Complex (LAC; southern Italy), Maghrebian Flysch Basin (MFB; Morocco) and External Dorsale Calcaire (Morocco). The LAC Units, cropping out in the southern Apennines include the sedimenary deep basin successions of Nord Calabrese, Parasicilide and Sicilide. Presently they are the highest tectonic units of the South Apennine fold and thrust belt. They are all characterized by a polyphasic and progressive deformation related to the Early Miocene inclusion in the tectonic accretionary wedge, by means of a frontal accretion mechanism, with a mean E/SE tectonic vergence. A subsequent deformation stage, associated to the eastward migration of the thrust front, affecting also the Middle-Upper Miocene unconformable wedge-top basin deposits, was characterized by a mean E/NE tectonic transport. In this orogenic phase the Apennine thrust sheet pile, formed by LAC and Apennine Platform Units, tectonically covered the successions located in the westernmost sector of the Lagonegro-Molise Basin. Finally a Pliocene-Middle Pleistocene regional fold set deformed the whole orogenic prism, comprised the LAC Units as consequence of a thick-skinned tectonics expressed by means of deeply rooted thrusts in the buried Apulian Platform carbonates. The metamorphic units of LAC, analyzed in this study, are the Frido and Diamante-Terranova Units, cropping out at Calabria-Basilicata boundary and northern Calabria, respectively. Both units are characterized by a HP/LT metamorphism reaching pressures of ca. 1.4/1.2 and 1.0 GPa and temperatures of 350 360 and 380 °C, respectively. The HP/LT parageneses include the Fe-carpholite, chlorite and phengite for the Frido and glaucophane, lawsonite, epidote and chlorite for the Diamante-Terranova Unit. The tectonic exhumation was recorded by Ca amphiboles. The P-T-paths, presented below, of both units indicate a cool and rapid exhumation. This is testified also by the preservation of HP/LT mineral parageneses and by non-isothermal exhumation such as marked in the P-T-paths of the Frido(this work) and Diamante-Terranova (Liberi and Piluso, 2009) Units. These units were subducted in the latest Oligocene and Early Eocene, respectively, with their complete exhumation in the middle Tortonian. The comparable geodynamic evolution of the LAC Units suggests an origin of all successions in a common oceanic domain (Ligurian Ocean) characterized by a western sector floored by oceanic crust (Diamante-Terranova domain), a central sector represented by an Ocean Continent Transition (Frido and Nord-Calabrese domain) and an eastern area formed by thinned continental crust (Parasicilide and Sicilide domain). A further aim of this study is the reconstruction of the tectonic evolution of some successions of the Maghrebian Flysch Basin (MFB) domain (Predorsalian and Massylian Units) and the External Dorsale Calcaire in a key area (Chefchaouen) of the Rif chain in the northern Morocco. Maghrebian Flysch Basin successions show a comparable stratigraphy with the sedimentary LAC successions, suggesting paleogeographic continuity between LAC, located to E/NE, and the MFB to the W. The Triassic-Lower Miocene External Dorsale Calcaire succession overthrust the Predorsalian Unit through a regional thrust fault well-exposed in Chefchaouen area. The kinematic analysis of this structure and all minor structures in the footwall, indicate a SW-tectonic vergence. The Predorsalian unit in turn overthrust the Massylian succession characterized by a similar progressive deformation. The whole tectonic pile was subsequentely deformed by thrust and folds verging to NW. Like the sedimentary LAC units, the MFB Units were deformed by frontal accretion in the Burdigalian-Langhian time. The External Dorsale Calcaire provides a good example of Inversion Tectonics. The Liassic succession (cherty limestones and conglomerates) recorded the extension related to the Jurassic rifting of the Neotethys Domain as normal faulting and veining.The subsequent inclusion of these rocks in the orogenic wedge, which mainly occurred in the Miocene time, deformed the most of pre-orogenic structures in a passive manner, with only few cases of reverse reactivation; whereas, frequently, pre-orogenic normal fault planes show only an indentation of hanging-wall and footwall (buttressing effect). The orogenic deformation includes two main stages; the first tectonic pulse, which occurred during the Burdigalian-Langhian interval, was characterized by a NE-SW shortening and recorded by folds, thrust and back-thrust faults. During this stage the carbonates of the External Dorsale Calcaire tectonically covered the Predorsalian succession, producing, in the thrust front, a SW verging regional fold. The second orogenic deformation, consisting of a NW-SE shortening, was expressed by thrust faults and related folds both verging to NW and SE, which probably occurred in the Late Miocene-Pliocene time.