Geology and Structural Evolution of the Southeastern Sorbas Basin, SE Spain

UoM administered thesis: Phd

  • Authors:
  • Lorenzo Valetti

Abstract

The continental collision between the Alborán domain and the Iberian passive margin gave rise to the Mesozoic to Neogene fold and thrust belt of the Betic Cordillera (southern Spain). The orogenic belt forms an arc-shaped arm which continues from north to south across the Straight of Gibraltar in the Rif Mountains of Morocco surrounding the western end of the Mediterranean known as the Alborán Sea. The Sorbas basin is part of a group of intramontane Miocene basins situated in the Internal Zone of the Cordillera, where the basement edifice formed by the stacking of metamorphic tectonic units underwent rapid exhumation and collapse during Late Oligocene – Early Miocene. The deformation that shaped the intramontane basins is closely related to the complex dynamics of the Cordillera's exhumation. This is thought to be driven by the westward motion of the Alborán basin subducting slab rollback and relative stretching of a wedge shaped area, containing the basins and bound by major strike slip faults such as the Alhama de Murcia, Palomares, and Carboneras fault zones, that continue via the Trans-Alborán Shear zone to the Moroccan Rif belt. Accommodation space for middle and upper Miocene sediments was created through ENE-WSW extensional faulting taking place at the same time as the uplift of basement massifs. The extensional Sorbas basin formed adjacent to the left-lateral Carboneras stretching fault, hence the evolution of both were anticipated to be closely linked. Most previous work on the Sorbas basin was focused on the fact that the presentday basin is clearly fault-bounded against uplifted basement rocks of the S. Alhamilla and S. Cabrera and studies have concentrated on the younger, uppermost Miocene (Messinian) portion of the sedimentary sequence. However, the geometry of the basin/basement boundary has not been previously studied in detail and the nature of the early fault interaction between the basement the lower portion of the sequence has only very recently been considered. Geological mapping and structural analysis of the boundary between basement and basin sequence in the southeastern Sorbas basin was therefore carried out, focusing on the detailed characterisation of the internal geometry of the entire basin-fill sequence. A detailed gravimetric survey and modelling of the Sorbas basin has also been completed with the aim of determining the shape of the basin floor, as well as constraining how the extension is accommodated by faulting. Fault rock friction experiments have been carried out in order to determine the behaviour of the major fault zones studied. As a result, the main period of extension and basin filling with 1.5+ km of rapidly deposited sediments has been found to extend from Serravallian to uppermost Tortonian, accompanied by uplift of the basement massifs, locally upending the lower basin sediments against them and distorting and rotating the basin-bounding faults. A markedly unconformable Messinian and Pliocene sequence buried the older basin fill, but these rocks have suffered little deformation. The main period of fault movement on the adjacent Carboneras fault has been found to mirror precisely the main period of deformation and stretching in the Sorbas basin, confirming the geometric and temporal link between these two elements of the Betic zone geodynamics. Throughout the Miocene basin evolution and continuing to the present day, the ENE-WSW extensional deformation has been complemented by the effects of the Iberia-Africa convergence, which is intimately related to the uplift of the basement blocks to form the present day basin-and-range topography.

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Original languageEnglish
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Award date31 Dec 2018