The Origin of the External Basins of the Betics, Southern Spain, and Their Use in Interpreting the Orogenic History

Stromberg, S. G. L (1994) The Origin of the External Basins of the Betics, Southern Spain, and Their Use in Interpreting the Orogenic History. PhD thesis, University of Glasgow.

Abstract

The Betic mountain chain of Southern Spain, together with the Rif Mountains of N.W. Africa forms the western-most extension of the Alpine mountain chain in Europe. The Orogen formed as a direct result of the interaction between the African and Iberian plates which took place from the late Cretaceous onwards. The origin of the Betics is far from understood and there are several conflicting hypotheses concerning the origin of the Orogen. There are two major external basins to the Betic Orogen in Southern Spain, the Guadalquivir Basin and the Gibraltar Arc Flysch, and both provide important insights into its tectonic history. The Guadalquivir Basin lies on the northern margin of the External Zone Tertiary fold-thrust belt of the Betic Orogen and south of the Palaeozoic Iberian Meseta. It can be subdivided into structurally distinct regions, an undeformed autochthonous basin which lies to the north of a deformed allochthonous basin. The origin of the Guadalquivir Basin (previously interpreted as being the foreland basin to the Orogen) is questioned. Structured sedimentological and provenance studies demonstrate that the Guadalquivir Basin is not a foreland basin because; 1. It formed as an integral part of the destruction of the Iberian passive margin during which time thin skinned thrusting generated a basin on the northern margin of the External Zones, 2. The fill and unconformities of this basin were controlled by eustasy rather by the tectonic incursion of an orogenic wedge being driven onto the Iberian Margin, 3. The basin did not form by the downward flexure of the lithosphere in response to an orogenic load. Therefore the basin cannot be considered to be a true foreland basin. The clastic sedimentation in the Guadalquivir Basin was controlled by the emergence of the External Zone thrust sheet, during the late Miocene, which was related to the thin skinned thrusting. During this time the recycling of material, that had originally been derived from the Palaeozoic Iberian Meseta. took place. A thrusting event at the the end of the Miocene/ early Pliocene led to the destruction of the Guadalquivir Basin which was subdivided into the allochthon and autochthon seen today. The Gibraltar Arc flysch nappes link the External Rif of North Africa to the External Zone of Southern Spain. The largest unit of the Gibraltar Arc is the Aljibe Flysch which can be subdivided into the Beneiza Flysch and Aljibe Arenites, which are Oligo-Miocene in age. The Beneiza Flysch is characterised by thin sandstones and siltstones that are interpreted to have been deposited by turbiditic currents. These pass rapidly upwards into the thick bedded and super-mature Aljibe Arenites, which are entirely dominated by water escape- structures. The contact between these two units marks a dramatic change in the depositional environment at the beginning of the Miocene. The Aljibe Flysch is interpreted as recording the development of a basin plain that became tectonically segregated at the beginning of the Miocene, at which time new and tectonically confined basins developed. Tectonic instabilities created elsewhere in the External Zone resulted in mobilisation of large amounts of sediment which was rapidly deposited in the newly created basins. The flysch units have subsequently been thrust westwards post-Lower Miocene during which time peridotites were emplaced into mid-crustal levels Consideration of the tectonic and sedimentary history of the Guadalquivir Basin and Gibraltar Arc Flysch provides an important insight into the tectonic history of the Betic Orogen. Data collected during the study of these basins, combined with important new published data from the Alboran Sea and Ronda Peridotites, has resulted in the rejection of the widely accepted 'extensional collapse' model and in the identification of strike-slip tectonism and transcurrent movements as the main mechanism for the building of the Betic Orogen. Miocene transcurrent movements in the Betic area resulted in the break up the Iberian passive margin, the emplacement of metamorphic terranes and in the formation of thrusts in the Gibraltar Arc through a complicated history of transtension and transpression in the region of the Alboran sea.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Brian Bluck
• Keywords: Geology, Plate tectonics
• Date of Award: 1994
• Depositing User: Enlighten Team
• Unique ID: glathesis:1994-75628
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 19:14
• Last Modified: 19 Nov 2019 19:14
• URI: https://theses.gla.ac.uk/id/eprint/75628