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Polyphase deformation of diapiric areas in models and in the eastern Prebetics (Spain)

¹ Grup de Geodinàmica i Anàlisi de Conques, Facultat de Geologia, Departament de Geodinàmica i Geofísica, Universitat de Barcelona, 08028 Barcelona, Spain; eduard{at}natura.geo.ub.es
² Grup de Geodinàmica i Anàlisi de Conques, Departament de Geodinàmica i Geofísica, Universitat de Barcelona, 08028 Barcelona, Spain; present address: Cal Rovireta, Pacs del Penedès, 08729 Barcelona, Spain; sansicia{at}eic.ictnet.es
³ Hans Ramberg Tectonic Laboratory, Department of Earth Sciences, Uppsala University, Villavägen 16, S-75236 Uppsala, Sweden; Hemin.Koyi{at}geo.uu.se

Eduard Roca is a professor of structural geology at the Universitat de Barcelona. He received his Ph.D. in 1992 from the Universitat de Barcelona, and then he worked for the Institut Français du Pétrole in Paris for one year until he joined the Universitat de Barcelona. His research interests include the structure of thrusts and fold belts, salt tectonics, tectonosedimentary relationships, and the tectonics of the western Mediterranean.Maura Sans received her M.Sc. degree in 1992 and her Ph.D. in 2000 from the Universitat de Barcelona. She worked on salt tectonics from 1990 to 2001 in extensional settings in the western Mediterranean and in contractional settings in the Pyrenees in collaboration with the potash mining companies in the Pyrenean foreland. Since 2001, she has been working as an independent consultant.

Hemin Koyi is a professor in tectonics and geodynamics at the Department of Earth Sciences in Uppsala. He is a native of Kurdistan (Iraq), where he received his B.Sc. degree. He received his M.Sc. degree and his Ph.D. in tectonics and geodynamics from Uppsala University (Sweden). He was a research fellow at the Bureau of Economic Geology (Austin, Texas) between 1991 and 1993. His main research interest is the modeling of geologic processes with special emphasis on salt and thrust tectonics. He is a member of the editorial board of the Journal of Petroleum Geology and the consulting editor's board of the Geological Quarterly.

Fingerlike bodies of evaporite rocks have been observed in many regions affected by multiple tectonic phases, such as the Atlas, the Pyrenees, or the Zagros Mountains, where they have been interpreted as fault-plane diapiric injections or collapse-related salt welds. In this article, we suggest a new interpretation of these structures as squeezed diapirs based on detailed structural and sedimentological field data of the Bicorb–Quesa diapir (eastern Prebetics) and offer five analog models, which simulate the polyphase deformation of the eastern Prebetics. In this area, diapirs formed from the Oligocene to Langhian during an extensional phase related to the opening of the Valencia Trough. These diapirs were later affected by a Serravallian contractional phase, which inverted the preexisting grabens and created new folds and thrusts. The preexisting diapirs were necked and/or squeezed, forming secondary welds with a fingerlike geometry that isolated the diapir bulbs from their source layer. Extrusion of diapiric material was also accelerated during this phase, but no new diapirs formed. Finally, the area was again affected by an extensional phase during the Tortonian, which reactivated the normal faults and created a new set of diapirs. The new diapirs formed where the overburden was thinner, that is, at the toe of the major reactivated faults. Commonly, these faults coincide with the bounding faults of the major grabens formed during the first extensional phase, and therefore, the new diapirs grow close to the location of the squeezed diapirs. The models also show that the faults created during the initial extension prevailed as the main focus for deformation during the polyphase history. Deformation in the overburden and the viscous layer was mainly accommodated along the major grabens formed during the first extensional stage. During shortening, the initial major grabens deformed as complex anticlines, and during the subsequent extensional phase, most deformation occurred by the collapse of these anticlines along preexisting faults, fault welds, and the flank of the squeezed diapirs. The source layer is compartmentalized, accumulating and withdrawing material in the same locations (the initial grabens and horst). As a result, the source layer is easily depleted beneath the initial horst, forming primary welds.