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Late Orogenic Strike-Slip Faulting and Escape Tectonics in Frontal

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Late Orogenic Strike-Slip Faulting and Escape Tectonics in Frontal Late orogenic strike-slip faulting AUTHOR Frank J. Picha ϳ International Petroleum and escape tectonics in frontal Consultant, 650 New Haven Court, Walnut Creek, California, 94598; [email protected] Dinarides-Hellenides, Croatia, Frank J. Picha received his M.S. degree (1955) and Ph.D. (1963) in geology from Charles Yugoslavia, Albania, University in Prague and a postdoctoral fellowship at the University of Wisconsin and Greece (1969–1970). From 1955 to 1989 he worked for the Geological Survey of Czechoslovakia, Frank J. Picha and in 1971–1976 he taught at Kuwait University in Kuwait. In 1980 he joined Gulf Oil and, in 1985, Chevron, from which he retired in 1999. Presently he works as a consultant. His assignments included regional ABSTRACT geology and exploration in Europe, the Middle The frontal zone of the Dinarides and its foreland are characterized East, North America, and the former Soviet by the presence of major late orogenic northwest-southeast faults Union. He was an AAPG Distinguished trending parallel to and locally dissecting the leading edge of the Lecturer in 1989–1990 and 1999–2000. thin-skinned thrust belt. On the basis of their geometry and regional distribution, these structures are interpreted as right-lateral strike- ACKNOWLEDGEMENTS slip faults and are related to the formation of en echelon compres- sional structures in the Split-Dubrovnik area of the central Adriatic This article is mainly based on the results of region and to the opening of the post-Messinian pull-apart Albanian my work on a project performed by Chevron foredeep (South Adriatic Basin) in the Pliocene–Holocene. These in the Adriatic region. The permission to pub- strike-slip faults represent the last stage of the mountain-building lish some results is gratefully acknowledged. I am also indebted to D. Drechsler of Naftaplyn process in the Pliocene and Holocene, when the forelandward prop- Zagreb for providing literature on the Croatian agation of the Dinaric thrust belt was inhibited by stacking of thrust structural geology. The quality of the article sheets and by overall thickening of the colliding continental crust. significantly benefited from critical reviews by In that respect, the Dinaric side of the Apulia (Adria) differs from J. R. Underhill and P. K. Webb. the Apenninic side, where the thin-skinned thrusting progressed normally toward the foreland until the Pliocene. On a regional scale, these northwest-southeast–trending strike- slip faults in the frontal Dinarides and their apparent continuation to the Hellenides of western Greece, as well as the dextral Vardar fault system, indicate the existence of escape tectonics in the Di- naric-Hellenic region. During the last stage of orogeny, the strike- slip faults provided a means of tectonic transport from the collision zone of Apulia with Europe toward the subduction zone of the Hellenic Trench. In southern Greece, the southeastward-moving Dinaric-Hellenic blocks apparently interfered with the westward- moving Anatolian plate and deflected it southwestward. The Albanian foredeep, in terms of tectonic setting, resembles the pull-apart Vienna basin, which formed within the attenuated southwest-northeast–trending transfer zone of the West Carpathi- ans during the last stages of the Alpine orogeny. Copyright ᭧2002. The American Association of Petroleum Geologists. All rights reserved. Manuscript received May 18, 2000;revised manuscript received March 18, 2002;final acceptance April 25, 2002. AAPG Bulletin, v. 86, no. 9 (September 2002), pp. 1659–1671 1659 Downloaded from https://pubs.geoscienceworld.org/aapgbull/article-pdf/86/9/1659/3362135/1659.pdf?casa_token=Tbfnl51AS5EAAAAA:sT46kZhNKw-Lsgsru-EGg-dsSb8_5hYOBeib28iQ61z5pvYNJS7KuMVFaR-uwp7DiSDvsorE by California Geological Survey, 19774 on 26 November 2019 The late orogenic strike-slip faulting may have tial of the Dinaric-Hellenic side of the peri-Adriatic breached seals and thus negatively affected the hydro- region. carbon potential of the Dinaric-Hellenic side of the peri-Adriatic region, as contrasted with that of the more prolific Apenninic side, which was not signifi- REGIONAL SETTING cantly disrupted by the late orogenic strike-slip faulting. The Dinaric thrust belt is a part of the European Alpine system. It evolved from the Tethyan seaway and its continental margins during the collision of the Euro- INTRODUCTION pean plate with Apulia (Adria) in the Late Cretaceous– Neogene (Figure 1). The wedge-shaped Dinaric belt, The complex structures of the frontal zone of the Di- consisting of numerous thrust sheets and imbricates, is naric-Hellenic belt and its foreland in the Adriatic re- thrust over the eastern side of the Apulian plate, gion are conventionally interpreted as being formed whereas the western side of the Apulian plate is solely by foreland-directed thrusting (e.g., Robertson bounded by the Apenninic thrust belt. To the north, and Dixon, 1984; Dragasevic, 1987; Brooks et al., the Apulian plate is enclosed by nappes of the 1988; Underhill, 1989; Tari Kovacic and Mrinjek, Southern Alps and the Insubric line, a major transpres- 1994). This article presents a nonconventional struc- sive fault system of Late Cretaceous–Miocene age tural interpretation of these structures as a combina- (Doglioni and Bosellini, 1987). The Apulian plate thus tion of older (Paleogene–Miocene) thrusting and represents a foreland for all three thrust belts. younger (Pliocene–Holocene) orogen-parallel strike- The Dinarides and Apennines have similar depo- slip faulting. Genetically associated with the late oro- sitional histories, beginning in the Late Permian–Early genic strike-slip faulting are some compressional and Triassic with continental rifting and deposition of sili- extensional structures in the Adriatic region, as well as ciclastic sediments followed by a restricted marine en- the post-Messinian pull-apart Albanian foredeep. The vironment of evaporites and local organic-rich lagoonal concept is based on the interpretation of numerous mudstones (D’Argenio et al., 1971; Radoicic, 1987). seismic and well data available to me by Chevron dur- By the Late Triassic, the passive margins of the Teth- ing exploration for hydrocarbons in the southern Adri- yan seaway were fully established in the peri-Adriatic atic region in the 1980s, as well as on an observation region. They were characterized by the development that the oblique set of en echelon compressional struc- of carbonate platforms and intervening pelagic carbon- tures in the Split-Dubrovnik area may be better ex- ate basins (examples given in Figure 2). Additional rift- plained by strike-slip faulting than by normal thrusting ing in the Early Jurassic initiated breaking of wide- and back thrusting. spread carbonate platforms and extension of the Following my work in the Apennines and other deep-water basinal environment (Zappaterra, 1994). parts of the European Alpine system (e.g., Picha, The passive continental margins lasted in the peri- 1996), the concept of orogen-parallel strike-slip fault- Adriatic region until the Late Cretaceous, when sub- ing in the Dinarides-Hellenides has been further de- duction began closing the Tethyan ocean, and the Di- fined and integrated into the geology of a broader re- naric and Apenninic thrust belts and foreland basins gion. The late orogenic strike-slip faults of the frontal evolved gradually along the newly formed active mar- Dinarides-Hellenides and their foreland, as well as the gins. In the external Dinarides and Apennines, how- transcurrent Vardar fault zone in the Dinaric hinter- ever, carbonate sedimentation prevailed until the mid- land and some northwest-southeast–trending faults in dle Eocene (late Lutetian) (Tari Kovacic, 1997), when the Adriatic foreland, are considered to be evidence for increasing orogenic activity led to its termination and the presence of escape tectonics on the eastern side of replacement by siliciclastics. Synorogenic flysch-type the Adriatic region since the Pliocene. foredeeps evolved in the Paleogene–middle Miocene, The tectonic setting of the late orogenic Albanian followed by late orogenic molasse-type foredeeps in foredeep is compared with the tectonic setting of the the middle Miocene–Holocene (Figure 2). During the pull-apart Vienna basin situated in the southwest- Neogene orogenic phases, the various depositional do- northeast–trending transfer zone of the West Carpa- mains of external Dinarides-Hellenides and Apen- thians. Attention is also paid to the impact of the late nines, including Mesozoic carbonate platforms and ba- orogenic strike-slip faulting on the hydrocarbon poten- sins and Cenozoic foreland basins, were detached, 1660 Adriatic Region Late Orogenic Strike-Slip Faulting and Escape Tectonics Downloaded from https://pubs.geoscienceworld.org/aapgbull/article-pdf/86/9/1659/3362135/1659.pdf?casa_token=Tbfnl51AS5EAAAAA:sT46kZhNKw-Lsgsru-EGg-dsSb8_5hYOBeib28iQ61z5pvYNJS7KuMVFaR-uwp7DiSDvsorE by California Geological Survey, 19774 on 26 November 2019 Figure 1. Schematic map of the Alpine system of Europe. The heavy lines represent the late orogenic strike-slip faults related to the escape tectonics in the Adriatic region. The large arrows indicate directions of escape of the Anatolian plate along the North Anatolian fault (NAF) toward the west-southwest and of the Dinaric-Hellenic block along the Adriatic strike-slip fault system (AF) Insubric ס Gargano fault; IL ס Eptahori fault; G ס Dugi Otok; E ס Albanian foredeep; DO ס .toward the southeast. ALB. F Theotokos ס salt structures; T ס Ravni Kotari
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