Successive Extensional Tectonic Regimes during the Mesozoic as Evidenced by Neptunian Dikes in the Pontide Magmatic Arc, Northeast Turkey

Abstract

The eastern Pontide magmatic arc extends ~600 km in an E-W direction along the Black Sea coast and was disrupted by a series of fault systems trending NE-SW, NW-SE, E-W, and N-S. These fault systems are responsible for the formation of diachronous extensional basins, rift or pull-apart, in the northern, southern, and axial zones of the eastern Pontides during the Mesozoic. Successive extensional or transtensional tectonic regimes caused the abortive Liassic rift basins and the Albian and Campanian pull-apart basins with deep-spreading troughs in the southern and axial zones. Lias sic, Albian, and Campanian neptunian dikes, which indicate extensional tectonic regimes, crop out within the Paleozoic granites near Kale, Gümüshane, and the Malm-Lower Cretaceous platform carbonates in Amasya and Gümüshane. These neptunian dikes correspond to extensional cracks that are filled and overlain by the fossiliferous red pelagic limestones. Multidirectional Liassic nep tunian dikes are consistent with the general trend of the paleofaults (NE-SW, NW-SE, and E-W), and active dextral North Anatolian fault (NAF) and sinistral Northeast Anatolian fault (NEAF) systems. The Albian neptunian dikes in Amasya formed in the synthetic oblique left-lateral normal faults of the main fault zone that runs parallel to the active North Anatolian fault zone (NAFZ).Kinematic interpretation of the Liassic and Albian neptunian dikes suggests N-S extensional stress or northward movement of the Pontides along the conjugate fracture zones parallel to the NAFZ and NEAFZ. This northward movement of the Pontides in Liassic and Albian times requires left-lateral and right-lateral slips along the conjugate NAFZ and Northeast Anatolian fault zones (NEAFZ), respectively, in contrast to the recent active tectonics that have been accommodated by N-S compressional stress. On the other hand, mutual relationships between the neptunian dikes and the associated main fault zone of Campanian age extending in an E-W direction in the Kale area, Gümüshane suggest the existence of a main left-lateral transtensional wrench zone. This system might be accommodated by the counterclockwise convergence of the Turkish plate with the AfroArabian plate relative to the Eurasian plate, and the southward oblique subduction of Paleotethys beneath the eastern Pontide magmatic arc during the Mesozoic.

Arc magmatism as a window to plate kinematics and subduction polarity: Example from the eastern Pontides belt, NE Turkey

“…This assemblage constitutes a thinning and fining upward sequence that accumulated above the basement rocks, with the neptunian dikes exposed around the Amasya city center. The dykes in the platform carbonate rocks occur in vertical crack zones that are filled and overlain by Albian red pelagic limestones of the m elange sequence (Bektas et al, 2001;Eyuboglu et al, 2006;Eyuboglu et al, 2007;Fig. 2C).…”

Determination of Tectonic and Crustal Structure of the Eastern Pontide Orogenic Belt (NE Turkey) Using Gravity and Magnetic Data

“…The geologic evolution of the Eastern Pontides essentially depends on the left-lateral movement of the Arabian-African plates with respect to the Eurasian Plate and the opening of the Atlantic Ocean (MASSON and MILES, 1986). According to DEWEY et al (1973), BEKTAS (1987, 1990) and EYUBOGLU et al (2007, the Eastern Pontide magmatic arc evolved as the active northern margin of Gondwana, from the Paleozoic to the Cenozoic, and the ophiolitic belts are remnants of backarc basins (DEWEY et al, 1973) that formed along the southerly oblique subduction zone of Paleotethys or of the pullapart basins with deep-spreading troughs of Albian and Campanian age BEKTAS et al, 2001). Paleomagnetic studies (VAN DER VOO, 1968;LAUER, 1981;SARIBUDAK, 1989;CHANNELL et al, 1996) are fairly consistent and suggest that the Eastern Pontides were situated 23°north of the equator, south of Eurasia during the Cretaceous.…”

Platform–slope transition during rifting: The mid-Cretaceous succession of the Amasya Region (Northern Anatolia), Turkey

“…5C,D), calciturbidites, red pelagic foraminiferal limestone and radiolarite (Aptian-Cenomanian pelagic carbonates of Rojay and Altiner, 1998). The thickness of this formation ranges from 10 to 500 m. The monogenic limestone breccias accumulated as fault scarp breccias by the break-up of the carbonate platform during the mid-Cretaceous (Bektas et al, 2001). The Upper Cretaceous Lokman Formation (Alp, 1972) consists of reefal limestone (Steuber et al, 1998) and volcanogenic turbidite (Campanian-Maastrichtian forarc sequences of Rojay and Altiner, 1998;Koçyigit et al, 1991).…”

“…They formed during the break-up of the carbonate platform under a transtensional tectonic regime and in mid-Cretaceous times the deep-marine pelagic facies sediments were deposited on them. According to Bektas et al (2001), parallel neptunian dykes of an oblique left-lateral crush zone attain maximum widths of 40 cm and are interpreted as second-order synthetic faults related to the main mid-Cretaceous fault zone, which is characterized by NW-SE trending limestone fault-scarp breccias parallel to the active North Anatolian Fault Zone (Fig. 3).…”

“…The redeposited sequence is a sensitive indicator of tectonosedimentary conditions (Bektas, 1986;Yilmaz, 1993;Bektas et al, 1995;Bektas and Ç apkinoglu, 1997;Bektas et al, 2001). The purpose of this paper is to illustrate the characteristics of the middle Cretaceous platform-basin transition, which has already been reported by numerous authors (Seymen, 1975(Seymen, , 1993Altiner et al, 1991;Tüysüz, 1996;Yilmaz, 1996;Yilmaz et al, 1996;Rojay and Altiner, 1998).…”