Aegean Extension Research Articles

Emplacement of volcanic vents and geodynamics of Central Anatolia, Turkey

Observations on Synthetic Aperture Radar (SAR) scenes of the European Remote Sensing (ERS) satellite and Digital Elevation Models (DEMs), complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late Miocene (10 Ma) in Central Anatolia. Volcanic edifices form elongate stratovolcanoes, linear clusters and volcanic ridges. They indicate emplacement on tension fractures and tail-crack or horsetail features. For instance, the Kara Dag volcano is rooted on a tail-crack which accommodates a horizontal left-lateral throw component at a fault termination. Caldera complexes of Cappadocia are associated with horsetail fault patterns. The emplacement of volcanoes also benefits from larger-scale tectonic structures: the Erciyes Dag volcano is localized by the Sultan Saz releasing bend which opens along the sinistral strike-slip Ecemis fault. Deformation has been analysed from tension fractures—which are perpendicular to the direction of extension—and from field structural analysis. On a regional scale, the tectonic regime responsible for the distribution of volcanic vents in this area of convergence and lateral extrusion, is not compression but extension. The Central Taurus range is the thermally uplifted shoulder of the Adana–Cilicia basin, which is related to lithosphere thinning. Westward movements in the northwestern part of the studied area are influenced by the active back-arc Aegean extension situated to the west. Farther to the south, the direction of motion turns southwest and south, under the influence of the opening of the Adana–Cilicia basin. We interpreted that extension in the Central Anatolian plateau is related to crustal blocks moving above sub-horizontal detachment surfaces located in the lower crust. This is based on several facts: the Tuz Gölü fault zone is a within-crust detachment; the Tuz Gölü basin does not affect the whole lithosphere because otherwise it would have been bordered by thermally uplifted shoulders; movements change trend within a small (50 km) region.

Seismicity in the Hellenic Volcanic Arc: relation between seismic parameters and the geophysical fields in the region

SUMMARY A study of the spatial distribution of seismicity and seismic hazard and geophysical parameters is undertaken along the Hellenic Volcanic Arc (HVA). Seismicity of the area is divided in a cellular manner allowing analysis of the localized seismicity parameters and representation of their regional variation as contour maps. Extreme value analysis locates a zone of highest seismicity just west of centre of the HVA, around the Cyclades Islands. Non-probabilistic modelling of the strain energy release process in terms of magnitudes equivalent to the average annual energy release rate (M,) and the maximum possible energy release in a seismic cycle (M3) enhances this picture. Maximum values of M, and M3 are more tightly localized in the central Cyclades west of Amorgos Island and also in the east of the HVA in the Sporadhes north-west of Rhodes. Isocyclic contours of the waiting times for M3 show values in excess of 70 years in the Cyclades and eastern Sporadhes, i.e. the zones of largest earthquakes show the longest strain accumulation periods. The waiting time for the HVA as a whole is about 54 years, and at present it appears to be about 75 per cent through to accumulation of the notional maximum strain energy. The b value of the magnitude-frequency distribution shows a consistent spatial variation along the HVA which is not sensitive to subdivision into different focal depth ranges. Regional contour maps of the b values, and maps of local values of heat flow, magnetic and electrical anomalies compared with the Bouguer gravity anomaly map, indicate correlations which reflect the deformation of the Aegean shallow crust in relation to the deep intrusive magmatic processes. The correlations between the different geophysical fields are displaced commensurate with an Aegean extension of approximately 45 km.

Discussion on a major Oligocene-Miocene detachment in southern Rhodope controlling north Aegean extension

Ivan S. Zagorèev writes: The problem of the Late Cenozoic extension in the Northern Aegean has been discussed for more than 30 years. The approach by Sokoutis et al. 1993 and by Dinter & Royden (1993) seeks the control of this extension in the displacements along very low-angle normal faults of great extent and offset (detachments) which resulted also in a fast unroofing of deep crustal levels in the footwall, and intense sediment deposition on the downthrown side (i.e., formation of depocentres). This problem is traditionally discussed without taking into account the abundant evidence from the adjacent to the north, and well-exposed and mapped Central-Balkan neotectonic region (Zagorèev 1992b). The following important facets of this problem should be taken into consideration. (1) Age of the faulting event, and identification of fault movements of a given age. The region is characterized by several Alpine phases of thrusting proven with fossildocumented sediments within the following limits: (i) Berriasian (Aptian?)—Turonian (Cenomanian?); (ii) Campanian (Maastrichtian?)—Late Eocene (Palaeocene?); (iii) Mid-Eocene—Late Eocene; (iv) Mid-Oligocene (?); (v) earliest Miocene—Badenian. Normal faulting is proven (again with fossiliferous sediments) in the following times: (i) Late Triassic (Carnian—Rhaetian); (ii) Early Jurassic (Hettangian—Pliensbachian); (iii) Bathonian; (iv) Callovian; (v) Tithonian—Berriasian; (vi), Cenomanian— Turonian; (vii) Coniacian—Campanian; (Viii) Maastrichtian; (ix) Palaeocene—Early Eocene; (X) Late Eocene; (xi) Mid-Oligocene—Early Miocene; (xii) Late Badenian—Maeotian; (xiii) Pontian—Romanian; (xiv) Pleistocene— Holocene (e.g. Boyanov et al. 1989 ; Zagorèev 1992a, b). Experience in southwest Bulgaria shows that some fault

A major Oligo-Miocene detachment in southern Rhodope controlling north Aegean extension

Plutonic and metamorphic rocks of the southwest part of the Rhodope massif in Greece correspond to ductile lower crust exhumed and deformed along a major detachment during post-thickening extensional tectonics. Extension started during the Oligocene and is responsible for the development of Miocene–Quaternary sedimentary basins. Both brittle and ductile deformations result from gravity collapse of previously thickened lithosphere, as proposed for others large extended terranes. This interpretation disagrees with the previous models which attributed Tertiary ductile deformation to Alpine thrusting and brittle extensional deformation to back arc tectonics above a subduction zone.