Tectonic evolution of the Kraishte area (southwestern Bulgaria and southeastern Serbia) - an overview

In the tectonic window of Doliana (central Peloponnesus, Greece) a variety of geological formations occurs deriving from different sedimentation palaeoenvironments and characterized by different tectonometamorphic evolution. These rocks initially formed thrust nappes of great extension and thickness which stacked one over the other during the Lower Oligocene-Lower Miocene. The early compressing structures that were formed by the emplacement of the nappes were almost totally overprinted by the later-orogenic extension that affected the nappe-column in the Upper Miocene-Lower Pliocene. Its main tectonic characteristic was the formation of low-angle normal faults, which constitute the tectonic contacts of the nappes. These faults led to the exhumation of the formerly deeply buried metamorphic rocks that are forming the core of the tectonic window. Apart from these structures during the evolution of this deformation phase an intense thinning of the units of the upper plate took place, causing the upper units coming closer or next to the lower ones. After the Lower Pliocene a second extensional phase affected the already thinned nappe-column with the formation of high-angle normal faults.

Development of the Mozambique and Ruvuma sedimentary basins, offshore Mozambique

SUMMARY We address the mechanism of sedimentary basin formation along strike-slip fault systems with 3-D numerical simulations based on a continuum damage rheology model. The formation of these basins is usually explained by a pull-apart mechanism that predicts a rhomb-shaped basin geometry bounded by two longitudinal strike-slip faults and two transverse listric faults. Significant ductile deformation of the lower crust and upper mantle associated with basin growth requires normal or elevated heat flux. The Dead Sea continental transform is associated with some of the larger and unusually deep basins, among which the southern Dead Sea is the deepest. The heat flow in the Dead Sea basin is anomalously low and it is associated with deep seismicity. Moreover, the basin is bounded by deep transverse normal faults rather than the listric faults required by the pull-apart model. Hence, the formation of the basin cannot be explained by the existing pull-apart model. Ben-Avraham and Schubert proposed an alternative conceptual model for the formation of the deepest basin at the southern Dead Sea. They suggested that an isolated block of lithosphere has dropped into the mantle. We simulate the formation of this and other deep basins along the Dead Sea fault and demonstrate that the ‘drop down’ mechanism of the Dead Sea basin formation suggested by Ben-Avraham & Schubert is possible. Density heterogeneities formed in the crust or upper mantle during a previous stage of regional magmatism, drop into the upper mantle when strike-slip faults are created and detach them from the surrounding lithosphere. The simulations indicate that the resulting basin is rhomb-shaped and that with time it grows by the addition of distinct segments to its edges. The proposed mechanism could account for the formation and evolution of large sedimentary basins along other strike-slip fault systems, such as the San Andreas fault and other continental transform faults.

Block rotations and continental extension in the central Aegean Sea: palaeomagnetic and structural evidence from Tinos and Mykonos (Cyclades, Greece)

Influence of the structural framework on the origin of multiple fault patterns

[1] In the Kraishte region, near the junction of the Balkanides and Dinarides, late Early Cretaceous compression led to the thrusting of the Morava unit over the Struma unit. Structural investigations, combined with zircon fission track and 40Ar/39Ar analyses, have been used to reconstruct the geological history of the area and to clarify the original tectonic position of the main units before Cenozoic extension. The results show that Early Cretaceous lower amphibolite facies metamorphism and deformation in the Osogovo-Lisets Metamorphic Complex were related to top-to-the-NE directed nappe stacking, whereas the deeper parts of the allochthonous Morava unit experienced low-grade metamorphic overprint at temperatures >∼260°C. The structurally intermediate Struma Diorites and their Mesozoic cover experienced temperatures between ∼170°C and 300°C. Thrusting of the Morava onto the Struma unit started probably in Valanginian times (140–136 Ma), soon after the cessation of preorogenic to synorogenic turbidite sedimentation on Struma. The metamorphic peak was reached before 112 Ma. Subsequent extension-related cooling of both units was probably accompanied by the formation of low-angle normal faults.

The Mohr-Coulomb criterion has been widely used to explain formation of fractures. However, it fails to explain large strain deformation that widely occurs in nature. There is presently a new theory, the MEMC, which is mathematically expressed as Meff = (σ1 — σ3) L · sin 2α sin α)/2, where σ1-σ3 represents the yield strength of the related rock, L is a unit length and α is the angle between σ1 and deformation bands. This criterion demonstrates that the maximum value appears at angles of ±54.7° to σ1 and there is a slight difference in the moment in the range of 55°±10°. The range covers the whole observations available from nature and experiments. Its major implications include: (1) it can be used to determine the stress state when the related deformation features formed; (2) it provides a new approach to determine the Wk of the related ductile shear zone if only the ratio of the vorticity and strain rate remains fixed; (3) It can be used to explain (a) the obtuse angle in the contraction direction of conjugate kink-bands and extensional crenulation cleavages, (b) formation of low-angle normal faults and high-angle reverse faults, (c) lozenge ductile shear zones in basement terranes, (d) some crocodile structures in seismic profiles and (e) detachment folds in foreland basins.

Infill history of the Ulleung Basin, East Sea (Sea of Japan) and implications on source rocks and hydrocarbons

We focus on the relationships between tectonic deformation and sedimentary basin formation. Resolving the interaction and feedback between tectonic crust-lithosphere scale deformation and surface processes through erosion of elevated areas and formation of sedimentary basins over multiple scales has been a long-standing challenge. Here I will report on recent advances in forward modelling linking crust-lithosphere deformation with surface processes over a large range of scales resolving tectonic plate scale deformation and sedimentary basin formation at stratigraphic scales. The forward numerical models indicate a linkage and interaction between the structural style of thick-skinned large-scale mountain belt and rift-passive margin formation, erosion-transport-deposition processes operating at the surface, and the thin-skinned deformation occurring in the associated sedimentary basins.

Saxifrago Ferdinandi-Coburgi-Seslerietum Actarovii - ANew Association from the Subalpine Belt of the Slavianka (Orvilos) MTS. (Bulgaria)The paper discusses the phytosociological and syntaxonomical position of the dry subalpine grasslands in the Slavianka (Alibutoush, Orvilos) Mts. (South-Western Bulgaria, Northern Greece). A new associationSaxifrago ferdinandi-coburgi-Seslerietum actaroviiass. nova has been established as a result of the phytosociological study. It is considered as an endemic vegetation unit from the calcareous subalpine terrains in the Central Balkan Peninsula high mountains (Southwestern Bulgaria, Former Yugoslav Republic of Macedonia, Northern Greece). The new syntaxon belongs to the allianceEdrajantho-SeslerionHorvat 1949. A comparison with related syntaxa from other calcareous mountains from Northern Greece and the Former Yugoslav Republic of Macedonia is discussed.

The Circum-Pacific belt, more than 50,000 km long and from 600 to 5,000 km wide, is a complex of crustal structures which were developed at different times since late Precambrian, have different makeup, and are confined to common ring zone. About 40% of all basins known in world are within Circum-Pacific belt. The sedimentary basins End_Page 1432------------------------------ within belt are of different size, age, and relief. Some contain oil and gas and account for almost one third of world oil production. These basins contain thick sedimentary sequences which form lens-like bodies. Sedimentary basins in which sediments are more than 3-3.5 km thick generally contain oil and gas. Tectogenesis is leading process in origin and formation of sedimentary basins and their transformation to oil and gas basins. Therefore, when classifying them, one should be guided by tectonic setting of basins. All basins in Circum-Pacific belt can be divided into five groups. The first group includes basins at junction of Circum-Pacific belt with ancient platforms. Such basins are composed of thick Mesozoic, Cenozoic, and some Paleozoic sequences and contain oil and gas. The second group is connected with intermountain areas. These basins usually are on continental-type crust and contain Mesozoic and Cenozoic sequences 3-5 or more km thick. This is most numerous group including more than 70 basins. The third group includes pericontinental folded basins at junction of folded continental structures and oceanic floor. They are mainly along American Pacific Coast and contain great thicknesses of predominantly Cenozoic deposits. The fourth group includes perioceanic basins connected with island arcs. These basins may be between an island-arc uplift and an oceanic floor or in a deep-sea depression. The fifth group includes intraplatform basins, which are rare and are chiefly within East Australian Paleozoic folded belt. The main criterion for oil and gas content is thickness of sedimentary rocks. The function of thickness is degree of katagenetic transformation of dispersed organic matter in subaqueous part of sedimentary section. All sedimentary basins more than 3.5 km thick contain oil and gas fields, irrespective of their hypsometric position. The thicknesses of rock sequences, rather than faults, control oil and gas content. No distinct relation has been observed between oil and gas accumulation and position of lithospheric plates defined by the new global tectonics concept. End_of_Article - Last_Page 1433------------

The Lower Cretaceous to Miocene South Shetlands Islands’ volcanic arc is a result of the subduction of the Phoenix Oceanic Microplate (part of the Pacific Plate) beneath the Antarctic Peninsula. The magmatic activity on Livingston Island has been going on for a long time: since the Early Cretaceous to the present. The evolution of the volcanic arc resulted in the formation of various sedimentary basins and paleoenvironments (turbiditic to shallow marine and continental) that formed varied sedimentary successions and tholeiitic to potassium calc-alkaline subduction-related magmatic rocks. Considering the magmatic activity on Livingston Island, a general trend of rejuvenation can be observed from the WNW (Byers Peninsula) to the ESE (to Hannah Point, Point Williams and further to the Hurd Peninsula and the Tangra Mountain). The rejuvenation of the magmatic rocks in the direction of the thrust plate can be explained as an effect of a flattening subduction that was active from the Early Cretaceous (135 Ma) up to around 90–70 Ma. The mixed ages of the dikes and small intrusions in the Hurd Peninsula are most probably due to periods of rotation and probably beginning of а slab-roll back. A regional Paleocene–Eocene (65–47 Ma) compressional episode that caused a low temperature to high-pressure metamorphism is registered on Smith and Elephant islands. The regional metamorphism was followed by a vast extension between 50–30 Ma that culminated with the opening of the Drake Passage around 34–30 Ma. The magmatic response of that regional scale extension was the intrusion of the Eocene Barnard Point Pluton (46–40 Ma) and dikes with youngest ages of around 30 Ma. The major uplift phase and the exhumation of the Tangra Mountain happened between 22–16 Ma as indicated by the Ap FT thermochronology. The last magmatic event on the island produced the contrastingly different in composition Quaternary alkaline mafic rocks that occupy the area between Innot Point and Burdick Peak. This episode is interpreted as related to a process of crustal extension that culminated in asthenospheric upwelling and rifting along the Bransfield Strait. The latter is due to a slab roll-back that led to the break-up of the South Shetlands from the Antarctic Peninsula and consequent subduction termination.

Middle to late cenozoic magmatism of the southeastern Colorado plateau and central Rio Grande rift (New Mexico and Arizona, U.S.A.) : a model for continental rifting

The Mount Kozak magmatic complex, Western Anatolia

Sedimentologic and provenance analyses for the Qaidam Basin in the northern Tibetan Plateau help to elucidate the stratigraphic signatures of initial deformation and exhumation in basin-bounding ranges. The basin recorded sedimentary transitions in response to uplift and unroofing of several distinctive source regions. Along the NE basin margin, a detrital record of exhumation and basin isolation is preserved in the 6200-m-thick Cenozoic succession at the Dahonggou anticline. An up-section shift from axial fluvial and marginal lacustrine deposition to transverse fluvial sedimentation suggests progradation and increasingly proximal sediment sources, reflecting activation and advance of crustal deformation. Provenance results from sandstone petrology, U-Pb geochronology, and heavy mineral analyses indicate initial late Paleocene–early Eocene derivation from igneous, metamorphic, and sedimentary sources, consistent with Permian–Triassic arc rocks dominating the southern (Kunlun Shan) or southwestern (Qimen Tagh) basin margins. Up-section variations in sediment composition and detrital zircon U-Pb age distributions are attributed to Eocene–Oligocene derivation from lower Paleozoic and Mesozoic igneous and metamorphic rocks of the central to northern Qilian Shan–Nan Shan. Disappearance of igneous sources and persistence of metamorphic sources are consistent with derivation from the southern Qilian Shan–Nan Shan during early–middle Miocene shortening along the frontal Nan Shan–North Qaidam thrust belt. These results are supported by paleocurrent analyses revealing an Eocene shift from roughly E-directed (axial) to SW-directed (transverse) dispersal of sediment. Variations in lithofacies, composition, U-Pb ages, and paleoflow are consistent with late Paleocene–early Eocene exhumation in the Kunlun Shan followed by middle Eocene–middle Miocene exhumation in the Qilian Shan–Nan Shan. The up-section disappearance and reappearance of diagnostic U-Pb age populations can be associated with progressive unroofing of multiple thrust sheets, successive input of sedimentary and magmatic sources, and southward encroachment of Qilian Shan–Nan Shan shortening into the Qaidam Basin. The sedimentary record presented here indicates that during the Paleogene, the unified Qaidam-Tarim Basin was partitioned and uplifted as it was incorporated into the growing Tibetan Plateau. Comparison with basins on and surrounding the Tibetan Plateau suggests that basement strength and lateral homogeneity, and formation of syndepositional structural dams are among the primary controls on formation of giant sedimentary basins.