Search

Initiation of subduction is rarely encountered in modern tectonic environments due to its ephemeral and destructive nature. We report the geological and geophysical evidence indicating a transitional phase from buckling to embryonic subduction along the eastern Korean margin. The transition appears to be caused by compressional reactivation of the strike-slip boundary between the continental (Korean Peninsula) and oceanic (Ulleung Basin) crusts since the Early Pliocene. Evidence for compressional reactivation includes (1) a west-dipping major thrust and coincident crustal buckling of the Ulleung Basin; (2) an east-west structural asymmetry inferred from the gravity anomaly and P-wave tomography; and (3) ongoing crustal uplift and high-angle faults along the eastern Korean margin. The juxtaposition of underthrusting and buckling of the crust in the Ulleung Basin, and its associated ubiquitous reverse faulting on the eastern Korean margin, imply the potential development of a new subduction system along the western margin of the East Sea (Japan Sea). We propose that the East Sea comprises two incipient subduction margins (i.e., the Korean and Japanese sides), which are now competing to reach a self-sustaining subduction stage. [ABSTRACT FROM AUTHOR]

Abstract In contrast to previously published models for the area, the seismic reflection Moho is essentially flat beneath the NE German Basin along the DEKORP deep seismic profile Basin'96. This raises the question, whether the present structure of the crust and flat Moho reflect the initial formation of the basin or modification by more recent processes. A 2D flexural model, developed for a thin elastic plate, is presented together with lithospheric strength profiles calculated along the BASIN 9601 reflection seismic line. The analysis shows a southward decrease of lithospheric strength below the Basin, with a lithospheric decoupling between the crust and the mantle. The modelling supports the hypothesis that the present Moho topography is caused by flexural buckling which caused subsidence of the NE German Basin during the Upper Cretaceous-Early Cenozoic inversion event. This suggests that the basin is in isostatic disequilibrium, and that compressive stresses are required to keep the present basin geometry. [ABSTRACT FROM AUTHOR]

The Casaglia Monte della Colonna (CMC) body, from the middle Miocene Marnoso-arenacea Formation of the Northern Apennines, covering more than 350 square kilometers, provides a rare opportunity to study the geometry and the internal deformation of a large, basin-wide submarine landslide. Although the head zone of the landslide has not been preserved, the body has a transitional zone, a contractional ramp cutting off more than 200 meters of the footwall stratigraphic succession, and a very wide lobe spilling over onto the adjoining basin plain deposits. The extent of the body, the depth of the ramp cut-off and the widening of the lobe are comparable with the largest present-day submarine landslides, not often observed in fossil examples. Internal deformation structures are distributed differently in the ramp and lobe zones. The ramp zone has antiformal stacking of duplexes and steeply inclined folds. The lobe has a well-defined strain partition: the upper part of the body is affected by extensional structures such as listric normal faults and extensional duplexes; the lower part is deformed by recumbent folds, boudinage and stacking of blocks, which are compatible with flow-induced, heterogeneous simple shear. This distribution is consistent with a kinematic model of extrusion-spreading, implying rear compression in the ramp zone with thickening and shortening of the body, and spreading in the lobe with thinning and stretching. The localized buckling present in the distal part of the lobe may be related to the onset of lateral confinement, due to local topographic features of the basin plain (synsedimentary intrabasinal high). The various degrees and styles of stratal disruption in the mass wasting body depend on the different combination of progressive simple shear, layer-parallel extension and shortening. Different structural associations occur in well-defined parts of the body due to kinematics of emplacement (spreading, flow and buckling). These associations may be diagnostic of gravitational mass wasting processes rather than shallow-level tectonic deformation. [ABSTRACT FROM AUTHOR]

The origin of large subsidence in intracratonic basins is still under debate. We propose a new and self-consistent model for the formation of those basins, where lithospheric shortening/buckling triggers metamorphism and densification of crustal mafic heterogeneities. We use a forward thermo-mechanical finite element technique to evaluate this mechanism for the typical example of the East Barents Sea basin ( EBB) where a very large and compensated subsidence, accommodating an up to 20-km-thick sediment succession, is observed. The lower crust in the dynamic model is modelled with petrologic-consistent densities for a wet mafic gabbroic composition that depend on pressure and temperature taking into account dehydration at high PT conditions. The model successfully explains the main characteristics of the EBB, notably the large anomalous and fast subsidence during the Late Permian-Early Triassic, its present-day geometry and the absence of a significant gravity anomaly. [ABSTRACT FROM AUTHOR]

Abstract: This finite element modelling study addresses the contraction of rheologically layered and laterally heterogeneous lithosphere representative for the Pannonian Basin and its surroundings. The time interval and strain rate adopted in the experiments reflect the Pliocene–Quaternary inversion of the basin. Several sets of fully coupled elastoviscoplastic thermo-mechanical, plane strain 2D models explore the evolution of buckling, and stress/strain changes across the lithosphere. The viscous rheology of the asthenosphere allows for a detailed simulation of isostatic rebound during deformation. The numerical models predict the successive development of surface undulations, caused by crustal and/or lithosphere folding, at three different characteristic wavelengths. Among these, the longest wavelength folds occur systematically at the rim of the basin as marginal bulges, while the short wavelength folds overprint the earlier folds and are observed at a later stage during compression. The thermo-mechanical evolution of the lithosphere in response to progressive horizontal contraction is described in terms of a characteristic delay of the changes in the stress regime and a reduction of elastic strain in the strong crustal layers. The models predict a change in stress state along the flanks of the basin, caused by the development of weak basin lithosphere in their vicinity. Comparing the modelling results with tectonic features of the Pannonian Basin has resulted in the identification of three different stages in the Pliocene–Quaternary basin inversion of the Pannonian–Carpathian system. [Copyright &y& Elsevier]

Abstract: The Sudbury Basin is a non-cylindrical fold basin occupying the central portion of the Sudbury Impact Structure. The impact structure lends itself excellently to explore the structural evolution of continental crust containing a circular region of long-term weakness. In a series of scaled analogue experiments various model crustal configurations were shortened horizontally at a constant rate. In mechanically weakened crust, model basins formed that mimic several first-order structural characteristics of the Sudbury Basin: (1) asymmetric, non-cylindrical folding of the Basin, (2) structures indicating concentric shortening around lateral basin termini and (3) the presence of a zone of strain concentration near the hinge zones of model basins. Geometrically and kinematically this zone corresponds to the South Range Shear Zone of the Sudbury Basin. According to our experiments, this shear zone is a direct mechanical consequence of basin formation, rather than the result of thrusting following folding. Overall, the models highlight the structurally anomalous character of the Sudbury Basin within the Paleoproterozoic Eastern Penokean Orogen. In particular, our models suggest that the Basin formed by pure shear thickening of crust, whereas transpressive deformation prevailed elsewhere in the orogen. The model basin is deformed by thickening and non-cylindrical synformal buckling, while conjugate transpressive shear zones propagated away from its lateral tips. This is consistent with pure shear deformation of a weak circular inclusion in a strong matrix. The models suggest that the Sudbury Basin formed as a consequence of long-term weakening of the upper crust by meteorite impact. [ABSTRACT FROM AUTHOR]

: Background and Aims The anatomical characterization and morphology of Guadua zuloagae nov. sp. (Poaceae–Bambusoideae) culm was determined. This material was collected at the Toma Vieja fossil locality, Paraná basin, Argentina. This fossil culm is the first record of Bambusoideae in sediments of the Pliocene from the Ituzaingó Formation. The studied specimen was compared with the taxa of the Bambusoideae sub-family, especially with the American woody bamboos and others taxa that have woody culms, including Arundo, Thysalonaena and Gynerium. : Methods The material was preserved by siliceous cellular permineralization, and it was prepared for microscopic examination by surface polishing and thin sections. The morphology and anatomy of this new species were described. The estimated height, critical buckling height and safety factor were calculated on the basis of the fossil bamboo diameter using the formula of Niklas. The relationship and comparison with the nearest living relatives (NLRs) are discussed. : Key Results Well-preserved petrified culm with internodes and nodes from the Pliocene of Argentina provides the basis for the description of a new fossil bamboo, Guadua zuloagae. The results of the anatomical analysis of the fossil bamboo showed a great affinity with the extant species Guadua angustifolia and constitute the first evidence of petrified bamboo culm. : Conclusions The new fossil bamboo culm constitutes the only fossil record, preserved as permineralized by silicification, in the world. This fossil record indicates that the genus Guadua was more widespread in the past than today. Discovery of G. zuloagae allows the presence of a Bambusoideae understorey in the mixed forests described for the Ituzaingó Formation to be inferred. The climatic conditions inferred from fossil bamboo and sedimentary deposits indicate a temperate-warm, humid climate. [ABSTRACT FROM AUTHOR]