Abstract Accretionary orogens form at intraoceanic and continental margin convergent plate boundaries. They include the supra-subduction zone forearc, magmatic arc and back-arc components. Accretionary orogens can be grouped into retreating and advancing types, based on their kinematic framework and resulting geological character. Retreating orogens (e.g. modern western Pacific) are undergoing long-term extension in response to the site of subduction of the lower plate retreating with respect to the overriding plate and are characterized by back-arc basins. Advancing orogens (e.g. Andes) develop in an environment in which the overriding plate is advancing towards the downgoing plate, resulting in the development of foreland fold and thrust belts and crustal thickening. Cratonization of accretionary orogens occurs during continuing plate convergence and requires transient coupling across the plate boundary with strain concentrated in zones of mechanical and thermal weakening such as the magmatic arc and back-arc region. Potential driving mechanisms for coupling include accretion of buoyant lithosphere (terrane accretion), flat-slab subduction, and rapid absolute upper plate motion overriding the downgoing plate. Accretionary orogens have been active throughout Earth history, extending back until at least 3.2 Ga, and potentially earlier, and provide an important constraint on the initiation of horizontal motion of lithospheric plates on Earth. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products but are also major sites of consumption and reworking of continental crust through time, through sediment subduction and subduction erosion. It is probable that the rates of crustal growth and destruction are roughly equal, implying that net growth since the Archaean is effectively zero.
Abstract The North China Craton contains one of the longest, most complex records of magmatism, sedimentation, and deformation on Earth, with deformation spanning the interval from the Early Archaean (3.8 Ga) to the present. The Early to Middle Archaean record preserves remnants of generally gneissic meta-igneous and metasedimentary rock terranes bounded by anastomosing shear zones. The Late Archaean record is marked by a collision between a passive margin sequence developed on an amalgamated Eastern Block, and an oceanic arc–ophiolitic assemblage preserved in the 1600 km long Central Orogenic Belt, an Archaean–Palaeoproterozoic orogen that preserves remnants of oceanic basin(s) that closed between the Eastern and Western Blocks. Foreland basin sediments related to this collision are overlain by 2.4 Ga flood basalts and shallow marine–continental sediments, all strongly deformed and metamorphosed in a 1.85 Ga Himalayan-style collision along the northern margin of the craton. The North China Craton saw relative quiescence until 700 Ma when subduction under the present southern margin formed the Qingling–Dabie Shan–Sulu orogen (700–250 Ma), the northern margin experienced orogenesis during closure of the Solonker Ocean (500–250 Ma), and subduction beneath the palaeo-Pacific margin affected easternmost China (200–100 Ma). Vast amounts of subduction beneath the North China Craton may have hydrated and weakened the subcontinental lithospheric mantle, which detached in the Mesozoic, probably triggered by collisions in the Dabie Shan and along the Solonker suture. This loss of the lithospheric mantle brought young asthenosphere close to the surface beneath the eastern half of the craton, which has been experiencing deformation and magmatism since, and is no longer a craton in the original sense of the word. Six of the 10 deadliest earthquakes in recorded history have occurred in the Eastern Block of the North China Craton, highlighting the importance of understanding decratonization and the orogen–craton–orogen cycle in Earth history.
We report 2.5 billion-year-old oceanic mantle podiform chromitite and mantle tectonite in ophiolitic mélange in the North China craton.Tectonic blocks of peridotite, wehrlite, pyroxenite, harzburgitic tectonite, dunite, podiform chromitite, layered gabbro, sheeted dikes, and pillow lava are embedded in a strongly deformed metasedimentary and metavolcanic matrix.The blocks are traceable belt, and the 2.5-2.4Ga Qinglong foreland basin and fold-thrust belt on the Eastern block, and provides an important record of the operation of plate tectonics in the Archean.
Abstract The Solonker suture zone in the southeastern Central Asian Orogenic Belt is generally regarded as the location of the final closure of the Paleo‐Asian Ocean, formed by complex and cryptic accretionary processes during late Paleozoic to early Mesozoic times. We recognize three tectonically juxtaposed lithotectonic units, including forearc basin sedimentary sequences, ophiolitic fragments, and ophiolitic mélange in the Solonker area, and here investigate the structural and kinematic features of the ophiolitic mélange in detail. The Solonker ophiolitic mélange has typical block‐in‐matrix fabrics with variably sized basalt, chert, sandstone, and ultramafic blocks embedded in siliceous‐argillaceous and siltstone matrices. Both extensional and contractional structures are well developed within the mélange, characterized by pervasive foliation, pinch‐and‐swell, boudinage, and S‐C fabrics. Kinematic analysis of the deformation structures indicates top‐to‐the‐N thrusting, correlated with the southward subduction of the southern margin of the Paleo‐Asian Ocean. Zircon U‐Pb ages of the matrices and a tonalite pluton intruded into the mélange constrain the formation age of the Solonker ophiolitic mélange to be middle Permian (ca. 268–260 Ma). Geochemical data from the ophiolitic rocks show subduction‐related characteristics with enriched large ion lithophile elements and depleted Nb, implying formation in a forearc setting. Our study provides robust evidence for the closure time of the Paleo‐Asian Ocean after the middle Permian. The late‐stage evolution of the Paleo‐Asian Ocean was characterized by subduction, forearc accretion with subsequent obduction of the kilometer‐scale upper plate, and soft collision, ultimately leading to the formation of the Solonker suture zone in the North China‐Mongolia segment.
We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike-pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting.
3 Abstract: Isfahak is located in the south of the city of Tabas, eastern Iran and is a region of rapid active tectonics with abundant strike-slip and thrust-related earthquakes. We used the interactions between faults characteristics and surface geomorphology to assess groundwater potential zones in the study area to promote development of ground water management in a seismic area. A groundwater prospects map has been generated by integration of the geomorphology, lineaments, active faults, slope, land-use/land-cover and drainage maps, using GIS techniques. Then the obtained results have been checked by check field works. The results show that the location of ground water potential zones and the artificial recharge regions have a great relationship with seismic activities, fractured zones and the earthquake epicenters, in the study area.
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