Multi-stage continental crust maturation in accreted oceanic terranes: Evidences from granitoids in the Qinling Orogen, Central China
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The has been highly successful as an analog to explain seismic velocities in the ocean crust. The elements of the ophiolite model have all been observed on the seafloor where tectonic processes have exposed the crust. For the Pacific Ocean crust, or that which forms at non-rifted mid-ocean ridges, the development of the ophiolite model appears to resolve the contentious issues of the composition of the lower oceanic crust, and the nature of the Moho; however, studies show that the seismic structure of the crust evolves as it ages, and the depths to boundaries between different layers change. Therefore, these zones cannot represent lithological boundaries, at least in older crust. In this sense, a strict use of the ophiolite model is incorrect.
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Convergent boundary
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A combination of seismic reflection and gravimetric imagery has been used to map four sectors of proto-oceanic crust along conjugate segments of the West African and Brazilian margins. These form corridors isolating oceanic crust, produced about the post-118 Ma pole of rotation, from continental crust. Seaward of the proto-oceanic crust/oceanic crust boundary, relatively uniform, thin oceanic crust (4.2–6.5 km thick) has been generated at the paleo-Mid-Atlantic Ridge. Structural variability is limited largely to fracture zones. Proto-oceanic crust in the northern sectors (i.e., Kribi, Mbini, and Ogooue) is up to 10 km thick, block-faulted, compartmentalized, and seismically layered. These sectors of proto-oceanic crust likely were generated by slow spreading, as the relative plate motions evolved from left-lateral dislocation along the
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Abstract The accretion of future allochthonous terranes (e.g., microcontinents or oceanic plateaus) onto the southern margin of Asia occurred repeatedly during the evolution and closure of the Tethyan oceanic realm, but the specific geodynamic processes of this protracted convergence, successive accretion, and subduction zone initiation remain largely unknown. Here, we use numerical models to better understand the dynamics that govern multiple terrane accretions and the polarity of new subduction zone initiation. Our results show that the sediments surrounding the future terranes and the structural complexity of the overriding plate are important factors that affect accretion of multiple plates and guide subduction polarity. Wide (≥400 km) and buoyant terranes with sediments behind them and fast continental plate motions are favorable for multiple unidirectional subduction zone jumps, which are also referred to as subduction zone transference, and successive terrane-accretion events. The jumping times (~3–20 + m.y.) are mainly determined by the convergence rates and rheology of the overriding complex plate with preceding terrane collisions, which increase with slower convergence rates and/or a greater number of preceding terrane collisions. Our work provides new insights into the key geodynamic conditions governing multiple subduction zone jumps induced by successive accretion and discusses Tethyan evolution at a macro level. More than 50 m.y. after India-Asia collision, subduction has yet to initiate along the southern Indian plate, which may be the joint result of slower plate convergence and partitioned deformation across southern Asia.
Convergent boundary
Eclogitization
Collision zone
continental collision
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Abstract Earth’s continental crust has evolved through a series of supercontinent cycles, resulting in a patchwork of Archean cores surrounded by terranes, fragments, and slivers of younger crustal additions. However, the dispersal (and/or stranding) of continental fragments during breakup is not well understood. Inherited structures from previous tectonic activity may explain the generation of continental terranes by controlling first-order deformation during rifting. Here, we explored the influence of lithospheric deformation related to ancient orogenesis, focusing on the impact of the Torngat orogen in the genesis of the Nain Province continental fragment in Eastern Canada. We present three-dimensional continental extension models in the presence of an inherited lithospheric structure and show that a narrow continental terrane could be separated and stranded by deep lithospheric scarring. The results show that continental terranes formed by this method would be limited to a width of 100–150 km, imposed by tectonic conditions during continental suturing. The findings have broad implications, demonstrating an original theory on the fundamental geologic problem of terrane generation and continent breakup.
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Continental Margin
continental collision
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Carbon sink
Adakite
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Carbon fibers
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Continental Margin
Upper crust
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The recognition of terranes and terrane accretion has fundamentally changed the way we view the development of continental crust. The terrane concept originated from studies of the western Cordillera of North America, where it was demonstrated in the 1970s that microplates had travelled substantial distances before being amalgamated to cratonic North America. Since these early studies, the terrane concept has been widely applied to older orogenic belts, including the Appalachians and most of the Precambrian shields. Despite the acceptance of the terrane concept, a number of fundamental questions remain regarding the process of terrane accretion and its interaction with transform faulting and igneous and metamorphic events. Still not fully understood are: the coupling processes of mantle with deeper crust, and of deeper crust with upper crust; how pieces of continental crust with different histories respond to juxtaposition; the mechanism of the Mono's formation; and the behavior of fluids (melt and aqueous) with the changing stress field during accretion.
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