Paleozoic tectonic evolution of the Tianshan Orogen, northwestern China
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Devonian
Passive margin
Continental Margin
Classical concepts of continental margins have been improved in the geological community. The updated continental passive margin models have a complex configuration, presenting a multiphase rifting process, in which hyper-extended continental blocks and mantle exhumation may occur (ocean-continent transition zone - OCT). Therefore, the enhanced model of passive margin basement inspires a renewal on its regional geophysical interpretation. Gravity and magnetics in Western Iberia allow us to interpret some possible regional basement changes, combining filtered regional geophysical data and new concepts of passive margins. In W-Iberia it is proposed four regional domains using regional potential field data: continental margin, two transitional zones, and classical oceanic crust. Furthermore, magnetic anomaly patterns in the western transitional zone seem to be controlled by Variscan trends, which is an evidence of sub-continental mantle composition in the Ocean-Continent Transition zone, and suggests the Variscan Front location. In summarizing, magnetic interpretation in W-Iberia presents deep basement features out of continental crust, overprinted by passive margin zonation. This interpretation brings some new insights about passive margins formation and its classical components. Also, it represents a review of gravity and magnetic regional interpretation and its applicability in continental margins studies.
Continental Margin
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The rifted continental margins off Brazil and West Africa encompass several morphological distinct regions that resulted from the plate separation and subsequent drift of South America and Africa. The main building blocks that controlled the development of the Atlantic-type continental margin basins consist of prerift, synrift, and postrift tectonic stages, and these events determined the basin infill. Oceanic fractures created by transform faults that indent the continental margins form basement highs that ultimately define the tectonic edges of the continental margin basins. These boundaries are involved in the marginal plateaus, marginal banks, and characteristic marginal volcanic ridges.
Continental Margin
Passive margin
Infill
Basement
Salt tectonics
Margin (machine learning)
Oceanic basin
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Abstract The evolution of a passive margin to a foreland basin is generally assumed to entail early load‐induced up warping of the stable continental platform followed by foreland subsidence. This relatively straightforward elastic response of the continental platform, however, may be complicated if the colliding passive margin is irregular in outline. In a tectonic scenario in which an irregular margin is migrating toward a trench (A‐subduction), those areas of the margin which project seaward, the continental promontories, would be the first to ‘feel’ the approaching thrust terrane by flexing upward and eroding to form shelf unconformities. Those parts of the continental margin that are convex to the craton, the continental re‐entrants, however, would remain subsiding depocentres unaffected by load‐induced uplift at the promontories. Careful analysis of the geographic distribution of shelf unconformities in orogenic belts, then, may help to reveal the pre‐deformation morphology of the passive continental margin. An example of this may be found in the early phases of Ordovician foreland basin development in the central Appalachian orogen. Here, the shelf unconformities are most pronounced (greatest erosional relief) at the inferred Virginia and New York continental promontories. An adjacent inferred continental re‐entrant, the Pennsylvania re‐entrant, is characterized by an uninterrupted Ordovician sequence suggesting that the area of the proto‐North American platform, represented by this segment of the orogen, remained a depocentre during uplift in adjacent areas of the continental margin.
Continental Margin
Passive margin
continental collision
Diachronous
Obduction
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The Australian North West Shelf(NWS) and Southern passive continental margin are both main hydrocarbon accumulation areas in Australia.Similarities and differences exist in tectonic evolution history,fracture system,development time,hydrocarbon distribution,etc.Study on the differences from three respects: tectonic evolution controlling basin framework,source-controlling regional structure and trap-controlling fault.The results show that:(1) The NWS develops multi-period rifting,completed structures,and there appears oil lies upon gas vertical layered structure.The intensity of tectonic activity and differences of development period causes hydrocarbon distribution heterogeneity.The Southern margin develops rifting late and short duration.Basins in this area are all produce oil only.(2) Regional structure controls distribution of hydrocarbon generation center.The NWS develops source rock in all Mesozoic.The Southern margin develops in late Cretaceous and Cenozoic.(3) Differences of fracture system cause the differences of trap types.In the NWS,early-trap is destroyed by late faults,developed fault block traps.The Southern margin develops anticline traps and tilted fault block traps.The developed features of the two passive continental margins are similar to the South China Sea passive continental margin.The hydrocarbon distributions of the two areas have the guiding significance for the South China Sea passive continental margin.
Passive margin
Continental Margin
Anticline
Fault block
Hydrocarbon exploration
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Zircon U-Pb data and zircon Hf isotopic data.
Continental Margin
Massif
Passive margin
Margin (machine learning)
Palaeogeography
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The south Atlantic passive margin formed during the Late Jurassic - Aptian due to rifting of South America and West Africa. The passive margin in offshore Gabon depicts excellent examples of structures in magma-poor passive margins. This chapter presents a map of West African passive margin near Gabon. It highlights the upper continental crust (cc), the lower continental crust (lcc), the continental upper lithospheric mantle (m), and the top of the continental basement (b). The map present in the chapter also highlights the sedimentary layers (s1-s3), the proto-oceanic crust (poc), the magmatic rock-dominated rock suites 1 and 2 (mrsl and mrs2), and the syn-rift strata (r). The chapter also presents an uninterpreted dip-oriented reflection seismic profile through the rifted continental margin of Gabon. The breakup process was delivered in the crust first-mantle second (magma-poor) scenario.
Continental Margin
Passive margin
Basement
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The shape and classification of continental margins are in general dependent on style of continental splitting, rifting, subsidence and their proximity to the tectonic plate boundaries, at times the margins undergo for modifications by sediment deposition and volcanic activity. Worldwide continental margins are broadly categorized into two groups: passive (Atlantic) and active (Pacific) type margins. The main features of passive continental margin are shelf, slope, rise and abyssal plain. Analyses of marine geophysical data across the eastern and western continental margins of India show that both the margins are different in shape although both belong to passive margin group. While continental slope along the western continental margin is wider and provides scope for multiple picks of foot-of-slope, it narrows along the eastern continental margin and is clear for single pick of foot-of-slope. Continental slope and rise on western margin and rise on eastern margin were modified to a major extent by Deccan-Reunion hotspot volcanism and Bengal Fan sedimentation respectively. Volcanism has dominated on the western continental margin of India, thereby the margin had been turned into a volcanic passive continental margin, while eastern continental margin of India remained as nonvolcanic passive margin.
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Abyssal plain
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