Examinando por Materia "fold and thrust belt"

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    Ítem
    Large-magnitude late Holocene seismic activity in the Pereira-Armenia region, Colombia
    (GEOLOGICAL SOC AMER INC, 2011-01-01) Lalinde, C.P.P.; Toro, G.E.; Velásquez, A.; Audemard, F.A.M.; Lalinde, C.P.P.; Toro, G.E.; Velásquez, A.; Audemard, F.A.M.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y Tectónica
    The Pereira-Armenia region, located west of the Colombian Central Cordillera, is crosscut by the Romeral fault system, which consists of an active north-south- trending, left-lateral, strike-slip fault system with a secondary thrust component in the Eje Cafetero zone (4°N-5°N). The terrain where the Liceo Taller San Miguel high school sits-9 km south of Pereira-is draped with an ~2-m-thick layer of volcanic ash younger than 30 k.y. in age. This locality has been affected by both N40°E- and E-W-trending faults that correspond to thrust faults or folds and normal rightlateral, strike-slip faults, respectively, in the tectonic model for the zone. Two kinds of strong fi eld evidence for the E-W faults were found at a site named Canchas: (1) the 50°N tilt of the late Quaternary interbedded sequence of volcanic ash and three paleosols, and (2) a vertical fault throw of ~1.70 m affecting the sequence (layers). A normal vertical throw of ~0.65 m at Parqueadero stands as a proof of the activity of the N40°E-trending faults. This latter faulting does not correspond with the stress tensor proposed for this region, and thus this deformation could be interpreted as being a consequence of fl exural slip induced by a NE-SW-striking blind thrust, where reverse faulting along bedding at depth is seen as normal faulting at the surface. Measured offsets could have generated seismic events of at least Mw 6.6 for the NE-trending fault that affected the paleosols and volcanic ash sequence at 13,150 ± 310 14C yr B.P., and a seismic event of Mw 6.9 for the E-W-trending fault that affected the paleosols and volcanic ash sequence at 19,710 ± 830 14C yr B.P. These two recently identifi edfaults are now named the Tribunas (NE-SW) and the Cestillal (E-W) faults. Up to now, the fault and its seismogenic potential determinations in this region have been based solely on morphologic evidence. The maximum seismic magnitude estimated for this region ranged from Mw 6.2 to Mw 6.6 for seismic sources 35 km away from the site. Seismic magnitudes like the one calculated in this work (Mw 6.9) were previously estimated only for source-site distances greater than 50 km. This work provides fi eld evidence that leads to a better understanding of the seismic activity of this region in the last 30 k.y. and confi rms the occurrence of local Mw >6.5 seismic events in this region. Although volcanic ash drapes and eventually hides the geomorphic evidence of active deformation, it turns out to be a perfect chronometer of a fault's activity whenever the deformation is revealed, as in this case. After the Armenia event of 1999, it is imperative to examine the seismic hazard assessments of this region in terms of local crustal seismicity. © 2011 The Geological Society of America. All rights reserved.
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    Regional controls in the distribution and morphometry of deep-water gravitational deposits along a convergent tectonic margin. Southern Caribbean of Colombia
    (Elsevier BV, 2020-08-06) Naranjo Vesga, Julián Francisco; Ortiz Karpf, Andrea; Wood, Lesli; Jobe, Z.; Paniagua, J.; Shumaker, L.; Mateus Tarazona, Darwin; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    Deep-water fold and thrust belts often develop in convergent tectonic margins, creating irregular slope profiles that control the distribution of deep-water gravity deposits. However, in areas with high sediment supply, the erosion and sedimentation can minimize structural relief and smooth the slope. Using multibeam bathymetry with 3D seismic data, we analyze the distribution of deep-water gravity-driven deposits along the convergent margin of the southern Caribbean of Colombia, comparing areas with different continental sediment supply, slope profile, and shelf width. We identify three geomorphological zones: The Northern, Central and Southern Zones. The Northern Zone is characterized by a gentle slope topography, high sediment supply, and large (>100 km length) channel-levee systems traversing the slope and basin floor. In this zone, shelf-attached mass-transport deposits erode and smooth sea-floor topography. The Central Zone is characterized by low sediment supply and steep and irregular slope topography. Here, short-runout mass-transport deposits sourced from the crests and steep flanks of emergent anticlines are common. The irregular relief created by tectonic deformation forms barriers for sediment transport, leading to tortuous sediment-flow pathways. Submarine canyons incise the thrust-cored anticlines, transporting sediment through interconnected, adjacent piggyback sub-basins. Finally, the Southern Zone is characterized by steep slope and moderate sediment supply. Here, tectonic deformation has been smoothed by numerous shelf-attached mass-transport deposits. The erosional scours carved by mass flows merge downslope and evolve into submarine canyons that can deliver mass-transport deposits more than 80 km into the basin. We analyze the impact of slope profile, sediment input and shelf width on the distribution and morphology of deep-water deposits along the southern Colombian Caribbean margin, and present a predictive model for the depositional patterns more likely to develop in other continental margins affected by deep-water fold and thrust belts. © 2020 Elsevier Ltd