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Mesoscale structures in Paleozoic rocks of the Ozark plateaus reveal four Pennsylvanian deformation episodes in midcontinent North America. The two earliest episodes can be assigned to progressive northwestward docking of the Ouachita terrane with North America. Early extensional structures (Event 1) indicate a northwest/southeast maximum horizontal stress (Hmax) during Early Pennsylvanian Ouachita terrane advance. Event 2 extensional and strike-slip structures indicate Hmax across the Ozark plateaus that varies systematically from north-northwest/south-southeast in the south to northeast/southwest in the north. This suggests development of a slip-line deformation field in response to minor northeastward lateral escape of lithospheric blocks away from the northwestward-moving Ouachita terrane's leading edge, which acted as an indenter in western Arkansas, southeastern Oklahoma, and Texas. Younger contractional and strike-slip structures of Event 3 indicate northeast/southwest Hmax across the entire Ozark plateaus, and deformation orientation and intensity are not readily assigned to Ouachita foreland deformation and may be related to Middle Pennsylvanian Ancestral Rockies contractional deformation. Finally, Event 4 contractional structures indicate northwest/southeast Hmax consistent with southern Appalachian late stage convergence.Deformation episodes are localized along basement fault zones, particularly at major bends, suggesting minor restraining-bend uplifts along strike-slip faults. Geometries of conjugate normal fault and hybrid shear joint arrays indicate localized areas of high differential stress consistent with basement block uplift at these bends. High-angle faults reactivated in a reverse sense and bedding-parallel veins suggest tensile minimum stresses and pore fluid pressures exceeding lithostatic stress, consistent with brine pulses driven into the midcontinent during Late Paleozoic orogeny (as proposed by other authors). 相似文献
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Kevin Hall 《地球表面变化过程与地形》1993,18(2):121-129
An indication of the extent of weathering on different aspects of rock outcrops on Livingston Island, Antarctica, was obtained by means of a Schmidt hammer, a cone indenter and measurement of weathering rind thickness. Results show that weathering, particularly chemical weathering, is enhanced on the lee side of outcrops where snow accumulates as a result of prolonged wetting by the melting snow. Rock moisture and temperature data indicate that the south-facing, snow-accumulation side of obstacles have high rock moisture levels and maintain relatively high temperatures. Whilst chemical weathering is greater on the leeward side of outcrops, mechanical processes are greater on the windward side. The presence of late-lying snow thus appears to exert a strong influence on weathering. 相似文献
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E. Laville B. Delcaillau M. Charroud O. Dugué L. Ait Brahim G. Cattaneo P. Deluca A. Bouazza 《International Journal of Earth Sciences》2007,96(3):497-515
The South Middle Atlas front constitutes a northeast-trending shear zone, located north of the Neogene Missour basin and east
of the Taza Guercif basin. This paper analyses the Southern Middle Atlas Fault Zone (SMAFZ) deformation since the Pliocene.
The set of structures observed suggests that reverse and thrust faulting along the central part of the SMAFZ are combined
with left-lateral slip along N–S striking faults of its south-western termination and right-lateral faulting along E–NE striking
faults of the east–northeast termination. Thrusts and oblique thrust-related anticlines of the two lateral ramps partly accommodate
north-west directed motion of the African plate. The Thrusts probably resulted from rejuvenation of Jurassic normal faults;
they were active during the Upper Miocene–Pliocene and the Pleistocene. The geometries of positive inversion structures and
buttressing effects are clearly dependent on the geometry and sedimentology of the original basin-controlling fault system
and on the presence of a décollement level. Field mapping is integrated with Landsat imagery and a digital elevation model
to investigate the morphotectonic evolution of the south-eastern range front of the Middle Atlas. Geomorphological features
provide significant information on the processes that govern lateral propagation of active anticlines. Both suggest that the
deformation front may have been active since Pliocene. 相似文献
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