Geodynamics of flat subduction: Seismicity and tomographic constraints from the Andean margin
Tóm tắt
The cause and geodynamic impact of flat subduction are investigated. First, the 1500 km long Peru flat slab segment is examined. Earthquake hypocenter data image two morphologic highs in the subducting Nazca Plate which correlate with the positions of subducted oceanic plateaus. Travel time tomographic images confirm the three‐dimensional slab geometry and suggest a lithospheric tear may bound the NW edge of the flat slab segment, with possible slab detachment occurring down dip as well. Other flat slab regions worldwide are discussed: central Chile, Ecuador, NW Colombia, Costa Rica, Mexico, southern Alaska, SW Japan, and western New Guinea. Flat subduction is shown to be a widespread phenomenon, occuring in 10% of modern convergent margins. In nearly all these cases, as a spatial and temporal correlation is observed between subducting oceanic plateaus and flat subduction, we conclude that flat subduction is caused primarily by (1) the buoyancy of thickened oceanic crust of moderate to young age and (2) a delay in the basalt to eclogite transition due to the cool thermal structure of two overlapping lithospheres. A statistical analysis of seismicity along the entire length of the Andes demonstrates that seismic energy release in the upper plate at a distance of 250–800 km from the trench is on average 3–5 times greater above flat slab segments than for adjacent steep slab segments. We propose this is due to higher interplate coupling and the cold, strong rheology of the overriding lithosphere which thus enables stress and deformation to be transmitted hundreds of kilometers into the heart of the upper plate.
Từ khóa
Tài liệu tham khảo
Bialas J., 1999, GEOMAR Report 94
Bialas J., 2000, GEOMAR Report 96
Boyd T. M., 1984, High‐resolution determination of the Benioff Zone geometry beneath Southern Peru, Bull. Seism. Soc. Am., 74, 559
Defant M. J., 1993, The geochemistry of young volcanism throughout western Panama and SE Costa Rica: An overview, J. Geol. Soc. London, 149, 569, 10.1144/gsjgs.149.4.0569
Engdahl E. R., 1998, Global teleseismic earthquake relocation with improved travel times and procedures for depth relocation, Bull. Seismol. Soc. Am., 88, 722, 10.1785/BSSA0880030722
Gutscher M. ‐A., 2000, An Andean model of interplate coupling and strain partitioning applied to the flat subduction of SW Japan (Nankai Trough), Tectonophysics
Hall M. L., 1985, Volcanotectonic segmentation of the N. Andes, Geology, 13, 203, 10.1130/0091-7613(1985)13<203:VSOTNA>2.0.CO;2
Hey R. N., 1977, Tectonic evolution of the Cocos‐Nazca spreading center, Geol. Soc. Am. Bull., 88, 1414
Monzier M., 1997, Les adakites d’Equateur: modele préliminaire, C. R. Acad. Sci., Ser. I, 324, 545
Pubellier M., 1998, Le changement de régime plio‐quaternairedans une zone d’échappement tectonique; controle par des intrusifs syntectoniques (Irian Jaya, Indonésie), Proc. Réunion des Sciences de la Terre (RST Meeting), Brest, France, 179