Observations and Dynamical Implications of Active Normal Faulting in South Peru

Wimpenny, Sam and Copley, Alex and Benavente, Carlos and Garcia, B. and Rossell, L. and O'Kane, Aisling and Aguirre, Enoch (2020) Observations and Dynamical Implications of Active Normal Faulting in South Peru. Geophysical Journal International, 222 (1). pp. 27-53. ISSN ISSN: 0956-540X, ESSN: 1365-246X DOI https://doi.org/10.1093/gji/ggaa144

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Orogenic plateaus can exist in a delicate balance in which the buoyancy forces due to gravity acting on the high topography and thick crust of the plateau interior are balanced by the compressional forces acting across their forelands. Any shortening or extension within a plateau can indicate a perturbation to this force balance. In this study we present new observations of the kinematics, morphology and slip rates of active normal faults in the South Peruvian Altiplano obtained from field studies, high-resolution DEMs, Quaternary dating and remote sensing. We then investigate the implications of this faulting for the forces acting on the Andes. We find that the mountains are extending NNE-SSW to NE-SW along a normal fault system that cuts obliquely across the Altiplano plateau, which in many places reactivates Miocene-age reverse faults. Radiocarbon dating of offset late Quaternary moraines and alluvial fan surfaces indicates horizontal extension rates across the fault system of between 1 and 4 mm/yr — equivalent to an extensional strain rate in the range of 0.5-2×10−8 1/yr averaged across the plateau. We suggest the rate and pattern of extension implies there has been a change in the forces exerted between the foreland and the Andes mountains. A reduction in the average shear stresses on the sub-Andean foreland detachment of <4 MPa (<20-25% of the total force) can account for the rate of extension. These results show that, within a mountain belt, the pattern of faulting is sensitive to small spatial and temporal variations in the strength of faults along their margins.

Item Type: Article
Uncontrolled Keywords: 2020AREP; IA76
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
12 - PhD
Journal or Publication Title: Geophysical Journal International
Volume: 222
Page Range: pp. 27-53
Identification Number: https://doi.org/10.1093/gji/ggaa144
Depositing User: Sarah Humbert
Date Deposited: 02 Jul 2020 23:55
Last Modified: 30 Nov 2020 19:40
URI: http://eprints.esc.cam.ac.uk/id/eprint/4778

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