Role of subducted sediments in plate interface dynamics as constrained by Andean forearc (paleo)topography

ARON, FELIPE A.; CREMPIEN, JORGE G. F.; COSENTINO, NICOLÁS J.; JORDAN, TERESA E.

Special Paper of the Geological Society of America

Geological Society of America

Año: 2018

0072-1077

Forearc topography and inferred paleotopography are key constraints on theprocesses acting at plate interfaces along subduction margins. Along-strike variationsover >2000 km of the Chilean margin of modern topography, trench sedimentthickness and instrumental seismic data sets are used to test previously proposedfeedbacks among subducted sediments, plate interface rheology, megathrustseismicity and forearc elevation. Observed correlations are consistent with subductedsediments playing a prominent role in controlling plate interface rheology, which, inturn, controls the down-dip distribution of megathrust seismicity and long-term forearcelevation. High (low) rates of trench sedimentation promote long-term interseismiccoupled offshore forearc uplift (subsidence) and onshore forearc platform subsidence(uplift). Low trench sedimentation rates also promote deeper megathrust seismic slip,enhancing short-wavelength coastal zone uplift. Shallowing of subducting slabscontributes to reducing coastal zone-onshore forearc relief, in turn preventing formationof onshore forearc basins. The extremely low denudation rates of hyperarid northernChile have allowed better reconstructions of the histories of paleoelevations andpaleoclimate compared to other sections of the forearc. Even if these histories are notsufficiently resolved to unequivocally assign causality among climate variability,changes in plate interface frictional properties, and forearc elevation, they areconsistent with the onset of hyperaridity in the coastal zone at 20-25 Ma (i) triggeringlong-term, long-wavelength offshore forearc subsidence and onshore forearc uplift, and(ii) accelerating short-wavelength coastal zone uplift.