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

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

Concepción

Congreso; XV Congreso Geológico Chileno; 2018

Sociedad Geológica de Chile

Forearc topography and inferred paleotopography are key constraints on the pro-cesses acting at plate interfaces along subduction margins. We used along-strike variationsin modern topography, trench sediment thickness, and instrumental seismic data sets over>2000 km of the Chilean margin to test previously proposed feedbacks among subductedsediments, plate interface rheology, megathrust seismicity, and forearc elevation. Observedcorrelations are consistent with subducted sediments playing a prominent role in control-ling plate interface rheology, which, in turn, controls the downdip distribution of megath-rust seismicity and long-term forearc elevation. High (low) rates of trench sedimentationpromote long-term interseismic coupled offshore forearc uplift (subsidence) and onshoreforearc platform subsidence (uplift). Low trench sedimentation rates also promote deepermegathrust seismic slip, enhancing short-wavelength coastal zone uplift. Shallowing ofsubducting slabs contributes to a reduction in coastal zone?onshore forearc relief, in turnpreventing formation of onshore forearc basins. The extremely low denudation rates ofhyperarid northern Chile have allowed better reconstructions of the histories of paleoel-evations and paleoclimate compared to other sections of the forearc. Even if these historiesare not sufficiently resolved to unequivocally assign causality among climate variability,changes in plate interface frictional properties, and forearc elevation, they are consistentwith the onset of hyperaridity in the coastal zone at 25?20 Ma (1) triggering long-term,long-wavelength offshore forearc subsidence and onshore forearc uplift, and (2) accelerat-ing short-wavelength coastal zone uplift.