Transient uplift of a long-term quiescent coast inferred from raised fan delta sediments

Abstract

We present the first example of a short-term uplift transient within the long-term stagnant forearc of the Arica Bend, northernmost Chile. We date a storm deposit embedded into fan delta sediments, which were deposited close to sea level and are now located ~40 m higher. The radiocarbon age is ca. 10 ka, yielding an average uplift rate of ~4 mm/yr. During the Holocene, the section has been dissected by the Lluta River, the long profile of which shows geomorphic response to coastal uplift. However, the coast of the Arica Bend is characterized by millionyear- scale relative subsidence and current global positioning system surveyed quiescence. We therefore interpret the inferred uplift signal to represent a transient increase in uplift rates throughout the Holocene. Similar short-term transients have been globally documented in relation to various subduction zone settings, although their causes still remain a matter of debate and need further investigation. We propose that periods of increased surface uplift may also occur in long-term quiescent forearcs, possibly due to temporal variations of plate interface properties (i.e., strength and/or seismic locking) that induce thickening beneath the coast.