Active transpressional tectonics in the Andean forearc of southern Peru quantified by¹⁰Be surface exposure dating of an active fault scarp

Abstract

Our understanding of the style and rate of Quaternary tectonic deformation in the forearc of the Central Andes is hampered by a lack of field observations and constraints on neotectonic structures. Here we present a detailed analysis of the Purgatorio fault, a recently recognized active fault located in the forearc of southern Peru. Based on field and remote sensing analysis (Pléiades DEM), we define the Purgatorio fault as a subvertical structure trending NW‐SE to W‐E along its 60 km length, connecting, on its eastern end, to the crustal Incapuquio Fault System. The Purgatorio fault accommodates right‐lateral transpressional deformation, as shown by the numerous lateral and vertical plurimetric offsets recorded along strike. In particular, scarp with a 5 m cumulative throw is preserved and displays cobbles that are cut and covered by slickensides. Cosmogenic radionuclide exposure dating (10Be) of quartzite cobbles along the vertical fault scarp yields young exposure ages that can be bracketed between 0 to 6 ka, depending on the inheritance model that is applied. Our preferred scenario, which takes in account our geomorphic observations, implies at least two distinct rupture events, each associated with ~3 and ~2 m of vertical offset. These two events plausibly occurred during the last thousand years. Nevertheless, an interpretation invoking more tectonic events along the fault cannot be ruled out. This work affirms crustal deformation along active faults in the Andean forearc of southern Peru during the last thousand years.

Extension and Dynamics of the Andes Inferred From the 2016 Parina (Huarichancara) Earthquake

“…Slip in these megathrust earthquakes is consistently parallel to independent estimates of the orientation of motion between the Nazca plate and the South American shield (DeMets et al, ; Norabuena et al, ; Figure a). Although there is evidence of recent reverse faulting within the Andean forearc (e.g., Benavente et al, ; Hall et al, ), motion on these faults is small compared to slip on the megathrust.…”

Deciphering the Late Cretaceous‐Cenozoic Structural Evolution of the North Peruvian Forearc System

“…From sea to land, these systems are classically composed of a distal trench basin, an outer subduction wedge, including a frontal accretionary prism and a middle prism (structural high) overlapped by trench slope basins, and an inner crustal wedge corresponding to the orogenic wedge/magmatic arc overlapped by a forearc depocenter (Bailleul et al, ; Noda, ). Modern forearc systems are tectonically active and associated with faulting, vertical motions, and volcanism, and they are the site of largest and most destructive earthquakes and tsunamis (e.g., Benavente et al, ; Bilek, ; Hall et al, ; Saillard et al, ; Schurr et al, ; Villegas‐Lanza et al, ). Although it is widely accepted that forearc deformation is the product of both compressional and extensional tectonics (Noda, ), the temporal and spatial variations as well as the origin of these tectonics mechanisms are still poorly understood.…”

Boron Industry, Sources, and Evaporitic Andean Deposits: Geochemical Characteristics and Evolution Paths of the Superficial Brines

“…A striking characteristic of this area in southern Peru and northern Chile is the extreme aridity that has prevailed for several million years [25]. Due to this longlived hyperaridity, the regional landscape experienced extremely low denudation rates (<0.5 m Ma À1 ), as supported by several cosmogenic nuclide studies [26,27] in southern Peru and in northern Chile [25,28,29], allowing a long-term preservation of geomorphology [30].…”