Crustal-scale block tilting during Andean trench-parallel extension: Structural and geo-thermochronological insights

Abstract

Despite a long history of plate convergence at the western margin of the South American plate that has been ongoing since at least the Early Paleozoic, the southern Peruvian fore‐arc displays little to no evidence of shortening. In the light of this observation, we assess the deformation history of the southern Peruvian fore‐arc and its geodynamic implications. To accomplish this, we present a new structural and geo‐thermochronological data set (zircon U‐Pb, mica 40Ar/39Ar, apatite and zircon fission‐track and zircon (U‐Th)/He analyses) for samples collected along a 400 km long transect parallel to the trench. Our results show that the Mesoproterozoic gneissic basement was mainly at temperatures ≤350°C since the Neoproterozoic and was later intruded by Jurassic volcanic arc plutons. Along the coast, a peculiar apatite fission‐track age pattern, coupled with field observations and a synthesis of available geological maps, allows us to identify crustal‐scale tilted blocks that span the coastal Peruvian fore‐arc. These blocks, bounded by normal faults that are orthogonal to the trench, suggest post‐60 Ma trench‐parallel extension that potentially accommodated oroclinal bending in this region. Block tilting is consistent with the observed and previously described switch in the location of sedimentary sources in the fore‐arc basin. Our data set allows us to estimate the cumulative slip on these faults to be less than 2 km and questions the large amount of trench‐parallel extension suggested to have accommodated this bending.

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

“…Furthermore, documented knickpoints in the river profiles of the northern Chilean fore arc are an indicator of transient topography (e.g., Cooper et al, 2016; Hoke et al, 2007). Vertical fault motion could imprint local changes in exhumation and has been demonstrated to be the case in southern Peru (Noury et al, 2016). Our limited distribution of samples across individual faults precludes any meaningful calculation of fault kinematic history.…”

Possible threshold controls on sediment grain properties of Peruvian coastal river basins

“…Since the number and altitude of the terraces increases closer to the area where the Nazca ridge currently subducts, uplift of the coastal area in a radius of approximately 200 km around the ridge (roughly 12 to 14 • S latitude) is attributed to ridge subduction (Sébrier et al, 1988;Macharé and Ortlieb, 1992). Between 15 and 18 • S latitude, uplift is associated with bending of the Bolivian orocline (Noury et al, 2016). The area south of 12 • S latitude is also the segment of the Andes in which the number of earthquakes with magnitudes > 4 has been larger relative to the segment farther north (Figs.…”

Response of a Rheologically Stratified Lithosphere to Subduction of an Indenter‐Shaped Plate: Insights Into Localized Exhumation at Orogen Syntaxes

“…(a) Predicted apatite fission track (AFT) ages for model 11 characterized by weakly coupled rheological structure and no upper plate advance contribution ( V Adv = 0%) in the total shortening and relatively narrow indenter width (150 km). (b–d) measured thermochronological cooling ages: (b) the Southeast Alaska (Arkle et al, ; Benowitz et al, , ; Ferguson et al, ; Haeussler et al, ; O'Sullivan et al, ; Plafker et al, ; Spotila et al, ); (c) the Olympic Mountains of the Cascadia subduction zone (Brandon et al, ; Currie & Grist, ; England et al, ; Johnson et al, ; Reiners et al, ); and (d) the South American subduction zone (Andriessen & Reutter, ; Avdievitch et al, ; Barnes et al, ; Gunnell et al, ; Juez‐Larré et al, ; Maksaev & Zentilli, ; McInnes et al, ; Noury et al, ; Schildgen et al, , ; Wipf, ; Wipf et al, ). White circles indicate the concentric zones of vertical advection (bull's‐eye pattern) in the modeled (a) and observed (b, c) AFT ages fields.…”