Stress field evolution above the Peruvian flat-slab (Cordillera Blanca, northern Peru)

Abstract

8In subduction settings, the tectonic regime of the overriding plate is closely related to the 9 geometry of the subducting plate. Flat-slab segments are supposed to increase coupling at the 10 plate interface in the Andes, resulting in an increase and eastward migration of the shortening 11 in the overriding plate. Above the Peruvian flat-slab, a 200 km-long normal fault trend 12 parallel to the range and delimits the western flank of the Cordillera Blanca. In a context of 13 flat subduction, expected to produce shortening, the presence of the Cordillera Blanca normal 14 fault (CBNF) is surprising. We performed a systematic inversion of striated fault planes in the 15 Cordillera Blanca region to better characterize the stress field above the Peruvian flat-slab. It 16 evidences the succession of different tectonic regimes. NE-SW extension is predominant in 17 most of the sites indicating a regional extension. We suggest that the Peruvian flat-slab trigger 18 extension in the Western Cordillera while the shortening migrated eastward. Finally, we 19propose that flat-slab segments do not increase the coupling at the trench neither the 20 shortening in the overriding plate but only favor shortening migration backward. However, 21 the stress field of the overriding plate arises from the evolution of plate interface properties 22 through time due to bathymetric anomaly migration. 23 24 Key-works 25Inversion of striated fault planes; crustal stress field; mountain building; Peruvian flat-slab; 26 Cordillera Blanca 27 28

Cenozoic Shift From Compression to Strike‐Slip Stress Regime in the High Andes at 30°S, During the Shallowing of the Slab: Implications for the El Indio/Tambo Mineral District

“…Our results are in agreement with the conclusion proposed by Margirier et al () who documented extension perpendicular to the trench during the flattening of the slab in the Peru flat‐slab segment and challenged the idea that a flat‐slab geometry increases plate coupling and induces compression in the upper plate. Here we propose that other factors controlling the location of compression in the upper plate and migration of the thrust front toward the foreland is the thickening of the crust, which may favor a change from compression to strike‐slip regime independent of the subduction geometry.…”

Sedimentología y Estructura del Complejo de la Morrena Laterofrontal de la Laguna Palcacocha en la Cordillera Blanca, Perú

“…Situated at the head of this valley is Lake Palcacocha, which is dammed by a large laterofrontal moraine (Figures 3 and 4). The Cojup Valley walls are composed primarily of intrusive granodiorites and granites that make up a regional batholith (Margirier et al, 2017). The lower sections of the valley walls dip at angles of 30-40° due to the accumulation of talus deposits at their bases, but steepen to 60-80° on the upper rock faces.…”

“…Localized pockets of better-sorted clasts also occur in this zone. They are most likely sourced from the regional batholith and are composed predominantly of granodiorite (Margirier et al, 2017). The SE lateral limb also contains an abundance of clasts coated in iron oxides ( Figure 13B), which are absent in the NW lateral limb and indicate a different sediment source ( Figure 12B).…”

“…Tropical glaciers, glacial bodies that form within the latitudes of ±23.5˚, are particularly sensitive to climatic pressures, and thus exhibit relatively rapid responses to shifts in temperature and humidity (Rodbell, Smith and Mark, 2009). Their occurrence depends on their altitude of formation: the extreme uplift of the Andes during the last 5.4 million years elevated the mountain peaks upwards of 6000 m (Margirier et al, 2017), enabling the formation and growth of glaciers despite the warmer tropical climates at lower altitudes (Clapperton, 1972). However, increases in humidity and temperature since the early 18 th century have caused these glaciers to retreat (Rabatel et al, 2013).…”

Role of erosion and isostasy in the Cordillera Blanca uplift: Insights from landscape evolution modeling (northern Peru, Andes)

“…The CBNF trends parallel to the Andean range and is the most spectacular normal fault in the Andes [Fig. 1;Margirier et al, 2017]: the CBNF is ~200 km long and shows ~7 km of vertical offset in total [Margirier et al, 2016], it has been active since ~5.4 Ma [Bonnot, 1984;Giovanni, 2007]. The CBNF is located above the Peruvian flat-slab [Barazangi and Isacks, 1976], a section of the convergent plate boundary between the Nazca Plate and the South American Plate characterized today by near-horizontal subduction geometry.…”