Quaternary normal and reverse faulting and the state of stress in the central Andes of south Peru

Abstract

Field studies in the Andes of southern Peru show that in the High Andes and Pacific Lowlands, Quaternary and Recent faults are normal. This extensional tectonics postdates compressional deformations of Pliocene‐early Quaternary age. In the sub‐Andes the observed deformations are compressional; they affect early Quaternary deposits. Some of the faults separate Quaternary deposits from the bedrock and thus are clearly of tectonic origin and not landslide effects. Striations on the fault planes indicate N–S trending extension in the High Andes and Pacific Lowlands. The total amount of crustal stretching is small, probably of the order of 1% during the last 1–2 m.y. In the sub‐Andes, folds and faults affecting Neogene and early Quaternary deposits result from N–S shortening. Nevertheless, it is supposed that this N‐S shortening is of early quaternary age. The present‐day compression probably strikes E‐W, judging from focal mechanisms in the sub‐Andes of central Peru, southern Bolivia, and northwest Argentina. Data from structural analysis of faults and from earthquake focal mechanisms allow us to surmise the state of stress in the Andes of southern Peru. The High Andes and Pacific Lowlands, subjected to N‐S trending extension, are bounded by two zones of E‐W trending compression: the sub‐Andes to the east, and the contact between the convergent Nazca and South America plates to the west. In our model the maximum horizontal compressive stress trajectory σ Hmax is roughly parallel with the E‐W convergence between the two plates; σ Hmax corresponds to σ 1, in the sub‐Andes and to σ 2 in the High Andes. The latter situation is caused by the elevated mass of the High Andes, where σ zz (the vertical stress) is inferred to be σ 1. Thus the third principal stress axis, being orthogonal to the other two axes, it is oriented N‐S, allowing extension to occur in that direction. On the other hand, in the sub‐Andes σ zz is σ 3, and horizontal E‐W shortening occurs. The state of stress in the Andean continental crust above the 30° dipping slab appears to be different from that in the Andes of Central Peru situated above the flat subducting segment. In this region, compressional deformantion affect a wider part of the Cordillera.

Tectonic and climatic controls on the Chuquibamba landslide (western Andes, southern Peru)

“…Local reverse and normal apparent surface movements are known to occur along major strike-slip faults in the forearcs of northern Chile (Victor et al, 2004) and southern Peru (Hall et al, 2012). The present-day main sinistral strike-slip kinematics of the Incapuquio fault system demonstrated by the seismicity is compatible with normal apparent displacements as observed by Schildgen et al (2009) and Sébrier et al (1985Sébrier et al ( , 1988.…”

“…In southern Peru, the Incapuquio fault zone has a strong geomorphic imprint on the Andean range (Huaman, 1985;Sébrier et al, 1985). Based on microtectonic studies, Sébrier et al (1985Sébrier et al ( , 1988 and Schildgen et al (2009) identified different kinematic episodes.…”

“…Starting at ∼ 9-10 Ma, these units were incised by 1-3 km deep canyons that strike perpendicular to NW-SE-striking range (Schildgen et al, 2007(Schildgen et al, , 2009Thouret et al, 2007;Gunnell et al, 2010). The Western Cordillera and Pacific piedmont are affected by Quaternary tectonic deformation mainly expressed in the Western Cordillera by an active fault system striking parallel to the range (Sébrier et al, 1985;Hall et al, 2008Hall et al, , 2012 (Fig. 2).…”

“…Based on microtectonic studies, Sébrier et al (1985Sébrier et al ( , 1988 and Schildgen et al (2009) identified different kinematic episodes. Sébrier et al (1985Sébrier et al ( , 1988 defined major Tertiary and early Quaternary compressional phases and a minor late Quaternary episode of normal faulting. Schildgen et al (2009) proposed that a Tertiary episode of strike-slip and normal faulting occurred between 14 and 2.2 Ma.…”

Deformation and seismicity near Sabancaya volcano, southern Peru, from 2002 to 2015

“…The most recent eruption of Sabancaya spanned 1990-1998, following about 200 years of dormancy [Gerbe and Thouret, 2004]. The volcano is surrounded by an extensive system of active faults and lineaments (Figure 1c)-the Huambo-Cabanaconde Fault Zone to the northwest, which is composed of the Trigal and Solarpampa normal faults and minor subparallel faults; the Ichupampa normal fault to the northeast; the Pampa Sepina fault zone and Sepina lineament to the east; and the Huanca normal fault to the southwest [Sebrier et al, 1985;Mering et al, 1996;Huamán-Rodrigo et al, 1993;Macharé et al, 2003].…”