Outer forearc high control in an erosional subduction regime: The case of the central Peruvian forearc (6–10°S)

Marie-Catherine Genge (1, 2) , César Witt (1) , Frank Chanier (1) , Jean-Yves Reynaud (3, 1) , Ysabel Calderon

1 LOG - Laboratoire d’Océanologie et de Géosciences (LOG) - UMR 8187
2 Unipd - Università degli Studi di Padova = University of Padua
3 Université de Lille

The forearc of the North-Central Peruvian Andes (FNCPA, 6–10°S) provides an exceptional opportunity to study the long-term processes that affect a convergent plate boundary. First, it shows long-term subsidence, depocenter superimposition and individualization. Second, although being mostly extensional and characterized as a typical erosive margin, the FNCPA shows complex uplifted regions. Older deformation is expressed by basement horst and grabens disposed in a complex geometry which onset may have resulted from strike-slip tectonics. A long-lived episode of regional subsidence affected the forearc and led to the relatively thick and regional deposition of the lower Miocene series coeval with a significant increase of the convergence velocity. This period was followed by an episodic uplift of trench-parallel corridors along the so-called Main Deformation Zone. Uplift ceased through the late Miocene and restarted during Pliocene and Quaternary, generating accommodation space by basin flank uplift for a forearc depocenter characterized by landward tilted strata. Significant along-strike differences in the degree of uplift resulted in either uplifting series producing sharp seaward dipping erosional surfaces or less uplifted areas covered by seawards prograding clinoforms. As a consequence of the shallow-water marine setting, the seismic strata geometry, lateral extent and thickness of the deposits for the Neogene successions in the FNCPA have been also tightly controlled by accommodation changes. Uplift is uneven along-strike independently of fault direction and closely followed the increase of the subsidence of the continental slope produced by subduction-erosion. Therefore, sediment underplating seems the most appropriate mechanism at the origin of uplift; as observed in other parts of the Peruvian and Chilean margins. Although the erosive character of the margin, the effects on basin geometry of the raised zone resemble that of typical outer forearc highs in accretionary margins such as in the Kumano basin in Japan.

Domaines: Planète et Univers [physics]

Marie-Catherine Genge, César Witt, Frank Chanier, Jean-Yves Reynaud, Ysabel Calderon. Outer forearc high control in an erosional subduction regime: The case of the central Peruvian forearc (6–10°S). Tectonophysics, 2020, 789, pp.228546. ⟨10.1016/j.tecto.2020.228546⟩. ⟨insu-03093929⟩