Tectonic record of strain buildup and abrupt coseismic stress release across the northwestern Peru coastal plain, shelf, and continental slope during the past 200 kyr

Abstract

[1] This paper presents a combined analysis of geological and geophysical data collected both onshore and offshore along the northwestern Peru forearc area (3°30 0 -7°30 0 S), from the coastal plain to the trench axis. Onshore, geomorphic analysis places constraints on the relative importance of eustatic versus tectonic factors in preserving and modifying the uplifted coastal landforms along the coastal plain. Breaking-wave morphologic markers were dated using the in situ produced 10 Be cosmonuclide. The data document a tectonic segmentation, allowing us to differentiate two areas with regard to their evolution through time: the northern Cabo Blanco and the southern Paita-Illesca segments. For the past 200 kyr, both segments uplifted at high rates of 10 to 20 mm yr À1 through tectonic pulses coeval with the eustatic deglacial sea level rises of isotope stage 1 and warm isotope substage 5e, respectively. The uplift and related extensive emersion of the coastal plain require high coupling along the subduction zone and/or underplating at depth. Offshore, industry-acquired reflection seismic lines combined with EM12 bathymetric data allow us to investigate the tectonic regime and deformation of the continental margin and shelf. Major dipping seaward detachments control the long-term subsidence of this area. These main tectonic features define a tectonic segmentation. The Talara, Paita, and Sechura segments are identified from north to south. No clear tectonic correlation in time exists between the onshore and the continental margin segmentations, or in space either. The longterm subsidence of the offshore, indicative of subduction erosion working at depth, requires low coupling along the subduction channel at depth. The distribution of permanent deformation along the northern Peru forearc area includes long-term uplift along the coastal plain and long-term subsidence along the continental margin, the neutral line being located within the 10 km seaward from the Present coastline. An extensive sequence of raised marine cliffs and associated notches evidences that the most recent uplift step (20-23 ka to Present) along the Cabo Blanco segment is related to a sequence of major earthquakes. We infer that eustacy exerts important feedback coupling to the seismogenic behavior of the North Peru subduction zone. We speculate that during sea level fall, pore fluid pressure diminishes along the subduction channel inducing a possible seaward migration of the locked zone (i.e., migration of the updip limit) reaching a maximum by the end of the eustatic low stand. During eustatic sea level rise, pore fluid pressure increases along the subduction channel. This in turn is capable of weakening the previously locked zone along the plate interface beginning an earthquake sequence. Earth's orbital variations are a potential external cause that may control the physical processes at work along plate interface.

A Review on Tectonic Record of Strain Buildup and Stress Release across the Andean Forearc along the Gulf of Guayaquil-Tumbes Basin (GGTB) near Ecuador-Peru Border

“…Subsequently, similar inference was suggested [2]. To the west, no evidence exists for the Tumbes-Zorritos detachment system to extend west of Banco Peru [23]. As opposed to the GGTB northern edge the Tumbes-Zorritos detachment system exhibits a pervasive tectonic activity at Present including strong signature along trace at seafloor.…”

“…The main geologic and tectonic features of the GGTB ( Figure 5) were identified on the basis of industrial multichannel seismic reflection profiles and well data [4,23,24]. The Pliocene series show no significant variations in thickness throughout the GGTB area suggesting that no significant tectonic deformation occurred from 5.2 to 1.8 -1.6 Ma, in association with a widespread and moderate subsidence.…”

“…These boundaries and tectonic evolution have been described in great details [4,23,28,29]. Only the main points are reminded here.…”

“…Along Southern Ecuador [20] and Northern Peru [17,[21][22][23]31] the Lower and the Upper slopes of the continental margin evolved controlled by normal faults and detachments. Off Northern Peru, these N-S trending tectonic features parallel the trench axis extending upslope to the continental shelf break area.…”

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

“…2c). Only in northernmost Peru (4 to 6 • S latitude) is uplift of the coastal area associated with subduction-induced earthquakes (Bourgois et al, 2007). Further south, the Cordillera Blanca area (around 12 • S latitude) may have been uplifted due to upwelling of magma (McNulty and Farber, 2002).…”