Geomorphic evidence for recent uplift of the Fitzcarrald Arch (Peru): A response to the Nazca Ridge subduction

Abstract

The 400 000 km 2 -wide Fitzcarrald Arch constitutes a wide topographic high of the Amazon Basin against the central Andes. In order to constrain its formation mechanisms and in particular to test its relationships to the Nazca ridge subduction, a quantitative geomorphology analysis of the Arch is performed using hypsometric integrals, elongation and azimuths of 7th-and 5th-order catchments. They all express a trend from high maturity to low maturity from NW towards SE. This maturity gradient coupled with the local drainage direction demonstrate that the Fitzcarrald Arch is not a 'classical' alluvial fan, since its apex is located 100 km east to the Subandean Thrust Front and the corresponding sedimentary pile is lacking. Nor is the Arch the superficial expression of an inherited transfer zone, because its geomorphic shape is radial and it does not diverge from a symmetry axis; moreover, such a reactivated structure is not found at depth on seismic profiles. In addition, our data show that underlying geomorphic control on catchment initiation and development has progressed from NW to SE, which in combination with the observation of crustal doming by Espurt et al. [Espurt, N., Baby, P., Brusset, S., Roddaz, M., Hermoza, W., Regard, V., Antoine, P.O., SalasGismondi, R., Bolaños, R., 2007. How does the Nazca Ridge subduction influence the modern Amazonian foreland basin? Geology 35, 515-518.] suggests that this relief is caused by the eastward sliding of the buoyant Nazca ridge beneath the South American lithosphere.

Landscape-scale changes in forest structure and functional traits along an Andes-to-Amazon elevation gradient

“…1). Higher elevations are usually associated with steeper slopes in tectonically active areas, consistent with coarser resolution data for the region (e.g., Regard et al, 2009). These threshold changes in topography were, to some extent, expressed in non-systematic changes in canopy functional traits.…”

Fluvial geomorphic elements in modern sedimentary basins and their potential preservation in the rock record: A review

“…At the distal 746 end of the DFS, a dendritic tributary drainage pattern is observed where incision from uplift of the 747 Fitzcarrald Arch extending beneath the DFS is taking place (Fig. 21; Dumont 1996; Regard et al 2009). 748 Accordingly, theactive channel and radial paleochannels have been incised and sit inside small valleys; 749 thus rivers are confined to these valleys through this portion of the uplifted DFS.…”

Neotectonics, flooding patterns and landscape evolution in southern Amazonia

“…It has been hypothesized that the Fitzcarrald Arch is the projection to the surface of a buoyant flat slab resulting from the subduction of the Nazca Ridge (Espurt et al, 2008). The formation of the flat slab about 4 Myr ago would have brought about the back-arc uplift of the Fitzcarrald Arch (Espurt et al, 2007(Espurt et al, , 2008Regard et al, 2009). The LM constitutes the foredeep of the southern Amazonian foreland basin.…”