Interactions between sedimentation and deformation in the Kumano forearc basin (Japan) and the Malargue foreland basin (Argentina)

Forearc and foreland basins are ubiquitous along most convergent plate boundaries, with the geometries and contents of their sedimentary packages representing a direct record of the processes that control plate subduction and orogen growth. This project evaluates the evolution of a forearc basin in the Nankai margin of southwest Japan, and a foreland basin in western Argentina, with the ultimate goal of improving our understanding of how large-scale sedimentary systems respond to regional tectonic inputs, such as changes in plate convergence rate and subducting slab angle. The sediments of what today constitutes the Kumano forearc basin began depositing during the Pliocene in a thrust-bound, actively deforming outer accretionary wedge setting. 3D reflection seismic analysis allows to define a series of unconformity-bound packages that represent the dynamic and gradual stabilization of the inner portion of the wedge, ultimately leading to fast forearc sedimentation since ~2 Ma. The process of wedge stabilization was linked to activity along a large out-of-sequence thrust that bounds the forearc basin on its seaward side. U-Pb detrital zircon provenance results, interpreted using multidimensional scaling (MDS), show that within both the basin and the upper accretionary prism sediments were largely sourced from local rivers flowing into the Nankai margin. During the late Miocene, prism sediments had a dominant source similar to the modern Yodo River, suggesting a period of highly oblique subduction and diminished frontal accretion. Upon Pliocene forearc basin initiation, terrigenous input from the Kumano River accounted for most of the basin fill, with secondary contributions from possible reworked upper accretionary prism sediments and longitudinal gravity flows transporting sediment from rivers located farther to the northeast. These sediment provenance results highlight the highly variable distribution –both in time and space- of wedge-top sedimentation in accretionary systems, which recent work has shown may be a critical factor controlling the internal structure of submarine accretionary wedges. In the Malargüe basin, Neogene synorogenic sediments show that modern Andean fold-thrust belt (FTB) tectonic inversion and regional uplift began at ~20 Ma with the deposition of the Agua de la Piedra Formation. The younger, ~10.5 Ma Loma Fiera formation represents a second event of regional compression characterized by a shift toward coarser, cobble-dominated conglomeratic facies. It coincides with a marked increase in volcanic activity in the frontal sector of the FTB, and with evidence of generalized slip along several thick- and thin-skin structures, suggesting a possible linkage with a flat-slab event that may have simultaneously affected an over 200 km long segment of the fold-thrust belt during the mid-late Miocene.