[1] The western flank of the Central Andean Plateau is a crustal-scale monoclinal fold, expressed in the geomorphology and in the westward tilt of fore-arc basin strata. Data from three fore-arc basins quantify the magnitude and time of displacement of the plateau system relative to the fore arc. From 18°30′S to 22°S there is a single monocline strand. There, other authors documented ∼2000 m (±500 m) of early and middle Miocene structural relief growth across small-scale monoclines, and our data reveal 810 m (±640 m) of ∼11-5 Ma relief growth and 400 m (±170 m) relief growth since ∼5 Ma across a long-wavelength monoclinal fold limb. This structural relief growth since ∼11 Ma approximates the topographic relief growth between the fore arc and the Altiplano plateau. From 22°S to 24°S there are two subparallel long-wavelength monoclines. Structural relief on the east side of the fore arc increased by 2840 m (±2510 m) during ∼17-10 Ma and by 2320 m (±1050 m) since ∼10 Ma.

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The Famatina belt, southern central Andes, records a circa 470 m.y. shortening episode (Ocloyic orogeny) affecting the peri‐Gondwanan back arc basin in response to the accretion of the Precordillera terrane. Collision created distinct features across and along the margin, some of which persisted into the present Andean structure. From east to west, the Ocloyic deformation is recorded across the telescoped region of Famatina, represented by (1) an east vergent fold‐thrust belt (EVFTB) involving a major angular unconformity between Early and Middle Ordovician rocks, (2) a highly deformed volcano‐sedimentary belt, and (3) an east vergent ductile shear zone affecting Famatinian granites. Axis attitudes of Ordovician refolded anticlines in the EVFTB show west‐east tectonic transport, in agreement with kinematics of Ocloyic high‐strain belts, indicating shortening orthogonal to the present Pacific margin. Eastward displacement of the Ordovician volcanic arc at ∼27°S latitude together with a documented sinistral slip zone across the proto‐Andean margin suggests tectonic indentation.

Convection in the Earth's mantle is mainly driven by cold, dense subducting slabs, but 15 relatively little is known about how 3D variations in slab morphology and buoyancy 16 affect mantle flow or how the surface above deforms in response (i.e. dynamic 17 topography). We investigate this problem by studying the dynamics of an active region of 18 flat-slab subduction located in Peru in South America. Here the slab geometry is well 19 known, based on the regional seismicity, and we have observations from the local 20 geological record to validate our models. Of particular interest is the widespread 21 subsidence and deposition of the Solimões Formation across western Amazonia that This formation covers an extensive area from the foredeep to the Purus Arch located 24 ~2 000 km away from the trench. Close to the Andes the preservation of several 25 kilometers of sedimentary thicknesses can be easily accounted for by flexure. Based on 26 an estimate of the Andean loading we predict 2.8 to 3.6 km of accommodation space that 27 spans 100 km. The spatial and temporal history of the Solimões Formation however, 28 particularly the thick distal foreland accumulations up to 1.2 km deep, can only be 29 matched with the addition of a longer-wavelength dynamic source of topography. 30 Following the transition from normal to flat subduction, we predict over 1 km of dynamic 31 subsidence (~1500 km wide) that propagates over 1000 km away from the trench, 32 tracking the subduction leading edge. This is followed by a pulse of dynamic uplift over 33 the flat segment behind it. We therefore propose that a combination of uplift, flexure and 34 dynamic topography during slab flattening in Peru is responsible for the sedimentation 35 history and landscape evolution of western Amazonia that eventually led to the 36 configuration of the Amazon Drainage Basin we know today.

In the distal region of the modern flat‐slab segment in the southern Central Andes, an unusual stack of middle Miocene paleosols together with regional upwarping and normal faulting indicate episodic aggradation and condensed sedimentation contemporaneous with the principal stage of foreland basin development associated with foreland flexure farther to the west. These features are consistent with development of a forebulge zone during the early stages of a proposed asymmetric foreland basin system. Sedimentary thickness farther east and far from the Cordilleran tectonic loads suggests accommodation and preservation driven by “nonisostatic” dynamic subsidence. Regional overlapping relationships and basin modeling suggest that the Modern broken foreland (present Sierras Pampeanas) can be interpreted as a reactivation of a formerly partitioned broad forebulge.

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Subduction exerts a strong control on surface topography and is the main cause of large vertical motions in continents, including past events of large-scale marine flooding and tilting. The mechanism is dynamic deflection: the sinking of dense subducted lithosphere gives rise to stresses that directly pull down the surface. Here we show that subduction does not always lead to downward deflections of the Earth's surface. Subduction of young lithosphere at shallow angles (flat subduction) leaves it neutrally or even positively buoyant with respect to underlying mantle because the lithosphere is relatively warm compared with older lithosphere, and because the thickened and hence drier oceanic crust does not undergo the transformation of basalt to denser eclogite. Accounting for neutrally buoyant flat segments along with large variations in slab morphology in the South American subduction zone explains alongstrike and temporal changes in dynamic topography observed in the geologic record since the beginning of the Cenozoic. Our results show that the transition from normal subduction to slab flattening generates dynamic uplift, preventing back-arc marine flooding.

In Famatina, at the modern northern fl atslab segment of the Central Andean belt, synorogenic conglomerate facies provide a unique opportunity to reconstruct paleogeography and tectonic setting. Stratigraphically constrained provenance analyses record a multievent history of the Andean foreland and a complex pattern of exhumed uplands, which, in turn, controlled the depocenter history. Western and eastern sources can be differentiated. The western domain was composed of equigranular granitoids and lower and upper Paleozoic volcano-sedimentary and sedimentary units, whereas the eastern domain was mainly formed by porphyrytic granitoids and minor slightly metamorphosed lower Paleozoic clastic rocks. The surrounding regions expose medium-to high-grade metamorphic rocks, which are not recorded in any Cenozoic conglomerate of Famatina. Unroofi ng sequences can be deduced from the compositional trends. Conglomerate composition and paleocurrent data show input from intrabasinal sources and important participation of basement since the beginning of the Neogene. We infer an early Miocene broken foreland during deposition of the Del Crestón Formation. A signifi cant source inversion, with clasts supplied from the eastern basement domain, is recorded ~2000 m from the base, within the middle Miocene Del Abra Formation; reactivation of western granitic thrust sheets occurred by the late middle Miocene and late Miocene, as indicated by provenance studies of the Santo Domingo and El Durazno Formations. In contrast to simple asymmetric foreland models, provenance analysis documents early participation of crystalline rocks, suggesting early development of intraforeland basement highs within the southern Central Andes. At a regional scale, basement thrusting and associated intermontane basin development were diachronous. This interpretation is supported by broad propagation of basement thrusting from the northern Sierras Pampeanas (and Famatina) toward the central and eastern Sierras Pampeanas between early-middle Miocene and late Miocene-Pliocene time. Early Miocene reconstructions of the Juan Fernandez Ridge position on the Central Andean margin suggest that during this interval, shallow subduction was likely unrelated to oceanic plateau subduction under the Sierras Pampeanas.