Punctuated shortening and subsidence in the Altiplano Plateau of southern Peru: Implications for early Andean mountain building

Abstract

Sedimentologic, provenance, geochronologic, and magnetostratigraphic results from clastic nonmarine deposits in the northern Altiplano Plateau of southern Peru (14-15°S) demonstrate late Eocene-Oligocene (37-26 Ma) accumulation of the >4-km-thick San Jerónimo (Puno) Group within a retroarc foreland basin related to early Andean shortening and crustal thickening. Punctuated Oligocene (29-26 Ma) displacement along deep-seated contractional structures, as revealed by growth stratal relationships, abruptly partitioned this regional flexural basin and established the structural boundaries of the smaller intermontane Ayaviri Basin, which continued to evolve in a hinterland setting during late Oligocene-Miocene shortening. This brief episode of shortening along the Altiplano-Eastern Cordillera boundary is correlated with exceptionally rapid sediment accumulation (>1100-1800 m/m.y.), tightly constrained to 30-28 Ma on the basis of U-Pb geochronology and magnetic polarity stratigraphy. Provenance data from detrital zircon U-Pb age populations and sandstone compositions indicate derivation from a complex belt of Paleogene shortening and probable basin inversion in the Western Cordillera that was subsequently overprinted by Andean arc magmatism. This early Andean zone is interpreted as the along-strike continuation of the better-exposed Marañon fold-thrust belt to the north (5-13°S) and a proposed belt of shortening to the south along the Chilean Precordillera and Western Cordillera of Bolivia and northern Argentina (17-25°S). Subsequent focusing of late Oligocene shortening along the Eastern Cordillera-Altiplano boundary may have been linked to shallowing of the subducting slab and potential reactivation of crustal anisotropies.

Peruvian Altiplano Stratigraphy Highlights Along‐Strike Variability in Foreland Basin Evolution of the Cenozoic Central Andes

“…Lithofacies codes were grouped into five lithofacies associations to aid interpretation of depositional environments. Associations are similar to those presented in Perez and Horton () and Horton et al (), as their study areas along strike to the south (Figure c) share many similar stratigraphic characteristics and to Altiplano strata in general (e.g., Hampton & Horton, ).…”

“…Mixture modeling further highlights the important role sediment recycling plays in this region. The presence of an angular unconformity from 23 to 9 Ma is consistent with previously documented periods of deformation along strike to the south (Horton et al, ; Perez & Horton, ). When combined with sediment provenance indicators, results are consistent with the development and northeastward migration of a flexural foreland basin system (sensu DeCelles & Giles, ).…”

“…Details of this system provide predictive power for local and regional geodynamic processes, in particular the timing and location of hinterland loading due to crustal thickening and/or surface uplift in the Western Cordillera, and basin subsidence to the east. Further, results provide a comparison to previously documented foreland systems in the modern Altiplano and Eastern Cordillera along strike to the south (e.g., DeCelles et al, ; DeCelles & Horton, ; Horton et al, , , ) and reveal an apparent southward younging in the onset of high sedimentation and accommodation rates resulting in thicker stratigraphic packages later in the process of foreland basin system evolution. Finally, consideration of the results of this research in the context of published records of magmatism, igneous geochemistry, and limited records of crustal shortening and surface uplift collectively supports models calling on cyclical orogenic processes (e.g., DeCelles et al, , ; Ramos, ; Ramos et al, ), but highlights major temporal differences in the onset and tempo of cyclicity along orogenic strike.…”

“…Despite hosting a nearly complete record of Cenozoic strata chronicling the mountain building history of the central Andes, the northernmost Altiplano of southern Peru has received less research focus compared to its central and southern counterparts in Bolivia, Chile, and Argentina (e.g., Carrapa et al, ; DeCelles & Horton, ; Horton et al, , ; Newell, , ). While recent work in southern Peru has focused on the Eocene‐Miocene sedimentary record by highlighting prolonged basin subsidence, episodes of punctuated deformation, and a broadly similar structural style of deformation and basin development to the Altiplano of Bolivia (Carlotto, ; Horton et al, ; Perez & Horton, ), geodynamic implications of foreland basin system development in the northernmost reaches of the Peruvian Altiplano have not been thoroughly addressed.…”

Tectonic Regimes of the Central and Southern Andes: Responses to Variations in Plate Coupling During Subduction

“…Spatially dissimilar records reveal a complex Paleogene history in which shortening in the northern transect overlapped with quiescence and upper crustal extension in the central and southern transects. Whereas the central Andes at 15–25°S shows a clear record of retroarc shortening in the 35–20 Ma window (Allmendinger et al, ; Carrapa & DeCelles, , ; Elger et al, ; Horton, , ; Horton et al, ; Müller et al, ; Oncken et al, ; Perez & Horton, ), regions south of ~28°S registered foreland quiescence with concurrent hinterland extension (Horton et al, ; Litvak et al, ; Winocur et al, ). Essential in this reconstruction is the profound along‐strike change from an extensional to a contractional record, with an apparent transition in the 20–30°S sector (Fosdick et al, ; Horton & Fuentes, ; Jordan et al, ).…”