Retroarc basin reorganization and aridification during Paleogene uplift of the southern central Andes

Abstract

Tectonic development of the Andean Cordillera has profoundly changed the topography, climate, and vegetation patterns of the southern central Andes. The Cenozoic Bermejo Basin in Argentina (~30°S) provides a key record of thrust belt kinematics and paleoclimate south of the high‐elevation Puna Plateau. Ongoing debate regarding the timing of initiation of upper plate shortening and Andean uplift persists, precluding a thorough understanding of the earlier tectonic and climatic controls on basin evolution. We present new sedimentology, detrital geochronology, sandstone petrography, and subsidence analysis from the Bermejo Basin that reveal siliciclastic‐evaporative fluvial and lacustrine environments prior to the main documented phase of Oligocene‐Miocene shortening of the Frontal Cordillera and Argentine Precordillera. We report the first radiometric dates from detrital zircons collected in the Ciénaga del Río Huaco Formation, previously mapped as Permian, that constrain a Late Cretaceous (~95–93 Ma) maximum depositional age. Provenance and paleocurrent data from these strata indicate that detritus was derived from dissected arc and cratonic sources in the north and northeast. Detrital zircon U‐Pb ages of ~37 Ma from the overlying red beds suggest that foredeep sedimentation began by at least the late Eocene. At this time, sediment dispersal shifted from axial southward to transversal eastward from the Andean Arc and Frontal Cordillera. Subsidence analysis of the basin fill is compatible with increasing tectonic deformation beginning in Eocene time, suggesting that a distal foredeep maintained fluvial connectivity to the hinterland during topographic uplift and unroofing of the Frontal Cordillera, prior to Oligocene‐Miocene deformation across the Precordillera.

Thermochronologic Evidence for Late Eocene Andean Mountain Building at 30°S

“…We interpret the two episodes of rapid cooling to reflect exhumation associated with the two main tectonic events that occurred in this part of the Andes during the Cenozoic. Our data support a Eocene contractional phase previously hinted at by indirect structural evidence (Pineda & Emparán, ), reconnaissance thermochronology (Cembrano et al, ; Rodríguez, ), and retroarc basin provenance analyses (Fosdick et al, ). Exhumation rate estimates for this compressional phase is on the order of 250–300 m/Myr.…”

“…In the Bermejo foreland basin and related intermontane basins within and adjacent to the Argentine Precordillera (Figure a), Neogene foredeep deposits linked with the Miocene deformation are well recognized (Jordan et al, ) and Eocene to early Oligocene foredeep deposits were absent. However, recent detrital zircon maximum depositional ages from Fosdick et al () and Suriano et al () reveal Eocene to early Oligocene ages for red beds and eolian deposits, previously interpreted as Permo‐Triassic (Borello & Cuerda, ; Limarino et al, ) or lower Miocene (Jordan et al, , ). These deposits are likely related to this older pulse of tectonic uplift of Frontal Cordillera at 30°S.…”

“…These deposits are likely related to this older pulse of tectonic uplift of Frontal Cordillera at 30°S. Moreover, backstripping analysis that includes the newly identified early Cenozoic sediments in the Bermejo basin suggests that flexural subsidence begin in the Eocene, and U‐Pb detrital zircon are dominated by ages predominantly sourced in the Frontal Cordillera (Fosdick et al, ). This indirect evidence for the onset of distal foredeep sedimentation in the Eocene, and coincident topographic growth in the hinterland, strongly supports our results documenting Eocene exhumation in the Frontal Cordillera.…”

Foreland Basin Record of Uplift and Exhumation of the Eastern Cordillera, Northwest Argentina

“…Continued deposition occurred in a wedge‐top basin as the deformation front stepped further east (DeCelles et al, ). Our findings do not support the suggestion that deformation began earlier in this area of Argentina during the Eocene (e.g., Fosdick et al, ). We also note the contrast between the deformation record in Argentina and that from farther north in Bolivia, where the onset of deformation is earlier and overall shortening magnitudes much greater (Anderson et al, ; Calle et al, ; McQuarrie, ).…”

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

“…As a prime example, the late middle Eocene to earliest Miocene (~40–20 Ma) record of deformation reveals an apparent contradiction in which shortening reported for the thickest part of the central Andes was synchronous with extension in the southern Andes (Echaurren et al, ; Encinas et al, ; Horton, , ; Jordan et al, ; Maksaev & Zentilli, ; McQuarrie et al, ; Oncken et al, ; Orts et al, ). This problem is accentuated at the transition from the central to southern Andes, where diverging interpretations of the Eocene‐Oligocene record invoke either extension or shortening for the magmatic arc, hinterland thrust belt, and retroarc basin system along an east‐west profile at ~30°S (Fosdick et al, ; Litvak et al, ; Winocur et al, ).…”