Middle Miocene tectonic development of the Transition Zone, Salta Province, northwest Argentina: Magnetic stratigraphy from the Metán Subgroup, Sierra de González

Abstract

Magnetostratigraphy, isotopic dating, and sandstone petrography establish age limits on the depositional history of ϳ2100 m of foreland basin strata in the Neogene Metán Subgroup of northwest Argentina. The strata were deposited between ca. 15.1 and 9.7 Ma in the eastern Sistema de Santa Bárbara. The region is positioned above the Cretaceous Salta rift basin, in the Transition Zone between modern relatively steep and flat subducting segments of the Nazca plate.Formations within the subgroup are shown to be diachronous over a 60 km distance; the younger ages are in the east. Changes in paleocurrent flow directions and the lithic clast component of sandstones collected from the Arroyo González section suggest that basal fluvial strata were derived from the craton to the east beginning in middle Miocene time, just prior to 15.1 Ma. By ca. 14.5 Ma, the paleocurrent flowed from a source in the west and sedi-*Second address: Magstrat, LLC, ment accumulation rates increased dramatically. These changes correlate with contemporaneous tectonism in the west. A local increase in basin accommodation may be partly related to a zone of weakness near the eastern boundary of the Salta rift.Uplift in the western Cordillera Oriental apparently began by 13.7 Ma and thrusting rapidly migrated eastward. The eastern Cordillera Oriental ranges began to rise between 25؇ and 26؇S ca. 10 Ma. As thrusting migrated eastward, low-energy depositional environments were overwhelmed ca. 13.7 Ma. Above an erosional unconformity that removed strata to an age of ca. 9.7 Ma, basal strata from the overlying Jujuy Subgroup were deposited beginning after 9 Ma.Sandstones from Río Yacones suggest that the Cordillera Oriental uplift continued for several million years longer between 24؇ and 25؇S. Uplift of the Sistema de Santa Bárbara, in the distal portion of the foreland, did not begin until after ca. 9 Ma.

Structural, Geomorphic, and Depositional Characteristics of Contiguous and Broken Foreland Basins: Examples from the Eastern Flanks of the Central Andes in Bolivia and NW Argentina

“…This is virtually identical to inverted extensional structures in the Eastern Cordillera of Colombia (e.g., Mora et al, 2006;Parra et al, 2009) and bears resemblance to the pattern of reactivated structures in the North American Laramide province (Marshak et al, 2000). Thus, the pre-Andean paleogeography of northwestern Argentina has left an imprint on the manner in which Cenozoic shortening is accommodated, resulting in a broad zone of deformation without a well-defined, tectonically active orogenic front and unsystematic lateral growth (e.g., Allmendinger et al, 1983;Grier et al, 1991;Mon and Hongn, 1991;Reynolds et al, 2000;Carrera et al, 2006;Ramos et al, 2006;Hongn et al, 2007;Hilley and Coutand, 2010). The broken foreland in Argentina therefore constitutes a morphotectonic province with spatially and temporally disparate range uplifts and intervening basins, a setting akin to the hydrologically isolated adjacent basins of the Altiplano-Puna in the orogen interior (Alonso et al, 1984(Alonso et al, , 1991Jordan and Alonso, 1987;Kraemer et al, 1999;Carrapa et al, 2005).…”

Age, distribution, tectonics, and eustatic controls of the Paranense and Caribbean marine transgressions in southern Bolivia and Argentina

“…more accurate methods have been developed in the last century); (2) poor biozonation due to long ranges of the fauna; (3) diachronism at the base and top of the marine transgression, interpreted as evidence of one undifferentiated event, though Haq et al (1987) and Galloway (1989) showed that sedimentary cycles are typically repetitive with durations shorter than the interval originally interpreted for the Paranense cycle; and (4) a poor understanding of the uplift history of the central Andes. Recent work by Reynolds et al (1994Reynolds et al ( , 2000Reynolds et al ( , 2001, Hernández et al (1999Hernández et al ( , 2002, and Echavarría et al (2003) provide significant insight into the tectonic evolution of this region.…”

“…The western limit appears to have been very irregular and is poorly constrained. Western areas, where the presence of the Paranense Sea is documented, are as follows: San Juan province with the marine extension of Chinches Formation (Perez et al, 1996), Tucumán and Salta provinces east of Sierra de Aconquija (Gavriloff and Bossi, 1992a,b), the valley of Río Salí (Rio Salí Formation), and Salta and Jujuy provinces (Anta Formation, Gebhard et al, 1974;Russo and Serraioto, 1978;Galli et al, 1996;Reynolds et al, 2000).…”

“…1) help resolve the temporal framework of these events. The new age controls include vertebrate evolution associations with the South American Land Mammal Ages (SALMA) from fossil rodents in Brazil (Räsänen et al, 1995;Webb, 1995), isotopic data from volcanic airfall strata in Bolivia and Argentina, and magnetic polarity stratigraphy in Argentina (Reynolds et al, 1994(Reynolds et al, , 2000(Reynolds et al, , 2001Galli et al, 1996;Hernández et al, 1996Hernández et al, , 1999.…”

Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)

“…3) records a transition from primary volcanic facies in a likely subaerial environment to resedimented volcaniclastic facies in a water-dominated setting. The regional context (Reynolds et al 2000;Hernandez et al 2005) constrains the setting to be continental, with the depositional environment probably ranging from shallowwater lacustrine, to swampy and alluvial.…”