Exhumation history of the Lomas de Olmedo basin: constraining multi-phase deformation using low-temperature thermochronology

WILLEMIJN S.M.T. VAN KOOTEN; EDWARD SOBEL; CECILIA EUGENIA DEL PAPA; PATRICIO PAYROLA; ALEJANDRO BANDE; STARCK, DANIEL

Congreso; EGU General Assembly 2021; 2021

The Cretaceous period in NW Argentina is dominated by the formation of the Salta rift basin, anintracontinental rift basin with multiple branches extending from the central Salta-Jujuy High. Oneof these branches is the ENE-WSW striking Lomas de Olmedo sub-basin, which hosts up to 5 km ofsyn- and post-rift deposits of the Salta Group, accommodated by substantial throw along SW-NEstriking normal faults and subsequent thermal subsidence during the Cretaceous-Paleogene. Earlycompressive movement in the Eastern Cordillera led to the formation of a foreland basin settingthat was further dissected in the Neogene by the uplift of basement-cored ranges. As aconsequence, the northwestern part of the Lomas de Olmedo sub-basin was disconnected fromthe Andean foreland and local depocenters such as the Cianzo basin were formed, whereas theeastern sub-basin area is still part of the Andean foreland. Thus, the majority of the Salta Group tothe east is located in the subsurface and has been extensively explored for petroleum, while innorthwestern part of the sub-basin, the Salta Group is increasingly deformed and is fully exposedin the km-scale Cianzo syncline of the Hornocal ranges. The SW-NE striking Hornocal fault delimitsthe Cianzo basin to the south and the Cianzo syncline to the north. During the Cretaceous, itformed the northern margin of the Lomas de Olmedo sub-basin, which is indicated by anincreasing thickness of the syn-rift deposits towards the Hornocal fault, as well as a lack of syn-riftdeposits on the footwall block. Structural mapping and unpublished apatite fission track (AFT) datashow that the Hornocal normal fault was reactivated and inverted during the Miocene. Althoughstructural and sedimentary features of the Cianzo basin infill provide information about therelative timing of fault activity, there is a lack of low-temperature thermochronology. Herein, weaim to constrain the exhumation of the Lomas de Olmedo sub-basin during the Cretaceous riftingphase, as well as the onset and magnitude of fault reactivation in the Miocene. We collected 74samples for low-temperature thermochronology along two major NW-SE transects in the Cianzobasin and adjacent areas. Of these samples, 59 have been analyzed using apatite and/or zircon (UTh-Sm)/He thermochronology (AHe, ZHe). Furthermore, 49 samples have been prepared for AFTanalysis. The ages are incorporated in thermo-kinematic modelling using Pecube in order to testthe robustness of uplift and exhumation scenarios. On the hanging wall block of the N-S strikingeast-vergent Cianzo thrust north of the Hornocal fault, Jurassic ZHe ages are attributed to preSalta Group exhumation. However, associated thrusts to the south show ZHe ages as young asEocene-Oligocene, which might indicate early post-rift activity along those thrusts. AHe data fromthe Cianzo syncline show a direct age-elevation relationship with Late Miocene-Pliocene coolingages, indicating the onset of rapid exhumation along the Hornocal fault in the Miocene. This isconsistent with regional data and suggests that pre-existing extensional structures werereactivated during Late Miocene-Pliocene compressive movement within this part of the CentralAndes.