In NW Argentina (~26°S), adjacent to the Puna Plateau of the central Andes, exhumation and deformation propagated from west to east across the Puna Plateau and Eastern Cordillera during early–late Cenozoic time. Presently existing data do not indicate a clear eastward younging trend in exhumation in the Precordillera and northern Sierras Pampeanas at the southeastern flank of the Puna Plateau at ~28°S. In this study, we mapped an ~80-km-wide transect at a latitude of ~28°S in the Sierra de Las Planchadas and the Fiambalá Basin. Apatite fission-track (AFT) ages from six samples from thrust fault hanging walls are between 20 and 14 Ma, and apatite helium (U-Th)/He ages from five samples range from 21 Ma west of the Sierra de Las Planchadas to 2 Ma in the Fiambalá Basin. Several samples record mixed apatite (U-Th)/He ages and pre-Cenozoic AFT ages, indicating partial resetting through the 120–60 °C temperature window and suggesting a depth of exhumation between ~6 and 3 km. Thermal modeling of AFT and (U-Th)/He ages indicates cooling from ca. 22 Ma until 2 Ma and a younging trend to the east. These ages are consistent with previously published AFT ages in the Fiambalá region and AHe ages in the Eastern Cordillera to the northeast and suggest Miocene exhumation and deformation in the Precordillera at 28°S and the Eastern Cordillera at 26°S. From a kinematic standpoint, the region of the Precordillera at 28°S may be considered a continuation to the south of the Eastern Cordillera at 26°S, implying a single continuous SW-NE–striking deformation front along this portion of the central Andes. Detrital zircon U-Pb ages from Upper Miocene strata in the Fiambalá Basin suggest that Permian–Miocene rocks in the Sierra de Las Planchadas are the primary source of the Miocene basin fill. This is consistent with previously published eastward-directed paleocurrent data and other provenance proxies and indicates that uplift of the Sierra de Las Planchadas began no later than ca. 9 Ma.

Abstract We apply low-temperature thermochronology, Rb/Sr geochronology, petrological data, and structural mapping to constrain the timing and kinematics of the Ios metamorphic core complex. Top-to-north extension in the lower plate Headland Shear Zone was active at 18–19 Ma under metamorphic conditions of 475–610 °C and 0.65–1.1 GPa. The South Cyclades Shear Zone/Ios Detachment Fault (SCSZ/IDF) system shows top-to-south extensional shear active at c. 19 Ma at 380–550 °C, with local top-to-north bands. Extensional shear above the SCSZ/IDF is dominantly top-to-south to top-to-SW. PT estimates from an eclogite boudin constrain Eocene high-pressure metamorphism to 430–560 °C and 1.21±0.42 GPa to 0.66±0.37 GPa. Similar low-temperature thermochronometric ages across Ios demonstrate that ductile extensional movement ceased by c. 15 Ma. Exhumation to shallow crustal levels took place between c. 15 and 9 Ma at cooling rates of up to 120 °C Ma −1 with a slow down to <20 °C Ma −1 between 12 and 9 Ma, most likely accommodated by extensional slip at rates of c. 3 km Ma −1 along the top-to-SW Coastal Fault System. We propose a model of bivergent extension for exhumation of the Ios core complex between 19 and 9 Ma, with Ios forming a secondary antithetic top-to-south to top-to-SW extensional fault system to a more dominant top-to-north Naxos/Paros detachment system.

Abstract We present apatite and zircon fission-track (AFT and ZFT) ages from the Amorgos detachment system in the Aegean Sea, Greece. The Amorgos detachment system consists of a basal and an upper detachment. The lower Amorgos detachment occupies the same tectonic position as the regionally important large-magnitude Cretan detachment and therefore can provide improved constraints on the evolution of the latter. AFT ages from the footwalls of both detachments show that detachment-related cooling occurred in the early Miocene, coeval with an important phase of cooling in the footwall of the Cretan detachment on Crete. We interpret the footwall AFT ages to indicate an early Miocene age of movement on the Amorgos detachments, essentially simultaneously with slip on the Cretan detachment. ZFT ages from rocks above the lower Amorgos detachment are not reset indicating that metamorphic temperatures during the Tertiary Hellenic orogeny did not exceed c. 300 °C significantly. We discuss a model in which top-to-the-north movement on the Cretan/Amorgos detachment commenced in the early Miocene. Soon after the inception of the Cretan/Amorgos detachment, top-to-the-south movement on the South Cyclades shear zone deformed the latter and brought the Amorgos detachment into a higher crustal position.