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The sample preparation and evaluation of the effects of impurities on the determination of 10Be and 26Al by accelerator mass spectrometry (AMS) was performed as an initial part of research project determining the timing of early hominin occupation at Korolevo, western Ukraine. The rock samples analysed exhibited various levels of weathering, lithology, and mass. The follow-up mass spectrometry scans revealed Ti impurity in BeO targets which stimulated quantification of Ti in quartz concentrate. The 26Al to 10Be ratios were independent on Ti and Al impurity for samples from the same depositional level. AMS Be current reduction was a function of BeO dilution by TiO2 molecules. [ABSTRACT FROM AUTHOR]

Abstract: Despite remarkable tectonostratigraphic similarities along the Himalayan arc, pronounced topographic and exhumational variability exists in different morphotectonic segments. The processes responsible for this segmentation are debated. Of particular interest is a 30‐ to 40‐km‐wide orogen‐parallel belt of rapid exhumation that extends from central Nepal to the western Himalaya and its possible linkage to a midcrustal ramp in the basal décollement, and the related growth of Lesser Himalayan duplex structures. Here we present 26 new apatite fission track cooling ages from the Beas‐Lahul region, at the transition from the Central to the Western Himalaya (~77°–78°E) to investigate segmentation in the Himalayan arc from a thermochronologic perspective. Together with previously published data from this part of the orogen, we document significant lateral changes in exhumation between the Dhauladar Range to the west, the Beas‐Lahul region, and the Sutlej area to the east of the study area. In contrast to the Himalayan front farther east, exhumation in the far western sectors is focused at the frontal parts of the mountain range and associated with the hanging wall of the Main Boundary Thrust fault ramp. Our results allow us to spatially correlate the termination of the rapid exhumation belt with a midcrustal ramp to the west. We suggest that a plunging anticline at the northwestern edge of the Larji‐Kullu‐Rampur window represents the termination of the Central Himalayan segment, which is related to the evolution of the Lesser Himalayan duplex. [ABSTRACT FROM AUTHOR]

Abstract: The deformation processes at work across the eastern margin of the Tibetan Plateau remain controversial. The interpretation of its tectonic history is often polarized between two deformation models: ductile flow in the lower crust and shortening and crustal thickening accommodated by brittle structures in the upper crust. Many geological investigations on this plateau margin focused on the Longmen Shan, at the western edge of the Sichuan Basin. However, the Longriba fault system (LFS) located 200 km northwest and parallel to the Longmen Shan structures provides an opportunity to understand the role of hinterland faults in eastern Tibet geodynamics. For this reason, we investigate the exhumation history of rocks across the LFS using (U‐Th)/He and fission track ages from apatite and zircon. Results show a significant contrast in cooling histories across the Maoergai fault, the southernmost fault of the LFS. South of the Maoergai fault, the bedrock records a rapid increase in exhumation rate since ~10–15 Ma. In contrast, the area north of the fault has experienced steady cooling since ~25–35 Ma. We attribute this cooling contrast to ~2 km of differential rock uplift across the Maoergai fault, providing the first evidence of activity of the LFS in the Late Cenozoic. Our results indicate that deformation of the eastern Tibetan margin has been partitioned into the LFS and the Longmen Shan over an ~200 km wide block, which should be incorporated in future studies on the region's deformation, and in both above‐mentioned deformation models. [ABSTRACT FROM AUTHOR]

The Himalayan thrust belt comprises three in-sequence foreland-propagating orogen-scale faults, the Main Central thrust, the Main Boundary thrust, and the Main Frontal thrust. Recently, the Munsiari–Ramgarh–Shumar thrust system has been recognized as an additional, potentially orogen-scale shear zone in the proximal footwall of the Main Central thrust. The timing of the Munsiari, Ramgarh, and Shumar thrusts and their role in Himalayan tectonics are disputed. We present 31 new zircon (U–Th)/He ages from a profile across the central Himachal Himalaya in the Beas River area. Within a ∼40 km wide belt northeast of the Kullu–Larji–Rampur window, ages ranging from 2.4 ± 0.4 Ma to 5.4 ± 0.9 Ma constrain a distinct episode of rapid Pliocene to Present exhumation; north and south of this belt, zircon (U–Th)/He ages are older ( 7.0 ± 0.7 Ma to 42.2 ± 2.1 Ma ). We attribute the Pliocene rapid exhumation episode to basal accretion to the Himalayan thrust belt and duplex formation in the Lesser Himalayan sequence including initiation of the Munsiari thrust. Pecube thermokinematic modelling suggests exhumation rates of ∼2–3 mm/yr from 4–7 to 0 Ma above the duplex contrasting with lower (<0.3 mm/yr) middle-late Miocene exhumation rates. The Munsiari thrust terminates laterally in central Himachal Pradesh. In the NW Indian Himalaya, the Main Central thrust zone comprises the sheared basal sections of the Greater Himalayan sequence and the mylonitic ‘Bajaura nappe’ of Lesser Himalayan affinity. We correlate the Bajaura unit with the Ramgarh thrust sheet in Nepal based on similar lithologies and the middle Miocene age of deformation. The Munsiari thrust in the central Himachal Himalaya is several Myr younger than deformation in the Bajaura and Ramgarh thrust sheets. Our results illustrate the complex and segmented nature of the Munsiari–Ramgarh–Shumar thrust system. [ABSTRACT FROM AUTHOR]

The timing of the closure of the Bangong Ocean between the Lhasa and South Qiangtang Terranes in central Tibet and the resulting crustal thickening are still under debate. We integrate published apatite fission track and (U-Th)/He thermochronometer data with new zircon (U-Th)/He ages from eight samples and with structural profiles to document that the South Qiangtang Terrane experienced slow exhumation between 200 and 150 Ma, associated with the opening of the Bangong Ocean. Accelerated exhumation (around 0.2-0.3 mm/a) of the South Qiangtang Terrane was initiated at around 150 Ma. This exhumation event is interpreted to reflect collision between the Lhasa and South Qiangtang Terranes after closure of the Bangong Ocean, associated with crustal thickening via thick-skinned folding and thrusting within the South Qiangtang Terrane. The amalgamation of the Lhasa and South Qiangtang Terranes recorded here may represent the first stage of crustal thickening in the central Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: Uplift of the Al Hajar Mountains in Oman has been related to either Late Cretaceous ophiolite obduction or the Neogene Zagros collision. To test these hypotheses, the cooling of the central Al Hajar Mountains is constrained by 10 apatite (U‐Th)/He (AHe), 15 fission track (AFT), and four zircon (U‐Th)/He (ZHe) sample ages. These data show differential cooling between the two major structural culminations of the mountains. In the 3 km high Jabal Akhdar culmination AHe single‐grain ages range between 39 ± 2 Ma and 10 ± 1 Ma (2σ errors), AFT ages range from 51 ± 8 Ma to 32 ± 4 Ma, and ZHe single‐grain ages range from 62 ± 3 Ma to 39 ± 2 Ma. In the 2 km high Saih Hatat culmination AHe ages range from 26 ± 4 to 12 ± 4 Ma, AFT ages from 73 ± 19 Ma to 57 ± 8 Ma, and ZHe single‐grain ages from 81 ± 4 Ma to 58 ± 3 Ma. Thermal modeling demonstrates that cooling associated with uplift and erosion initiated at 40 Ma, indicating that uplift occurred 30 Myr after ophiolite obduction and at least 10 Myr before the Zagros collision. Therefore, this uplift cannot be related to either event. We propose that crustal thickening supporting the topography of the Al Hajar Mountains was caused by a slowdown of Makran subduction and that north Oman took up the residual fraction of N‐S convergence between Arabia and Eurasia. [ABSTRACT FROM AUTHOR]

Large domes of crystalline, middle to deep crustal rocks of Asian provenance make the Pamir a unique part of the India-Asia collision. Combined major-element and trace element thermobarometry, pseudosections, garnet-zoning deconstruction, and geochronology are used to assess the burial and exhumation history of five of these domes. All domes were buried and heated sufficiently to initiate garnet growth at depths of 15-20 km at 37-27 Ma. The Central Pamir was then heated at ~10-20°C/Myr and buried at 1-2 km/Myr to 600-675°C at depths of 25-35 km by 22-19 Ma. The Shakhdara Dome in the South Pamir was heated at ~20°C/Myr and buried at 2-8 km/Myr to reach 750-800°C at depths of ≥50 km by ~20 Ma. All domes were exhumed at >3 km/Myr to 5-10 km depths and ~300°C by 17-15 Ma. The pressures, temperatures, burial rates, and heating rates are typical of continental collision. Decompression during exhumation outpaced cooling, compatible with tectonic unroofing along mapped large-scale, normal-sense shear zones, and with advection of near-solidus or suprasolidus temperatures into the upper crust, triggering exhumation-related magmatism. The Shakhdara Dome was exhumed from greater depth than the Central Pamir domes perhaps due to its position farther in the hinterland of the Paleogene retrowedge and to higher heat input following Indian slab breakoff. The large-scale thickening and coincident ~20 Ma switch to extension throughout a huge area encompassing the Pamir and Karakorum strengthens the idea that the evolution of orogenic plateaux is governed by catastrophic plate-scale events. [ABSTRACT FROM AUTHOR]

Glacial chronologies provide insight into the evolution of paleo-landscapes, paleoclimate, topography, and the erosion processes that shape mountain ranges. In the Pamir of Central Asia, glacial morphologies and deposits indicate extensive past glaciations, whose timing and extent remain poorly constrained. Geomorphic data and 15 new 10 Be exposure ages from moraine boulders and roches moutonnées in the southwestern Pamir document multiple Pleistocene glacial stages. The oldest exposure ages, 113 ± 10 ka , underestimate the age of the earliest preserved glacial advance and imply that the modern relief of the southwestern Pamir (peaks at ∼5000–6000 m a.s.l.; valleys at ∼2000–3000 m a.s.l.) already existed in the late Middle Pleistocene. Younger exposure ages (∼40–80 ka, ∼30 ka) complement the existing Central Asian glacial chronology and reflect successively less extensive Late Pleistocene glaciations. The topography of the Pamir and the glacial chronologies suggest that, in the Middle Pleistocene, an ice cap or ice field occupied the eastern Pamir high-altitude plateau, whereas westward flowing valley glaciers incised the southwestern Pamir. Since the Late Pleistocene deglaciation, the rivers of the southwestern Pamir adjusted to the glacially shaped landscape. Localized rapid fluvial incision and drainage network reorganization reflect the transient nature of the deglaciated landscape. [ABSTRACT FROM AUTHOR]

Asian deep crust exposed in the Pamir permits determination of the amount, sequence, and interaction of shortening, extension, and lateral extrusion over ~30 km of crustal section during the India-Asia collision. In the Central Pamir, gneiss domes and their hanging walls record Paleogene tripling of the 7-10 km thick Phanerozoic upper crustal strata; total crustal thickness may have amounted to 90 km. Two thrust sheets, comprising Cambro-Ordovician, respectively, Carboniferous to Paleogene strata, straddle the domes. Amphibolite-facies metamorphic rocks within the domes-equivalent to lower grade rocks outside the domes-form fold nappes with dome-scale wavelengths. E-W stretching occurred contemporaneously with top-to- ~ N imbrication and folding. At ~22-12 Ma, bivergent (top-to-N and top-to-S), normal-sense shear zones exhumed the crystalline rocks; most of the extension occurred along the northern dome margins. Shortening resumed at ~12 Ma with opposite-sense thrusting and folding focused along the dome margins. Throughout the building of the Central and South Pamir, dominant ~N-S shortening interacted with ~E-W extension along mostly dextral shear/fault zones. In the Neogene, shear is concentrated along a dextral wrench corridor south of the domes. We interpret the Paleogene shortening to record thickening and northward growth of the Pamir-Tibetan Plateau and short-lived Miocene crustal extension as gravitational adjustment, i.e., collapse, of the thickened Asian crust to Indian slab breakoff. Synconvergent Paleogene lateral extrusion thickened the Afghan Hindu Kush crust west of the India-Asia collision, and the Miocene-Recent dextral shear and ~E-W extension have accommodated collapse of the Pamir Plateau into the Tajik depression. [ABSTRACT FROM AUTHOR]

Geothermochronologic data outline the temperature-deformation-time evolution of the Muskol and Shatput gneiss domes and their hanging walls in the Central Pamir. Prograde metamorphism started before ~35 Ma and peaked at ~23-20 Ma, reflecting top-to- ~N thrust-sheet and fold-nappe emplacement that tripled the thickness of the upper ~7-10 km of the Asian crust. Multimethod thermochronology traces cooling through ~700-100°C between ~22 and 12 Ma due to exhumation along dome-bounding normal-sense shear zones. Synkinematic minerals date normal sense shear-zone deformation at ~22-17 Ma. Age-versus-elevation relationships and paleoisotherm spacing imply exhumation at ≥3 km/Myr. South of the domes, Mesozoic granitoids record slow cooling and/or constant temperature throughout the Paleogene and enhanced cooling (7-31°C/Myr) starting between ~23 and 12 Ma and continuing today. Integrating the Central Pamir data with those of the East (Chinese) Pamir Kongur Shan and Muztaghata domes, and with the South Pamir Shakhdara dome, implies (i) regionally distributed, Paleogene crustal thickening; (ii) Pamir-wide gravitational collapse of thickened crust starting at ~23-21 Ma during ongoing India-Asia convergence; and (iii) termination of doming and resumption of shortening following northward propagating underthrusting of the Indian cratonic lithosphere at ≥12 Ma. Westward lateral extrusion of Pamir Plateau crust into the Hindu Kush and the Tajik depression accompanied all stages. Deep-seated processes, e.g., slab breakoff, crustal foundering, and underthrusting of buoyant lithosphere, governed transitional phases in the Pamir, and likely the Tibet crust. [ABSTRACT FROM AUTHOR]

A balanced cross-section spanning the Eastern Cordillera and Subandean Zone of southern Peru (13–15°S) constrains ~130 km (38%) of Cenozoic orogen-normal SW–NE Andean deformation accommodated by thick- and thin-skinned retro–arc fold–thrust belt shortening that overprinted pre-Andean Triassic normal faults. Zircon and apatite (U–Th)/He ages demonstrate continuous Oligocene to Miocene cooling of the Permo-Triassic Coasa pluton in the Eastern Cordillera. Zircon (U–Th)/He ages (~34–18 Ma) are reset and define a steep age versus elevation relationship. Apatite (U–Th)/He results reveal reset ages that define two spatially separated groups with ages of ~30–26 Ma and ~17–11 Ma. Detrital zircon U–Pb geochronologic results from Cretaceous–Cenozoic siliciclastic rocks from the Altiplano/Eastern Cordillera record Andean fold–thrust belt and magmatic-arc sediment sources. Correlative Subandean Zone rocks preserve a cratonic sediment contribution, with minor Andean sediment appearing in some Cenozoic rocks. We propose that earliest Andean deformation and structural compartmentalization of the Eastern Cordillera was linked to selective inversion of inherited Permo-Triassic basement-involved normal faults that guided subsequent thick- and thin-skinned deformation. Provenance variations between the hinterland and foreland depocentres reveal competing eastern and western sediment sources, reflecting an axial zone in the Eastern Cordillera that coincided with the inherited Triassic graben and impeded sediment source mixing. Our zircon and apatite (U–Th)/He ages are consistent with published constraints along strike and support pulses of Eocene to late Miocene exhumation that were likely driven by normal fault reactivation and protracted Eastern Cordillera deformation. [ABSTRACT FROM PUBLISHER]

We investigate the spatiotemporal evolution of exhumation in the ice-covered St. Elias syntaxis area, southeast Alaska, using multiple thermochronometers and geochronometers from cobble-sized glacial detritus. Multiple thermochronometers reveal the cooling histories from 500 to 60°C of 27 glacially transported cobbles from the two largest catchments of the syntaxis. Cobble lithologies and 21 zircon U-Pb ages (~277-31 Ma) were examined to determine sample provenance. Furthermore, eight amphibole and seven biotite 40Ar/39Ar ages (~276-16 Ma and ~50-42 Ma, respectively), four zircon and six apatite (U-Th)/He ages (~35-4.8 Ma and ~4.2-0.6 Ma, respectively), and four apatite fission track ages (~17-1.6 Ma) were used to reconstruct the individual cobble cooling histories. An additional four bedrock samples from the Fairweather Range yielded three biotite 40Ar/39Ar ages between ~42 and 5 Ma. A compilation of published bedrock and new cobble cooling histories from the St. Elias Mountains and Fairweather Range reveals the regional Cenozoic cooling and exhumation history, emphasizing the position of the St. Elias syntaxis as a transitional zone between transpression and subduction settings. The new cobble and bedrock data indicate an onset of rapid exhumation at ~5 Ma that was limited in duration (2-3 Myr) and amount (~10 km) in the syntaxial region. This study also demonstrates the usefulness of cobbles for revealing thermal histories of otherwise inaccessible regions as cobble analysis combines advantages of bedrock and detrital thermochronology. [ABSTRACT FROM AUTHOR]

Upper crustal extensional structures range from steep normal faults to shallow-dipping detachments. The relationship between extension and formation of synkinematic hanging wall basins including their relative timing is not well understood. The South Rhodope core complex, Southern Balkans, has experienced extension for >40 Ma leading to a number of extensional structures and Cenozoic sedimentary basins. We present new bedrock and basin detrital zircon and apatite (U-Th-Sm)/He ages from the Pirin and Rila Mountains and the Sandanski basin. Results identify three episodes of Cenozoic extension in SW Bulgaria accommodated by (1) the Eocene/Oligocene Mesta detachment; (2) the early to middle Miocene Gorno Spanchevo fault (circa 18-15 Ma), which is the northern prolongation of the Strymon low-angle detachment; and (3) the late Miocene West Pirin fault (≤10 Ma). Detachment faulting on the Strymon fault accommodated tens of kilometers of ENE-WSW extension and created ~1500 m topographic relief, but because the resulting hillslopes were gentle (≤10°), extension did not lead to enhanced footwall erosion or formation of a hanging wall basin. In contrast, the West Pirin normal fault resulted in mostly vertical motion of its footwall causing steep topography, rapid erosion, and formation of the synrift Sandanski basin. Digital topographic analysis of river channel profiles identifies the latest episodes of deformation including westward tilting of the Sandanski and Strymon basins and Quaternary N-S extension. This study demonstrates that basin formation in the South Rhodope core complex is related to normal faulting postdating the main episode of crustal stretching by detachment faulting. [ABSTRACT FROM AUTHOR]

Cenozoic gneiss domes-exposing middle-lower crustal rocks-cover ~30% of the surface exposure of the Pamir, western India-Asia collision zone; they allow an unparalleled view into the deep crust of the Asian plate. We use titanite, monazite, and zircon U/Th-Pb, mica Rb-Sr and 40Ar/39Ar, zircon and apatite fission track, and zircon (U-Th)/He ages to constrain the exhumation history of the ~350 × 90 km Shakhdara-Alichur dome, southwestern Pamir. Doming started at 21-20 Ma along the Gunt top-to-N normal-shear zone of the northern Shakhdara dome. The bulk of the exhumation occurred by ~NNW-ward extrusion of the footwall of the crustal-scale South Pamir normal-shear zone along the southern Shakhdara dome boundary. Footwall extrusion was active from ~18-15 Ma to ~2 Ma at ~10 mm/yr slip and with vertical exhumation rates of 1-3 mm/yr; it resulted in up to 90 km ~N-S extension, coeval with ~N-S convergence between India and Asia. Erosion rates were 0.3-0.5 mm/yr within the domes and 0.1-0.3 mm/yr in the horst separating the Shakhdara and Alichur domes and in the southeastern Pamir plateau; rates were highest along the dome axis in the southern part of the Shakhdara dome. Incision along the major drainages was up to 1.0 mm/yr. Thermal modeling suggests geothermal gradients as high as 60°C/km along the trace of the South Pamir shear zone and their strong N-S variation across the dome; the gradients relaxed to ≤40-45°C/km since the end of doming. [ABSTRACT FROM AUTHOR]

Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir and provide a window into the deep crustal processes of the India-Asia collision. The largest of these are the doubly vergent, composite Shakhdara-Alichur domes of the southwestern Pamir, Tajikistan, and Afghanistan; they are separated by a low-strain horst. Top-to-SSE, noncoaxial pervasive flow over the up to 4 km thick South Pamir shear zone exhumed crust from 30-40 km depth in the ~250 × 80 km Shakhdara dome; the top-to-NNE Alichur shear zone exposed upper crustal rocks in the ~125 × 25 km Alichur dome. The Gunt shear zone bounds the Shakhdara dome in the north and records alternations of normal shear and dextral transpression; it contributed little to bulk exhumation. Footwall exhumation along two low-angle, normal-sense detachments resulted in up to 90 km syn-orogenic ~N-S extension. Extension in the southwestern Pamir opposes shortening in a fold-thrust belt north of the domes and in particular in the Tajik depression, where an evaporitic décollement facilitated upper crustal shortening. Gravitational collapse of the Pamir-plateau margin drove core-complex formation in the southwestern Pamir and shortening of the weak foreland adjacent to the plateau. Overall, this geometry defines a 'vertical extrusion' scenario, comprising frontal and basal underthrusting and thickening, and hanging gravitationally driven normal shear. In contrast to the Himalayan vertical extrusion scenario, erosion in the Pamir was minor, preserving most of the extruded deep crust, including the top of the South Pamir shear zone at peak elevations throughout the dome. [ABSTRACT FROM AUTHOR]

The Pamir mountains at the western end of the Himalaya–Karakorum–Tibet mountain belt are characterized by landscape extremes: The western Pamir has an extreme local relief of >2000 m. The eastern Pamir is a low-relief orogenic plateau at ~4100 m. In most of the Pamir, modern glaciers are small and often are rock glaciers restricted to the north sides of the crests but significant ice caps occur in the eastern Pamir (Muztagh Ata, Kongur Shan) and in the northwestern Pamir, where the Fedchenko glacier is the longest glacier outside the polar regions. Glaciation of the Pamir contrasts with the strong glaciation of the Karakorum ranges farther south reflecting differences in annual precipitation beween the Monsoon-influenced Karakorum and the arid, Westerlies-controlled Pamir.Glacial and glaciogenic sediments that have been mapped throughout the Pamir suggest much more widespread glaciation during the Pleistocene. Cosmogenic radionuclide (CRN) dates indicate that one or several glacial maxima occurred ≥100 ka, but the extent of the mid-Pleistocene ice cover is currently not known. While CRN exposure ages of glacially polished bedrock in the west-Pamir valleys suggest that these may have been formed by mid-late Pleistocene Alpine glaciers there is little record of the glacial advances on the east-Pamir plateau. We present new CRN exposure ages that elucidate the glacial and post-glacial history of the Pamir. We also present a geomorphological analysis focusing on the strong east-west difference in topography and on morphological evidence of glaciation in the eastern Pamir. Our analysis sheds light on the landscape evolution and on the competing effects of fluvial and glacial erosion and mass-wasting processes in an arid mountain environment. [ABSTRACT FROM AUTHOR]

The article discusses the phenomena of gneiss dome formation in the Pamir Mountains in Central Asia. It notes that unlike the Tibetan plateau, high-grade metamorphic rocks are widely exposed in at least seven gneiss domes in the Pamir, several of were said to share similar exhumation histories, indicating that they were formed through a single mechanism. Dome formation was attributed to overall transpressional thickening with long-wavelength-low-amplitude buckling of the entire crust.

Tectonics and climate are major contributors to the topographic evolution of mountain ranges. Here, we investigate temporal variations in exhumation due to the onset of Pleistocene glaciation in the Olympic Mountains (Washington State, USA). We present 29 new apatite and zircon (U-Th)/He ages (AHe and ZHe), showing a decrease in ages toward the interior of the mountain range for both thermochronometric systems. Young AHe ages (<2 Ma) can be found on the western side and the interior of the mountain range. Thermokinematic modeling of sample cooling ages suggests, that ZHe ages can be explained by an ellipse-shaped exhumation pattern with lowest/highest rates of ~0.25 and 0.9 km/m.y. These rates are interpreted as tectonically driven rock uplift, where the pattern of rates is governed by the shape of the subducted plate. However, the youngest AHe ages require a 50-150% increase in exhumation rates in the past 2-3 m.y. This increase in rates is contemporaneous with Pliocene-Pleistocene alpine glaciation of the orogen, indicating that tectonic rock uplift is perturbed by glacial erosion. [ABSTRACT FROM AUTHOR]

We report two 40 Ar/ 39 Ar illite ages from fault gouge directly above the current trace of the Alpine Fault in New Zealand at Gaunt Creek (1.36 ± 0.27 Ma) and Harold Creek (1.18 ± 0.47 Ma), and one 40 Ar/ 39 Ar illite age from fault gouge from the Two Thumbs Fault on the east side of the Southern Alps. Metamorphic muscovite clasts inherited into the Alpine Fault gouge yielded 40 Ar/ 39 Ar ages of 2.04 ± 0.3 Ma at Gaunt Creek and 11.46 ± 0.47 Ma at Harold Creek. We also report Rb-Sr muscovite-based multimineral ages of Alpine Schist mylonite adjacent to the dated fault gouge at Harold Creek (13.1 ± 4.3 Ma) and Gaunt Creek (8.9 ± 3.2 Ma). 40 Ar/ 39 Ar muscovite ages from the Gaunt Creek mylonite yielded plateau ages of 1.47 ± 0.08 Ma and 1.57 ± 0.15 Ma. Finally, we report zircon fission track (0.79 ± 0.11 and 0.81 ± 0.17 Ma) and zircon (U-Th)/He ages (0.35 ± 0.03 and 0.4 ± 0.06 Ma) from Harold Creek. We interpret the fault gouge ages to date growth of newly formed illite during gouge formation at temperatures of ~ 300–350 °C towards the base of the seismogenic zone. Simple backcalculation using current uplift/exhumation and convergence rates, and dip angles of 45–60° at the Alpine Fault support that interpretation. We infer that the fault gouge ages record faulting and gouge formation as the rocks passed very rapidly through the brittle-ductile transition zone on their way to the surface. Rb-Sr and 40 Ar/ 39 Ar ages on muscovite from Alpine Schist mylonite date muscovite growth at ~ 11 Ma together with a younger phase of cooling/shearing at ~ 1.5–2 Ma. Our ages from the Alpine Schist indicate extremely rapid cooling exceeding 200 °C/Ma. The fault gouge age from the Two Thumbs Fault is significantly too old to have formed as part of the late Neogene/Quaternary Southern Alps evolution. [ABSTRACT FROM AUTHOR]