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Prospecting efforts to located Au mineralization within the Altai-Sayan fold area (ASFA) over previous decades have revealed that Devonian epithermal Au-Ag mineralization is more widespread than previously recognized. The preservation of this type of mineralization in Paleozoic rocks offers new prospects for the exploration of Au-Ag deposits in the underexplored region of Gornaya Shoria. The Kalarskoe epithermal Au-Ag occurrence represents Devonian epithermal mineralization within the Kaburchak cluster, Gornaya Shoria, Russia. This occurrence is confined to zones of argillic alteration that were superimposed on previously formed propylites. The argillic-altered rocks host quartz-sulfide veinlet zones. The mineralization of the Kalarskoe site is characterized by a high abundance of sulfide minerals: commonly, 5%–10%; often, up to 20%; and in some cases, up to 60%–70%. The ore minerals are represented by pyrite, arsenopyrite, sphalerite, galena, chalcopyrite, fahlores, native Au, and electrum, as well as by the sulfosalts Pb, Bi, Ag, Cu, and the tellurides of Au, Ag, and Pb. Based on mineralogical observations, at least four generations of sulfide mineral formations are distinguished within the ore occurrence. The mineralization of the Kalarskoe ore occurrence may be assigned to the intermediate sulfidation (IS) type. The results of the (U,Th)-He dating of pyrite from the pyrite-arsenopyrite massive body (pyr-3 and 4) revealed the protracted history of the mineralization in the intervals from ~399 to ~371 Ma. The obtained results substantially enhance the prospecting models for the exploration of epithermal Au-Ag deposits in the western part of the Altai-Sayan fold area (ASFA). [ABSTRACT FROM AUTHOR]

We report ten new zircon (U-Th)/He ages from psammitic greyschists collected in a southwest-northeast profile in the Otago Schist across the Dunstan and Cairnmuir Mountains, New Zealand. Six of the samples have accompanying new detrital zircon U-Pb ages. In this part of the Otago Schist, a broad antiformal core of garnet-biotite-albite zone schist defines a range-scale footwall block to the gently northeast-dipping Thomsons Gorge Fault and the gently southwest-dipping Cromwell Gorge faults. Hanging wall blocks above the faults comprise lower-grade chlorite zone schists. Nine schist samples from footwall and hanging wall blocks close to the low-angle faults exhibit a weighted mean (U-Th)/He age of 82 ± 3 Ma. We interpret that both low-angle fault systems were active prior to c. 82 Ma and confirm that they were extensional. We interpret the antiformal schist core as the late Early Cretaceous (c. < 122–109 Ma) ductile extensional lower plate of a metamorphic core complex. The lower plate (footwall) core was juxtaposed against the upper plate (hanging wall) schists by the low-angle normal decollement faults. Detrital zircon U-Pb ages indicate Carboniferous, Permo-Triassic, Jurassic and Cretaceous maximum depositional ages of schist protoliths which demand more complex terrane and metamorphic interpretations for the Otago Schist than previously recognised. [ABSTRACT FROM AUTHOR]

Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift (SNLU) of the Qiongdongnan Basin. These findings indicate that the bedrock buried hills in this basin hold great potential for exploration. Borehole samples taken from the granite buried hills in the SNLU were analyzed using apatite fission track (AFT) and zircon (U-Th)/He data to unravel the thermal history of the basement rock. This information is crucial for understanding the processes of exhumation and alteration that occurred after its formation. Thermal modeling of a sample from the western bulge of the SNLU revealed a prolonged cooling event from the late Mesozoic to the Oligocene period (∼80–23.8 Ma), followed by a heating stage from the Miocene epoch until the present (∼23.8 Ma to present). In contrast, the sample from the eastern bulge experienced a more complex thermal history. It underwent two cooling stages during the late Mesozoic to late Eocene period (∼80–36.4 Ma) and the late Oligocene period (∼30–23.8 Ma), interspersed with two heating phases during the late Eocene to early Oligocene period (∼36.4–30 Ma) and the Miocene epoch to recent times (∼23.8–0 Ma), respectively. The differences in exhumation histories between the western and eastern bulges during the late Eocene to Oligocene period in the SNLU can likely be attributed to differences in fault activity. Unlike typical passive continental margin basins, the SNLU has experienced accelerated subsidence after the rifting phase, which began around 5.2 Ma ago. The possible mechanism for this abnormal post-rifting subsidence may be the decay or movement of the deep thermal source and the rapid cooling of the asthenosphere. Long-term and multi-episodic cooling and exhumation processes play a key role in the alteration of bedrock and contribute to the formation of reservoirs. On the other hand, rapid post-rifting subsidence (sedimentation) promotes the formation of cap rocks. [ABSTRACT FROM AUTHOR]

The Whitehorse Trough formed during early Mesozoic accretion of the Intermontane terranes to northwestern North America. Here we investigate its thermal history using detrital mineral thermochronology, including 171 single-crystal (U–Th)/He zircon (ZHe) ages from 35 samples, 158 single-crystal (U–Th)/He apatite (AHe) ages from 33 samples, and apatite fission track (AFT) ages from 12 samples. ZHe single crystal ages range from 222 to 42 Ma and define Triassic–Early Jurassic, Late Jurassic, and Cretaceous–Paleogene age groups. AFT central ages range from 95 to 30 Ma with a dominant age peak at ∼50 Ma, and AHe single crystal ages range from 228 to 13 Ma with a dominant age peak between 50 and 40 Ma. Forward and inverse models of thermochronological data are compatible with two regional burial/heating stages that variably reset He in zircon. Maximum temperatures of the Whitehorse Trough strata locally exceeded 150 °C during Early Jurassic burial and shortening into a fold and thrust belt. Following Middle to Late Jurassic exhumation-related cooling and development of a prominent unconformity, Whitehorse Trough strata were buried again. Temperatures locally exceeded 150 °C during the Cretaceous, suggesting maximum burial of between ∼4 and 7.5 km. Heating and cooling rates during the Early–Middle Jurassic were ∼10 °C/myr, coinciding with deposition, fold and thrust belt development, and regional crustal thickening during the final stages of Intermontane terrane accretion. Maximum heating rates during the Cretaceous were ∼4–7 °C/myr and likely correspond to regional crustal thickening of the northern Cordillera hinterland and establishment of an outboard, Andean-type continental arc system. [ABSTRACT FROM AUTHOR]

Translating thermochronological ages to geological models requires knowledge of the thermal sensitivity of the applied thermochronometer, i.e. the closure temperature or the partial annealing/retention zone. Zircon Raman dating is a thermochronometer that uses radiation-damage measurements and matched analyses of actinide contents in zircon. Experimental work placed its closure temperature at 330–370 °C for the internal ν2(SiO4) and ν3(SiO4) Raman bands at 439 and 1008 cm−1, and 260–310 °C for the external rotation (ER) band at 356 cm−1. However, experimental annealing models also predict partial radiation-damage annealing over a broad temperature range (> 500 °C). We test these closure temperatures by dating zircon from the U–Pb reference material FC-1. We matched Raman-based radiation-damage measurements with U and Th concentrations measured with a secondary ion mass spectrometer. The zircon Raman ages for the ν2, ν3, and ER bands are 942 ± 23 Ma (2 s), 978 ± 38 Ma, and 1033 ± 32 Ma. This is lower than the expected range of 1040–1080 Ma, between the apatite U–Pb (~ 490 °C) and zircon (U-Th)/He (ZHe; ~ 200 °C) ages. We discuss long-term, low-temperature annealing of radiation damage during protracted cooling of the sample as a cause of age reduction. This explanation fits both, experimental annealing models and zircon Raman data from other geological settings. Long-term, low-temperature annealing complicates the interpretation of standalone zircon Raman data. However, exploiting this effect by combining zircon Raman and ZHe dating on the same sample provides thermal-history information beyond that revealed by either of them. [ABSTRACT FROM AUTHOR]

Ancient magnetization(s), often recorded by hematite (Fe2O3), provide key paleomagnetic constraints on plate interactions through time. Primary remanent magnetizations may be modified or overprinted by secondary processes that complicate interpretations of paleomagnetic data. Hematite (U‐Th)/He (hematite He) dating has the potential to resolve when secondary magnetizations were acquired. Here, we compare hematite He data and paleomagnetic results in Paleoproterozoic crystalline rocks, meters below a major nonconformity in the Colorado Front Range, USA. Prior work and new rock magnetic data indicate that pervasive hematite alteration records a secondary chemical remanent magnetization (CRM) during the Permo‐Carboniferous Reverse Superchron, coincident with the Ancestral Rocky Mountain orogeny. We target minor hematite‐coated faults cutting basement for (U‐Th)/He analyses because they are of sufficient hematite purity to yield geologically meaningful dates. Two samples yield overlapping and scattered individual hematite He dates ranging from ∼138 to 27 Ma (n = 33), significantly younger than the age of the late Paleozoic CRM. Scanning electron microscopy, electron probe microanalysis, and Raman spectroscopy indicate that aliquots have variable grain size distributions and fluorocarbonate impurities. Thermal history models support hematite on fault surfaces mineralized coeval with CRM acquisition during the late Paleozoic, and hematite He data scatter reflects variable He loss during Mesozoic burial owing to differences in grain size distribution from fault slip comminution and in chemistry among aliquots. Our results underscore the differences in temperature sensitivity and sampling requirements between paleomagnetic and hematite He investigations and illustrate that hematite He dates will usually be younger than preserved remanent magnetizations. Plain Language Summary: Minerals such as hematite are capable of recording the direction of the Earth's magnetic field during formation and this paleomagnetic information helps geoscientists estimate the age of rocks and the past motions of tectonic plates. During geologic events like mountain‐building, primary paleomagnetic signatures in rocks may be modified or replaced by new, secondary paleomagnetic recordings. Such secondary magnetizations can be challenging to interpret, especially if the age of these magnetizations is unknown. (U‐Th)/He analysis, a form of radiometric dating, may aid paleomagnetic studies by revealing the age of minerals that carry secondary magnetizations. In this study, we compare hematite (U‐Th)/He data and a secondary magnetization carried by hematite from Colorado's Front Range and find that (U‐Th)/He dates are scattered and considerably younger than the reported age of the secondary magnetization. We interpret the variability of hematite (U‐Th)/He dates to reflect differences between aliquots relating to crystal size and the presence of non‐hematite minerals. Our results suggest that the (U‐Th)/He system was partially to fully reset by a more recent phase of burial and associated reheating that was not hot enough to fully reset the paleomagnetic system. We conclude that (U‐Th)/He and paleomagnetic investigations in hematite may not record the same geologic events. Key Points: We compare new hematite (U‐Th)/He dates with previously published paleomagnetic data from the same exposure of crystalline basement rockHematite (U‐Th)/He dates are younger than the inferred timing of magnetization and imply partial He loss since magnetization acquisition(U‐Th)/He dates may not relate to remanence acquisition because of differences in sampling requirements and temperature sensitivity [ABSTRACT FROM AUTHOR]

Abstract Ancient magnetization(s), often recorded by hematite (Fe2O3), provide key paleomagnetic constraints on plate interactions through time. Primary remanent magnetizations may be modified or overprinted by secondary processes that complicate interpretations of paleomagnetic data. Hematite (U‐Th)/He (hematite He) dating has the potential to resolve when secondary magnetizations were acquired. Here, we compare hematite He data and paleomagnetic results in Paleoproterozoic crystalline rocks, meters below a major nonconformity in the Colorado Front Range, USA. Prior work and new rock magnetic data indicate that pervasive hematite alteration records a secondary chemical remanent magnetization (CRM) during the Permo‐Carboniferous Reverse Superchron, coincident with the Ancestral Rocky Mountain orogeny. We target minor hematite‐coated faults cutting basement for (U‐Th)/He analyses because they are of sufficient hematite purity to yield geologically meaningful dates. Two samples yield overlapping and scattered individual hematite He dates ranging from ∼138 to 27 Ma (n = 33), significantly younger than the age of the late Paleozoic CRM. Scanning electron microscopy, electron probe microanalysis, and Raman spectroscopy indicate that aliquots have variable grain size distributions and fluorocarbonate impurities. Thermal history models support hematite on fault surfaces mineralized coeval with CRM acquisition during the late Paleozoic, and hematite He data scatter reflects variable He loss during Mesozoic burial owing to differences in grain size distribution from fault slip comminution and in chemistry among aliquots. Our results underscore the differences in temperature sensitivity and sampling requirements between paleomagnetic and hematite He investigations and illustrate that hematite He dates will usually be younger than preserved remanent magnetizations.

Mesozoic intrusive rocks are extensively outcropped in the Cathaysia Block (CB), indicating that they underwent significant exhumation after being formed. However, tectonothermal evolution of the CB during Mesozoic–Cenozoic times is still poorly constrained and associated geodynamic mechanisms driving the regional exhumation remain elusive. Toward this end, we present first zircon and apatite (U‐Th)/He data of eight Mesozoic granitic plutons distributed across the intracontinental CB. Our new dating results are integrated with a compilation of regional low‐temperature thermochronological data to determine the CB evolution in a tectonic and topographic evolution framework. Zircon and apatite (U‐Th)/He central ages of the eight granitoids range from 146 to 30 and 82 to 31 Ma, respectively, implying a long‐lasting exhumation of the intracontinental CB. Inverse thermal modeling of the thermochronological data for the eight plutons indicates that the intracontinental CB underwent three exhumation phases at 150–110, 110–85, and 66–38 Ma, of which the former two exhumation phases were prolonged and significant. A compilation of regional thermochronological data reveals a propagating locus of fast exhumation phase from the intracontinental CB to the seaward epicontinental CB over time. Combined with other geological evidence, we infer that primary exhumation events of the CB resulted from changing subduction processes of the Paleo‐Pacific Plate, which include slab break‐off and foundering in the Late Jurassic, progressive slab retreat in the Early Cretaceous, and normal subduction in the Late Cretaceous, with minor exhumation events presumably triggered by the Paleogene opening of the South China Sea Basin. Plain Language Summary: The Cathaysia Block (CB) is characterized by extensive outcrops of Mesozoic intrusive rocks. However, low‐temperature thermochronological history of the CB, particularly in the far hinterland, is poorly constrained and variably interpreted. Consequently, geodynamic processes driving the remarkable crustal exhumation remain elusive. To address this issue, we report firsthand zircon and apatite (U‐Th)/He dating results of eight Mesozoic granitoid plutons in the intracontinental CB and use these to unravel the detailed thermal history by applying inverse modeling. The integrated thermochronological data and inverse thermal history models indicate two major exhumation phases of the intracontinental CB in the Cretaceous, followed by a minor exhumation phase in the Paleogene. Further, regional thermochronological data were integrated into a map and spatiotemporal patterns over time were restored, enabling us to reconstruct a precise geochronological framework of regional exhumation events. The results reveal a migration locus of fast exhumation phase from the intracontinental CB to the seaward epicontinental CB over time. The propagating exhumation events, together with other geological observations, are explainable with advancing and retreating oceanic subduction processes. Therefore, we argue that the changing subduction processes were likely a primary inducement that set off significant tectonic and topographic changes of the CB. Key Points: First ZHe and AHe data spanning the intracontinental Cathaysia BlockThree‐stage exhumation occurred in the intracontinental Cathaysia Block during Late Jurassic–Eocene timesRegional thermochronological data favor significant exhumation triggered by the changing Paleo‐Pacific Plate subduction processes [ABSTRACT FROM AUTHOR]

Timing and duration of ore deposit formation are crucial to understanding the mineralization process. To address this, the geochronological (U-Th)/He method, geochemical and H- and O-isotope compositions of pure goethite formed in the Imini karst-hosted Mn district (High Atlas, Morocco) were examined in detail. Two main generations of cavity-filling and fracture-filling goethite are identified, and both precipitated prior to the massive Mn oxide ore. The δD and δ18O values reveal that the mineralizing fluid of cavity and fracture-filling goethite is meteoric-derived but enriched in 18O due to fluid–rock interactions with the host rock dolostone or mixing with O2-rich surface water resident in an open karst system. The cavity-filling goethite precipitated between 95 to 80 Ma, whereas fracture-filling goethite formed between 80 to 50 Ma. Ore deposition occurred discontinuously during the early Atlas doming associated with one or more early compressional events in the Atlas tectonism. The increase in δD values and depletion in U content result from a change in the mineralizing fluid within the karst system. At about 50 Ma, the fluid is notably enriched in U, Cu and trace metals. [ABSTRACT FROM AUTHOR]

Sporadic pulses of basaltic volcanism in the Western Carpathians during the Late Miocene to Middle/Late Pleistocene were contemporaneous with the formation of modern topography. Low-viscosity basaltic lavas entering river valleys influenced the evolution of drainage systems and the surrounding terrain. This study targets two important alkali basalt occurrences in the Western Carpathians – the Ostrá Lúka (OL) basalt complex and the Putikov vŕšok Volcano (PvV). These basalt complexes are unique in their spatial proximity to the Hron River valley, yet their age is unclear. We present new geochronological constraints for both basalt effusions and investigate their potential impact on the evolution of the Hron River valley. 40Ar/39Ar dating of plagioclase from two OL basalt samples yielded Late Tortonian plateau ages of 7.6 ± 0.1 Ma and 7.8 ± 0.1 Ma. The zircon (U-Th)/He age of 5.9 ± 0.6 Ma from one of the OL samples indicates post-eruption rejuvenation likely by younger lava flows. While fluvial morphometric indices extracted from the current Hron River channel in the OL area likely reflect younger uplift events, χ-elevation profiles of the Hron River left-side tributaries still indicate past drainage reorganisations. We hypothesise that the Hron River was diverted westward in the Late Tortonian when voluminous OL lavas blocked its earlier southward-trending paleo-valley. However, more data is required to confirm this hypothesis. Luminescence dating applied to sediments from a fluvial terrace underlying PvV basalt flow revealed minimum depositional ages of >165 ± 23 ka and > 163 ± 27 ka. These ages are older than the currently accepted OSL age (102 ± 11 ka) but consistent with the recently published K/Ar age of PvV basalts (450 ± 30 ka). The older terrace age suggests delayed incision and challenges the validity of the currently used classification of river terraces in the study area. The valley damming by lava flow followed by younger aggradation phase(s) can explain the seemingly low average incision rate (up to ∼0.03 mm yr−1) in this segment of the Hron River, which is supported by the linear inversion of its tributary profiles in the PvV area. • New robust 40Ar/39Ar and (U-Th)/He age constraints of the Ostrá Lúka alkali basalts • Revisited age limits of the Putikov vŕšok volcanic activity based on new OSL data • Interactions of basaltic lavas with the paleo-Hron revealed by morphometric indices • Valley damming and anomalous sediment supply were responsible for delayed incision. • OSL data put the terrace classification system in the study area into question. [ABSTRACT FROM AUTHOR]

The Late Mesozoic tectono-thermal evolution and geodynamic setting of the Great Xing'an Range (GXR), particularly in the south margin, are still ambiguous. In this study, we present original low-temperature thermochronological data of six granitoid samples collected from Maanzi pluton in the south margin of the GXR. The apatite and zircon (U-Th)/He ages vary of 70.8 ± 4.3–119.0 ± 7.0 Ma and 120.0 ± 7.1–146.7 ± 8.7 Ma, respectively. Further numerical inverse modeling results reveal that the granitoid plutons experienced a rapid cooling and exhumation stage during Early Cretaceous with a rate of ∼5.0–6.0 °C/Ma and ∼0.14–0.17 mm/yr, respectively, including the western minor pluton emplaced during Early Permian and the major pluton crystallized in latest Jurassic, corresponding to the extensional tectonics in NE China. The rapid exhumation processes in the south margin of the GXR during the Early Cretaceous could be related to both the rollback of Paleo-Pacific oceanic plate and the collapse of thickened crust in the Mongol-Okhotsk Orogen. [ABSTRACT FROM AUTHOR]

The Jueluotage area, which is located in the southern branch of the Eastern Tianshan and northeast of the Tarim Basin, represents a vital locality for investigating intracontinental reactivation induced by the tectonic events at the Eurasian plate margin. This study applies zircon and apatite (U–Th)/He and apatite fission-track thermochronology to the Jueluotage area in the Eastern Tianshan. Our data and thermal history modelling show that the Jueluotage area experienced Triassic–Early Jurassic (˜240–180 Ma) cooling, reflecting the closure of the North Tianshan Ocean and subsequent far-field effects of collision/accretion of the Qiangtang Block and Kunlun terrane. Following this period of fast cooling, a differential exhumation process occurred between the various tectonic belts in the Jueluotage area. The Aqishan–Yamansu belt was exposed at the surface during the Triassic–Early Jurassic cooling phase and experienced subsequent burial, which continued until Early Cretaceous time when a pulse of exhumation occurred. However, the major fault zones (Kanggurtag ductile shear zone and Aqikkuduk Fault) and Central Tianshan arc have remained tectonically stable since Early Jurassic time. No Cenozoic rapid cooling was recorded by the low-temperature thermochronology results in this study, indicating that much of the Jueluotage area was exhumed to the upper crust in the late Mesozoic period. [ABSTRACT FROM AUTHOR]

The age of central Yunnan fragment uplift has long been debated, with estimates ranging from the Late Eocene to about 1 Ma. To determine the central Yunnan fragment uplift time in the Cenozoic, apatite (U-Th)/He (AHe) was used to analyze the low-temperature thermochronology of samples from the Jiaozi Mountain area of the eastern central Yunnan fragment. The sampling area is located in the Dongchuan District of Kunming, Yunnan Province, near the Xiaojiang fault zone. The results show that AHe ages from the eastern part of central Yunnan fragment were mainly concentrated around 25.7–37.9 Ma, and intensive uplift had happened before 36.5 Ma. Together with previous low-temperature thermochronology research on the western and eastern central Yunnan fragment, we concluded that the Yunnan Plateau uplifted prior to 36.5 Ma, in a west to east sequence. The uplift caused a change in paleo-geographical terrain, which may have altered the ancient river systems of the southeast Tibetan Plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • Determination of tilting of crystalline bodies by low-T thermochronology tools. • The methodology applied to determine tilting is crucial for the exploration of PCDs. • Halilaga deposit exhumed by the coupling effects of Aegean extension and westward propagation of the North Anatolian Fault. • Aegean back-arc extension initiated at ∼ 24 Ma in the north of Western Anatolia. • Westward propagation of the North Anatolian Fault occurred no earlier than 2 Ma. Because most crystalline bodies lack intrinsic paleo-horizontal information, their tilting cannot be measured directly. Their vertical movement, however, may be tracked by low-T thermochronology (LTT) tools. Because tilting is caused by differential vertical movements, it can be understood if the rate of differential movements is determined. In this regard, here we apply a new LTT-based approach to calculate the orientation of a tilted crystalline body, the Halilaga Cu-Au deposit, in NW Anatolia. Orientation is consistent with the one calculated from a drillhole-based 3D model of the deposit. This reveals the significance of tilting calculations for the exploration of porphyry Cu deposits. On the other hand, and more importantly, it emphasizes the importance of tilting calculations for geological applications such as LTT-based exhumation histories of samples taken from vertical profiles, and paleomagnetic studies. AHe data from the Halilaga deposit reveals the earliest response to the Aegean back-arc extension at ∼ 24 Ma in the north of Western Anatolia. Lastly, thermal models, the new complementary datasets for the tectonic evolution of the region, show that the Halilaga deposit was exhumed to the surface by the coupling effects of Aegean extension and westward propagation of the North Anatolian Fault, which occurred not earlier than 2 Ma. [ABSTRACT FROM AUTHOR]

We have developed the first laboratory for (U-Th-Sm)/He thermochronology measurements in South America. Helium is measured using a high-sensitivity magnetic sector mass spectrometer (GVI-Helix-SFT) and a double focusing single collector inductively coupled plasma mass spectrometer (Thermo Scientific ELEMENT2) is used for U, Th and Sm determinations. Repeated analyses of fragments of Durango fluorapatite crystals yields an average age of 31.6 ± 1.6 Ma (2σ) (n=62). This overlaps the long-term average of Durango fluorapatite measured in laboratories worldwide. The analysis of multiple single apatite crystals of a Precambrian basement sample from Serra do Mar, southeastern Brazil, yields an average He age (60.5 ± 8.7 Ma; n=8) that overlaps that measured in the SUERC laboratory (59.6 ± 3 Ma; n=3). This confirms that the UNESP laboratory is capable of routinely measuring the (U-Th-Sm)/He ages of single apatite crystals.

Apatite fission‐track (AFT) thermochronology and (U‐Th)/He (AHe) dating, combined with paleothermometers and independent geologic constraints, are used to model the thermal history of Devonian Catskill delta wedge strata. The timing and rates of cooling determines the likely post‐orogenic exhumation history of the northern Appalachian Foreland Basin (NAB) in New York and Pennsylvania. AFT ages generally young from west to east, decreasing from ~185 to 120 Ma. AHe single‐grain ages range from ~188 to 116 Ma. Models show that this part of the Appalachian foreland basin experienced a non‐uniform, multi‐stage cooling history. Cooling rates vary over time, ~1–2 °C/Myr in the Early Jurassic to Early Cretaceous, ~0.15–0.25 °C/Myr from the Early Cretaceous to Late Cenozoic, and ~1–2 °C/Myr beginning in the Miocene. Our results from the Mesozoic are broadly consistent with earlier studies, but with the integration of multiple thermochronometers and multi‐kinetic annealing algorithms in newer inverse thermal modeling programs, we constrain a Late Cenozoic increase in cooling which had been previously enigmatic in eastern U.S. low‐temperature thermochronology datasets. Multi‐stage cooling and exhumation of the NAB is driven by post‐orogenic basin inversion and catchment drainage reorganization, in response to changes in base level due to rifting, plus isostatic and dynamic topographic processes modified by flexure over the long (~200 Myr) post‐orogenic period. This study compliments other regional exhumation data‐sets, while constraining the timing of post‐orogenic cooling and exhumation in the NAB and contributing important insights on the post‐orogenic development and inversion of foreland basins along passive margins. [ABSTRACT FROM AUTHOR]

Abstract The topographic evolution of a mountain system provides key information for understanding surface processes. We present a new and relatively simple method to reconstruct two-dimensional paleotopography composed of two steps: (1) construction of thermal history using low-temperature thermochronological data and (2) conversion of the thermal history into topographic evolution. A new computer program " Low-T Topo " was developed to perform the suggested conversion of thermal history to paleotopography. This approach, when applied to the coastal mountain system (CMS) in Southeastern China, suggests an uneven topographic evolution along the Changting-Zhangzhou section since the Late Cretaceous. According to our modeling, the SE segment of the section was higher (maximum peak elevation = ~3.8 km) than the NW segment (~3.4 km) during ~80–50 Ma. The modeling also suggests that both the SE and NW segments experienced an initially higher exhumation rate of ~0.14 km/Myr at 80–70 Ma, which steadily decreased to about 0.03 km/Myr at 40 Ma. Since then, exhumation rates stayed relatively low (≤~0.05 km/Myr). The elevation reduction in the CMS since the Late Cretaceous played an important role introducing the warm and humid Pacific air to the inland. Graphical abstract Unlabelled Image Highlights • An inversion method is developed to reconstruct 2-D topographic evolution. • The method is based on conversion of low-T thermochronology to paleotopography. • The method revealed uneven topographic evolution of SE China since Late Cretaceous. [ABSTRACT FROM AUTHOR]

Abstract Conventional (U-Th(-Sm))/He thermochronology requires accurate determination of the grain shape and dimension for calculation of 4He loss by alpha particle ejection and diffusion. In routine practice, calculations of 4He loss and diffusion are calculated assuming that measured grains approximate symmetric grain shapes with perfectly smooth crystal surfaces. This may introduce uncertainties that are virtually impossible to quantify if grains that do not pass the latter criteria are used. Alternatively, this leads to a selection bias for the analyses of detrital minerals if only grains with perfect crystal surfaces are measured. To address this limitation, we introduce a flexible, open-source numerical approach in Matlab™ to accurately determine the three-dimensional grain shape and numerically model He loss by alpha ejection and diffusion on individual grains. The three-dimensional surface of a mineral grain is interpolated from photomicrographs taken orthogonal to the principal grain axes. He ejection and diffusion is simulated using a coupled Monte Carlo and Brownian motion algorithm. Comparing our approach to high-resolution X-ray microtomography, we demonstrate that our "3D-He" approach improves the accuracy of He loss corrections when mineral grains do not approximate perfect crystal shapes by avoiding constraints inherent to standard manual-analytical approaches. Importantly, this method mitigates any bias introduced by user-dependent grain selection, measurements and assigning grains to a mineral shape for which analytical solutions of He production have been derived. In routine practice, we find that our 3D-He approach improves the accuracy of geometric measures (volume and surface area) and associated sphere-equivalent radii (SER) significantly, reducing the average deviation from true values from ~7–8% (manual-analytical approach) to ~2.5% (3D-He approach). The difference in SER significantly impacts the resulting apatite (U-Th-Sm)/He ages, which may deviate up to 40% when long held at temperatures where He production roughly matches diffusive loss of He. Using the 3D-He approach, the average deviation and overall spread of He loss corrections due to alpha ejection (F T factors) could be reduced from 1.6 ± 4.6% to 0.6 ± 0.8%. In summary, our 3D-He approach is a significant refinement to (U-Th(-Sm))/He age calculation considering relatively low analytical uncertainty in U, Th, Sm and He measurement (~2%). Importantly, our 3D-He approach should mitigate the selection bias introduced through manual grain selection. Toward this end, we discuss additional advantages of our numerical approach to handling broken grains or grains with known parent isotope zonation. [ABSTRACT FROM AUTHOR]

The typically high U and Th contents of xenotime ([Y,HREE]PO4) make this accessory mineral a promising candidate for (U‐Th)/He thermochronometry if the 4He diffusivity can be constrained well enough to estimate its closure temperature. We report new results for two 4He step‐heating experiments on different‐sized fragments of a natural xenotime crystal from the Torghar district of Pakistan (FPX‐1). This material, which has a composition within the range of most natural xenotimes (72 mol % YPO4), yields a laser ablation 238U/206Pb date of 28.82 ± 0.13 Ma and a (U‐Th)/He date of 15.32 ± 0.61 Ma (2σ). Results for our more detailed diffusion experiment display excellent linearity on an Arrhenius diagram and indicate kinetic parameters of E = 131.4 ± 1.1 kJ/mol and ln(D0/a2) = 10.61 ± 0.20 ln(s−1). These results suggest that the bulk closure temperature for 4He in the degassed crystal fragment is ∼75 °C for the nominal cooling rate of 10 °C/Ma. At equivalent cooling rates and for crystals with equivalent diffusion dimensions, the closure temperature for helium in xenotime is ∼20 °C lower than the closure temperature for helium in apatite. Because xenotime typically has high U and Th contents, it may serve as a high‐precision method for dating young, low‐temperature cooling histories of rocks in which it crystallized. Helium diffusion in xenotime is likely to be moderately anisotropic and moderately dependent on crystal chemistry, so closure temperature interpretations should be made cautiously. Key Points: Kinetic parameters are reported for helium diffusion in natural xenotimeThe bulk closure temperature for helium in xenotime is ∼20 °C lower than that for helium in apatiteHelium diffusion in xenotime is likely only moderately, not extremely, anisotropic [ABSTRACT FROM AUTHOR]

Abstract: The sinistral Altyn Tagh strike‐slip fault demarcates the northern boundary of the Qinghai‐Tibetan Plateau; however, the significance and timing of activity along the fault are debated. Here new apatite and zircon (U‐Th)/He data are presented, revealing the exhumation history of the Altyn Tagh Mountains from crustal depths of ~2–7 km. Studies of rock samples from the Altun Shan region show that they were located close to the surface during the Early Cretaceous and remained so until about 40 Ma. Samples from the Subei and Dangjin Pass areas, on the other hand, record a period of rapid exhumation at 20 ± 2 Ma, and samples from the Qiemo area record a period of continuous exhumation between ~20 and 12 Ma at a rate of 0.046 − 0.013 + 0.007 mm/year, plus a further rapid cooling event at 7–5.5 Ma. Thus, significantly more exhumation has occurred toward the southwestern section of the Altyn Tagh Fault Zone, indicating a decrease in tectonic uplift toward the northeast since the Miocene. During the late Miocene, the Tarim Block began to subduct beneath the northern Tibetan margin, resulting in rapid exhumation of the central section of the Altyn Tagh Fault Zone. In accordance with previous studies, the present results support a model of northward propagation and expansion of the Qinghai‐Tibetan Plateau during the Cenozoic. [ABSTRACT FROM AUTHOR]

The coastal mountain system (CMS) of southeastern China has been a natural place to study paleotopographic changes primarily due to its marked topographical contrast since the Late Cretaceous. For a quantitative reconstruction of the paleotopographic evolution of the CMS, this paper provides key information from along the Ningde–Jianyang and Huilai–Longchuan cross-sections using apatite (U-Th)/He (AHe) and zircon (U-Th)/He (ZHe) data combined with thermal history and paleotopographic modeling. For the Ningde–Jianyang section, the AHe dates are in the range of 44.3–70.8 Ma, and the ZHe dates are between 58.5 and 102.9 Ma. For the Huilai–Longchuan section, the resulting AHe dates are in the range of 37.9–73.8 Ma, and ZHe dates are between 65.5 and 119.7 Ma. The modeling results suggest that: 1) the CMS had an asymmetric topography during the Late Cretaceous with the SE segment being significantly higher (peak elevation = 3.8 km) than the NW segment (peak elevation = ~2 km). The marked decreases in elevation and relief of the CMS occurred during 80–40 Ma, followed by relatively minor topographic changes since ~40–30 Ma; 2) The SE segment of the southern CMS experienced significantly faster exhumation (~0.44 km/Myr) than northern CMS (0.16 km/Myr) during 70–60 Ma, which was probably related to thinning of the crust and orogenic collapse linked to the initial-rifting of the South China Sea; 3) The SE segment of southern CMS experienced slower exhumation than northern CMS during 60–40 Ma, likely resulting from the lower elevations in the southern CMS than in the northern CMS during 60–40 Ma. • The coastal mountain system forms a climatic boundary in southeastern China. • Thermochronological data collected along two horizontal transects. • Transect thermochronology results used for topography modeling. • Rapid exhumation from 70-60 Ma along the south 2-D transect linked to rifting. • Rapid exhumation from 60–40 Ma along the north 2-D transect linked to climate change. [ABSTRACT FROM AUTHOR]

Abstract: (U‐Th)/He geochronology and cosmogenic 3He in iron oxides reveal mineral precipitation ages as old as 55 Ma and exposure ages greater than 5 Ma for canga‐cemented plateaus in the Quadrilátero Ferrífero, Brazil, showing that lateritic profiles overlying banded iron‐formation (BIF) landscapes in tropical regions have a long history of surface exposure. The long‐term erosion history obtained from cosmogenic 3He on BIF plateaus confirms that relic surfaces persist in the landscape for millions of years. Combined 3He and (U‐Th)/He dating shows that cangas are preferentially goethite cemented by biogeochemical reactions in the subsurface. Importantly, pebbles of hematite‐magnetite in colluvia or shallow creeks draining the canga‐cemented plateaus record a much longer exposure history than in situ canga blocks, showing that even older duricrusts, now eroded, once blanketed these plateaus. Physically stable but biogeochemically dynamic, cangas armor the landscape by pervasive and recurrent iron cycling and cementation, slowing down the delivery of weathered BIF or friable hematite–magnetite ore to erosion. [ABSTRACT FROM AUTHOR]

The timing of the development of the highland topography along the northern margin of the Tibetan Plateau is the key to understanding the manner of Tibetan growth and the far-field effects of the collision between India and Eurasia. Although various studies have investigated the exhumation and uplift of the basement rocks, thermochronological studies on the detritus from a continuous depositional sequence inan intermontane basin are lacking but might shed light on this issue. In this study, a set of detrital apatites from an upper Eocene to Pliocene depositional sequence in the Kumukol Basin, the largest intermontane basin in the East Kunlun, were dated by using the (U-Th)/He technique. The detrital apatites had consistent ages of ∼40 Ma for all deposit formations from bottom to top, which were older than the depositional ages. The ages and their consistency suggested that these detrital apatites were not reset and that the ages represented the original ages in the provenance region. These detrital apatite ages from the upper Eocene to Pliocene formations strongly suggested that the high mountains surrounding the Kumukol Basin formed at or before ∼40 Ma and have remained high since then. The process of mountain building resulted in a prolonged period of erosion from ∼40 to 2.6 Ma. The coupling of mountain and basin at ∼40 Ma was widespread along the East Kunlun. Our present results constrain the time of onset of the mountain building along the northern margin of the Tibetan Plateau, which may represent a rapid response to the India-Eurasian collision. [ABSTRACT FROM AUTHOR]

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) provides the spatial distribution of elements within crystals and therefore can constrain the rates of geological processes. Spatial resolution of LA-ICP-MS is limited by the requirement to ablate sufficient material to surpass the detection limit of the instrument: too little material and the concentration cannot be measured; too much material from the same spatial location and the possibility of depth dependent variations in concentration increases. Because of this requirement and typical analytical setup, this commonly places a lower bound on the diameter of an ablation ‘spot’ size of approximately 20 μm for elements with ppm concentration. Here we present a means to achieve sub-spot size resolution using inverse methods. We discretize the space sampled in an analysis into pixels and note that the average concentration of the pixels sampled by a spot equals the measured concentration. As multiple overlapping spots sample some of the same pixels, we can combine discrete expressions for each spot as a system of linear equations. Through linear inversion with smoothness constraints we can solve for unknown pixel concentrations. We highlight this approach with two natural examples in which diffusive processes are important: magmatic ascent speeds and (U-Th)/He noble gas thermochronometry. In these examples, accurate results require that the true concentration gradients can be recovered from LA-ICP-MS data. We show that the ability to infer rapid rates of magma ascent is improved from months to weeks and that we are able to interpret previously un-interpretable thermochronometric data. [ABSTRACT FROM AUTHOR]

We obtained (U–Th)/He formation ages and cosmogenic 3 He concentrations for pisoliths from a paleosol of the Bohnerz Formation (Siderolithic) of Central Europe. The paleosol is exposed in the Almenbühl quarry near Lohn, Canton Schaffhausen, Switzerland. The paleosol consists of red clay of 3–4 m thickness developed on deeply weathered Jurassic limestone and overlain by Early Miocene conglomerates. The (U–Th)/He formation ages of the pisoliths are between 50 Ma and 8 Ma, with most ages being older than 17 Ma. There is a sharp decline in the frequency of ages at the time of burial of the paleosol at 17 Ma. These ages are inconsistent with the previous assumption that the Bohnerz Formation formed in a Cretaceous to Early Eocene laterite in a tropical climate. We propose that the Bohnerz Formation more closely resembles Terra Rossa soils, which do not require a tropical climate to form. The 3 He concentration in the pisoliths is roughly constant with depth throughout the paleosol at 300 Matoms/g. We interpret this as the result of soil convection during cosmic ray exposure. The minimum exposure duration at the surface of the paleosol is ∼5 Ma. A simple model of soil convection shows that the true exposure duration of the paleosol is approximately 10–20 Ma. These results indicate that the clay soils of the Bohnerz formation were continuously exposed at the surface for millions of years. Since the paleosol was covered by conglomerate since 17 Ma, the 3 He measured here was produced by cosmic ray exposure before burial. Cosmogenic 3 He concentrations measured in fine-grained soil iron-oxides (<1 μm) are similar to those measured in pisoliths. This might indicate that fine-grained iron-oxides are retentive to helium and might be used for studying the formation and cosmic ray exposure of modern soils and paleosols. [ABSTRACT FROM AUTHOR]

The combination of U-Th disequilibrium/U-Pb and (U-Th)/He dating of zircon (ZDD) has provided a relatively new radiometric approach suitable for dating Quaternary zircon-bearing volcanic and pyroclastic deposits. This approach permits the dating of zircon as young as ca. 2.5 ka and has huge potential for tephrochronology and other fields of Quaternary science. Its applicability range covers the critical time-window in Quaternary geochronology beyond the range of 14 C and below the limit of routine Ar/Ar dating (i.e. between ca. 50 ka and 1.5 Ma). The combined U-Th disequilibrium/U-Pb and (U-Th)/He dating approach can also be applied to other actinide-rich minerals such as allanite or monazite. In <1 Ma young volcanic samples, the integration of the low-temperature (U-Th)/He geochronometer with the high-temperature U-Th disequilibrium/U-Pb geochronometers is essential in order to correct for disequilibrium in the U-decay chains which, when ignored, may result in erroneous underestimation of true eruption ages. In this review paper we summarize past developments and the current state of the ZDD method, explain the theoretical principles, and document the necessity of combining (U-Th)/He with U-Th-disequilibrium and/or U-Pb methods when dating young volcanic material. We then describe analytical procedures and highlight the advantages of the ZDD method. Finally, we present some examples that illustrate the efficacy of this method to derive reliable eruption ages for young tephras, and outline future directions in methodological development and application for this geochronological tool. [ABSTRACT FROM AUTHOR]

Post-orogenic extension in the southeastern Canadian Cordillera manifested in the form of metamorphic core complexes exhumed during the Paleocene–Eocene, but new thermochronology data suggest this interval may be longer. The Columbia River Fault is a brittle-ductile normal fault bounding the eastern margin of the Monashee Complex, southeastern British Columbia. Vertical motions along this fault are investigated here using apatite fission-track and (U-Th)/He thermochronology and samples from two elevation profiles. Apatite fission track ages range from 29.3 to 17.7 Ma, and apatite (U-Th)/He ages range from 26.6 to 7.0 Ma. Inverse thermal history modeling of these profiles suggests the footwall underwent rapid cooling between 18 and 16 Ma, whereas the hanging wall experienced more protracted cooling since 40 Ma, with two small cooling pulses at 20 and 10 Ma. These new data suggest the Columbia River Fault was reactivated in the early Miocene and continued to exhume the Monashee Complex an additional ∼2 km. Combining all thermochronology data from the region suggests three phases of accelerated cooling in the Monashee Complex; 1) Eocene (56–40 Ma); 2) Miocene (20–16 Ma); and 3) Pliocene to recent. Thermal history modeling of thermochronometric data reported from elevation profiles from across the wider region of the southern Canadian Cordillera find early Miocene cooling phases contemporaneous with that seen along the Columbia River Fault. This widespread exhumation coincides with early Miocene plate tectonic reorganization of the Pacific-North American margin which resulted in increased transtension in northwestern North America. We propose that the early Miocene reactivation of the Columbia River Fault is a splay fault associated with dextral strike slip faulting along the Rocky Mountain Trench, driven by an increase in transtensional stresses along the Pacific-North American plate boundary. Building on earlier models, pre-existing gravitational instabilities in the southeastern Canadian Cordillera aided in lateral extension of the upper crust along unstable inherited structures throughout the Shuswap Metamorphic Core Complex • Apatite thermochronology reveals Miocene reactivation of the Columbia River Fault. • Widespread early Miocene transtension occurred west of the Rocky Mountain Trench. • Changes in Pacific–North American plate motion caused inboard deformation • Late Miocene to recent erosion of the Columbia Mountains was <2 km. [ABSTRACT FROM AUTHOR]

The structural and thermal evolution of major low-angle normal faults in the Colorado River extensional corridor has been a controversial topic since the pioneering studies of metamorphic core complexes in the early 1980s. We present new geo-thermochronometry data from the Harquahala Mountains in west-central Arizona to determine the timing of extension, displacement magnitude, and slip rates along the Eagle Eye detachment fault (EED) during large-magnitude Miocene extension. Zircon and apatite (U-Th)/He data (ZHe and AHe, respectively) from 31 samples along a ~55 km extension-parallel transect indicate active slip along the EED occurred between ~21 ± 1 Ma and ~14 Ma. The spatial extent of ZHe ages and exhumation of the zircon partial retention zone indicated ~44 ± 2 km of total displacement, whereas lithologic similarity and identical U-Pb ages between correlated footwall rocks in the Little Harquahala Mountains and breccia clasts at Bullard Peak in the NE Harcuvar Mountains indicated ~43-45 km of displacement across the EED. AHe and ZHe data indicated slip rates of ~6.7 + 7.8/−2.3 km/Myr, and ~6.6 + 7.1/−2.0 km/Myr, respectively, both consistent with the duration and displacement estimates. The EED initiated as a listric fault with an ~34 ± 9° dip that decreased to ~13 ± 5° below ~7 km depth. Secondary breakaway development and footwall exposure occurred by ~17 Ma, during active EED slip. Lithologic and geo-thermochronometric offset constraints show excellent agreement and provided a rare opportunity to fully resolve the timing, rates, and total displacement magnitudes along a major continental detachment fault. [ABSTRACT FROM AUTHOR]

How does the rising Tibetan Plateau affect its peripheral region? The current understanding of the mechanism of orogenic plateau development is incomplete and thus no consensus yet exists in this regard. However, our new 40 Ar/ 39 Ar and (U–Th)/He dataset presented in this study may shed some light on this issue. 40 Ar/ 39 Ar dating, on two vertical transects from the massif between Nuomuhong and Golmud, indicates that the Eastern Kunlun Range was built-up and exhumated during the later Triassic initially, and a minimum overburden of ~ 11.7–14.0 km has been eroded since ~ 220 Ma. (U–Th)/He age–elevation relationships (AERs) indicate a rapid exhumation event at ~ 40 Ma following a long period of slow exhumation phase from late Mesozoic to early Eocene time. In this study, two scenarios – one assuming a single stage and the other assuming multiple stages of evolution history – are modeled. Modeling of a multiple stage scenario is reasonable and is able to reflect the “actual” situation, which reveals the entire denudation and relief history of the northern Tibet from late Mesozoic to the present time. After prolonged denudation before 50 Ma, a low topography (~ 0.17 times the relief of the present) developed by 50 Ma with an erosion rate of 0.013 -0.013 + 0.025 mm/yr. The highest relief (~ 1.82 times the relief of the present) of the Cenozoic time came into being at 40 Ma with an erosion rate of 0.052 ± 0.025 mm/yr, which was possibly a result of the collision between India and Eurasia. Subsequently, the relief steadily decreased to the present level due to continued denudation. This suggests that deformation propagation from the continued convergence boundary between India and Eurasia was insignificant after the construction of the highest relief. This observation is broadly consistent with published accounts on the stratigraphic, cooling, and faulting histories of the northern Tibet margin. [ABSTRACT FROM AUTHOR]

[Display omitted] • Over 4 km of cover was eroded during the late Paleozoic–Early Jurassic exhumation. • AHe and AFT age–elevation profiles show exhumed PRZ and PAZ. • Tectonic stability occurred during the middle–late Mesozoic–early Cenozoic. • The late Cenozoic uplift merely caused limited exhumation (∼0.9 km). Numerous Paleozoic deposits have been found in the Tianshan Mountains. Postmineralization burial plays an important role in the preservation of Paleozoic epizonal deposits. However, the preservation mechanisms for mesozonal deposits in the Tianshan Mountains need further investigation. The late Paleozoic Katebasu gold–copper deposit (with a reported mineralization age varying from ∼ 270 Ma to ∼ 330 Ma) in the Chinese Western Tianshan is a mesothermal magmatic hydrothermal deposit that formed at mesozonal depths. The exhumation process and preservation mechanisms of this deposit remain ambiguous. In this study, (U–Th)/He and fission-track dating were applied to samples from a vertical profile to constrain the exhumation history of the Katebasu deposit. Apatite (U–Th)/He and fission-track ages vary systematically with elevation, ranging from 32.4 ± 9.0 Ma to 176.4 ± 18.0 Ma and 106.4 ± 3.1 Ma to 181.7 ± 5.1 Ma, respectively. Zircon (U–Th)/He ages range from 220.4 ± 11.0 Ma to 260.1 ± 17.4 Ma. The age–elevation relationship and inverse thermal modeling reveal that the Katebasu deposit underwent two phases of exhumation. The first phase of exhumation, which caused at least 4 km of erosion, occurred during the late Paleozoic to Early Jurassic. The second exhumation started during the Early Oligocene, resulting in ∼ 0.9 km of erosion. A protracted period of tectonic stability during the middle–late Mesozoic to early Cenozoic and limited exhumation during the late Cenozoic uplift played important roles in the preservation of the Katebasu deposit. [ABSTRACT FROM AUTHOR]

This study investigates the long-term deformation and rock exhumation of the subducting Yakutat microplate corner at the St. Elias syntaxis region with a special focus on the area east and west of Yakutat Bay, where major coseismic surface uplift occurred during a MW 8.2 earthquake in 1899. We use low-temperature thermochronology to quantify the long-term activity of thrust and reverse faults. We present new apatite and zircon (U-Th-Sm)/He ages from 35 bedrock samples collected along profiles crossing major faults that compose a one-sided flower structure at the northern end of the Fairweather Fault. The cooling ages reveal that rapid rock exhumation is accommodated by the eastern Esker Creek Fault and the Yakutat Fault with rates of 2-3 mm/yr and slower rates of <1.5 mm/yr occur along the Boundary Fault. Exceptionally high exhumation rates of 3-5 mm/yr are recorded by <1 Ma apatite ages at the western part of the Esker Creek Fault and the Chaix Hills Fault. This area is closest to the intersection line of the northwest striking reverse faults associated with the northern Fairweather Fault and the shallow dipping northeast striking thrusts of the Pamplona-Malaspina fault zone. The long-term exhumation patterns derived from this new thermochronology data are compared with the observed coseismic uplift pattern caused by the 1899 earthquake, revealing good agreement and supporting the speculation that the 1899 rupture propagated along the western part of the Esker Creek Fault and the Chaix Hills Fault. Thus, this study illustrates that low-temperature thermochronology can support seismic hazard analyses particularly in area where preservation of paleoseismic field evidence is challenged. [ABSTRACT FROM AUTHOR]

In this paper, we use several analytical methods in an effort to better understand the systematics of the (U-Th)/He chronometer in hematite and manganese oxides. 4He diffusion data from a polycrystalline hematite sample is consistent with diffusion from hematite crystals with a range of sizes similar to those directly observed in sample material. Combined with a compilation of hematite He diffusion data from previous studies, this supports the interpretation that in general crystal size is a primary control on He retentivity in hematite. 4He/³He diffusion data from a single fragment of a larger hematite crystal imply the presence of multiple diffusion domains smaller than the observed size of the crystal fragment, which may be related to cracks, inclusions, or other internal features, as well as higher concentrations of 4He in smaller domains. We use kinetic values determined in this and other studies and measurements of hematite crystal size in each dated sample to estimate approximate closure temperatures for each sample, most of which range from 140 to 240 °C. Relationships between minor element and parent nuclide concentrations and (U-Th)/He dates measured in aliquots of some analyzed hematite samples suggest that, in some cases, U and Th are concentrated in interstitial phases other than hematite. We identify two processes responsible for much of the dispersion in hematite dates from single samples. Removal of U- and Th-rich interstitial phases from analyzed material during sample preparation or analysis leaves behind unsupported 4He implanted in hematite crystals. This removal results in apparent (U-Th)/He dates artificially older than the time of hematite He closure. A smaller source of dispersion that is likely to still be significant in some samples can be attributed to the high He diffusivities of observed interstitial phases, which do not retain implanted He. (U-Th)/He dating of hematite from upper and lower-plate rocks in the Buckskin and Rawhide detachment fault system of western Arizona yields ages that coincide with the timing of rapid extension along the detachment fault. Comparisons of estimated hematite closure temperatures and hematite sample ages to data from other studies of the Buckskin-Rawhide detachment system lead us to conclude that hematite dates record rapid cooling that followed detachment zone mineralization. Mn oxide (U-Th)/He dates are interpreted as formation ages of minerals formed by hydrothermal fluids that circulated through upper-plate rocks after cessation of extension along the detachment fault. Overall, we find that (U-Th)/He dating of hematite and Mn oxide minerals are promising methods for obtaining temporal information about the formation and cooling of these common secondary phases. [ABSTRACT FROM AUTHOR]

This study reconstructs the late stages in the exhumation history of a nappe derived from the Meliatic accretionary wedge in the Western Carpathians by means of zircon and apatite (U-Th)/He dating. The Meliatic accretionary wedge formed due to the closure of the Neotethyan Triassic–Jurassic Meliata–Hallstatt Ocean in the Late Jurassic. The studied fragments of the blueschist-bearing Meliatic Bôrka Nappe were metamorphosed at low-temperature and high- to medium-pressure conditions at ca. 160–150 Ma and included into the accretionary wedge. The time of the accretionary wedge formation constrains the beginning of the Bôrka Nappe northward thrusting over the Gemeric Unit of the evolving Central Western Carpathians (CWC) orogenic wedge. The zircon (U-Th)/He data on four samples recorded three evolutionary stages: (i) cooling through the ∼180 °C isotherm at 130–120 Ma related to starting collapse of the accretionary wedge, following exhumation of the high-pressure slices in the Meliatic accretionary wedge; (ii) postponed exhumation and cooling of some fragments through the ∼180 °C isotherm from 115 to 95 Ma due to ongoing collapse of this wedge; and (iii) cooling from 80 to 65 Ma, postdating the thrusting (∼100–80 Ma) of the Bôrka Nappe slices during the Late Cretaceous compression related to formation of the CWC orogenic wedge. The third stage already documents cooling of the Meliatic Bôrka Nappe slices in the CWC orogenic wedge. The apatite (U-Th)/He data may indicate cooling of a Bôrka Nappe slice to near-surface temperatures at ∼65 Ma. The younger AHe age clusters indicate that at least one, or possibly two, reheating events could have occurred in the longer interval from ∼40 to ∼10 Ma during the Oligocene–Miocene. These were related to sedimentary burial and/or the magmatism as documented in other parts of the CWC. [ABSTRACT FROM AUTHOR]

This paper presents new thermochronological data and reviews a set of recently published data for the Sierras Pampeanas in central and northwestern Argentina, which constitutes a distinct morphotectonic feature between 27°S and 33°S. Thermochronological data, derived from zircon and apatite (U–Th)/He, as well as apatite fission-track dating, reveal that cooling below 200 °C commenced locally during the Carboniferous period. In Permo-Triassic times, pronounced cooling propagated from east to west in the Southern Sierras Pampeanas, being time-equivalent and spatially equivalent to a flat-slab subduction period at these latitudes. Mesozoic rifting, accompanied by sedimentation and burial re-heating, only affected the thermal history of sampled rocks locally, suggesting that substantial sedimentary thicknesses were only accumulated along narrow and spatially-restricted Cretaceous rift basins. Final cooling in the northern Pampean ranges occurred during the Miocene. Contrastingly, in the Southern and Southwestern Sierras Pampeanas, cooling to near-surface temperatures occurred between the Late Cretaceous and the Paleogene, supporting the idea that a positive topography already existed in these areas before the Neogene. This contradicts the previous hypothesis that the uplift of the Pampean ranges is completely related to the Neogene flat-slab subduction. Instead, this process just accentuated a pre-existing relief built up by diachronously developed Mesozoic land surfaces. Calculated long-term denudation rates, varying between 0.010 and 0.024 km/Ma, also support the idea of diachronous surfaces preserved since Mesozoic times. [ABSTRACT FROM AUTHOR]

Channel iron deposits (CID) supply 40% of Australia's iron ore but their genesis is still the subject of debate. Two well-characterised samples of goethite/hematite CID from a diamond drill core in Mesa J of the Robe River area in Western Australia were dated using (U–Th)/He methods in order to constrain the timing of iron oxide formation and thereby provide a temporal context for CID genesis. (U–Th)/He ages (He ages) range from 25.7±0.6 to 7.0±0.8Ma and, despite a high degree of scatter, they corroborate relationships expected from the internal ooidal stratigraphy. For individual ooids, the hematitic core is older than or indistinguishable from the age of the surrounding goethitic cortex. The goethitic cortices are, in turn, older than the ferruginised wood fragments recovered from the cementing goethitic matrix. The data suggest the following paragenesis: (i) Hematitic cores in ooids formed in the Early to Middle Miocene as documented by ages of ~14.3±3.7Ma and 18.3±3.5Ma measured in the shallower (8.2m deep) and deeper (32.8m) sample, respectively; (ii) Goethitic cortices of both samples formed in the late Middle to early Late Miocene at 11.6±3.0Ma; (iii) Wood fragments form a prominent component of the matrix and were ferruginised during the Late Miocene (He ages ranging from 9.4±0.5 to 8.2±0.4Ma in the deeper core and 8.4±0.9 to 7.0±0.8Ma in the shallower core). The data suggest that the unique environmental conditions conducive to CID formation existed during the Miocene and that a “typical Robe River CID sequence” likely took 4 to 8Myr to accumulate. A methodological implication of this study is that it confirms the previous observation of Vasconcelos et al. (2013) suggesting that the temperature utilised for He-extraction from iron oxides has a critical impact on the mobility of parent nuclides. The typical ~1000°C laser heating used for crystalline minerals like apatite or zircon induces loss of U and Th and results in erroneously old ages. Modest extraction temperature (<500°C), utilising a low-power laser or, preferably, a temperature-controllable resistance furnace is recommended. [ABSTRACT FROM AUTHOR]

Abstract: The caldera-forming Rotoiti eruption from Okataina volcano was one of the largest rhyolite events of the last 100ka in the Taupo Volcanic Zone, New Zealand. Its associated widespread tephra layer (Rotoehu tephra) is a significant time marker in terrestrial–marine paleoclimate correlation studies in the SW Pacific. However, the accurate and precise age of this eruption, and of the subsequent, smaller volume Earthquake Flat (EQF) eruption, has been the subject of controversy despite numerous studies. We have applied combined 238U/230Th disequilibrium and (U–Th)/He dating of zircon from Rotoiti and EQF deposits, and obtained overlapping ages of 45.1(7)±3.3ka and 45.1(6)±2.9ka, respectively. These results are supported by new and published high-precision radiocarbon data bracketing the age of the Rotoiti eruption between 44.8±0.3 and 47.5±2.1ka cal BP. These age data are also in good agreement with a range of previously published estimates based on paleoclimate (palynology), luminescence dating of enclosing sediment, and sedimentation rates in terrestrial and marine settings. However, these results are at variance with a commonly quoted age of ∼60ka, largely constrained by a single 40Ar/39Ar age of an overlying glassy lava flow at a distal tephra site. This study demonstrates the potential for combined 238U/230Th disequilibrium and (U–Th)/He dating of zircon in tephra and other volcanic deposits to provide age control in the 40–100ka time interval, a period difficult to constrain using more traditional radiocarbon, K/Ar and 40Ar/39Ar methods. [Copyright &y& Elsevier]

Abstract: According to new apatite fission track, zircon- and apatite (U–Th)/He data, we constrain the near-surface history of the southeastern Tauern Window and adjacent Austrolapine units. The multi-system thermochronological data demonstrate that age-elevation correlations may lead to false implications about exhumation and cooling in the upper crust. We suggest that isothermal warping in the Penninic units that are in the position of a footwall, is due to uplift, erosion and the buildup of topography. Additionally we propose that exhumation rates in the Penninic units did not increase during the Middle Miocene, thus during the time of lateral extrusion. In contrast, exhumation rates of the Austroalpine hangingwall did increase from the Paleogene to the Neogene and the isotherms in this unit were not warped. The new zircon (U–Th)/He ages as well as zircon fission track ages from the literature document a Middle Miocene exhumation pulse which correlates with a period of enhanced sediment accumulation during that time. However, enhanced sedimentation- and exhumation rates at the Miocene/Pliocene boundary, as observed in the Western- and Central Alps, cannot be observed in the Eastern Alps. This contradicts a climatic trigger for surface uplift, and makes a tectonic trigger and/or deep-seated mechanism more obvious to explain surface uplift in the Eastern Alps. In combination with already published geochronological ages, our new data demonstrate Oligocene to Late Miocene fault activity along the Möll valley fault that constitutes a major shear zone in the Eastern Alps. In this context we suggest a geometrical and temporal relationship of the Katschberg-, Polinik–Möll valley- and Mur–Mürz faults that define the extruding wedge in the eastern part of the Eastern Alps. Equal deformation- and fission track cooling ages along the Katschberg–Brenner- and Simplon normal faults demonstrate overall Middle Miocene extension in the whole alpine arc. [Copyright &y& Elsevier]

The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural laboratory for studies of postorogenic landscape evolution. This work reveals both the exhumation history of the region and the paleoactivity along the Sudetic Marginal Fault (SMF) using zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th)/He (AHe) dating of crystalline basement and postorogenic sedimentary samples. Most significantly, and in direct contradiction of traditional paleogeographic reconstructions, this work has found evidence of a large Cretaceous sea and regional burial (to >6.5 km) of the Carboniferous-Permian basement in the Late Cretaceous (∼95-80 Ma). During the burial by sediments of the Bohemian Cretaceous Basin System, the SMF acted as a normal fault as documented by offset ZHe ages across the fault. At 85-70 Ma, the basin was inverted, Cretaceous strata eroded, and basement blocks were exhumed to the near surface at a rate of ∼300 m/Ma as evidenced by Late Cretaceous-Paleocene AFT ages and thermal modeling results. There is no appreciable difference in AFT and AHe ages across the fault, suggesting that the SMF acted as a reverse fault during exhumation. In the late Eocene-Oligocene, the basement was locally heated to <70°C by magmatic activity related to opening of the Eger rift system. Neogene or younger thermal activity was not recorded in the thermochronological data, confirming that late Cenozoic uplift and erosion of the basement blocks was limited to less than ∼1.5 km in the study area. [ABSTRACT FROM AUTHOR]

ABSTRACT. We dated 86 borehole and surface samples from basement-cored Laramide uplifts of the northern Rocky Mountain foreland (Wind River, Beartooth, Bighorn and Laramie Ranges) using the apatite (U-Th)/He system, and eleven samples using the apatite fission-track system (Wind River and Bighorn Ranges). Apatite (U-Th)/He ages generally decrease with increasing subsurface depth (decreasing elevation), and typically range from ~100 to 50 Ma (Cretaceous to Eocene) within ~1 km of the surface, to ~20 Ma (Miocene) and younger ages at depths greater than ~2 to 2.5 km. Most samples display (U-Th)/He age dispersion ranging from tens to hundreds of Ma, and for some samples we find ages that are older than corresponding fission-track ages. At least one sample per range shows a correlation between apatite (U-Th)/He age and effective U concentration (eU = [U] + 0.235[Th]) of the crystal, indicating that radiation damage has affected He diffusivity, and hence (U-Th)/He age. Forward modeling of simple Laramide-type thermal histories using a radiation damage diffusion model predicts: 1) fossil apatite fission-track partial annealing and apatite (U-Th)/He partial retention zones over similar elevation ranges, 2) (U-Th)/He age dispersion within a fossil partial retention zone up to hundreds of Ma, and 3) (U-Th)/He ages older than fission-track ages within a fossil partial retention zone if eU ≥ 20 ppm. We observe these features in our data from the Bighorn and Laramie Ranges. Most of our samples, however, do not show the correlation between (U- Th)/He age and eU predicted by radiation damage diffusion models. The age dispersion of these samples could be due to the influence of both grain size and eU content, or alternatively due to high U or Th secondary rims around the apatite crystals. (U-Th)/He ages that are older than fission-track ages from Gannett Peak and Fremont Peak in the Wind River Range, and some samples from the Beartooth Range, are most likely the result of He implantation from high eU secondary rims. Best-fit time-temperature paths from inverse modeling of (U-Th)/He age-eU pairs, when extrapolated to other elevations to create model age-elevation plots, reproduce the general distribution and dispersion of (U-Th)/He ages from the Bighorn, Beartooth and Wind River Ranges and suggest that rapid exhumation within the Laramide province likely began earlier in the Bighorn Range (before ~71 Ma) than the Beartooth Range (before -58 Ma). Inverse modeling of borehole data at the northern end of the Laramie Range suggests that the well penetrated a fault sliver at depth. The amount and timing of post-Laramide burial and exhumation cannot be determined from these data. [ABSTRACT FROM AUTHOR]

Abstract: Oceanic spreading ridges are Earth''s most productive crust generating environment, but mechanisms and rates of crustal accretion and heat loss are debated. Existing observations on cooling rates are ambiguous regarding the prevalence of conductive vs. convective cooling of lower oceanic crust. Here, we report the discovery and dating of zircon in mid-ocean ridge dacite lavas that constrain magmatic differentiation and cooling rates at an active spreading center. Dacitic lavas erupted on the southern Cleft segment of the Juan de Fuca ridge, an intermediate-rate spreading center, near the intersection with the Blanco transform fault. Their U–Th zircon crystallization ages (29.3−4.6 +4.8 ka; 1σ standard error s.e.) overlap with the (U–Th)/He zircon eruption age (32.7±1.6ka) within uncertainty. Based on similar 238U−230Th disequilibria between southern Cleft dacite glass separates and young mid-ocean ridge basalt (MORB) erupted nearby, differentiation must have occurred rapidly, within ~10–20ka at most. Ti-in-zircon thermometry indicates crystallization at 850–900°C and pressures >70–150MPa are calculated from H2O solubility models. These time-temperature constraints translate into a magma cooling rate of ~2×10−2 °C/a. This rate is at least one order-of-magnitude faster than those calculated for zircon-bearing plutonic rocks from slow spreading ridges. Such short intervals for differentiation and cooling can only be resolved through uranium-series (238U–230Th) decay in young lavas, and are best explained by dissipating heat convectively at high crustal permeability. [Copyright &y& Elsevier]

Abstract: Models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary. Yet a growing body of evidence in the Tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen''s history and thus our current mechanical understanding of orogenic plateau development is incomplete. New apatite (U–Th)/He ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures. Accelerated erosion is used as a proxy of fault timing, and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins. Helium results are synthesized with published geologic, thermochronometric, and sedimentologic data from which a growing picture of regional compressional deformation in Middle to Late Eocene time in northern Tibet emerges. We relate the early Cenozoic period of deformation to the initiation of collision between India and Eurasia, despite the fact that the plate boundary was located >3000km to the south. Regardless of whether or not high topography was built simultaneously as a result of this deformation, early Cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time. [Copyright &y& Elsevier]

Apatite and zircon (U-Th)/He and fission track ages were obtained from ridge transects across the central Southern Alps, New Zealand. Interpretation of local profiles is difficult because relationships between ages and topography or local faults are complex and the data contain large uncertainties, with poor reproducibility between sample duplicates. Data do form regional patterns, however, consistent with theoretical systematics and corroborating previous observations: young Neogene ages occur immediately southeast of the Alpine Fault (the main plate boundary structure on which rocks are exhumed); partially reset ages occur in the central Southern Alps; and older Mesozoic ages occur further toward the southeast. Zircon apparent ages are older than apatite apparent ages for the equivalent method. Three-dimensional thermokinematic modeling of plate convergence incorporates advection of the upper Pacific plate along a low-angle detachment then up an Alpine Fault ramp, adopting a generally accepted tectonic scenario for the Southern Alps. The modeling incorporates heat flow, evolving topography, and the detailed kinetics of different thermochronometric systems and explains both complex local variations and regional patterns. Inclusion of the effects of radiation damage on He diffusion in detrital apatite is shown to have dramatic effects on results. Geometric and velocity parameters are tuned to fit model ages to observed data. Best fit is achieved at 9 mm a−1 plate convergence, with Pacific plate delamination on a gentle 10°SE dipping detachment and more rapid uplift on a 45-60° dipping Alpine Fault ramp from 15 km depth. Thermokinematic modeling suggests dip-slip motion on reverse faults within the Southern Alps should be highest ∼22 km from the Alpine Fault and much lower toward the southeast. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Duolong ore district experienced two periods of exhumation and two periods of burial. • The periods of burial are attributed to northeast-southwest striking fault and thrust nappe structure related to the Lhasa-Qiangtang collision. • The India-Asia collision is the main reason for the exhumation and uplift of the Duolong ore district since Paleocene. The Early Cretaceous Duolong porphyry-epithermal copper ore district is one of the largest copper ore districts in the central Tibetan Plateau. In order to investigate the preservation mechanism of Early Cretaceous porphyry-epithermal mineralization, new apatite and zircon fission track dating and (U-Th)/He dating of pre-ore sandstone, ore-related and barren intrusive rocks, and post-ore igneous rock, thermal modeling together with previous thermochronological data of the Duolong ore district were combined to study the burial and exhumation processes. Apatite fission track ages range from 68 ± 4 to 40 ± 4 Ma, with mean track lengths varying from 12.1 ± 2.0 to 12.8 ± 2.4 μm. Zircon fission track ages range from 106 ± 4 to 86 ± 4 Ma. In addition, apatite (U-Th)/He yields average age ranging from 62.7 ± 4.2 to 22.6 ± 1.2 Ma, and zircon (U-Th)/He yields average age of 112.3 ± 5.1 Ma. The thermal modeling shows that the Duolong ore district experienced two periods of exhumation and two stages of burial. The first period of exhumation with rate of 0.14 km/m.y. took place immediately after the ore formation which caused the erosion of orebody. Two periods of burial are thought to be related to northeast-southwest striking fault and thrust nappe structure induced by Lhasa-Qiangtang collision between 110 and 65 Ma when the overlying rocks of orebodies were thickened to 4 km. The last period of exhumation with rate of 0.062 km/m.y. (since 65 Ma) is attributed to lithospheric delamination related to India-Asia collision. The preservation of the Duolong ore district mainly benefited from the burial related to the Lhasa-Qiangtang collision. The exhumation and uplift of Duolong ore district was mainly attributed to the India-Asia collision since Paleocene. [ABSTRACT FROM AUTHOR]

Abstract: The Antioqueño Plateau (AP) in the northern Cordillera Central, Colombia, is the largest high elevation erosional surface in the Northern Andes. Apatite (U–Th)/He thermochronometry (AHe) of samples collected from two elevation profiles spanning ∼2 km of exhumed crustal sections reveal the long-term erosional exhumation of the AP. Sample profiles exhibit AHe ages that increase with elevation from ca. 22 Ma (∼760 m) at the bottom of regional scarps to ca. 49 Ma (∼2350 m) on top of the AP. A marked inflection point in age versus elevation data at ca. 25 Ma defines the bottom of the exhumed post-Oligocene He partial retention zone (He-PRZ). Elevation-invariant ages below ca. 25 Ma record the onset of rapid exhumation and surface uplift of the AP that led to river incision. A subtle change in slope within the He-PRZ, ca. 41 Ma, is interpreted as a less intense, exhumation-related cooling episode. These two exhumation pulses coincide with the Proto-Andina and Pre-Andina orogenic phases previously proposed for the Colombian Andes, and are synchronous with tectonically driven exhumation events reported for the Peruvian, Bolivian and Argentinean Andes, and for some orogenic systems in the Caribbean. The pulses are correlated with variations in the rates of convergence between Nazca (Farallon) and South America documented for the Middle Eocene and the Late Oligocene suggesting continental-scale controls on uplift and denudation throughout the Andean range. AHe data provide an average erosion rate of ∼0.04 mm/yr for the last 25 million years. Erosion rates during the exhumation pulses were in the order of ∼0.2–0.4 mm/yr. Similarity between AHe profiles indicates the whole AP was uplifted and exhumed as a coherent structural block, corroborating previous structural evidence for the rigidity and coherence of this crustal block in the Northern Andes. Our results are in agreement with tectonostratigraphic data in the Magdalena and Cauca basins and with proposed scenarios for paleogeographic evolution in the Northern Andes. [Copyright &y& Elsevier]

The thermal evolution of the only known Alpine (Cretaceous) granite in the Western Carpathians (Rochovce granite) is studied by low-temperature thermochronological methods. Our apatite fission track and apatite (U-Th)/He ages range from 17.5 ± 1.1 to 12.9 ± 0.9 Ma, and 12.9 ± 1.8 to 11.3 ± 0.8 Ma, respectively. The data thus show that the Rochovce granite records a thermal event in the Middle to early Late Miocene, which was likely related to mantle upwelling, volcanic activity, and increased heat flow. During the thermal maximum between ~17 and 8 Ma, the granite was heated to temperatures ⪞ 60 °C. Increase of cooling rates at ~12 Ma recorded by the apatic fission track and (U-Th)/He data is primarily related to the cessation of the heating event and relaxation of the isotherms associated with the termination of the Neogene volcanic activity. This contradicts the accepted concept, which stipulates that the internal parts of the Western Carpathians were not thermally affected during the Cenozoic period. The Miocene thermal event was not restricted to the investigated part of the Western Carpathians, but had regional character and affected several basement areas in the Western Carpathians, the Pannonian basin and the margin of the Eastern Alps. [ABSTRACT FROM AUTHOR]

Abstract: The low-temperature thermal evolution of the Azov Massif (eastern part of the Ukrainian Shield, Ukraine) is investigated by combined zircon fission track (ZFT), apatite fission track (AFT) and apatite (U–Th)/He (AHe) thermochronology. The data help to better understand the geodynamic evolution of the Azov Massif and the adjacent intra-cratonic rift basin (Dniepr–Donets Basin) as follows: ZFT data reveal that the Precambrian crystalline basement of the Azov Massif was heated to temperatures close to ∼240 °C during the Late Palaeozoic. The heating event is interpreted in terms of burial of the basement beneath a several kilometres thick pile of Devonian and Carboniferous sedimentary deposits of the adjacent Dniepr–Donets Basin. During Permo-Triassic times, large parts of the basement were affected by a thermal event related to mantle upwelling, associated magmatic activity and increased heat flow in the adjacent rift. The major part of the basement cooled to near-surface conditions in the Early to Middle Triassic and since then was thermally stable as suggested by AFT and AHe data. Further, AFT data confirm Late Triassic magmatic activity in the Azov Massif, which, however, did not influence regional thermal pattern. The northern part of the basement and its sedimentary cover record a cooling event in the Jurassic, which was probably related to erosion. However, although Ar–Ar data of Jurassic magmatic activity in the Donbas Foldbelt are about 20 My younger than the AFT data, thermal relaxation after elevated heat flow associated with this magmatic event cannot be completely ruled out. Our results reveal apparent inconsistencies between AFT and AHe data: the AHe ages corrected for alpha ejection according to the standard procedure [Farley, K.A., Wolf, R.A., Silver, L.T., 1996. The effect of long alpha-stopping distances on (U–Th)/He ages. Geochim. Cosmochim. Acta 60(21), 4223–4229.; Farley, K.A., 2002. (U–Th)/He dating: Techniques, calibrations, and applications. Mineral. Soc. Am. Rev. Mineral. Geochem. 47, 819–844] are older than corresponding AFT ages. In order to test the relevance of alpha ejection correction, mechanical abrasion of several apatite grains was applied. We found that in case of relatively slow cooling, alpha ejection correction of raw (U–Th)/He ages leads to erroneously high ages. This shows that alpha ejection correction should be used with caution. We propose that this correction should only be applied to samples with a fast cooling history, whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means. [Copyright &y& Elsevier]

We use a combination of apatite 4He/³He, (U-Th)/He, and fission-track thermochronology to date slip on the Surprise Valley fault in northeastern California by analyzing a single sample from the Warner Range in the footwall of the fault. This sample, a granitic clast from a conglomerate, yielded a fission-track age of 11.6 ± 2.8 Ma and a (U-Th)/He age of 3.02 ± 0.52 Ma. Geologic relationships indicate that this sample was buried to a depth of ∼3.3 km prior to exhumation during slip on the Surprise Valley fault. Fission-track age and length data indicate that the sample was fully reset (>120 °C) prior to exhumation, which began sometime after 14 Ma. A single aliquot of nine apatite grains was step-heated for 4He/³He analysis; modeling of the resulting 4He distribution indicates that cooling from >80 °C to ∼20 °C occurred between 3 and 1 Ma. Interconsistent time-temperature (t-T) solutions to the combined 4He/³He, (U-Th)/He, and fission-track data require two distinct periods of cooling, consistent with noncontinuous slip on the Surprise Valley fault. Early cooling and fault slip took place between 14 and 8 Ma, followed by more recent fault slip ca. 3 Ma. This timing is consistent with both local geologic relationships and with the regional timing of faulting along the western margin of the Basin and Range Province. These data demonstrate the resolving power of combined fission-track, (U-Th)/He, and 4He/³He thermochronometric data to extract low-temperature t-T information from a single sample close to Earth's surface. [ABSTRACT FROM AUTHOR]