Fission Track Thermochronology Research Articles

Insights into the Phanerozoic evolution of the São Francisco Craton based on detrital zircon thermochronology and U-Pb-Hf geochronology

Basins within cratonic environments offer valuable insights into the fragmentation, dispersion, and agglutination of the lithosphere within supercontinents. The southern São Francisco Craton is home to sedimentary basins that formed in both intraplate tectonic settings (late Paleoproterozoic to Neoproterozoic and Mesozoic) and convergent tectonic settings (Ediacaran to Cambrian). To elucidate the Phanerozoic thermal history of the craton and the long-term depositional history of the southern São Francisco Craton’s cover, a comprehensive study was conducted utilizing detrital zircons through zircon fission-track (ZFT) thermochronology and U-Pb-Hf geochronology. This study analyzed samples from the following units: (1) the intracratonic basin—Lower and Upper Espinhaço Supergroup, with depositional age intervals ranging 1800−1600 Ma and 1200−920 Ma, respectively; (2) the rift-related passive margin basin—Lower Macaúbas Group (720 Ma and 640 Ma) and Jequitaí Formation, which is likely of Cryogenian age (650−635 Ma); (3) and the foreland basin—Bambui Group and Três Marias Formation, with ages of ca. 600−520 Ma and 520−480 Ma, respectively. U-Pb-Hf detrital zircon geochronology revealed the complex depositional history of the southern São Francisco Craton, and indicated changing source rocks over time. Conversely, the ZFT analysis of Precambrian to Cambrian samples allowed for the identification and characterization of Phanerozoic events in the southern São Francisco Craton. These events include: (1) the exhumation and late orogenic uplift of the foreland at ca. 500−480 Ma (mean age of 499 ± 5.5 Ma) during the late stages of the Brasiliano−Pan-African Cycle, which was associated with the Araçuaí Belt and lithospheric rebound of the peripheral cratonic margin of the southern São Francisco Craton; and (2) an age of 330−280 Ma (mean age of 306.6 ± 4.8 Ma) that possibly resulted from ice retreat and isostatic rebound interior of the Gondwana Paleocontinent. Additionally, analysis of detrital zircons from the Areado Group shows a later tectonic event recorded at 128.1 ± 9.4 Ma, which indicates Mesozoic intracontinental rifting. Based on these results and interpretations, the timing and exhumation of the southern São Francisco Craton during the Phanerozoic can be attributed to the final stages of the continental collision of the southern São Francisco Craton and Congo Craton and large-scale continental uplift during the Permo-Carboniferous late Paleozoic Ice Age of Gondwana. Overall, the findings demonstrate a direct correlation between known tectonic events at the plate margins of Western Gondwana and periods of cratonic basin formation.

Compilation of Apatite Fission-Track Data from the Northeast Atlantic Realm: A Jigsaw Puzzle with Missing Pieces

Abstract The northeast (NE) Atlantic is one of the best-studied geological regions in the world, incorporating a wide array of geological phenomena including extensional tectonism, passive margin development, orogenesis, and breakup-related volcanism. Apatite fission-track (AFT) thermochronology has been an important tool in studying the onshore evolution of the NE Atlantic for several decades. Unfortunately, large regional-scale studies are rare, making it difficult to study geological processes across the whole region. In this work, a compilation of published AFT data is presented from across Fennoscandia, the British Isles, East Greenland, and Svalbard, with the goal of providing an accessible overview of the data and how this vast body of work has improved our understanding of the region’s evolution. Alongside a review of previous literature, interpolated maps of fission track age and mean track length (MTL) highlight regional trends in the data that may result from major first-order processes and areas of low sample density that should be targeted for future study. Additionally, in the absence of metadata required for thermal history modeling, apparent exhumation rate estimates are calculated from available elevation profiles and the timing of major exhumation events inferred from “boomerang plots” of fission track ages against MTL values. Across Fennoscandia, data suggests that the opening of the NE Atlantic and exhumation of the margin have clearly played a major role in the thermal history of the upper crust. The remaining areas of Britain, Ireland, East Greenland, and Svalbard all present more complex trends consistent with a combination of the NE Atlantic’s opening and the interplay between specific bedrock geology of sampling sites and localized geological processes. Areas of low sample density include southern Britain, NE Britain, southeast Greenland, southern Svalbard, and Eastern Fennoscandia, each of which provides the natural laboratory required to answer many unresolved questions.

Late Oligocene to Pleistocene thermo-tectonic evolution of the Karakoram Fault Zone: New insights from basement and detrital apatite fission track thermochronology

The Karakoram Fault Zone displays distinctive topographic and tectonic characteristics, with intricate river drainage systems. Although there are extensive thermochronological datasets for the western Tibetan Plateau, limited investigations have been carried out to uncover the low-temperature thermal history of the Karakoram Fault Zone, which connects the Lhasa terrane with the Pamir. In this contribution, apatite fission track (AFT) thermochronology was conducted on 13 basement and 4 conglomerate samples collected from the western Gangdese batholith and the Ayi Mountain Range, on either side of the Karakoram fault. Inverse thermal history modeling results reveal that the western Gangdese batholith experienced two stages of rapid basement cooling at 27–23 Ma (late Oligocene-early Miocene) and 16–4 Ma (middle Miocene-Pliocene). The adjacent Ayi Mountain Range experienced cooling in the late Miocene (∼8 Ma) and during the Pliocene to Pleistocene (4–1 Ma). We suggest that tectonic forces associated with rollback and lateral break-off of the Indian continental lithosphere, and the dextral strike-slip activity of the Karakoram fault were responsible for the first cooling phase. The second accelerated cooling phase was due to the deep fragmentation of the Indian slab, the activity of the Karakoram normal fault, and associated ∼E-W extension. Additionally, since the late Oligocene, the Indus River incision has likely also contributed to the exhumation of the western Tibetan Plateau. Subsequently, the western Gangdese batholith reached high elevations, resulting in the reversal of the Yarlung River. The dextral-normal motion of the Karakoram fault, which is still active today, was the main cause of the Pliocene to Pleistocene accelerated cooling detected in the Ayi Mountain Range.

Apatite Fission Track Thermochronology of Granite from the Xiazhuang Uranium Ore Field, South China: Implications for Exhumation History and Ore Preservation

AbstractXiazhuang uranium ore field, located in the southern part of the Nanling Metallogenic Belt, is considered one of the largest granite‐related U regions in South China. In this paper, we contribute new apatite fission track data and thermal history modeling to constrain the exhumation history and evaluate preservation potential of the Xiazhuang Uranium ore field. Nine Triassic outcrop granite samples collected from different locations of Xiazhuang Uranium ore field yield AFT ages ranging from 43 to 24 Ma with similar mean confined fission track lengths ranging from 11.8 ± 2.0 to 12.9 ± 1.9 μm and Dpar values between 1.01 and 1.51 μm. The robustness time‐temperature reconstructions of samples from the hanging wall of Huangpi fault show that the Xiazhuang Uranium ore field experienced a time of monotonous and slow cooling starting from middle Paleocene to middle Miocene (∼60–10 Ma), followed by relatively rapid exhumation in the late Miocene (∼10–5 Ma) and nearly thermal stability in the Pliocene–Quaternary (∼5–0 Ma). The amount of exhumation after U mineralization since the Middle Paleogene was estimated as ∼4.3 ± 1.8 km according to the integrated thermal history model. Previous studies indicate that the ore‐forming ages of U deposits in the Xiazhuang ore field are mainly before Middle Paleocene and the mineralization depths are more than 4.4 ± 1.2 km. Therefore, the exhumation history since middle Paleocene plays important roles in the preservation of the Xiazhuang Uranium ore field.

Exhumation and preservation of the Bangbule Pb-Zn-Cu deposit in the western Gangdese metallogenic Belt, Tibet: Constraints from fission track thermochronology and fault gouge dating

The Bangbule Pb-Zn-Cu deposit is a large-scale skarn deposit that was recently discovered in the western Gangdese Metallogenic Belt. Previous studies have focused mainly on ore genesis and ore-forming fluid, while exhumation and preservation after mineralization have not been the focus. We report fission track ages (ZFT: 43 ± 3 to 52 ± 3 Ma; AFT: 24 ± 2 to 32 ± 3 Ma, MTL: 12.2 ± 1.9 to 13.0 ± 1.6 μm) and the timing of fault activation (44.3 ± 0.9 Ma), revealing the processes of cooling/exhumation and we evaluate the preservation of the deposit. The Bangbule deposit experienced two rapid exhumation events since the Eocene (52–24 Ma and 12 Ma to present) and a slower stage during the late Oligocene to middle Miocene (24–12 Ma). The exhumation thickness (1.6–3.1 km) after mineralization was similar to the metallogenic depth (peak: 1.5–2.5 km). The volcanic rocks of the Dianzhong Formation partially protect the deposit, making mineral exploration of the Bangbule deposit feasible. Since the Oligocene, due to climate change and deep subducted slab tearing, the exhumation thickness in the western Gangdese (∼0.6–3.1 km) has generally been lower than that in the middle-eastern part (∼3–8 km). The lower degree of exhumation may be one of the reasons why less large-scale deposits have been discovered in the western Gangdese.

Extensional exhumation of cratons: insights from the Early Cretaceous Rio Negro–Juruena belt (Amazonian Craton, Colombia)

Abstract. This study presents results from apatite fission track (AFT) thermochronology to investigate the thermal history and exhumation dynamics of the Rio Negro–Juruena basement, situated within the western Guiana Shield of the Amazonian Craton. AFT dating and associated thermal history modeling in South America has largely been restricted to the plate's margins (e.g., Andean active margin, Brazilian passive margin, and others). Our paper reports on low-temperature thermochronological data from the internal part of the western Guiana Shield for the first time. This area is part of a vast cratonic lithosphere that is generally thought to be stable and little influenced by Mesozoic and Cenozoic tectonics. Our data, however, show AFT central ages ranging from 79.1 ± 3.2 to 177.1 ± 14.8 Ma, with mean confined track lengths of ca. 12 µm. Contrary to what might be expected of stable cratonic shields, inverse thermal history modeling indicates a rapid basement cooling event in the early Cretaceous. This cooling is interpreted as a significant exhumation event of the basement that was likely driven by the coeval extensional tectonics associated with back-arc rifts in the Llanos and Putumayo–Oriente–Maranon basins. The extensional tectonics facilitated both basement uplift and subsidence of the adjoining basins, increasing erosional dynamics and consequent exhumation of the basement rocks. The tectonic setting shifted in the late Cretaceous from extensional to contractional, resulting in reduced subsidence of the basins and consequential diminishing cooling rates of the Guiana Shield basement. Throughout the Cenozoic, only gradual, slow subsidence occurred in the study area due to regional flexure linked to the Andean orogeny. Comparative analysis with low-temperature thermochronology data from other west Gondwana cratonic segments highlights that exhumation episodes are highly controlled by tectonic inheritance, lithospheric strength, and proximity to rift zones. This study underscores the complex interplay between tectonic events and the response of cratonic lithosphere over geological timescales and highlights extensional settings as an important geological context for craton exhumation.

Cretaceous–Neogene Exhumation of the Daqing Shan, North China Constrained by Apatite Fission Track Thermochronology

Cretaceous–Neogene Exhumation of the Daqing Shan, North China Constrained by Apatite Fission Track Thermochronology

Mid-Cretaceous Accelerated Cooling of the Beishan Orogen, NW China: Evidence from Apatite Fission Track Thermochronology

Abstract The Beishan orogen, a significant component of the southern Altaids, presents an opportunity for investigating the intracontinental deformation and exhumation history of the Altaids during the Mesozoic era. Although previous studies indicated that the Beishan orogen has experienced multiple reactivation since the late Mesozoic, the precise extent of these events remains poorly constrained. Here, we provide a comprehensive synthesis of field observations and apatite fission track (AFT) thermochronological dating throughout the Beishan orogen. Detailed field observations confirmed four major E-W trending thrusts in our study area. Based on the youngest truncated strata associated with the thrusts and previous dating results from neighboring regions, we propose that these thrust sheets likely developed in the late Middle Jurassic. AFT dating results from seven pre-Mesozoic granitoid samples and associated with thermal history modeling demonstrate that the Beishan orogen experienced a rapid basement cooling during the mid-Cretaceous (~115–80 Ma). Moreover, a compilation of previously published and newly gained AFT data reveals a comparable mid-Cretaceous cooling event in other parts of Central Asia, such as Qilian Shan, Eastern Tianshan, and Altai-Sayan. This observation suggests that the mid-Cretaceous cooling event is more likely to be regional rather than localized. This mid-Cretaceous cooling pulse is interpreted as a tectonic exhumation controlled by boundary faults and related to the rotation of the Junggar and Tarim basins. These processes are linked to distant plate-margin events along the Eurasian continent.

Jurassic–cretaceous exhumation history of the Northern Qaidam Basin and its implications for Northeastern Qinghai–Tibet plateau tectonism: evidences from zircon fission track thermochronology

ABSTRACT Reconstructing the growth model of the Northeastern Qinghai–Tibet Plateau is of significant importance in understanding its tectonic evolution through time. We present 20 new zircon fission track data on samples collected from the Chakabeishan-Shaliuquan district in the North Qaidam Tectonic Belt (NQTB) to constrain its Mesozoic mineralization and exhumation history. Sample ages and characteristics are differentiated by regional thrust fault systems. The mineralized pegmatite ages with high U concentrations can be divided into two groups of 170–168 Ma and 149–137 Ma, recording exhumation and hydrothermal mineralization events, with average cooling and exhumation rates of 0.074 mm/y and 2.305°C/Ma, respectively. Two ZFT ages groups characterized by low U concentrations at the deposit periphery of 125–106 Ma and 99–80 Ma, respectively, are associated with accelerated cooling and exhumation, with mean values of 7.662°C/Ma and 0.245 mm/y. We suggest that the NQTB was positioned in the high background thermal field in the Triassic, and subsequent tectonic extension resulted in the unroofing, cooling and mineralization of the region. The transition from extensional to contractional deformation in the Cretaceous tectonic setting has reactivated regional thrust fault systems and reset the Jurassic ZFT ages, and this exhumation event was influenced by the closure of the Middle-Tethys and Mongol-Okhotsk Oceans, consistent with the double-sided subduction model.

Late Cenozoic Cooling History of the Xigaze Fore-Arc Basin along the Yarlung–Zangbo Suture Zone (Southern Tibet): New Insights from Low-Temperature Thermochronology

Abstract The Tibetan Plateau is currently the widest and highest elevation orogenic plateau on Earth. It formed as a response to the Cenozoic and is still ongoing collision between the Indian and Eurasian plates. The Xigaze fore-arc basin distributed along the Indus–Yarlung suture zone in southern Tibet preserves important information related to the late Cenozoic tectonic and topographic evolution of the plateau. In this study, apatite fission track (AFT) thermochronology was carried out on twelve sandstone samples from the middle segment of the Xigaze basin and additionally on four sedimentary rocks from the neighboring Dazhuka (Kailas) and Liuqu Formations. Inverse thermal history modeling results reveal that the fore-arc basin rocks experienced episodic late Oligocene to Miocene enhanced cooling. Taking into account regional geological data, it is suggested that the late Oligocene-early Miocene (~27–18 Ma) cooling recognized in the northern part of the basin was promoted by fault activity along the Great Counter thrust, while mid-to-late Miocene-accelerated exhumation was facilitated by strong incision of the Yarlung and Buqu rivers, which probably resulted from enhanced East Asian summer monsoon precipitation. Sandstone and conglomerate samples from the Dazhuka and Liuqu Formations yielded comparable Miocene AFT apparent ages to those of the Xigaze basin sediments, indicative of (mid-to-late Miocene) exhumation soon after their early Miocene burial (> ~3–4 km). Additionally, our new and published low-temperature thermochronological data indicate that enhanced basement cooling during the Miocene prevailed in vast areas of central southern Tibet when regional exhumation was triggered by both tectonic and climatic contributing factors. This recent and widespread regional exhumation also led to the formation of the high-relief topography of the external drainage area in southern Tibet, including the Xigaze fore-arc basin.

Mesozoic–Cenozoic cooling, exhumation and tectonic implications of Chaqiabeishan–Shaliuquan Li[sbnd]Be ore district in the northeastern Qinghai–Tibet Plateau

The Mesozoic-Cenozoic exhumation and deformation of the northeastern Qinghai–Tibetan Plateau generated extensive regional rugged mountains. We aimed to explore the prolonged kinematic evolutionary history since the Mesozoic. We collected Mesozoic magmatic rock samples from the Chaqiabeishan-Shaliuquan lithium‑beryllium ore district in the Northern Qaidam tectonic belt (NQTB) to constrain the cooling exhumation history using apatite fission track (AFT) thermochronology. Twenty samples yielded AFT ages from 111 to 11 Ma, including four age groups:111–103, 89–75, 71–47, and 30–11 Ma, with mean track lengths of 12.5–11.2 μm. Four thermal history phases of 120–90, 90–50, 50–20, and 20–0 Ma were established based on the inverse thermal model and isostatic adjustment of the lithosphere. Additionally, the average cooling rates of the four phases were 1.67 ± 0.17, 1.25 ± 0.13, 0.33, and 1.75 ± 0.5 °C/Myr, with a corresponding exhumation amount of 1.15 ± 0.07 km, 0.98 ± 0.06 km, 0.86 ± 0.05 km, and 1.09 ± 0.06 km respectively, and the maximum exhumation was 6.021–6.787 km since 120 Ma. In the first phase, the far-field effects of Mid-Tethys Ocean subduction and closure drove the rapid exhumation of the research area. The closure of the Neo-Tethys Oceans and the continuing collision of the India-Asia plate disturbed the northeastern plateau, inducing regional backlash fault events in the NQTB, demonstrated in the second phase of thermal history. The third phase of the stable tectonic setting is consistent with previous research results, suggesting a similar cooling history for the NQTB and Qilian Mountains, evidenced by the widespread absence of Eocene to Miocene cooling signals. The rapid exhumation and reactivation of the NQTB and Qilian thrust fault system since 20 Ma represents the final stage of growth and expansion of the northeastern Qinghai–Tibet Plateau.

Tectonic-thermal history and hydrocarbon potential of the Pearl River Mouth Basin, northern South China Sea: Insights from borehole apatite fission-track thermochronology

The Pearl River Mouth Basin (PRMB) is one of the most petroliferous basins on the northern margin of the South China Sea. Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evolution and for unraveling its poorly studied source-rock maturation history. Our investigations in this study are based on apatite fission-track (AFT) thermochronology analysis of 12 cutting samples from 4 boreholes. Both AFT ages and length data suggested that the PRMB has experienced quite complicated thermal evolution. Thermal history modeling results unraveled four successive events of heating separated by three stages of cooling since the early Middle Eocene. The cooling events occurred approximately in the Late Eocene, early Oligocene, and the Late Miocene, possibly attributed to the Zhuqiong II Event, Nanhai Event, and Dongsha Event, respectively. The erosion amount during the first cooling stage is roughly estimated to be about 455–712 m, with an erosion rate of 0.08–0.12 mm/a. The second erosion-driven cooling is stronger than the first one, with an erosion amount of about 747–814 m and an erosion rate between about 0.13–0.21 mm/a. The erosion amount calculated related to the third cooling event varies from 800 m to 3419 m, which is speculative due to the possible influence of the magmatic activity.

Low-temperature thermochronology of the Longmala - Mengya’a Pb-Zn deposits (southern Tibet): Implications for ore exhumation and preservation

The large Gangdese metallogenic belt, located in the southern part of the Tibetan Plateau, hosts a variety of magmatic-hydrothermal ore deposits. Previous works in the area primarily concerned the ore genesis, while the exhumation history of these ore deposit has received less attention. In this contribution we explore the multi-stage thermo-tectonic evolution of the Longmala and Mengya’a Pb-Zn deposits, two large magmatic-hydrothermal ore deposits in the central Lhasa sub-terrane. In more detail, the thermal history of granitoids and deformed Paleozoic sediments inside and on the periphery of the ore districts have been constrained by low-temperature thermochronological methods, including the zircon (U-Th)/He and apatite fission track thermochronology. Additionally, zircon U-Pb geochronology was conducted on granitic host rocks to determine their emplacement ages. Our thermochronological data and inverse thermal history modeling results reflect two phases of accelerated basement cooling during the Cenozoic (i.e., ∼46–41 Ma and ∼20–5 Ma), interpreted as exhumation phases. The ore body was exhumed to the near surface during the Miocene, which provides essential information for ore exploration in the region. We also explore the degrees of basement rock exhumation along the Gangdese metallogenic belt and their spatio-temporal relations to major ore deposit distributions. It is suggested that complex interactions between tectonic-structural activities and surface erosion occurred during the late Oligocene-Miocene (∼25–5 Ma), which resulting in widespread exhumation along the Gangdese batholith. During this period, the ore-bearing rocks were gradually (with medium to high cooling rates) exhumed to the near-surface from ∼3–4 km crustal depth, making these ore deposits feasible for commercial mining.

Tectonic-Thermal Evolution of the Wadi El-Dahal Area, North Eastern Desert, Egypt: Constraints on the Suez Rift Development

The Suez Rift developed as a northern extension of the Red Sea rift during the Oligocene-Miocene, whose flanks were constructed from the Neoproterozoic basement rocks of the Arabian–Nubian Shield. These basement rocks are comprised of the whole tectonic history since their formation. The Suez Rift initiation model and proposed thermal overprint role in the rifting process and flank development remain uncertain. Additionally, the amplitude of different regional tectonic events’ effects on the region is still debatable. Integration of fission-track thermochronology data with modeling of the time-temperature history has demonstrated efficiency in addressing such issues. In the context of this study, eleven representative samples were collected from the different rock units in the Wadi El-Dahal area at the northern tip of the western flank of the Suez Rift. These samples revealed Carboniferous zircon fission-track cooling ages of 353 ± 9 Ma and 344 ± 11 Ma. Meanwhile, the apatite fission-track analysis provided two spatially separated age groups: Permian-Triassic and Late Cretaceous, with average ages of 249 ± 11 Ma and ca. 86 ± 10 Ma, respectively. The time-temperature modeling revealed four possible cooling pulses representing exhumation events, which were initiated as a response to four tectonic activities: the accretion-subsequent event of erosion during the Neoproterozoic, the Hercynian (Variscan) tectonic event during the Devonian-Carboniferous, the Mid-Atlantic opening during the Cretaceous, and the Suez Rift opening during the Oligocene-Miocene. The western flank of the Suez Rift suggests a passive mechanical type with no extra thermal overprint, as indicated by the dominance of older thermochronological ages, modest rift flank elevations, and a reduction in the heat flow.

New Constraints on the Late Oligocene‐Miocene Thermo‐Tectonic Evolution of the Southeastern Tibetan Plateau From Low‐Temperature Thermochronology

AbstractThe southeastern (SE) Tibetan Plateau (Yunnan) is characterized by low‐relief uplands that were deeply incised by large rivers. The thermal history of basement rocks in this region remains poorly investigated, while this data is needed to elucidate the complex relationship between tectonics and climate in shaping the surface. To better understand its thermo‐tectonic evolution, we carried out apatite fission track thermochronology on 31 samples collected from a large area that covers different tectonic units, including a vertical profile in the middle Mekong River valley; additional zircon LA‐ICP‐MS U‐Pb dating was performed on four basement rocks. Our results confirm that a large portion of Mesozoic crystalline rocks constitute the basement of the SE Tibetan Plateau. Inverse thermal history modeling of fission track data reveal extensive late Oligocene to Miocene rapid basement cooling and exhumation episodes from both inside and outside the active zones (i.e., ductile shear zone and river valley). These thermal events were coincident with the activities of large‐scale strike‐slip faults that dominate the structural framework. Combined with the published data, we propose that widespread crustal shortening and thickening took place in the SE Tibetan Plateau during the Oligocene‐Miocene in the context of a compressive tectonic regime. Low‐temperature thermochronological data reveal that both tectonic forcing and climate‐driven erosion have played important roles in exhuming the basement rocks in the region. It is also deduced that the present‐day relatively low‐elevation landscape of the Yunnan area resulted from complex interaction between regional tectonic activity and surficial erosion since the late Oligocene.

Late Triassic Tectonic Setting in Northeastern Margin of North China Craton: Insight into Sedimentary and Apatite Fission Tracks

The closure timing of the Paleo-Asian Ocean and the terminal stage of the Central Asian Orogenic Belt have been widely debated in the geological community. It’s known that the gradual scissor-like closure of the Paleo-Asian Ocean occurred from west to east during the Paleozoic period. However, it was not until the Triassic period that the complete closure of the ocean occurred at the northeastern margin of the North China Craton. Nevertheless, there is still much uncertainty regarding the Late Triassic tectonic setting in Northeast China. In this study, we focused on the Upper Triassic Dajianggang Formation, located in the Shuangyang area of central Jilin Province, which is situated on the northeastern margin of the North China Plate. Our aim was to determine the formation age of the Dajianggang Formation by analyzing the detrital particle composition, petrogeochemistry, detrital zircon U-Pb isotope dating, and apatite fission track thermochronology. Our results indicated that the primary sandstone provenance area of the Dajianggang Formation in the Shuangyang area is the island arc orogenic belt. The tectonic background of the sandstone provenance area is mainly a continental island arc environment. The provenance area is mostly composed of felsic rocks with sedimentary tendencies, and some of its material may have originated from the northern margin of the North China Craton or the eroded recycle orogenic belt. LA-ICP-MS U-Pb dating of detrital zircons shows that the Dajianggang Formation formed after 226.8 ± 5 Ma. Moreover, analysis of the thermal evolution history modelling shows that the Dajianggang Formation in the Shuangyang area continued to be deposited and heated in the early stage, and then experienced rapid exhumation around 30 Ma. This suggests that the study area underwent an orogenic process during the early stage of formation, but then transitioned into a post-orogenic extension period, which constrained the final closure of the Paleo-Asian Ocean prior to the Late Triassic period. In addition, our study indicates that the remote effect of the Pacific subduction did not reach the study area until 30 Ma. The central age of the detrital apatite fission track of sample 19DJ-1 is 94.2 ± 8.3 Ma, which is younger than its corresponding stratigraphic age. The two peak ages of the fission track analysis are 62.9 ± 5.4 Ma and 126 ± 11 Ma. These findings provide new evidence for the tectonic evolution of Northeast China and shed light on the Late Triassic tectonic setting, as well as the influence time of subsequent tectonic domains in the southern part of Northeast China.

Thermal history of the Peel Plateau, northern Canadian Cordillera, resolved through multikinetic apatite fission-track dating

The Peel Plateau of the northern Canadian Cordillera has undergone multiple burial and unroofing events throughout the Phanerozoic, including subsidence and uplift associated with emergence of the Mackenzie Mountains. Episodic unroofing events are evinced by unconformities that represent a period where an unknown amount of material was deposited and eroded. Thermochronological studies have been conducted in neighboring physiographic regions, however no work has been conducted in the Peel Plateau and there is interest to determine whether it shares a similar thermal evolution as the surrounding regions. Apatite fission-track thermochronology (AFT) is a useful method for reconstructing basinal thermal histories as the system is sensitive to upper crustal temperatures, although the kinetics of the thermochronometer are complicated by numerous elemental substitutions within apatite that are known to control the specific temperature window within which fission-tracks anneal. This study uses three strategically positioned AFT samples from Phanerozoic sedimentary rocks to investigate the thermal history of the region from the Devonian to the present. Pooled AFT ages from all samples fail the χ2 test, implying there is a high level of intra-sample age dispersion and potentially indicating the samples contain multiple age populations. To assess whether the data are consistent with multiple kinetic AFT populations, we use grain-specific apatite compositions to derive rmro, a kinetic parameter that accounts for elemental substitutions known to control annealing kinetics of fission-tracks. By plotting AFT ages and track lengths against rmro we identify more-retentive and less-retentive apatite populations within each sample, which serve as independent thermochronometers when incorporated into inverse thermal history modelling. Results from a thermal history model of the Upper Devonian Imperial Formation indicate that the uppermost Paleozoic strata in the Peel Plateau reached maximum burial temperatures (∼165°C–185 °C) in the Triassic and were reheated to lower temperatures (∼90°C–100 °C) under a Cretaceous-Paleocene foreland basin. The temperature regime of the latter burial event is supported by thermal history models of two Cretaceous samples that record peak burial temperatures (∼80°C–90 °C) in the Paleocene to Eocene. This study highlights the capabilities of thermal history modelling from multikinetic AFT data and serves as a reminder that addressing variable annealing kinetics of apatite grains can improve the resolution of thermal models and the associated geologic interpretations.

Late Paleozoic–Cenozoic Tectonothermal Evolution of Transbaikalia: Thermochronology of the Angara–Vitim Granitoid Batholith

Abstract —The tectonothermal evolution of Transbaikalia is reconstructed using U/Pb, 40Ar/39Ar, and apatite fission track thermo-chronology of samples from the Late Paleozoic Angara–Vitim granitoid batholith (AVB). Successive closure of the zircon and amphibole isotope systems provides evidence that the AVB rocks cooled down rapidly soon after crystallization and 7–4 km of rocks were denuded subsequently during an extensive late Paleozoic orogeny in southern Siberia. The isotopic system of feldspar closed in the Middle Jurassic–Early Cretaceous (170–140 Ma) after a period of tectonic stability and slow closure of the biotite isotopic system in the early Permian–Middle Jurassic (295–170 Ma). The 170–140 Ma span was the time when the Mongol–Okhotsk orogen began its evolution, and the orogeny caused denudation of ~3 km of rocks. Denudation was slow in the Paleogene–Miocene (60–5 Ma) but accelerated over the past 5 million years (a ~3–2 km thick layer) during rapid cooling of rocks and activity under a far-field effect of the India–Eurasia collision.

Unexpectedly narrower track diameter at site of fission event

Fission events in minerals create a damage track, which provides critical information for events that occur over a wide range of time scales, ranging from nuclear fission events (10−20 to 10−12 seconds) to track formation (10−17 to 10−9 seconds) and geological processes (millions of years). However, the site where fission occurs has never been identified along a fission track, as it is long (∼20 μm), thin (diameter <10 nm), and randomly oriented in the mineral matrix. Here, we, for the first time, observe an unexpectedly narrower track diameter (∼1 nm), rather than the conventionally assumed largest diameter, near the fission-event site by a novel technique that confines fission events to the sample surface. The low-charge states of fission fragments produce the narrower track nearest the fission site due to the instantaneous partitioning of negatively charged electrons between two positively charged fission fragments, roughly scaling to their proton numbers. Because a narrower fission track is easier to anneal, the nanostructure nearest the fission site provides spatial information necessary for understanding the atomic-scale mechanisms of track formation and track annealing, with significant implications for fission track thermochronology.

Exhumation History and Exploration Potential of Gold Deposits in the NE Jiaodong Peninsula, North China: Evidence from Apatite and Zircon Fission Track Thermochronology

Exhumation History and Exploration Potential of Gold Deposits in the NE Jiaodong Peninsula, North China: Evidence from Apatite and Zircon Fission Track Thermochronology