Detrital Apatite Fission Track Research Articles

Old detrital AFT ages from East Greenland do not require plateau erosion

Accurate estimates of past topography are required to reliably reconstruct past ice sheets to infer palaeoclimate. For this reason, understanding erosion rates across East Greenland is crucial to constrain landscape evolution driven by tectonics and climate-dependent erosion rates. Here we analyse published apatite fission-track (AFT) data to constrain the spatial pattern of AFT bedrock ages across the landscape. We compare these bedrock ages with published detrital distribution to highlight ambiguity in the pattern of erosion. In contrast to earlier work, we regress a simple model of exhumation pace through the bedrock ages such that age can vary as a function of both elevation and position. The resulting iso-age surfaces allow us to determine potential source areas for detrital AFT age distributions. We find that old ages observed in detrital distributions are just as likely to be sourced from low-elevation locations that are far from the coast as from high-elevation locations close to the coast. Additional data from lower temperature systems are thus required to make firm conclusions on landscape evolution in the region and distinguish between the two landscape-forming scenarios.

Meso–Cenozoic Exhumation in the South Qinling Shan (Central China) Recorded by Detrital Apatite Fission-Track Dating of Modern River Sediments

The Qinling Shan is located between the North China Craton and the South China Block. Not only is investigating the exhumation process of the Qinling Shan beneficial for comprehending the tectonic collision history of mainland China but also for enhancing our understanding of the development of the Yellow and Yangtze Rivers. Previous studies have predominantly focused on bedrock analysis in the Qinling Shan. However, modern fluvial detrital samples offer a more extensive range of thermal history information. Therefore, we gathered modern fluvial debris samples from the Hanjiang River, which is the largest river in the South Qinling Shan. Subsequently, we conducted apatite fission-track analysis using the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method. A total of 214 valid track ages were obtained, with an age distribution ranging from 9.5 to 334.0 Ma. The Density Plotter software was employed to decompose the data and generate four prominent age peaks: 185, 103, 69, 35, and 12 Ma. The exhumation events of the Early Jurassic (185 Ma) and Cretaceous (103–69 Ma) in the Southern Qinling Shan were strongly influenced by the collision between the South China Block and the North China Craton, as well as the subduction of the West Pacific Plate, respectively. The far-field effect of the collision between the Indian Plate and the southern Asian continent influenced the exhumation of the South Qinling Shan during the Late Eocene (35 Ma) and Middle Miocene (12 Ma), respectively. In conjunction with the reported findings, we comprehensively analyzed the geological implications of the Mesozoic and Cenozoic exhumations of the Qinling Shan. The Qinling Shan emerged as a watershed between the Ordos and Sichuan Basins in the early Mesozoic and Cenozoic, respectively. However, the exhumation and expansion of the Tibetan Plateau has forced the Yangtze River to flow eastward, resulting in its encounter with the South Qinling Shan in the late Cenozoic. The exhumation of the Qinling Shan has resulted in fault depression in the southern Ordos Basin. This geological process has also contributed to the widespread arid climatic conditions in the basin. During the Miocene, the Yellow River experienced limited connectivity due to a combination of structural and climatic factors. As a result, the Qinling Shan served as an obstacle, dividing the connected southern Yangtze River from the northern segment of the Yellow River during the late Cenozoic era.

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.

Mesozoic-Cenozoic Exhumation History of the Bogda Range, Eastern Tianshan: Insights from Apatite Fission Track Thermochronology

The Bogda Range (hereafter referred to as the Bogda) is located in the Eastern Tianshan. Interpreting its tectono-thermal history is critical to understanding the intra-continental evolution of the Tianshan. In this study, we report new apatite fission track data from the late Paleozoic–Mesozoic sedimentary rocks in the northern Bogda and the Late Paleozoic granites in the southern Bogda to investigate the exhumation history of the Bogda. Apatite fission track ages dominantly range from the Jurassic to earliest Cenozoic (~143–61 Ma), except for one siliciclastic sample from the Early Permian strata with an older age of ~251 Ma. Thermal history modeling, together with detrital apatite fission track age peaks, reveal that the Bogda underwent three episodes of cooling during the Late Triassic, the Late Cretaceous, and the Late Miocene. The Late Triassic rapid cooling may represent the initial building of the Bogda, which is probably related to the final closure of the Paleo-Asian Ocean. During the Late Cretaceous, the Bogda may have experienced a moderate exhumation, which was possibly triggered by the extensive tectonic extension in the central–eastern Asian regime during the Cretaceous. The Late Miocene rapid cooling may be a response to the rapid uplift of the whole Tianshan, due to the far-field effect of the continuous India–Eurasia collision since the beginning of the Cenozoic.

Exhumation timing of the Cordón del Portillo, Frontal Cordillera, supports the east-vergent model for the growth of the southern central Andes

The timing of contraction, uplift and exhumation of the Cordón del Portillo (33.5–34°S), Frontal Cordillera, southern Central Andes, remains unresolved. This fact has led previous studies to postulate opposite west- and east-growing orogen models. Here, we present the first apatite fission-track (AFT) ages from samples at the Cordón del Portillo, and apatite (U–Th)/He dates (AHe), which allow us to clearly recognize a ca. 15 to 5 Ma period of rapid cooling, interpreted as the record of exhumation of the Frontal Cordillera basement. We present a kinematic evolution of the area that supports these timing of exhumation and a tectonic transport towards the east. Our results agree with previous AHe dating and detrital AFT, which suggest ongoing exhumation pre-14 Ma and peak of exhumation at ca.15 Ma, respectively. It is also in concordance with regional geology and thermochronology pointing to a similar onset of exhumation of the Cordón del Plata, Frontal Cordillera, further north. Moreover, a rising Cordón del Portillo during the early to middle Miocene, contemporaneous with the beginning of sedimentation in the intermontane Alto Tunuyán Basin, implies that Miocene sedimentary rocks were not deposited in a contiguous foreland basin but in an isolated basin separated by topographic highs in the Frontal Cordillera. Finally, our data indicate an eastward shift in the focus of Andean deformation during the Miocene, jumping into the Frontal Cordillera after contraction started in the fold-and-thrust belt of the Principal Cordillera (west of the Cordón del Portillo) at ca.18 Ma, standing for the east-vergent model of tectonic evolution proposed for the Andes.

A re-evaluation of the Meso-Cenozoic thermo-tectonic evolution of Bogda Shan (Tian Shan, NW China) based on new basement and detrital apatite fission track thermochronology

ABSTRACT Bogda Shan is a mountain belt located at the eastern extremity of the Chinese Tianshan and records a complex and debated exhumation history. Previous studies have reported a young Cenozoic thermal history for the exhumation of Bogda Shan, which is in conflict with the observation of preserved Mesozoic erosion surfaces in the area. This study re-evaluates the Meso-Cenozoic thermo-tectonic evolution of Bogda Shan using apatite fission track (AFT) thermochronology. Palaeozoic basement (meta-sandstone) samples collected from the northern and southwestern flanks of the mountain ranges reveal apparent Mesozoic AFT ages ranging from ~202 Ma to ~97 Ma. Inverse thermal history modelling results reveal slow to moderate basement cooling during the early Mesozoic, corresponding to relatively low levels of exhumation. This accounts for the preservation of low-relief Mesozoic peneplanation surfaces recognized at elevations of ~3500–4000 m. None of the presented AFT data and thermal history models show any evidence for significant deep Cenozoic exhumation. In the neighbouring Junggar Basin, a Middle Jurassic sandstone sample records partial resetting of the AFT system during the Cretaceous. This observation conflicts with previous data (from the same Jurassic strata) where complete resetting of the AFT clock during the Cenozoic was suggested. Furthermore, Lower Cretaceous and Palaeogene sediments from the Turpan-Hami Basin show non-reset detrital AFT age populations of ~197, ~135, and ~104 Ma, which are coincident with the main pulses of exhumation recorded in the Chinese North Tianshan. Based on a comprehensive summary of the published data, we argue for a Mesozoic building of the Bogda–Balikun–Harlik mountain chain in the eastern Chinese Tianshan. Subsequent Cenozoic exhumation must have been relatively modest at most (<2 km) as it was not recorded by AFT thermochronology.

Exhumation and erosion of the Northern Apennines, Italy: new insights from low-temperature thermochronometers

Abstract. Analysis of new detrital apatite fission-track (AFT) ages from modern river sands, published bedrock and detrital AFT ages, and bedrock apatite (U-Th)/He (AHe) ages from the Northern Apennines provides new insights into the spatial and temporal patterns of erosion rates through time across the orogen. The pattern of time-averaged erosion rates derived from AHe ages from the Ligurian side of the orogen illustrates slower erosion rates relative to AFT rates from the Ligurian side and relative to AHe rates from the Adriatic side. These results are corroborated by an analysis of paired AFT and AHe thermochronometer samples, which illustrate that erosion rates have generally increased through time on the Adriatic side but have decreased through time on the Ligurian side. Using an updated kinematic model of an asymmetric orogenic wedge, with imposed erosion rates on the Ligurian side that are a factor of 2 slower relative to the Adriatic side, we demonstrate that cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data. These results suggest that horizontal motion is an important component of the overall rock motion in the wedge, and that the asymmetry of the orogen has existed for at least several million years.

Uplift and Expansion of the North Qilian Shan Recorded by Detrital Fission Tracks in the Jiudong Basin, NW China

The North Qilian Shan, located in the northeastern front of the Tibetan Plateau, is an ideal region to study the expansion process of the plateau, which is not clearly revealed due to the lack of direct evidence and an accurate age control. In the Jiudong Basin (foreland basin of the North Qilian Shan), a continuous late Cenozoic sedimentary sequence and a reliable chronostratigraphic framework (post-7 Ma) provide us the material to study this process. In this study, we first analyzed the provenance changes of the sediment by detrital apatite fission track age distributions and apatite particle textures. The result shows that the first provenance change occurred at 4.6–3.6 Ma, when the sediment source changed from the southern to the northern parts of the North Qilian Shan, and it indicates that the North Qilian Shan Fault had propagated to its modern location. The second provenance change occurred at 3.0–2.4 Ma, at when the Yumu Shan and its south region began to provide sediments for the Jiudong Basin, and it indicates that the tectonic deformation in the North Qilian Shan had expanded to the North Yumu Shan Fault. Our finding suggests that two significant expansion events happened since the Pliocene for the North Qilian Shan.

Mesozoic building of the Eastern Tianshan and East Junggar (NW China) revealed by low-temperature thermochronology

The Eastern Tianshan and East Junggar orogenic belts are major constituents of the southwestern Central Asian Orogenic Belt. This study applies low-temperature thermochronology to constrain the thermo-tectonic history of these two domains. Apatite fission track (AFT) dating of Paleozoic basement samples from the Eastern Tianshan and East Junggar dominantly yield Cretaceous (∼126–70 Ma) AFT ages, except for two granitic samples from the East Junggar with older ages of ∼239 and ∼157 Ma, respectively. Thermal history modeling reveals that the Eastern Tianshan and southern part of the East Junggar experienced moderate to rapid basement cooling throughout the Cretaceous. We interpret it as a far-field effect of accretion and collision along the south Eurasia margin since the Early Cretaceous. Major faults were reactivated and thus may have played an important role in controlling localized fast uplift and cooling. We also dated seven Mesozoic sandstone samples collected from the eastern margin of the Junggar Basin. The detrital AFT age peaks, together with inverse thermal history modeling of the basement, reveal that the East Junggar underwent late Permian to Early Jurassic cooling episodes. These cooling events are thought to be related to post-orogenic transpression along major faults and distal effect of Qiangtang-Eurasia collision. Combined with already published evidence, our new data suggest that the Eastern Tianshan and East Junggar did not undergo significant exhumation during the Cenozoic.

Mesozoic-Cenozoic multistage tectonic deformation of the Qilian Shan constrained by detrital apatite fission track and zircon U[sbnd]Pb geochronology in the Yumu Shan area

The Qilian Shan on the northeastern edge of the Tibetan Plateau contains structural, sedimentary and tectonothermal records of plateau formation and growth in response to the Indian-Asian continental collision. In this study, we reveal the tectonic deformation evolution of the Qilian Shan by detrital apatite fission track (AFT) thermochronology and provenance analysis of a sedimentary section on the northern flank of the Qilian Shan based on paleocurrent measurements and detrital zircon UPb geochronology. The unannealed detrital AFT peak ages span ~154–10 Ma, and the zircon UPb ages range between ~3260 Ma and ~ 178 Ma. Detrital AFT ages showing that the initial exhumation occurs ca. 154–135 Ma and ca. 105–81 Ma and abundant ages of ca. 61–24 Ma indicate the prominent exhumation of the sedimentary provenance from the Qilian Shan at those times. Zircon UPb analysis suggests that the sediments were generally sourced from the Qilian Shan to the south, with moderate provenance changes at ~10 Ma and 5.1 Ma. These geochronological datasets imply that the Qilian Shan experienced multistage deformation during the Mesozoic-Cenozoic, i.e., late Jurassic-early Cretaceous (153.6–135.2 Ma), late Cretaceous (104.5–80.9 Ma), late Paleocene-Oligocene (61–43.1 Ma;38.2–24.6 Ma), mid-late Miocene (10 ± 4 Ma) and Pliocene (5.1–3.6 Ma). During the Cenozoic, the deformation initiated in the late Paleocene reflects the synchronous far-field response of the northeastern Tibetan Plateau margin to the Indian-Asian plate collision.

Intensified Late Miocene Deformation in the Northern Qaidam Basin, Northern Tibetan Plateau, Constrained by Apatite Fission-Track Thermochronology

The Cenozoic tectonic evolution of the North Qaidam-Qilian Shan fold-thrust belt in the northern Tibetan Plateau is important to understanding the tectonic rejuvenation of orogeny and growth of the plateau. However, the deformation processes in this region remain controversial. This study presents new apatite fission track (AFT) data from Paleogene strata in the northern Qaidam Basin to investigate the time of deformation in this site. Thermal modeling of these partially annealed detrital AFT ages shows a thermal history with a noticeable transition from heating to cooling after ∼10 Ma. This transition is attributed to the intensified thrusting and folding of the northern Qaidam Basin since ∼10 Ma. Integrated with published tectonics and thermochronology results, we suggest the North Qaidam-Qilian Shan fold-thrust belt experienced prevailing tectonism since the late Miocene.

New Detrital Apatite Fission Track Thermochronological Constraints on the Meso-Cenozoic Tectono-Thermal Evolution of the Micangshan-Dabashan Tectonic Belt, Central China

The Micangshan-Dabashan tectonic belt, located in the southern Qinling-Dabie Orogen near the northeastern Tibetan Plateau, is a crucial area for understanding the processes and mechanisms of orogenesis. Previous studies have been focused on the cooling process via thermochronology and the mechanism and process of basement uplift have been investigated. However, the coupling process of basement exhumation and sedimentary cap cooling is unclear. The tectono-thermal history constrained by the detrital apatite fission track (AFT) results could provide valuable information for understanding crustal evolution and the coupling process. In this study, we provided new detrital AFT thermochronology results from the Micangshan-Dabashan tectonic belt and obtained nine high-quality tectono-thermal models revealing the Meso-Cenozoic cooling histories. The AFT ages and lengths suggest that the cooling events in the Micangshan area were gradual from north (N) to south (S) and different uplift occurred on both sides of Micangshan massif. The cooling in Dabashan tectonic zone was gradual from northeast (NS) to southwest (SW). The thermal histories show that a relatively rapid cooling since ca. 160 Ma occurred in the Micangshan-Dabashan tectonic belt, which was a response to the event of Qinling orogenic belt entered the intracontinental orogenic deformation. This cooling event may relate to the northeastward dextral compression of the Yangtze Block. The sedimentary cap of Cambriano-Ordovician strata responded positively to this rapid cooling event and entered the PAZ since ca. 63 Ma. The deep buried samples may be limited affected by climate and water erosion and the accelerated cooling was not obvious in the Late Cenozoic. Collectively, the cooling processes of basement and sedimentary cap in Micangshan-Dabashan tectonic belt were inconsistent. The uplift of the sedimentary area is not completely consistent with that of the basement under thrust and nappe action. The rigid basement was not always continuous and rapidly uplifted or mainly showed as lateral migration in a certain stage because of the different intensities and modes of thrust and nappe action, and the plastic sedimentary strata rapidly uplifted due to intense folding deformation.

The role of preexisting upper plate strike-slip faults during long-lived (ca. 30 Myr) oblique flat slab subduction, southern Alaska

Upper plates of subduction zones commonly respond to flat slab subduction by structural reactivation, magmatic arc disruption, and foreland basin inversion. However, the role of active strike-slip faults in focusing convergent deformation and magmatism in response to oblique flat slab subduction remains less clear. Here, we present new detrital apatite fission-track (dAFT) ages from 12 modern catchments in the eastern Alaska Range, Alaska, USA, to reveal how the dextral Denali fault system has facilitated bedrock exhumation and topographic growth during ca. 30 Ma-to-present oblique flat slab subduction of the Yakutat oceanic plateau. Additionally, a 940 ka (40Ar/39Ar whole rock) basalt flow is spatially associated with Cenozoic structures, locally reset AFT ages and provides the first evidence for Quaternary volcanism along the southern flank of the eastern Alaska Range. We integrate our new data with other thermochronologic, geochronologic, and regional geologic datasets to show that (1) most high topography regions in southern Alaska have undergone rapid bedrock cooling and exhumation since ca. 30 Ma; (2) elevated terrain and young cooling are spatially associated with long-lived active strike-slip fault systems; (3) topographic growth associated with strike-slip fault deformation led to local inversion of basin systems and drainage reorganization; (4) the onset of oblique oceanic plateau subduction is coeval with a southward shift in arc magmatism from one region of active strike-slip faulting to another above the northeastern edge of the flat slab; and (5) Quaternary volcanism marks the revival of magmatism in the eastern Alaska Range above the geophysically imaged northeastern edge of the flat slab. Our analysis of the post-30 Ma geologic evolution of southern Alaska demonstrates that strike-slip fault systems that were active at the time of slab flattening evolved into transpression zones that focused bedrock cooling, rock exhumation, and topographic growth.

Determining the tempo of exhumation in the eastern Himalaya: Part 2. Integrating bedrock and detrital cooling ages through thermokinematic modelling

AbstractThe exhumation record of a fold‐thrust belt is preserved by thermochronologic minerals, such as zircon and apatite, both in exposed bedrock and in synorogenic sedimentary rocks in the foreland basin. Treating these as separate records can lead to potentially contrasting interpretations of a single exhumation history. Integrating the bedrock and detrital records with thermokinematic models of sequential deformation of a fold‐thrust belt can identify viable exhumation pathways of the bedrock and elucidate both how bedrock exhumation varies in space and time and how accurately the basin records exhumation changes in the source region. Predicted bedrock cooling ages and modelled basin thickness are used to estimate the amount and source of sediments supplied to the foreland basin during each increment of deformation to predict the detrital cooling signal over time. Applying this integrated bedrock‐detrital model to a cross‐section in Arunachal Pradesh, NE India demonstrates spatial and temporal variability in exhumation, with a background exhumation rate of &lt;2 mm/yr, periods of rapid exhumation at rates of 3–7 mm/yr, and short pulses of 10–12 mm/yr rates during out‐of‐sequence thrusting. Our results predict that the detrital apatite fission track (DAFT) system records a constant lag time of 0.5–1 Myr. Although the response of the detrital zircon fission track (DZFT) system is more complex, the system records changes in lag time (1–5 Myr) as a function of the kinematics, deformation rates and thermal profile of the crust in the hinterland. However, the DZFT cooling signal is delayed by 1–2 Myr relative to the age of marked shifts in location, magnitude and rate of exhumation in the source region. Our models also highlight the importance of recycled foreland deposits in matching the ca. 20 Ma static peak in the DZFT record and ca. 14 Ma static peak in the DAFT record.

Hints on the Late Miocene Evolution of the Tonale-Adamello-Brenta Region (Alps, Italy) Based on Allochtonous Sediments From Raponzolo Cave

Raponzolo is a paleo-phreatic cave explored in 2011 in the Brenta Dolomites (Trentino, Italy), at the remarkable altitude of 2,560 m a.s.l. Differently to all other caves of the area, it hosts well-cemented fine to medium sands of granitic-metamorphic composition. The composition suggests a sediment source from the Adamello and Tonale Unit, separated from the Brenta by one of the most important tectonic lineaments of the Alps (Giudicarie Line). The fine-sand sediment was sampled to determine burial time and thus a minimum age of the cave. Cosmogenic isotopes (26Al and 10Be) in quartz grains allowed to estimate a minimum burial age of 5.25 Ma based on the mean sediment transport time at the surface and infer original altitude of the catchment area. Detrital apatite fission-track (AFT) and U-Pb dating on zircons provide information on the source, both from a regional and altitude (exhumation) perspective. Two populations of detrital AFT ages center at 17 (−2.3 + 2.6) Ma and 23 (−3.3 + 3.9) Ma, whereas the main detrital zircon U-Pb age populations are younger than 40 Ma. These correspond to intrusive and metamorphic sources nowadays outcropping exclusively above 2,200–2,300 m a.s.l. in Northern Adamello and Tonale. The results point to a late Miocene erosion and infilling of the cave by allochtonous sediments, with important implications on the timing of cave speleogenesis, as well as the paleogeographical connection, tectonic evolution and uplift of different structural units of the Alps. The roundness and the well sorted size of the quartz grains suggest a fluvial or aeolian origin, possibly recycled by glacial activity related to cold events reported in high latitude areas of the world at 5.75 and 5.51 Ma. These glacial phases have never been documented before in the Alps. This information confirms that the valleys dividing these geological units were not yet deeply entrenched during the onset of the Messinian Salinity Crisis (5.6–5.5 Ma), allowing an efficient transport of sediments across major tectonic lineaments of the Alps. This study shows the potential of cave sediments to provide information not only on the age of speleogenesis but also on the paleogeography of a wide area of the Alps during the late Miocene.

Early Cenozoic activated deformation in the Qilian Shan, northeastern Tibetan Plateau: Insights from detrital apatite fission‐track analysis

AbstractThe evolution of the tectonic deformation of the northeastern Tibetan Plateau (TP) in the Cenozoic is significant for understanding plateau growth during India‐Asia convergence. However, when deformation began and how it has developed in this pivotal region remain controversial. We focus on the temporal progress of Cenozoic deformation in the Qilian Shan, a major tectonic belt of the northeastern TP. In the present study, detrital apatite fission‐track (AFT) thermochronological analysis was performed on Oligocene‐Quaternary synorogenic sediments in the northern Qaidam Basin, where detritus is sourced from the Qilian Shan. Age components of buried but unannealed detrital AFT samples reveal two static peaks (i.e., peak ages that are consistent upsection) at ca. 60–50 Ma and ca. 40–36 Ma and a moving peak (i.e., peak ages that are younger upsection) with increased lag time during ca. 30–8 Ma. These new detrital AFT ages, integrated with the analysis of sedimentary provenance and data from previously published studies, indicate that Cenozoic tectonic deformation began in the Qilian Shan in the late Paleocene‐early Eocene. Furthermore, the Qilian Shan experienced a subsequent episodic deformation event in the late Eocene and the deformation or erosion of some terranes in the Qilian Shan decelerated during the Oligocene‐Miocene. Our results suggest that the northeastern TP responded to the India‐Asia collision almost instantaneously.

Neogene shallow-marine and fluvial sediment dispersal, burial, and exhumation in the ancestral Brahmaputra delta: Indo-Burman Ranges, India

ABSTRACTThe stratigraphic record of Cenozoic uplift and denudation of the Himalayas is distributed across its peripheral foreland basins, as well as in the sediments of the Ganges–Brahmaputra Delta (GBD) and the Bengal–Nicobar Fan (BNF). Recent interrogation of Miocene–Quaternary sediments of the GBD and BNF advance our knowledge of Himalayan sediment dispersal and its relationship to regional tectonics and climate, but these studies are limited to IODP boreholes from the BNF (IODP 354 and 362, 2015-16) and Quaternary sediment cores from the GBD (NSF-PIRE: Life on a tectonically active delta, 2010-18). We examine a complementary yet understudied stratigraphic record of the Miocene–Pliocene ancestral Brahmaputra Delta in outcrops of the Indo-Burman Ranges fold–thrust belt (IBR) of eastern India. We present detailed lithofacies assemblages of Neogene delta plain (Tipam Group) and intertidal to upper-shelf (Surma Group) deposits of the IBR based on two ∼ 500 m stratigraphic sections. New detrital-apatite fission-track (dAFT) and (U-Th)/He (dAHe) dates from the Surma Group in the IBR help to constrain maximum depositional ages (MDA), thermal histories, and sediment accumulation rates. Three fluvial facies (F1–F3) and four shallow marine to intertidal facies (M1–M4) are delineated based on analog depositional environments of the Holocene–modern GBD. Unreset dAFT and dAHe ages constrain MDA to ∼ 9–11 Ma for the Surma Group, which is bracketed by intensification of turbidite deposition on the eastern BNF (∼ 13.5–6.8 Ma). Two dAHe samples yielded younger (∼ 3 Ma) reset ages that we interpret to record cooling from denudation following burial resetting due to a thicker (∼ 2.2–3.2 km) accumulation of sediments near the depocenter. Thermal modeling of the dAFT and dAHe results using QTQt and HeFTy suggest that late Miocene marginal marine sediment accumulation rates may have ranged from ∼ 0.9 to 1.1 mm/yr near the center of the paleodelta. Thermal modeling results imply postdepositional cooling beginning at ∼ 8–6.5 Ma, interpreted to record onset of exhumation associated with the advancing IBR fold belt. The timing of post-burial exhumation of the IBR strata is consistent with previously published constraints for the avulsion of the paleo-Brahmaputra to the west and a westward shift of turbidite deposition on the BNF that started at ∼ 6.8 Ma. Our results contextualize tectonic controls on basin history, creating a pathway for future investigations into autogenic and climatic drivers of behavior of fluvial systems that can be extracted from the stratigraphic record.

Deformation and cooling history of the Central Qiangtang terrane, Tibetan Plateau and its tectonic implications

ABSTRACT The Qiangtang terrane preserves an important record of the growth of the Tibetan Plateau since the Mesozoic; however, its deformation and cooling history remain poorly understood. To unravel this issue, we conducted geological mapping in the Esima area and detrital apatite fission track and (U–Th)/He analyses of the Esima–Rongtang region in the east segment of Central Qiangtang terrane. Our results indicate that the east segment underwent two stages of structural deformation and rapid cooling during 120–110 Ma and 55–38 Ma. By combining our results with those of previous studies of the deformation and cooling history in the west segment, we reconstructed the early spatial and temporal geological evolution of the Central Qiangtang terrane since the Late Jurassic–Early Cretaceous. The structural deformation and cooling of the west segment at 150–130 Ma was related to northward flat subduction of the Bangong–Nujiang oceanic slab. The structural deformation and cooling of the east segment at 120–110 Ma and the west segment at 110–70 Ma was controlled by oblique convergence between Lhasa and Qiangtang terranes. The structural deformation and cooling of the west and east segments at 55–38 Ma was associated with northward intracontinental subduction beneath the Qiangtang terrane induced by the Indo–Asian collision.

Early Cenozoic exhumation in the Qilian Shan, northeastern margin of the Tibetan Plateau: Insights from detrital apatite fission track thermochronology

AbstractThe Qilian Shan is a reactivated fold‐thrust belt at the northeastern margin of the Tibetan Plateau (TP). The initiated timing of the Qilian Shan's tectonic response to Indian‐Asian plate convergence has significant implications for our understanding of the growth of the TP, yet remains a controversial topic. We conducted apatite fission track analyses of the Cenozoic synorogenic sediments in the Subei Basin on the northwestern flank of the Qilian Shan to investigate the time of initial Qilian Shan deformation during the Cenozoic. An integration of new and existing detrital apatite fission track ages indicates that terranes in the Qilian Shan experienced a prominent tectonic exhumation event at ~60–50 Ma. This result suggests that tectonism initiated on the northeastern margin of the TP nearly simultaneously with the India‐Asia collision.

Ongoing exhumation of the Taiwan orogenic wedge revealed by detrital apatite thermochronology: The impact of effective mineral fertility and zero-track grains

In clastic detritus derived from the erosion of young active orogens, the geologic interpretation of apatite fission-track (AFT) data is hampered by the occurrence of grains without spontaneous tracks and by contributions from multiple eroding sources with different apatite fertilities. Here, we use the Taiwan orogen as a test case to illustrate how to overcome these problems and deal with zero-track grains in detrital AFT studies following long-established principles of fission-track statistics. Our results support the effectiveness of Raman spectroscopy for a reliable identification of apatite grains. We found that zero-track grains are dominant in Taiwan modern sands, and generally contain enough U to provide useful AFT age constraints to exhumation. The absence of spontaneous tracks in most of these grains is due to a short residence time below the temperature of total AFT annealing rather than to low U concentration. Detrital AFT data shows that the extent of the Taiwan AFT reset zone previously inferred from bedrock data was partly underestimated. The revised AFT reset zone includes the southernmost part of the island and, when combined with published ZFT data, supports a scenario of southward progressing exhumation during arc-continent collision. The application of the Taiwan lesson to clastic detritus derived from the Himalaya resolves paradoxical interpretations of detrital fission-track data sets recently published in the framework of IODP Expedition 354, pointing to a major role of the Namche Barwa syntaxis as a source of apatite grains shed to the Bengal Fan.