Fission-track Ages Research Articles

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.

Intense metamorphism-generated radiogenic Sr regulated Cenozoic water Sr isotope evolution on the NE Tibetan Plateau: A perspective on Qilian orogen denudation and Asian eolian transport

The India-Asia collision reactivated the early Paleozoic Qilian orogen with an intense metamorphic belt that promoted the release of metamorphism-generated radiogenic Sr into the drainage systems on the NE Tibetan Plateau. This metamorphic impact on the regional dissolved Sr cycle is well observed at the recent−modern scale, but its onset and evolutionary histories are unclear. We present the first basin-scale 52−5 Ma regional dissolved Sr isotopic record in water on the NE Tibetan Plateau by analyzing well-dated basin fluvial-lacustrine sediments in the Xining, Linxia, and Tianshui Basins. The Xining Basin displays an increase in basin water 87Sr/86Sr ratio and a decrease in the sediment εNd values at ca. 25 Ma. This Sr-Nd isotope-deduced provenance change coincides with the reorganization of drainage and erosion regimes that is suggested by an evident rise in the youngest peak and the lag time of detrital apatite fission-track ages from Cenozoic sedimentary basins surrounding the Qilian orogen. The Qilian-sourced eolian dust during ca. 9−8 Ma significantly elevated the river and lake water 87Sr/86Sr ratios in the downwind Linxia and Tianshui Basins, which is consistent with the expansion of the Asian dust system. Our results suggest that large-scale denudation of the Qilian orogen in response to the India-Asia collision initiated in the late Oligocene. Given the remarkable hydrological impact of the Cenozoic reactivation of the Qilian orogen, our study highlights the potentially important role of continental collision−formed metamorphic belts in regulating past regional and even seawater Sr isotope evolution.

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.

Detecting the Laramide event in southern Mexico by means of apatite fission-track thermochronology

AbstractIn this study, we present apatite fission-track results obtained for ten rock samples collected from three different areas across the Sierra Madre del Sur, southern Mexico. The central objective of our study is the timing of the exhumation event that took place in southern Mexico during Late Cretaceous–Palaeogene time. The thermochronometric data obtained during this work indicate that a Late Cretaceous–Eocene cooling is recorded within the Sierra Madre del Sur, and this is interpreted as resulting from exhumation, an orogenic event that is contemporaneous with the Laramide sensu lato (or the Mexican Orogeny). The fission-track ages become younger from west to east across the Sierra Madre del Sur, whereas the cooling rates also increased in the same direction approximately during Campanian–middle Eocene time. Here, we suggest that the activity of the major fault systems of southern Mexico, such as the Caltepec and the Oaxaca faults, played a primary role in the development of geological structures and the exhumation of the Sierra Madre del Sur. Active magmatism during the evolution of the Mexican Orogen implicates the subducted Farallon slab as the main driver of crustal thickening. Moreover, the possible influence of the eastward movement of the Chortis Block on the deformation of the Sierra Madre del Sur cannot be ruled out.

Exhumation history of the Katebasu gold–copper deposit, Western Tianshan, NW China: Constraints from (U–Th)/He and fission-track thermochronology

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.

First application of low temperature thermochronology as a tool for geothermal exploration: A promising, preliminary test from the Larderello-Travale geothermal field (Italy)

High enthalpy geothermal fields are typically associated with magmatic intrusions providing the heat source that makes the system working. To identify and locate these features, geothermal exploration generally uses expensive, time-consuming approaches that could also require complex logistics. Here we present the result of a pilot study carried out in the well-known Larderello-Travale geothermal field (Tuscany, Italy), exploring the possibility of an advantageous use of low temperature thermochronology to obtain useful information implementing the geothermal exploration workflow. The majority of the collected samples (except one retaining the apatite fission-track age of undisturbed, or almost undisturbed country rocks) cluster in a close time span ranging between 3.1±0.8 and 1.9±1.1 Ma, which clearly matches the known ages of magmatic bodies in the region. We propose that this approach can contribute to the identification of sectors recently affected by thermal perturbations that could have led to the development of hydrothermal systems. This approach has allowed us to achieve clues for the presence of subsurface magmatic intrusions even in areas where currently there are no direct indications. Given the small number and distribution of analyzed samples, our contribution represents a first attempt that demonstrates the potentiality of the method in geothermal exploration, but that needs to be verified by further studies involving a larger sampling density. Overall, our results suggest how low temperature thermochronology can be a powerful, fast, and cost-effective tool for geothermal exploration, to be used jointly with the classical methods.

Testing the cenozoic lower crustal flow beneath the Qinling Orogen, northeastern Tibetan Plateau

The E–W-trending Qinling Orogen lies in the transitional zone between the northeastern extent of the Tibetan Plateau and the lower-elevation portion of the continent. This region is suggested to have accommodated flow of the low-viscosity lower crust from the Tibetan Plateau northward around the Sichuan Basin during the Cenozoic Himalayan–Tibetan orogeny. To test this model, we combined field geologic mapping, balanced cross-section construction, thermochronology, and geophysical interpretation to constrain the history of crustal thickening from the Mesozoic to the present. In this study, we obtained new thermochronological data from four samples, which yielded 40Ar/39Ar ages of ∼194 Ma for hornblende and 208-151 Ma for biotite and apatite fission track ages of 69-42 Ma. The new thermochronological data and field mapping demonstrate that most shortening structures initially formed in the Mesozoic and underwent minor structural overprinting in the Cenozoic. Systematic structural analyses and restoration of balanced cross-sections demonstrate that the Qinling Orogen was shortened by a minimum of 35% strain (80 km shortening magnitude) after the Mesozoic Paleotethys Ocean closure and continental collision. The crust thickened substantially to >60 km, and the thermochronological data demonstrate that erosion and denudation were minor, such that the crust would have remained thick into the Cenozoic. An additional balanced cross-section across Cenozoic strata suggests >11% Cenozoic shortening, and the observed shortening alone is enough to thicken the crust to the presently observed ∼40–45 km. Therefore, we argue that lower crustal flow is not needed to account for the crustal thickness of the Qinling Orogen and that the data do not support the occurrence of processes associated with lower crustal flow beneath the Qinling Orogen.

Zircon U-Pb and fission-track ages of felsic tuff from the Ryujin Complex in the Shimanto Accretionary Prism on the eastern part of the Kii Peninsula, Japan

Zircon U-Pb and fission-track ages of felsic tuff from the Ryujin Complex in the Shimanto Accretionary Prism on the eastern part of the Kii Peninsula, Japan

Nappe Imbrication Within the Phyllite‐Quartzite Unit of West Crete: Implications for Sustained High‐Pressure Metamorphism in the Hellenide Subduction Orogen, Greece

AbstractWe report four K‐Ar fault‐gouge and eight U‐Pb calcite ages from the high‐pressure Phyllite‐Quartzite Unit (PQ) and the overlying, strongly thinned non‐high‐pressure Tripolitza and Pindos units of western Crete, Greece. We relate consistent 26–21 Ma fault‐gouge ages to a discrete top‐to‐the‐S, brittle‐ductile, contractional shear zone (Intra‐PQ Thrust) that formed during high‐pressure conditions within the Phyllite‐Quartzite Unit. The Intra‐PQ Thrust separates the Phyllite‐Quartzite Unit into an upper and a lower unit and is associated with gypsum deposits and high finite strain. Below the Intra‐PQ Thrust, U‐Pb calcite ages between about 16 and 13 Ma are also associated with top‐to‐the‐S kinematic indicators and, in part, developed during aragonite stability. The brittle‐ductile contact zone to the overlying Tripolitza and Pindos units yielded U‐Pb calcite ages of 13 to 12 Ma. Our data imply that the upper Phyllite‐Quartzite Unit underwent high‐pressure metamorphism at the commonly envisaged time of 24–21 Ma. However, the lower Phyllite‐Quartzite Unit started to be underthrust at 26–21 Ma and was high‐pressure metamorphosed at 16–13 Ma, as suggested by the U‐Pb calcite ages of aragonite‐bearing samples and published zircon fission track ages. We discuss a tectonic model of successive underthrusting, high‐pressure metamorphism and subsequent exhumation of both Phyllite‐Quartzite units in extrusion wedges until 12–11 Ma, after which Crete underwent crustal extension. Our work suggests that there might be more than one Cretan Detachment. It also has implications for sustained underthrusting and exhumation of continental crust in subduction zones.

Late Paleocene – Middle Eocene magmatic flare-up in western Anatolia

A 3000-km long magmatic belt of predominantly Eocene age extends from Anatolia into Iran representing a major magmatic flare-up. We present new zircon U-Pb, Ar/Ar mica and apatite fission-track ages for this magmatism from northwestern Turkey, and review its geochemistry and geodynamic setting. The new age data show that magmatism started at the Late Paleocene (58 Ma) during the final stages of continental collision and continued into the early Middle Eocene (45 Ma) with most of the magmatism taking place in the Early-Middle Eocene (54 to 45 Ma). The Late Paleocene-Middle Eocene magmatism is separated from Late Cretaceous and Oligo-Miocene magmatic flare-ups by periods of magmatic quiescence. The Late Paleocene-Middle Eocene magmatism consists of plutonic and volcanic belts. The plutonic belt cuts across and post-dates the İzmir-Ankara suture. The plutonic rocks are mainly middle- to high-K calc-alkaline I-type granodiorite and granite, and the volcanic rocks are middle- to high-K calc-alkaline basalt, basaltic andesite and andesite. Geochemically, all the rocks are similar to those found in subduction-related environments. Crustal thicknesses calculated based on geochemistry suggest a thickened crust (60–70 km) at 58 to 54 Ma, and a relatively thin crust (ca. 40 km) at 54 to 45 Ma, which match with uplift and erosion during the Late Paleocene, and marine sedimentation during the Early-Middle Eocene in northwest Anatolia, respectively. The Late Paleocene-Middle Eocene magmatism is tentatively assigned to subduction of the southern branch of the Neo-Tethys.

Spurious age-eU associations in thermochronological data

The He and fission-track ages of individual apatite, titanite, and zircon grains, and the Raman ages of zircon grains are often correlated with their effective uranium concentrations (eU). These correlations are thought to result from closure-temperature differences related to lattice damage from self-irradiation. We present apatite fission-track and zircon-Raman data with negative age-eU correlations even though the track lengths and the agreement between Raman bands with different annealing sensitivities rule out radiation-damage-related age differences. Age-eU plots are vulnerable to spurious correlation due to the fact that the age- and eU-estimates both depend on measurements of the parent concentration. Correlation between age and eU is thus an inescapable component of datasets in which the daughter and parent concentrations are not in fixed proportion. Non-linear D-P relationships due to radiation-damage effects create true age-eU correlations, whereas systematic or random deviations from proportionality lead to spurious correlations. Plotting the daughter against parent concentrations (D-P plot) helps to distinguish causal and spurious age-eU associations. Some cases are inconclusive, for example when similar causal and spurious effects combine to form the age-eU trend, but a significant number is less ambiguous. Apart from detecting spurious correlations, D-P plots can be used for validating causal age-eU associations by corroborating the D-P relationships predicted by radiation-damage models for specific thermal histories. Suspected causal age-eU correlations should also be backed up by evidence of differential annealing such as fission-track-length or multi-band Raman measurements.

Development of an In SituU‐Th Disequilibrium Dating Method Utilising Multiple‐Spot Femtosecond Laser Ablation‐CRC‐ICP‐MS

In situ 238U‐230Th dating was conducted using an ICP‐mass spectrometer coupled with a laser ablation sampling system (LA‐ICP‐MS). To minimise the contribution of mass spectrometric interferences on 230Th, a kinetic energy discrimination technique using a collision/reaction cell (CRC) system was employed. The major problem associated with the CRC‐ICP‐MS system is the lower transmission efficiencies of ions than sector field mass spectrometers. To improve the signal‐to‐background ratio for analytes, a combination of a multiple‐spot laser ablation (msLA) system together with a sensitivity‐enhanced dry plasma cone was employed. Analytical accuracy was evaluated through analyses of three zircon reference materials (GJ‐1, OD‐3 and Plešovice) and the resulting 230Th/238U ratios for GJ‐1 and Plešovice zircons agreed with the secular equilibrium value. The developed technique was applied to Quaternary volcanic zircon and monazite samples from Japan. The resulting ages are 113.5 +5.4‐5.2 ka for the Toya tephra, 105.1 +6.4‐6.1 ka for the Sambe Kisuki tephra, 55.2 +7.7‐7.2 ka for the Hikageyama lava and 16.2 +4.2‐4.1 ka for the Susaki pumice (95% confidence levels). The resulting ages are consistent with previous chronological constraints including zircon fission track ages. The data obtained here demonstrate clearly that the combination of the CRC‐ICP‐MS system and the msLA protocol can become a powerful analytical tool for in situ U‐Th disequilibrium dating.

Cretaceous−Cenozoic cooling history of the Qiangtang terrane and implications for Central Tibet formation

Reconstructing the growth process of the Qiangtang terrane in space and time is crucial for understanding the geological evolution of Central Tibet. However, its growth process and dynamic mechanism remain unclear. Here, we present new fission track data obtained along a N-S transect near the Puruo Kangri Mountain in the central zone of the Northern Qiangtang terrane. The completely reset apatite fission track ages of detrital samples range from 65.1 to 89.6 Ma, which show a northward younging trend. The thermal history modeling results indicate that this region underwent northward-propagating exhumation during the Late Cretaceous (ca. 92−65 Ma). Our data, combined with previously reported low-temperature thermochronology data for the Qiangtang terrane, suggest that the Qiangtang terrane experienced three main stages of cooling: ca. 120−65, ca. 55−35, and <25−0 Ma. The first stage (ca. 120−65 Ma) displays an outward-propagating cooling pattern from the Central Qiangtang terrane, which was related to the crustal shortening and thickening driven by the Lhasa-Qiangtang collision. The low exhumation rate, flat lavas, and paleoaltimetry studies imply that the central and southern zones of the Northern Qiangtang terrane and Central Qiangtang terrane may form plateau landscape by 65−55 Ma. The second stage (ca. 55−35 Ma) of cooling is mainly documented in the Southern Qiangtang terrane, and the northern zone of the Northern Qiangtang terrane. This cooling event was caused by the crustal deformation and shortening driven by intracontinental subduction related to ongoing convergence of the Indian and Asian plates. Subsequently, both the transition to low erosion rates (<0.05 mm/yr) and paleoaltimetry data indicate that the Qiangtang terrane became a primitive plateau by ca. 35 Ma. The final stage (<25−0 Ma) of cooling was linked to the E-W extension in the Qiangtang terrane.

Mesozoic–Cenozoic multistage tectonic evolution of the Pamir: Detrital fission‐track constraints from the Tajik Basin

AbstractKnowledge of the tectonic history of the Pamir contributes to our understanding of both the evolution of collisional orogenic belts as well as factors controlling Central Asian aridification. It is, however, not easy to decipher the Mesozoic–Cenozoic tectonics of the Pamir due to extensive Neogene deformation in an orogen that remains largely understudied. This study reports detrital apatite and zircon fission‐track (FT) ages from both the eastern Tajik Basin sedimentary rocks and Pamir modern river sands. These FT data, supported by vitrinite reflectance and zircon and apatite U–Pb double dating, suggest that the majority of the FT ages are unreset and record exhumation stages of the Pamir, which has served as the source terrane of the Tajik Basin since the Cretaceous. Furthermore, we combine the new data with a compilation of published detrital apatite and zircon FT data from both the Tajik Basin sedimentary rocks and Pamir modern river sands, to explore the Mesozoic–Cenozoic tectonic history of Pamir. Deconvolved FT Peak Ages document two major Mesozoic exhumation events associated with the Late Triassic–Early Jurassic Cimmerian orogeny that reflects accretion of the Pamir terranes, as well as the Early–early Late Cretaceous deformation associated with the northward subduction of the Neo‐Tethys Ocean beneath Pamir. The compiled data also show significant Late Eocene–Neogene exhumation associated with the ongoing formation of the Pamir, which peaks at ca. 36, 25, 14 and 7 Ma.

Extensional stress accompanied by Miocene near-trench magmatism in the southern Kii Peninsula, SW Japan

Voluminous near-trench magmatism began in the Kumano area, SW Japan, at ca. 15 Ma. The magmatism formed batholiths, cauldrons, and numerous dikes. It has been known that The dikes are oriented perpendicular to the Nankai Trough, and are hosted by young formations that are folded with axes parallel to the trench. Therefore, it has been considered that the magmatism was accompanied by trench-perpendicular compression during the period shortly after backarc opening in the Japan Sea. For this study, we obtained orientation data from 14 felsic and 151 mafic dikes in the early to middle Miocene Kumano Group and Shionomisaki Igneous Complex. Inversion of both datasets yields a normal-faulting stress regime with NE–SW extension. This orientation meets at a high angle with that of the trench. We also obtained zircon fission-track ages of 14.5 ± 1.5 and 13.9 ± 1.4 Ma from two felsic dikes. These ages and existing radiometric and micropaleontological data show that both the groups of dikes were formed at ca. 14.5 Ma. Large- and meso-scale structures indicating trench-perpendicular shortening in igneous rocks suggest that the folding took place after the magmatism. We interpret that the extensional stress resulted from uplift caused by the emplacement of a batholith under the Kumano area. The inferred normal-faulting stress regime raises doubts about popular tectonic models of SW Japan that rely on a transition from extension to compression at ca. 15 Ma.

Late Cretaceous–Early Cenozoic exhumation across the Yalong thrust belt in eastern Tibet and its implications for outward plateau growth

Rapid denudation and uplift of eastern Tibet have accelerated during the Late Miocene due to lateral lower crustal flow, without a significant contribution from upper crustal shortening. However, growing lines of evidence have revealed that Early Cenozoic faulting controlled enhanced denudation and shortening. Here, we report 51 new zircon and apatite (U Th)/He and apatite fission-track ages from seven granite samples along one primary branch fault (the Yunongxi fault) of the Yalong thrust belt in eastern Tibet. Cooling ages and inverse thermal modeling revealed two pulses of accelerated exhumation during the Late Cretaceous (70–65 Ma) and the Late Eocene–Early Oligocene (40–30 Ma). We suspect that the surface uplift of eastern Tibet, due to the convergence rate acceleration between India and Eurasia, triggered the first cooling stage. A synchronous out-of-pace Early Cenozoic cooling pattern across the Yunongxi fault was further identified and could be due to fault initiation at ca. 40–30 Ma. We argue that the Late Eocene–Early Oligocene rapid cooling and exhumation and the associated outward plateau growth were primarily accommodated through upper-crust faulting along the Yalong–Longmen Shan thrust belt. This deformation pulse was the first-stage response of fault activity to the India–Eurasia collision in eastern Tibet. More extensive Late Miocene deformation driven by lateral lower crustal flow consequently bypassed these early-stage fault systems and overwhelmed the Late Cretaceous and Late Eocene–Early Oligocene deformation in eastern Tibet. • The footwall of Yunongxi fault underwent accelerated exhumation during the Late Cretaceous and Late Eocene–Early Oligocene. • The striking differential cooling across the Yunongxi fault was most likely due to fault initiation ca. 40–30 Ma. • The second exhumation pulse was the first-stage response of fault activity to the India–Eurasia collision in eastern Tibet.

Tectonic segmentation by N-S-trending cona cross structure in the Eastern Himalaya: Evidence from thermochronology and thermokinematic modeling

The Main Himalayan Thrust (MHT), the most prominent tectonic boundary between the subducting Indian crust and the overthrusting Himalaya, occurs as a key structure dominating the active tectonics of the Himalaya. Previous studies indicate that the MHT forms a major buried ramp in the mid-crust, which with varying geometry and kinematics leads to a distinctive pattern of uplift along the Himalaya. However, it is unknown if and how these along-strike variations are correlated with the well-known active N-S-trending normal faults across the Himalaya and Tibetan Plateau. In this study, we report 39 new apatite and zircon fission track ages in the Cona area (~92°E) in the eastern Himalaya, coinciding with the easternmost N-S-trending extensional system in southern Tibet, the Cona Cross Structure (CCS). Spatial patterns of surface cooling ages are consistent with an overthrusting of the Himalayan wedge above a mid-crustal ramp in the MHT. Thermokinematic inverse modeling yields contrasting geometries and kinematics for the mid-crustal ramp on both sides of the CCS. Specifically, to the west of the CCS, the MHT developed a major ramp (with a dip angle of 20.4 ± 2.9°) spanning 50–70 km, which initiated at ~11.7 ± 0.6 Ma. To the east, thermokinematic inversion suggests a much less developed ramp spanning only ~10–15 km, initiated at ~6.8 ± 0.3 Ma. These results imply an ~14-km deeper depth of the MHT to the west of the CCS than to the east. Our modeling also suggests distinctive and evolving ramp-thrusting rates for the MHT on both sides of the CCS. This suggests an independent deformation accommodation by the MHT ramp thrusting in segments divided by the CCS along strike. Our study highlights a genetic correlation between the active orogenic-parallel ramp evolution and the N-S-trending faulting across the Himalaya, which divides the orogenic-parallel tectonics into independent structural segments.

Late Cenozoic topographic growth of the South Tianshan Mountain Range: Insights from detrital apatite fission-track ages, northern Tarim Basin margin, NW China

• Rocks with Mesozoic fission track ages were resided in the paleo-partial annealing zone for a long time. • The deformation commenced in the late Oligocene-early Miocene in South Tianshan. • The provenance of the Tarim Basin changed at 10 Ma due to rapid uplift of the South Tianshan Mountain Range. The Cenozoic deformation of the Tianshan Mountain Range within the framework of the India-Eurasia collision has been extensively studied. Previous thermochronologic studies of bedrocks in this range suggest a complex Triassic-Early Cretaceous tectonic evolution and subsequent tectonic quiescence in the Late Cretaceous-Palaeogene. Thus, constraining the exhumation and topographic growth of the Tianshan Mountain Range during the Cenozoic remains a challenge. In this study we report new detrital apatite fission-track ages for a Cenozoic sedimentary succession on the northern margin of the Tarim Basin (Kuqa River section). Thermochronologic age trends along the analyzed succession reveal two major age-shifts in sediments deposited at ∼ 23 Ma and ∼ 10 Ma, which we ascribe to major drainage reorganizations in response to uplift of the South Tianshan Mountain Range, an interpretation corroborated by published detrital zircon U-Pb and heavy mineral data. By comparing detrital apatite fission-track data with existing bedrock data, we infer that both North Tianshan, Yili-Central Tianshan and South Tianshan provided detritus to the Tarim Basin during the early and middle Miocene. At ∼ 10 Ma, the South Tianshan Mountain Range experienced rapid uplift and started forming a topographic barrier that blocked sediments flowing from North Tianshan and Yili-Central Tianshan into the Tarim Basin. We suggest that progressive topographic growth of the South Tianshan Mountain Range favored the aridification of the Tarim region by acting as a barrier to westerly winds.

Constraining Andean Propagation of Exhumation at the Limit of the Eastern Cordillera, NW Argentina, Using Low‐Temperature Thermochronology in a Structural Context

AbstractWithin the Central Andes of NW Argentina, the spatiotemporal distribution and style of deformation is strongly influenced by pre‐Cenozoic heterogeneities, mostly related to the Salta rift extension in the Cretaceous. At the enigmatic junction of the thin‐skinned Subandean belt and the thick‐skinned Santa Barbara System, the Tilcara Range and adjacent San Lucas block, located within the Eastern Cordillera, show thermochronological and field evidence of multiple exhumation events. Mesozoic (140‐115 Ma), pre‐Andean exhumation of basement highs is constrained by unconformities between basement and syn‐rift strata, as well as zircon (U‐Th‐Sm)/He cooling ages. Cenozoic Andean exhumation is quantified by apatite (U‐Th‐Sm)/He and fission track cooling ages, which were reset between the Late Cretaceous and Miocene. These data show that the westernmost Tilcara Range began exhuming in the late Oligocene‐early Miocene (26‐16 Ma), after which exhumation propagated to the border of the Eastern Cordillera in the middle Miocene (22‐10 Ma). The onset of rapid exhumation in the San Lucas block, which is located east of the Tilcara Range, occurred in the late Miocene (10‐8 Ma) in its western part, and in the late Miocene‐early Pliocene (6‐4 Ma) in its eastern part. Internal deformation of the San Lucas block, disturbing zircon (U‐Th‐Sm)/He and apatite fission track age patterns, predates propagation of rapid exhumation. The here presented low‐temperature thermochronology data set thus quantifies the multi‐phase exhumation history of the Eastern Cordillera of NW Argentina and constrains the timing of Andean propagation of exhumation within the Eastern Cordillera and the adjacent structural transition zone.

Late Mesozoic to Cenozoic exhumation of the SE South China Block: Constraints from zircon and apatite fission-track thermochronology

The late Mesozoic to Cenozoic tectonothermal history of the basin-and-range system within the Cathaysia Block in the southeastern South China Block remains poorly constrained, despite its significance in the tectonic and topographic evolution of eastern China. Zircon and apatite fission-track thermochronometers were applied to reconstruct the cooling histories of NE-trending mountain ranges mantled by late Mesozoic granites and older basement rocks in southwest Fujian. New zircon and apatite fission-track data record post-magmatic cooling of the sampled granites since their emplacement of ~164–118 Ma. Thermal modeling of the thermochronology data revealed two episodes of accelerated cooling events at ~110–85 Ma and ~40–25 Ma. The late Early Cretaceous initiation of an accelerated cooling event at rates of ~6 °C/Ma was considered to be the cause of the formation of the basin-and-range system in a back-arc extensional setting related to the rollback of the Paleo-Pacific Plate. The second cooling event at ~40–25 Ma at a rate of ~20 °C/Ma, reflected by the youngest apatite fission track ages (~25–20 Ma), was likely ascribed to headwater erosion along the drainage divide related to the intensification of the East Asian Monsoon and extensional tectonism. The sharp discrepancy in apatite fission track ages across the Zhenghe-Dapu Fault zone implies that the collapse of the late Mesozoic coastal magmatic arc in the early Eocene (51.4–45.6 Ma). This is attributed to the northward propagation of extension related to the rollback of the Paleo-Pacific Plate that formed the eastward-dipping topography. Furthermore, the long-lasting extension due to the rollback of the Pacific Plate since the ridge subduction of the Izanagi-Pacific at ~50 Ma likely drove the exhumation of the Cathaysia Block and opening of the South China Sea.