Cenozoic Exhumation History Research Articles

The Cenozoic spatiotemporal exhumation of the SE Tibetan Plateau: insight from the data mining and modeling of low-temperature thermochronology

Introduction: The SE Tibetan Plateau is distinct from other margins due to its high elevation, long wavelength, and low relief. A clear understanding of the Cenozoic exhumation history of this region is the key to understanding the special geomorphological process and the associated mechanisms. Previous thermochronological studies have either focused on vertical sections or horizontal variations in the local regions. However, the spatiotemporal exhumation pattern of the entire SE Tibetan Plateau is enigmatic.Methods: In this article, we have compiled 1,202 thermochronological data using joint kernel density estimation (KDE) and linear inversion approaches to address the exhumation process.Results: The results reveal that at least six episodes of rapid cooling have occurred since the Cenozoic, which include ∼61–58 Ma, 38–35 Ma, 32–23 Ma, 18–13 Ma, 11–6 Ma, and 4–3 Ma. Furthermore, the entire SE Tibetan Plateau underwent spatially inhomogeneous exhumation throughout the main episodes.Discussion: We infer that all cooling episodes may be attributed to the lateral extrusion and continuous convergence between the Indian and Eurasian continents. Meanwhile, climate changes (e.g., intensified Asian summer monsoon and glacial processes) have also played a non-negligible role in shaping the landscape since the Miocene. Our results will provide new insights into geodynamic mechanisms of the exhumation processes throughout the whole SE Tibetan Plateau since the Cenozoic.

Deciphering the Cenozoic Exhumation History of the Eastern Pyrenees Along a Crustal‐Scale Normal Fault Using Low‐Temperature Thermochronology

AbstractThe timing of transition between the contractional and extensional regimes along the Pyrenean range remains debated. Compared to its central and western parts, the eastern part of the chain was significantly affected by extensional tectonics mostly related to the opening of the Gulf of Lion. The Têt normal fault is the best example of this tectonic activity, with topographic reliefs above 2,000 m in its footwall. In this study, we synthetized previous thermochronological data and performed new (U‐Th)/He and fission track dating in the Eastern Pyrenean massifs. Output apparent exhumation rate and thermal modeling in the hanging wall of the Têt fault highlight a rapid exhumation (0.48 km/Ma) and cooling (∼30°C/Ma) phase between 38 and 35 Ma, followed by slower exhumation/cooling afterward. In the footwall, cooling subsequently propagated westward along the fault during Priabonian (35–32 Ma), upper Oligocene and lower Miocene (26–19 Ma), and Serravallian‐Tortonian times (12–9 Ma). These data and modeling outcomes suggest that the exhumation of the Têt fault hanging wall related to southward thrusting ended at 35 Ma, and was followed by different extensional stages, with a propagation of the deformation toward the West during the upper Miocene. We propose that the onset of extension in the Eastern Pyrenees occurred during the late Priabonian period, contemporaneously with the large‐scale rifting episode recorded in Western Europe. After this event, the Têt fault activity and the westward propagation of the deformation appear mainly controlled by the opening of the Gulf of Lion.

Low‐temperaturethermochronological insights into the Mesozoic–Cenozoic exhumation history of the Taihang–Lvliangshan region: A review

The Taihang–Lvliangshan region is located in the central part of the North China Craton (NCC), which has undergone significant reactivation and reconstruction during the Mesozoic–Cenozoic period. Documenting its long‐term uplift and exhumation history is critical for accurately characterizing the reformation extent of the NCC. In order to further reveal the Mesozoic and Cenozoic exhumation stages and spatial exhumation pattern of the Taihang–Lvliangshan, we present a comprehensive low‐temperature thermochronometric datasets from the region. The compilation revealed five distinct rapid exhumation episodes within the Taihang–Lvliangshan, including the Middle‐Late Jurassic (~160–150 Ma), Early Cretaceous (~120–110 Ma), Late Cretaceous (~100–60 Ma), Eocene (~50–40 Ma), and Late Oligocene–Early Miocene (~30–20 Ma). During the Middle–Late Jurassic, the Taihang–Lvliangshan underwent a strong thrusting deformation caused by the synthesis of northwestward subduction of the Palaeo‐Pacific Plate and southward subduction/collision of the Mongol–Okhotsk suture zone. Subsequently, rapid exhumation under an extensional tectonic environment occurred during the Early Cretaceous primarily owing to the subduction of the Palaeo‐Pacific Plate. During the Late Cretaceous, the collision between the Okhotomorsk Block and East Asia resulted in the regional northwest–southeast shortening and uplift of the Taihang–Lvliangshan. During the Eocene, normal fault activations were occurring throughout the range, likely owing to the change in the convergence rate and direction between the Palaeo‐Pacific Plate and East Asia. Another important exhumation event occurred during the Late Oligocene–Early Miocene period, which was likely attributed to the result of combined effects from both the India–Eurasia collision and Pacific Plate subduction. Furthermore, differential exhumation of the Taihang–Lvliangshan were clearly revealed according to the five separate E–W elevation–distance profiles of the Taihang–Lvliangshan. They displayed greater exhumation thicknesses at the southern regions than those along the northern regions, which can be explained by the development of the Shanxi Rift that began to form following the Oligocene–Miocene period.

Cenozoic Exhumation History of the Eastern Margin of the Northern Canadian Cordillera

AbstractNew low‐temperature thermochronology data from clastic sedimentary rocks in the northern Richardson Mountains, Canada, indicate significant exhumational cooling during late Eocene–early Oligocene time. Apatite (U‐Th‐Sm)/He (AHe) data were collected from 19 Proterozoic–Paleocene rocks across a 115 km transect. Eighty‐eight single‐grain AHe dates range from 16–300 Ma and are generally younger than stratigraphic ages, indicative of thermal resetting by burial. Additionally, zircon (U‐Th)/He (ZHe) dates from two Proterozoic–Cambrian rocks range from 49–123 Ma and suggest burial to >160°C. In contrast, ZHe dates from Jurassic sandstones are older than the stratigraphic age, which limits maximum burial to <160°C. Thermal history modeling reveals three phases of cooling, during the Paleocene–early Eocene (>65–50 Ma), late Eocene–early Oligocene (40–30 Ma), and late Oligocene–early Miocene (30–15 Ma). Most samples cooled during the first and second phases, whereas the third phase is less well constrained. In general, most rocks were below the sensitivity of AHe analysis since the early–middle Miocene. The results suggest a previously unrecognized phase of inferred deformation in the northern Richardson Mountains between 40–30 Ma. Our findings contribute to previous work that recognizes Late Cenozoic deformation along the eastern margin of the Northern Cordillera. We further investigated the potential mechanisms of this widespread deformation and suggest exhumation may relate to kinematic changes of the North American plate relative to structural trends along the margin of the Northern Cordillera.

Cenozoic Exhumation of the Ailaoshan‐Red River Shear Zone: New Insights From Low‐Temperature Thermochronology

AbstractContinental‐scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the Ailaoshan‐Red River shear zone (ASRRSZ) in the SE Tibetan Plateau. This study presents 13 apatite (U‐Th)/He, 11 zircon (U‐Th)/He, and three apatite fission track dates, together with thermal modeling in the Ailaoshan and Xuelongshan segments (ALSZ and XLSZ) of the shear zone to investigate its Cenozoic exhumation history and mechanism, which are critical for understanding its tectonic and landscape evolution. Our results, combined with published chronologic data, reveal that shear zone rocks along the ALSZ experienced prominent and rapid cooling from high temperature (>500°C) to 120–60°C at a rate of 75–100°C/Myr during 29–17 Ma with northwestward younging onset. A second, lower magnitude accelerated cooling occurred at 14–10 Ma along the ALSZ at a rate of 20–30°C/Myr, with a later initiation on the XLSZ at ~5 Ma and continuing to present with a cooling rate of ~20°C/Myr. Thermal modeling reveals a single rapid cooling phase with a rate of 17–14°C/Myr in the Eocene to early Oligocene for samples outside the shear zones. These three fast cooling episodes are directly related to deformation stages including crustal shortening across the SE plateau, sinistral ductile shearing along the ASRRSZ, and dextral faulting with a dip‐slip component on the Red River and Weixi‐Qiaohou faults along the shear zone flanks. Furthermore, the northward migration of kinematic reversal and associated cooling along strike since the mid‐late Miocene likely reflects the northward advance of the eastern Himalayan syntaxis.

Cenozoic exhumation history at the core of the Andes at 31.5°S revealed by apatite fission track thermochronology

The Andes at ~31°-32°S lie above the Chilean-Pampean flat slab zone (~27–33°S), where several morphostructural units developed resulting in a large orogenic width. The core of the Andes is composed of the La Ramada fold-and-thrust belt in Principal Cordillera and the basement blocks of Frontal Cordillera. While rock uplift of these blocks has been broadly constrained to the middle Miocene based on structural and provenance studies, thermochronologic approaches with the potential to directly constrain the timing and amount of exhumation have not been exploited until recently. Apatite fission track data from a ~1 km vertical profile collected within the Carboniferous Pico Los Sapos Batholith in the High Andes at 31.5°S places some constraints on the thermal evolution of the region since the Paleocene. The age-elevation profile combined with inverse thermal modeling and previous AHe thermochronology, indicates an episodic cooling/exhumation history. Rocks cooled rapidly in the early Cenozoic (ca. 65-55 Ma), followed by a period of relative thermal and tectonic stability when residence in an apatite partial annealing zone (PAZ) from at least ~52 Ma to ca.15 Ma, followed by final rapid cooling beginning ca. 15 Ma. We interpret early Cenozoic and middle Miocene rapid cooling events as to be related to erosional exhumation during Andean contractional phases, associated with thrust activity along the Mondaquita Fault. The age-elevation profile is partially duplicated, with upper samples being offset ~500 m due to back-thrusting since the late Miocene. The preservation of part of an exhumed PAZ indicates 3–5 km of exhumation since the onset of rapid cooling/exhumation at ~15 Ma. Although evidence for an early Cenozoic compressional phase in the High Andes at this latitude is scarce, the occurrence of a regional K-T (~65 Ma) unconformity supports our results. The Eocene Inca phase, registered north of 30°S, on the other hand, is not shown in our thermochronological data, suggesting that this tectonic phase did not affect the core of the Andes south of this latitude. Independent geological evidence both from the hinterland (structural, geochemical and thermochronological analyses) and foreland (provenance studies) corroborate our findings of a middle Miocene deformational event in the core of the Andes at 31.5°S.

Mesozoic and Cenozoic exhumation history and magmatic-hydrothermal events of the central Tianshan Mt. Range, NW China: Evidence from (U–Th)/He and 40Ar/39Ar dating

The thermal history of rocks in the Awulale area, central Chinese Tianshan, is significant to understanding the formation and tectonothermal evolution of the Tianshan orogen. K-feldspar 40Ar/39Ar and apatite (U–Th)/He age data reveal at least four Mesozoic–Cenozoic tectonothermal events in the central Tianshan, which occurred during the Middle–Late Triassic (244.4–216.5 Ma), Early Jurassic (ca. 180.3 Ma), Early Cretaceous (99.1–98.1 Ma), and early Miocene (18.6–13.7 Ma). This thermal history is consistent with that throughout the Tianshan orogenic belt and surrounding blocks. Modeling of the thermal history shows that intrusive rocks in the central Tianshan have experienced four stages of cooling in the Mesozoic–Cenozoic. Stage I occurred from ca. 310 to 230 Ma, after magma emplacement, and resulted in cooling to the 40Ar/39Ar closure temperature of K-feldspar (200–180 °C). During this time, tectonism in the central Tianshan was not intense and the rapid cooling was due mainly to thermal exchange, with a maximum cooling rate of ~7.1 °C/Myr. Stage II occurred from ca. 230 to 180 Ma. Collision between the Qiangtang microcontinent and the Eurasia continental margin resulted in active tectonism in the central Tianshan, and cooling was caused mainly by tectonic uplift, with the maximum uplift of intrusive rocks exceeding 9 km. Stage III occurred from ca. 180 to 45 Ma, when regional tectonism was weak and cooling was gradual. During this stage, the apatites in the syenite-porphyry remained in the He partial retention zone for a long time. This indicates that during this stage the central Tianshan was only weakly influenced by the far-field collisions of Lassa and Karakoram–Pamir with the southern margin of Eurasia. Stage IV occurred from 45 Ma to the present-day, and was related to the far-field influence of the middle–late Himalayan Orogeny, during which tectonism in the central Tianshan became more intense. In this final stage, many types of intrusive rock were exhumed to the surface, with the maximum uplift exceeding 2 km. Furthermore, the cooling history and regional structural trends indicate that since the Mesozoic, under the influence of tectonic compression, there has been differential uplift on the northern and southern sides of the east Awulale area. The cooling and exhumation rates of intrusive rocks are much higher on the northern side of the area than the southern side. This was related to reverse movement on the Yuximolegai Fault, as exhumation rate of the hanging wall (northern region) was higher than that of the footwall (southern region) under N–S compression. These findings, combined with the inversion model results, indicate that this differential uplift occurred mainly from the Late Triassic to Early Jurassic.

Cretaceous to Middle Cenozoic Exhumation History of the Cordillera de Domeyko and Salar de Atacama Basin, Northern Chile

AbstractSpatiotemporal patterns of deformation and exhumation in the central Andes are key parameters for reconstructing the kinematic history of the orogenic belt. Previous studies of the retroarc thrust belt document overall eastward propagation of deformation since the late Eocene, but the amount and timing of exhumation during the early phase of Andean orogeny remains largely unconstrained, particularly in the modern forearc region. In order to determine the timing and amount of exhumation prior to the late Eocene, we employed a multidating approach combining zircon U‐Pb geochronology with apatite fission track and apatite (U‐Th)/He thermochronology. We focus on the low‐temperature cooling history of the Cordillera de Domeyko thrust belt and synorogenic deposits in the Salar de Atacama basin. Our results show Late Cretaceous to Oligocene cooling and exhumation in the Cordillera de Domeyko. The distribution of cooling ages in the forearc indicates three periods of exhumation: ~86–65, ~65–50, and 50–28 Ma. The amount of cooling was variable in space and time but requires total exhumation of ~2.5–3.3 km of rocks above major structures in the thrust belt. Regional unconformities in the Salar de Atacama basin correlate with periods of eastward migration of the orogenic front at ~65 Ma and ~50–40 Ma. Pulses of deformation at the front of the thrust belt alternated with periods of out‐of‐sequence hinterland deformation and exhumation. Overall, our data show that shortening in the central Andes commenced during the Late Cretaceous (as early as ~86 Ma) and that deformation (shortening) and exhumation were coupled in space and time.

Cenozoic Exhumation History of the East Kunlun Orogenic Belt Constrained by Apatite Fission‐Track Thermochronology

Cenozoic Exhumation History of the East Kunlun Orogenic Belt Constrained by Apatite Fission‐Track Thermochronology

Cenozoic exhumation history of South China: A case study from the Xuefeng Mt. Range

New apatite fission track (AFT) dating was applied to the Xuefeng Mt. Range and Yuanma Basin to constrain the Cenozoic exhumation process of the southeastern Yangtze Block, South China. The analyzed samples in this study have AFT ages ranging from 27.9±2.5 to 61.5±5.9 Ma, which are younger than the deposition or crystallization ages of the host rocks. The AFT analysis and thermal history modeling indicate that both the Xuefeng Mt. Range and the Yuanma Basin underwent significant exhumation during the early Cenozoic (ca. 60–40 Ma). These samples were rapidly exhumed to near the surface during this period. Our results suggest that an important tectonic event occurred along or near regional fault zones (e.g., the Qinhang Fault) in South China during the early Cenozoic (ca. 60–40 Ma). However, it is difficult to relate this event to the Eastern Sichuan fold belt, which is much older and is characterized by large-scale folding and thrusting. Combined with fieldwork in the Yuanma, Xupu, and Xinning basins, we refute the Cretaceous “Pan-Yangtze Basin” that was proposed to have been separated by the uplifted Xuefeng Mt. Range after the Late Cretaceous. The exhumation stage from ca. 60 Ma to 40 Ma was an important period during which plate movements across the eastern Asian and Pacific regions were reorganized. The early Cenozoic tectonothermal event in South China can be attributed to a change in the direction and speed of the subduction of the Pacific Plate beneath the Eurasian Plate. An Oligocene-Miocene cooling event was also recorded in the eastern Xuefeng Mt. Range, which we tentatively attribute to the activity of dextral faults in this area as a far-field effect of the collision between the Indian and Eurasian plates.

Cenozoic exhumation of the Danba antiform, eastern Tibet: Evidence from low-temperature thermochronology

The Danba antiform (DA) exposes the highest grade metamorphic rocks in eastern Tibet. The metamorphic grades characterizing the DA evolve from sillimanite-migmatite grade to greenschist grade over a relatively short distance of ∼20 km from core to limb. This metamorphic event indicates an important Mesozoic to Cenozoic doming and exhumation history. However, the Cenozoic history of the antiform is poorly constrained due to a lack of data. Consequently, we used fission track dating on zircon and apatite from 22 samples collected throughout the DA. The zircon fission track (ZFT) data show a transition from Cenozoic non-reset (202 Ma), to partially reset (53–37 Ma), to totally reset (24–8 Ma) ages from the periphery to the core of the DA. The oldest totally reset ZFT ages are ca. 25 Ma and likely indicate the onset of Cenozoic folding of the DA. Compared to the apatite fission track (AFT) ages of ca. 10 Ma in the peripheral region, the youngest AFT ages are younger than 3 Ma in the core of the DA, suggesting that folding could be ongoing. Based on these multithermochronometer data, the cooling rate increases from ∼8 °C/m.y. on the periphery to ∼12–56 °C/m.y. in the core of the DA since ca. 12 Ma. The DA shares a similar cooling history with the Longmen Shan (LMS) fault belt, implying that the detachment fault of the LMS may extend to the DA, resulting in linked uplift histories. The differential exhumation among the samples in the core of the DA and the surrounding area indicates that both upper crustal deformation and crustal channel flow may have developed simultaneously (mainly since ca. 12 Ma) in the DA.

Late Cenozoic exhumation history of the Luoji Shan in the southeastern Tibetan Plateau: insights from apatite fission-track thermochronology

Denudational history inferred from bedrock low-temperature thermochronological data provides significant constraint to tectonic models for explaining the growth of the Tibetan Plateau. Here, we present new apatite fission-track ages from the Luoji Shan, bounded by the Anninghe and Zemuhe faults in the southeastern Tibetan Plateau. Cooling ages vary from c. 5 to c. 13 Ma from the bottom to the top of a vertical profile. The age–elevation relationship can be interpreted as either (1) a phase of river incision at a rate of c. 0.16 km Ma −1 from c. 13 to c. 5 Ma or (2) a phase of denudation of c. 0.40 km Ma −1 between c. 13 and c. 10 Ma, followed by a phase of extremely slow denudation ( c. 0.03 km Ma −1 ). The results suggest that initiation of river incision started before c. 13 Ma in the study area. Combined with previously published data from adjacent sites, our results indicate that denudation in this region displayed substantial spatial variation. This finding does not support the existing lower crustal flow model for Tibetan Plateau growth, which predicts uniform denudation. We further speculate that the vertical component of slip along the southern extension of the Anninghe fault might have significantly declined since late Miocene time, explaining the decreased rate of erosion c. 10 Ma.

Exhumation history of the western Kyrgyz Tien Shan: Implications for intramontane basin formation

The dextral Talas-Fergana Fault separates the western from the central Tien Shan. Recent work has shed light on the Cenozoic evolution of the eastern and central Tien Shan; much less attention has been paid to the western Tien Shan. In this contribution we present new thermochronological ages for the Fergana and Alai ranges that, combined with the available data set, constrain the Cenozoic exhumation history of the western Tien Shan. Following a tectonically quiet early Cenozoic period, we suggest an onset of exhumation at ~25 Ma. This early onset was followed by a period of slower exhumation and in some areas minor reheating. A final, strong late Miocene rapid cooling event is well represented in the western Tien Shan as in other sectors of the range. The early onset of uplift of the western Tien Shan dissected the previously continuous westernmost Parathethyan Sea, progressively isolating basins (e.g., Fergana, Tarim, and Alai basins) in the central Asian hinterland. Moreover, the coeval timing of late Miocene uplift along the length of entire Tien Shan implies that neither the Pamir nor Tarim can be the sole driver for exhumation of the entire range.

Cenozoic exhumation history of Sulu terrane: Implications from (U–Th)/He thermochrology

The Qinling–Dabie–Sulu orogen is the most prominent Phanerozoic orogenic belt in China. The discovery of ultra-high pressure (UHP) minerals in zircon inclusions suggests that the crust was subducted to deeper than 120km into the mantle and then exhumed to shallow crustal. Recently, low temperature thermochronology has been applied to constrain the final exhumation of Dabie Shan, while there are few studies describing the Cenozoic exhumation history of the Sulu belt. Here we report some (U–Th)/He ages for various lithologies from Sulu Orogenic belt and its northern part-Jiaobei terrane. The single grain He ages range between 18 and 154Ma, and most of the samples having large intra-sample age scattering. Several reasons such as invisible U/Th-rich inclusions, grain size effect, slow cooling rate, and zonation of parent nuclide or radiation damage effect may account for this dispersion. For all samples, the pattern of the single grain age data exhibits a peak at ~45Ma which is consistent with the borehole fission-track age pattern in adjacent Hefei Basin. Both (U–Th)/He and fission track ages of the Sulu area suggest an enhanced exhumation/cooling in Early-Middle Eocene in the southern part of Tan-Lu fault zone. This enhanced cooling event coincides with rapid subsidence of North China Basin and rapid uplift of its surrounding reliefs, which indicates basin-mountain coupling. This Eocene event is widespread in central China and could be far-field consequence of India–Asia collision. The convergence rate between Pacific Plate and Eurasia decreased substantially during early Tertiary and reached a minimum in Eocene (~30–40mm/yr) while at the same time the collision between India and Asia was completed. Therefore, the Cenozoic exhumation history of the Sulu Orogenic Belt was a combined result of far-field effect of India–Asia collision and declined subduction rate of the Pacific Plate under Eurasia.

Mesozoic and Cenozoic exhumation history of the SW Iberian Variscides inferred from low-temperature thermochronology

The post-Paleozoic tectonothermal evolution of the SW Iberian Variscides is poorly known mainly due to the scarce low-temperature geochronological data available. We have obtained new apatite fission-tracks and apatite (U–Th)/He ages to constrain the Mesozoic and Cenozoic tectonic evolution of this portion of the Iberian Massif located just north of the Betic-Rif Alpine orogen.We have obtained nine apatite fission-track ages on samples from Variscan and pre-Variscan granitoids. These ages range from 174.4 (±10.8) to 54.1 (±4.9) Ma, with mean track lengths between 10.3 and 13.9μm. We have also performed 5 (U–Th)/He datings on some of the same samples, obtaining ages between 74.6 (±1.6) and 18.5 (±1.4) Ma. Time–temperature path modeling of these low-temperature geochronological data leads us to envisage four post-Paleozoic tectonically controlled exhumation episodes in the SW Iberian Variscides. Three of these episodes occurred in Mesozoic times (Middle Triassic to Early Jurassic, Early Cretaceous, and Late Cretaceous) at rates of ≈1.1 to 2.5°CMa−1, separated by periods with almost no cooling. We relate these Mesozoic cooling events to the formation of important marginal reliefs during the rifting and opening of the central and northern Atlantic realm. The fourth exhumation episode occurred in Cenozoic times at rates of ≈3.2 to 3.6°CMa−1, being only recorded in samples next to faults with topographic escarpments. These samples cooled below 80°C at ≈20Ma at rates of 3–13°CMa−1 due to roughly N–S oriented compressional stresses affecting the whole Iberian plate, which, in the particular case of SW Iberia, reactivated some of the previous Late Paleozoic thrusts.

Cenozoic deformation and exhumation history of the Central Kyrgyz Tien Shan

AbstractNew low‐temperature thermochronological data from 80 samples in eastern Kyrgyzstan are combined with previously published data from 61 samples to constrain exhumation in a number of mountain ranges in the Central Kyrgyz Tien Shan. All sampled ranges are found to have a broadly consistent Cenozoic exhumation history, characterized by initially low cooling rates (<1°C/Myr) followed by a series of increases in exhumation that occurred diachronously across the region in the late Cenozoic that are interpreted to record the onset of deformation in different mountain ranges. Combined with geological estimates for the onset of proximal deformation, our data suggest that the Central Kyrgyz Tien Shan started deforming in the late Oligocene‐early Miocene, leading to the development of several, widely spaced mountain ranges separated by large intermontane basins. Subsequently, more ranges have been constructed in response to significant shortening increases across the Central Kyrgyz Tien Shan, notably in the late Miocene. The order of range construction is interpreted to reflect variations in the susceptibility of inherited structures to reactivation. Reactivated structures are also shown to have significance along strike variations in fault vergence and displacement, which have influenced the development and growth of individual mountain ranges. Moreover, the timing of deformation allows the former extent of many intermontane basins that have since been partitioned to be inferred; this can be linked to the highly time‐transgressive onset of late Cenozoic coarse clastic sedimentation.

Thermochronologic constraints on the late Cenozoic exhumation history of the Gurla Mandhata metamorphic core complex, Southwestern Tibet

AbstractHow the Tibetan plateau is geodynamically linked to the Himalayas is a topic receiving considerable attention. The Karakoram fault plays key roles in describing the structural relationship between southern Tibet and the Himalayas. In particular, considerable debate exists at the southeastern end of the Karakoram fault, where its role is interpreted in two different ways. One interpretation states that slip along the dextral Karakoram fault extends eastward along the Indus‐Yalu suture zone, bypassing the Himalayas. The other interprets that fault slip is fed southward into the Himalayan thrust belt along the Gurla Mandhata detachment (GMD). To evaluate these competing models, the late Miocene history of the GMD was reconstructed from thermokinematic modeling of zircon (U‐Th)/He data. Three east‐west transects reveal rapid cooling of the GMD footwall from 8.0 ± 1.3 Ma to 2.6 ± 0.7 Ma. Model simulations show a southward decrease in slip magnitude and rate along the GMD. In the north, initiation of the GMD range between 14 and 11 Ma with a mean fault slip rate of 5.0 ± 0.9 mm/yr. The central transect shows an initiation age from 14 to 11 Ma with a mean fault slip rate of 3.3 ± 0.6 mm/yr. In the south, initiation began between 15 and 8 Ma with a mean fault slip rate of 3.2 ± 1.6 mm/yr. The initiation ages and slip rates match the Karakoram fault across several timescales, supporting the idea that the two are kinematically linked. Specifically, the data are consistent with the GMD acting as an extensional stepover, with slip transferred southward into the Himalayas of western Nepal.

Thermochronologic insight into late Cenozoic deformation in the basement‐cored Terskey Range, Kyrgyz Tien Shan

AbstractBasement‐cored ranges formed by reverse faulting within intracontinental mountain belts are often composed of poly‐deformed lithologies. Geological data capable of constraining the timing, magnitude, and distribution of the most recent deformational phase are usually missing in such ranges. In this paper, we present new low temperature thermochronological and geological data from a transect through the basement‐cored Terskey Range, located in the Kyrgyz Tien Shan. Using these data, we are able to investigate the range's late Cenozoic deformation for the first time. Displacements on reactivated faults are constrained and deformation of thermochronologically derived structural markers is assessed. These structural markers postdate the earlier deformational phases, providing the only record of Cenozoic deformation and of the reactivation of structures within the Terskey Range. Overall, these structural markers have a southern inclination, interpreted to reflect the decreasing inclination of the reverse fault bounding the Terskey Range. Our thermochronological data are also used to investigate spatial and temporal variations in the exhumation of the Terskey Range, identifying a three‐stage Cenozoic exhumation history: (1) virtually no exhumation in the Paleogene, (2) increase to slightly higher exhumation rates at ~26–20 Ma, and (3) significant increase in exhumation starting at ~10 Ma.

Post‐Variscan exhumation of the Central Anti‐Atlas (Morocco) constrained by zircon and apatite fission‐track thermochronology

AbstractThe origin of the Anti‐Atlas relief is one of the currently debated issues of Moroccan geology. To constrain the post‐Variscan evolution of the Central Anti‐Atlas, we collected nine samples from the Precambrian basement of the Bou Azzer‐El Graara inlier for zircon and apatite fission‐track thermochronology. Zircon ages cluster between 340 ± 20 and 306 ± 20 Ma, whereas apatite ages range from 171 ± 7 Ma to 133 ± 5 Ma. Zircon ages reflect the thermal effect of the Variscan orogeny (tectonic thickening of the ca. 7 km‐thick Paleozoic series), likely enhanced by fluid advection. Apatite ages record a complex Mesozoic–Cenozoic exhumation history. Track length modelling yields evidence that, (i) the Precambrian basement was still buried at ca. 5 km depth by Permian times, (ii) the Central Anti‐Atlas was subjected to (erosional) exhumation during the Triassic‐Early Cretaceous, then buried beneath ca. 1.5 km‐thick Cretaceous‐Paleogene deposits, (iii) final exhumation took place during the Neogene, contemporaneously with that of the High Atlas.

Cenozoic exhumation history of the Alborz Mountains, Iran: New constraints from low‐temperature chronometry

The Alborz Mountains in the north of the Turkish‐Iranian Plateau mainly developed in the Cenozoic as a consequence of the closure of Neo‐Tethys and continental collision between Arabia and Eurasia. Cenozoic growth of the fold‐and‐thrust belt exploited an older Palaezoic‐Mesozoic crustal fabric but the extent to which this governed the overall form of the mountain belt is unclear. To determine when and how the Alborz mountain belt has grown, apatite fission track (AFT) and (U‐Th)/He (AHe) thermochronometry were performed on 46 bedrock samples collected along 8 transects across the range. AFT central ages range from 157 ± 24 Ma to 10 ± 1 Ma with most ages falling between 40 Ma and 10 Ma. AHe ages range from 17 ± 2 Ma to 6 ± 1 Ma. The data revealed enhanced exhumation ca. 35 ± 5 Ma, minor exhumation between ca. 30–20 Ma and an increase in exhumation thereafter. This pattern matches the tripartite Mid‐Cenozoic stratigraphy of Central Iran, where Upper Oligocene‐Lower Miocene carbonates are sandwiched between terrestrial clastic formations. The most intriguing thermochronometric signal found is a major acceleration of exhumation that initiated in the late Miocene to early Pliocene, recorded by the AHe data. There does not appear to be a direct tectonic cause for Pliocene intensified erosion, as convergence rates between Arabia and Eurasia have remained relatively constant. Enhanced exhumation at this time may reflect a climatically induced intensification of erosion during Caspian isolation and base level fall, or a regional tectonic re‐organization of the Arabia‐Eurasia collision, or both.