Apatite Fission Track Thermochronology Research Articles

Meso-Cenozoic building of the northern Central Asian Orogenic Belt: Thermotectonic history of the Tuva region

The Tuvinian and West-Sayan mountain ranges form part of the Central Asian Orogenic Belt (CAOB); more specifically, they align along the Altai–Sayan–Hangay zone. Its Precambrian–Paleozoic basement has been subjected to Mesozoic and Cenozoic tectonic reactivation. Two north-south transects across the mountain belts and intervening basins of Tuva were sampled for apatite fission-track (AFT) thermochronology in order to elucidate the thermal history of the Tuvinian basement in relation to the Mesozoic and Cenozoic reactivation of the CAOB. Most AFT ages are Late Cretaceous and range between 55 and 115 Ma. Mean lengths of confined fission tracks are relatively long with most values between 13 and 14 μm. Thermal history modeling shows a rapid Late Jurassic–Cretaceous cooling for the sampled Tuvinian crystalline rocks, related to exhumation of the Paleozoic basement. This exhumation is possibly related to the building and subsequent orogenic collapse of the Mongol–Okhotsk orogen that formed between the Siberian and North China–Mongolian (Sino-Korean or Amurian) continental blocks during the Late Mesozoic. Far-field effects of this orogeny and its collapse, might have affected the Baikal, Altai and Sayan units of the Central Asian Orogenic Belt, including the Tuvinian basement. Also, at the Mesozoic southern Eurasian margin, growth of the Asian continent continued and several collision–accretion events asserted distal tectonic influence into the CAOB. After a Paleogene period of stability, thermal history models for some samples hint at a renewed period of basement cooling during the Neogene. In support of this Neogene event, a single sample from the main West Sayan fault zone contains an apatite population with ~ 2 Ma reset AFT ages. This is interpreted in the framework of ongoing building of the modern Central Asian orogens and associated fault movements and exhumation of the basement, presumably related with the ongoing India–Eurasia convergence.

Late Cretaceous–Cenozoic thermal evolution of the northern part of the Central Western Carpathians (Slovakia): revealed by zircon and apatite fission track thermochronology

Abstract Tectono-thermal evolution of the northern part of Central Western Carpathians (Slovakia) was revealed by zircon and apatite fission track thermochronology of Neogene deposits, volcanic rocks, and crystalline basement. New fission track ages combined with previous geochronological data are correlated with main tectonic events and important palaeogeographic changes. (1) The palaeo-Alpine burial to more than 10 km depths, heating (> 320 °C) and low-grade metamorphism of the crystalline basement was caused by crustal thickening due to nappe stacking driven by the collisional processes (~ 90–75 Ma). (2) Extensional collapse and exhumation of basement complexes during the Late Cretaceous to Middle Eocene (~ 75–40 Ma). (3) The extension process resulted in a new sedimentary cycle of the Central Carpathian Palaeogene Basin (~ 40–25 Ma) in the northern part of the Central Western Carpathians. During the ensuing burial under the thick sedimentary cover, the crystalline basement of the northern zone resided at ‘hotter’ conditions (ca. > 120 °C and

Uplift and denudation history of the eastern Dead Sea rift flank, SW Jordan: Evidence from apatite fission track thermochronometry

AbstractThe Dead Sea rift (DSR), developed along the Dead Sea transform plate boundary, is characterized by salient flanks and morphotectonic asymmetry. Apatite fission track thermochronology (AFT) along ~1200 m high vertical profiles in Neoproterozoic basement and overlying Cambrian sandstone in southwestern Jordan is used to reconstruct timing, magnitude, and rate of uplift and denudation of the eastern DSR flank and examine its relationship to rift development and its flank landscape. Time‐temperature models based on AFT data suggest three major Phanerozoic heating and cooling episodes, Late Paleozoic, Early Cretaceous, and Oligocene. The latest episode, on which this study focuses, indicates uplift of ~3.8±0.3 km under a moderate paleogeothermal gradient. About 40% of the uplift was tectonically driven with the remainder attributed to isostatic rebound in response to denudation and erosion. Models suggest that uplift commenced in the Oligocene with a considerable part occurring prior to development of the DSR, despite being ~200 km from the Red Sea‐Gulf of Suez rift margin. Uplift is probably part of a regional rearrangement along the western Arabian platform margin occurring at the time of Red Sea rift initiation. Transition from primarily sedimentary layer stripping, most likely by scarp retreat, to one of dominantly incision of the underlying crystalline basement occurred in Late Miocene‐Pliocene time following enhanced subsidence and development of a low base level in the DSR. Consequently, the magnitude of uplift by isostatic rebound due to incision exceeded lowering by surface truncation and increased summit elevation and riftward flexing of the flank.

Reconstruction of low temperature (

The thermal evolution of sediments in the shallowest part of sedimentary basins is challenging to investigate as most of the geothermometers are at their application limits. This is typically the case of the Callovian–Oxfordian claystones at the eastern border of the Paris Basin. A recent 2000 m deep well penetrated the entire Jurassic and Triassic sedimentary series and permitted coring of sediments never reached by previous drilling in this part of the basin. Thanks to the use of several independent geothermometers (apatite fission track thermochronology, fluid inclusion microthermometry, clay mineralogy and sedimentary organic matter evolution) the burial history of the Mesozoic series has been reconstructed, modeled and calibrated using kinetic algorithms relevant to the various paleothermometers used. In addition to these conventional methods, an innovative approach was developed using the temperature-dependence of the magnetic mineral assemblage within clay-rich sediments (“MagEval”). Thermal modeling indicates that the Callovian–Oxfordian and the Lower Triassic experienced maximum burial temperatures of 50 ± 5 °C and 90 ± 10 °C respectively, i.e., about 25 °C higher than present-day. This temperature offset implies the erosion of several hundred meters of sediments which, depending on the thermal flux and conductivity considered, most likely constituted Upper Cretaceous chalk deposits. Falling sea level resulted in the exposure and subsequent dismantling of the chalk cover at the beginning of Cenozoic times. The eastern border of the basin was then subjected to slow erosion and discrete tectonic deformation.

Transient fluid flow in the Binbei district of the Songliao Basin, China: Evidence from apatite fission track thermochronology

The Songliao Basin is famous for the Daqing Oilfield, the biggest in China. However, no economic hydrocarbon reservoir has been found in the northeastern Binbei district. Its thermal history, which is of great importance for hydrocarbon generation and migration, is studied with apatite fission track (AFT) thermochronology. Samples with depositional ages of the late Cretaceous (∼108–73 Ma) are analyzed. The AFT ages of the samples from reservoir rock (depositional age > 76.1 Ma) fall between the late Cretaceous (72±5 Ma) and the early Eocene (41±3 Ma) period, indicating their total annealing after deposition. In contrast, two samples from the main seals of the Qingshankou (depositional age > 89.3 Ma) and the Nenjiang Formation (depositional age > 73.0 Ma) are not annealed or partially annealed (AFT ages of 97±9 Ma and 70±4 Ma, respectively). Because the maximum burial temperature (<90 °C) evidenced by low vitrinite reflectance (Ro<0.7) is not high enough to account for the AFT total annealing (110–120 °C), the transient thermal effect arising from the syntectonic fluid flow between the late Cretaceous and the early Eocene is proposed. Transient thermal effects from fluid flow explains the indicated temperature discrepancies between the AFT thermometer and the Ro thermometer because the transient thermal effect from the fluid flow with a temperature high enough (110–120 °C) to anneal the AFT thermometer does not last long enough (104–105 yrs.) for an enhancement of the Ro (minimum 106–107 yrs. under the same temperature). This indicates that dating thermal effect from fluid flow might be a new means to reconstruct the tectonic history. It also answers why the samples from the main seals are not annealed because the seals will prohibit fluid flow and supply good thermal insulation. The large-scale fluid flow in the Binbei district calls for a new idea to direct the hydrocarbon exploration.

Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology

The external detector method (EDM) is a widely used technique in fission track thermochronology (FTT) in which two different minerals are concomitantly employed: spontaneous tracks are observed in apatite and induced ones in the muscovite external detector. They show intrinsic differences in detection and etching properties that should be taken into account. In this work, new geometry factor values, g, in apatite, were obtained by directly measuring the ρ ed /ρ is ratios and independently determined [GQR] ed/is values through the measurement of projected lengths. Five mounts, two of which were large area prismatic sections and three samples composed of random-orientation pieces have been used to determine the g-values. A side effect of applying EDM is that the value of the initial confined induced fission track, L 0 , is not measured in routine analyses. The L 0 -value is an important parameter to quantify with good confidence the degree of annealing of the spontaneous fission tracks in unknown-age samples, and is essential for accurate thermal history modeling. The impact of using arbitrary L 0 -values on the inference of sample thermal history is investigated and discussed. The measurement of the L 0 -value for each sample to be dated using an extra irradiated apatite mount is proposed. This extra mount can be also used for determining the g value as an extension of the ρ ed /ρ is ratio method. Eight apatite samples from crystalline basement, with grains at random orientation, were used to determine the g-values. The results found are statistically in agreement with the values found for apatite samples (from Durango, Mexico) measured in prismatic section and also measured at random orientation. There was no observable variation in efficiency regarding crystal orientation, showing that it is relatively safe using non-prismatic grains, especially in samples with paucity of grains, as it is the case of most basin samples. Implications for the ζ-calibration and for the calibration of the direct (spectrometer-based) fission-track dating are also discussed.

Exhumation of the southern Pyrenean fold‐thrust belt (Spain) from orogenic growth to decay

The deformation and exhumation history of an orogen reflects the interactions between tectonic and surface processes. We investigate orogenic wedge deformation, erosion, and sedimentation in the Pyrenees by (a) quantifying the spatiotemporal patterns of exhumation across the southern fold‐thrust belt (FTB) with bedrock apatite fission track (AFT) thermochronology and (b) comparing the results with existing deformation, exhumation, and sedimentation chronologies. Eighteen new samples record exhumation during and after orogenesis between 90 and 10 Ma. Rocks from the range core (Axial Zone) record rapid exhumation that progresses east to west and north to south, consistent with patterns of tectonically driven uplift. Synorogenic sediments shed into piggyback basins on the southern fold‐thrust belt during mountain building retain a detrital exhumation signal from the Axial Zone. In contrast, samples from other structural positions record exhumation of the thin‐skinned Pyrenean thrust sheets, suggesting sediment burial and heating of sufficient magnitudes to reset the AFT system (&gt;~3 km). In some locations, exhumation of these fold‐thrust structures is likely an erosional response to thrust‐driven rock uplift. We identify an exhumation phase ~25–20 Ma that occurs along the central and eastern Spanish Pyrenees at the boundary between thick‐ and thin‐skinned portions of the wedge. We suggest that this distributed exhumation event records (a) a taper response in the southern orogenic wedge to sediment loading and/or (b) a shift to wetter, stormier climate conditions following convergence‐driven uplift and full topographic development. A final exhumation phase between ~20 and 10 Ma may record the excavation of the southern fold‐thrust system following base level lowering in the Ebro Basin.

The Eisenhower Range, Transantarctic Mountains: Evaluation of qualitative interpretation concepts of thermochronological data

The Transantarctic Mountains (TAM) were one of the first regions where apatite fission track (AFT) thermochronology was applied routinely to study exhumation processes and long term landscape evolution. Pioneering publications from the region introduced or refined interpretation concepts of thermochronological data such as the break in slope in vertical age profiles as qualitative marker for the onset of accelerated rock cooling.New AFT data were compiled from vertical profiles in the Eisenhower Range, northern TAM, and compared with published data. Samples originally examined by the population technique were re-analyzed via the external detector technique. AFT ages increase from 32±2Ma at an elevation of 220m to 175±14Ma at 2380m. Geological evidence and thermal history modeling of the AFT data require Jurassic to Late Eocene reheating of the samples and an onset of cooling at ~35–30Ma. This requires the deposition of an ~3 to 3.5km thick sedimentary sequence on the granitic basement subsequent to Jurassic Ferrar magmatism at ~180Ma. The regression of paleotemperatures against sample altitudes infers a high Jurassic geothermal gradient of ~60°C/km related to rifting processes and Ferrar magmatism, and a moderate Cretaceous/Eocene geothermal gradient of ~30°C/km.Comparison of ages generated with population and external detector technique shows the importance of determining single-grain ages for each sample, even from granitic rocks of the same intrusion, and thus strongly supports previous cases made for the determination of annealing kinetics and grain-age evaluation. Age comparison additionally illustrates that samples above a break in slope record larger deviations between population and external detector ages than samples below a break in slope.We demonstrate that the position and shape of a break in slope result from various factors, such as the thermal history prior to final cooling, maximum paleotemperatures, cooling rate, and geothermal gradient. A break in slope does not straightly date the onset of final cooling and cannot substitute thermal history modeling. Therefore, earlier studies from the TAM and similar settings elsewhere need to be validated by combining thermal history modeling of thermochronological data and supplementary geological information.

Thermal history of the Krishna–Godavari basin, India: Constraints from apatite fission track thermochronology and organic maturity data

The Krishna–Godavari (KG) basin, a passive margin Late Carboniferous to Holocene basin along the rifted east coast of India, includes the deltaic and inter-deltaic regions of the Krishna and Godavari rivers onshore and extends into the offshore. It is one of India’s premier hydrocarbon-bearing basins. In an attempt to better understand the thermal history of the basin, apatite fission track (AFT) data has been obtained from six exploration wells (five onshore and one offshore). AFT thermal history models as well as other thermal indicators e.g. vitrinite reflectance (VR), Rock–Eval Tmax data reveal that the host rocks are currently at their maximum post-depositional temperatures and that any possible heating related to small-scale tectonism or rifting episodes in the basin bears little significance on the maturation of the sediments. In the case of one borehole (M-1) however, the organic maturity data reveals a period of Oligocene cooling across an unconformity when ∼1000m of section was eroded due to falling sea-level. This information offers the potential for improved basin modeling of the KG basin.

Post-Triassic thermal history of the Tazhong Uplift Zone in the Tarim Basin, Northwest China: Evidence from apatite fission-track thermochronology

The Tarim Basin is a representative example of the basins developed in the northwest China that are characterized by multiple stages of heating and cooling. In order to better understand its complex thermal history, apatite fission track (AFT) thermochronology was applied to borehole samples from the Tazhong Uplift Zone (TUZ). Twelve sedimentary samples of Silurian to Triassic depositional ages were analyzed from depths coinciding with the apatite partial annealing zone (∼60–120 °C). The AFT ages, ranging from 132 ± 7 Ma (from a Triassic sample) to 25 ± 2 Ma (from a Carboniferous sample), are clearly younger than their depositional ages and demonstrate a total resetting of the AFT thermometer after deposition. The AFT ages vary among different tectonic belts and decrease from the No. Ten Faulted Zone (133–105 Ma) in the northwest, the Central Horst Zone in the middle (108–37 Ma), to the East Buried Hill Zone in the south (51–25 Ma). Given the low magnitude of post-Triassic burial heating evidenced by low vitrinite reflectance values (Ro < 0.7%), the total resetting of the AFT system is speculated to result from the hot fluid flow along the faults. Thermal effects along the faults are well documented by younger AFT ages and unimodal single grain age distributions in the vicinity of the faults. Permian–early Triassic basaltic volcanism may be responsible for the early Triassic total annealing of those samples lacking connectivity with the fault. The above arguments are supported by thermal modeling results.

Differential exhumation at eastern margin of the Tibetan Plateau, from apatite fission-track thermochronology

New apatite fission-track (AFT) ages from Mesozoic sediments in the Sichuan basin, combined with previous fission-track data, demonstrate differential uplift and exhumation across the basin. Particularly significant change in exhumation (at least ~2000m) was found across the Huaying Mts. Modeled temperature–time histories and the Boomerang plot of AFT dataset across the basin suggest rapid cooling and exhumation events during 120–80Ma and at 20–10Ma. They reflect the start of the basin-scale differential uplift and exhumation which effected the eastern growth of Tibetan Plateau. In particular, nested old-age center separated by Huaying Mts. was found in the center-to-northwest part of the Sichuan basin. A simplified one-dimensional, steady-state solution model was developed to calculate the mean exhumation rate, which is 0.05–0.2mm/yr in most parts of the basin. It suggests a slow exhumation across much of the basin. The regional pattern of AFT age, length and erosion rate supports a progressive change from the nested old-age center towards the southwest. This pattern supports the idea of a prolonged, steady-state uplift and exhumation process across the basin, controlled by cratonic basin structure. The eastern growth of the Tibetan Plateau has exerted a significant effect on the rapid exhumation of the southwestern part of the Sichuan basin, but not on all of the basin during the Late Cenozoic.

Miocene thrusting in the eastern Sila Massif: Implication for the evolution of the Calabria-Peloritani orogenic wedge (southern Italy)

Alpine orogens in the central Mediterranean region have revealed the concomitance of crustal extension in back-arc domain and crustal shortening in frontal domain. Quantitative data of deformation in the frontal orogenic wedges are necessary to understand how the shortening-extension pair evolves in terms of structures, orogenic transport, timing, and exhumation rate. This paper deals with kinematics and ages of the frontal thrust systems of the Calabria-Peloritani Arc (Italy) exposed in the eastern Sila Massif. We first present structural fieldwork, onshore and offshore well log data, and new apatite fission-track (AFT) thermochronology. Then, we describe the structural architecture of the studied area as an ENE-verging stacking of thrust sheets involving basement units and syn-orogenic sediments. The AFT study documents that thrust sheets entered the partial annealing zone from 18Ma to 13Ma. This Early-Middle Miocene thrusting phase was coeval with exhumation of high-pressure/low temperature metamorphic rocks in the hinterland of the orogen (Coastal Chain area), mainly driven by top-to-the-W extensional tectonics. Opposite kinematic shear senses (contractional top-to-the-E and extensional top-to-the-W) and different exhumation rates (slow in the frontal, more rapid in the hinterland) are framed in a tectonic scenario of a critically tapered orogenic wedge during the eastward retreating of the Apennine slab.

Eocene onset and late Miocene acceleration of Cenozoic intracontinental extension in the North Qinling range–Weihe graben: Insights from apatite fission track thermochronology

Intracontinental extension in central China is accommodated by Cenozoic grabens flanking the Ordos Block, such as the Weihe graben, which accommodate 5–6mm/yr of extension. To define the onset and evolution of major Cenozoic extension, we examine the cooling history of exhumed footwall rocks in the North Qinling range adjacent to the Weihe graben. We present results from 47 new apatite fission track (AFT) samples—primarily from two vertical transects of 1.5–2.5km relief located on the northern flank of the North Qinling footwall. AFT ages that get progressively older with increasing distance from the active, range bounding, normal fault suggest that Cenozoic uplift and southward tilting was a response to range-parallel extension. Correlations between AFT ages and both elevation and track lengths, combined with thermal modeling of representative samples, reveal that the North Qinling experienced two major stages of Cenozoic exhumation: (1) relatively slow exhumation in response to a small magnitude of extension that initiated at ~50Ma; (2) relatively rapid exhumation in response to a large magnitude of accelerated extension that initiated at ~10Ma. In addition, small changes in cooling rate at ~35Ma and ~25Ma may reflect minor changes in faulting rate. We interpret initial extensional at ~50Ma to be a far-field effect of initial India–Asia continental collision. In contrast, accelerated extension after ~10Ma along the Qinling is likely linked to the upward and outward growth of the Tibetan Plateau. Alternatively, lower crustal flow beneath the Qinling may have progressively accelerated exhumation in late Miocene time.

New evidence on the Neogene uplift of South Tianshan: constraints from the (U–Th)/He and AFT ages of borehole samples of the Tarim basin and implications for hydrocarbon generation

We identified a Neogene rapid uplift-denudation event of the South Tianshan based on apatite (U–Th)/He and apatite fission track (AFT) ages in Tertiary rocks of the Tarim basin, using borehole samples. The (U–Th)/He thermochronology can be used to reveal the tectono-thermal events with lower temperature than that of AFT thermochronology and has not been used previously to study the uplift of the Tianshan Mountain. Using these data, we show the relationship between the uplift of the South Tianshan and the subsidence/deposition of the northern Tarim basin during the Neogene. The apatite helium ages reveal the migration of uplift, erosion and deposition in the northern Tarim basin. A rapid uplift of the South Tianshan during the Miocene and a corresponding rapid subsidence in the northern Tarim basin occurred. However, in the Pliocene, the Kuqa Depression and South Tianshan uplifted and eroded at the same time and in turn provided the detrital source rocks for the Northern Uplift of the Tarim basin. In contrast to earlier studies, we arrive at the conclusion that the South Tianshan experienced rapid uplift in the Miocene based on (U–Th)/He data of apatite obtained from borehole samples collected in the Tarim basin itself, and not from the bordering mountain chain. Combined apatite (U–Th)/He and fission track thermochronometry enables reconstruction of thermal histories of sedimentary rocks between 40 and 120°C, and this has implications for the generation of liquid hydrocarbon in the 65–120°C range in the basin. Thermal and burial histories of typical samples were also modelled to show the rapid uplift in our study. Our works not only provide a new evidence for the South Tianshan uplift but also indicate that there is a coupling between uplift and subsidence in the South Tianshan and adjacent northern part of the Tarim basin, which controlled hydrocarbon accumulation in the Kuqa Depression and Northern Uplift of the Tarim basin.

Diverse exhumation of the Mesozoic tectonic belt within the Yangtze Plate, China, determined by apatite fission-track thermochronology

New and mostly published apatite fission-track (AFT) data are compiled to reveal the exhumation of the Mesozoic tectonic belt (MTB) within the Yangtze Plate, China. New AFT ages ranging from 51 ± 3 to 108 ± 5 Ma with mean measured track lengths between 11.8 ± 1.6 and 12.8 ± 2.0 μm, are obtained for the bedrock samples collected along a southeast to northwest transect across the MTB, including the exceptional Huangling Dome in the northern Yangtze Plate. The diverse, involving the first rapid, following by a slow, and the final accelerating, cooling and inferred exhumation from the Late Mesozoic to the Cenozoic have been identified in the study region based on the AFT data and modeling. The onset of exhumation is earlier in the Huangling Dome than in the southeastern and northwestern MTB, and in the southeastern MTB than in the northwestern MTB. Similarly, the final stage of accelerating exhumation seemed to start earlier in the Huangling Dome than in the southeastern and northwestern MTB, but in the northwestern MTB than in the southeastern MTB. The diverse exhumation of the MTB should have been attributed to the far-field effect of the Pacific plate subduction in the Cretaceous to the east, and to the eastward and southeastward tectonic escape from the Tibetan plateau imposed by the India-Eurasia collision since ∼55 Ma to the west.

Late Mesozoic–Cenozoic exhumation history of northern Svalbard and its regional significance: Constraints from apatite fission track analysis

The late Mesozoic–Cenozoic was a time of profound tectonic activity in the Arctic, with incipient spreading in the Arctic Ocean, Baffin Bay–Labrador Sea and North Atlantic, as well as the northward movement of the Greenland microplate leading to collision and deformation in Greenland, Arctic Canada and Svalbard (Eurekan Orogeny). It is, however, still unclear, how northern Svalbard, situated at the northwestern edge of the Barents Shelf, was affected by these processes. Furthermore, northern Svalbard has been proposed to have been a Cretaceous–Cenozoic sediment source to surrounding regions because it lacks a post-Devonian sedimentary cover. When erosion took place and how that related to the tectonic history of the Arctic, is yet unresolved. In order to reconstruct the erosion history of northern Svalbard, we constrained its thermal evolution using apatite fission track (AFT) thermochronology. Our data reveal AFT ages between 62 ± 5 and 214 ± 10 Ma, recording late Mesozoic–early Paleogene exhumation. Our data show that northern Svalbard was emergent and experienced erosion from the Early Jurassic and presumably through the Cenozoic, although total exhumation was restricted to ~ 6 km. Pronounced exhumation took place during Jurassic–Cretaceous time, probably linked to the extensional tectonics during the opening of the Amerasian Basin (Arctic Ocean). In contrast, Cenozoic ocean basin formation and the Eurekan deformation did not cause significant erosion of northern Svalbard. Nonetheless, AFT data show that Late Cretaceous–Early Paleocene fault-related exhumation affected some parts of northern Svalbard. Fault zones were reactivated due to the reorganization of Arctic landmasses during an early phase of the Eurekan deformation, which implies that this episode commenced ~ 20 m.y. earlier in Svalbard than previously understood.

Geomorphic Mesozoic and Cenozoic evolution in the Oka-Jombolok region (East Sayan ranges, Siberia)

The East Sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far-field effects of the India–Asia collision and the extension linked to the opening of the Baikal Rift System. The active deformation that affects this range is very recent (around 5Ma) but occurs in a very complex morphotectonic setting and the understanding of the Tertiary deformation relies entirely on a detailed knowledge of the pre-deformation situation. Using apatite fission track thermochronology, cosmogenic 10Be and morphological study on Tertiary lava flows we demonstrate that prior to the Oligocene the morphology of the East Sayan area was characterized by a wide, constantly rejuvenated erosion surface. Apatite fission track thermal modelling indicates that this surface started to form at least in Late Jurassic–Early Cretaceous (140–120Ma). The long-term exhumation rates (several tens of million years) derived from apatite fission track data (17.5m/Ma) and the short-term erosion rates (over a few hundred thousand years) derived from cosmogenic 10Be data (12–20m/Ma) are coherent implying a near constant mean erosion rate since Late Jurassic. This constant, slow erosion prevented the formation of a lateritic–kaolinic weathering crust on the planation surface. By Oligocene–early Miocene times a long wavelength uplift that remains to be explained, induced incision that created shallow valleys later filled by basaltic lava flows. Finally, the present short-wavelength topography initiated during the Pliocene.

Multi‐stage exhumation of the NE Tarim Precambrian bedrock, NW China: constraints from apatite fission track thermochronology in the Kuluketage area

Terra Nova, 23, 324–332, 2011AbstractFourteen samples of Precambrian bedrocks from the Kuluketage area, located in the north‐eastern Tarim Craton, yield apatite fission track ages ranging from 166 to 82 Ma. These ages are far younger than their Precambrian age of stratigraphy or metamorphism, indicating that the samples experienced total annealing before Mesozoic exhumation. The samples were subdivided into three groups based on locations and ages. Multi‐stage Mesozoic exhumation is linked to collisions of the Qiangtang, Lhasa and Kohistan terranes with the South Eurasian continental margin. The three cooling phases are also shown by stratigraphy and seismology. Considering modelling results with different constraint boxes, seismic profiles and the stratigraphic sequences of surrounding sedimentary basins, faint Cenozoic reheating and recooling were likely to take place in the Kuluketage area by northwards propagating deformation from India–Eurasia collision and continued convergence.

Apatite fission-track thermochronology of the Western Pontides (NW Turkey)

AbstractThe results of apatite fission-track analyses of the Western Pontides of NW Turkey point to three discrete episodes of Cenozoic exhumation correlatable with major supraregional tectonic events. (1) Paleocene–early Eocene exhumation reflected the closure of the İzmir–Ankara ocean. (2) Late Eocene–earliest Oligocene exhumation was the result of renewed tectonic activity along the İzmir–Ankara suture. (3) Late Oligocene–early Miocene exhumation recorded the onset of northern Aegean extension. Samples collected north and south of the tectonic contact between the two terranes forming the Western Pontides (i.e. İstanbul and Sakarya terranes) record the same cooling events, suggesting that such terranes were amalgamated in pre-Cenozoic times.

Denudational response to surface uplift in east Tibet: Evidence from apatite fission-track thermochronology

East Tibet preserves broad areas of low relief that occur at elevations >3000 m and are dissected by major strike-slip faults that have been repeatedly reactivated since the late Mesozoic. Apatite fission-track samples from these low-relief, high-elevation surfaces indicate Cretaceous cooling (ca. 90 Ma). Fast rock uplift of the 110 °C isotherm and a fossilized partial annealing zone began in the plateau interior of east Tibet in the Miocene. Low denudation rates in the plateau interior during the Cenozoic, which are constrained by thermal history modeling and a consistency in ages from apatite fission tracks, suggest that dip-slip displacement on faults has been minor. Some localized areas have experienced the effects of structurally enhanced rock uplift and denudation or fault-related hydrothermal reheating. Cooling ages in Eocene sediments deposited on the older plateau surface suggest that rapid denudation occurred from the Miocene to Holocene. Other evidence of significant Cenozoic denudation comes from river valleys, in particular, the Yalong River valley, where incision was initiated in the Oligocene to Miocene (28–12 Ma). Estimated mean denudation in east Tibet during the Cenozoic was ~1–2 km in the low-relief, high-elevation plateau interior and at least 5 km at the high-relief plateau margin in the Longmen Shan. The region south of the Longmen Shan and the Sichuan Basin was not uplifted with the main Tibetan Plateau in the Miocene, but it has undergone enhanced denudation since the Eocene. Due to an orographic effect, most of the denudation in the east Tibetan Plateau interior has occurred in major river valleys. Incision in the major rivers of the Longman Shan occurred simultaneously and has kept pace with surface uplift that began in the middle–late Miocene (12 Ma), with acceleration of denudation rates in the late Miocene (>5 Ma).