Zircon Fission Track Thermochronology Research Articles

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

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

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

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

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

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

Apatite and zircon fission-track thermochronology constraining the interplay between tectonics, topography and exhumation, Arunachal Himalaya

Apatite and zircon fission-track thermochronology constraining the interplay between tectonics, topography and exhumation, Arunachal Himalaya

Exhumation of the southern transpressive Bucaramanga fault, eastern Cordillera of Colombia: Insights from detrital, quantitative thermochronology and geomorphology

New detrital apatite and zircon fission-track thermochronology ages were determined in four rivers (Onzaga, Los Micos, Mogoticos, and Chaguacá) located along the southern termination of the Bucaramanga Fault System in the Eastern Cordillera of Colombia. Younger populations of apatite fission-track (AFT) ages were found in the Onzaga and Los Micos rivers, both draining the central zone of a transpressive system. The detrital thermochronological data are used to estimate erosion rates, assuming topographic steady-state and spatially variable conditions. We also tested the link between long-to short-term erosion patterns employing Hotspot and Cluster Analysis (HCA) of Hack's stream length index (SL), which enables us to detect transient signals related to landsliding, lithologic variability, or tectonic processes. Based on this classification, we identified 175 SL-HCA anomalies distributed across the study area but mainly concentrated on the western side of the Chicamocha River where gigantic landslides are present. This topographic analysis reveals knickzones where higher erosion rates are expected. Consequently, those hotspots are the source of much of the sediment being evacuated through the Chicamocha River system. This favours the hypothesis that the area has spatially variable topographic conditions over time. To test this, we compare observed and predicted detrital age distributions derived from 3D thermal-kinematic inversions of existing in-situ thermochronological data assuming the two different topography conditions. We show that exhumation rates calculated with the bootstrapping method are closer to the predictions obtained from our 3D thermal-kinematic models with a spatially variable topography assumption. Furthermore, for the Onzaga River, the comparison of cumulative density functions between observed and predicted ages are statistically similar, which validates our hypothesis. Our results demonstrate that the topography has been variable over time, mainly from 40 Ma to the present. Exhumation rates in the study area evolved from ~2 km/m.y. between ~40 and 30 Ma, decreasing to values below 0.1 km/m.y. from 30 to 25 Ma, before increasing to 0.5 km/m.y. from ~20 Ma to the present. The results also indicate that a paleotopography representing 10 to 50% of the current topography was present from 80 to 40 Ma. During the interval between 40 Ma to the present, the model suggests that more than 50% of the present-day topography was created.

Linking orogeny and orography in the Southern Alps of New Zealand: New observations from detrital fission-track thermochronology of the Waiho-1 borehole

Numerical modeling coupling erosion with crustal deformation predicts that development of an orographic rain shadow may explain the asymmetric exhumation of convergent plate boundary orogens. This prediction is consistent with observations from the Southern Alps of New Zealand, where bedrock thermochronology indicates crustal exhumation has been concentrated along the wet, windward side of the mountains. While the spatial correspondence of exhumation and precipitation patterns is compelling, a robust evaluation of the link between orographic and orogenic processes further requires a temporal comparison between exhumation history, plate reconstructions and paleoclimatic records. We present a detailed exhumation history of the Southern Alps from detrital apatite and zircon fission-track thermochronology of the Waiho-1 borehole, a 3.6 km-thick sequence of proximal foreland basin sediments. Inverse thermal modeling of a 2062-grain dataset predicts two periods of rapid exhumation in the Early and Late Miocene. Rapid exhumation in the Early Miocene was synchronous with the development of transpression along the Alpine Fault and a ca. 20–22 Ma pulse of exhumation may reflect cooling during inversion of preexisting extensional basins. Rapid exhumation in the Late Miocene was not synchronous with a discrete change in plate convergence but increased exhumation rates after 7.4 Ma may instead reflect localization of plate boundary deformation along the Alpine Fault as orographic precipitation concentrated exhumation in the Alpine Fault hanging wall. We propose that, similar to prior interpretations from bedrock thermochronology, detrital thermochronology of the Southern Alps foreland basin is consistent with numerical model predictions linking asymmetric exhumation of the orogen to the growth of an orographic rain shadow.

Detrital Zircon Fission-Track Thermochronology of the Present-Day River Drainage System in the Mt. Kailas Area, Western Tibet: Implications for Multiple Cooling Stages of the Gangdese Magmatic Arc

It is still controversial how the high elevation of the Tibetan Plateau established after the Indian-Asian collision during the Cenozoic. The timing of Gangdese magmatic arc exhumation and uplift history would provide useful message for this disputation. We present six zircon fission-track (ZFT) data from modern river sand in the western Tibet, around the Mt. Kailas, to decipher the long-term exhumation histories of the Gangdese magmatic arc. The data suggests that all the Gangdese magmatic arc rocks experienced rapid cooling during the Eocene (∼46’35 Ma) and Oligocene (∼31’26 Ma). The movement along the north-south trending extensional fault and dextral strike-slip Karakoram fault induced the adjacent rocks exhumed at the Middle Miocene (∼15’16 Ma) and Late Miocene (∼10’11 Ma), respectively. According to the minimum and central AFT ages for each sample, the fastest exhumation rate is about 0.4 km/Ma, with average long-term exhumation rates on the order of ∼0.3 km/Ma since the Oligocene. This result supports the outward growth model for plateau forming, indicating the southern margin of the Gangdese magmatic arc attained high elevation after the Oligocene.

New zircon fission track analysis constraints on tectonic-mineralization epochs in the Ganzi-Litang gold belt, eastern Qinghai-Tibet plateau

The Ganzi-Litang gold belt, as a part of the Sanjiang Tethys orogen, is located between the Yidun block and Songpan-Ganzi Block/Terrane in the eastern Qinghai-Tibetan plateau and experienced oceanic slab subduction, continent-arc collision and intracontinental convergence since the Indosinian orogeny. A series of gold ore deposits have been found within the region. This paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track (FT) thermochronology. A total of 15 zircon FT analysis results were obtained that can be divided into four age groups (217–213 Ma, 190–160 Ma, 155–93 Ma and 72–67 Ma) representing four distinct episodes of gold mineralization, of which the middle two episodes predominate. Eruption of the auriferous volcanic rocks that comprise the belt started at 217–213 Ma when the Ganzi-Litang Meso-Tethys ocean began to subduct. The mineralization episode at 190–160 Ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional-convergence of the Ganzi-Litang belt. Finally, the episodes at 155–93 Ma and 72–67 Ma are respectively related to the closing times of the Bangong-Nujiang and Yarlung Zangbu oceans, corresponding to tectonic quiet episodes.

Thermal imprints of late Permian Emeishan basalt effusion: Evidence from zircon fission-track thermochronology

Late Permian Emeishan large igneous province (LIP) developed in response to an ascending mantle plume beneath the southwestern Yangtze Craton, China. Mantle plume models predict two types of thermal effect on the lithosphere: (1) high lithospheric heat flow anomalies due to the ascending magma, and (2) heating of underlying country rocks by erupted lava flow. Evidence for these two effects of the Emeishan LIP may be documented in pre-LIP strata. As such, we determined the maximum temperature of sedimentary rocks deposited before and after the LIP using zircon fission-track (ZFT) thermochronology, which is sensitive to temperatures of 150–250 °C. ZFT ages of post-LIP sedimentary rocks are variable and overlap with depositional ages, reflecting post-LIP burial heating should be lower than the ZFT closure temperature. Pre-LIP samples yield scattered ZFT ages younger than their depositional ages, and contain an older age component that increases with depth. This indicates that the upper part of the pre-LIP strata should have experienced higher temperature than lower ones. Such a heating pattern cannot be explained by pre- or post-LIP burial heating, which predict higher temperatures and thus younger ages for stratigraphically lower samples. We propose that the downward increasing age pattern is evidence for massive top-down lava heating. Forward thermal modelling suggests that a >1.5-km-thick effusive basalts is required to reset the ZFT ages of rocks that are ∼3 km beneath the LIP. Our results support the existence of massive effusive basalts in the intermediate zone of the Late Permian Emeishan LIP.

Late Triassic-Cenozoic Thermochronology in the Southern Sanjiang Tethys, SW China, New Insights from Zircon Fission Track Analysis

The Sanjiang Tethys orogenic belt is located in the southeast side of the Qinghai-Tibet Plateau. It has undergone the opening and closing movements in different periods of Tethys oceans, complex accretive orogeny and strong mineralization from Paleozoic to Mesozoic. Using zircon fission track (ZFT) thermochronology, this study reveals the Sanjiang Tethys has experienced multi-stage tectonic activities during the Late Triassic-Cenozoic. The 15 ZFT ages with their decomposition components obtained from Sanjiang Tethysian region range from 212 to 19 Ma, which not only shows 6 age groups of 212, 179–172, 156–133, 121–96, 84–70 and 50–19 Ma, but also constrains the age limit of the tectonothermal events. These age groups recorded the Paleo-Tethys main and branches ocean opening/closure time. The age-elevation plot indicates the Sanjiang region had differential uplifting and exhumation and fast uplifting times of ca. 133, 116 and 80 Ma, coinciding with the age groups mentioned above. These results show new geochronological evidences and viewpoints.

Evolution and provenance of the Xuefeng intracontinental tectonic system in South China: Constraints from detrital zircon fission track thermochronology

The Xuefeng Intracontinental Tectonic System (XITS) is a large-scale compressional tectonic system in the central South China block. It is characterized by northeast-trending fold-thrust belts involving the Xuefeng zone, the Chevron syncline fold-thrust zone, the Chevron anticline fold-thrust zone and the Central Sichuan basin. This paper reports detrital zircon fission track (ZFT) analyses of the sandstones sampled from Neoproterozoic to Middle Jurassic sequences, and further discusses their relation with low-temperature tectonic evolution and sediment provenance. The totally annealed ZFT data of 452–377 Ma from the Neoproterozoic and Devonian sandstones were related to an Early Paleozoic low-temperature exhumation of the Jiangnan orogen due to intracontinental orogeny in the South China block. Those annealed ZFT components from Triassic to Jurassic sandstones, grouped 236–189 Ma, 189–142 Ma, and 142–124 Ma decreasingly from east to west structurally imply a northwestward progressively squeezing by the Xuefeng intracontinental orogeny as a result of the Paleo-Pacific subduction. The unannealed age components (411 Ma, 362–377 Ma, 270–216 Ma, and 209–183 Ma) of the Upper Triassic to Middle Jurassic sandstones, are comparable to the multistage tectonic evolution of the Qinling orogen through subduction, accretion and collision and are therefore indicative of sample potential provenance.

Cenozoic cooling history of the North Qilian Shan, northern Tibetan Plateau, and the initiation of the Haiyuan fault: Constraints from apatite- and zircon-fission track thermochronology

The growth of the Tibetan Plateau resulted primarily from India-Asia convergence since initial collision at 65–55 Ma. The Cenozoic Qilian Shan thrust belt and the left-slip strike Haiyuan fault system together define the northeastern margin of the plateau. Although these thrust and strike-slip fault systems play an important role in accommodating continental convergence, our knowledge of the temporal and spatial distribution of upward and outward growth of the northeastern Tibetan Plateau is still lacking. In this study, we integrate new geologic mapping and low-temperature themochronometry (apatite- and zircon-fission-track ages) to provide constraints on the uplift and cooling history of the North Qilian Shan and the initiation of the Haiyuan fault. Cooling ages and thermal history modeling from a traverse across a prominent restraining bend on the Haiyuan fault suggest the North Qilian Shan experienced a three-phase cooling history, including: (1) broad cooling during the Late Triassic to early Cenozoic, (2) long-term tectonic quiescence from late Cretaceous to middle Miocene, and (3) rapid cooling and exhumation from ~15–10 Ma to present. We relate this most recent local cooling (~15–10 Ma) to the initiation of strike-slip faulting along the central Haiyuan fault, which corroborates other recent studies, suggesting a middle Miocene activation of strike-slip deformation along the Haiyuan fault in northern Tibet.

Detrital zircon fission-track thermochronology and magnetic fabric of the Amagá Formation (Colombia): Intracontinental deformation and exhumation events in the northwestern Andes

New detrital zircon-fission track (ZFT) and magnetic fabric data are presented to constrain the time of deposition, provenance and deformation of the of Lower and Upper members of the Amagá Formation in the Amagá Basin. The Amagá Basin is located in the northern Andes, between the Western and Central Cordilleras of Colombia. The Amagá Formation was deposited in a transpressive geodynamic context and is allegedly synchronous with tectonic events such as the Andean orogeny and the Panama-Choco Block collision with the northwestern South American Plate. Detrital ZFT data confirm an Oligocene age for the Lower Member and a middle-Miocene age for the Upper Member of the Amagá Formation. In addition to constraining the depositional age, the ZFT data presented in this study also reflect Paleocene-Eocene, late to early Oligocene and late to middle Miocene cooling in sediment source areas mainly located in the Central and Western Cordilleras of Colombia. These ages can be associated with regional exhumation events in the central and northern Andes of South America. Collisional stages of the Panama-Choco Block against northwestern South America, subduction of the Farallon-Nazca Plate and strike-slip reactivation periods of the Cauca-Romeral fault system, caused NW-SE compression and NE-SW simple shear in the Amagá Basin. This deformational regime, identified by magnetic fabric data, induces syn- and post-depositional deformation over the Amagá Formation.

A new approach for electron microprobe zircon fission track thermochronology

Fission track thermochronology (FTT) has been applied for decades to quantify rates and timing of processes in the shallow crust. The most widely used approach is the external detector method (EDM). In this conventional approach, an age is obtained by counting both the fossil (238U spontaneous fission) and the induced (235U induced fission) tracks using an optical microscope. The induced tracks are obtained through the irradiation of the sample with thermal neutrons in the nuclear reactor, which causes fission of 235U. Based on the studies carried out by Gombosi et al. (2014), we present an alternative method of dating zircons using electron probe microprobe analysis (EPMA) to measure uranium concentration [U]. The electron microprobe analysis fission track (EPMA-FT) method was applied to three samples of rapidly cooled zircons: the Fish Canyon Tuff, Poços de Caldas (syenite) and Serra Geral zircons. The analyses were performed using two approaches: 1) using the age equation described in Gombosi et al. (2014) and 2) using a new age equation calibration developed for this work. The results using the Gombosi et al. (2014) age equation were 26.7±4.1Ma, 80.6±12.8Ma and 130.9±20.1Ma, respectively, and the results using the age equation from this work were 27.8±1.9Ma, 83.8±7.7Ma and 136±12Ma, respectively. The uncertainty of the age is affected mainly by 238U concentration and ρS (the spontaneous fission track density) determinations. Other factors can affect the uncertainty of the age, but their contributions are smaller. For all samples, the yield ages found by the two methods are consistent and overlap within two standard deviations of published reference ages determined from other radiometric techniques (i.e., K/Ar, 40Ar/39Ar, and/or U/Pb) and traditional FTT by the EDM.

Exhumation mechanisms of the Tauern Window (Eastern Alps) inferred from apatite and zircon fission track thermochronology

Exhumation mechanisms of the Tauern Window (Eastern Alps) inferred from apatite and zircon fission track thermochronology

Evidence of post-Gondwana breakup in Southern Brazilian Shield: Insights from apatite and zircon fission track thermochronology

Apatite and zircon fission track thermochronology studies are applied to basement and sedimentary rocks from the Sul-Rio-Grandense Shield to unravel the tectonic history of the onshore southernmost Brazilian margin. The Sul-Rio-Grandense Shield is a major geotectonic feature of southernmost Brazil that includes Paleoproterozoic basement areas and Neoproterozoic fold belts linked to the Brasiliano/Pan-African orogeny. Crustal reworking and juvenile accretion events related to this cycle were dated in the region between 900 and 500Ma and were responsible for the assembly of southwestern Gondwana in southeastern South America. Apatite fission track (AFT) ages range from 340±33 to 77±6Ma and zircon fission track (ZFT) ages range from ca. 386 to 210Ma. Based on thermal history modeling, the most part of the samples record an early cooling event during the Carboniferous, which reflect the main tectonic activity of the final stages of the Gondwanides at the Pacific margin of West Gondwana. Subsequently, the Permo-Triassic cooling event is related to the last stages of the Gondwanides, with convergence along the southern border of Western Gondwana and consequent reactivation of N-S and NE-SW trending basement structures. The onset of initial breakup of southwestern Gondwana with opening of the South Atlantic Ocean is mostly recorded in the eastern terrain and ZFT ages show that the temperature during this period was high enough for total or at least partial resetting of fission tracks in zircon. The last cooling event of the Sul-Rio-Grandense Shield records the final breakup between South America and Africa, which began during the Late Cretaceous. However, the Cenozoic rapid cooling episode probably is a result of plate adjustment after breakup and neotectonic reactivation of faults associated with South Atlantic rift evolution.

Tectonothermal history of the NE Jiangshan–Shaoxing suture zone: Evidence from 40Ar/39Ar and fission-track thermochronology in the Chencai region

The Jiangshan–Shaoxing suture zone, a component of the Neoprotozoic orogenic belt between the Yangtze and Cathaysia blocks in South China, has experienced a complex history of tectonic reactivation. Previous investigations of this significant tectonic boundary have focused on earlier stages of its tectonic history pre-dating the Early Paleozoic Wuyi–Yunkai orogeny, with more recent episodes rarely addressed. We here improve understanding of the later reactivation history of this suture zone through new 40Ar/39Ar and fission track thermochronological constraint derived for the ductilely strained Chencai Complex and the Lipu–Huangshan quartz diorite, together with sedimentological investigations of the proximal Wuzao Formation.This combined constraint demonstrates the occurrence of as many as five discrete episodes of tectonic reactivation and deformation of the Jiangshan–Shaoxing suture zone. The 431±4Ma 40Ar/39Ar biotite cooling age of the Lipu–Huangshan quartz diorite records retrograde cooling of the Chencai region following high-grade metamorphism at c. 460–450Ma during the Early Paleozoic Wuyi–Yunkai orogeny. Consistent younger 40Ar/39Ar ages of the gneissic Chencai Complex suggest that this retrograde cooling episode may extend to c. 390–400Ma, with later ductile strain and/or thermal overprinting of biotite at c. 386Ma suggesting that the terminal stage of the Early Paleozoic Wuyi–Yunkai orogeny may have continued significantly later than previously assumed. Although not reflected directly in the thermotectonic records compiled for the Chencai Complex, lithoclasts of these distinctive ductilely deformed gneisses represent a significant component of the conglomeratic gravels appearing in the late Triassic Wuzao Formation, demonstrating substantial uplift and erosion of the suture zone at this time, coincident with the Indosinian orogeny. Zircon fission track thermochronology of the samples from both Lipu–Huangshan quartz diorite and Chencai Complex yield much younger Cretaceous cooling ages of 144±8 to 103±6Ma, with apatite fission track ages ranging from 66±4 to 41±3Ma and mean apatite fission track lengths between 12.1 and 13.1μm. Thermal history modeling of these low-temperature controls demonstrates significant cooling during the Cenozoic. These later activities reflect brittle deformation in the upper crust and erosional exhumation of these rocks coincident with the Yanshanian extension event and Himalayan tectonism.These results together imply that the Jiangshan–Shaoxing suture zone represents a significant and long-lived lithospheric weakness that was preferentially reactivated during at least two episodes of tectonic activity in regional far-field domains. Examining the complex reactivation history of the fossil suture zone thus provides a useful window into the timing of episodes of broader tectonic activity across the wider region.

Mesozoic cooling history of the “Bachu Uplift” in the Tarim Basin, China: Constraints from zircon fission-track thermochronology

We applied zircon fission-track analysis to outcrop and borehole samples to study the Mesozoic cooling history of the Bachu Uplift, the Central Uplift of the Tarim Basin. Zircon fission-track (ZFT) ages of 182 Ma – 249 Ma are younger than the sample depositional ages indicating substantial post burial thermal annealing and can effectively reveal cooling events in the Bachu Uplift. The strong correlation between single grain ZFT age and U content indicates that most of the zircon grains represent ages that have been partially annealed and so the age is not directly indicative of the time of cooling. The youngest ZFT age populations with modal peak ages of 151 ± 8 Ma (Well HT1 samples), 126 ± 6 Ma (Well T1 samples) and 192 ± 10 Ma (Xiaohaizi Reservoir profile samples) from the decomposition of the ZFT single-grain ages represent the onset of cooling events in the Bachu Uplift, which were related to the collisions of the Qiangtang Terrane and Lhasa Block with the southern margin of the Eurasia continent, respectively. This study provides new insights into the tectonic and sedimentary evolution of the Tarim Basin and even Central Asia by constraining the higher temperature (c. 250–180 °C) part of the basin thermal history.

Detrital Zircon Fission-Track Thermochronology of the Present-Day Isère River Drainage System in the Western Alps: No Evidence for Increasing Erosion Rates at 5 Ma

The Isère River system drains parts of the Western Alps in south-eastern France. Zircon fission-track data of the Isère River and its tributaries show a range of apparent cooling ages from about 7 to 150 Ma. Zircons with Jurassic to early Tertiary cooling ages are derived from partially reset or non-reset sedimentary cover units of the internal and external Alps, while grains belonging to the minimum age fraction are derived from areas of active river incision in the external crystalline massifs or from the Penninic front. With the absence of major normal faults, upper crustal exhumation in the Western Alps is driven by erosion. First-order long-term exhumation rate estimates based on minimum ages are about 0.5–0.6 km/Myr for the fastest exhuming areas, while drainage basin average rates based on central ages are about 0.2–0.4 km/Myr. These rates are slower than published short-term erosion rates determined from detrital quartz 10Be analyses in the Pelvoux massif. While present-day erosion is faster than the long-term average exhumation rates, the Isère River drainage zircon fission-track data do not show evidence for increasing erosion rates at 5 Ma. Exhumation has not been sufficient in this area to expose rocks with <5 Ma cooling ages today. The increase in erosion may have happened only in glaciated areas between 1 and 2 Ma.

Polyphase movement on the Lavanttal Fault Zone (Eastern Alps): reconciling the evidence from different geochronological indicators

The Lavanttal Fault Zone (LFZ) is generally considered to be related to Miocene orogen-parallel escape tectonics in the Eastern Alps. By applying thermochronological methods with retention temperatures ranging from ~450 to ~40°C we have investigated the thermochronological evolution of the LFZ and the adjacent Koralm Complex (Eastern Alps). 40Ar/39Ar dating on white mica and zircon fission track (ZFT) thermochronology were carried out on host rocks (HRs) and fault-related rocks (cataclasites and fault gouges) directly adjacent to the unfaulted protolith. These data are interpreted together with recently published apatite fission track (AFT) and apatite (U-Th)/He ages. Sample material was taken from three drill cores transecting the LFZ. Ar release spectra in cataclastic shear zones partly show strongly rejuvenated incremental ages, indicating lattice distortion during cataclastic shearing or hydrothermal alteration. Integrated plateau ages from fault rocks (~76 Ma) are in parts slightly younger than plateau ages from HRs (>80 Ma). Incremental ages from fault rock samples are in part highly reduced (~43 Ma). ZFT ages within fault gouges (~65 Ma) are slightly reduced compared to the ages from HRs, and fission tracks show reduced lengths. Combining these results with AFT and apatite (U-Th)/He ages from fault rocks of the same fault zone allows the recognition of distinct faulting events along the LFZ from Miocene to Pliocene times. Contemporaneous with this faulting, the Koralm Complex experienced accelerated cooling in Late Miocene times. Late-Cretaceous to Palaeogene movement on the LFZ cannot be clearly proven. 40Ar/39Ar muscovite and ZFT ages were probably partly thermally affected along the LFZ during Miocene times.