Radiometric Dating Methods Research Articles

Cosmogenic 3He chronology of postglacial lava flows at Mt Ruapehu, Aotearoa / New Zealand

Abstract. Accurate volcanic hazard assessments rely on a detailed understanding of the timing of past eruptions. While radiometric methods like 40Ar/39Ar or K/Ar are by far the most conventional lava flow dating tools, their low resolution for young (<20 ka) deposits interferes with the development of precise chronologies of recent effusive activity on most volcanoes. Mt Ruapehu (Aotearoa / New Zealand) has produced many lava flows throughout its history, but the precise timing of many recent eruptions remains largely unknown. In this study, we use cosmogenic 3He exposure dating to provide 23 eruption ages of young lava flows at Ruapehu. We then compare our results with existing 40Ar/39Ar and paleomagnetic constraints, highlighting the value of cosmogenic nuclide exposure dating in refining recent eruptive chronologies. Of the 23 sampled flows, 16 provided robust eruption ages (5 %–20 % internal 2σ; n≥3) between ca. 20 and 8 ka, except for one lava flow that erupted at around 43 ka, and their age distribution indicates that, during the last 20 kyr, effusive activity at Ruapehu peaked at 17–12 ka and at 9–7.5 ka. Nearly identical eruption ages of lavas located in different flanks of the volcanic edifice suggest concurrent activity from multiple vents during relatively short time intervals (0–2 kyr) at around 13, 10, and 8 ka. We analysed four individual lava flows previously dated by 40Ar/39Ar, two of which yield eruption ages older than the older limit of the 2σ interval of the radiometric dates, but the good clustering of individual samples from our sites suggests that our results better represent the real eruption age of these flows. Our 3He-based chronology shows excellent agreement with paleomagnetic constraints, suggesting that production rate uncertainties are unlikely to impact the accuracy of our eruption ages. This study demonstrates how cosmogenic nuclide dating can provide greater detail on the recent effusive chronology of stratovolcanoes, helping to resolve the low resolution of and difficulty in applying radiometric dating methods to young lava flows.

Multitechnique Geochronology of Intrusive and Explosive Activity on Piton des Neiges Volcano, Réunion Island

AbstractThe construction of ocean island basaltic volcanoes consists of a succession of eruptions, intrusions, and metamorphism. These events are often temporally ill‐constrained because the most widely used radiometric dating methods applicable to mafic volcanic rocks (K‐Ar or40Ar/39Ar on whole rock or groundmass) are prone to inaccuracy when applied to slowly cooled, altered, or vesicular and aphyric products. Here, we adopt a multitechnique geochronology approach (including zircon U‐Pb, phlogopite40Ar/39Ar, zircon and apatite (U‐Th)/He, and zircon double‐dating) to demonstrate its efficacy when applied to basaltic volcanoes. Taking the main volcano of Réunion Island (Piton des Neiges) as a case study, we establish the time of the major plutonic, metamorphic, and explosive events that had resisted previous dating attempts. We document four stages of pluton emplacement and metamorphism at 2,200–2,000 ka, 1,414 ± 8 ka, 665 ± 78 ka, and 150–110 ka, all coinciding with volcanism revival after quiescent intervals. We also date a major Plinian eruption at 188.2 ± 10.4 ka, coeval with the formation age of a large caldera, and, finally, we constrain the last eruption of Piton des Neiges to 27 ka, revising a previous estimate of 12 ka. By resolving several conundrums of Réunion's geological history, our multitechnique geochronology approach reveals that endogenous growth of a volcanic island proceeds as pulses at the beginning of renewed volcanism. We also demonstrate that crosschecking eruptions ages by diversified dating techniques is important to better assess the timing and recurrence of basaltic volcanic activity, with implications for hazard prediction.

Extraction of 40Ar-39Ar Ages from a Multicomponent Mixture: A Case Study From the Tatra Mountains, Poland

AbstractExtraction of meaningful information on the timing of fault activity from clay gouges using radiometric dating methods, such as those based on the K-Ar system, can be challenging. One of the factors complicating interpretation of the radiometric dating results is the presence of multiple K-bearing components in the gouge material. In the current study, an attempt was made to develop a new interpretative method for K-Ar and 40Ar-39Ar dating, capable of handling a three-component mixture. In addition, the mineral composition of clay gouges from the Tatra Mountains (Poland), which has not been investigated before, is reported. The mineral compositions of the bulk clay gouge material and separated size fractions were determined by X-ray diffractometry and Fourier-transform infrared spectroscopy. The gouge samples were composed of quartz, dioctahedral mica (as a discrete phase and as a component of mixed-layered illite-smectite), and chlorite, commonly with plagioclase and more rarely with K-feldspar, dioctahedral smectite, calcite, anatase, or trace kaolinite. One feldspar-free sample containing three mica polytypes (1Md, 1M, and 2M1) was chosen for dating with the 40Ar-39Ar method. The results of 40Ar-39Ar dating were interpreted using three concepts: Illite Age Analysis (IAA), a method based on the MODELAGE software, and a newly developed three-component concept. The age values obtained with IAA were −14 Ma ± 31 Ma and 180 ± 91 Ma for authigenic (1Md) and inherited (1M + 2M1) components, respectively. The MODELAGE-based approach returned –4 ± 40 Ma and 165 ± 62 Ma. The three-component approach returned age values of polytypes as follows: 1Md, 15 ± 37 Ma; 1M, 135 ± 57 Ma; 2M1, 121 ± 56 Ma based on the medians and the interquartile ranges of non-normal distributions of Monte Carlo-simulated age values. The results obtained indicated that the 1Md polytype was probably formed during the most recent stage of fault activity, while 1M and 2M1 polytypes are of equal age, roughly.

Recent Developments in Instrumentation and its Application in Absolute Dating: Historical Perspective and Overview

The discovery of radioactivity in the early 20 th century led to the development of several radiometric dating methods (e.g., Rb-Sr, Sm-Nd, Re-Os, U-Pb, etc.). These radiometric dating methods are frequently used in earth science studies to constrain the deposition/formation timing of various natural archives (e.g., bulk rocks, minerals, carbonaceous materials , detrital clastic sedimentary materials, ore deposits , hydrocarbon deposits). The last few decades have witnessed significant improvements in overall accuracy and precision of these absolute radiometric dating methods due to continuous developments and refinements in sample processing and analytical techniques. In this contribution, we discuss some of the frequently used radiometric dating techniques for obtaining absolute ages in various natural archives and associated advancements in the instrumentation. The present attempt emphasizes on a multi-mineral and multi-isotopic approach with continuous developments in obtaining better precision and accuracy in the ages through improved analytical and measurement protocols that are the pre-requisite in absolute dating.

Apatite fission‐track analysis of Cretaceous alkaline rocks of Ponta Grossa and Alto Paranaíba Arches, Brazil

AbstractThis work presents fission‐track ages and thermal history modelling of apatite samples from two Brazilian alkaline formations: Alto Paranaíba and Ponta Grossa Arches. The apatite fission‐track ages obtained for Alto Paranaíba Arch agree with those determined by other radiometric dating methods presenting higher closure temperatures. The ages given by the fission‐track thermochronometer suggest that no strong tectonic event has occurred after Alto Paranaíba Formation during Upper Cretaceous. This event is also supported by thermal history modelling of this arch, which is characterized by fast cooling followed by residence at lower temperatures. On the other hand, apatite fission‐track ages from Ponta Grossa Arch are systematically lower than other radiometric ages, suggesting that at least one tectonic event occurred after Ponta Grossa Formation, around 130 Ma. Copyright © 2015 John Wiley & Sons, Ltd.

Reconstruction of the Northeast Asian monsoon climate history for the past 400 years based on textural, carbon and oxygen isotope record of a stalagmite from Yongcheon lava tube cave, Jeju Island, Korea

Paleoclimatic changes over the past 400 years were investigated based on textural and geochemical characteristics of the YC-2 stalagmite which grew in Yongcheon Cave (lava tube cave) on Jeju Island, Korea. The stalagmite is about 68 mm long and annual growth laminae are distinctively identified. The age of the stalagmite was mainly determined by counting annual growth laminae supplemented by other radiometric dating methods, and it is estimated that the stalagmite grew at least for ca. 242 years including the hiatus. This hiatus is located at about 15 mm from the base and is present in the form of one thick brown growth lamina which was formed when the stalagmite stopped to grow. Texturally, the stalagmite can be divided into two phases: Fluid inclusion-poor, compact columnar calcite (Phase A) and fluid inclusion-rich, sparse columnar calcite (Phase B). This textural division is intimately related to the spacing of growth laminae, that is, Phase A is characterized by narrower spacing of growth laminae. Phase A with narrow-spaced growth laminae indicates the slower growth rate due to lower amount of rainfall when Northeast Asian summer monsoon intensity was relatively lower. Based on high resolution carbon isotope trend, the stalagmite can be divided into three stages (Stages I, II and III). The relatively more positive carbon isotopic compositions of the Stage I (δ13C = −3.3–0.4‰, PDB) in the lower part indicate that it grew during the Little Ice Age (LIA) under cold and dry climate with less vegetation. The Stage II is a transitional period from cold and dry to warm and wet climate with a continuous decrease in carbon isotope values (from 0.6 to −9.6‰ in δ13C). This stage shows the gradual weakening of the LIA climate. Carbon isotope trend also suggests that the LIA interval was terminated near middle 1870's around Korean peninsula. Relatively low carbon isotopic compositions during Stage III (δ13C = −11.0 ∼ −8.0‰) in the upper part should indicate that climate was changed to the warm and wet Current Warm Period. Warming since 1960 can also be recognized. Complete coincidence between textural data (internal calcite texture and growth laminae spacing) and high resolution carbon isotope compositions strongly suggests that past climate changes such as monsoonal variations in Northeast Asia have been clearly recorded in the stalagmite in Yongcheon Cave.

New luminescence ages for the Galería Complex archaeological site: resolving chronological uncertainties on the acheulean record of the Sierra de Atapuerca, northern Spain.

The archaeological karstic infill site of Galería Complex, located within the Atapuerca system (Spain), has produced a large faunal and archaeological record (Homo sp. aff. heidelbergensis fossils and Mode II lithic artefacts) belonging to the Middle Pleistocene. Extended-range luminescence dating techniques, namely post-infrared infrared stimulated luminescence (pIR-IR) dating of K-feldspars and thermally transferred optically stimulated luminescence (TT-OSL) dating of individual quartz grains, were applied to fossil-bearing sediments at Galería. The luminescence dating results are in good agreement with published chronologies derived using alternative radiometric dating methods (i.e., ESR and U-series dating of bracketing speleothems and combined ESR/U-series dating of herbivore teeth), as well as biochronology and palaeoenvironmental reconstructions inferred from proxy records (e.g., pollen data). For the majority of samples dated, however, the new luminescence ages are significantly (∼50%) younger than previously published polymineral thermoluminescence (TL) chronologies, suggesting that the latter may have overestimated the true burial age of the Galería deposits. The luminescence ages obtained indicate that the top of the basal sterile sands (GIb) at Galería have an age of up to ∼370 thousand years (ka), while the lowermost sub-unit containing Mode II Acheulean lithics (base of unit GIIa) was deposited during MIS 9 (mean age = 313±14 ka; n = 4). The overlying units GIIb-GIV, which contain the richest archaeopalaeontological remains, were deposited during late MIS 8 or early MIS 7 (∼240 ka). Galería Complex may be correlative with other Middle Pleistocene sites from Atapuerca, such as Gran Dolina level TD10 and unit TE19 from Sima del Elefante, but the lowermost archaeological horizons are ∼100 ka younger than the hominin-bearing clay breccias at the Sima de los Huesos site. Our results suggest that both pIR-IR and single-grain TT-OSL dating are suitable for resolving Middle Pleistocene chronologies for the Sierra de Atapuerca karstic infill sequences.

Recalibration of U-doped standard glasses through uranium thin film for neutron-fluence measurements

This work presents a recalibration of U-doped standard glasses using natural uranium thin films to be used as most dedicated neutron monitor for fission-track dating. The recalibrated U-doped glasses were used to determine fission-track ages in apatite samples from Brazilian alkaline formations (Alto Paranaiba) and standard Durango apatite. Samples were irradiated in two nuclear reactors with different characteristics and the results were compared. For well-thermalized neutron facility, metal activation monitor was also used. The ages of Alto Paranaiba arch and Durango apatite agree with those determined by other radiometric dating methods and metal activation monitors. These results suggest that the presented recalibration is suitable to be used routinely for fission-track dating studies even in a non-well thermalized neutron facility.

Construction and validation of calendar-year time scale for annually laminated sediments – an example from Lake Szurpiły (NE Poland)

The composite sediment profile (12.39 m) from Lake Szurpiły (NE Poland) represents an annually laminated organic-carbonaceous gyttja occasionally interrupted by turbidites and massive sand layers. This study focuses on the 7.58-m long and almost continuously varved top section of the profile, which produced a 8410-year long varve chronology with a cumulative counting error of ± 1.24%. The age-depth model was established by multiple microscopic varve counts and improved by the application of independent radiometric dating methods (210Pb, 137Cs). Ten additional AMS 14C dates are consistent with varve counts. In some sections, missing varves were identified as a result of erosional processes related to turbidite deposition. Varve thickness ranges from less than 0.1 to 13.7 mm (mean: 0.83 mm; std: 0.75 mm) with highest variability during the last 1500 years. The accuracy of the varve chronology depends mostly on the regularity of the varve thickness and the distinctness of varve boundaries, and was not influenced by the varve thickness itself. Even though manual and semiautomated varve counting show similar results of the total amount of varves, with the difference of only 0.56%, the comparison between those two methods in intervals of 200 years indicates potential problems, especially for sections with complex lamination and turbidites. We found that semiautomatic varve counting overestimated the varve boundaries in sections with erosive turbidites. Our results confirm the importance of validation of varve chronologies by independent dating methods and caution in relying on automated methods.

Issues in dating young rocks from another planet: Martian shergottites

Abstract The 40 Ar/ 39 Ar ages of a group of Martian meteorites called shergottites are systematically older by about 25% or more than ages obtained using Sm–Nd and other radiometric dating methods. The older 40 Ar/ 39 Ar ages indicate the presence of 40 Ar not derived in situ from the radiogenic decay of 40 K. The ‘excess’ argon can be associated with several different components, including the Martian atmosphere and mantle. We discuss the sources of Ar in shergottites, and the methods used to separate and identify them.

Coastal wetland accretion and response to sea-level rise: reading the recent sedimentary record using radiometric dating methods, with special reference to N W European marsh settings

Coastal wetland accretion and response to sea-level rise: reading the recent sedimentary record using radiometric dating methods, with special reference to N W European marsh settings

Investigation of the Holocene fire history of Northern Germany using charcoal records with various spatial resolutions and from various archive types: a comparative approach

Downcore counting of laminations in varved sediments offers a direct and incremental dating technique for high-resolution climatic and environmental archives with at least annual and sometimes even seasonal resolution. The pioneering definition of varves by De Geer (1912) had been restricted to rhythmically deposited proglacial clays. One century later the meaning of ‘varve’ has been expanded to include all annually deposited laminae in terrestrial and marine settings. Under favourable basin configurations and environmental conditions, limnic varves are formed due to seasonality of depositional processes from the lake's water column and/or transport from the catchment area. Subsequent to deposition of topmost laminae, the physical preservation of the accumulating varved sequence requires the sustained absence of sediment mixing, for example via wave action or macrobenthic bioturbation. Individual (sub)laminae in varved lake sediments typically express contrasting colours, always differ in terms of their organic, chemical and/or mineralogical compositions, and often also differ with regard to grain-size. Various predominating climatic and depositional conditions may result in clastic, biogenic or endogenic (incl. evaporitic) varved sediments and their mixtures.To reliably establish a varve chronology, the annual character of laminations needs to be determined and verified in a multidisciplinary fashion. Sources and influences of possible errors in varve chronologies are best determined and constrained by repeated varve counts, and by including radioisotopes and correlation with historically documented events. A well-established varve chronology greatly enhances the scientific value of laminated limnic archives by securely anchoring the wealth of multi-proxy palaeoenvironmental information in the form of time-series for multidisciplinary investigations.Applications of varved records are discussed with special reference to advances since the 1980s. These span fields like calibrating radiometric dating methods, reconstructing past changes of the Earth's magnetic field or detecting fluctuations in solar forcing. Once a varve chronology is established it can be applied to precisely date events like volcanic ash layers, earthquakes or human impact, as well as short- and long-term climate (temperature, precipitation, wind, hydroclimatic conditions or flooding) and environmental changes (eutrophication, pollution). Due to their exceptional high temporal resolution and in combination with their robust and accurate “internal” time scale in calendar years, annually laminated sediments can be regarded as one of the most precious environmental archives on the continents. These records are necessary to extend temporally limited instrumental records back in time. As such they have societal relevance with regard to risk assessments related to natural hazards arising from e.g. flooding or volcanic eruptions.

Characteristics of sedimentary varve chronologies – A review

We constructed a varve data base (VDB) to study the worldwide distribution of varved sediment records and the fidelity of their varve chronologies. Clusters of lakes with varved sediments exist in central North America, in the Canadian Arctic, and in northern and central Europe. Among the 108 sites included in the VDB, varved records are typically 200–500 cm long and cover a period of 1000–2000 years. Their varve chronologies are often based on counting of annual layers from fresh sediment surfaces and photographs or from epoxy embedded sediment blocks and thin sections. The VDB indicates that chronological errors associated with counting sedimentary varves fall generally between 1 and 3% but only 57% of published records are providing quantitative error estimations for their chronologies. With a careful documentation of varves and by applying radiometric dating methods to surface sediments as well as using historical events as time markers, there is the potential of having centennial-long varved records with a very precise age–depth control. However, it is unrealistic to expect errors significantly below ±1% from several millennia long sections. We found no indication that varve chronologies would have been substantially more accurate and precise in some parts of the world than in others or statistically dependent on varve thickness or temporal extension of a varved sequence. According to the VDB, close to 90% of the published varve chronologies have been cross-checked with some independent dating methods.

Uranium-series dating and growth characteristics of the deep-sea scleractinian coral: Enallopsammia rostrata from the Equatorial Pacific

The deep-sea coral, Enallopsammia rostrata, a member of the Dendrophylliidae family, is a major structure-forming species that creates massive dendroid colonies, up to 1 m wide and 0.5 m tall. Living colonies of E. rostrata have been collected using the PISCES submersibles from three locations from 480 to 788 m water depth in the Line Islands (∼160°W) in the Equatorial Pacific. We have applied to these colonies a high sensitivity, low blank technique to determine U-series ages in small quantities (70 ± 15 mg) of modern and near modern calcareous skeletons using MC-ICP-MS (Multi-collector Inductively Coupled Plasma Mass Spectrometer). The application of this method to living slow-growing colonies from a range of sites as well as the observations of axial growth patterns in thin sections of their skeletons offer the first expanded and well constrained data on longevity, growth pattern and mean growth rates in E. rostrata. Absolute dated specimens indicate life spans of colonies ranging from 209 ± 8 yrs to 605 ± 7 yrs with radial growth rates from 0.012 to 0.072 mm yr −1 and vertical extension rates from 0.6 to 1.9 mm yr −1. The linear growth rates reported here are lower than those reported for other deep-sea scleractinian corals ( Lophelia pertusa and Madrepora oculata). The U-series dating indicates that the growth ring patterns of E. rostrata are not consistent with annual periodicity emphasizing the importance of absolute radiometric dating methods to constrain growth rates. Slow accretion and extreme longevity make this species and its habitat especially vulnerable to disturbances and impacts from human activities. This dating method combined with observation of growth patterns opens up new perspectives in the field of deep-sea corals since it can provide quantitative estimates of growth rates and longevity of deep-sea corals in general.

フィッション・トラック熱年代に基づいた六甲地域の冷却・削剥史

Quantitatively estimating denudation is generally difficult because it essentially involves the removal and loss of materials in situ. The denudation rate of mountainous areas in Japan has commonly been studied from the volume of sediment in a basin or catchment. Nonetheless, the availability of these methods is constrained spatially by upstream area and temporally by depositional age. In the last few decades, thermochronometric methods that evaluate thermal history using radiometric-dating methods have been used to evaluate the denudation and tectonic history of orogenic belts around the world. The advantages of thermochronometric methods are that we can calculate the denudation rate at each sampling point and that combining multiple methods and/or target minerals enables us to calculate denudation rates in multiple periods. However, thermochronometric methods have been applied to areas with extraordinarily high denudation rates in island arc areas such as Japan. Thus, the effectiveness of thermochronometric methods for estimating denudation rates in island arc areas has not been demonstrated. We applied apatite and zircon fission-track thermochronometry to granitic rock samples collected from outcrops and a borehole to estimate the tectonic history of the Rokko area, southwest Japan. Previous studies suggested that the Rokko Mountains have been uplifted by active faulting along their northern and southern margins during the Rokko movements, a Quaternary tectonic movement in the Kinki district. However, the tectonic history of the Rokko area prior to 1 Ma has not been revealed due to a lack of prevalent geologic markers. We estimated average denudation rates in various periods based on apatite and zircon FT ages and previously reported radiometric ages. We obtained denudation rates at about 0.04-0.10 mm/yr after about 30 Ma, 0.05-0.7 mm/yr during 50-30 Ma, 0.7-4.0 mm/yr during 70-50 Ma. The denudation rate after the deposition of the Kobe Group (36.9-30.4 Ma) is estimated to be in the 0.01-0.1 mm/yr order, while bedrock uplift rate after about 1 Ma is estimated to be about 0.5 mm/yr. Thus, the tectonic activity of the Rokko Mountains area prior to 1 Ma has been relatively low.

About this title - Thermochronological Methods: From Palaeotemperature Constraints to Landscape Evolution Models

Thermochronology - the use of temperature-sensitive radiometric dating methods to reconstruct the thermal histories of rocks - has proved to be an important means of constraining a wide variety of geological processes. Fission track and (U–Th)/He analyses of apatites, zircons and titanites are the best-established and most sensitive methods for reconstructing such histories in the uppermost kilometres of the crust, over time scales of millions to hundreds of millions of years. The papers published in this volume are divided into two sections. The first section on ‘New approaches in thermochronology’, presents the most recent advances of existing thermochronological methods and demonstrates the progress in the development of alternative thermochronometers and modelling techniques. The second section, ‘Applied thermochronology’, comprises original papers about denudation, long-term landscape evolution and detrital sources from the European Alps, northwestern Spain, the Ardennes, the Bohemian Massif, Fennoscandia and Corsica. It also includes case studies from the Siberian Altai, Mozambique, South Africa and Dronning Maud Land (East Antarctica) and reports an ancient thermal anomaly within a regional fault in Japan.

Geology and radiometric 14C-, 36Cl- and Th-/U-dating of the Fernpass rockslide (Tyrol, Austria)

One of the largest mass movements in the Alps, the fossil Fernpass rockslide in the Northern Calcareous Alps (Tyrol, Austria), was dated absolutely for the first time. Three independent radiometric dating methods were applied to geologically individual sample sites and enabled a cross-checking of the results. Close to the scarp-front, rockslide-dammed torrent deposits indicate a 14C minimum age of at least 3380–3080 cal. yrs BP. The chronostratigraphic base of this backwater sequence has not been dated yet, but is assumed to date somewhat older into the middle Holocene. However, this coincides with two cosmogenic radionuclide 36Cl ages of sliding planes at the steep and rugged scarp. Exposure data thus obtained are 3400 ± 900 and 4800 ± 1200 yrs respectively with an arithmetic mean of 4100 ± 1300 yrs. Additional age data were acquired from post-depositional calcareous cements, which locally lithified the rockslide debris. These meteoric cements contain remarkably high Uranium total contents and yielded a 230Th/ 234U minimum age of about 4150 ± 100 yrs for the accumulation of the rockslide deposits. All dating data agree well and indicate that the Fernpass rockslide is of Subboreal age. Thus the intensively structured present morphology, characterised by the well-known cone-shaped Toma-hills and several lakes in the depressions, is indicative of primary rockslide morphology and clearly not shaped by late-glacial ice as assumed formerly.

Zircon Fission-Track Thermochronology and Applications to Fault Studies

Zircon is one of the most useful minerals used to unravel the Earth’s history recorded in rocks. After the success of etching fission tracks in zircon (Fleischer et al. 1964; Naeser 1969; Krishnaswami et al. 1974), early studies focused primarily on dating young volcanic horizons for stratigraphic purposes (e.g., Naeser et al. 1973; Hurford et al. 1976; Seward 1979; Gleadow 1980; Kowallis et al. 1986; Kohn et al. 1992). Subsequently, fission-track analysis of zircon has been extensively employed, along with other radiometric dating methods, such as U/Pb and (U-Th)/He techniques (e.g., Davis et al. 2003; Reiners 2005), to understand the thermochronology of rocks in a variety of geological settings: i.e., thermal history analysis of basement rocks for orogenic studies (e.g., Zeilter et al. 1982; Hurford 1986; Kamp et al. 1989; Sorkhabi 1993; Seward and Mancktelow 1994; Hasebe and Tagami 2001; Spikings et al. 2001), thermochronology using detrital zircon grains in sedimentary rocks for provenance analysis and thermal history analysis in or near faults, which will be highlighted below. In this present chapter, the thermal sensitivity of the zircon fission-track thermochronometry is reviewed in the context of laboratory and field studies. Then, laboratory procedures of the zircon fission-track analysis using the external detector method are outlined, as practiced in the fission-track laboratory of Kyoto University. For basic fundamentals of these fission-track analyses, including data analysis and graphical displays, see the chapter by Tagami and O’Sullivan (2005). Finally, as an example of recent geological applications of the technique, the results of zircon fission-track analysis of the Nojima fault zone, Japan, are presented. These rocks were the target of systematic drilling of an active fault system using five boreholes and a trench. Applications to other geological settings and the …

Visualizing Thermotectonic and Denudation Histories Using Apatite Fission Track Thermochronology

Thermochronology, the use of temperature-sensitive radiometric dating methods to reconstruct the time-temperature histories of rocks, has proved to be an important means of constraining a variety of geological processes. In general, different depths within the Earth’s crust are characterized by different temperature regimes and processes. Within the upper crustal environment, temperature can often be used as a proxy for depth, so that reconstructed cooling histories may reveal a record of rock movement towards the surface. That portion of this process which involves temperature variations within the uppermost ~150–200 °C of crustal depth has been the basis for the application of low temperature thermochronology to a range of interdisciplinary problems in the Earth Sciences. The last fifteen or so years have sparked widespread interest in this field and this proliferation has been driven in part by advances in analytical techniques, numerical modeling, and fundamental changes of perspectives on the significance of radioisotopic ages (e.g., McDougall and Harrison 1999; Gleadow et al. 2002a; Farley 2002). One area of rapidly growing interest, which has provided unprecedented insights in this regard, has been the quantification in time and space of surface processes and shallow crustal tectonism using low temperature thermochronology, often combined with complementary techniques structural analysis, geomorphic, numerical modeling, and cosmogenic isotope studies (e.g., House et al. 1998; Ehlers and Farley 2003; Belton et al. 2004; Ehlers 2005). One of the best established and most sensitive low temperature thermochronology methods available for reconstructing such histories in the upper ~3–5 km of the continental crust, over time scales of millions to hundreds of millions of years, is apatite fission track (AFT) thermochronology which responds to temperatures of typically <110 ± 10 °C. As for other thermochronological methods, fission track analysis involves a geological dating technique in which the …

A date for volcanic eruption inferred from a siltstone xenolith

We present a TL age determination of a heated siltstone xenolith found at Kueishantao, a volcanic island 10 km off the northeastern shoreline of Taiwan. Before this study, no reliable numeric age determination had been obtained for the volcanic rocks. Its age has long been desired due to its active tectonic environment. Previous studies of the other radiometric dating methods indicate a very young age for the eruption of this volcano, possibly later than 10 ka. However, reliable age is not allowed because it is younger than the lower dating limit. Our result shows a TL age of 7±0.7 ka for the lower part of the volcanic sequence, indicating that other volcanic eruptions occurred later than 7 ka. This finding suggests that the volcanic island, Kueishantao, has not ceased its igneous activity and is still active geologically.