(U-Th)/He dating

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Helium trapping in apatite damage: insights from (U Th Sm)/He dating of different granitoid lithologies

Helium trapping in apatite damage: insights from (U Th Sm)/He dating of different granitoid lithologies

Recanati, A. and Gautheron, C. and Barbarand, J. and Missenard, Y. and Pinna-Jamme, R. and Tassan-Got, L. and Carter, Andrew and Douville, E. and Bordier, L. and Pagel, M. and Gallagher, K. (2017) Helium trapping in apatite damage: insights from (U-Th-Sm)/He dating of different granitoid lithologies. Chemical Geology 470 , pp. 116-131. ISSN 0009-2541.

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Quantifying exhumation at the giant Pulang porphyry Cu Au deposit ssing U Pb He dating

Quantifying exhumation at the giant Pulang porphyry Cu Au deposit ssing U Pb He dating

In general, three to five single zircon and apatite grains were analyzed for each sample. The detailed results are given in Electronic Appendix Tables A3 and A4, and a summary with the weighted mean age for each sample is provided in Table 2. Overall, 32 single-grain zircon (U-Th)/He ages, varying from 167.1 ± 9 to 86.7 ± 4.7 Ma, were obtained from the samples. Notably, the age variations between single crystals from some samples (e.g., PLZK2812-1196.1m, PLZKE002- 3.5m) exceed the analytical precision of <6%. In addition, 36 single-grain apatite (U-Th)/He ages, ranging from 156 ± 16.2 to 24.3 ± 0.9 Ma, were obtained. Similarly, there are also large intrasample age variations, which are beyond the ana- lytical uncertainty of <2.5%. In order to avoid the potential influence of outliers on averaging dates of each sample, the Chauvenet criterion was utilized. This method has been used for outlier detection in previous studies (e.g., Fitzgerald et al., 2006; Liu et al., 2017). Consequently, seven single-grain zir- con (U-Th)/He ages and nine single-grain apatite (U-Th)/He ages that failed the Chauvenet’s criterion test were excluded from the determination of the mean and weighted mean ages (Electronic App. Tables A3, A4). Although the single-grain ages are relatively scattered, the weighted mean zircon and apatite (U-Th)/He ages generally display a positive correla- tion with elevation (Table 2; Fig. 4), allowing us to estimate long-term erosion rates of the Pulang complex. Using a least squares regression routine, we obtained two regression lines to fit the age-elevation data. The two lines predict two differ- ent exhumation processes, with an apparent erosion rate of 33.6 m/m.y. during the interval of 142 to 110 Ma and a rate of 15.3 m/m.y. from 106 to 54 Ma.
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Iron Oxide Geochronology to Constrain the Formation of Soils and Paleosols

Iron Oxide Geochronology to Constrain the Formation of Soils and Paleosols

ments (Reiners et al., 2014), and thermochronology (Farley and Flowers, 2012). In this thesis, I apply the goethite and hematite (U-Th)/He techniques to soils and pa- leosols and explore new phases and analytical methods to broaden their application. Chapters II and III are an exploration of the capabilities of the goethite (U-Th)/He method and its applicability to paleosols. In these chapters, I combine (U-Th)/He dating with measurements of cosmogenic 3 He to study when cosmic-ray exposure occurred in goethite pisoliths of the Bohnerz deposits of Central Europe. In Chapter II, I measure both (U-Th)/He ages and 3 He concentrations in pisoliths of a paleosol of the Bohnerz deposits to show that it formed over more than 25 Ma. Since the pa- leosol has been covered and shielded from cosmic rays, cosmogenic 3 He in goethite pisoliths represents paleo-exposure, which occurred before burial. In Chapter III, I apply this approach to outcrops of Bohnerz deposits in Germany and Switzer- land. Goethite (U-Th)/He ages demonstrate that Bohnerz deposits formed from at least 55 Ma to 2 Ma, while it was previously assumed that they formed in the Late Cretaceous-early Eocene (e.g. Borger, 1990). I also map out the paleo-extent of the Bohnerz deposits to show that they represent a widespread mode of continental weathering. Since this process occurred over more than 50 Ma, the Bohnerz de- posits represent a significant archive of continental climate throughout most of the Cenozoic.
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Cosmogenic ³He and ²¹Ne Dating in Accessory Mineral Phases

Cosmogenic ³He and ²¹Ne Dating in Accessory Mineral Phases

Helium extraction is performed by thermal degassing in a double-walled resistance furnace or by Nd-YAG laser heating of sample loaded in a platinum packet. In the resistance furnace, samples are heated to 1500°C for 20 minutes following standard procedures (Patterson and Farley, 1998). However in many cases a variant of the laser method developed for (U/Th)- He dating is preferred because grains can be recovered after He outgassing for additional analyses or to demonstrate sample purity (House et al., 2000). For cosmogenic dating, large (6 x 3 mm) platinum tubes are used, which can typically accommodate up to 35 mg of zircon or 25 mg of apatite. Previously degassed capsules are loaded with sample and placed into wells in a copper planchet. To minimize thermal conduction to the copper, the capsules are placed on top of small lengths of tungsten wire. The capsules are heated to about 1200°C by rastering the laser beam across the surface of the capsule. Although the exact temperature achieved by each sample is not monitored, complete degassing is verified by re-extraction steps at the same temperature.
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U Pb and Th Pb dating of apatite by LA ICPMS

U Pb and Th Pb dating of apatite by LA ICPMS

U atoms. These induced fission events are then recorded in an external detector (typically low U muscovite) to give a map of uranium distribution (Gleadow, 1981). This irradiation step is one of the disadvantages of the external detector method. However U concentrations in apatite fission track dating can also be determined by LA-ICPMS (Hasebe et al., 2004) with 44 Ca typically used as an internal standard. Although modification of the analytical protocol to include a peak jump to 44 Ca would be prohibitively slow on a magnetic sector instrument such as the one used in this study, U concentrations could be easily determined on a spot adjacent to the site of the U-Th-Pb analysis. Combining U-Th-Pb apatite dating by LA-ICPMS with the apatite (U-Th)/He thermochronometer is slightly more challenging as (U-Th)/He dating is performed on whole crystals, not polished grain mounts. However several studies have undertaken U-Pb detrital zircon dating by LA-ICPMS on the exterior of unmodified zircon grains (e.g., Rahl et al., 2003), and modifying this procedure for apatite double dating is entirely possible. Combining U-Th-Pb apatite dating with Nd isotopic analysis (e.g., Foster and Vance, 2006) is also feasible. This would yield similar information to combined U-Pb and Hf isotopic studies on zircon, with the U- Th-Pb age data and the Nd isotopes yielding information concerning the apatite crystallization age and melt source respectively.
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Geochemistry and Geochronology of Peraluminous High K Granitic Leucosomes of Yaoundé Series (Cameroon): Evidence for a Unique Pan African Magmatism and Melting Event in North Equatorial Fold Belt

Geochemistry and Geochronology of Peraluminous High K Granitic Leucosomes of Yaoundé Series (Cameroon): Evidence for a Unique Pan African Magmatism and Melting Event in North Equatorial Fold Belt

Two samples of leucosomes (OL3A & OL3B) were se- lected for U-Th-Pb monazite ages. These samples were chosen because they are more enriched in monazite crys- tals than other samples. The analyzed monazite crystals are of two main types: 1) globular or ovoid crystals, often crackled with no optical zoning (Figures 12(a) and (b)); 2) prismatic crystals, also with no optical zoning, but spotted by opaque granules which form inclusions in biotite flakes (Figures 12(b) and (c)). No systematic core-to-rim optical age zonation of were observed. This observation implies that monazite crystallize from melt- ing liquid. This allows the calculation of ages composed of several single analyses by regression through zero 34 and of weighted means 41. Chemical Th-U-Pb ages (Tables 4 and 5) have been gotten by Electron micro- probe analysis (EMP). Two groups of ages, correspond- ing probably to the two events of monazite crystallisation, are recognised in the diagrams of mineral chemistry of monazite element vs Th-U-Pb chemical ages (Figures 13 and 14). The first event (younger) occurs at around 600 Ma and the second (older) at around 660 Ma. The ana- lysed monazite age data are compared in the PbO vs ThO 2 * diagram (Figure 15(a)) of Suzuki et al. 46. On
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U–Th isotopic microanalysis of zircon reference materials and KBSI working standards

U–Th isotopic microanalysis of zircon reference materials and KBSI working standards

Zircon UTh isotopic analyses were carried out at the KBSI using a Plasma II MCICPMS (Nu Instru- ments) equipped with an NWR193-nm ArF excimer laser ablation system (ESI). Typical laser ablation and ICPMS parameters are summarized in Table 1. Signal intensities were measured with Faraday collectors (for 238 U and 232 Th) and ion counters (for 230 Th and 228 mass) simultaneously. The raw data were proc- essed using Iolite 2.5 running within Igor Pro 6.3.5.5 software (Paton et al. 2011). The activity ratios were calculated using the decay constants proposed by Steiger and Jäger (1977) (for 238 U and 232 Th) and Cheng et al. (2013) (for 230 Th).
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Contrasting Mesozoic evolution across the boundary between on and off craton regions of the South African plateau inferred from apatite fission track and (U Th Sm)/He thermochronology

Contrasting Mesozoic evolution across the boundary between on and off craton regions of the South African plateau inferred from apatite fission track and (U Th Sm)/He thermochronology

The data presented here, combined with previously published low-temperature thermochronology data sets, provide evidence that, while the center of the Kaapvaal Craton has remained at relatively low temperatures ( < 60°C) since the end of the Carboniferous, the craton margins and off-craton regions have experienced younger Mesozoic cooling. The thermal history models suggest that interior craton samples underwent their main cooling phase between 600 and 400 Ma, which is coeval with the Pan-African Orogeny. Although only two samples de fi ne this preserved Paleozoic history, they are immensely important, as until now, AFT and AHe data have shown that parts of the elevated cratonic interior and its margins were signi fi cantly eroded during the Mesozoic [Stanley et al., 2013, 2015; Flowers and Schoene, 2010; Tinker et al., 2008]. Diamond- bearing gravels unconformably overlying the Transvaal Supergroup rocks ~30 km N and NW of sample V- 10 have previously been interpreted as post-Gondwana drainage deposits [e.g., Partridge and Maud, 1987]. However, a reinterpretation of these gravels based on their lithofacies and age dating from inclusions in dia- mond and zircon suggest that the gravels are most likely semilithi fi ed paleoeskers associated with the degla- ciation of the Dwyka ice sheet during the Permian to Carboniferous [de Wit, 2016]. The preservation of these features and presence of only limited remnants of Ecca Group sediments [Beukes et al., 1999] support the pro- posal that this part of the craton was only covered by a thin layer of Karoo sediments and did not experience signi fi cant erosion over the last 300 Ma (Figure 9).
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Th-U-total Pb timing constraints on the emplacement of the granitoid pluton of Stolpen, Germany

Th-U-total Pb timing constraints on the emplacement of the granitoid pluton of Stolpen, Germany

In general, two stages of granite emplacement within the Saxo-Thuringian and Moldanubian zones can be distinguished. Förster and Romer (2010) con- cluded that igneous activity in the Saxo-Thuringian Zone, including the northern and northwestern part of the Bohemian Massif, occurred at 335–320 Ma and 305–280 Ma. Some of the plutons, e.g. the granitoid pluton of Karkonosze, formed over several My, with the oldest rocks from this intrusion dated at 319–320 Ma (U-Pb in zircon, Žák et al. 2013), and the youngest at 302 ± 4 Ma (U-Pb in zircon, Kusiak et al. 2014). Finger et al. (2009) and Siebel et al. (2003) studied the Moldanubian part of the Bohemian Massif and also distinguished two major intrusive events; one more vo- luminous between 328–320 Ma, and the second one, less voluminous, between 317–310 Ma. Moreover, Finger et al. (2009) subdivided Variscan granitoid in- trusions into five groups of granite belts characterized by slightly different ages, geotectonic settings and magma generation mechanisms. The oldest are: “North Variscan Granite Belt”, “Central Bohemian Granite Belt” and “Durbachitic Granites”, with ages of ca. 330 to 350 Ma, 360 to 335 Ma and 335 to 340 Ma, re- spectively. Intrusions with a younger age (330 to 310 Ma) include the south-western sector of the Bohemian Massif, and the granites from the western Erzgebirge and Fichtelgebirge. According to Finger et al. (2009) they form a coherent plutonic belt (“Saxo-Danubian Granitic Belt”), formed most probably due to the de- lamination of lithospheric mantle (Bird 1979). The fifth group, involving the youngest granites located in the Sudetes, is called the “Sudetic Granite Belt” (in- cluding e.g., Karkonosze Massif, Strzegom-Sobotka Massif, Strzelin Massif and Kłodzko-Złoty Stok Mas- sif; Mazur et al. 2007) and is dated at ca. 315 to 300 Ma. Gerdes et al. (2003) reported a bimodal timing of magmatism in the South Bohemian Massif, with the first pulse at 331–323 Ma (with a higher mantle input) and the second, less significant, at 319–315 Ma. Ac- cording to Siebel et al. (2010), one of the youngest magmatic impulses in the Bohemian Massif was the Fichtelgebirge intrusive complex, with U-Pb zircon ages ranging from 291.2 ± 6.4 Ma to 298.5 ± 3.9 Ma for different types of granites comprising the intrusion. Late-Variscan granitoids from the Erzgebirge fall within the older group of intrusions (Romer et al. 2010), whereas the younger magmatic event is ab- sent. The ages of the amphibole-bearing granitoids
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Optimum Heavy Water Percentage in Moderator for a Th-Pu-U Fueled Nuclear Reactor

Optimum Heavy Water Percentage in Moderator for a Th-Pu-U Fueled Nuclear Reactor

Abstract- A Monte-Carlo parametric study was carried out to investigate the nuclear properties of Th-Pu-U fueled model of the LR-0 reactor when moderated by mixtures of heavy/light water at molecular ratios ranging from 0% up to 100% D2O at increments of 10% in D2O. The mass of control rods needed to make the reactor critical and the potential reactivity in heavy water were tallied at the 11 heavy water percentage moderators being studied. It was found that the changes in these tallied parameters with heavy water percentage in moderator were not monotonic. Very large negative reactivity was found at 90% heavy water moderator. Index Terms- Mixed water moderator, Nuclear reactor, LR-0, Heavy water
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The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U Th Sm)/He thermochronology

The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U Th Sm)/He thermochronology

Multiple single-grain (U-Th-Sm)/He analyses were performed on a subset of 16 samples that were chosen based on the high quality of the apatite separates and optimal geographical location for the study (Table 2). Between 5 and 21 single-grain ages were determined for each sample in an attempt to quantify and utilize the intersample grain date dispersion (see below). Details on analytical techniques can be found in Text S4. Mean AHe ages, uncorrected for alpha ejection, range from 55.8 ± 31.34 to 120.6 ± 31.4 Ma, and alpha ejection corrected ages [after Farley et al., 1996] range from 74.0 ± 43.9 to 156.9 ± 40.9 Ma. Although “ mean ” AHe sample ages provide a useful frame of reference for comparison with AFT ages and the wider geological context, they do not necessarily correspond to a speci fi c geological event at that time. In a similar manner to an AFT age, an AHe age is a product of a thermal history that is initially unknown. Depending on the form of this thermal history and the chemical and physical properties of individual apatite grains, mean AHe ages can be associated with large degrees of single-grain age dispersion. Dispersion (standard deviation of age/mean age) is large for samples in our data set, ranging from 12 to 56%. As thermal diffusion of 4 He dominates at elevated temperatures [Brown et al., 2013], the style of thermal history experienced by a sample will almost always lead to an over- correction of the 4 He age using a single alpha-correction factor [Farley et al., 1996; Meesters and Dunai, 2002a, 2002b; Herman et al., 2007; Gautheron et al., 2012]. This effect may be a contributing cause of some of the cor- rected AHe ages being older than their corresponding AFT age (Figure 3c) and the magnitude of single-grain age dispersion (Figure 4 and Text S5). However, as the interaction between alpha ejection, radiation damage effects, and He diffusion remains poorly understood, we have chosen to quote raw, uncorrected, AHe ages and we deal
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Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy

Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy

The measured 21 Ne/ 22 Ne ratio in NWA 7034 is at the lower limit of the range observed in stony meteorites (24). Combined GCR and SCR irradiation, as has been observed in some shergottites and ordinary chondrites with small recovery masses ( 39 , 40 ), could explain the dis- parate results obtained from 3 He, 21 Ne, 22 Ne, and 38 Ar. However, NWA 7034 would be required to come from the surface of a sufficiently large meteoroid such that it is irradiated by SCRs on the surface and receives secondary neutrons at epithermal or thermal energies from the back side to produce 80 Kr and 82 Kr by neutron capture on 79 Br and 81 Br, re- spectively. This is problematic because most large meteorites do not pre- serve their SCR record because of ablation during passage through Earth ’ s atmosphere ( 41 ). If solely GCR production is considered, then an irradiation location in either a small meteoroid (<10 cm) or at depth in a larger meteoroid (>50 cm) can reproduce the measured 21 Ne/ 22 Ne ratio (fig. S3) ( 10 ). However, irradiation in a small meteoroid does not yield concordant CRE ages. For example, a shielding depth of 6.6 to 6.8 cm in a meteoroid with a radius of 7 cm reproduces the 21 Ne/ 22 Ne ratio, but the resulting CRE ages are 2.55 ± 0.26, 4.82 ± 0.48, and 6.58 ± 0.66 Ma for 3 He, 21 Ne, and 38 Ar, respectively, assuming a 10% un- certainty on production rates. Irradiation at the center of a meteoroid with radius >120 cm reproduces the 21 Ne/ 22 Ne ratio and yields CRE ages with a relative SD of ~10% or less, comparable to the uncertainties on GCR production rates. For example, the best-fit irradiation history is at a depth of 280 to 284 cm in a meteoroid with a radius of 300 cm, which yields 21 Ne/ 22 Ne = 0.792 Ma and 3 He, 21 Ne, and 38 Ar exposure ages of 263 ± 26, 252 ± 25, and 256 ± 26 Ma, respectively. Such an extended transit duration is inconsistent with that of other martian me- teorites and is older than the U-Th-Sm/He ages of 135 ± 6 and 113 ± 4 Ma but could reflect pre-ejection irradiation after brecciation, followed
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Application of Multivariate Statistic of U, Th and Pb Concentrations and Pb Isotopic Signatures in the Assessment of Geogenic and Anthropogenic Sources in a U Mineralized Area

Application of Multivariate Statistic of U, Th and Pb Concentrations and Pb Isotopic Signatures in the Assessment of Geogenic and Anthropogenic Sources in a U Mineralized Area

DOI: 10.4236/gep.2019.76001 7 Journal of Geoscience and Environment Protection Figure 2 shows the score plot of the first two components (PC1 and PC2) for water, sediment and orthogneiss samples. The score of a sample represents the contribution of each variable measured and its respective weights to the charac- teristics of the sample. Sediment and rock samples are grouped around the ori- gin of the diagram, showing little difference from each other, which shows the geogenic character of the sediments, since in the process of weathering they did not undergo enrichment, i.e. , anthropic influence. Sample P19S stands out from this group. Its high score values of PC1 and PC2 suggests enrichment of U and Th whose increase in concentration leads to an increase in the score value for the score of the samples in each component. Also noteworthy is the sample P35S with positive score value of PC1 and negative score value of PC2. In this case, the sample is enriched in U rather than Th, being the U enrichment due to anthrop- ic influence. The water samples stand out from the group with negative score values for both PC1 and PC2. This means that, in general, the values of the va- riables for this matrix are low, which is a reflex of the low solubility of U, Th and Pb species (and their isotopes) in water. Samples P22AP is enriched in these spe- cies while P18A is enriched in Th. Samples P22AP and P18AP stand out from the rest of the groundwater samples, resembling the sediment and orthogneiss group of samples, probably because their isotopic signatures are under the geo- genic influence of the orthogneiss.
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Do U/Pb SHRIMP Dating and Pb Stepwise Leaching (PbSL) Analyses Confirm the Lack of Precambrian Basement Outcrops in Thailand?

Do U/Pb SHRIMP Dating and Pb Stepwise Leaching (PbSL) Analyses Confirm the Lack of Precambrian Basement Outcrops in Thailand?

mines the source area of the protoliths for the gneiss to be Paleoproterozoic. The age information of provenance given by the upper intercept of the U/Pbdiscordia is slightly older for the history of the zircon minerals, also pointing to the Paleoproterozoic. The cooling history of the Muang Pan gneissis documented by Rb-Sr and K-Ar dating on micas presented in Table 2 and Table 3. Rb-Sr analyses on muscovite-WR yielded an age of 357 ± 1 Ma considered to reflect the 500 ˚C ± 50˚C cooling ( [20]). The Rb-Srbiotite-WR reference line led to an age of 346 ± 0.2 Ma, which is interpreted as cooling below 300 ˚C ± 50˚C ( [20]). K-Ar datingon muscovite yielded 352.2 ± 7 Ma and 352.0 ± 7 Ma for biotite, respectively. These ages are considered to document the cooling be- low 425 ˚C for muscovite ( [21]) and 300 ˚C ± 50˚C for biotite [22], respectively. In sum, all mica data indicate rapid cooling in the Early Carboniferous time, around 357 to 346 Ma. This cooling is most probably related to tectonic activities like uplift and exhumation.
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Logarithmic asymptotics in Queueing Theory and Risk Theory

Logarithmic asymptotics in Queueing Theory and Risk Theory

In queueing networks service rates at switches are often fixed. Most of the m odehng effort focuses on developing stochastic models which exhibit phenom ena found in data-sets. One such phenom ena is long range dependence, this is where correlations w ithin a traffic source decay in time, t, more slowly than ex p (-iC '), for some positive constant C. Long range dependence has been of interest to teletraffic engineers since claims have been made th a t it is found in certain data-sets (see Leland et. al [42], Crovella and Bestavros [9], and Beran et al. [2]), leading to the suggestion of fractional Brownian motion, which exhibits long range
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Die priesterskap van die gelowiges soos Calvyn dit gesien het

Die priesterskap van die gelowiges soos Calvyn dit gesien het

D a t wij d a a rto e g eh e el onbekw aam zijn, d a t zulks e c h te r n ie t aan de geboden, m aar aan ons ligt. De W et is heilig, zij m oet niet alleen naar de le tte r , m a a r n a a r d e n g e e st g e h o u d e n w o rd e n ; wij d a a re n te g e n zijn vleeschelijk, verkocht onder de zonde. D at m oet bij ons vaststaan, dat wij v o lstrek t in overeenstem m ing m et de W et m oeten zijn, en juist daarom h eb b e n wij ons aa n C hristus, h e b b e n wij ons aa n Z ijne genade vast te houden, en zoo zullen wij door Zijnen G eest, naar Zijne belofte, wandelen aan Zijne hand en naar Zijne raad, in eene door H em vervulde Wet, zoo dat wij daarbij zondaars blijven en alleen Zijne heiligmaking roeme.
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Characteristics and origins of breccias in a volcanichosted
alkalic epithermal gold deposit, Ladolam,
Lihir Island, Papua New Guinea

Characteristics and origins of breccias in a volcanichosted alkalic epithermal gold deposit, Ladolam, Lihir Island, Papua New Guinea

In the preliminary analyses of the nine samples, three (Lmst 1, 6 and 7) had the required U, Th and Pb levels, were free of inclusions and were homogenous or had homogenous zones that were easily extractable. Of these three samples, two (Lmst 6 and 7) had more than 2% calcite and are suspected to have undergone diagenetic alteration. Although alteration is a problem in Lmst 6 and 7, they were submitted for U-Th dating along with unaltered Lmst 1, in the hope of extracting maximum ages. Two sub-samples were analysed from Lmst 6 to assess within-sample age variability.
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Extensional faulting on Tinos Island, Aegean Sea, Greece: how many detachments?

Extensional faulting on Tinos Island, Aegean Sea, Greece: how many detachments?

Miocene detachments and a characteristic feature of these footwalls is that they cool rapidly as they are dragged toward the surface. Therefore low-temperature thermochro- nology is a powerful tool for establishing cooling and slip rates and the timing of the detachments. Zircon and apatite fission track (ZFT and AFT) and (U-Th)/He (ZHe and AHe) data, as well as 40 Ar/ 39 Ar mica ages have been used to constrain the timing, speed and footwall cooling rates of major Aegean extensional detachments. For the Messaria, Naxos/Paros, Mykonos, Vari and Simav detachments (Figure 1) reported time-averaged slip rates are >5–8 km Ma 1 [John and Howard, 1995; Ring et al., 2003a, 2003b; Kumerics et al., 2005; Brichau et al., 2006, 2007; Thomson and Ring, 2006]. These five detachments are associated with huge syntectonic granites that intruded into their foot- walls. The only so far known extensional fault that slipped at a distinctly smaller rate is the Pliocene/Recent Kuzey detachment in western Turkey (Figure 1) with a rate of 2 km Ma 1 [Gessner et al., 2001].
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Conversion of U 238 and Th 232 Using a Fusion Neutron Source

Conversion of U 238 and Th 232 Using a Fusion Neutron Source

In any operating nuclear reactor containing U-238, some plutonium-239 will accumulate in the nuclear fuel due to continuous neutron capture by U-238 followed by two-beta decays. Plutonium present in reactor fuel can ab- sorb neutrons and fission just as U-235 can. Fission of plutonium-239 provides about one-third of the total energy produced in a typical commercial nuclear power plant. Spent nuclear fuel commonly contains about 0.8%

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Thermochronology of mineral grains in the Red and Mekong Rivers, Vietnam: provenance and exhumation implications for Southeast Asia

Thermochronology of mineral grains in the Red and Mekong Rivers, Vietnam: provenance and exhumation implications for Southeast Asia

close to the mouths of the Mekong and Red Rivers can be used to make general observations about the history of exhumation on a regional scale within the current drainage basins (Figure 11). The U-Pb ages measured from zircon grains constrain the timing of cooling below 750°C, corresponding to igneous crystallization. Because there is a wide range of these ages in each basin we infer that the crust in each drainage was formed in a series of events spread over the last 2500 my, but this tells us little about when these rocks were exhumed. Instead the mica Ar-Ar and fission track methods can be used to get a regional picture of exhuma- tion. Following the guidelines of Brandon [2002] and Ruhl and Hodges [2005] such estimates are much more accurate for the Red River where the number of apatite fission track analyses is higher (67) and the exhumation history is simpler than the larger, more tectonically diverse Mekong drainage. Zircon fission and Ar-Ar mica age analyses are just below but close to the 50 grain threshold of Ruhl and Hodges [2005] for the Red River, but can only provide a poorly constrained image of the Mekong. [ 36 ] Ar-Ar mica ages in both basins fall approxi-
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