Chemical Geology: Isotope Geoscience section最新文献

{"title":"Isotopic evidence on the age and origin of the Fraser Complex, Western Australia: a sample of Mid-Proterozoic lower crust","authors":"Ian R. Fletcher ,&nbsp;John S. Myers,&nbsp;Anthony L. Ahmat","doi":"10.1016/0168-9622(91)90021-N","DOIUrl":"10.1016/0168-9622(91)90021-N","url":null,"abstract":"<div><p>SmNd, RbSr and Pb isotopic data have been obtained for a variety of samples from within and around the Fraser Complex, a large (&gt; 400 × 30 km) composite body of metagabbro which is a major component of the Proterozoic Albany-Fraser Orogen.</p><p>Granites to the north and east of the complex and a granite sheet near its centre have SmNd model ages (<em>t</em>_DM) of ∼2000 to ∼ 2300 Ma, similar to values recorded in the western portion of the orogen. SmNd data for Fraser Complex gabbros scatter significantly on an isochron plot, but well-preserved igneous minerals extracted from one sample give 1291 ± 21 Ma with initial <em>ϵ</em>_<em>Nd</em>= -1.3 ± 0.2. RbSr for the biotite-rock pair gives a cooling age of 1268 ± 20 Ma with initial ⁸⁷Sr/⁸⁶Sr≈0.706. Slices cut from a mixed gneiss/ amphibolite zone of ductile deformation and retrogression along the western margin of the complex give a ∼ 1300-Ma Pb/Pb date for final tectonic emplacement. Intrusion, granulite-facies metamorphism and upper-crustal tectonic emplacement of the complex were probably all achieved within ≤ 30 Ma.</p><p>SmNd and RbSr characteristics of the western deformation zone suggest flushing by large volumes of fluid derived from a moderately depleted mantle source (ϵ_Nd ≈ + 2.4; ϵ_Sr, ≈ − 5 at 1300 Ma). The precursors to the Fraser Complex could have been derived from the same (or a similar) source at ∼ 1900 Ma.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 3","pages":"Pages 197-216"},"PeriodicalIF":0.0,"publicationDate":"1991-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90021-N","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76498805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oxygen isotope evidence for multi-stage hydrothermal alteration at a fossil slow-spreading center: the Silurian Trinity ophiolite (California, U.S.A. )","authors":"Christophe Lécuyer,&nbsp;Serge Fourcade","doi":"10.1016/0168-9622(91)90023-P","DOIUrl":"10.1016/0168-9622(91)90023-P","url":null,"abstract":"<div><p>The Trinity ophiolite consists of a widespread mantle unit (the Trinity Peridotite) and a thin crustal sequence ( ∼2 km) outcropping discontinuously. The well-exposed massifs of layered and isotropic gabbros, diabasic dikes and pillow lavas define a complete oceanic crustal sequence. The basalts, dikes and gabbros are characterized by retrograde metamorphic associations. Previous work has shown that the extent of alteration is directly correlated to the amount of circulating seawater and decreases downwards for increasing temperatures.</p><p>Oxygen isotopic compositions were measured on whole-rock samples and a few mineral separates across the ophiolite section. Clearly, hydrothermal alteration in the presence of seawater has introduced large variations of '80/'60 ratios with respect to those of the starting rocks whose composition is assumed to be typical of mantle-derived materials. The evolution of δ ¹⁸O-values as a function of depth is similar to the Oman example but there are some significant differences: with respect to the mantle reference composition, the upper section (pillow lavas) is '80 enriched up to 10.1‰. Low δ ¹⁸O-values down to +4‰ are recorded by some sheeted dikes, isotropic and cumulate gabbros. However, the Trinity ophiolite strongly differs from the Oman ophiolite by the presence of ¹⁸O-enriched rocks at deep levels of the ophiolite section.</p><p>Microthermometry on fluid inclusions from a few quartz-bearing samples and water/rock ratios inferred from previous Sr isotope data allow us to calculate a pattern of alteration temperatures consistent with a complex regime of water-rock interactions: low-temperature ( ∼ 110–170°C) exchange occurred pervasively through the pillow lava section but also irregularly affected deeper parts of the crust (isotropic and layered gabbros) in which a previous episode of high-temperature ( ∼ 300–390°C) interaction took place. Deep channelized penetration of seawater at low temperature could be related to the wider and deeper faulting pattern which characterizes slow-spreading centers. Such a low-temperature, off- axis interaction (pervasive in the upper section and heterogeneous at deeper levels) could destroy the δ ¹⁸) balance possibly established during the axial hydrothermal activity.</p><p>The oxygen isotope composition of hydrothermally-altered rocks in the Trinity complex is consistent with a δ ¹⁸O-value of 0 ± 2‰ for Silurian seawater.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 3","pages":"Pages 231-246"},"PeriodicalIF":0.0,"publicationDate":"1991-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90023-P","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73151428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Direct comparison of zeta calibration constants for fission-track dating by double-checking of two irradiation facilities with different degrees of neutron flux thermalization","authors":"Seong-Cheon Shin ,&nbsp;Susumu Nishimura","doi":"10.1016/0168-9622(91)90018-R","DOIUrl":"10.1016/0168-9622(91)90018-R","url":null,"abstract":"<div><p>Zeta (ζ) constants were determined using zircon, apatite and sphene age standards for a systematic calibration of fission-track dating. Identical crystals were double-checked in two facilities having significantly different degrees of neutron flux thermalization: Irradiation Pit-6 (IP-6) of the Korea Atomic Energy Research Institute (KAERI) TRIGA III reactor and the Graphite Pneumatic Tube (GrPn) of the Kyoto University Research Reactor (KUR-<em>1</em>) which have Cd ratios of 12.5 and ∼200, respectively, for Au. The final single weighted mean ζ baselines are given with errors (2σ) as: 324.5 ± 7.9 for SRM<em>612</em>, 110.9±2.7 for CN<em>1</em> and 118.8±2.9 for CN<em>2</em> from KAERI IP-<em>6</em>; and 333.7±8.5 for SRM<em>612</em>, 109.0±2.8 for CN<em>1</em> and 119.5 ± 3.1 for CN<em>2</em> from KUR GrPn. The final results from both facilities show anexcellent consistency in ζs for CN<em>1</em> and CN<em>2</em> and a discrepancy ( ∼2.8%) in SRM<em>612</em>-ζ values despite of a rough agreement within the error (2σ). Lower ratios (∼2.5–4%) of <em>ϱ</em>_d^CN1/<em>ϱ</em>_d^<em>SRM</em>612, <em>ϱ</em>_d^CN2/<em>ϱ</em>_d^SRM612 and <em>ϱ</em>_i^mineral/<em>ϱ</em>_{d^{<em>SRM</em>612}} in KAERI IP-<em>6</em> strongly imply such a decrease of <em>ζ</em>_{SRM6<em>l</em>2}.</p><p>The consistency in <em>ζ</em>_CN1 and <em>ζ</em>_CN2 in both facilities implies that the large difference in ²³²Th/²³⁵5U ratio between the mineral and CN<em>1</em> or CN<em>2</em> may not significantly affect thermal neutron dosimetry, even for apatite which has the largest difference of the ratio against dosimeter glasses. The larger (n,f ) reaction cross-section of ²³⁸U than that of ²³²2Th in epithermal and fast neutron energy regions also suggests that the difference of ²³⁸U /²³⁵U ratio as seen in glass SRM<em>612</em>, which has depleted U, may affect the thermal neutron dosimetry more significantly than that of ²³²Th/²³⁵U ratio regardless of Th/U ratios of the three minerals. Therefore, the discrepancy in <em>ζ</em>_SRM612 results mainly from the larger contribution of ²³⁸U fission induced by non-thermal neutrons to the thermal neutron dosimetry in the less thermalized KAERI IP-<em>6</em>. In consequence, the final <em>ζ</em>_{SRM6<em>l</em>1} from KAERI IP-<em>6</em> is significantly less precise. The final ζ baselines for CN<em>1</em> and CN<em>2</em>, obtained independently from both facilities, are to be recommended for accurate fission-track analyses in preference to the SRM<em>612</em>-ζ baseline, even in the well-thermalized facility, e.g. KUR GrPn.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 3","pages":"Pages 147-166"},"PeriodicalIF":0.0,"publicationDate":"1991-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90018-R","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76021824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism","authors":"Yemane Asmeroma ,&nbsp;Paul Damon ,&nbsp;M. Shafiqullah ,&nbsp;William R. Dickinson ,&nbsp;Robert E. Zartman","doi":"10.1016/0168-9622(91)90019-S","DOIUrl":"10.1016/0168-9622(91)90019-S","url":null,"abstract":"<div><p>We report a nine-point RbSr whole-rock isochron age of 70±3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ± 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO₂ content as low as 57 wt.%, are susceptible to complete resetting.</p><p>The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 3","pages":"Pages 167-173"},"PeriodicalIF":0.0,"publicationDate":"1991-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90019-S","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81232753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Contents volume 87, 1991","authors":"","doi":"10.1016/0168-9622(91)90027-T","DOIUrl":"https://doi.org/10.1016/0168-9622(91)90027-T","url":null,"abstract":"","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 3","pages":"Pages 279-280"},"PeriodicalIF":0.0,"publicationDate":"1991-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90027-T","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92116190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measurement of the radon-222 content of soil gas by liquid scintillation counting","authors":"David P. Genereux,&nbsp;Harold F. Hemond","doi":"10.1016/0168-9622(91)90025-R","DOIUrl":"10.1016/0168-9622(91)90025-R","url":null,"abstract":"<div><p>A method is described for measuring the ²²²Rn content of soil gas using a conventional liquid scintillation counter. Gas samples, collected in wetted ground-glass syringes, are equilibrated with a scintillation cocktail which is then expelled into a scintillation vial and counted. The method is straightforward and relatively fast (5–6 min. of operator's time per sample), and yields results having 95% confidence limits of ∼ ± 10% for samples containing ≥ 2·10⁴ Bq m⁻³ of ²²²Rn. The method is applied to a watershed near Bickford Reservoir in Massachusetts, U.S.A., where soil-gas ²²Rn content is found to be reasonably constant horizontally, but strongly and systematically increasing with depth, to &gt; 5·10⁴ Bq m⁻³ at soil depths of ∼ 1 m.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 3","pages":"Pages 265-275"},"PeriodicalIF":0.0,"publicationDate":"1991-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90025-R","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87175870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radium isotopes and 222Rn in shallow brines, Kharaghoda (India)","authors":"S. Krishnaswami,&nbsp;Ravi Bhushan,&nbsp;M. Baskaran","doi":"10.1016/0168-9622(91)90046-Y","DOIUrl":"10.1016/0168-9622(91)90046-Y","url":null,"abstract":"<div><p>The concentrations of Ra isotopes (²²⁴Ra, ²²³Ra, ²²⁸Ra and ²²⁶Ra) and ²²²Rn have been determined in brines from Kharaghoda, western India. The Ra isotopes concentrations in these samples are orders of magnitude higher than that reported in potable groundwaters. The ²²⁴Ra activities lie between 28 to 277 dpm per kg; about 4% to 96% of that expected from its production, calculated using ²²²Rn as a recoil flux monitor. The low [²²⁴Ra/²²²Rn] activity ratios are typical of less saline brines. Retardation factors for Ra in these brines, derived from the ²²²Rn-²²⁴Ra-²²⁸Ra system and based on a reversible exchange model, are in the range of about 0.3–114. These values are 3–4 orders of magnitude lower than that in potable groundwaters. The residence time of Ra in Kharaghoda brines is approximately one day. Our data suggest that in briny aquifers Ra is considerably less ‘particle-reactive’ than in potable groundwaters. The retardation factor for Ra shows a strong negative correlation with salinity. This anticorrelation suggests that salinity would play a crucial role in determining the mobility of Ra and its geochemical homologues through groundwater systems.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 2","pages":"Pages 125-136"},"PeriodicalIF":0.0,"publicationDate":"1991-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90046-Y","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90374976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Isotopic evidence of the depositional environment of Late Proterozoic stratiform barite mineralisation, Aberfeldy, Scotland","authors":"A.J. Hall ,&nbsp;A.J. Boyce ,&nbsp;A.E. Fallick ,&nbsp;P.J. Hamilton","doi":"10.1016/0168-9622(91)90044-W","DOIUrl":"10.1016/0168-9622(91)90044-W","url":null,"abstract":"<div><p>Sulfur, carbon and oxygen stable isotope analyses of sulfides, barite, quartz, magnetite and carbonate and initial ⁸⁷Sr/⁸⁶Sr ratios (<em>I</em>_Sr) of barite have been undertaken on representative samples from barite horizons mainly in the Foss sector of the Late Proterozoic, Middle Dalradian stratiform mineralisation, near Aberfeldy in the central Scottish Highlands. The main objective of the study was to use new isotope studies to test a SEDEX depositional model which involved mixing of reduced hydrothermal solution with contemporaneous anoxic and oxygenic seawater.</p><p>The assemblages studied were: massive pyrrhotite+pyrite +sphalerite+galena (scarce, and probably formed sub-seafloor only); barite +pyrite (common); and barite +magnetite (relatively uncommon). The sulfur isotope results (gd¹⁸<span>SCDT</span>) for the Foss samples, mainly from the open pit area, are: pyrrhotite and associated sulfides ( + 21 to + 24‰); pyrite (+ 27‰) with barite (+40‰); and barite (+35 to +38‰) with magnetite. Oxygen isotope analyses (δ¹⁸0_VSMOW) are: about + 14‰ for barite with pyrite and about + 16‰ for barite with magnetite. The variation in <em>I</em>_Sr is small; <em>I</em>_Sr being about 0.715 for barite with pyrite and about 0.714 for barite with magnetite. <em>δ</em>¹⁸O of magnetite is around +7.5‰.</p><p>The observed assemblages and the analytical results are considered to be reasonably consistent with the mixing model but with oxygenic seawater playing a very minor and localised role. The massive sulfide has inherited a <em>δ</em>³⁴S value of about +22‰ from hydrothermal sulfide. The end-member isotopic compositions of the sulfate resulting from mixing are likely to have been: sulfate from hydrothermal sulfide oxidised using oxygen dissolved in seawater, <span><math><mtext>δ</mtext><msup><mi></mi><mn>34</mn></msup><mtext>S</mtext><mtext>=+22‰</mtext></math></span> and <span><math><mtext>δ</mtext><msup><mi></mi><mn>18</mn></msup><mtext>O</mtext><mtext> = +25±5‰</mtext></math></span> and seawater sulfate, <span><math><mtext>δ</mtext><msup><mi></mi><mn>34</mn></msup><mtext>S</mtext><mtext> = +40‰</mtext></math></span> and <span><math><mtext>δ</mtext><msup><mi></mi><mn>18</mn></msup><mtext>O</mtext><mtext> = +14‰</mtext></math></span>. A plot of <em>δ</em>³⁴S against <em>δ</em>¹⁸O for barite sulfate gives a line with a correlation coefficient of 0.766 (<em>n</em>=10), which is significant above the 99% level although most points cluster close to the seawater end of the expected variation. The <em>I</em>_Sr values of the barite suggest that the dominant source for this Sr was from the hydrothermal solution. There is no evidence for a significant contribution to sulfide by bacterial reduction of sulfide and this lack of a geochemical barrier of bacteriogenic sulfide could account for the dispersal of hydrotherma","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 2","pages":"Pages 99-114"},"PeriodicalIF":0.0,"publicationDate":"1991-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90044-W","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83190717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Argon isotope and halogen chemistry of phlogopite from South African kimberlites: a combined step-heating, laser probe, electron microprobe and TEM study","authors":"D. Phillips","doi":"10.1016/0168-9622(91)90043-V","DOIUrl":"10.1016/0168-9622(91)90043-V","url":null,"abstract":"<div><p>Argon isotopic analyses were undertaken on phlogopite from the Swartruggens kimberlite dyke and a Premier kimberlite (1200 Ma) peridotite xenolith. Groundmass phlogopite from Swartruggens yields a plateau age of 145.0± 0.4 Ma, consistent with previous age determinations. Phlogopite phenocrysts from Swartruggens and macrocrysts from the Premier xenolith yield complex age spectra, with anomalously old ages, attributed to incorporation of excess radiogenic argon.</p><p>Laser probe analyses on single phlogopite grains reveal systematic zonations in excess Ar and CI concentrations across (001) cleavage surfaces. One Premier macrocryst exhibits ages in excess of 2.3 Ga and CI levels of 1600 ppm at its centre. These values decrease systematically to 1.2 Ga and 1300 ppm Cl along grain margins. Similar results were obtained from a single Swartruggens phenocryst, which exhibits a range in values of 340—800 Ma and 300—1300 ppm Cl. A second Swartruggens phenocryst is characterised by smaller variations in age (140–230 Ma) and CI content (390–470 ppm ). Fluorine concentrations, determined by electron microprobe, are relatively constant or increase slightly towards grain edges. The laser probe profiles cannot be reconciled with the step-heating results, probably due to phlogopite degradation during <em>invacuo</em> furnace heating.</p><p>Transport of Ar and CI in kimberlitic phlogopite appears to be dominated by radial diffusion (cylindrical geometry). The variety of laser probe profiles obtained suggests that Ar and Cl diffusion is governed by factors such as lattice diffusion, diffusion anisotropy, and structural defects, which reduce the effective radii of diffusion and may impart a component of pipe diffusion.</p><p>It is suggested that the xenolith phlogopite entrapped excess ⁴⁰Ar and halogens in the mantle lithosphere, in response to elevated Ar and halogen fluid pressures. Swartruggens phenocrysts appear to have crystallised from a volatile-rich kimberlite melt. Subsequent magma devolatilisation prior to emplacement reduced Ar partial pressure and CI content. Possible reasons for enhanced F levels after devolatilisation include increased F solubility in the kimberlite melt, extraction of F from infiltrating hydrothermal fluids and local heterogeneities in fluid composition.</p><p>The final distributions of Ar, Cl and F in kimberlitic phlogopite are variably dependent on several parameters, including local fluid composition, timing of melt devolatilisation, diffusion/ exchange mechanisms, and mineral composition.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 2","pages":"Pages 71-98"},"PeriodicalIF":0.0,"publicationDate":"1991-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90043-V","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83356846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the calculation of isochrons","authors":"Lars Kullerud","doi":"10.1016/0168-9622(91)90045-X","DOIUrl":"10.1016/0168-9622(91)90045-X","url":null,"abstract":"<div><p>Most isochrons are calculated with well established methods that account for the analytical uncertainties in both <em>x</em> and <em>y</em>. The results of the calculations are slope, intercept, uncertainties for these values, and a measure of line quality (<em>MSWD</em>). The dependence of these values on analytical uncertainties is discussed, and it is shown that the commonly used values for analytical precision are too inaccurate to give reliable results. These problems generally do not cause significant changes in the slope (age), but is is shown that such situations may be possible. Recommendations are given on the presentation and calculation of isochron data.</p></div>","PeriodicalId":100231,"journal":{"name":"Chemical Geology: Isotope Geoscience section","volume":"87 2","pages":"Pages 115-124"},"PeriodicalIF":0.0,"publicationDate":"1991-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-9622(91)90045-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78771973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}