scholarly journals Hafnium isotope composition of zircon from the Kondyor clinopyroxenite-dunite massif (Khabarovsk territory, Russia)

2019 ◽  
Vol 486 (5) ◽  
pp. 588-592
Author(s):  
I. Yu. Badanina ◽  
E. A. Belousova ◽  
K. N. Malitch
Keyword(s):  
Isotopic Composition ◽  
Mantle Source ◽  
Siberian Craton ◽  
Isotope Composition ◽  
Subcontinental Lithospheric Mantle ◽  
Basement Rocks ◽  
Magma Sources ◽  
Hf Isotopic Composition ◽  
T Values ◽  
First Time

This study evaluates for the first time Hf-isotope characteristics of zircon from dunite of the Kondyor massif, which is closely related to an economic platinum placer deposit. The significant range in εHf(t) values (from -8.4 ± 0.8 to 10.5 ± 1.3) in Mesozoic zircons indicates the interaction of a ‘juvenile’ mantle source with distinct magma sources, equivalent to a subcontinental lithospheric mantle and/or a continental crust. The peculiarities of the Hf-isotopic composition of Precambrian zircons (εHf(t) from -2.3 to +0.3) is consistent with their xenogenic origin and inheritance from basement rocks of the Siberian Craton.

scholarly journals Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12 and CFC-113 isotopologues

2020 ◽  
Author(s):  
Max Thomas ◽  
Johannes C. Laube ◽  
Jan Kaiser ◽  
Samuel Allin ◽  
Patricia Martinerie ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotope ◽  
Ozone Depletion ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Isotopic Fractionation ◽  
Base Case ◽  
Model Base ◽  
The Difference ◽  
First Time

Abstract. We present novel measurements of the carbon isotope composition of CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CF2ClCFCl2), three atmospheric trace gases that are important for both stratospheric ozone depletion and global warming. These measurements were carried out on air samples collected in the stratosphere – the main sink region for these gases – and on air extracted from deep polar firn snow. We quantify, for the first time, the apparent isotopic fractionation, εapp(13C), for these gases as they are destroyed in the high- and mid-latitude stratosphere: εapp(CFC-12, high-lat) = (−20.2 ± 4.4) ‰ and εapp(CFC-113, high-lat) = (−9.4 ± 4.4) ‰, εapp(CFC-12, mid-lat) = (−30.3 ± 10.7) ‰, and εapp(CFC-113, mid-lat) = (−34.4 ± 9.8) ‰. Our CFC-11 measurements were not sufficient to calculate εapp(CFC-11) so we instead used previously reported photolytic fractionation for CFC-11 and CFC-12 to scale our εapp(CFC-12), resulting in εapp(CFC-11, high-lat) = (−7.8 ± 1.7) ‰ and εapp(CFC-11, mid-lat) = (−11.7 ± 4.2) ‰. Measurements of firn air were used to construct histories of the tropospheric isotopic composition, δT(13C), for CFC-11 (1950s to 2009), CFC-12 (1950s to 2009), and CFC-113 (1970s to 2009) – with δT(13C) increasing for each gas. We used εapp(high-lat), which were derived from more data, and a constant isotopic composition of emissions, δE(13C), to model δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113). For CFC-11 and CFC-12, modelled δT(13C) was consistent with measured δT(13C) for the entire period covered by the measurements, suggesting no dramatic change in δE(13C, CFC-11) or δE(13C, CFC-12) has occurred since the 1950s. For CFC-113, our modelled δT(13C, CFC-113) did not agree with our measurements earlier than 1980. While this discrepancy may be indicative of a change in δE(13C, CFC-113), it is premature to assign one. Our modelling predicts increasing δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113) into the future. We investigated the effect of recently reported new CFC-11 emissions on background δT(13C, CFC-11) by fixing model emissions after 2012, and comparing δT(13C, CFC-11) in this scenario to the model base case. The difference in δT(13C, CFC-11) between these scenarios was 1.4 ‰ in 2050. This difference is smaller than our model uncertainty envelope and would therefore require improved modelling and measurement precision, as well as better quantified isotopic source compositions, to detect.

scholarly journals Epigenetic graphitization in the basement of the Siberian craton - evidence of the migration of hydrocarbon-enriched fluids in the paleoproterozoic

2019 ◽  
Vol 486 (2) ◽  
pp. 217-222
Author(s):  
V. B. Savelyeva ◽  
Yu. V. Danilova ◽  
T. G. Shumilova ◽  
A. V. Ivanov ◽  
B. S. Danilov ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Intermetallic Compounds ◽  
Siberian Craton ◽  
Carbon Isotopic Composition ◽  
Structural Studies ◽  
Copper Sulfides ◽  
Carbon Isotopic ◽  
Hydrocarbon Fluid ◽  
Hydrocarbon Radicals ◽  
First Time

For the first time, diagnostics and structural studies of the сarbonaceous material (СM) of quartz-muscovite dinamoschists from schistase zones in biotite migmatites, pegmatites and diabases of the southern part of the Baikal ledge of the Siberian craton were performed. The сarbonaceous material is represented by clearly and microcrystalline graphite with residual hydrocarbon radicals. Native Ni, Sn, zincous Cu, intermetallic compounds of Fe-Ni composition, copper sulfides, rutile, monazite, and zircon were found in intergrowths with СM. The carbon isotopic composition is from -29.19 to -31.58‰, with the exception of CM from schistated diabase with δ13C = -24.93 ‰. The 40Ar/39Ar-dating of muscovite gave an age of 1947 ± 7.8 Ma, indicating a relationship between dynamometamorphism and the accretion of the Akitkan folded system with ancient craton complexes. It is concluded that the deposition of native carbon and metals is caused by the migration of essentially hydrocarbon fluid in the upper crustal formations.

Hafnium Isotopic Composition of the Bushveld Complex Requires Mantle Melt–Upper Crust Mixing: New Evidence from Zirconology of Mafic, Felsic and Metasedimentary Rocks

2019 ◽  
Vol 60 (11) ◽  
pp. 2169-2200 ◽  
Author(s):  
Armin Zeh ◽  
Allan H Wilson ◽  
Dominik Gudelius ◽  
Axel Gerdes
Keyword(s):  
Isotopic Composition ◽  
Lithospheric Mantle ◽  
Bushveld Complex ◽  
Subcontinental Lithospheric Mantle ◽  
Upper Crust ◽  
Bulk Rock ◽  
Metamorphic Zircon ◽  
Isotopic Data ◽  
Metasedimentary Rocks ◽  
Hf Isotopic Composition

Abstract The origin of magmas that formed the Bushveld Complex remains highly debated in spite of many decades of intense research. Previous geochemical–petrological studies have shown a strong mantle derivation resulting ultimately in highly economic ore bodies of platinum group elements and chromium. However, geochemistry also points to the contribution of a significant crustal component, which may have been derived singly or in combination from a number of different sources. These include subcontinental lithospheric mantle that was enriched prior to Bushveld magma formation, possibly by subduction, assimilation of lower and upper crust during magma ascent, and contamination during magma chamber accretion within sedimentary rocks of the enclosing Transvaal Supergroup. In this study, the contributions of these various reservoirs will be evaluated by employing Hf isotopic data of well-characterized zircon grains in mafic, felsic and metasedimentary rocks, together with Zr–Hf bulk-rock compositions. The results reveal that magmatic zircon grains in mafic cumulate rocks from the floor to the roof of the c. 9 km thick Rustenburg Layered Suite (RLS) show essentially the same variations in εHf2·055 Ga from −7·5 to −10·2 as those of metamorphic zircon grains and overgrowths in the immediate surrounding quartzite and metapelitic rocks, as well as in granitic melt batches, granophyres, and the upper Rooiberg volcanics. The same values are also obtained by estimating the average Hf isotopic compositions of detrital zircon grains in many quartzite and metapelitic rocks from the surrounding Magaliesberg (εHf2·055 Ga = −6·2 to −10·8, six samples, maximum deposition age at 2080 Ma) and Houtenbeck formations (εHf2·055 Ga = −7·1 to −8·9, three samples, maximum deposition age at 2070 Ma), and by a six-point isochron of a garnet-schist from the Silverton Formation (εHft = −6·6 ± 0·7; age = 2059·4 ± 2·7 Ma). Zircon morphologies, zoning patterns, Hf isotopic data and petrological constraints furthermore reveal that metamorphic zircon was precipitated from aqueous fluids and/or felsic melts at temperatures between 550 and 900 °C, and that the Hf isotopic composition became homogenized during fluid transport in the contact aureole. However, results of numerical modelling indicate that fluid infiltration had only a minor effect on the Zr–Hf budget and Hf isotopic composition of the RLS, and that these parameters were mainly controlled by the mixing of melts derived from three major sources: (1) the asthenospheric mantle (>20 %); (2) enriched subcontinental lithospheric mantle (<80 %); (3) assimilation of significant amounts of crust (up to 40 %). The modelling furthermore suggests that assimilation of lower Kaapvaal Craton crust was minor (<15 %) during B1 (high-Mg andesite) magma formation, but up to 40 % during B3 (tholeiite) magma formation. The minor variation in εHft of zircon throughout the entire stratigraphy of the RLS resulted from the interplay of three dominant contributing factors: (1) intrusion of hot (>1200 °C) mantle-derived magmas with relatively low Zr–Hf concentrations having a similar εHf2·055 Ga of −8·5 ± 1·9 to that of upper crust rocks surrounding the RLS; (2) significant assimilation of volcanic and metasedimentary rocks with high Zr–Hf concentration; (3) mingling, mixing and/or diffusive exchange of Zr and Hf between crust and mantle-derived melts and aqueous fluids prior to late-magmatic crystallization of zircon at temperatures between 700 and 900 °C. This study shows that the combination of Zr–Hf bulk-rock data with Hf isotopic data of well-characterized zircon grains provides a powerful tool to quantify various mantle and crustal reservoirs of mafic layered intrusions, and allows new insights into magma chamber and related contact metamorphic processes.

scholarly journals Sunda arc mantle source δ18O value revealed by intracrystal isotope analysis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Frances M. Deegan ◽  
Martin J. Whitehouse ◽  
Valentin R. Troll ◽  
Harri Geiger ◽  
Heejin Jeon ◽  
...  
Keyword(s):  
Mantle Source ◽  
Secondary Ion Mass Spectrometry ◽  
Isotope Composition ◽  
Isotope Analysis ◽  
Sunda Arc ◽  
Mid Ocean Ridge ◽  
Plumbing Systems ◽  
Ocean Ridge ◽  
Secondary Ion ◽  
Magma Plumbing

AbstractMagma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) δ18O values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30 km at Merapi to ≤20 km at Agung. Here we show that mean clinopyroxene δ18O values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt δ18O values of 5.7 ‰ (±0.2 1 SD) indistinguishable from the δ18O range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member.

scholarly journals Geochronology, Geochemistry, and Pb–Hf Isotopic Composition of Mineralization-Related Magmatic Rocks in the Erdaohezi Pb–Zn Polymetallic Deposit, Great Xing’an Range, Northeast China

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 274
Author(s):  
Zhitao Xu ◽  
Jinggui Sun ◽  
Xiaolong Liang ◽  
Zhikai Xu ◽  
Xiaolei Chu
Keyword(s):  
Lower Crust ◽  
Western Slope ◽  
Quartz Porphyry ◽  
Late Mesozoic ◽  
Hypabyssal Intrusions ◽  
Polymetallic Mineralization ◽  
Great Xing’An Range ◽  
Hf Isotopic Composition ◽  
Back Arc ◽  
T Values

Late Mesozoic intermediate–felsic volcanics and hypabyssal intrusions are common across the western slope of the Great Xing’an Range (GXAR). Spatiotemporally, these hypabyssal intrusions are closely associated with epithermal Pb–Zn polymetallic deposits. However, few studies have investigated the petrogenesis, contributions and constraints of these Pb–Zn polymetallic mineralization-related intrusions. Therefore, we examine the representative Erdaohezi deposit and show that these mineralization-related hypabyssal intrusions are composed of quartz porphyry and andesite porphyry with concordant zircon U–Pb ages of 160.3 ± 1.4 Ma and 133.9 ± 0.9 Ma, respectively. These intrusions are peraluminous and high-K calc-alkaline or shoshonitic with high Na2O + K2O contents, enrichment in large ion lithophile elements (LILEs; e.g., Rb, Th, and U), and depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), similar to continental arc intrusions. The zircon εHf(t) values range from 3.1 to 8.0, and the 176Hf/177Hf values range from 0.282780 to 0.282886, with Hf-based Mesoproterozoic TDM2 ages. No differences exist in the Pb isotope ratios among the quartz porphyry, andesite porphyry and ore body sulfide minerals. Detailed elemental and isotopic data imply that the quartz porphyry originated from a mixture of lower crust and newly underplated basaltic crust, while the andesite porphyry formed from the partial melting of Mesoproterozoic lower crust with the minor input of mantle materials. Furthermore, a magmatic–hydrothermal origin is favored for the Pb–Zn polymetallic mineralization in the Erdaohezi deposit. Integrating new and published tectonic evolution data, we suggest that the polymetallic mineralization-related magmatism in the Erdaohezi deposit occurred in a back-arc extensional environment at ~133 Ma in response to the rollback of the Paleo-Pacific Plate.

ISOTOPE-GEOCHEMICAL FEATURES OF AUTHENIC CARBONATES OF THE YU1 PRODUCING HORIZON OF THE VERKH-TARSKOYE OIL FIELD (SOUTH OF WESTERN SIBERIA)

2020 ◽  
pp. 20-28
Author(s):  
L. G. Vakulenko ◽  
◽  
O. D. Nikolenko ◽  
D. A. Novikov ◽  
P. A. Yan ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbonate Rocks ◽  
Western Siberia ◽  
Oil Field ◽  
Third Generation ◽  
The Third ◽  
First Time ◽  
Different Sources ◽  
Sources Of Co2 ◽  
Comprehensive Study

A comprehensive study of the composition of sand and silt deposits of the Yu1 horizon of the Vasyuganskaya Formation upper part of the Verkh-Tarskoye oil field has been carried out. Associations of authigenic minerals have been determined in their cement, among which the calcite is the most widespread. According to petrographic parameters, three generations of calcite have been identified for which detailed isotopicgeochemical and ultramicroscopic studies were carried out for the first time. Wide and multi directional changes in the isotopic composition of carbon and oxygen and in the chemical composition of carbonate minerals were recorded, they indicate significant variations in the conditions of diagenesis and catagenesis, primarily temperature, and different sources of CO2. Significant variations in the isotopic composition of formation waters and its relationship with the isotopic composition of carbonates have been established. Thus, a narrow interval of close δ13C values was revealed, amounting to –10.5 to –9.1 ‰ in the formation waters of group II, and from –10.7 to –9.1 ‰ in calcites of the third generation. The source of CO2 in this system should be considered a carbon dioxide, which is formed in the process of metamorphism of carbonate rocks of the Paleozoic age.

Tectonic affinity and evolution of the A lxa B lock during the N eoproterozoic: C onstraints from zircon U‐Pb dating, trace elements, and Hf isotopic composition

2018 ◽  
Vol 54 (6) ◽  
pp. 3700-3719
Author(s):  
Wenzhou Xiao ◽  
Jianqing Lai ◽  
Jeffrey M. Dick ◽  
Xiancheng Mao ◽  
Yan Chen ◽  
...  
Keyword(s):  
Trace Elements ◽  
Isotopic Composition ◽  
Hf Isotopic Composition

scholarly journals Seasonal variations in nitrate isotope composition of three rivers draining into the North Sea

2010 ◽  
Vol 7 (4) ◽  
pp. 6051-6088 ◽  
Author(s):  
A. Deek ◽  
K. Emeis ◽  
U. Struck
Keyword(s):  
Isotopic Composition ◽  
North Sea ◽  
Isotope Composition ◽  
Atmospheric Oxygen ◽  
Isotope Effects ◽  
Nitrate Sources ◽  
Particulate Nitrogen ◽  
Soil Nitrification ◽  
Mean Values ◽  
Δ 15N

Abstract. Nitrate loading of coastal ecosystems by rivers that drain industrialised catchments continues to be a problem in the South Eastern North Sea, in spite of significant mitigation efforts over the last 2 decades. To identify nitrate sources, sinks, and turnover in three German rivers that discharge into the German Bight, we determined δ 15N-NO3- and δ18O- NO3- in nitrate and δ 15N of particulate nitrogen for the period 2006–2009 (biweekly samples). The nitrate loads of Rhine, Weser and Ems varied seasonally in magnitude and δ 15N-NO3- (6.5–21‰), whereas the δ 18O-NO3- (-0.3–5.9‰) and δ 15N-PN (4–14‰) were less variable. Overall temporal patterns in nitrate mass fluxes and isotopic composition suggest that a combination of nitrate delivery from nitrification of soil ammonia in the catchment and assimilation of nitrate in the rivers control the isotopic composition of nitrate. Nitrification in soils as a source is indicated by low δ 18O-NO3- in winter, which traces the δ 18O of river water. Mean values of δ 18O-H2O were between –9.4‰ and –7.3‰; combined in a ratio of 2:1 with the atmospheric oxygen δ 18O of 23.5‰ agrees with the found δ 18O of nitrate in the rivers. Parallel variations of δ 15N-NO3- and δ 18O-NO3- within each individual river are caused by isotope effects associated with nitrate assimilation in the water column, the extent of which is determined by residence time in the river. Assimilation is furthermore to some extent mirrored both by the δ 15N of nitrate and particulate N. Although δ 15-NO3- observed in Rhine, Weser and Ems are reflected in high average δ 15N-PN (between 6‰ and 9‰, both are uncorrelated in the time series due to lateral and temporal mixing of PN. That a larger enrichment was consistently seen in δ 15N-NO3- relative to δ 18O-NO3- is attributed to constant additional diffuse nitrate inputs deriving from soil nitrification in the catchment area. A statistically significant inverse correlation exists between increasing δ 15N-NO3- values and decreasing NO3- concentrations. This inverse relationship – observed in each seasonal cycle – together with a robust relationship between human dominated land use and δ 15N-NO3- values demonstrates a strong influence of human activities and riverine nitrate consumption efficiency on the isotopic composition of riverine nitrate.

New Discovery and Zircon Hf Isotopic Composition of the Early Yanshannian Monzogranite in the Yingyangguan Group of Eastern Guangxi, China

2018 ◽  
Vol 92 (4) ◽  
pp. 1653-1655
Author(s):  
Xiang LI ◽  
Bing TU ◽  
Lingzhan WANG ◽  
Yang TIAN ◽  
Guogang XIE ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Hf Isotopic Composition ◽  
New Discovery
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