Re-Os Isotope Research Articles

Lithospheric Evolution in Circum-Cratonic Settings: A Re-Os Isotope Study of Peridotite Xenoliths from the Vitim Region, Siberia

The lithospheric mantle beneath most cratonic regions appears to be of comparable age to the overlying crust and is tectonically robust. Less clear is the age and robustness of the lithospheric mantle beneath circum-cratonic regions. Questions of particular interest are (1) whether the cratonic mantle extends beyond the craton cover for significant distances, (2) the nature of circumcratonic lithospheric mantle and its relationship to the age and geologic history of the overlying crust, and (3) the relationship of the lithospheric mantle to the modem tectonic setting, particularly continental rifting. One of the regions that these questions can be addressed is Siberia. The Siberian craton is intruded by numerous kimberlites that carry mantle peridotite xenoliths of Archaean age (Pearson et al., 1995), which are petrologically similar to Archaean lithospheric mantle elsewhere (Boyd et al., 1997). The poly-stage Sayan-Baikal fold belt originated in the Early Palaeozoic from closure of the palaeoAsian ocean and collision of several Precambrian micro-continents with the Siberian craton to the north. It experienced repeated orogenic and intracontinental magmatic episodes; the last of them producing the Cenozoic Vitim volcanic field, in which Miocene and younger alkali basalts and tufts contain xenoliths of spineland garnet-bearing peridotites that provide a valuable insight of the lithospheric mantle (Ionov et al., 1993). The Vitim Highland region that the xenoliths are erupted through is not thought to have undergone significant modification of lithospheric mantle due to recent rifting in the Baikal rift zone, some 100-200 km to the west, and so the xenoliths should provide a record of pre-rift lithospheric evolution (Ionov et al., 1993). We have analysed a suite of these xenoliths, described by Ionov et al. (1993), plus new samples, for Re-Os isotopic composition, with the aim of constraining the age and evolution of the lithospheric mantle beneath the region.

Evidence for Interaction of Proterozoic (2 Ga) Sub-Continental Mantle with an Enriched Mantle Plume from Re-Os Isotope Systematics in French Massif Central Peridotite Xenoliths

Evidence for Interaction of Proterozoic (2 Ga) Sub-Continental Mantle with an Enriched Mantle Plume from Re-Os Isotope Systematics in French Massif Central Peridotite Xenoliths

Os Isotopic Compositions of Basaltic Andesites and Hawaiites of the Mexican Volcanic Belt

The east-to-west-trending Mexican volcanic belt is a complex active continental arc related to the subduction of the Rivera and Cocos plates beneath western Mexico. The basement beneath the arc is Grenville-age continental crust in eastern and central Mexico and Triassic age oceanic crust in western Mexico. Where the basement is old continental crust, the arc has large stratovolcanoes and cinder cones. In western Mexico, where the basement is young oceanic crust, the arc consists of cinder cones and fissure basalts. In western Mexico, the volcanic arc contains basaltic andesite, alkali basalt, andesite, hawaiite and mugerite. The hawaiite and mugerite are unusual rocks for continental-arc settings suggesting that both hydrous, fluid-enriched sub arc mantle and oceanic island type mantle may be present beneath western Mexico (Righter and Carmichael, 1992). Basaltic andesite and hawaiites were analysed for Re-Os isotopes in an effort to constrain the source region of their melts. The Os isotopic system is ideal for this question because the system has been shown to be robust to changes in the mantle by metasomatizing fluids, and the incompatibility of Re gives the asthenospheric and lithospheric mantle, as well as the crust, distinct Os isotopic compositions over time. Olivine and magnetite phenocrysts from basaltic andesite and hawaiites, as well as whole rocks, were analysed for their Re and Os concentrations and isotopic compositions. Osmium concentrations range from about 10 ppt for the whole-rock powders to over 500 ppt for an olivine separate. Rhenium concentrations vary from 300-500 ppt for whole-rocks and olivine separates to several parts-per-billion for magnetite-rich separates. The lS7Os/lSSOs initial isotopic ratio for basaltic andesites and hawaiite range from c. 0.15 to 0.25. The elevated isotopic composition of these rocks indicates that the primary mantle-derived magmas have been contaminated by the crust. In this region, the arc is underlain by Triassic oceanic crust and a thick sequence of Mesoproterozoic sediments derived from nuclear Mexico. The osmium data indicate that modelling of the magmatic systems in the Mexican volcanic arc in western Mexico need to take into account that the overall compositions of the primary mantle-derived magmas have been altered by the assimilation crustal components.

Re-Os Isotopic Study of Komatiitic Volcanism and Magmatic Sulphide Formation in the Southern Abitibi Greenstone Belt, Canada

We have investigated the Re–Os isotope geochemistry of 2.7-Ga metakomatiitic flows and associated Ni–Cu sulfide deposits from Alexo, Texmont and Hart in the Abitibi greenstone belt of Ontario in order to refine the thermal erosion model and evaluat e the superimposed effects of metamorphism and hydrothermal alteration on ore environments and non-ore environments. Although the geochemical characteristics of these komatiites have led to the belief that these lavas were uncontaminated, radioge nic Os isotopic compositions (Os = +20.2 and +33.2) obtained from well-preserved komatiites and olivine separates suggest that the Alexo flow has been contaminated by crust-derived material. These data are compatible with the trace-element enrichment observed in melt inclusions trapped within olivine. Redistribution of Os and Re did occur at least at the mineral scale and most likely during the Grenville orogeny. Hydrothermal fluids were channeled along the contact between the komatiites and their basement, and were responsible for the remobilization of Re or Os (or both) within the sulfides at Alexo and Hart. Matrix and disseminate d sulfides from Texmont are located within the pile of cumulates and seem to have escaped this localized alteration. Although the Abitibi sulfides have experienced various degrees of metamorphism (from prehnite–pumpellyite to low amphibolite facies), the initial Re–Os isotopic composition of the flows appears to have been preserved at the whole-rock scale. Re–Os isotopic heterogeneity of the Abitibi sulfides is best explained by variable R-factor of the sulfides. Re and Os concentrations and Os isotopic heterogeneity of the Abitibi sulfides are consistent with the current model of nickel sulfide formation, which implies that the assimilation of sulfidic sedimentary rocks was the trigger for sulfide saturation.

Re-Os Isotope Systematics Applied to the Tharsis Mine, Iberian Pyrite Belt Spain

The Tharsis mine, a volcanogenic massive sulphide deposit, lies within a syncline of the Iberian Pyrite Belt. The sulphide ores occur in the VolcanogenicSedimentary Complex, with its massive and stockwork ores crosscutting Famennian to Visean (365-345 Ma) palinologically dated black shales. Intense structural deformation and moderate metamorphism (lower greenschist facies, prehnitepumpeyllite) altered the deposit during the Hercynian orogeny. Previous geochemical studies used oxygen, hydrogen, sulphur, and lead isotopes to model depth/temperature conditions, biogenic input, and size of hydrothermal convection systems (Munha et al. (1986), Kase et al (1990), and Marcoux (1998). In general, each of the proposed models involved hydrothermal activity (generated by proximal or distal magmatic heat sources) in which metals were transported by reduced, metalliferous, seawater brines that leached metals from the surrounding crust, or were derived from a hydrous phase partitioned from a partial melt magmatic source, None of these investigations provided direct evidence for the origin of the ore forming metals or precise mineralization age determinations.

Re-Os isotope systematics of sulfides from felsic igneous rocks: Application to base metal porphyry mineralization in Chile

Dating sulfides and determining the source of ore-forming metals have been limiting factors in our understanding of processes that produce hydrothermal ore deposits. Here we analyze sulfides from base metal porphyry deposits from Chile to demonstrate the potential of the Re-Os system to determine both the age and the source of metals for hydrothermal mineralization. Cogenetic chalcopyrite, bornite, pyrite, and sphalerite from El Teniente (ca. 5 Ma) have 187 Re/ 188 Os ratios from 0.3 to 21.8 and initial 187 Os/ 188 Os ratios from 0.17 to 0.22. A paragenetically late pyrite that has an initial 187 Os/ 188 Os of 0.88 indicates that the ore deposit is not isotopically homogeneous in Os throughout the formation of the deposit. Pyrite samples from Andacollo (ca. 100 Ma) have 187 Re/ 188 Os ratios from 15 to 3600, and different isochrons yield ages between 87 and 103 Ma, consistent with different sericite K-Ar ages. Initial 187 Os/ 188 Os ratios of 0.2 to 1.1 are similar to those of El Teniente. The relatively homogeneous 187 Os/ 188 Os ratios (~0.19) for cogenetic sulfides from El Teniente suggest that most of the Os in the ore was from the causal intrusive. The latestage pyrite probably incorporated Os leached from the country rock by meteoric fluids, which mixed with magmatic fluids at the periphery of the hydrothermal system. We demonstrate that the Re-Os isotope system can be a powerful geochronological tool in hydrothermal ore deposits. The large range in Re/Os ratios of sulfides permits the age of mineralization to be well constrained, despite isotopic heterogeneities of the hydrothermal fluids.

Growth of subcontinental lithospheric mantle beneath Zimbabwe started at or before 3.8 Ga: Re-Os study on chromites

Research Article| November 01, 1997 Growth of subcontinental lithospheric mantle beneath Zimbabwe started at or before 3.8 Ga: Re-Os study on chromites Th. F. Nägler; Th. F. Nägler 1Gruppe Isotopengeologie, Mineralogisch-Petrographisches Institut, Universität Bern, CH-3012 Bern, Switzerland Search for other works by this author on: GSW Google Scholar J. D. Kramers; J. D. Kramers 1Gruppe Isotopengeologie, Mineralogisch-Petrographisches Institut, Universität Bern, CH-3012 Bern, Switzerland Search for other works by this author on: GSW Google Scholar B. S. Kamber; B. S. Kamber 2Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom Search for other works by this author on: GSW Google Scholar R. Frei; R. Frei 1Gruppe Isotopengeologie, Mineralogisch-Petrographisches Institut, Universität Bern, CH-3012 Bern, Switzerland Search for other works by this author on: GSW Google Scholar M. D. A. Prendergast M. D. A. Prendergast 3M. D. Prendergast Consultancy, Greendale, Harare, Zimbabwe Search for other works by this author on: GSW Google Scholar Geology (1997) 25 (11): 983–986. https://doi.org/10.1130/0091-7613(1997)025<0983:GOSLMB>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Th. F. Nägler, J. D. Kramers, B. S. Kamber, R. Frei, M. D. A. Prendergast; Growth of subcontinental lithospheric mantle beneath Zimbabwe started at or before 3.8 Ga: Re-Os study on chromites. Geology 1997;; 25 (11): 983–986. doi: https://doi.org/10.1130/0091-7613(1997)025<0983:GOSLMB>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Re-Os isotope results on chromites separated from age-constrained Archean (2.7 to 3.5 Ga) ultramafic intrusions in the Zimbabwe craton show that chromites average a present-day 187Os/188Os ratio of 0.1066, significantly below the bulk silicate Earth value. The source reservoir is interpreted to reflect the Zimbabwean subcontinental lithospheric mantle (SCLM). Archean Re depletion of the SCLM has previously been postulated on the basis of xenolith studies from southern Africa, Siberia, and the Wyoming craton. Because our samples are age constrained, however, the Re-Os data also shed light on the evolution of the Archean SCLM through time. They indicate that the Zimbabwean SCLM began to be separated from asthenospheric mantle before 3.8 Ga and grew quasi-continuously throughout the Archean. This result is reconciled with present-day SCLM data in forward modeling. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Efficient N-TIMS rhenium isotope measurements on outgassed tantalum filaments: very low filament blanks determined by a “standard addition” approach

We have successfully tested two sets of Ta filaments for their suitability to measure Re isotopes by negative thermal ionization mass spectrometry. No significant Re contribution from the filament material itself could be detected. Therefore Ta filaments are a viable, low cost alternative to high purity Pt filaments which are commonly used for Re-Os isotope analyses. A technique whereby Re is directly loaded with H 2SO 4 into Ba(NO 3) 2 and precipitated together with BaSO 4 on the filament has resulted in stable and constant ion beams. Furthermore, slight oxidation of the Ta filament surface significantly facilitates point loading in the center of the filament. The BaSO 4 loading technique has proved to be less sensitive towards time-consuming pre-analytical heating procedures than Ba(NO 3) 2 on Pt filaments. Furthermore, Re isotopic ratios remained constant over a wider range of measuring temperatures, in contrast to what we observed during Re analysis from Pt filaments loaded with Ba(NO 3) 2 or BaSO 4.

Re-Os isotope and geochemical study of the Vredefort Granophyre: Clues to the origin of the Vredefort structure, South Africa

Research Article| October 01, 1996 Re-Os isotope and geochemical study of the Vredefort Granophyre: Clues to the origin of the Vredefort structure, South Africa Christian Koeberl; Christian Koeberl 1Institute of Geochemistry, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria Search for other works by this author on: GSW Google Scholar Wolf Uwe Reimold; Wolf Uwe Reimold 2Department of Geology, University of the Witwatersrand, Johannesburg 2050, South Africa Search for other works by this author on: GSW Google Scholar Steven B. Shirey Steven B. Shirey 3Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, D.C. 20015 Search for other works by this author on: GSW Google Scholar Author and Article Information Christian Koeberl 1Institute of Geochemistry, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria Wolf Uwe Reimold 2Department of Geology, University of the Witwatersrand, Johannesburg 2050, South Africa Steven B. Shirey 3Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, D.C. 20015 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1996) 24 (10): 913–916. https://doi.org/10.1130/0091-7613(1996)024<0913:ROIAGS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christian Koeberl, Wolf Uwe Reimold, Steven B. Shirey; Re-Os isotope and geochemical study of the Vredefort Granophyre: Clues to the origin of the Vredefort structure, South Africa. Geology 1996;; 24 (10): 913–916. doi: https://doi.org/10.1130/0091-7613(1996)024<0913:ROIAGS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The origin of granophyric rock dikes (the Vredefort Granophyre) at the 2 Ga Vredefort structure in South Africa has been controversial. They have been interpreted as either impact melt or igneous intrusions. Most Vredefort Granophyre samples have considerably higher Os contents than the country rocks and 187Re/188Os and 187Os/188Os ratios that scatter about a 2 Ga isochron. Their initial 187Os/188Os ratios (at 2 Ga) overlap the meteoritic data range, indicating that all the granophyre samples contain some meteoritic Os. The Re-Os isotopic composition of the granophyre is significantly different from that of local precursor rocks and indicates that up to 0.2% of a chondritic component could be contained in the granophyre. Our results confirm the interpretation that the Vredefort Granophyre represents an impact melt rock. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

New approaches to crustal evolution studies and the origin of granitic rocks: what can the Lu-Hf and Re-Os isotope systems tell us?

ABSTRACT:The Lu-Hf and Re-Os isotope systems have been applied sparsely to elucidate the origin of granites, intracrustal processes and the evolution of the continental crust. The presence or absence of garnet as a residual phase during partial melting will strongly influence Lu/Hf partitioning, making the Lu–Hf isotope system exceptionally sensitive to evaluating the role of garnet during intracrustal differentiation processes. Mid-Proterozoic (1·1–1·5Ga ) ‘anorogenic’ granites from the western U.S.A. appear to have anomalously high εHf values, relative to their εNd values, compared with Precambrian orogenic granites from several continents. The Hf-Nd isotope variations for Precambrian orogenic granites are well explained by melting processes that are ultimately tied to garnet-bearing sources in the mantle or crust. Residual, garnet-bearing lower and middle crust will evolve to anomalously high εHf values over time and may be the most likely source for later ‘anorogenic’ magmas. When crustal and mantle rocks are viewed together in terms of Hf and Nd isotope compositions, a remarkable mass balance is apparent for at least the outer silicate earth where Precambrian orogenic continental crust is the balance to the high-εHf depleted mantle, and enriched lithospheric mantle is the balance to the low-εHf depleted mantle.Although the continental crust has been envisioned to have exceptionally high Re/Os ratios and very radiogenic Os isotope compositions, new data obtained on magnetite mineral separates suggest that some parts of the Precambrian continental crust are relatively Os-rich and non-radiogenic. It remains unclear how continental crust may obtain non-radiogenic Os isotope ratios, and these results have important implications for Re-Os isotope evolution models. In contrast, Phanerozoic batholiths and volcanic arcs that are built on young mafic lower crust may have exceptionally radiogenic Os isotope ratios. These results highlight the unique ability of Os isotopes to identify young mafic crustal components in orogenic magmas that are essentially undetectable using other isotope systems such as O, Sr, Nd and Pb.

Re-Os Isotope ages of molybdenum deposits in East Qinling and their significance

Dating of metallic ore deposits has been one of the problems concerned with by ore geologists for many years. The establishment of the Re-Os Isotope Laboratory at the Institute of Rock and Mineral Analysis, Chinese Academy of Geological Sciences, has provided us with a new technique to carry out geochronological studies of molybdenum ores. As one of the most important Re-bearing minerals, molybdenite contains almost no common osmium, but187Os was derived completely from decay of187Re, with187Os content as the function of Re content in the mineral. An ID-ICP-MS technique has been used in this study, and Re-Os isotopic ages of several large molybdenum deposits of different types from the East Qinling molybdenum belt have been determined. It is indicated that the Huanglongpu carbonatite vein-type molybdenum-(lead) deposit has a Re-Os age corresponding to Indosinian, while the rest porphyry-type molybdenum deposits and porphyry-skarn-type molybdenum-(tungsten) deposits have Re-Os ages corresponding to Yenshanian.

Evidence for a meteoritic component in impact melt rock from the chicxulub structure

The Chicxulub structure in Yucatan, Mexico, has recently been recognized as a >200-km-diameter multi-ring impact crater of K-T boundary age. Crystalline impact melt rocks and breccias from within the crater, which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects, have been studied for trace element and Re-Os isotope compositions. Re-Os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact-derived rocks. A melt rock sample shows elevated indium concentrations, an osmium concentration of 25 ppb and a low 187 Os 188 Os ratio of 0.113, which are incompatible with derivation from the continental crust. Even though the 187 Os 188 Os ratio is slightly lower than the range so far measured in meteorites, a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material. The data support the hypothesis of a heterogeneously distributed meteoritic component in the Chicxulub melt rock. A sample of impact glass from the Haitian K-T boundary at Beloc yielded about 0.1 ppb osmium and an 187 Os 188 Os ratio of 0.251, indicating the presence of a small meteoritic component in the impact ejecta as well.

Re-Os isotope systematics of Ni-Cu sulfide ores, Sudbury Igneous Complex, Ontario: evidence for a major crustal component

Sudbury Igneous Complex sublayer ores from the Levack West, Falconbridge and Strathcona mines were analyzed for their Re and Os concentrations and Os isotopic compositions. The Re-Os isotope systematics of three ores from the different mines give isochron ages of1 840 ± 60 Ma, 1770 ± 60 Ma and 1780 ± 110 Ma, suggesting that the Re-Os system became closed at the time of, or soon after the 1850 ± 1 Ma crystallization age of the complex. The Os isotopic compositions of different portions of the complex at the time of crystallization varied considerably, with initial 187Os/ 186Os 1850 ranging from 4.64 at Levack West to 7.55 at Strathcona. These heterogeneities require that the Os, and probably also the other platinum-group elements contained in the ores, were derived from at least two sources. In addition, the high initial 187Os/ 186Os ratios indicate that the Os was derived predominantly from ancient crust. Previous studies have suggested that the complex either crystallized from a mixture of mantle-derived basaltic melt and ancient continental crust, or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact. Results of modelling suggest that if a contemporaneous mantle-derived basaltic melt was involved in the origin of the SIC, it likely contributed < 50% of the Os to all three ores. The large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact.

Major and trace element associations in carbonates of Bhima Basin, Karnataka South India

We determined highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) concentrations and 187Os/188Os ratios for ultramafic rocks distributed over the Eoarchean gneiss complex of the Saglek-Hebron area in northern Labrador, Canada in order to constrain to what extent variations in HSE abundances are recorded in Early Archean mantle that have well-resolved 182W isotope anomalies relative to the present-day mantle (∼+11 ppm: Liu et al., 2016). The samples analysed here have been previously classified into two suites: mantle-derived peridotites occurring as tectonically-emplaced slivers of lithospheric mantle, and metakomatiites comprising mostly pyroxenitic layers in supracrustal units dominated by amphibolites. Although previous Sm-Nd and Pb-Pb isotope studies provided whole-rock isochrons indicative of ∼3.8 Ga protolith formation for both suites, our whole-rock Re-Os isotope data on a similar set of samples yield considerably younger errorchrons with ages of 3612 ± 130 Ma (MSWD = 40) and 3096 ± 170 Ma (MSWD = 10.2) for the metakomatiite and lithospheric mantle suites, respectively. The respective initial 187Os/188Os = 0.10200 ± 18 for metakomatiites and 0.1041 ± 18 for lithospheric mantle rocks are within the range of chondrites. Re-depletion Os model ages for unradiogenic samples from the two suites are consistent with the respective Re-Os errorchrons (metakomatiite TRD = 3.4–3.6 Ga; lithospheric mantle TRD = 2.8–3.3 Ga). These observations suggest that the two ultramafic suites are not coeval. However, the estimated mantle sources for the two ultramafics suites are similar in terms of their broadly chondritic evolution of 187Os/188Os and their relative HSE patterns. In detail, both mantle sources show a small excess of Ru/Ir similar to that in modern primitive mantle, but a ∼20% deficit in absolute HSE abundances relative to that in modern primitive mantle (metakomatiite 74 ± 18% of PUM; lithospheric mantle 82 ± 10% of PUM), consistent with the ∼3.8 Ga Isua mantle source and Neoarchean komatiite sources around the world (∼70–86% of PUM). This demonstrates that the lower HSE abundances are not unique to the sources of komatiites, but rather might be a ubiquitous feature of Archean convecting mantle. This tentatively suggests that chondritic late accretion components boosted the convecting mantle HSE inventory after core separation in the Hadean, and that the Eoarchean to Neoarchean convecting mantle was depleted in its HSE content relative to that of today. Further investigation of Archean mantle-derived rocks is required to explore this hypothesis.