scholarly journals Re-Os isotope systematics in carbonates from Serpent Mound, Ohio: Implications for Re-Os dating of crustal rocks and the osmium isotopic composition of Ordovician seawater

2004 ◽  
Vol 5 (3) ◽  
Author(s):  
Elisabeth Widom ◽  
Sarah J. Gaddis ◽  
Norman E. Wells
Keyword(s):  
Isotopic Composition ◽  
Crustal Rocks ◽  
Isotope Systematics ◽  
Os Isotope

scholarly journals Re-Os Isotope Systematics of Sulfides in Chromitites and Host Lherzolites of the Andaman Ophiolite, India

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 686 ◽  
Author(s):  
José González-Jiménez ◽  
Sisir Mondal ◽  
Biswajit Ghosh ◽  
William Griffin ◽  
Suzanne O’Reilly
Keyword(s):  
Lithospheric Mantle ◽  
South India ◽  
Subcontinental Lithospheric Mantle ◽  
Volcanic Arc ◽  
Crustal Rocks ◽  
Isotopic Heterogeneity ◽  
Icp Ms ◽  
Subduction System ◽  
Isotope Systematics ◽  
Os Isotope

Laser ablation MC-ICP-MS was used to measure the Os-isotope compositions of single sulfide grains, including laurite (RuS2) and pentlandite [(Fe,Ni)9S8], from two chromitite bodies and host lherzolites from ophiolites of North Andaman (Indo-Burma-Sumatra subduction zone). The results show isotopic heterogeneity in both laurite (n = 24) and pentlandite (n = 37), similar to that observed in other chromitites and peridotites from the mantle sections of ophiolites. Rhenium-depletion model ages (TRD) of laurite and pentlandite reveal episodes of mantle magmatism and/or metasomatism in the Andaman mantle predating the formation of the ophiolite (and the host chromitites), mainly at ≈0.5, 1.2, 1.8, 2.1 and 2.5 Ga. These ages match well with the main tectonothermal events that are documented in the continental crustal rocks of South India, suggesting that the Andaman mantle (or its protolith) had a volume of lithospheric mantle once underlaying this southern Indian continental crust. As observed in other oceanic lithospheres, blocks of ancient subcontinental lithospheric mantle (SCLM) could have contributed to the development of the subduction-related Andaman–Java volcanic arc. Major- and trace-element compositions of chromite indicate crystallization from melts akin to high-Mg IAT and boninites during the initial stages of development of this intra-oceanic subduction system.

Status-quo of carbonate cadmium isotope compositions as a paleo-productivity proxy

2021 ◽  
Author(s):  
Simon V. Hohl
Keyword(s):  
Isotopic Composition ◽  
Isotope Composition ◽  
Status Quo ◽  
Ambient Seawater ◽  
Isotopic Compositions ◽  
Marine Carbonates ◽  
The Status ◽  
State Changes ◽  
Underlying Processes ◽  
Isotope Systematics

<p>Cadmium (Cd) and isotope systematics are emerging tools for studying the biogeochemical cycling of micronutrients in the oceans, and sedimentary archives, as Cd concentrations in seawater show a nutrient-like behaviour, with surface depletion and deep water enrichments. However, the underlying processes are yet to be fully understood. The Cd concentration and isotopic composition of seawater are set by the balance of Cd inputs (and their isotopic composition) and the fractionation on removal to sedimentary sinks. The most favoured explanation is the Cd utilisation by marine phototrophic biomass, causing the surface water’s dissolved Cd pool depletion creating a depth gradient of increasing Cd concentrations and lighter isotopic compositions. Under incomplete oxidative recycling, organic matter may act as an effective Cd sink and authigenic minerals may store the ambient seawater’s Cd isotope composition.</p><p>Consequently, stable Cd isotope compositions in marine carbonates show broad variations linked to paleo-productivity and redox state changes. Additional fractionation processes govern the Cd isotopic compositions of marine sediments. Besides biological utilisation, experimental Cd partitioning into authigenic calcites or sulphides under variable redox and salinity conditions has been shown.  Therefore, when applying Cd isotopes in carbonates, other geochemical proxies must be evaluated very carefully to understand the involved Cd fractionation processes. This presentation aims to present the status quo of research done on authigenic and biologic carbonates and carbonate leachates in carbonatic shales to show the strengths and pitfalls of this new emerging bio-geoscience isotope proxy and its use for paleoenvironmental reconstructions on Earth and beyond.</p><p> </p><p> </p>

Re-Os isotope systematics of sediments of the Brahmaputra River system

2003 ◽  
Vol 67 (21) ◽  
pp. 4101-4111 ◽  
Author(s):  
Sunil K. Singh ◽  
Laurie Reisberg ◽  
Christian France-Lanord
Keyword(s):  
River System ◽  
Brahmaputra River ◽  
Isotope Systematics ◽  
Os Isotope

scholarly journals Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada)

2020 ◽  
Author(s):  
Emilie Bruand ◽  
Clementine Antoine ◽  
Martin Guitreau ◽  
Jean-Luc Devidal
Keyword(s):  
Pb Isotope ◽  
Crustal Rocks ◽  
Discriminating Power ◽  
Gneiss Complex ◽  
Apatite Crystals ◽  
Chemical Signatures ◽  
The Matrix ◽  
The Impact ◽  
Isotope Systematics ◽  
Melt Evolution

<p>A novel way to investigate the petrogenesis of ancient poly-metamorphosed terranes is to use zircon as a vessel and study protected mineral inclusions which are sensitive to melt evolution such as apatite. Recent contributions have shown that zircon-hosted apatite inclusions of unmetamorphosed granitoids can provide valuable petrogenetic information about a given pluton and, in turn, represent a way to circumvent effects of metamorphism. Yet, the impact of metamorphism on apatite inclusion has never been studied in detail. To address the issue of chemical and isotopic preservation of primary signals in apatite crystals both in the matrix and armored within zircons, we have studied apatite crystals from four 3.6-4.0 Ga orthogneisses of TTG affinity from the Acasta Gneiss Complex (Canada). Our results demonstrate that U-Th-Pb isotope systematics in matrix apatite crystals are reset at the time of the Wopmay orogen (1.8-1.7 Ga) whereas primary REE signatures were preserved in many crystals. On the contrary, zircon-hosted apatite inclusions all preserved primary REE signatures despite U-Th-Pb isotope systematics giving ages between 1.7 and 4.0 Ga. We interpret the variable resetting of these ages as a consequence of radiation damage accumulation in zircon lattice. Only the most pristine zircon has an apatite inclusion with a concordant age consistent with the magmatic age of the zircon (4.0 Ga). In addition, our results show that apatite crystals from TTG have distinct REE composition from post-Archean granitoids apatites, and that even apatites with reset ages preserved some of the chemical signatures characterizing TTG compositions (e.g. HREE). This capacity to retain primary information together with its discriminating power for granitoids makes apatite a very valuable tool for reconstructing the nature and evolution of ancient crustal rocks through the use of either detrital minerals or detrital-zircon hosting inclusions.</p>

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