The 3.49 Ga Dresser Formation has been considered to host evidence of the earliest microbes metabolising sulfur species on Earth.However, previous bulk analyses and in situ measurements conclude disparate metabolisms based on opposite Δ 33 S 1 .This study first established the generations of pyrite growth, and then measured the multiple sulfur isotopes in situ using Sensitive High Resolution Ion MicroProbe-Stable Isotope analyses.Two main generations of pyrite were revealed based on core-rim textures and multiple sulfur isotopic compositions: Δ 33 S-positive Generation One (G1) and δ 34 S-and Δ 33 S-negative Generation Two (G2).In the chert-barite unit, the diluted Δ 33 S-positive and Δ 33 S-negative photochemical products were mainly sequestered in G1 and barite, respectively.G2 were formed via the sulfide pathway with sulfur derived from sulfate reduction and magmatic H 2 S. The δ 34 S-Δ 33 S-Δ 36 S 1 systematics suggests an abiological origin for G1, and thermochemical and possible (minor) microbial sulfate reduction for G2.
Research Article| May 01, 1995 Mesozoic invasion of crust by MORB-source asthenospheric magmas, U.S. Cordilleran interior Janet A. Leventhal; Janet A. Leventhal 1Department of Earth and Space Sciences, University of California, Los Angeles, California 90095-1567 Search for other works by this author on: GSW Google Scholar Mary R. Reid; Mary R. Reid 1Department of Earth and Space Sciences, University of California, Los Angeles, California 90095-1567 Search for other works by this author on: GSW Google Scholar Art Montana; Art Montana 1Department of Earth and Space Sciences, University of California, Los Angeles, California 90095-1567 Search for other works by this author on: GSW Google Scholar Peter Holden Peter Holden 1Department of Earth and Space Sciences, University of California, Los Angeles, California 90095-1567 Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (5): 399–402. https://doi.org/10.1130/0091-7613(1995)023<0399:MIOCBM>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 Janet A. Leventhal, Mary R. Reid, Art Montana, Peter Holden; Mesozoic invasion of crust by MORB-source asthenospheric magmas, U.S. Cordilleran interior. Geology 1995;; 23 (5): 399–402. doi: https://doi.org/10.1130/0091-7613(1995)023<0399:MIOCBM>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 Mafic and ultramafic xenoliths entrained in lavas of the Cima volcanic field have Nd and Sr isotopic ratios indicative of a source similar to that of mid-ocean ridge basalt (MORB). Nd and Sr internal isochrons demonstrate a Late Cretaceous intrusion age. These results, combined with evidence for emplacement in the lower crust and upper mantle, indicate invasion of the lower crust by asthenospheric magmas in the Late Cretaceous. Constituting the first prima facie evidence for depleted-mantle magmatism in the Basin and Range province prior to late Cenozoic volcanism, these results lend key support to models suggesting crustal heating by ascent of asthenosphere in the Mesozoic Cordilleran interior. 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.
The long-favored paradigm for the development of continental crust is one of progressive growth beginning at approximately 4 billion years ago (Ga). To test this hypothesis, we measured initial 176Hf/177Hf values of 4.01- to 4.37-Ga detrital zircons from Jack Hills, Western Australia. epsilonHf (deviations of 176Hf/177Hf from bulk Earth in parts per 10(4)) values show large positive and negative deviations from those of the bulk Earth. Negative values indicate the development of a Lu/Hf reservoir that is consistent with the formation of continental crust (Lu/Hf approximately 0.01), perhaps as early as 4.5 Ga. Positive epsilon(Hf) deviations require early and likely widespread depletion of the upper mantle. These results support the view that continental crust had formed by 4.4 to 4.5 Ga and was rapidly recycled into the mantle.
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