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  • Geological Society of America  (2)
  • 1
    Online Resource
    Online Resource
    Mercury isotopic composition of igneous rocks from an accretionary orogen: Implications for lithospheric recycling
    Geological Society of America ; 2022
    In:  Geology Vol. 50, No. 9 ( 2022-09-01), p. 1001-1006
    Details
    In: Geology, Geological Society of America, Vol. 50, No. 9 ( 2022-09-01), p. 1001-1006
    Abstract: Mercury (Hg) provides critical information on terrestrial planet formation and evolution due to its unique physicochemical properties and multiform isotopic compositions. Current knowledge of Hg is mainly limited to Earth's surface environments, and the understanding of Hg in the Earth's interior remains unclear. Accretionary orogens are major settings for continental crustal growth and crust-mantle interactions. We studied the Hg concentration and isotopic composition of igneous rocks in the eastern Central Asian orogenic belt, using Hg as a proxy to trace the recycling of surface materials in Earth's lithosphere. Our results show low Hg abundances in mafic through felsic igneous rocks (4.93 ± 4.35 ppb, standard deviation [SD], n = 267). Mafic rocks show slightly lower δ202Hg (−2.9‰ ± 0.5‰, SD, n = 24) than intermediate (−2.4‰ ± 0.8‰, SD, n = 58) and felsic (−1.5‰ ± 0.8‰, SD, n = 185) rocks, indicating a chemical stratification of Hg isotopic composition in the continental crust with isotopically lighter Hg in the lower part and heavier Hg in the upper part. Slightly positive Δ199Hg values are observed in mantle-derived mafic (0.07‰ ± 0.06‰, SD) and intermediate (0.06‰ ± 0.07‰, SD) rocks, which agree well with those reported for marine sediments, indicating the involvement of fluids or melts from the oceanic crust. Larger variations of Δ199Hg values (−0.26‰ to +0.21‰, average: 0.01‰ ± 0.08‰, SD, n = 185) are observed in felsic rocks, further indicating recycling of surface Hg from the marine reservoir via slab subduction (reflected by positive values) plus magmatic assimilation of terrestrial Hg (reflected by negative values). Our study demonstrates that Hg isotopes can be a promising tracer for the chemical dynamics of Earth's lithosphere.
    Type of Medium: Online Resource
    ISSN: 0091-7613 , 1943-2682
    URL: Article
    DOI: 10.1130/G50131.1
    Language: English
    Publisher: Geological Society of America
    Publication Date: 2022
    detail.hit.zdb_id: 184929-3
    detail.hit.zdb_id: 2041152-2
    SSG: 13
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Extreme serpentinization and desulfurization in an early Earth setting
    Geological Society of America ; 2023
    In:  Geology Vol. 51, No. 6 ( 2023-06-01), p. 602-606
    Details
    In: Geology, Geological Society of America, Vol. 51, No. 6 ( 2023-06-01), p. 602-606
    Abstract: The ca. 3.5 Ga Bon Accord Ni deposit was located in the Barberton Greenstone Belt of the Kaapvaal Craton, South Africa, and contained a unique assemblage of Ni-rich minerals including trevorite (NiFe2O4). It was initially interpreted as a metamorphosed extraterrestrial body, recently ruled out by Cr isotope data, and subsequently as a fragment of the Archean Earth’s core. More recent suggestions have highlighted similarities between Bon Accord and Archean magmatic sulfide mineralization. We present a geochemical (rare earth element [REE] , halogen, and highly siderophile element [HSE] abundance) and isotopic (noble gases, Zn, Cr, and Re-Os) study to elucidate the origin of this enigmatic body. Bon Accord is enriched in the REE relative to primitive mantle (PM), with a pattern resembling that of Aldepleted komatiites. The bulk material has & gt;10 × PM Os and Ir, & gt;100 × PM Ru, Pt, Pd, and Re, and radiogenic 187Os/188Os. Trevorite, silicates, and two bulk-rock samples are consistent with chondritic to sub-chondritic initial 187Os/188Os at the time of formation. The new REE data implicate a komatiite precursor in the formation of Bon Accord, and the HSE data bear striking similarities to those of Ni-enriched Archean magmatic sulfide deposits. Enrichment in the heavier Zn isotopes supports desulfurization of a sulfide (isotopically light) deposit during serpentinization to produce the trevorite-dominated body. We conservatively estimate this process could have mobilized as much as ~9.2 × 104 tonnes of H2S, offering an intriguing possibility for sourcing of the sulfur that fixes the historically important gold mineralization in the Barberton Greenstone Belt.
    Type of Medium: Online Resource
    ISSN: 0091-7613 , 1943-2682
    URL: Article
    DOI: 10.1130/G51030.1
    Language: English
    Publisher: Geological Society of America
    Publication Date: 2023
    detail.hit.zdb_id: 184929-3
    detail.hit.zdb_id: 2041152-2
    SSG: 13
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
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