Role of degassing of the Noril’sk nickel deposits in the Permian–Triassic mass extinction event

Abstract

The largest mass extinction event in Earth's history marks the boundary between the Permian and Triassic Periods at circa 252 Ma and has been linked with the eruption of the basaltic Siberian Traps large igneous province (SLIP). One of the kill mechanisms that has been suggested is a biogenic methane burst triggered by the release of vast amounts of nickel into the atmosphere. A proposed Ni source lies within the huge Noril’sk nickel ore deposits, which formed in magmatic conduits widely believed to have fed the eruption of the SLIP basalts. However, nickel is a nonvolatile element, assumed to be largely sequestered at depth in dense sulfide liquids that formed the orebodies, preventing its release into the atmosphere and oceans. Flotation of sulfide liquid droplets by surface attachment to gas bubbles has been suggested as a mechanism to overcome this problem and allow introduction of Ni into the atmosphere during eruption of the SLIP lavas. Here we use 2D and 3D X-ray imagery on Noril’sk nickel sulfide, combined with simple thermodynamic models, to show that the Noril’sk ores were degassing while they were forming. Consequent “bubble riding” by sulfide droplets, followed by degassing of the shallow, sulfide-saturated, and exceptionally volatile and Cl-rich SLIP lavas, permitted a massive release of nickel-rich volcanic gas and subsequent global dispersal of nickel released from this gas as aerosol particles.

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

“…Our proposed "sulfide buoyancy aid" process, operating from the metasomatized lithospheric mantle through to base of the continental crust, is analogous to the established mechanism where aqueous or saline vapor bubbles are suggested to "float" sulfide and/or magnetite at mid-upper crustal depths 12,14,15,17 . However, the critical difference is the deeper lithospheric window where this process operates, which provides a first order mechanism to fertilize the continental crust with mantle-derived chalcophile and siderophile metals.…”

“…Although supercritical CO 2 seems to be most critical for the transport of sulfides at mantle and lower crustal conditions, its solubility and low preservation potential increases the likelihood that H 2 O or other volatiles may overprint any originally C-driven textural signature and erase any geological record of its former occurrence. In such cases, other phases may appear to be the dominant volatiles preserved within upper crustal sulfide occurrences (e.g., hydrous silicate caps 15 ), rather than CO 2 . The preservation of intimately associated sulfide-carbonate in the upper crust is thus rare and the opportunity for study inherently limited.…”

“…In the upper crust, hydrous volatile phases have been demonstrated experimentally to provide a viable mechanism of upward physical transport for relatively dense sulfide liquid droplets 12 , 13 and magnetite crystals 14 . Empirically, this process is reflected in the recent identification of sulfides in magmatic systems associated with coarse-grained hydrous silicate caps 15 – 17 . In these cases, there is a strong physical attraction of sulfides and oxides to low-density hydrous or saline bubbles or droplets.…”

Assimilation of sulfate and carbonaceous rocks: Experimental study, thermodynamic modeling and application to the Noril’sk-Talnakh region (Russia)

“…A close association between sulfide globules and vapor phase has been already documented in experimental samples by Mungall et al (2015), who proposed that droplets of sulfide melt can attach to vapor bubbles and float through the magma. Natural samples from Noril'sk area also show textural evidence for sulfide flotation, suggesting S and Ni degassing during the crystallization of the orebearing intrusions (Le Vaillant et al, 2017). A complete model of S partitioning is required to simulate S distribution between the fluid phase, the silicate melt and the sulfide liquid, and to estimate sulfide melt production in the magma due to the assimilation of organic compounds.…”

What caused Earth's largest mass extinction event? New evidence from the Permian-Triassic boundary in northeastern Utah

“…Other observations of the Permian-Triassic boundary include 3) the presence of pyrite framboids in marine sediments indicating an anoxic event that was remarkably shallow and sudden during the interval (Wignall & Hallam, 1992;Wignall & Twitchett, 2002;Wignall et al 2005;Shen et al 2007;Kakuwa, 2008;Bond & Wignall, 2010;Brennecka et al 2011;Schoepfer et al 2012;Schoepfer et al 2013;Liao et al 2017), and 4) a dramatic decrease in carbonate deposition indicating increasing acidity in the world's ocean, and shallowing of the carbonate compensation depth (CCD; Kakuwa, 1996;Kershaw et al 1999;Payne et al 2007). More recently discovered indicators include 5) a 3-fold increase in mercury (Hg) restricted to the boundary layer (Sanei et al 2012;Grasby et al 2016); and 6) a 3 to 10-fold increase in nickel (Ni) and zinc (Zn) within the boundary layer (Liu et al 2017;Rampino et al 2017), which is interpreted as a result of volcanic ash fallout from the Siberian Traps large igneous province eruptions (Le Vaillant et al 2017).…”