Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis

Abstract

A vast portion of the plumbing system of the Siberian Traps Large Igneous Province (STLIP) is emplaced in the Tunguska Basin, where borehole data reveal ubiquitous and abundant sills with great lateral extension. These intrusions intersect Cambrian–Ordovician evaporite, carbonate and siliciclastic series, and locally coal-bearing Permian host rocks, with a high potential for thermogenic gas generation. Here we present new geochemical data from 71 magmatic and 4 sedimentary rock samples from the Tunguska Basin center and periphery, recovered from 15 deep sills intercepted by boreholes. The studied samples are all low-Ti basalt and basaltic andesites, confirming absence of high-Ti and alkaline STLIP magmatism in the Tunguska Basin. The sills derive from picritic parental melts produced by extensive melting of a mantle source with recycled crustal components below a thinned lithosphere (50–60 km), within the spinel stability field. The mantle source was dominantly peridotitic, with enriched pyroxenitic domains formed by recycled lower crust, in agreement with previous models for the main tholeiitic STLIP phase. Limited amounts (up to 5%) of highly radiogenic granitoids or moderately radiogenic metapelites were assimilated in upper crustal magma reservoirs. After emplacement, sills intruded in Cambrian evaporites assimilated marlstones and interacted with the evaporitic host rocks, probably via fluids and brines. This is the first time that such process is described in subvolcanic rocks from all across the volcanic basin. The sills are correlated geochemically with the established chemostratigraphy for the on-craton STLIP lava piles and intrusions (Norilsk region). Sills correlated with the Morongovsky–Mokulaevsky Fm. and the Norilsk-type intrusions are the most voluminous, present all across the central Tunguska Basin, and bear the strongest evidence of interaction with evaporites. Massive discharge of thermogenic volatiles is suggested by explosive pipes and hydrothermal vent structures throughout the Tunguska Basin. We propose that this voluminous pulse of magmatism is a good candidate for the hitherto unidentified early intrusive phase of the STLIP, and may link the deep Tunguska basin sills to the end-Permian environmental crisis.

Halogen Enrichment of Siberian Traps Magmas During Interaction With Evaporites

“…caused by varying degrees of assimilation of crustal sedimentary rocks (including evaporites) by the Siberian Traps magmas during their emplacement, as has been suggested by others (Lightfoot et al, 1990;Wooden et al, 1993;Callegaro et al, 2021).…”

“…The brine's ability to flow into the sill is supported by observations of veins and fissures in the sill filled in with salt precipitates 5-8 m from the contacts. In addition, high chlorine concentration on the rims of biotites in sills in the Lower Tunguska area have been interpreted as being due to chlorine transfer via a hydrous fluid (Heimdal et al, 2019;Callegaro et al, 2021) as observed for aureoles surrounding mafic sills at Norilsk (Pang et al, 2013).…”

Timing and provenance of volcanic fluxes around the Permian-Triassic Boundary Mass Extinction in South China: U-Pb zircon geochronology, volcanic ash geochemistry and mercury isotopes

“…The ashes show intermediate to acidic chemical compositions, plotting in the field of basaltic andesite, trachy-andesite and rhyolite/dacite (Fig. 6a), and are chemically distinct from volcanic rocks originating from the STLIP (Callegaro et al, 2021;Reichow et al, 2005;Sibik et al, 2015;Sobolev et al, 2009). In addition, a mid-oceanic ridge basalt (MORB)-normalized trace element (Th vs. Nb) discriminant plot (Saccani et al, 2015(Saccani et al, , 2018 of the volcanic ashes from the Pingtang syncline suggests that they originate from a continental margin volcanic arc tectonic setting (Fig.…”

Late Permian to Late Triassic Large Igneous Provinces: Timing, Eruptive Style and Paleoenvironmental Perturbations

“…0.40 Ma, building the vast network of sills in the Tunguska Basin. These tholeiitic magmas were produced by shallower and extensive melting of a mixed peridotitic-pyroxenitic mantle (Sobolev et al, 2011;Callegaro et al, 2021). Renewed extrusive activity is recognized from 251.48 ± 0.09 Ma, marking the beginning of the third phase of the Siberian Traps.…”

“…The beginning of the second (intrusive) phase is considered as the deadly subinterval of the Siberian Traps (Burgess et al, 2017), since it coincides with the beginning of the extinction horizon at Meishan (251.94 ± 0.04 Ma; Burgess et al, 2014), Dongpan and Penglaitan (251.94 ± 0.03 Ma and 251.98 ± 0.03 Ma; Baresel et al, 2017), China. Even if these tholeiitic magmas were probably volatile poor (Sibik et al, 2015), the interaction between the sills and the sedimentary host-rocks (i.e., evaporites, carbonates, marlstones, and coal) likely produced large amounts of thermogenic carbon, sulfur and halocarbon species (Svensen et al, 2018;Callegaro et al, 2021;Sibik et al, 2021).…”