TY - JOUR

T1 - Helium isotopic evidence for modification of the cratonic lithosphere during the Permo-Triassic Siberian flood basalt event

AU - Barry, Peter H.

AU - Hilton, David R.

AU - Day, James M.D.

AU - Pernet-Fisher, John F.

AU - Howarth, Geoffrey H.

AU - Magna, Tomas

AU - Agashev, Aleksey M.

AU - Pokhilenko, Nikolay P.

AU - Pokhilenko, Lyudmila N.

AU - Taylor, Lawrence A.

PY - 2015/2/1

Y1 - 2015/2/1

N2 - Major flood basalt emplacement events can dramatically alter the composition of the sub-continental lithospheric mantle (SCLM). The Siberian craton experienced one of the largest flood basalt events preserved in the geologic record - eruption of the Permo-Triassic Siberian flood basalts (SFB) at ~250Myr in response to upwelling of a deep-rooted mantle plume beneath the Siberian SCLM. Here, we present helium isotope (3He/4He) and concentration data for petrologically-distinct suites of peridotitic xenoliths recovered from two temporally-separated kimberlites: the 360Ma Udachnaya and 160Ma Obnazhennaya pipes, which erupted through the Siberian SCLM and bracket the eruption of the SFB. Measured 3He/4He ratios span a range from 0.1 to 9.8 RA (where RA=air 3He/4He) and fall into two distinct groups: 1) predominantly radiogenic pre-plume Udachnaya samples (mean clinopyroxene 3He/4He=0.41±0.30 RA (1σ); n=7 excluding 1 outlier), and 2) 'mantle-like' post plume Obnazhennaya samples (mean clinopyroxene 3He/4He=4.20±0.90 RA (1σ); n=5 excluding 1 outlier). Olivine separates from both kimberlite pipes tend to have higher 3He/4He than clinopyroxenes (or garnet). Helium contents in Udachnaya samples ([He]=0.13-1.35μcm3STP/g; n=6) overlap with those of Obnazhennaya ([He]=0.05-1.58μcm3STP/g; n=10), but extend to significantly higher values in some instances ([He]=49-349μcm3STP/g; n=4). Uranium and thorium contents are also reported for the crushed material from which He was extracted in order to evaluate the potential for He migration from the mineral matrix to fluid inclusions. The wide range in He content, together with consistently radiogenic He-isotope values in Udachnaya peridotites suggests that crustal-derived fluids have incongruently metasomatized segments of the Siberian SCLM, whereas high 3He/4He values in Obnazhennaya peridotites show that this section of the SCLM has been overprinted by Permo-Triassic (plume-derived) basaltic fluids. Indeed, the stark contrast between pre- and post-plume 3He/4He ratios in peridotite xenoliths highlights the potentially powerful utility of He-isotopes for differentiating between various types of metasomatism (i.e., crustal versus basaltic fluids).

AB - Major flood basalt emplacement events can dramatically alter the composition of the sub-continental lithospheric mantle (SCLM). The Siberian craton experienced one of the largest flood basalt events preserved in the geologic record - eruption of the Permo-Triassic Siberian flood basalts (SFB) at ~250Myr in response to upwelling of a deep-rooted mantle plume beneath the Siberian SCLM. Here, we present helium isotope (3He/4He) and concentration data for petrologically-distinct suites of peridotitic xenoliths recovered from two temporally-separated kimberlites: the 360Ma Udachnaya and 160Ma Obnazhennaya pipes, which erupted through the Siberian SCLM and bracket the eruption of the SFB. Measured 3He/4He ratios span a range from 0.1 to 9.8 RA (where RA=air 3He/4He) and fall into two distinct groups: 1) predominantly radiogenic pre-plume Udachnaya samples (mean clinopyroxene 3He/4He=0.41±0.30 RA (1σ); n=7 excluding 1 outlier), and 2) 'mantle-like' post plume Obnazhennaya samples (mean clinopyroxene 3He/4He=4.20±0.90 RA (1σ); n=5 excluding 1 outlier). Olivine separates from both kimberlite pipes tend to have higher 3He/4He than clinopyroxenes (or garnet). Helium contents in Udachnaya samples ([He]=0.13-1.35μcm3STP/g; n=6) overlap with those of Obnazhennaya ([He]=0.05-1.58μcm3STP/g; n=10), but extend to significantly higher values in some instances ([He]=49-349μcm3STP/g; n=4). Uranium and thorium contents are also reported for the crushed material from which He was extracted in order to evaluate the potential for He migration from the mineral matrix to fluid inclusions. The wide range in He content, together with consistently radiogenic He-isotope values in Udachnaya peridotites suggests that crustal-derived fluids have incongruently metasomatized segments of the Siberian SCLM, whereas high 3He/4He values in Obnazhennaya peridotites show that this section of the SCLM has been overprinted by Permo-Triassic (plume-derived) basaltic fluids. Indeed, the stark contrast between pre- and post-plume 3He/4He ratios in peridotite xenoliths highlights the potentially powerful utility of He-isotopes for differentiating between various types of metasomatism (i.e., crustal versus basaltic fluids).

KW - Helium

KW - Helium isotopes

KW - Noble gases

KW - Peridotites

KW - SCLM

KW - Siberia

KW - Udachnaya and Obnazhennaya

UR - http://www.scopus.com/inward/record.url?scp=84919935007&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2014.12.001

DO - 10.1016/j.lithos.2014.12.001

M3 - Article

AN - SCOPUS:84919935007

VL - 216-217

SP - 73

EP - 80

JO - Lithos

JF - Lithos

SN - 0024-4937

ER -