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Titel |
Age and isotopic marks of K-rich Manning Massif trachybasalts: an evidence
for Lambert-Amery rift-system initiation (East Antarctica) |
VerfasserIn |
German Leitchenkov, Boris Belyatsky, Elena Lepekhina, Anton Antonov, Robert Krymsky, Alex Andronikov, Sergey Sergeev |
Konferenz |
EGU General Assembly 2017
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250152972
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Publikation (Nr.) |
EGU/EGU2017-17888.pdf |
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Zusammenfassung |
Volcanic rocks from the Manning Massif, which is situated in the western flank of the
Paleozoic-Late Mesozoic Lambert Rift (East Antarctica), belong to a rare type of alkaline
magmatism within the Precambrian East Antarctic Craton. K-rich olivine trachybasalts
compose some flows resting upon a surface of Precambrian granulite terrain, each flow
of 2.5-7 m in thickness and total section not less than 30 m. Each flow sequence
comprises of glassy chilled base with vitroporphyritic texture, fine-plated vesicular
basalt with interstitial texture, massive fine-grained basalt with porphyritic microlitic
texture, amigdaloidal aphanitic basalt with poikilophytic texture, and vesicular
mandelstone of slag crust with vitroporphyritic texture [Andronikov et al., 1998].
Rb-Sr and K-Ar isotopic age of this eruption was estimated as 40-50 Ma and the
main reason for this Cenozoic continental volcanism was supposed the post-rift
tectonic activity [Andronikov et al., 1998]. But the isotopic characteristics of these
trachybasalts are very similar to those obtained for the part of spinel lherzolite and
spinel-garnet lherzolite xenoliths from the Mesozoic alkaline picrite of the adjacent
Jetty Peninsula region. That could be evidence of the trachybasalt mantle source in
long-lived enriched upper mantle beneath the region, either under the lowermost
levels of spinel lherzolite facies or on the highest levels of garnet lherzolite facies
conditions.
To reveal tectonic position of these enigmatic volcanics, we have studied 16 samples from
different parts of basaltic flows for U-Pb geochronology and Pb-Sr-Nd-Os isotopic
characteristics. U-Pb SIMS SHRIMP-II analysis was performed for 68 apatite grains from 5
samples. All obtained data-points are approximated by discordia line (MSWD=1.6) on
Tera-Wasserburg diagram, corresponding to the age of 346±46 Ma. Common Pb isotope
composition of these apatites differs from the model by increased 206Pb/204Pb (19.8) and
207Pb/204Pb (18.3) that means the source of contamination was an ancient material (> 2.4
Ga) and/or with high μ (26.5). The initial isotope characteristics of the studied basalts are the
same for different individual flows: ɛNd=-3.4±0.4; 87Sr/86Sri=0.7061±0.0003,
206Pb/204Pbi=18.421±0.001; 207Pb/204Pbi=15.667±0.001; 208Pb/204Pbi=39.845±0.001;
187Os/186Osi = 0.2012±0.0004 and reflect minimal influence of host-rock contamination
during or after melts crystallization and correspond to enriched mantle source signatures akin
to plume-like.
Thus the Manning Massif K-rich basalts correlate with the time of formation of the
Late-Paleozoic coal-bearing sediments of the Lambert Glacier Rift and basic dykes of Jetty
Peninsula [Mikhalsky, Sheraton, 1993] and can be interpreted to mark the earliest, Lower
Carboniferous stage of the rifting. This event corresponds to the initial intracontinental
stretching in the Eastern Gondwana wich was previously detected only in Perth Basin of
western Australia.
The research was done under financial support by RSF grant N 16-17-10139.
References:
Andronikov A.V., Foley S.F., Beliatsky B.V. 1998. Sm-Nd and Rb-Sr isotopic
systematics of the East Antarctic Manning Massif alkaline trachybasalts and the
development of the mantle beneath the Lambert-Amery rift. Mineral. Petrol. 63.
243–261.
Mikhalsky E.V., Sheraton J.W. 1993. Association of dolerite and lamprophyre dykes,
Jetty Peninsula (Prince Charles Mountains, East Antarctica). Antarctic Sciences. 5(3).
297–307. |
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