Computer Science
Scientific paper
Apr 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990gecoa..54.1061f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 54, Issue 4, pp.1061-1081
Computer Science
20
Scientific paper
Archean sandstone and shale samples from turbiditic (TF) and alluvial facies (AF) in the Southern Volcanic Zone of the Abitibi greenstone belt, Canada, have been analyzed for major and trace elements. The sandstones from TF are mainly greywackes, whereas those from AF are lithic arenite. SiO 2 ranges from 51 to 68%. Geochemically, the clastic sediments cluster into mafic element (MEP) and low mafic element (LMEP) populations. The MEP sediments, which include turbiditic facies sediment samples from the Larder Lake Group in the Kirkland Lake area, are characterized by elevated abundances of MgO (>5%), Ni (>200 ppm), Cr (>400 ppm), Sc (>22 ppm), and FeO (>7.5%) abundances; lower contents of incompatible elements, such as Th, U, Ta, Hf, Zr, and total REEs (<45 ppm); and lower contents of alkaline earth elements, Sr, Ba, and Cs, relative to the LMEP sediments. La/Yb N ratios are 4.5, with Eu/Eu* 1. The LMEP sediments (which include samples from the Beatty, Dome, and Three Nations Lake formations in Timmins, the Kewagama Group, Noranda area, and Timiskaming Group in the Kirkland Lake area), however, show reverse abundance distributions. The geochemical gaps shown by the major and trace elements define two populations of sediments, suggesting contrasting provenances for them: the MEP sediments require a dominantly mafic and ultramafic (90%) source with 10% felsic contribution, whereas the LMEP sediments require a mixture of felsic (75%) and mafic (25%) rocks. This compositional distribution of the sediments is closely related to their tectonic environments. The MEP was formed in basins proximal to or within an active oceanic rift, consequently having ultramafic and mafic rocks as the major source. For the LMEP, calc-alkaline volcanic sequences formed in an island arc-like setting were the major source. These two contrasting volcanic-plutonic terranes were tectonically juxtaposed during late Archean collisional tectonics.
Feng Rongquan
Kerrich Rob
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