Proterozoic (1.91-0.72 Ga) mafic magmatism of the southern flank of the siberian craton: geochemical systematics of dolerites
O.M. Turkina
Sobolev Institute of Geology and Mineralogy, SB RAS, Novosibirsk, Russia
Novosibirsk State University, Novosibirsk, Russia
Keywords: Dolerite, Proterozoic, geochemical indicator, southern flank of Siberian craton, magma source
Abstract
This paper presents an analysis of compositional data on Proterozoic dolerites from dikes and sills on the southern flank of the Siberian Craton, formed in an intracontinental setting between 1.91 and 0.72 Ga. Indicator geochemical parameters have been established for four age groups of dolerites, reflecting differences in their of mantle sources and the conditions of generation of the initial melts. Neoproterozoic dolerites of the Nersa complex are characterized by lowest (Sm/Yb)n and (Nb/Y)pm
ratios and were formed with the contribution from enriched subduction-modified lithospheric mantle (SZLM) and a depleted (asthenospheric) source. Dolerites aged 1.35 Ga are distinguished by the maximum concentrations of incompatible rare elements and high (Sm/Yb)n and (Nb/Y)pm values, their formation occurred from an enriched plume mantle source. Mesoproterozoic (~1.6 Ga) dolerites of the Prisayan Trough are characterized by elevated contents of TiO2 and high-field strength (Nb, Ta) elements compared to dolerites of the Nersa Complex. They are dominated by an enriched plume source with high (Nb/Y)pm and TiO2/Yb ratios, with limited contribution from SZLM. Paleoproterozoic (1.91 Ga) dolerites, while similar in (Sm/Yb)n values to Neoproterozoic ones, have lower (Nb/Y)pm
and (Nb/La)pm ratios, indicating a more depleted mantle source. The proposed diagrams (Sm/Yb)n – (Nb/Y)pm and (Nb/La)pm
– (Nb/Y)pm allow us to systematize dolerites from the dike swarms of the southern flank of the Siberian craton based on the similarity in composition with dolerites of four stages of Proterozoic basic magmatism.
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