Sources of Melts of Early Neoproterozoic – Middle Paleozoic Granitoides in Western Sayan
S.N. Rudneva, G.A. Babinb , P.A. Serovc, A.V. Somsikovad
a V.S. Sobolev institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
b A.P. Karpinsky Russian Geological Research institute, St.Petersburg, Russia
с Geological institute of the Kola Science Center, Russian Academy of Sciences, Apatity, Russia
d Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, Moscow, Russia
Keywords: Altai–Sayan Fold Belt; Western Sayan; granitoid and gabbroid magmatism; geochemistry; Nd and Sr isotopes
Abstract
This study synthesizes petrochemical, geochemical, and isotopic (Sm–Nd and Rb–Sr) data on granitoid and gabbroid complexes of the Western Sayan, formed in a range of geodynamic settings (including island arc, accretion–collision, transform–shear, and active continental margin environments) between the Late Vendian and Late Devonian. The results provide constraints on the physicochemical conditions of parental melt generation, the nature of magma sources, and their temporal evolution throughout successive geodynamic stages.
These findings highlight the long-term evolution of magma sources in response to changing geodynamic regimes during the Vend–Paleozoic development of the Western Sayan. The intrusive complexes display a systematic decrease in ɛNd and increase 87Sr/86Sr0 values in granitoid and gabbroid complexes from early to later geodynamic stages: island arc (545–524 Ma, ɛNd = +7.5 – +4.9, 87Sr/86Sr0
= 0.7042–0.7056), accretion–collision (505–460 Ma, ɛNd = +6.9 – +0.6, 87Sr/86Sr0
= 0.7036–0.7041), transform–shear (437–433 Ma, ɛNd = +8.4 – +7.2, 87Sr/86Sr0 = 0.7031–0.7057), and active continental margin (425–370 Ma, ɛNd = +5.7 – +1.0, 87Sr/86Sr0 = 0.7035–0.7103). This progressive shift reflects a declining contribution of mantle sources (island-arc and oceanic types) and a concomitant increase in the role of ancient crustal components (metamorphic complexes, turbidites, and flysch-type sediments) in the generation of parental magmas.
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