The alkaline and carbonatitic rocks of Gorny Altai (Edel’veis complex) as indicators of Early Paleozoic plume magmatism in the Central Asian Fold Belt

Abstract

The minor intrusions of the Edel’veis alkaline–carbonatite complex are bounded by the spurs of the North Chuya Ridge in southeastern Gorny Altai. According to Ar–Ar isotope data, the complex formed in the Middle Cambrian (∼507 Ma). All of its components (alkali clinopyroxenite–melanogabbro–alkali syenite + Ca-carbonatite) occur in only one pluton. Silicate igneous rocks are equivalent in silica content and alkalinity to potassic alkaline and subalkalic mafic rocks. Apatite-phlogopitic Ca-carbonatites are enriched in P2O5 (up to 3.6 wt.%), Sr (∼2500–5500 ppm), and REE (up to ∼2000 ppm) and are, presumably, of liquation genesis. A PREMA-type plume component was a predominant magma source for the complex (ɛNd(T) = +6.56 to +6.85). According to isotope data (87Sr/86Sr(T) ∼ 0.7032–0.7039; δ18O ∼ 7.5–14.9‰; δ13C ∼ –2.7 to –8.4‰), the fractionation of the melts was accompanied by their crustal contamination. The trace-element composition of the rocks suggests that the complex developed on a continental margin and its development was accompanied by late-collisional rifting and the mixing of moderately depleted (PREMA) and enriched suprasubductional lithospheric mantle (EM I or EM II) with continental crust. It is presumed that the alkaline and carbonatite complexes in the western Central Asian Fold Belt are of primary plume origin and form a LIP within this belt together with other associations produced by Early Paleozoic (510–470 Ma) magmatism.

Geochemistry, isotope triad (Nd–Sr–O), and 40Ar–39Ar age of Paleozoic alkaline mafic intrusions of the Kuznetsk Alatau (by the example of the Belaya Gora pluton)

“…The radiogenic Sr isotope composition and high δ 18 O values of rocks suggest involvement of crustal material in magma. Precision analytical studies showed similar isotope effects in other alkaline igneous complexes of the CAOB (Doroshkevich et al, 2012;Pokrovskii et al, 1998;Vrublevskii et al, 2012aVrublevskii et al, , 2014d.…”

Isotope (U–Pb, Sm–Nd, Rb–Sr) geochronology of alkaline basic plutons of the Kuznetsk Alatau

“…Note that products of Early Paleozoic alkaline magmatism are also present in other parts of the CAFB. Close ages were established for some intrusive massifs in Cisbaikalia and western Transbaikalia (~470-520 Ma), East Sayan (~490-520 Ma), Gorny Altai (~510 Ma), and Tuva (~490 Ma) (Doroshkevich et al, 2012;Kozakov et al, 2003;Nikiforov and Yarmolyuk, 2007;Sklyarov et al, 2009;Vrublevskii et al, 2012a).…”

“…These ages fall in the interval ~470-510 Ma typical of many products of the CAFB magmatism united into an Early Paleozoic Large Igneous Province (Izokh et al, 2007;Vladimirov et al, 1999b;Vrublevskii et al, 2009Vrublevskii et al, , 2012a. Most of these rocks formed from mantle plume.…”

The role of earth mantle in the development of early Paleozoic oceanic islands volcanism (for the geochemical data of OIB from SE Altai Mountains)

“…TAS and SiO 2 -K 2 O diagrams are given according to Le Maître et al;1989, Peccerillo, Taylor, 1976[Vrublevskii et al, 2012…”

“…а -ε Nd T -ε Sr T diagram. 1 and 2 sections -compositions of subalkaline-alkaline rocks and carbonatites of Edelweiss complex (1, ~ 507 Ma), Terangik pluton (2 ~ 247 Ma) at Gorny Altai [Vrublevskii et al, 2012;Krupchatnikov, Vrublevskii, Kruk, 2015]; isotopic variations in basalts of late Precambrian and early Paleozoic Kuray, Katun, Zasuryin accretionary complexes (АК) are shown [Safonova, 2008;. Mantle array section and MORB, PREMA, HIMU, EM I locations are given in accordance with their modern isotopic parameters [Zindler, Hart, 1986].…”