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Russian Geology and Geophysics

2019 year, number 5

MANTLECRUSTAL NATURE OF EARLY PALEOZOIC ALKALINE INTRUSIONS IN CENTRAL SANGILEN, TUVA (from Nd, Sr, Pb, C, and O isotope data)

V.V. Vrublevskii1, A.V. Nikiforov2, A.M. Sugorakova3, and T.V. Kozulina1
1 Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
2 Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
3 Tuva Institute for Exploration of Natural Resources, Siberian Branch of the Russian Academy of Sciences, ul. Internatsionalnaya 117a, Kyzyl, Tyva Republic, 667010, Russia
Keywords: Alkaline magmatism, isotope geochemistry and geochronology, plumelithosphere interaction, Sangilen upland, Central Asian Orogenic Belt

Abstract

The Paleozoic foidolitefoyaite plutons of the Sangilen upland (Bayan-Kol, Dakhu-Nur, Chik, and Kharly ones) might have formed in the Late CambrianEarly Ordovician (~490500 Ma, SmNd and UPb); they are the result of the oldest alkaline magmatism in southeastern Tuva. The intrusion was accompanied by the formation of high-temperature (up to ~600900 ºC) endogenous carbonate rocks containing calcite, alkali pyroxene, NaCa amphibole, biotite, fluorapatite, microcline, and nepheline. Silicate and carbonate derivates were produced, most likely, from genetically related heterogeneous sources with εNd(T) varying from 3.0 to 6.3 and from 0.5 to 6.5, respectively, which might be due to the mixing of the depleted (PREMA) and enriched (EM) mantle materials. Initial ratios 207Pb/206Pb ≈ 0.89 and 208Pb/206Pb ≈ 2.15 in K-feldspar from calcitic rocks are close to those of EM 1. The correlation between the stable-isotope ratios (δ18O ~ 7.219.5, δ13C from 6.0 to 1.4 ) and the high 87Sr/86Sr(T) ratio (0.70570.7076) indicates a significant crustal contamination of magma in the upper horizons of the lithosphere and a minor impact of a meteoric fluid. The assumed synchronous formation of the studied plutons and other alkaline rock complexes of the Early Paleozoic Large Igneous Province in the west of the Central Asian Orogenic Belt as well as their isotope similarity do not rule out that the intrusion took place in the plumelithosphere interaction setting.

DOI: 10.15372/RGG2019032