TY - JOUR

T1 - Mesoarchean bimodal volcanic rocks of the Onot greenstone belts, southwestern Siberian craton

T2 - Implications for magmatism in an extension/rift setting

AU - Turkina, O. M.

AU - Sukhorukov, V. P.

AU - Sergeev, S. A.

N1 - Publisher Copyright: © 2020 Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/7

Y1 - 2020/7

N2 - This paper shows that Mesoarchean bimodal felsic and mafic metavolcanic rocks of the Onot greenstone belt (Sharyzhalgay uplift, the southwestern margin of the Siberian craton) formed as a result of rifting of Paleoarchean continental crust. Evidence for this comes from U-Pb zircon ages, whole-rock geochemical and Nd isotope data and Hf-in-zircon isotope data from a metarhyolite-basaltic unit. The over 80 km long Onot greenstone belt consists of tectonic sheets composed of metasedimentary-volcanogenic and tonalite-trondhjemite-granodiorite (TTG) rocks thrusted to the southwest onto high-grade rocks of the Kitoy terrane. The greenstone sequence includes a bimodal metavolcanic unit overlain by metavolcanogenic-sedimentary units. The felsic volcanic rocks formed at ~2.88 Ga and were metamorphosed at 660–690 °C and ~6 kbar during the Late Paleoproterozoic. The high-Fe metarhyolites are enriched in the REE and HFSE and are compositionally similar to felsic volcanic rocks of Archean greenstone belts with lower La/Yb and Zr/Y (FIIIa and FIIIb types after Hart et al., 2004), and A-type granitoids. The high- and low-Ti metabasalts (amphibolites) possess geochemical affinities to both subduction-related basalts and continental flood basalts contaminated by crustal material. The metarhyolites yielded negative εNd(t) values (−3.8 to −0.8). Their zircons yielded negative to positive εHf(t) values (−8.5 to +1.1). The isotopic data suggest melting of heterogeneous crust, consisting of Paleoarchean plagiogneisses of the TTG basement complex and a juvenile source. The contribution of a mafic source resulted in enrichment of metarhyolites in FeO, MgO and TiO2. The crustal melting probably occurred at shallow depths at 2–4 kbar and at high temperatures higher than 900 °C. The coeval formation of Onot basalts and low-P - – high-T felsic melts could be triggered by decompressional mantle upwelling and subsequent extension and thinning of the subcontinental lithosphere. Worldwide, evidence for extension/rifting comes from Meso-Neoarchean mafic dikes and coeval intra-plate bimodal basalt-rhyolite volcanism. The events of extension/rifting and the formation of subcontinental lithospheric mantle suggest formation of stable and rheologically rigid continental plates.

AB - This paper shows that Mesoarchean bimodal felsic and mafic metavolcanic rocks of the Onot greenstone belt (Sharyzhalgay uplift, the southwestern margin of the Siberian craton) formed as a result of rifting of Paleoarchean continental crust. Evidence for this comes from U-Pb zircon ages, whole-rock geochemical and Nd isotope data and Hf-in-zircon isotope data from a metarhyolite-basaltic unit. The over 80 km long Onot greenstone belt consists of tectonic sheets composed of metasedimentary-volcanogenic and tonalite-trondhjemite-granodiorite (TTG) rocks thrusted to the southwest onto high-grade rocks of the Kitoy terrane. The greenstone sequence includes a bimodal metavolcanic unit overlain by metavolcanogenic-sedimentary units. The felsic volcanic rocks formed at ~2.88 Ga and were metamorphosed at 660–690 °C and ~6 kbar during the Late Paleoproterozoic. The high-Fe metarhyolites are enriched in the REE and HFSE and are compositionally similar to felsic volcanic rocks of Archean greenstone belts with lower La/Yb and Zr/Y (FIIIa and FIIIb types after Hart et al., 2004), and A-type granitoids. The high- and low-Ti metabasalts (amphibolites) possess geochemical affinities to both subduction-related basalts and continental flood basalts contaminated by crustal material. The metarhyolites yielded negative εNd(t) values (−3.8 to −0.8). Their zircons yielded negative to positive εHf(t) values (−8.5 to +1.1). The isotopic data suggest melting of heterogeneous crust, consisting of Paleoarchean plagiogneisses of the TTG basement complex and a juvenile source. The contribution of a mafic source resulted in enrichment of metarhyolites in FeO, MgO and TiO2. The crustal melting probably occurred at shallow depths at 2–4 kbar and at high temperatures higher than 900 °C. The coeval formation of Onot basalts and low-P - – high-T felsic melts could be triggered by decompressional mantle upwelling and subsequent extension and thinning of the subcontinental lithosphere. Worldwide, evidence for extension/rifting comes from Meso-Neoarchean mafic dikes and coeval intra-plate bimodal basalt-rhyolite volcanism. The events of extension/rifting and the formation of subcontinental lithospheric mantle suggest formation of stable and rheologically rigid continental plates.

KW - Geochemistry

KW - Nd and Hf isotopes

KW - Onot greenstone belt

KW - Stabilization of subcontinental lithospheric mantle

KW - U-Pb zircon age

KW - A-TYPE GRANITES

KW - TRACE-ELEMENT GEOCHEMISTRY

KW - HF ISOTOPE COMPOSITION

KW - U-PB

KW - SHARYZHALGAI-UPLIFT

KW - CONTINENTAL-CRUST

KW - LU-HF

KW - PILBARA CRATON

KW - SM-ND

KW - RE-OS

UR - http://www.scopus.com/inward/record.url?scp=85083017108&partnerID=8YFLogxK

U2 - 10.1016/j.precamres.2020.105731

DO - 10.1016/j.precamres.2020.105731

M3 - Article

AN - SCOPUS:85083017108

VL - 343

JO - Precambrian Research

JF - Precambrian Research

SN - 0301-9268

M1 - 105731

ER -