TY - JOUR

T1 - Early Paleozoic juvenile crustal growth in the Paleo-Asian Ocean: A contribution from the Zasur'ya accretionary complex of NW Altai

AU - Safonova, Inna

AU - Krutikova, Anastasiya

AU - Perfilova, Alina

AU - Obut, Olga

AU - Kovach, Victor

AU - Kulikova, Anna

N1 - We thank Prof. W. Xiao for inviting us to contribute to the “Altaid” Special Issue. More thanks go to Dr. Nikolai Sennikov for fruitful discussions about the Zasur'ya Series, to Drs. P. Kotler, I. Savinskiy, B. Gan and R. Mamlin for joint field works and to A. Gurova for help with figure drawing and to N. Soloshenko for help with Nd analyses (Geoanalyst Analytical Center, IGG UrB RAS, Yekaterinburg). The study was supported by the Russian Science Foundation (#21-77-20022 ; geochronology, stratigraphy, geochemistry), Fundamental Research Funds for the Central Universities of China (2682023CX016, geodynamic implications, paper preparation), and Ministry of Science and Higher Education of Russia, State Assignment Projects (122041400044-2, FSUS-2020-0039) (petrography, geodynamic implications, paper preparation).

PY - 2023/12/14

Y1 - 2023/12/14

N2 - Reconstruction of proportions between juvenile and recycled crust remains challengeable because a big part of juvenile source magmatic rocks formed at intra-oceanic arcs, can be destroyed by surface and tectonic erosion leaving, at best, greywacke sandstones. Such sandstones are typically hosted by accretionary complexes, which study, therefore, is of crucial importance. In this paper we review available geological and micropaleontological data and present first U[sbnd]Pb detrital zircon ages, geochemical data and isotope (Sm[sbnd]Nd, Lu[sbnd]Hf) data from sandstones of the late Cambrian-early Ordovician Zasur'ya accretionary complex (AС) of NW Altai. No island-arc units have ever been reported there. The Zasur'ya AC includes ocean plate stratigraphy (OPS) magmatic and sedimentary rocks of three formations, Listvenny (l. Cambrian), Talitsa (Tremadocian) and Marcheta (Floian), which age was constrained by microfossils. The OPS assemblage includes basalt, pelagic chert and hemipelagic siliceous mudstone and siltstone, and sandstone. We analyzed zircons in five samples. The distributions of U[sbnd]Pb ages of detrital zircons from five samples of sandstones are all unimodal with main peaks at ca. 488 Ma (Listvenny Fm.), 491 Ma (Talitsa Fm.) and 485 Ma (Marcheta Fm.). The Precambrian ages are very few. The maximum deposition ages inferred from the youngest populations of zircon ages are ca. 464 Ma. Compositionally, the sandstones are greywackes or feldspar litharenites. The Listvenny and Talitsa sandstones are higher silicic (SiO2av. = 68.5 wt%) compared to Marcheta samples (SiO2av. = 60.5 wt%). The major and trace element features of all sandstones are similar to supra-subduction intermediate-felsic (Listvenny, Talitsa) and mafic-intermediate (Marcheta) magmatic rocks. All samples yielded positive values of zircon ɛHf(t) (+4.3 to +20.1) and bulk-rock ɛNd(t) (+0.6 to +4.8) indicating juvenile magmatic rocks in the provenance. However, the Listvenny and Talitsa samples show lower ɛNd(t) (1.3 and 0.8, respectively) than those of the Marcheta Fm. (4.7). Probably the Zasur'ya sandstones were deposited in a back-arc basin (Listvenny, Talitsa), and fore-arc basin (Marcheta). All Zasur'ya greywacke sandstones were derived by destruction of a single late Cambrian - Early Ordovician intra-oceanic arc. The Zasur'ya intra-oceanic arc was identified in NW Altai for the first time and it represents a new site of juvenile crustal growth in the CAOB.

AB - Reconstruction of proportions between juvenile and recycled crust remains challengeable because a big part of juvenile source magmatic rocks formed at intra-oceanic arcs, can be destroyed by surface and tectonic erosion leaving, at best, greywacke sandstones. Such sandstones are typically hosted by accretionary complexes, which study, therefore, is of crucial importance. In this paper we review available geological and micropaleontological data and present first U[sbnd]Pb detrital zircon ages, geochemical data and isotope (Sm[sbnd]Nd, Lu[sbnd]Hf) data from sandstones of the late Cambrian-early Ordovician Zasur'ya accretionary complex (AС) of NW Altai. No island-arc units have ever been reported there. The Zasur'ya AC includes ocean plate stratigraphy (OPS) magmatic and sedimentary rocks of three formations, Listvenny (l. Cambrian), Talitsa (Tremadocian) and Marcheta (Floian), which age was constrained by microfossils. The OPS assemblage includes basalt, pelagic chert and hemipelagic siliceous mudstone and siltstone, and sandstone. We analyzed zircons in five samples. The distributions of U[sbnd]Pb ages of detrital zircons from five samples of sandstones are all unimodal with main peaks at ca. 488 Ma (Listvenny Fm.), 491 Ma (Talitsa Fm.) and 485 Ma (Marcheta Fm.). The Precambrian ages are very few. The maximum deposition ages inferred from the youngest populations of zircon ages are ca. 464 Ma. Compositionally, the sandstones are greywackes or feldspar litharenites. The Listvenny and Talitsa sandstones are higher silicic (SiO2av. = 68.5 wt%) compared to Marcheta samples (SiO2av. = 60.5 wt%). The major and trace element features of all sandstones are similar to supra-subduction intermediate-felsic (Listvenny, Talitsa) and mafic-intermediate (Marcheta) magmatic rocks. All samples yielded positive values of zircon ɛHf(t) (+4.3 to +20.1) and bulk-rock ɛNd(t) (+0.6 to +4.8) indicating juvenile magmatic rocks in the provenance. However, the Listvenny and Talitsa samples show lower ɛNd(t) (1.3 and 0.8, respectively) than those of the Marcheta Fm. (4.7). Probably the Zasur'ya sandstones were deposited in a back-arc basin (Listvenny, Talitsa), and fore-arc basin (Marcheta). All Zasur'ya greywacke sandstones were derived by destruction of a single late Cambrian - Early Ordovician intra-oceanic arc. The Zasur'ya intra-oceanic arc was identified in NW Altai for the first time and it represents a new site of juvenile crustal growth in the CAOB.

KW - Altai orogen

KW - Bulk-rock Nd isotopes

KW - Central Asian Orogenic Belt

KW - Charysh-Terekta suture-shear zone

KW - Geochemistry

KW - Hf-in-zircon isotopes

KW - U-Pb zircon ages

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85185964626&origin=inward&txGid=2fa2a4e18475d6c1ce1864e95c7006fe

UR - https://www.mendeley.com/catalogue/00bce7e8-c6de-3dba-9dcc-eafec8d98a8e/

U2 - 10.1016/j.earscirev.2023.104648

DO - 10.1016/j.earscirev.2023.104648

M3 - Article

VL - 249

JO - Earth-Science Reviews

JF - Earth-Science Reviews

SN - 0012-8252

M1 - 104648

ER -