TY - JOUR

T1 - Sandstones of the Itmurundy accretionary complex, central Kazakhstan, as archives of arc magmatism and subduction erosion: Evidence from U-Pb zircon ages, geochemistry and Hf-Nd isotopes

AU - Safonova, Inna

AU - Perfilova, Alina

AU - Savinskiy, Ilya

AU - Kotler, Pavel

AU - Sun, Min

AU - Wang, Bo

N1 - Funding Information: We would like to express our cordial thanks to Prof. Santosh for editorial handling and to Dr. T. Ota and two anonymous reviewers for their constructive and useful comments and suggestions, which all helped us to improve the manuscript to a significant extent. Many thanks to the staff of the analytic centers in Novosibirsk and Yekaterinburg (CUC “Geoanalyst”). The study was supported by the Russian Science Foundation, Project # 21-77-20022 (geochronology, stratigraphy, petrography, geochemistry, geodynamic implications, paper preparation). We also acknowledge the Ministry of Science and Education of Russia, Projects #0330-2019-0003 (regional geology), AAAA-A19-119072990020-6 (Nd isotopes), FSUS-2020-0039 (tectonics), the Ministry of Science and Education of Kazakhstan (project #AP08855920; local geology), the Hong Kong Research Grants Council (HKU17302317, U-Pb isotopes), the National Nature Science Foundation of China (projects # 41772225, 42161144013, Hf isotopes). Contribution to IGCP#662. Publisher Copyright: © 2022 International Association for Gondwana Research

PY - 2022/11

Y1 - 2022/11

N2 - Sandstones hosted by Pacific-type orogenic belts and related accretionary complexes carry records of their source intra-oceanic or continental magmatic arcs. Study of arc-derived sandstones is important for reconstructing tectonic evolution of Pacific-type convergent margins in case such arcs get partly or completely eroded during subduction. In this paper, we present first U-Pb detrital zircon ages and Hf-in-zircon isotope ratios and whole-rock geochemical and Nd data from Ordovician to early Silurian clastic sediments (sandstones) of the Itmurundy Pacific-type orogenic belt and its hosted accretionary complex (AC). The Itmurundy AC is located in the northern Balkhash area of central Kazakhstan and includes sandstones of the Itmurundy and Kazyk fms. (central segment) and Tyuretai Fm. (eastern segment). The U-Pb ages of detrital zircons from Group 1 sandstones show unimodal distributions with major peaks at ca. 467–456 Ma and the youngest clusters of ages from 442 to 439 Ma Ma suggesting post-Llandovery deposition. The distributions of the U-Pb ages of detrital zircons from Group 2 sandstones are polymodal with major peaks at ca. 462–461 Ma and subordinate peaks at 788, 992, 2472 Ma. The Group 2 zircons yielded two youngest clusters of U-Pb ages: 458 Ma and 424 Ma suggesting post-middle Ordovician and post-Ludlow maximum depositional ages. According to petrographic classifications, both Group 1 and 2 sandstones are poorly-sorted and poorly-rounded greywacke or litharenite. The chemical compositions imply that these sandstones are immature and weakly weathered sediments. The Group 1 greywackes are characterized by relatively low SiO2 (63 wt%) compared to Group 2 greywackes (SiO2 = 66 wt% in average). The major and trace element compositions of both groups of sandstones resemble those of supra-subduction andesitic to dacitic volcanic rocks. The positive values of whole-rock ɛNd(t) (+1 to + 5.3) and zircon ɛHf(t) (+9.8 to +17.5) obtained from the Group 1 greywackes suggest juvenile igneous rocks in the source area. On the contrary, the negative values of ɛNd(t) (−7.2) and variable values of zircon ɛHf(t) (−24.5 to +11.5) from the Group 2 sandstones suggest that their parental igneous rocks were derived from mantle sources possessing both juvenile and recycled characteristics. Conclusively, the greywacke sandstones of both groups formed by erosion of an Ordovician intra-oceanic volcanic arc once existed at an active margin of the Paleo-Asian Ocean, however those of Group 1 deposited in a fore-arc basin and trench, while those of Group 2 deposited in a back-arc basin.

AB - Sandstones hosted by Pacific-type orogenic belts and related accretionary complexes carry records of their source intra-oceanic or continental magmatic arcs. Study of arc-derived sandstones is important for reconstructing tectonic evolution of Pacific-type convergent margins in case such arcs get partly or completely eroded during subduction. In this paper, we present first U-Pb detrital zircon ages and Hf-in-zircon isotope ratios and whole-rock geochemical and Nd data from Ordovician to early Silurian clastic sediments (sandstones) of the Itmurundy Pacific-type orogenic belt and its hosted accretionary complex (AC). The Itmurundy AC is located in the northern Balkhash area of central Kazakhstan and includes sandstones of the Itmurundy and Kazyk fms. (central segment) and Tyuretai Fm. (eastern segment). The U-Pb ages of detrital zircons from Group 1 sandstones show unimodal distributions with major peaks at ca. 467–456 Ma and the youngest clusters of ages from 442 to 439 Ma Ma suggesting post-Llandovery deposition. The distributions of the U-Pb ages of detrital zircons from Group 2 sandstones are polymodal with major peaks at ca. 462–461 Ma and subordinate peaks at 788, 992, 2472 Ma. The Group 2 zircons yielded two youngest clusters of U-Pb ages: 458 Ma and 424 Ma suggesting post-middle Ordovician and post-Ludlow maximum depositional ages. According to petrographic classifications, both Group 1 and 2 sandstones are poorly-sorted and poorly-rounded greywacke or litharenite. The chemical compositions imply that these sandstones are immature and weakly weathered sediments. The Group 1 greywackes are characterized by relatively low SiO2 (63 wt%) compared to Group 2 greywackes (SiO2 = 66 wt% in average). The major and trace element compositions of both groups of sandstones resemble those of supra-subduction andesitic to dacitic volcanic rocks. The positive values of whole-rock ɛNd(t) (+1 to + 5.3) and zircon ɛHf(t) (+9.8 to +17.5) obtained from the Group 1 greywackes suggest juvenile igneous rocks in the source area. On the contrary, the negative values of ɛNd(t) (−7.2) and variable values of zircon ɛHf(t) (−24.5 to +11.5) from the Group 2 sandstones suggest that their parental igneous rocks were derived from mantle sources possessing both juvenile and recycled characteristics. Conclusively, the greywacke sandstones of both groups formed by erosion of an Ordovician intra-oceanic volcanic arc once existed at an active margin of the Paleo-Asian Ocean, however those of Group 1 deposited in a fore-arc basin and trench, while those of Group 2 deposited in a back-arc basin.

KW - Central Asian Orogenic Belt

KW - Greywacke sandstones

KW - Ordovician-early Silurian

KW - Paleo-Asian Ocean

KW - U-Pb-Hf zircon data

UR - http://www.scopus.com/inward/record.url?scp=85134646592&partnerID=8YFLogxK

U2 - 10.1016/j.gr.2022.06.018

DO - 10.1016/j.gr.2022.06.018

M3 - Article

AN - SCOPUS:85134646592

VL - 111

SP - 35

EP - 52

JO - Gondwana Research

JF - Gondwana Research

SN - 1342-937X

ER -