TY - JOUR

T1 - Late Paleozoic–Early Mesozoic granitoids in the Khangay-Khentey basin, Central Mongolia: Implication for the tectonic evolution of the Mongol-Okhotsk Ocean margin

AU - Ganbat, Ariuntsetseg

AU - Tsujimori, Tatsuki

AU - Miao, Laicheng

AU - Safonova, Inna

AU - Pastor-Galán, Daniel

AU - Anaad, Chimedtseren

AU - Baatar, Munkhtsengel

AU - Aoki, Shogo

AU - Aoki, Kazumasa

AU - Savinskiy, Ilya

N1 - Funding Information: This research was supported by CNEAS and FRIS of Tohoku University and in part by grants from the MEXT/JSPS KAKENHI JP18H01299 and JP21H01174 to TT and JP19K04043 to KA, by the National Natural Science Foundation of China (grant number 41772230 ) to L. Miao, and by the Russian Science Foundation (grants # 20-77-10051 to Ilya S., Nd isotopes, and # 21-77-20022 to Inna S., tectonic implications). AG gratefully acknowledges the Japanese Government MEXT Scholarship. We also thank Isamu Morita, and Manzshir Bayarbold, Sanchir Dorjgochoo for their assistance in the laboratory and for providing geological material. We are grateful for the constructive reviews of V. Kovach, Xian-Hua Li, and an anonymous reviewer, which all helped us to improve the manuscript. Contribution to IGCP#662. Publisher Copyright: © 2021 Elsevier B.V.

PY - 2021/12/1

Y1 - 2021/12/1

N2 - The Mongol-Okhotsk Belt is the youngest segment of the Central Asian Orogenic Belt, which is the venue of the massive juvenile crust emplacement, and its formation and evolutions are still pending problems. This paper presents the first up-to-date U–Pb zircon ages, Hf-in-zircon isotope, geochemical and whole-rock Nd isotope data from igneous rocks of the Khangay-Khentey basin, Central Mongolia. The U–Pb zircon ages indicate three groups of magmatism at ~296 Ma, ~280 Ma, and ~230 Ma. The ~296 Ma magmatic rocks are characterized by negative εHf(t) and εNd(t) values and old Hf and Nd model ages suggesting their derivation by the melting of the crustal source. The ~280 Ma rocks are A2-type monzonites, granitoids, and rhyolites show positive εHf(t) and εNd(t) values and Neoproterozoic Hf and Nd model ages. The geochemical and isotope data suggest that ~280 Ma magmatism derived by the melting of a crustal source, induced by mantle upwelling. The ~230 Ma rock assemblage includes granitoids and volcanic rocks. The I-type calc-alkaline granitoids are enriched in K, Rb, U, and Th. The geochemical characteristics suggest that they have formed by the melting of a hornblende-bearing crustal source with the participation of fluids separated from the subducting slab. The positive εHf(t) and εNd(t) ~230 Ma rocks suggest partial melting of a depleted lower crustal material with the contribution of ancient crustal material. The ~296 Ma granitoids possess coherent/coupled Nd–Hf isotopic compositions supporting their origin from the ancient crust. Although the number of ~296 Ma samples are small, we suggest that they were probably emplaced at an active continental setting, ~280 Ma samples could have formed in a setting of local extension environment, ~230 Ma granitoids were also formed at an active continental margin. These magmatic rocks formed during the subduction of the Mongol-Okhotsk oceanic plate beneath the Central Mongolia-Erguna Block.

AB - The Mongol-Okhotsk Belt is the youngest segment of the Central Asian Orogenic Belt, which is the venue of the massive juvenile crust emplacement, and its formation and evolutions are still pending problems. This paper presents the first up-to-date U–Pb zircon ages, Hf-in-zircon isotope, geochemical and whole-rock Nd isotope data from igneous rocks of the Khangay-Khentey basin, Central Mongolia. The U–Pb zircon ages indicate three groups of magmatism at ~296 Ma, ~280 Ma, and ~230 Ma. The ~296 Ma magmatic rocks are characterized by negative εHf(t) and εNd(t) values and old Hf and Nd model ages suggesting their derivation by the melting of the crustal source. The ~280 Ma rocks are A2-type monzonites, granitoids, and rhyolites show positive εHf(t) and εNd(t) values and Neoproterozoic Hf and Nd model ages. The geochemical and isotope data suggest that ~280 Ma magmatism derived by the melting of a crustal source, induced by mantle upwelling. The ~230 Ma rock assemblage includes granitoids and volcanic rocks. The I-type calc-alkaline granitoids are enriched in K, Rb, U, and Th. The geochemical characteristics suggest that they have formed by the melting of a hornblende-bearing crustal source with the participation of fluids separated from the subducting slab. The positive εHf(t) and εNd(t) ~230 Ma rocks suggest partial melting of a depleted lower crustal material with the contribution of ancient crustal material. The ~296 Ma granitoids possess coherent/coupled Nd–Hf isotopic compositions supporting their origin from the ancient crust. Although the number of ~296 Ma samples are small, we suggest that they were probably emplaced at an active continental setting, ~280 Ma samples could have formed in a setting of local extension environment, ~230 Ma granitoids were also formed at an active continental margin. These magmatic rocks formed during the subduction of the Mongol-Okhotsk oceanic plate beneath the Central Mongolia-Erguna Block.

KW - CAOB

KW - Crustal evolution

KW - Geochronology

KW - Hf-in-zircon

KW - Mongol-Okhotsk Ocean

KW - Nd isotope

UR - http://www.scopus.com/inward/record.url?scp=85114668342&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2021.106455

DO - 10.1016/j.lithos.2021.106455

M3 - Article

AN - SCOPUS:85114668342

VL - 404-405

JO - Lithos

JF - Lithos

SN - 0024-4937

M1 - 106455

ER -