TY - JOUR

T1 - New constraints on volcanism during Ordovician-Silurian transition: Insights from marine bentonites in northern Yili Block (NW China)

AU - Wang, Yanjun

AU - Wang, Bo

AU - Li, Ming

AU - Cao, Shengnan

AU - Wang, Hongbin

AU - Pan, Shuxin

AU - Guo, Juanjuan

AU - Ma, Delong

AU - Song, Fang

AU - Cao, Tingting

AU - Safonova, Inna Y.

AU - Zhong, Linglin

AU - Ni, Xinghua

N1 - Funding Information: We thank Mr. B. Wu (NJU) for his kind help in the zircon LA-ICP-MS dating. Two anonymous reviewers and the Editor Prof. S.Z. Shen are appreciated for their constructive comments and suggestions. This study was co-sponsored by the National Nature Science Foundation of China ( 42161144013 , 41772225 ), Scientific Research and Technology Development Project of CNPC ( China National Petroleum Corporation ) (Grant No. 2021DJ0201 ), the Fundamental Research Funds for the Central Universities of China , the Open Fund of State Key Laboratory for Mineral Deposits Research ( ZZKT-201603 ), the Russian Science Foundation (project #21-77-20022) and Ministry of Education and Science (project АААА-А19-119072990020-6). Publisher Copyright: © 2022 Elsevier B.V.

PY - 2022/8/15

Y1 - 2022/8/15

N2 - The Yili Block is located at the Chinese western Tianshan and is a constituent of the Kazakhstan microcontinent. It played an important role in the evolution of the SW Central Asian Orogenic Belt (CAOB). The Yili Block underwent the Paleozoic orogeny during the subduction and closure of the Junggar Ocean. Late Paleozoic arc-type magmatic rocks have been widely recorded in the Yili Block; however, it remains poorly constrained when and how the Junggar Ocean started to subduct beneath the Yili Block. In this study, we report new results of zircon LA-ICP-MS U[sbnd]Pb dating and Lu[sbnd]Hf isotopic analysis on a series of bentonite beds in tightly folded upper Ordovician siliceous black shales of the Guozigou Section in the northern Yili Block. The occurrence of bentonite layers and associated sulfides within graptolite-bearing siliceous black shales indicates multiple marine volcanic eruptions. Magmatic zircons separated from seven representative bentonite samples yielded consistent U[sbnd]Pb ages ranging from 449.5 ± 2.4 Ma to 444.8 ± 2.0 Ma (Katian). In situ zircon Lu[sbnd]Hf isotopic analyses show mostly positive εHf(t) values (−0.01 and 1.31 to 11.7) and Neoproterozoic single-stage Hf model ages (TDM1 = 0.6– 1.0 Ga). A linear correlation between the εHf(t) and TDM1 suggests that these zircons likely crystallized from a common magma originated from a depleted mantle source with variable involvement of Precambrian continental crust. Our new zircon ages and Hf isotopic data are comparable with those of the Middle-Late Ordovician continental arc-type magmatic rocks in the nearby Wenquan area, both indicating that the subduction of the Junggar Ocean beneath the northern Yili Block started in the Middle-Late Ordovician, and are therefore important for early Paleozoic paleogeographic and tectonic reconstruction of the Paleo-Asian Ocean domain. In addition, the Late Ordovician marine bentonites and black shales coincide with the worldwide intensive volcanic activities and related climate/environment changes during late Katian to Hirnantian. Thus, these new data also provide further arguments for possible causes of the global climate change and mass extinction during the Ordovician-Silurian transition.

AB - The Yili Block is located at the Chinese western Tianshan and is a constituent of the Kazakhstan microcontinent. It played an important role in the evolution of the SW Central Asian Orogenic Belt (CAOB). The Yili Block underwent the Paleozoic orogeny during the subduction and closure of the Junggar Ocean. Late Paleozoic arc-type magmatic rocks have been widely recorded in the Yili Block; however, it remains poorly constrained when and how the Junggar Ocean started to subduct beneath the Yili Block. In this study, we report new results of zircon LA-ICP-MS U[sbnd]Pb dating and Lu[sbnd]Hf isotopic analysis on a series of bentonite beds in tightly folded upper Ordovician siliceous black shales of the Guozigou Section in the northern Yili Block. The occurrence of bentonite layers and associated sulfides within graptolite-bearing siliceous black shales indicates multiple marine volcanic eruptions. Magmatic zircons separated from seven representative bentonite samples yielded consistent U[sbnd]Pb ages ranging from 449.5 ± 2.4 Ma to 444.8 ± 2.0 Ma (Katian). In situ zircon Lu[sbnd]Hf isotopic analyses show mostly positive εHf(t) values (−0.01 and 1.31 to 11.7) and Neoproterozoic single-stage Hf model ages (TDM1 = 0.6– 1.0 Ga). A linear correlation between the εHf(t) and TDM1 suggests that these zircons likely crystallized from a common magma originated from a depleted mantle source with variable involvement of Precambrian continental crust. Our new zircon ages and Hf isotopic data are comparable with those of the Middle-Late Ordovician continental arc-type magmatic rocks in the nearby Wenquan area, both indicating that the subduction of the Junggar Ocean beneath the northern Yili Block started in the Middle-Late Ordovician, and are therefore important for early Paleozoic paleogeographic and tectonic reconstruction of the Paleo-Asian Ocean domain. In addition, the Late Ordovician marine bentonites and black shales coincide with the worldwide intensive volcanic activities and related climate/environment changes during late Katian to Hirnantian. Thus, these new data also provide further arguments for possible causes of the global climate change and mass extinction during the Ordovician-Silurian transition.

KW - Central Asian Orogenic Belt

KW - Junggar Ocean

KW - North Tianshan (Tien Shan)

KW - Ordovician-Silurian transition

KW - Paleogeographic reconstruction

KW - Subduction-related magmatism

UR - http://www.scopus.com/inward/record.url?scp=85130584094&partnerID=8YFLogxK

U2 - 10.1016/j.palaeo.2022.111073

DO - 10.1016/j.palaeo.2022.111073

M3 - Article

AN - SCOPUS:85130584094

VL - 600

JO - Palaeogeography, Palaeoclimatology, Palaeoecology

JF - Palaeogeography, Palaeoclimatology, Palaeoecology

SN - 0031-0182

M1 - 111073

ER -