Abstract
The northwestern Erguna Block, where a wide range of volcanic rocks are present, provides one of the foremost locations to investigate Mesozoic Paleo-Pacific and Mongol-Okhotsk subduction. The identification and study of Late Jurassic mafic volcanic rocks in the Badaguan area of northwestern Erguna is of particular significance for the investigation of volcanic magma sources and their compositional evolution. Detailed petrological, geochemical, and zircon U-Pb dating suggests that the Late Jurassic mafic volcanic rocks formed at 157–161 Ma. Furthermore, the geochemical signatures of these mafic volcanic rocks indicate that they are calc-alkaline or transitional series with weak peraluminous characteristics. The rocks have a strong MgO, Al2O3, and total alkali content, and a SiO2 content of 53.55–63.68 wt %; they are enriched in Rb, Th, U, K, and light rare-earth elements (LREE), and depleted in high-field-strength elements (HFSE), similar to igneous rocks in subduction zones. These characteristics indicate that the Late Jurassic mafic volcanic rocks in the Badaguan area may be derived from the partial melting of the lithospheric mantle as it was metasomatized by subduction-related fluid and the possible incorporation of some subducting sediments. Subsequently, the fractional crystallization of Fe and Ti oxides occurred during magmatic evolution. Combined with the regional geological data, it is inferred that the studied mafic volcanic rocks were formed by lithospheric extension after the closure of the Mongol-Okhotsk Ocean.
Highlights
The northwestern margin of the Erguna Block underwent a complex tectonic evolution during the Phanerozoic, including ancient Asia, the Mongol-Okhotsk subduction, and the westward subduction of the Paleo-Pacific Ocean [1,2,3,4,5]
With the increasing focus on the Mesozoic volcanic rocks in the Da Xing’anling region, a large amount of high-precision zircon U-Pb and 40Ar/39Ar age and geochemical data have been obtained. These data indicate that most of the Mesozoic volcanic rocks in the Da Xing’anling region formed during the Early Cretaceous [10,11], with most of the volcanic rocks consisting of calc-alkaline and alkaline types in southern and northern Da Xing’anling, respectively
Acidic volcanic rocks are divided into high Sr rhyolite and low Sr rhyolite types; high Sr rhyolite types were formed by the differentiation of calc-alkaline basaltic magma, and low Sr rhyolite types were produced by the partial melting of lower crustal rocks [13]
Summary
The northwestern margin of the Erguna Block underwent a complex tectonic evolution during the Phanerozoic, including ancient Asia, the Mongol-Okhotsk subduction, and the westward subduction of the Paleo-Pacific Ocean [1,2,3,4,5]. With the increasing focus on the Mesozoic volcanic rocks in the Da Xing’anling region, a large amount of high-precision zircon U-Pb and 40Ar/39Ar age and geochemical data have been obtained. These data indicate that most of the Mesozoic volcanic rocks in the Da Xing’anling region formed during the Early Cretaceous [10,11], with most of the volcanic rocks consisting of calc-alkaline and alkaline types in southern and northern Da Xing’anling, respectively. Existing studies mainly focused on subduction, while understanding of the Late Jurassic–Early Cretaceous tectonic evolution after the closure of the Mongol-Okhotsk Ocean remains limited [22,23,24]. In combination with available chronological, geochemical, and isotopic data, our results provide a basis for exploring the tectonic evolution of Northeast China and its surrounding areas, and a deeper understanding of the southward subduction of the Mongol-Okhotsk Ocean
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