Temporal variations in the geochemistry of Mesozoic mafic–intermediate volcanic rocks in the northern Great Xing'an Range, Northeast China, and implications for deep lithospheric mantle processes

Abstract

Identifying the composition of the recycled materials in the lithospheric mantle is crucial for establishing links between mantle geochemical ‘reservoirs’ and deep mantle geodynamic processes. However, studies that focus on deep mantle processes under multiple subduction tectonic regimes have been absent. In this paper, we present 40 Ar/ 39 Ar age, whole-rock geochemical, and Sr–Nd–Pb–Hf isotope, zircon Hf-O isotope, and in situ plagioclase Pb isotope data for Mesozoic mafic–intermediate volcanic rocks in the northern Great Xing'an Range, northeast China. These and published data are used to constrain the deep processes that occurred in the lithospheric mantle during the Mesozoic, in the context of the evolution of the Mongol–Okhotsk Ocean and whether subduction of the Paleo-Pacific Plate affected the formation of volcanic rocks in the western part of northeast China. The Mesozoic mafic–intermediate volcanic rocks in the northern Great Xing'an Range can be divided into three stages: Early Jurassic (~180 Ma), Late Jurassic (~155 Ma), and late Early Cretaceous (~120 Ma). These rocks are mainly basalt, basaltic andesite, andesite, and trachyandesite. The Mesozoic mafic–intermediate volcanic rocks have SiO 2 = 47.34–60.00 wt%, TFe 2 O 3 = 4.73–11.63 wt%, and Mg # = 26–66, belong to the medium- to high-K calc-alkaline series, exhibit enrichment in light rare earth elements and large-ion lithophile elements, exhibit depletions in heavy rare earth elements and high-field-strength elements (e.g., Nb and Ta), and have no obvious Eu anomalies. These geochemical features are similar to those of arc igneous rocks. Relative to mid-ocean ridge basalts, these mafic–intermediate volcanic rocks exhibit more radiogenic Sr-Pb and less radiogenic Nd-Hf isotopic compositions. The Th/Yb (1.47–3.43) and (Hf/Sm) PM (0.80–1.15) ratios of the Early Jurassic mafic–intermediate volcanic rocks are much lower than those of the Late Jurassic mafic–intermediate volcanic rocks (Th/Yb = 4.31–5.25; (Hf/Sm) PM = 1.49–2.60), whereas the late Early Cretaceous igneous rocks exhibit large variations in these ratios (Th/Yb = 0.37–14.8; (Hf/Sm) PM = 0.59–2.14). The above features show that: (1) the primary magmas of the mafic–intermediate volcanic rocks were mainly derived by partial melting of depleted lithospheric mantle; (2) the lithospheric mantle was mainly metasomatized by sediment-derived fluids related to subduction of the Mongol–Okhotsk oceanic plate during the Early Jurassic, whereas the mantle source was mainly modified by sediment-derived melts triggered by the collapse of thickened lithosphere after closure of the Mongol–Okhotsk Ocean in the Late Jurassic; and (3) sediment-derived fluids associated with subduction of the Paleo-Pacific Plate caused further enrichment of the lithospheric mantle in the western part of northeast China during the late Early Cretaceous. • J 1 , J 3 and K 1 mafic magmas were derived by melting of depleted lithospheric mantle. • J 1 lithospheric mantle was modified by the Mongol-Okhotsk slab-derived fluid. • J 3 lithospheric mantle was modified by the Mongol-Okhotsk slab sediment-derived melt. • K 1 lithospheric mantle was re-modified by the Paleo-Pacific slab-derived fluid.