Roles of Subducted Pelagic and Terrigenous Sediments in Early Jurassic Mafic Magmatism in NE China: Constraints on the Architecture of Paleo‐Pacific Subduction Zone

Abstract

The role of subducted sediments in arc magmatism has been widely documented. However, identifying the sedimentary provenance (e.g., pelagic vs. terrigenous) input in subduction systems is difficult because of the wide compositional range of sedimentary components and the complex magmatic evolution of arcs. Here we report zircon U‐Pb‐Hf‐O isotopes and whole‐rock elemental and Sr‐Nd‐Hf isotopic compositions of four Early Jurassic subduction‐related mafic intrusions from the Yanbian area, NE China. These rocks show typical trace element and isotopic features of arc magmas. In combination with the published data, we discover two distinct elemental‐isotopic arrays of the Early Jurassic mafic rocks across the arc magmatic belt. Such geochemical variations are mainly attributed to variable subducted sediment input into the mantle wedge instead of crustal contamination or assimilation during magmatic evolution. The mantle source for the southern Yanbian mafic rocks was enriched by addition of a crustal component dominated by terrigenous sediments, whereas that for the northern Lesser Hinggan‐Zhangguangcai Range, mafic rocks was modified by another crustal component comprising mainly pelagic sediments. The results can be best interpreted if the southern part was a continental arc as opposed to an oceanic arc in the north, which is analogous to the modern Kamchatka‐Honshu‐Izu‐Bonin‐Mariana arc systems in the western Pacific. Our reconstructed architecture, based mainly on the geochemical data, further suggests that the Khanka‐Jiamusi‐Buleya Massif was probably sinistrally and northwardly displaced to the present position after Mesozoic subduction of the Paleo‐Pacific Ocean.

Nature of the Mantle Plume Under the Emeishan Large Igneous Province: Constraints From Olivine‐Hosted Melt Inclusions of the Lijiang Picrites

“…Pelagic sediments are considered to be typically enriched in Ba and to have high Th/U ratios (Othman et al., 1989; Weaver, 1991). Furthermore, pelagic sediments commonly have low Th/La ratios (Elliott et al., 2007; Zhao et al., 2019) and are considered deficient in zircon, which would lead to radiogenic Hf at a given ε Nd (Bayon et al., 2009; Blichert‐Toft et al., 1999; Vervoort et al., 2011). In contrast, the Lijiang melt inclusions are depleted in Ba relative to other large‐ion lithophile elements (LILEs) (Figures 2 and 8), and the Ba/Nb and Ba/Th ratios of the Lijiang melt inclusions are relatively low (Ba/Nb = 5.7–11.8; Ba/Th = 41.3–140.6) compared with those of typical OIB (Figure S6).…”

Discovery of Ultra‐Depleted Melt Inclusion in Late Cretaceous Intracontinental Basaltic Andesites in South China: Implications for Recycling of Lower Oceanic Crust

“…Such isotopic features are likely attributed to the input of recent pelagic sediments rather than old terrigenous sediments into the mantle source (Chauvel et al., 2008). However, these rocks also show distinctly low Lu/Hf (0.07–0.08) and high Th/La (0.21–0.22) and Th/Yb (2.26–2.58) ratios, which are similar to continental arc magmas with the input of dominant terrigenous sediments into the mantle source (Guo et al., 2021; L. Zhao et al., 2019). This paradox likely reflects that the transport and deposition time of the terrigenous sediments (e.g., eroded materials from a new arc crust) is too short to produce the obvious decoupling of Nd‐Hf isotopes (L. Zhao et al., 2019).…”

“…The Hengyang basaltic andesites show positive Pb and K anomalies in the PM‐normalized trace element spidergrams (Figure 5a), lower Nb/U (29–32) and Ce/Pb (5.1–8.4) ratios than that of oceanic basalts (47 ± 7 and 25 ± 5, respectively) (Hofmann, 1997), and enriched Sr‐Nd‐Hf isotopic compositions relative to MORBs (Data Set S3). Such geochemical characteristics could be ascribed to the input of crustal components into the melting source or crustal assimilation and fractional crystallization during magmatic evolution (e.g., L. Zhao et al., 2019). Thus, it is critical to determine the effects of crustal contamination and fractionation for these rocks before the source characteristics can be discussed.…”

Detrital Zircon U‐Pb Geochronology of the Xilin Group: Constraints for the Early Paleozoic Tectonic Evolution of the Songliao Massif

“…(2) Wang et al (2012aWang et al ( , 2017 believed that the eastern Songliao Massif experienced westward subduction of the paleo-oceanic plate and amalgamation with the Jiamusi Massif from north to south from the Middle Cambrian to Late Silurian; (3) Xu et al (2012Xu et al ( , 2019 and Liu et al (2017Liu et al ( , 2019 proposed that the paleo-oceanic plate subducted under the eastern Songliao Massif during the Late Cambrian to Silurian and the Songliao Massif amalgamated with the Jiamusi Massif during the Middle-Late Silurian (Li et al, 2020). Furthermore, there remain differing opinions on the aggregation time or models for the Songliao and Jiamusi massifs, such as Proterozoic amalgamation (Cao et al, 1992), reopening model (amalgamation-rift-second amalgamation; Xu et al, 2012Xu et al, , 2019Liu et al, 2017Liu et al, , 2019Chen et al, 2019;Li et al, 2020;Long et al, 2020;Zhang et al, 2020) and Early-Middle Jurassic amalgamation (Wu et al, 2008;Zhou et al, 2013a, b;Zhao et al, 2019).…”