Generation of the Early Cretaceous granitoid in the Dazeshan region, Jiaodong Peninsula: Implications for the crustal reworking in the North China Craton

Abstract

Lower crust-derived granitic rocks provide constraints on the crustal reworking process and consequently give hints on the destruction mechanism of the cratons. The North China Craton (NCC) underwent extensive crustal melting in the Mesozoic. This study investigated granitic intrusions in the Dazeshan region of the Jiaodong Peninsula. Whole-rock major and trace element analyses and zircon U-Pb ages coupled with Hf isotopes were used to reveal the crustal reworking processes. Zircons separated from the quartz porphyry, Linglong granite, rhyolite porphyry, and biotite granite showed weighted mean 206Pb-238U ages of 119.2 ± 1.0 Ma, 140.2 ± 1.0 Ma, 120.6 ± 0.5 Ma, and 119.9 ± 0.7 Ma, respectively. The quartz porphyry, rhyolite porphyry, and biotite granite had high silica contents (SiO2 = 74–77 wt.%) but low MgO, Co, and Ni concentrations. The calculated εHf(t) values for the rhyolite porphyry and the biotite granite ranged from −18.3 to −20.0 and −17.8 to −20.2, respectively. These geochemical features imply ancient crust sources. The quartz porphyry showed distinct primitive mantle-normalized rare earth element (REE) patterns and was characterized by lower ΣREE content and lack of pronounced negative Eu anomalies. Whole-rock and zircon Dy/Yb ratios showed no correlation with whole-rock Rb/Sr ratios and zircon Hf contents, reflecting limited effects of crystal fractionation. The Ba/La ratios were also high (>150), but the Sr/Y and La/Yb ratios were low (Sr/Y < 50; La/Yb < 15). These features likely indicate that the quartz porphyry was generated by water-fluxed melting without differentiation. The rhyolite porphyry and biotite granite shared many geochemical similarities, denoting a unified source. The high La/Yb (>30) but low Sr/Y (<20) ratios and apparent negative Eu anomalies indicated plagioclase fractionation. Decreased zircon Dy/Yb with increasing Hf concentrations reflected noticeable amphibole fractionation. These two suites had fairly low Ba/La ratios. These data together point toward an identical source: dehydration melting of a relatively thickened crust. These melts experienced crystal fractionation after extraction. We propose that the intrusions were generated by the underplating of water-rich mafic magma, which provided both fluid and heat and finally induced two kinds of melting.

Crustal thickness of the Jiaodong Peninsula in the Mesozoic: Implications for the destruction of the North China Craton

“…Eu/Eu* values in the Late Jurassic and Early Cretaceous zircons (both for the >120 Ma and <120 Ma) display insignificant increasing or decreasing trends with elevated Hf contents (Figures 5A, C, E), although there are large Eu/Eu* variations in these zircon grains. Compiled data also exhibit overlapping Eu/Eu* values and variational trends to our data (Dong et al, 2023a;Dong et al, 2023b). This would mean that there is no plagioclase fractionation after extraction of the melt and prior to the crystallization of zircon for all three groups of zircon grains.…”

“…The data from this study show that Dy/Yb ratios for the Late Jurassic zircons decrease with increasing Hf contents (Figure 5B). However, this trend is not apparent when considering all the zircon data from published literature (Dong et al, 2023a;Dong et al, 2023b). Dy/Yb ratios for the Early Cretaceous (>120 Ma) zircons remain constant with increasing Hf concentrations (Figure 5D).…”

Origin of the Bohai Sea, North China Craton and implication for bi-directional back-arc extension in East Asia continental margin

“…The Jiaobei Terrane is the most southern part of the NCC, mainly composed of Archean TTG rocks, i.e., tonalites, trondhjemites, and granodiorites, gneisses, such as biotite gneisses and plagioclase amphibolites, and Archean to Paleozoic metamorphic rocks. Intrusive rocks include Triassic granites (225-200 Ma;Koua et al, 2022), Jurassic composite Linglong pluton (170-145 Ma;Yang et al, 2017), and two-stage Early Cretaceous granites (130-126 Ma and 121-116 Ma;Koua et al, 2022;Dong et al, 2023). The Jiaobei Terrane experienced rapid exhumation in 120-95 Ma (Zhang et al, 2022a), with development of extensional structures, such as the Linglong extensional dome (Fig.…”

“…The Sulu Orogen is located on the southeast side of the Wulian-Qingdao-Yantai fault zone (WQYF), characterized by the occurrence of high to ultra-high pressure metamorphic rocks. It is an Indosinian collisional suture zone between the NCC and South China block (Zhu et al, 2020;Dong et al, 2023). The Jiaolai Basin is located between the Jiaobei Terrane and Sulu Orogen, as a graben basin formed in late Early Cretaceous.…”

“…They have undergone intracontinental Yanshanian orogeny in late Middle Jurassic to early Early Cretaceous, and extensional faulting in the late Early Cretaceous, with extensive crustal melting in Mesozoic (Dong et al, 2015;Yang et al, 2017;Clinkscales and Kapp, 2019;Zhu et al, 2020;Yan et al, 2021;Chen et al, 2022a;Sun et al, 2022;Dong et al, 2023).…”