Petrogenesis of Mesozoic Magmatic Suites in the Jiaodong Peninsula: Implications for Crust-Mantle Interactions and Decratonization

Abstract

The North China Craton (NCC) has thick lithosphere in the Paleozoic (>200 km) but appears to be decratonized in the Mesozoic. However, the actual processes operated in the lower crust-deep mantle are still unclear. The Mesozoic granitic rocks can provide important clues to the NCC decratonization mechanism. Here, we conducted trace element modeling to check whether partial melting of the Archean lower crust can generate these Mesozoic magmatic suites. Meanwhile, zircon Hf isotope analysis was conducted to reveal crust-mantle interaction processes and further give constraints on the decratonization of the NCC. Zircon Hf isotope data of the Linglong, Guojialing, and Aishan suites, the mafic microgranular enclaves (MMEs) in the Guojialing suite, and mafic dykes display minor differences: the Linglong (160–150 Ma), Guojialing (~130 Ma), and Aishan (118–116 Ma) suites have zircon εHft=–25.4 to –14.5, –15.3 to –10.4, and –23.1 to –11.9, respectively. The Cretaceous mafic dyke (126 Ma) has a highly negative εHft value (–22.8 to –17.7). Meanwhile, the MMEs (in the Guojialing granodiorite, DCW-2A, 129 Ma) have zircon εHft=–13.0 to –8.9. Temperature-pressure conditions calculated using amphibole compositions for both the Guojialing granodiorite and its MMEs are basically identical, implying possible magma mixing. Our modeling results show that certain trace elements (e.g., Tb, Yb, and Y) have to be retained in the source to match the composition of the Linglong suite, which requires substantial garnet residues (high-pressure melting) in the Jurassic. The Early Cretaceous garnet-dominated lower crust is Yb-/Y-enriched but depleted in elements like Sr and La. Therefore, it could not form geochemical features like high Sr/Y and La/Yb ratios akin to the Guojialing suite. Integrating the modeling results and zircon Hf isotope data, we propose that the crust in the eastern NCC had thickened and partially melted by dehydration to produce an eclogitic residue containing a large amount of garnet (>50% by weight) during the Jurassic (Linglong granite), whereas upwelling of hot and hydrous mafic magma from the asthenospheric mantle induced fluxed melting of both the lower crust and lithospheric mantle in the Early Cretaceous, during which the lithospheric mantle and part of the lower crust in the Jiaodong were removed by the convective mantle. About 10 Mys later while the Aishan suite formed, the crust was not thick anymore, and melting occurred under moderate pressure which does not necessarily require abundant garnet as the residue phase.

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

“…This estimated thickness agrees with the conclusion from geochemical modeling, which suggests that the magmatic suite formed at ca. 110 Ma was generated by the melting of the lower crust at moderate pressure (Dong et al, 2023c). Additionally, we also used the whole-rock La/Yb proxy (Profeta et al, 2015) to constrain crustal thickness for the three magmatic suites with published data (Yang K. F. et al, 2012;Ma et al, 2013;Li et al, 2019).…”

“…For the three groups of zircons, the REE patterns are, in general, similar and are not further distinguished. The literature data source isDong et al, 2023b;Dong et al, 2023c.…”

Petrogenesis of the Laoshan Suite in the Jiaodong Peninsula (Eastern China): An Oxidized Low Ba–Sr A1-Type Granite

“…The Mesozoic granites are mainly distributed in the Jiaobei terrane and the Sulu orogen (Figure 1B), panning two periods: the Middle Jurassic and Early Cretaceous [4]. The Middle Jurassic granites (~160 Ma) are mainly composed of Linglong, Luanjiahe, Kunyushan, and Wendeng plutons (Figure 1B) (hereafter collectively referred to as the Linglong suite), which have similar mineral compositions and geochemical characteristics [26]. The Early Cretaceous granites are classified into Guojialing (132-125 Ma), Weideshan (125-110 Ma), and Laoshan (125-109 Ma) suites based on their formation age, mineral assemblage, and geochemical information [26,27].…”

“…The Middle Jurassic granites (~160 Ma) are mainly composed of Linglong, Luanjiahe, Kunyushan, and Wendeng plutons (Figure 1B) (hereafter collectively referred to as the Linglong suite), which have similar mineral compositions and geochemical characteristics [26]. The Early Cretaceous granites are classified into Guojialing (132-125 Ma), Weideshan (125-110 Ma), and Laoshan (125-109 Ma) suites based on their formation age, mineral assemblage, and geochemical information [26,27]. Over 200 gold deposits have been discovered in the Jiaodong Peninsula, with most of them hosted in granites (77% hosted in the Linglong type, 10% in the Guojialing type [4]), and the formation time of the Jiaodong gold deposits are concentrated around ~120 Ma [1,[3][4][5][6][7].…”

“…Adakitic geochemical features are widely regarded as important for the formation of large deposits (e.g., porphyry Cu deposits [48][49][50][51][52]). The Linglong, Guojialing, and Weideshan suites have highly variable Sr/Y (35.54-136.50) and La/Yb (1.43-176.43) ratios, and low Y (3.26-11.20 ppm) and Yb (0.33-0.97 ppm) contents [26,[36][37][38][39]42,43], indicating an adakitic affinity. Furthermore, in the Sr/Y vs. Y and (La/Yb) N vs. Yb N discrimination diagrams, these samples fall in the adakite field (Figure 8).…”