Abstract
The Hongshan complex, located in the southern part of the Taihang Mountains in the central part of the North China Craton, consists of syenite stocks (including fine-grained biotite aegirine syenite, medium-grained aegirine gabbro syenite, coarse-grained aegirine gabbro syenite, syenite pegmatite, and biotite syenite porphyry), with monzo-diorite and monzo-gabbro dikes. This paper presents zircon U-Pb ages and Hf isotope data and whole-rock geochemical data from the Hongshan complex. LA–ICP-MS zircon U–Pb age from the fine-grained biotite aegirine syenite, monzo-diorite, and monzo-gabbro are 129.3 ± 2.0 Ma, 124.8 ± 1.3 Ma, and 124.1 ± 0.9 Ma, respectively, indicating their emplacement in the Early Cretaceous when the North China Craton was extensively reactivated. The monzo-diorite and monzo-gabbro have low SiO2 contents (48.94–57.75 wt%), total alkali contents (5.2–9.4 wt%), and εHf (t) values of −22.3 to −18.4 and are enriched in MgO (4.0–8.2 wt%), Al2O3 (14.3–15.8 wt%), light rare earth elements (LREEs) and large ion lithophile elements (LILEs). Interpretation of elemental and isotopic data suggests that the magma of monzo-diorite and monzo-gabbro were derived from partial melting of the enriched lithospheric mantle metasomatized by slab-derived hydrous fluids. Syenites with high alkali (K2O + Na2O = 9.4–13.0 wt%) and Sr contents (356–1737 ppm) and low Yb contents (0.94–2.65 ppm) are enriched in Al (Al2O3 = 16.4–19.1 wt%), but depleted in MgO (0.09–2.56 w%), Cr (Avg = 7.16 ppm), Co (Avg = 6.85 ppm) and Ni (Avg = 9.79 ppm), showing the geochemical features of adakitic rocks associated with thickened lower crust. Combining zircon 176Hf/177Hf ratios of 0.282176 to 0.282359, εHf(t) values of −18.3 to −11.8 and εNd (t) values of −11.1 to −8.2, we conclude that the syenite magma was derived from the mixing of the thickened lower crust and the enriched lithospheric mantle magma. These magma processes were controlled by Paleo-Pacific plate subduction and resulted in the destruction and thinning of the central North China Craton.
Highlights
The North China Craton (NCC), one of the oldest landmasses on Earth [1], experienced stable development from the formation of the basement at ~1.8 Ga to the Triassic
The zircon U-Pb data in this study are provided in Table 1, and the representative zircon cathodoluminescence (CL) images and concordia diagrams are shown in Figures 5 and 6
Geochronological, geochemical, and isotopic features, we propose a model to interpret the petrogenesis of the Hongshan complex (Figure 15)
Summary
The North China Craton (NCC), one of the oldest landmasses on Earth [1], experienced stable development from the formation of the basement at ~1.8 Ga to the Triassic. The margins and interior of the NCC are associated with Mesozoic large-scale mantle-crust magma activities, accompanied by the uplift and extension of the continental crust [5,6,7]. The Mesozoic regional magmatic activity is strong [13,14], which is a good place to study the lithospheric thinning mechanism in the central NCC. This paper selects the early Cretaceous Hongshan alkaline complex exposed in the southern end of the Taihang Mountains tectonomagmatic belt as the focus of this study [22,23] (Figure 1a). We systematically carry out field investigations, the petrology, elemental geochemistry, zircon U-Pb geochronology, and zircon Hf isotopic analysis of the Hongshan complex aimed at constraining the petrogenesis and related crust-mantle process during the craton destruction
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