The AMGRS is a suite of anorthosite-mangerite-alkali granitoid-rapakivi granite in the northern North China Craton (NCC). New zircon SHRIMP and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb dating of the Damiao anorthosite, Changsaoying K-feldspar granite, Lanying anorthosite and quartz syenite and the Gubeikou K-feldspar granite yielded emplacement ages of 1726 ± 9 Ma, 1753 ± 23 Ma, 1739 ± 43 Ma, 1712 ± 15 Ma and 1692 ± 19 Ma, respectively. Combined with previous geochronological data from the Damiao norite and mangerite and Shachang rapakivi granite, it indicates that the whole AMGRS was intruded between 1750 Ma and 1680 Ma. The Damiao anorthosites and norites exhibit a high Mg#, and this decreases from mafic (up to 63) to felsic (<10) end members. The alkali granitoids of the AMGRS are characterized by high contents of alkali (K2O + Na2O), HSFE, TFeO/MgO, molecular (K2O + Na2O)/Al2O3 and Ga/Al values, that are typical features of A-type granites. All of the diverse components of the AMGRS have similar Sr-Nd-Hf isotopic compositions with low whole-rock initial 87Sr/86Sr ratios of 0.703-0.704, εNd(T) values of -5.0 to -6.3 (with TDM model ages of 2.34 to 2.58 Ga), and zircon εHf(T) values ranging from -4.1 to -7.5 (with Hf isotopic model TDM and TDM C ages ranging from 2.32 Ga to 2.43 Ga and 2.70 Ga to 2.88 Ga, respectively).This suggests that these rocks are the fractional crystallization products of one parental magma. Zircon Hf and whole-rock Sr-Nd-Pb isotopic systematics combined with high La/Yb (>10) and intermediate Th/Ta ratios, suggest that the parental magma of the AMGRS could have been derived from EM-I lithosphere mantle enriched by recycled Archean continent crustal materials, accompanied by some assimilation of lower crustal components. The mafic to felsic compositions of the AMGRS are different from typical bimodal rocks formed in an anorogenic intra-continent rift setting, but resemble those emplaced during post-collisional/post-orogenic extensional tectonic setting. This is compatible with their age of <1.85 Ga, indicating they postdate the continent-continent collision between the Western and Eastern blocks of the NCC at ∼1.85 Ga.
- Alkali granotoid
- In situ zircon Lu-Hf analysis
- Late Paleoproterozoic
- North China Craton
- Post-collisional/post-orogenic extension
- Zircon U-Pb chronology