Geochronology and geochemistry of 2.3 Ga mafic intrusions in the Dengfeng area: Evidence for early Paleoproterozoic subduction in the southern North China Craton.

• The Jingwan mafic intrusions in the south North China Craton ware emplaced at 2301 ± 16 Ma. • The intrusions were originated from melts of slab fluids-metasomatized mantle wedge in a subduction zone. • The prevalence ca. 2.3 Ga magmatic events of the TNCO were generated in a continental margin arc setting. • The early Paleoproterozoic subduction likely continued from ca. 2.5 Ga to ca. 2.3 Ga, at least 200 Ma. The time of 2.45–2.2 Ga in the early Paleoproterozoic era is called as 'Quiet Interval' because of the decreased magmatic activity worldwide. However, tectonic evolution of old continents during this time interval is still in dispute due to the rare geological records, especially for magmatism. In the southern North China Craton (NCC), the Jingwan mafic intrusions intruded into the Songshan Group and its zircon U-Pb dating yielded a weighted mean 207Pb/206Pb age of 2301 ± 16 Ma, and thus they are the only ca. 2.3 Ga mafic magmatic records founded in this region. These diabases belong to low-K tholeiitic series with relatively low K 2 O (0.1–0.7 wt%) and total alkalis (Na 2 O + K 2 O) (2.4–4.7 wt%). They have low SiO 2 (44.8–54.1 wt%), slightly variable Fe 2 O 3 T (10.1–14.4 wt%), Al 2 O 3 (14.8–17.0 wt%), CaO (5.5–10.6 wt%), and medium to high MgO (6.1–10.8 wt%) and Mg# values (58–65). The rocks display LREE enrichment ((La/Yb) N = 3.02–3.58) without obvious Eu anomaly (Eu/Eu* = 0.87–1.18). They are characterized by obvious depletion in Nb, Zr and Ti, and enrichment of Sr, Ba and Pb, indicative of geochemical features of island arc magmas. The rocks have experienced crystallization from clinopyroxene to orthopyroxene, then plagioclase, suggesting the hydrous fractionation order. They also exhibit variable ε Nd (t) values ranging from − 0.2 to + 0.8 and zircon ε Hf (t) values from − 3.0 to + 6.6. These features suggest that the mafic intrusions are formed by partial melting of a garnet-spinel lherzolite and derived from an enriched mantle source metasomatized by slab-derived fluids at a shallow depth. Combined with the previous reported magmatic records, the ca. 2.3 Ga magmatic activity may be a result of the oceanic slab subduction beneath the Eastern Block of the NCC, and the subduction probably continue throughout the early Paleoproterozoic from ca. 2.5 Ga to ca. 2.3 Ga, at least 200 Ma. Therefore, the prevalence of early Paleoproterozoic magmatic activities in the southern NCC indicate that the tectonic activity did not shutdown globally during the interval of the 'tectono-magmatic lull'. [ABSTRACT FROM AUTHOR]