The significance of Mesozoic basement uplift for interpreting the NCC’s Precambrian tectonic regime: Evidence from the Paleoproterozoic magmatic rocks along the eastern margin of the Lishi Fault

Abstract

This study offers the first comprehensive geochronological and geochemical results for the Paleoproterozoic magmatic rocks exposed along the eastern margin of the Lishi Fault in the North China Craton (NCC). Their emplacement age, petrogenesis, and relationship with the basement provide critical constraints for inferring the subdivisions and tectonic evolution of the NCC basement. The U-Pb ages, Hf-O isotopes, in combination with whole-rock major and trace element data, identify three episodes of magmatism along the eastern margin of the Lishi Fault at ca. 2.33–2.29 Ga, 2.20–2.17 Ga and 1.97–1.94 Ga. The magmatic rocks include the 2.33–2.29 Ga granites, 2.20–2.17 Ga tonalites, granodiorites, granites and meta-gabbros, and 1.97–1.94 Ga granites. The 2.33–2.29 Ga granites are characterized by high SiO₂, K₂O contents, and Ce/Pb and Nd/Sm values ranging from 2.50 to 5.62 and 4.74–7.61, respectively. The zircon Hf isotope compositions (ε_Hf(t) = -1.71-+3.0, T_DM2 = 3.0–2.6 Ga), suggest their origin through a recycled Archean crustal. The 2.20–2.17 Ga felsic rocks (SiO₂ = 63.83–74.30 wt%) show relatively high Mg# values, large variation in Cr and Ni abundances, and low (La/Yb)_N value. These characteristics and zircon Hf isotope compositions (ε_Hf(t) = -4.24-+2.69, T_DM2 = 2.8–2.6 Ga) suggest their evolution through high-temperature melting of a Neoarchean mafic source and a significant role of mantle-derived materials. The 2.20–2.17 Ga gabbros (subsequently metamorphosed) with high K (K₂O = 0.91–2.20 wt%) and depleted Nb-Ta-Ti, were derived from an enriched lithospheric mantle source. The 1.97–1.94 Ga granites are moserately peraluminous (A/CNK = 1.02–1.12) and display high zircon δ¹⁸O values (5.51–8.15 ‰, Ave. 6.72 ‰). Such characteristics underline their S-type nature and derivation from partial melting of (meta)sedimentary source. The 2.33–2.29 Ga granite and 2.20–2.17 Ga tonalite show variably low zircon δ¹⁸O values of 3.29–6.07 ‰ and 2.94–6.27 ‰ respectively, which are below the normal mantle zircon values. A general increase in zircon δ¹⁸O values in the Paleoproterozoic magmatic rocks along the eastern margin of the Lishi Fault underlines a change in the tectonic regime from extension to collision setting. The zircon U-Pb age and Lu-Hf isotope data of the early Precambrian basement rocks reveal a close similarity in the tectono-thermal regime and crustal growth between OB and other tectonic domains of NCC, such as the northern Khondalite Belt and Yinshan Block (KB + YB), Trans-North China Orogen (TNCO), and the Eastern Block (EB). We propose that the lithosphere of the NCC was significantly thinned since the Mesozoic and was accompanied by extensive magmatic activities. The geomorphology of present day NCC was shaped by multiple stages of uplift-denudation events. The Mesozoic uplift-exhumation of the basement significantly obliterated the tectonic and thermal records in the entire NCC’s Precambrian basement.