Abstract
The Mesozoic-Cenozoic succession of the Bohai Bay Basin (BBB), located within the Eastern Block of the North China Craton (NCC), overlies a heterogeneous Archean basement. This sedimentary cover obscured insights into the region's early crustal evolution. To constrain the cryptic Archean history of the BBB, we present new in-situ zircon U-Pb ages, whole-rock geochemistry, and zircon Hf-O isotope data for TTG gneisses recovered from deep drill cores. This new data provides constraints on crustal growth and evolution of the Precambrian basement under the BBB in the NCC. Magmatic zircon U-Pb dating reveals two distinct episodes of crustal generation at ∼3.1 Ga and ∼2.5 Ga. The Mesoarchean (∼3.1 Ga) TTG rocks differ from previously published TTGs of the NCC. They exhibit high-K calc-alkaline affinities, with pronounced enrichment in large-ion lithophile elements (LILE) and depletion in high-field-strength elements (HFSE), consistent with generation from evolved granitoid magmas. Isotopic data further highlight their distinct character: highly positive εHf(t) values point to a juvenile mantle source, while their unusually low δ18O signatures indicate incorporation of isotopically light material during magma genesis. These isotopic signatures, specifically the δ18O-depletion, suggest that the petrogenesis of the ∼3.1 Ga TTGs involved the fluxing of fluids derived from hydrothermally altered oceanic slabs. Our results, integrated with previous studies, lead to three main conclusions. First, the Bohai Bay Basin experienced two major Archean magmatic events at ∼3.1 Ga and ∼ 2.5 Ga. Second, the ∼3.1 Ga TTG magmatism was influenced by oceanic fluids introduced during slab subduction. Third, the tectonic setting of the BBB region in the eastern NCC at ∼3.1 Ga reflects the combined effects of mantle plume activity and plate subduction. These findings provide important constraints on the tectonic evolution of the Eastern Block of the North China Craton.
Paper Information：
Tianyi Bian, Fanchao Meng, Andrew C. Kerr, Yonghua Liu. (2026). Zircon Hf-O Isotopes and geochemistry of TTG in the basement of the Bohai Bay Basin: Petrogenesis and implications for ~3.1 Ga crustal growth in the North China Craton, Lithos, 540-541: 108643.
