Petrogenesis of Archean TTG-series rocks from the Jiaodong complex, eastern China: Implications for crustal evolution in the North China Craton

Abstract

Rocks of the tonalite-trondhjemite-granodiorite (TTG) series with associated supracrustal rocks are dominant components of many Archean terranes, but their petrogenesis remain controversial. Here, we present whole-rock major and trace elements, zircon U-Pb ages, Sm-Nd and zircon Hf isotopes of the three phases of TTG gneisses (2.9, 2.7 and 2.5 Ga) and amphibolites in the Jiaobei terrane, China, to investigate their petrogenesis and implications for crustal evolution. The 2.5 Ga TTGs are characterized by high Sr, Sr/Y and (La/Yb)N values, enrichment in LILE and depletion in HFSE, positive or negligible Eu anomalies and similarity to medium- to high-pressure (MP-HP) TTGs. In combination with their geochemical modeling results and high contents of MgO, Mg#, Cr and Ni, it is considered that the 2.5 Ga TTGs were subduction-related and mainly from melting of rutile-bearing eclogite and garnet amphibolite. In contrast, the 2.7 and 2.9 Ga TTGs show similarity to low- to medium-pressure (LP-MP) TTGs and have lower Sr contents and negligible Eu anomalies. Combining their Y/Yb and (Ho/Yb)N ratios, the geochemical modeling results and their MgO, Mg#, Cr and Ni contents, it can be inferred that they were mostly produced by melting of garnet amphibolite and amphibolite at the base of thickened lower crust. The available geochronological and zircon Hf isotopic data suggest that the major crustal growth period was around 2.7 Ga with the subordinate growth peroid at ~2.9–3.0 Ga. Synthesizing all lines of evidence, we propose that the Jiaodong complex possibly witnessed a transition of tectonic regime during the Meso-Neoarchean.