Formation and evolution of Archean continental crust: A thermodynamic – geochemical perspective of granitoids from the Tarim Craton, NW China

• Published in: Earth-science reviews 2022-11, Vol.234, p.104219, Article 104219
• Main Authors: Ge, Rongfeng, Wilde, Simon A., Zhu, Wenbin, Zhou, Teng, Si, Yang
• Format: Article
• Language: English
• Subjects: Archean; Continental crust; Tarim Craton; Thermodynamic modelling; TTG gneisses; Zircon
• ISSN: 0012-8252; 1872-6828
• DOI: 10.1016/j.earscirev.2022.104219

When and how continental crust formed and evolved to its current state is a fundamental question regarding crust – mantle evolution and geodynamic regimes on the early Earth. Earth's Archean continental crust is dominated by sodic granitoids comprising tonalite – trondhjemite – granodiorite (TTG), whereas diverse high-K granitoids appear relatively late in the geological record. Therefore, the formation and secular evolution of Archean TTGs and high-K granitoids is key to many issues regarding early Earth geodynamics. The Tarim Craton, NW China, is an ancient continental block containing some of the oldest rocks (∼3.7 Ga TTGs) on Earth, but its Archean evolution is poorly known due to limited outcrop. Here we review the Archean geological record of the Tarim Craton and present the new findings of ∼3.2–3.0 Ga TTG, ∼2.8 Ga high-K granite and ∼2.35 Ga A-type granitoids (mostly syenogranite and syenite) in the southwestern Tarim. The ∼3.2–3.0 Ga TTG gneisses have homogenous and highly radiogenic zircon Hf isotopic compositions (weighted mean εHf = +3.5 to +4.4), indicating crustal growth from a long-term depleted mantle. In contrast, the ∼2.8 Ga high-K granite and ∼2.35 Ga A-type granitoids have lower εHf values (weighted mean + 2.0 and − 4.3 to −7.8, respectively) that plot on the evolution trend of the Mesoarchean juvenile crust, indicating repeated crustal reworking and progressive crustal differentiation. Thermodynamic – geochemical modelling demonstrates that water-fluxed melting is an efficient way to produce large volumes of TTG melts, and that melting pressure plays a primary role in determining the trace element systematics of diverse TTGs. Water-fluxed melting at crustal (10–12 kbar) and mantle (18–20 kbar) depths explains not only the compositions of the ∼3.2–3.0 and ∼3.7 Ga TTGs in the Tarim Craton, respectively, but also the global average compositions of median- to low-pressure and high-pressure TTGs. Partial melting of the Mesoarchean gneisses at shallow depth (≤5 kbar) reproduces the trace element patterns of the ∼2.35 Ga A-type granitoids in SW Tarim, but cannot explain the low SiO2 of the syenites, which probably originated from partial melting of an enriched mantle resulting from recycling of Archean continental crust during continental rifting. This process also contributed to the diversification of granitoids and maturation of continental crust. Based on these results, we propose a new model for the formation and evolution of Archean conti