Chapter 7 - The Formation of Tonalites–Trondjhemite–Granodiorites in Early Continental Crust

Abstract

About 60%–70% of the present volume of continental crust formed during the Archean (4.0–2.5Ga), whereas only less than 1% of the earliest remnants are preserved in high-grade gneiss terranes of the present cratonic cores. Here we present a synopsis of the current state of approaches investigating the onset of continental crust formation. These include field studies, geochemistry, geophysics, geodynamic, petrological, and geochemical modeling, as well as isotope geochemistry. We briefly discuss recent modeling attempts on compositional changes of crustal composition throughout the Archean and experimental approaches on early felsic crust formation. We focus on tonalites and trondhjemite genesis, as well as on the early stages of diversification of felsic crustal melts. Possible source rocks, melting depth, and other parameters are discussed based on the current state of the art.