Chapter 7 - Crustal and Mantle Evolution

Abstract

This chapter reviews how closely the evolution of the crust is tied to that of the mantle, and how this dynamic system has evolved as planet Earth has cooled during the last 4.6 Ga. Most investigators agree that the history of Earth's crust and mantle are closely related, and that processes in the mantle control many of the features found in the crust. This chapter begins with an account on the Hadean, the period time prior to 4 Ga extending back to the accretion of Earth around 4560 Ma. It moves to the discussion of continental growth with elaborate accounts on growth by underplating and by plate collisions. The most important mechanism for growth is magma additions by crustal underplating and by terrane collisions with continental margins. Continental growth is the net gain in mass of continental crust per unit time. Oxygen, neodymium, and hafnium isotopes are used to identify juvenile additions to continental crust. This chapter presents a model for continental growth. It also discusses secular changes in the continental crust and how the composition of crust has changed with time. It uses direct and indirect techniques to study secular changes in the mantle. It closes with a detailed discussion on Earth's thermal pointing out that the mantle was hotter during the Archean.