MILESTONE · From mineral inclusions in zircon to continents: An in situ isotopic perspective on the evolution of the continental crust, the onset of plate tectonics and the development of a habitable Earth

The continental crust is the principal record of conditions on Earth during the past 4.4 billion years, yet how it formed and evolved through time remains unresolved. Zircon lies at the core of crustal evolution studies, and yet our knowledge has remained restricted to the geochemical information that can be extracted from this mineral with current techniques. This CoG moves the debate to a different scale analytically, to the scale of mineral inclusions encapsulated within zircons. A key motivation is the recent analytical breakthrough in the microanalysis of minute samples, which was achieved by the PI and the team he led at the University of Bristol, using state-of-the-art instruments similar to those now available at the PI’s host laboratory. The integrated analysis of Sr and Pb isotopes of mineral inclusions, along with the trace elements, U-Pb, Hf and O isotopes analysis of their host zircons, for over 5000 zircons of different ages and provenance, will provide new and different information to that available from the 'zircon only' record – ultimately to i) probe the inferred transition from intraplate- to subduction-related magmatism associated with the onset of plate tectonics; ii) date this transition and its duration precisely in different places; iii) develop a global model of continental crust evolution from the Hadean (i.e. >4 Ga) to the Present, in which the Earth has progressively, or more suddenly, become a habitable planet. These goals will be achieved through:1. Building a worldwide collection of inclusion-bearing zircons with a range of ages and provenance (WP1).2. Evaluating changes in the degree of differentiation of the newly generated continental crust through time, using the Sr isotope record of apatite inclusions (WP2).3. Addressing changes in the tectonic settings of new crust formation, using the Pb isotope record of feldspar inclusions (WP3). 4. Modelling the variation in the new crust thickness through space and time (WP4).