Novel Isotopic Insights Into Continent Evolution: tracing juvenile and reworked crust with titanium stable isotopes.

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The Earth is the only planet in the solar system having continents roaming at its surface. The presence of continental landmasses in contact with the atmosphere has played a pivotal role in the evolution of the Earth surface over the entire Earth history, and ultimately its habitability. Yet, it is currently unknown what sequence of events led to the development of these landmasses. This research aims to answer a key yet unresolved question: How did continents form? We will do so by using a novel isotopic tracer that is sensitive to specific chemical reactions occurring during the formation and evolution of continental crust.Continent ages tend to cluster around specific dates in Earth history, but the reasons for this remain unclear. Is it because continents formed episodically in environments akin to present day oceanic plateaux? Or is it because crustal rocks were preferentially preserved during episodes of continental collision? To date, attempts to solve these questions have mainly focused on explaining patterns in the ages of continental rocks or by estimating the composition of the continental crust through time. These studies hint that the mechanism of continent formation may have changed through time with the onset of plate tectonics 2.5 to 3 billion years ago, yet direct evidence for this is lacking. Here, we propose to use a novel geochemical tool, purposely designed by the PI, to directly identify the processes involved in the generation of juvenile crust and its reworking.First, we will identify the tectonic setting in which the magmas forming juvenile crust were formed through time. Existing models each imply a very different role for rutile, a Titanium-rich mineral for which involvement in magma generation can be traced through its impact on the titanium stable isotope composition of magmas. By measuring magmatic rocks forming juvenile crust throughout Earth's entire history, we will determine the role played by rutile in their generation and link it with a specific tectonic setting.Second, we will directly determine when reworking of continental crust started. Reworking of pre-existing continental crust occurs during continental collision. It affects the composition of the upper level of the continental crust, which can be accessed by measuring terrigenous sediments through time. The titanium stable isotope composition of these sediments will reflect the relative amount of juvenile and reworked crust and indicate the onset of continent collisions. Therefore by combining these two objectives we will learn about where crust is formed and survives. Overall, answering these questions will provide new evidence for the mechanisms by which continental crust formation occurs, and will greatly enhance our understanding of how processes occurring in Earth's interior have influenced Earth's surface.