Reconstructing Early Archaean Crust formation and Tectonics (REACT)
Lead Research Organisation:
UNIVERSITY OF EDINBURGH
Abstract
Earth is 4.56 billion years old and is unique among known planets in having a life-supporting atmosphere, liquid-water oceans, and continents made of silica-rich granitic crust that cover forty percent of its surface. The remaining sixty percent of the crustal surface is oceanic crust, which is thinner and composed of silica-poor basaltic rock. Plate-tectonic processes re-shape the Earth’s surface today by forming new oceanic crust at mid-ocean ridges and subducting it at convergent margins. Silica-rich magmas formed in subduction zones solidify as igneous rocks and are then recycled through erosion, deposition and mountain-building processes to form new continental crust. The continents began to grow and stabilise ~4.0-3.5 billion years ago, at a time when the Earth already had liquid water oceans but an oxygen-free atmosphere. Crucially, although plate tectonics explains continental crust formation on the present-day Earth, the tectonic processes operating on the early Earth are poorly understood. This lack of knowledge about early crust-forming processes, and the influences that these processes may have had on early environments, means that we have limited understanding of: (1) what tectonic processes operated on the early Earth; (2) how the early Earth’s surface differentiated compositionally; (3) how early surface environments were chemically modified during continental growth; and (4) how early continental growth could potentially influence the development of life on our planet.
The oldest continental crust is predominantly composed of distinctive granitic rocks called tonalites and trondhjemites (and later granodiorites) that are rarely formed on the modern Earth. REACT aims to understand the tectonic processes that formed the oldest continent crust by determining how these tonalites, trondhjemites and granodiorites were generated. We will use an integrated and multidisciplinary strategy using a strong research team to bring together a blend of field-work and state-of-the-art geochemical, thermodynamic and experimental methods to address our aim. Through an improved and timely understanding of the field geology of ancient rocks and the development of new analytical and modelling methods we will implement complex computer models and carry out laboratory experiments to synthesise melts that match the composition of the earliest continental tonalites, trondhjemites and granodiorites using starting materials that have never been tested before. For the first time, novel isotope analyses coupled with new experiments and models will give us all of the conditions (source region compositions, pressures, temperatures, oxidation states, volatile contents) needed to form the ancient tonalites, trondhjemites and granodiorites. In turn, understanding the conditions responsible for forming the oldest tonalites, trondhjemites and granodiorites will allow us to propose the likely tectonic settings on the early Earth to establish how its crustal surface differentiated 4.0-3.5 billion years ago. These new insights will also allow scientists in other fields to discover how the magmatic and volcanic activity that accompanied the formation of the earliest continental crust would have modified the composition of Earth’s surface environments at a critical stage in the emergence of life on Earth. Our results will have broad appeal to earth and planetary scientists, biologists, and chemists in order to understand how our planet began its evolutionary path towards forming our modern tectonically active and habitable world.
The oldest continental crust is predominantly composed of distinctive granitic rocks called tonalites and trondhjemites (and later granodiorites) that are rarely formed on the modern Earth. REACT aims to understand the tectonic processes that formed the oldest continent crust by determining how these tonalites, trondhjemites and granodiorites were generated. We will use an integrated and multidisciplinary strategy using a strong research team to bring together a blend of field-work and state-of-the-art geochemical, thermodynamic and experimental methods to address our aim. Through an improved and timely understanding of the field geology of ancient rocks and the development of new analytical and modelling methods we will implement complex computer models and carry out laboratory experiments to synthesise melts that match the composition of the earliest continental tonalites, trondhjemites and granodiorites using starting materials that have never been tested before. For the first time, novel isotope analyses coupled with new experiments and models will give us all of the conditions (source region compositions, pressures, temperatures, oxidation states, volatile contents) needed to form the ancient tonalites, trondhjemites and granodiorites. In turn, understanding the conditions responsible for forming the oldest tonalites, trondhjemites and granodiorites will allow us to propose the likely tectonic settings on the early Earth to establish how its crustal surface differentiated 4.0-3.5 billion years ago. These new insights will also allow scientists in other fields to discover how the magmatic and volcanic activity that accompanied the formation of the earliest continental crust would have modified the composition of Earth’s surface environments at a critical stage in the emergence of life on Earth. Our results will have broad appeal to earth and planetary scientists, biologists, and chemists in order to understand how our planet began its evolutionary path towards forming our modern tectonically active and habitable world.