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Summary of recent research covering experimental methods and numerical modelling, for graduate students and researchers.
This comprehensive reference volume surveys the development of crusts on solid planets and satellites in the solar system.
The formation of the continental crust is a major consequence of Earth differentiation. Understanding how the crust formed and evolved through time is paramount to locate the vast mineral deposits hosted therein and address its influence on the global climate, ultimately affecting the development of terrestrial life. Recent advances on the topic of continental crust evolution benefited from improvements of analytical techniques enabling in situ measurements of U-Pb- Hf-O isotope compositions in zircon, a widespread accessory mineral of continental igneous rocks. The time constrains derived from the U-Pb chronometer coupled with the petrogenetic information retrieved from Hf-O isotope signatures are currently used to unravel the diversity and succession of magmatic events affecting the continental crust at the regional and global scales. This study reconstructs the evolutionary path followed by the crust segment today exposed in the eastern part of the French Massif Central (FMC), a portion of the Variscan belt of Western Europe, with the aim to investigate the potential flaws of the zircon record of crust evolution. In this scope, the origin and geodynamic significance of the constituent FMC lithological units are tackled by combining conventional petrological observations with zircon U-Pb-Hf-O isotope data. The results obtained following this integrated approach are then confronted to the conclusions that would have been drawn solely from zircon isotopic signatures, taken out of their petrological context, as is commonly performed in studies investigating crust evolution. The oldest rocks of the FMC correspond to Ediacaran (590_550 Ma) meta-sediments deposited in back-arc basins along the northern Gondwana margin. Such basins were fed by a mixed detritus originating from the adjacent Cadomian magmatic arc and a distal Gondwana source, presumably the Sahara Metacraton. Partial melting of these meta-sediments at the Ediacaran/Cambrian boundary led to voluminous S-type granitic magmatism, pinpointing a first major crust reworking event in the FMC. The origin of anatexis likely stems from the transient thickening of the hot, back-arc crust caused by the flattening of the Cadomian subduction. Subordinate melting of the depleted backarc mantle at that time is also documented. During the Lower Paleozoic, rifting of the northern Gondwana provoked coeval crust and (limited) mantle melting. Mantle-derived igneous rocks show markedly diverse trace element and isotopic signatures, consistent with a very heterogeneous mantle source pervasively modi_ed by the Cadomian subduction. Finally, the Variscan collision resulted in crustal melting as evidenced by the emplacement of S-type granites and the formation of migmatite domes, the spatial distribution of which being partly controlled by the crustal architecture inherited from pre-orogenic events. Synchronous intrusion of mafic mantle-derived magmas and their differentiates testify for Variscan post-collisional new continental crust production in the FMC. Two major inconsistencies exist between these results and the zircon record. First, zircon Hf model ages would point to substantial Mesoproterozoic crust formation in the FMC whereas more than 60% of the crust is actually Neoproterozoic in age. Second, new additions to the continental crust volume during the Variscan orogeny are not recorded even though 5 to 10% of the exposed crust formed at that time. The origin of both discrepancies inherently lies in the mixed isotopic signature carried by many zircon grains. Such equivocal information can only be detected when additional petrological constrains on the zircon host rocks are available and provide guidance in interpreting the zircon record of crust evolution.
The continental crust is our archive of Earth history, and the store of many natural resources; however, many key questions about its formation and evolution remain debated and unresolved: What processed are involved in the formation, differentiation and evolution of continental crust, and how have these changed throughout Earth history?How are plate tectonics, the supercontinent cycle and mantle cooling linked with crustal evolution?What are the rates of generation and destruction of the continental crust through time?How representative is the preserved geological record? A range of approaches are used to address these questions, including field-based studies, petrology and geochemistry, geophysical methods, palaeomagnetism, whole-rock and accessory-phase isotope chemistry and geochronology. Case studies range from the Eoarchaean to Phanerozoic, and cover many different cratons and orogenic belts from across the continents.
Graduates in geology, geochemistry and geophysics will find this volume in the Geoscience Texts series a valuable reference text. The book begins by describing the known composition of the present upper crust, then deals with possible compositions for the total crusts and the inferred composition of the lower crust. The question of the uniformity of crustal composition throughout geological time is discussed. The rate of growth of the crust through time is assessed, and the effects of the extraction of the crust on mantle compositions are considered. Finally, the question of early pre-geological crusts on the Earth is debated, and comparisons are given with crusts on the Moon, Mercury, Mars, Venus and the Galilean Satellites.
"This book contains landmark papers on the processes of formation of continental crust from its beginnings in the Archean to modern processes, as well as discussions of several ancient and modern orogenic belts. The book is international in scope, with contributions from geoscientists dealing with crustal processes on five continents, and articles from more than 50 non-U.S. authors and co-authors."--Publisher's website.
Earth as an Evolving Planetary System, Second Edition, explores key topics and questions relating to the evolution of the Earth's crust and mantle over the last four billion years. This updated edition features exciting new information on Earth and planetary evolution and examines how all subsystems in our planet—crust, mantle, core, atmosphere, oceans and life—have worked together and changed over time. It synthesizes data from the fields of oceanography, geophysics, planetology, and geochemistry to address Earth’s evolution. This volume consists of 10 chapters, including two new ones that deal with the Supercontinent Cycle and on Great Events in Earth history. There are also new and updated sections on Earth's thermal history, planetary volcanism, planetary crusts, the onset of plate tectonics, changing composition of the oceans and atmosphere, and paleoclimatic regimes. In addition, the book now includes new tomographic data tracking plume tails into the deep mantle. This book is intended for advanced undergraduate and graduate students in Earth, Atmospheric, and Planetary Sciences, with a basic knowledge of geology, biology, chemistry, and physics. It also may serve as a reference tool for structural geologists and professionals in related disciplines who want to look at the Earth in a broader perspective. Kent Condie's corresponding interactive CD, Plate Tectonics and How the Earth Works, can be purchased from Tasa Graphic Arts here: http://www.tasagraphicarts.com/progptearth.html Two new chapters on the Supercontinent Cycle and on Great Events in Earth history New and updated sections on Earth's thermal history, planetary volcanism, planetary crusts, the onset of plate tectonics, changing composition of the oceans and atmosphere, and paleoclimatic regimes Also new in this Second Edition: the lower mantle and the role of the post-perovskite transition, the role of water in the mantle, new tomographic data tracking plume tails into the deep mantle, Euxinia in Proterozoic oceans, The Hadean, A crustal age gap at 2.4-2.2 Ga, and continental growth