Evolution of the Continental Crust and Significance of the Zircon Record, a Case Study from the French Massif Central

Evolution of the Continental Crust and Significance of the Zircon Record, a Case Study from the French Massif Central
Author: Simon Couzinié
Publisher:
Total Pages: 0
Release: 2017
Genre:
ISBN:

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 Geology of Central Europe: Precambrian and Palaeozoic

The Geology of Central Europe: Precambrian and Palaeozoic
Author: Tom McCann
Publisher: Geological Society of London
Total Pages: 804
Release: 2008
Genre: Science
ISBN: 9781862392458

Publishers Weekly Top 10 Best of the Year In her new collection, Story Prize finalist Maureen F. McHugh delves into the dark heart of contemporary life and life five minutes from now and how easy it is to mix up one with the other. Her stories are post-bird flu, in the middle of medical trials, wondering if our computers are smarter than us, wondering when our jobs are going to be outsourced overseas, wondering if we are who we say we are, and not sure what we'd do to survive the coming zombie plague. Praise for Maureen F. McHugh: "Gorgeously crafted stories."—Nancy Pearl, NPR "Hauntingly beautiful."—Booklist "Unpredictable and poetic work."—The Plain Dealer Maureen F. McHugh has lived in New York; Shijiazhuang, China; Ohio; Austin, Texas; and now lives in Los Angeles, California. She is the author of a Story Prize finalist collection, Mothers & Other Monsters, and four novels, including Tiptree Award-winner China Mountain Zhang and New York Times editor's choice Nekropolis. McHugh has also worked on alternate reality games for Halo 2, The Watchmen, and Nine Inch Nails, among others. io9 Best SF&F Books of 2011 Tiptree Award Honor List Philip K. Dick Award finalist Story Prize Notable Book

Evolution and Differentiation of the Continental Crust

Evolution and Differentiation of the Continental Crust
Author: Michael Brown
Publisher: Cambridge University Press
Total Pages: 550
Release: 2006-02-27
Genre: Science
ISBN: 0521782376

Summary of recent research covering experimental methods and numerical modelling, for graduate students and researchers.

Exposed Cross-Sections of the Continental Crust

Exposed Cross-Sections of the Continental Crust
Author: M.H. Salisbury
Publisher: Springer Science & Business Media
Total Pages: 658
Release: 2012-12-06
Genre: Science
ISBN: 9400906757

In the Fall of 1988, 64 geologists and geophysicists from 11 countries met in Killarney, Ontario, on the north shore of Lake Huron to examine evidence that suggests that the continental crust is exposed in cross-section at several key locations on the Earth's surface. The meeting, which was held under NATO auspices as an Advanced Study Institute, was a landmark event in that it was the first time that many of the lead scientists working on these complexes in relative isolation around the world had' ever gathered together to compare results. The present volume is a compendium of the invited lectures given on the principle sections, plus an array of supporting papers on these and other sections as well as on related topics such as crustal emplacement mechanisms, deformation and rheology. Nearly all of the best known sections are represented, including the Ivrea Zone, Calabria, the Kapuskasing Zone, Fiordland and many others. It is our hope that this Volume will serve as a reference for Earth scientists who are trying to understand levels of the crust not normally exposed to view, as well as a point of departure for new research and a teaching aid to new entrants in this relatively new field of study.

4-D Framework of Continental Crust

4-D Framework of Continental Crust
Author: Robert D. Hatcher
Publisher: Geological Society of America
Total Pages: 656
Release: 2007
Genre: Science
ISBN: 0813712009

"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.

Archean Continental Crust Formation and the Rise of Atmospheric Oxygen

Archean Continental Crust Formation and the Rise of Atmospheric Oxygen
Author: Ann M. Bauer (Ph. D.)
Publisher:
Total Pages: 376
Release: 2017
Genre:
ISBN:

This thesis examines critical aspects of the terrestrial environment that have resulted in a habitable planetary surface: the establishment of the continental crust and the progressive rise of an oxygenated atmosphere. The volume of continental crust on the earliest Earth is a critical parameter for constraining the chemical evolution of major terrestrial reservoirs, and radiogenic isotope signatures document this varying geochemical character. Chapter 1 presents a Lu-Hf and U-Pb isotopic characterization of zircons from the 4.0-2.9 Ga Acasta Gneiss Complex (AGC) and documents the magmatic extraction history of this domain, including changes in source compositions. These results are compared with a complementary dataset obtained using solution methods in Chapter 2. The integration of these results demonstrates the utility of performing coupled solution- and laser-based analyses on the same zircon populations to parse out U-Pb and Lu-Hf systematics. Zircons from many of these orthogneisses exhibit isotopic complexity due to the combined effects of accumulated radiation damage and repeated metamorphic episodes. For this reason, it is best to subsample zircon grains to isolate domains of distinct age and isotopic composition. In order to obtain suitable precision for subsampled domains, it was necessary to develop analytical techniques (Chapter 3) suited to small-volume analysis of the U-Pb and Lu-Hf isotope systems in zircon (via both laser ablation and solution analysis). In contrast to the whole rock Nd isotopic record of the AGC, the zircon Hf isotopic record does not indicate that rocks within the AGC were derived from a strongly depleted mantle. In order to evaluate the polymetamorphic evolution of these rocks, in Chapter 4 1 present a combined U-Pb and Sm-Nd isotope and trace element study of MREE-rich accessory minerals. In Chapter 5, I investigate sedimentary pyrite formation pathways and the oxygenation history of the late Archean atmosphere using combined sulfur and iron isotope signals as recorded in distinct morphologies of pyrite. This work represents a critical step in deconstructing the pathways of S-MIF production, transfer and preservation in the sedimentary record. Collectively, these studies contribute to our understanding of the establishment and evolution of the early continental crust and an oxygenated atmosphere.

Origin and Evolution of the Deep Continental Crust

Origin and Evolution of the Deep Continental Crust
Author: N. R. Karmalkar
Publisher: Narosa Publishing House
Total Pages: 0
Release: 2010
Genre: Continental crust
ISBN: 9788184870558

Origin and Evolution of the Deep Continental Crust provides the recent research in the field of Deep Continental Crust in India. Several new data sets on the interesting aspects of petrology and geochemistry of the Indian lithosphere and glimpses of the regional geology and geodynamics of parts of the Indian Shield have been provided. It includes articles on sapphirine bearing granulites from Karur, amphibolites from Hutti-Maski Gold mine, granites from Varshanadu and mataconglomerate-quartzite from Malvan which provide vital clues to the Pre Cambrian evolution of South India. The articles from Bastar Craton are related to felsic magmatism -- Dongargargh granites from Gadchiroli and the Bijli rhyolite while the Paleoproterozic high-MgO dykes represents the basic magmatism from this craton. Studies related to Kimberlite magmatism from the Wajrakarur and Manipur kimberlite, The Jungel valley alkaline lamprophyre, the dyke-flow co-relation and fluid inclusions from the Deccan Traps, and xenolith bearing host alkaline magmatism from Kutch provide important clues to the evolution of the sub-continental lithospheric mantle (SCLM). The possibility of the Lonar impact glass as potential natural analogue for nuclear waste galss is also discussed. The paleomagnetic data of some litho-tectonic units from the Indus Suture Zone, Ladakh also provide insight into the paleo-latitude reconstruction of India. The book thus serves as a useful and up-to-date reference for students, academicians and researchers.

From the Guajira Desert to the Apennines, and from Mediterranean Microplates to the Mexican Killer Asteroid

From the Guajira Desert to the Apennines, and from Mediterranean Microplates to the Mexican Killer Asteroid
Author: Christian Koeberl
Publisher: Geological Society of America
Total Pages:
Release: 2022-08-01
Genre: Science
ISBN: 0813725577

"This volume pays tribute to the career and scientific accomplishments of Walter Alvarez with papers related to the many topics he has covered : tectonics of microplates, structural geology, paleomagnetics, Apennine sedimentary sequences, geoarchaeology and Roman volcanics, Big History, and the discovery of evidence for a large asteroidal impact event at the Cretaceous-Tertiary (now Cretaceous-Paleogene) boundary site in Gubbio, Italy"--