Caracterisation geochimique (elements majeurs et elements en traces), tracage isotopique (samarium-neodymium, lutetium-hafnium) et geochronologie (lead-lead, uranium-lead) du groupe de Wakeham, N.E. Quebec: Bassin sedimentaire proterozoique dans la province de Grenville (French text).

摘要

The Wakeham Group is located in the eastern part of Grenville Province. It consists of arenites, arkoses, shales with minor amounts of rhyolite and mafic lavas resting unconformably on a Proterozoic gneissic basement and intruded by peraluminous granitic and gabbroic plutons, late syn-tectonic. The Wakeham Group rocks are distinct amongst the sedimentary sequences of the Grenville Province because of their weakly deformed and greenschist facies metamorphosed rocks. Geochemical, isotopic (Sm-Nd and Lu-Hf) and geochronological (Pb-Pb and U-Pb) studies are used to constrain the character of the sediment source and depositional age of the Wakeham Group sedimentary rocks.; Major element abundances indicate that sedimentary rocks of the Wakeham Group contain a mature material rich SiO2 and low MgO, and immature material low SiO2 and rich MgO. The Wakeham Group rocks are generally arenitic to arkosic and potassic in composition, consistent with a source area dominated by quartzitic and granitic compositions. However, trace element data are similar for both and REE profiles are comparable to the NASC witch is representative of the Proterozoic crust composition.; Sedimentary rocks from the Wakeham Group yield initial ϵNd (1.6 Ga) values ranging from −5 to +6; and depleted mantle model ages groupings at 1800, 1900, 2300 and 2700 Ma. The Nd data suggests that the materiel for the sedimentary rocks was derived from at least two main sources, one Proterozoic the other Archean: (1) sources with ages 1900–1800 Ma that overlap the ages of Trans-Labradorian orogeny; (2) sources with ages 2700–2600 Ma witch resemble to the Archean cratons ages such as the Superior, Rae and Nain provinces. The late peraluminous granites (1495–1510 Ma) have ϵNd values of +1 to +3 and model ages of 1800 to 1900 Ma that reflect the formation of the granites from melting of a predominantly Proterozoic crustal source or their contamination by a proterozoic crust. The Hf isotope data for detrital zircons from the Wakeham Group yield a range of model ages comparable to the Nd model ages and support the concept of a predominantly Proterozic source with minor Archean contribution. (Abstract shortened by UMI.)