Archean crustal evolution of the Suthern São Francisco Craton\ud reviewed

The Southern São Francisco Craton contains a number of ancient granite-greenstone associations and medium- to high grade rocks (TIG type) encompassing migmatites which collectively address an isotopic record of sialic crust from ca. 3.8 to 2.5 Ga. We present an integrated interpretation based on new and compiled U-Pb ages and Nd-Sr-Pb isotope constraints, and trace element geochemistry, providing inferences for the Archean geodynamic processes through time and space. In addition, \ud U-Pb detrital zircon dating of both the Rio das Velhas and Minas Supergroups is merged to infer \ud main Archean sources as landmarks of the protracted, polycyclic history. Considering the geologic \ud framework and ages, two crustal segments (Mesoarchean; Neoarchean) can be distinguished, \ud although there is indirect isotopic evidence of Paleoarchean protholithS given by a smallnumber of \ud Pb inherited ages and some Sm-Nd TOM ages. The Mesoarchean remnant (Campo Belo and Santa \ud Bárbara metamorphic complexes) originated through juvenile accretion episodes (3.21-3.20 Ga; 3.0- \ud 2.90 Ga), herein termed the Campo Belo orogeny. Some occurrences of ancient greenstone belts \ud within the Proterozoic framework marginal to the Craton suggest a larger extent of the Mesoarchean \ud core. The Neoarchean segment, formed during the so-called Rio das Velhas orogeny, comprises \ud two tectonic-magmatic episodes. The early episode (2.79-2.75 Ga), marking vigorous crustal growth \ud by juvenile accretion, originated the granite-greenstone terrain comprised by the Belo Horizonte \ud and Bonfim gneissic complexes and the coeval Rio das Velhas Supergroup. In contrast, the latest \ud episode (2.75-2.69 Ga) included development of tholeiitic to calc-alkaline magmatism, high grade \ud metamorphism having the fingerprintof polyphase defomnation and sub-arc cnustal anatexis, \ud highlighted by mafic-ultramafic layered suites and the Passa Tempo granulitic complex - now exposed \ud as roots of a continental collision that eventually assembled the landmass. This stage also generated \ud granitic plutons and mafic dikes between 2.66 and 2.55 Ga, as post-tectonic to anorogenic activity

National metrology institute - its value to Canadian economy and society

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A case for a national metrology agenda for Canada

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Reaction of organotin hydrides with acid chlorides. Mechanism of aldehyde and ester formation

Tri-n-butyltin hydride reacts with acid chloride, RCOCl, spontaneously at ambient temperatures to form n-Bu 3SnCl, RCHO, RC(O)OCH 2R, and a number of minor products. The reaction is not a radical chain process, nor are radicals involved as intermediates. The initial products are n-Bu 3SnCl and RCHO; it is not known whether these are formed in a direct reaction between n-Bu 3SnH and RCOCl or via an unstable chloroalkoxytin species, n-Bu 3SnOCHClR. The remaining products are formed by subsequent reactions of the aldehyde. Thus, the alkoxytin species, n-Bu 3SnOCH 2R, is formed from aldehyde and tin hydride. This can react further with RCOCl to form the ester RC(O)OCH 2R, with RCHO to form n-Bu 3SnOCH(R)OCH 2R, and with n-Bu 3SnH to form RCH 2OH. The aldehyde can also react with RCOCl to form the \u3b1\u2032-chloro ester, RC(O)OCHClR.Peer reviewed: YesNRC publication: Ye

Reaction of acyl halides with organotin hydrides. Mechanism of aldehyde formation

Peer reviewed: YesNRC publication: Ye