Pseudotachylyte in muscovite-bearing quartzite: Coseismic friction-induced melting and plastic deformation of quartz

Thin (0.5\u20132 mm thick) pseudotachylyte veins occur within muscovite-bearing ( 3c10% volume), amphibolite-facies quartzites of the Schneeberg Normal Fault Zone (Austroalpine, Southern Tyrol, Italy). Pseudotachylytes are associated with precursor localized plastic microshear zones (50\u2013150 \u3bcm thick) developed sub-parallel to the host-rock foliation and with conjugate sets oriented at a high angle to the foliation. Such microshear zones are characterized by recrystallization to ultrafine-grained (1\u20132 \u3bcm grain size) mosaic aggregates of quartz showing a transition from a host-controlled to a random crystallographic preferred orientation towards the shear zone interior. Subsequent coseismic slip mainly exploited these microshear zones. Microstructural analysis provides evidence of extensive friction-induced melting of the muscovite-bearing quartzite, producing a bimodal melt composition. First, the host-rock muscovite was completely melted and subsequently crystallized, mainly as K-feldspar. Then, about 60% volume of the ultrafine-grained quartz underwent melting and crystallized as spherulitic rims (mostly consisting of quartz \ub1 Ti \ub1 Fe) around melt-corroded quartz clasts. The two melts show immiscibility structures in the major injection veins exploiting microshear zones at high angles to the quartzite foliation. In contrast, they were mechanically mixed during flow along the main fault veins

Electroreductive radical cyclization of ethyl 2-bromo-3-allyloxy- and -3-(propargyloxy)propanoates catalyzed by (tetramethylcyclam)nickel(I) electrogenerated at carbon cathodes in dimethylformamide

Prova tipográfica (In Press)Reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-methylenedioxophenyl)-3-(propargyloxy)propanoate (1) and ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-(allyloxy)propanoate (2) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes in dimethylformamide containing tetraalkylammonium salts, has been investigated. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 and 2 reveal that [Ni(tmc)]+ catalytically reduces these two compounds at potentials significantly more positive than those required for direct reduction of the bromoesters. During controlled-potential electrolyses of solutions of [Ni(tmc)]2+ in the presence of 1 and 2, catalytic reduction of each substrate proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford, respectively, 2-(3′,4′-methylenedioxophenyl)-3-ethoxycarbonyl-4-methylenetetrahydrofuran (3) and 2-(3′,4′-dimethoxyphenyl)-3-ethoxycarbonyl-4-methyltetrahydrofuran (6). A mechanistic scheme is proposed to account for the formation of each major product.Fundação Calouste GulbenkianCRUPFundação para a Ciência e Tecnologia (FCT)Government Assistance in Areas of National Need (GAANN)Fellowship awarded by Indiana Universit

Electroreductive intramolecular cyclization of a bromo propargyloxy ester catalyzed by nickel(I) tetramethylcyclam electrogenerated at carbon cathodes in dimethylformamide

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate and characterize the reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-propargyloxy-propanoate (1) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes in dimethylformamide containing tetraalkylammonium salts. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 reveal that [Ni(tmc)]+ catalytically reduces 1 at potentials more positive than those required for direct reduction of 1. During controlled-potential electrolyses of solutions containing [Ni(tmc)]2+ and 1, catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methylene-tetrahydrofuran (2). In the presence of a base (either electrogenerated or deliberately added as potassium tert-butoxide), 2 rearranges to give 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methyl-2,5-dihydrofuran (3). A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and controlled-potential electrolysis.Fundação Calouste Gulbenkian