@misc{10481/64293, year = {2003}, url = {http://hdl.handle.net/10481/64293}, abstract = {Chlorites containing appreciable amounts of Cr were recognized by AEM in an anchizonal metapelite of the Puncoviscana Formation during a TEM study. Cr-bearing chlorites are restricted inside a rounded crystal of quartz several microns diameter, they form a group of tabular crystals all with the same crystallographic orientation. AEM analysis reveals Cr contents from 0.07 to 0.25 a.f.u., and a low sum of octahedral cations. Average analysis is Si3.07Al1.92Mg262Fe2.07Cr0.19O10(OH)8. Rock-forming chlorites do not contain Cr, a mean formulae based on AEM analyses is Si2.76Al2.46Mg2.43Fe2.29Mn0.03O10(OH)8. This Cr-bearing chlorites are unusual in sediments; their presence in the rock together with chlorites having the usual composition in metapelites is significant regarding the absence of chemical equilibrium in low-grade metamorphic systems.}, abstract = {Durante un estudio por TEM se reconocieron, mediante AEM, cloritas que contenían cantidades apreciables de Cr en una metapelita de anquizona de la Formación Puncoviscana (Argentina) . Las cloritas con Cr están restringidas en el interior de un cristal redondeado de cuarzo de varias micras de diámetro y forman un grupo de cristales tabulares todos con la misma orientación cristalográfica. El análisis AEM revela contenidos de Cr de 0.07 a 0.25 a.f.u., y una baja suma de cationes octaédricos. El análisis promedio es Si3.07Al1.92Mg2.62Fe2.07Cr0.19O10 (OH) 8. Las cloritas constituyentes de la roca no contienen Cr, su fórmula media basada en análisis AEM es Si2.76Al2.46Mg2.43Fe2.29Mn0.03 O10 (OH)8. Las cloritas que contienen Cr son inusuales en los sedimentos; su presencia en la roca junto con cloritas que tienen la composición habitual de metapelitas es significativa en cuanto a la ausencia de equilibrio químico en sistemas metamórficos de baja grado.}, publisher = {Elsevier}, keywords = {Cr}, keywords = {Chlorites}, keywords = {Anchizone}, keywords = {Puncoviscana}, keywords = {Argentina}, keywords = {TEM}, keywords = {AEM}, title = {Cr-bearing chlorites in low-grade metapelites of the Puncoviscana Formation (Neoproterozoic), northwestern Argentina}, author = {do Campo, Margarita and Nieto García, Fernando}, }