SEM observation of grain boundary structures in quartz-iron oxide rocks deformed at intermediate metamorphic conditions

Muitos estudos t?m demonstrado o efeito de uma segunda fase sobre a distribui??o de fase fluida e dissolu??o de gr?os de quartzo. Entretanto, como a maioria das observa??es v?m de agregados deformados sob condi??es de tens?o hidrost?tica e em rochas quartzosas ricas em mica, a distribui??o 3D de poros em bordas quartzo-quartzo (BQQ) e quartzo-hematita (BQH) tem sido estudada. V?rias superf?cies de fraturas orientadas segundo o elips?ide de deforma??o finita foram analisadas. A distribui??o dos poros caracteriza a porosidade e a forma dos gr?os como altamente anisotr?picas, o que resulta da natureza e orienta??o das bordas. BQH t?m propriedades f?sico/qu?micas muito diferentes de BQQ, uma vez que as plaquetas de hematita t?m forte efeito no comportamento do fluido, de maneira similar ?s micas em quartzitos. Elas s?o superf?cies planas, livres de poros, normais ? dire??o de m?ximo encurtamento, sugerindo que estiveram, em um momento, cobertas por um filme cont?nuo de fluido agindo como um caminho mais r?pido de difus?o. Nas BQQ, os poros s?o facetados, isolados, concentrados nos limites das mesmas refletindo o controle cristalogr?fico e uma rede interconectada de fluido ao longo das jun??es dos gr?os. As BQQ normais ? dire??o de m?xima extens?o s?o s?tios de concentra??o de flui crescimento de gr?os foram respons?veis pela forma??o de plaquetas de hematita e gr?os de quartzo tabulares contribuindo significativamente para a gera??o da folia??o observada nas rochas estudadas.Several studies have demonstrated the effect of a second phase on the distribution of fluid phase and dissolution of quartz grains. However, as most observations came from aggregates deformed under hydrostatic stress conditions and mica-bearing quartz rocks, 3-D distribution of pores on quartz-quartz (QQB) and quartz-hematite boundaries (QHB) has been studied. Several fracture surfaces oriented according to finite strain ellipsoid were analyzed. The pore distribution characterizes the porosity and grain shape as highly anisotropic, which results from the nature and orientation of boundaries. QHB have physical/chemical properties very different from QQB, once the hematite plates have Strong effect on wetting behavior of fluid, likewise micas in quartzites. They are pore-free flat surfaces, normal to compression direction, suggesting that they were once wetted with a continuous fluid film acting as faster diffusion pathway. At QQB, the pores are faceted, isolated, close to its edges reflecting the crystallographic control and an interconnected network of fluid along grain junctions. The QQB facing the extension direction are sites of fluid concentration. As consequence, the anisotropic dissolution and grain growth were responsible for the formation of hematite plates and tabular quartz grains significantly contributing for the generation of the foliation observed in the studied rocks