Abstract
A TEM investigation of amphibole development in granulitic metagabbros is presented. Three different sites of amphibole nucleation and growth are observed: (i) in the clinopyroxene-plagioclase interphase boundaries, corresponding to a reconstructive transformation involving intercrystalline diffusion; (ii) along pyroxene fractures, with competition between inter- and intracrystalline diffusion; (iii) within the pyroxene crystals, through a topotactic conversion, controlled by intracrystalline diffusion. These different reaction sites are studied in order to discuss some aspects of reaction mechanisms within undeformed metamorphic rocks, putting into balance intracrystalline versus intercrystalline processes. According to the possible paths (crystal lattice and its defects, fractures and mineral interfaces), contrasted amounts of reaction products, together with different amphibole compositions are evidenced. These results indicate that the diffusion rate of Al, Fe, Mg and OH is the rate controlling factor for amphibole-forming reaction.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
