Calcite-corundum oxygen isotope fractionations in Naxos metabauxites; selecting samples for thermometry- Academic Article uri icon

abstract

  • Discontinuous horizons of corundum-rich lenses, interpreted as meta-karst bauxites, are enclosed within greenschist (~ 400 C) to amphibolite facies (~ 700 C) marble on Naxos, Cyclades, Greece. The large range of metamorphic temperature, mineralogy, grain size, and modal proportions permit tests of different strategies to improve accuracy of oxygen isotope thermometry. Diffusion modeling predicts that Refractory Accessory Minerals (RAM) will provide accurate thermometers when applied to rocks modally dominated by a mineral with faster diffusion and below the closure temperature (Tc, for diffusion of oxygen) of the RAM (Valley, RIMG 2001). Corundum (Crn) has Tc> 700 C even for slow cooling and fine grain size. Calcite (Cc) has significantly faster diffusion. Appropriate samples for RAM thermometry should have:(1) high modal Cc/Crn ratio;(2) absence of thick Ca-Al silicates …

publication date

  • November 5, 2001