Formation of corundum in metapelites around ultramafic bodies. An example from the Saualpe region, Eastern Alps

摘要: This paper describes corundum formation in a metasomatic reaction zonation around an ultramafic body within metapelitic sequence. The investigated is about 100 m diameter and located the Saualpe of Austroalpine nappe complex Eastern Alps. surrounded by 10 wide zone (here called 3) containing paragenesis garnet–staurolite–biotite–margarite–chlorite–corundum. Beyond further transition 2), there are undisturbed host rocks (zone 1) that have metamorphic peak garnet–biotite–plagioclase–staurolite–muscovite–quartz. It shown formed 7.2 kbar 615 °C during regional metamorphism, just above serpentine breakdown reactions system MgO–SiO2–H2O. Detailed analysis whole rock compositions shows infiltration metasomatism caused significant mass loss two alteration zones. These zones particularly depleted SiO2, Na2O possibly K2O. An XNa2O–XSiO2 thermodynamic pseudosection presented includes parageneses both unaltered corundum-bearing parageneses. suggests process can be explained transfer SiO2 alone. We interpret driven water liberated from previously serpentinised prograde dehydration Eo-Alpine metamorphism. fluid flowed outwards depleting surrounding pelites silica causing margarite plagioclase muscovite. interpretation driving mechanism consistent with our knowledge low activities orogenic cycle.