Corundum-bearing ultramafic veins in the Rymmen gabbro, southern Sweden: isochemical mineral alteration
Claeson, Dick T.
published: Jul 1, 1999
ArtNo. ESP154017501001, Price: 29.00 €
Ultramafic veins occur in the outer part of the 1.7 Ga Rymmen gabbro in southern Sweden. Their orientation is at random and no tectonic overprint is seen in the veins or in their host-rocks. Thus tectonic overprinting and synchronous or subsequent hydration can be ruled out as a hypothesis for the generation of these veins. A model is suggested, in which volatile-rich (aqueous) residual igneous fluids, formed entirely within the cumulates, caused the formation of veins. Whole-rock geochemical data show that the severe mineral alteration was more or less isochemical. One vein contains 2 vol. % corundum. The corundum is anhedral and corroded. Two in-situ alteration models are proposed for the genesis of corundum in the Rymmen gabbro. Minerals found in the vein have low silica and high alumina contents. Tschermakitic hornblende and pleonaste are associated with corundum. Temperature and pressure estimates are 700-800 °C and 6-10k bars based on hornblende-plagioclase geothermometry and the mineral assemblages corundum + amphibole + spinel + olivine + orthopyroxene and chlorite + amphibole + spinel + clinopyrocene found in the veins.