Impact-induced frictional melting in ordinary chondrites: A mechanism for deformation, darkening, and vein formation

available online at http://meteoritics.org 1521 © Meteoritical Society, 2003. Printed in USA. Impact-induced frictional melting in ordinary chondrites: A mechanism for deformation, darkening, and vein formation C. H. VAN DER BOGERT,1* P. H. SCHULTZ,1 and J. G. SPRAY2 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA 2Planetary and Space Science Centre, Department of Geology, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada *Corresponding author. E-mail: [email protected] (Received 14 March 2003; revision accepted 18 September 2003) Abstract–High speed friction experiments have been performed on the ordinary chondrites ElHigh speed friction experiments have been performed on the ordinary chondrites El Hammami (H5, S2) and Sahara 97001 (L6, S3) using an axial friction-welding apparatus. Each sample was subjected to a strain rate of 103 to 104 s-1, which generated 250 to 500 mm-deep darkened zones on each sample cube. Thin section analyses reveal that the darkened areas are composed of silicate glass and mineral fragments intermingled with dispersed submicron-size FeNi and FeS blebs. Fracturing of mineral grains and the formation of tiny metallic veins define the extent of deformation beyond the darkened shear zone. These features are not present in the original meteorites. The shear zones and tiny veins are quite similar to certain vein systems seen in naturally deformed ordinary chondrites. The experiments show that shock deformation is not required for the formation of melt veins and darkening in ordinary chondrites. Therefore, the presence of melt veins and darkening does not imply that an ordinary chondrite has undergone severe shock deformation. In fact, high strain rate deformation and frictional melting are especially important for the formation of veins at low shock