Dynamic analysis and two types of kink bands in quartz veins deformed under subgreenschist conditions

In order to clarify deformation mechanisms and behaviours of quartz in a lo w-temperature regime in the earth's crust, microstructural analyses, partic ularly on kink bands have been carried out for quartz veins moderately defo rmed under subgreenschist conditions. Both the dominance of subbasal deform ation lamellae and geometry of kink bands suggest that basal (0001) slip wa s the sole active slip system in the deformed quartz. On a morphological ba sis, kink bands in the quartz were classified into two types: type I is cha racterized by conjugate and narrow bands with angular hinge zones, and type II by a wide monoclinal band. Dynamic analyses using deformation lamellae and kink bands have revealed that type I kink bands were formed in grains w ith basal plane (sub-)parallel to the compression axis, whereas type II kin k bands were formed in grains with basal planes inclined to it. Using a num erical model of kinking of elastic multilayers modified after Honea and Joh nson (Tectonophysics 30, 197-239, 1976), changes of the level of yielding s tress for kinking and the width of kink bands as a function of the angle a between the slip plane and the compression axis have been examined. The the ory predicts that type I kink bands were formed at a higher stress level th an type II kink bands, and hence occurrence of type I kink bands suggests t hat a significant strain hardening occurred in the deformed quartz veins. T he theory also well explains the fact that the width of type I kink bands ( theta = 0 to 10 degrees) is narrower by an order of magnitude than type II kink bands (theta = 10 to 80 degrees). (C) 1999 Elsevier Science B.V. All r ights reserved.