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

Abstract

In order to clarify deformation mechanisms and behaviours of quartz in a low-temperature regime in the earth's crust, microstructural analyses, particularly on kink bands have been carried out for quartz veins moderately deformed under subgreenschist conditions. Both the dominance of subbasal deformation lamellae and geometry of kink bands suggest that basal (0001) slip was the sole active slip system in the deformed quartz. On a morphological basis, kink bands in the quartz were classified into two types: type I is characterized 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 with basal plane (sub-)parallel to the compression axis, whereas type II kink bands were formed in grains with basal planes inclined to it. Using a numerical model of kinking of elastic multilayers modified after Honea and Johnson (Tectonophysics 30, 197–239, 1976), changes of the level of yielding stress for kinking and the width of kink bands as a function of the angle θ between the slip plane and the compression axis have been examined. The theory predicts that type I kink bands were formed at a higher stress level than type II kink bands, and hence occurrence of type I kink bands suggests that a significant strain hardening occurred in the deformed quartz veins. The theory also well explains the fact that the width of type I kink bands ( θ=0 to 10°) is narrower by an order of magnitude than type II kink bands ( θ=10 to 80°).