Evidence for regional Dauphiné twinning in quartz from the Santa Rosa mylonite zone in Southern California. A neutron diffraction study
نویسندگان
چکیده
Preferred orientation in granitic mylonites from the Santa Rosa mylonite zone in Southern California is investigated with time-of-flight neutron diffraction. Quartz and biotite display strong preferred orientation, whereas, feldspar alignment is weak. For quartz, a c-axis maximum in the intermediate fabric direction is consistent with dynamic recrystallization. Pole figures for positive and negative rhombs, such as rZ{10 11} and zZ{01 11}, are distinct over a wide region, suggesting that the pattern reflects tectonic deformation and was not affected by local late-stage mechanical Dauphiné twinning. Indeed, modeling based on the elastic properties of quartz indicates that compression perpendicular to the foliation may have induced Dauphiné twinning and this mechanism may thus be useful as a paleopiezometer to record tectonic stresses in quartz-bearing rocks. q 2005 Elsevier Ltd. All rights reserved.
منابع مشابه
Mechanical twinning in quartz: Shock experiments, impact, pseudotachylites and fault breccias
a r t i c l e i n f o Increasing use of diffraction methods to study preferred orientation of minerals has established that quartz in deformed rocks not only displays characteristic c-axis orientation patterns, but that there is also generally a distinct difference in the orientation of positive and negative rhombs. In the trigonal quartz crystal structure positive and negative rhombs are struc...
متن کاملDauphiné twinning and texture memory in polycrystalline quartz. Part 1: Experimental deformation of novaculite
Mechanical Dauphiné twinning in quartz has been of long-standing interest, both in single crystals and polycrystalline aggregates. This study investigates texture development in fine-grained quartz rock novaculite with no initial texture using compression experiments conducted in the Paterson gas apparatus to explore the influence of stress and temperature. Texture patterns are measured with ti...
متن کاملDauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation
Samples of quartz-bearing rocks were heated above the a (trigonal)–b (hexagonal) phase transformation of quartz (625–950 C) to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of cand a-axes, but posit...
متن کاملDauphiné twinning as evidence for an impact origin of preferred orientation in quartzite: An example from Vredefort, South Africa
Large meteorite impacts cause great changes to geologic features on Earth, ranging from cratering and ejecta blankets to phase transformations in minerals. In this report we describe the effect of a shock wave on the crystallographic orientation of quartz crystals in quartzite from the Vredefort impact site in South Africa. Preferred orientation of bulk quartzite samples was measured by time-of...
متن کامل