A quantitative study of deformation mechanisms and finite strain in quartzites
Abstract
The Weverton quartzites in the Maryland Blue Ridge are deformed by one major period of greenschistgrade deformation. The components of finite strain due to different independent mechanisms have been measured for these rocks. The total strain is split up into two major components: 410_2004_Article_BF00371309_TeX2GIFE1.gif \varepsilon ^t = \varepsilon ^p + \varepsilon ^d . The finite natural strain caused by dislocation creep (∊^{ d }) is measured by a new technique using folded and stretched rutile needles which are good strain markers within the quartz crystals. Pressure solution strain (∊^{ p }) is measured from the ratio of the area of new crystals and fibers to the whole rock area in principal sections. Grain boundary sliding is a dependent process which accompanies both mechanisms. Pressure solution obeys a linear Newtonian flow law, left {dot γ _0^p } right = A_p left {tau _0 } right, while dislocation creep obeys a power law of the form left {dot γ _0^d } right = A_d left {tau _0 } right^n where dot γ _0^p ,dot γ _0^d are octahedral shear strain rates, τ_{0} is the octahedral shear stress and A _{ p }, A _{ p } and n are constants. A direct correlation between finite strain measurements and the operating flow laws can be made. Application of these methods and principles to a few field examples indicates that the rocks obey a flow law partly governed by each mechanism. Any set of physical conditions defines a unique flow law and there is a transition in creep behavior from dominantly Newtonian to a power law with increasing strain rate.
 Publication:

Contributions to Mineralogy and Petrology
 Pub Date:
 December 1976
 DOI:
 10.1007/BF00371309
 Bibcode:
 1976CoMP...59..203M