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Brett, Have found the discussion most interesting. Rigidly defined types of 'ideal' strain help us understand/label parts of strain (and deformation) in geological materials. However, to expect rigid adherence to a strain type throughout a geological body would seem to totally disregard scale concepts and bulk versus component strains. Regarding the fault problem, it is not uncommon to find a poor correlation between fault length and displacement. One reason for this is raised in your comments; namely, that the movement history may be complex and involve inconsistent/even opposing movement senses such that the apparent displacement vector is minimal. If there is a real displacement (that is one not resulting from volume loss and/or shortening normal to the fault plane) then there must be a component of simple shear within the general strain. Lack of a well-defined lineation in such a fault will depend on many factors including the amount of simple shear and the interaction between the rock material and physical conditions during faulting. But yes, it would be nice to know! Regards, Brian. At 09:40 PM 6/09/99 +0800, you wrote: >Well, the discussion that my query on pure shear started was very interesting and informative. I was wondering if anyone subscribed to this group until the recent submissions. I would like to go back to where my original question stemmed from. It is interesting to look at the Archaean of Western Australia, which is dominated structurally by northerly trending faults of significant strike length, commonly 10's of km to greater than 100 km. However, as best we can ascertain (given the lack of exposure) many of these have very little displacement across them, either in a dip-slip sense or strike-slip sense. Certainly the magnitudes of displacement would be at first glance be expected to be greater given the magnitude of these zones. Also, a number of these don't display consistent movement senses. Hence, my concern that these may be (perish the thought) akin to pure shear zones. Is this a common occurrence in other orogenic belts? > >Brett > >Dr Brett Davis >PO Box 265, Kalgoorlie Business Centre, >Western Australia, Australia, 6433. >Ph: 61-8-9022 3980 (H), 61-8-9021 7622 (W) >Fax: 61-8-9021 3200 **************************************************** Professor Brian Marshall, Tel: (+61-2)-9514 1775 Applied Geology - UTS, Fax: (+61-2)-9514 1755 P O Box 123 Broadway, NSW 2007, AUSTRALIA **************************************************** %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%