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Call for research papers visit www.research-sites.nstemp.com Publish your research papers to the web ----- Original Message ----- From: Enrico Tavarnelli <[log in to unmask]> To: <[log in to unmask]> Sent: Monday, January 08, 2001 11:27 AM Subject: Re: Passive and Flexural Folding > >Dear All, > > > >Highlighted recently at TSG, there seems to be some discrepancy of > >understanding between passive and flexural folding. > > > >My understanding of passive folding is that pressure solution modifies an > >original fold shape (ie. buckling first, then intense pressure solution). > >This would produce the deck of cards effect (ie. regular thickened hinge, > >thinned limbs). The limb volume of a layer is not reduced by shear along > >the cleavage plane (which I further understand cannot happen), but by > >material loss, therefore rotation is an irrelevant issue. Is this the > >correct description of the term 'passive folding'? If not, what is. > > > >Flexural folding, as I understand it, occurs by shear between or within > >layers (slip/flow) and the original volume is maintained - the buckling > >effect. If this is so, cleavage within a flexural fold that shows no sign > >of bedding misalignment between cleavage surfaces would need to have > >developed prior to the buckling. Further, any fold containing a cleavage > >that does not show bedding misalignment between cleavage surfaces must be > >deemed to be flexural? Comments welcome please. > > > >As an aside, does anyone know the upper temperature limit of cleavage > >development. > > > > Dear Joanie, > the questions you raise seem of primary interest, and to my knowledge there > has been much debate on whether natural folding is passive, or flexural, or > both. > Although I am not updated with the most recent advances in the field, I am > aware of two recent contributions that contain discussions aiming to a > clearer understanding of the folding process and the cleavage-folding > relationships within natural folds. > > So, try with the followings: > > -Luneburg & Lebit (1998) "The development of a single cleavage in an area > of repeated folding" - Journal of Structural Geology, 20, 11, 1531-1548. > > -Treagus, Hudleston & Labao (not necessarily in this order) (1996? or 1997) > "Flexural-slip folding: does it exist in nature?" Geology (must be 1996 or > 1997). > > I hope you find these references of use. > Best wishes > Enrico Tavarnelli > > \\\\\\ > ( @ @ ) > -----o00-(_)-00o----- > Enrico Tavarnelli > Dipartimento di Scienze Geologiche, > Universita' della Basilicata, > Campus Macchia Romana, 85100, Potenza (Italy), > phone: ++39-(0)971-206 179; fax: ++39-(0)971-206 077; > e-mail: [log in to unmask]