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Brett Jees you are a stirring bastard! I was not going to step into this one. I do not have the time. However, Jochens original question "Does the strike of regional foliation in metamorphic rocks mimic past continental contact?" is something that I am very interested in, as you bloody well know. I suspect, very briefly, that when a collisional plate boundary first initiates, and folds and foliations have formed for the first time, they basically will end up following the belt of collision, which of course is the plate boundary, for a whole range of reasons. This means that most subsequently formed matrix foliations will also follow the plate boundary because bedding is the major heterogeneity and it will always reactivate at the larger scale, destroying or rotating the orientation of any newly forming matrix foliations towards the trend of local bedding. Very large old folds never die - they just reorientate (it could make a good T-Shirt slogan in the right context). So it does not really matter what the relative direction of plate motion is across that plate boundary. Even if a portion of a plate boundary was sheared at a high angle by a shift in relative plate motion to form a large arc, the matrix foliation would still follow the new trend of the plate boundary. Of course Brett's stirring poses the question, "But what do the foliations preserved in porphyroblasts do!" If you want to know read Bell, T.H. & Mares, V.M., 1999. Correlating deformation and metamorphism around arcs in orogens. American Mineralogist, 84, 1727-1740. Of course all of this only applies to orogenic belts that are narrow relative to their length. Cheers Tim >Jochen > >I'll yank the chain a bit here and ask "What about foliation trend lines >that may be able to be constructed from inclusion trails within >porphyroblasts?". Some people have suggested that porphyroblasts have not >rotated over immense distances along orogens. > >Cheers >Brett > >Disclaimer: The views expressed above are not necessarily those of the >writer. > >-----Original Message----- >From: Jochen Mezger [SMTP:[log in to unmask]] >Sent: Wednesday, 16 February 2000 0:01 >To: [log in to unmask] >Subject: Re: Foliation > >Hi Barry, > >Regarding your question if strike of regional foliation in metamorphic >rocks can trace a former continental contact. I think this is certainly the >case in younger orogenic belts where strike of regional foliation parallels >that of the orogen (Northern NA Cordillera). And if you have other proof >for a suture, such as isotope data, etc. But if you go into older terrains >with multiple metamorphism and deformation, development of large >strike-slip faults, shear zones, etc., you would need extra independent >evidence. Regional trend of foliation alone in an Archaean schist would not >convince me. > >Ciao, > >Jochen > > >>How Now Everyone >> >>Does the strike of regional foliation in metamorphic rocks mimic past >>continental contact? >>-- >>;-) >>Barry Bowman > > > > >*************************************************************************** >Dr. Jochen Mezger > >Postdoctoral Fellow >Johannes Gutenberg-University Mainz Tel.: 49-(0)6131-3924767 >Institut fuer Geowissenschaften Fax.: 49-(0)6131-3923863 >Tectonophysics Group >Becherweg 21 Email: [log in to unmask] >55099 Mainz >GERMANY > >============================================================ > > "We're all recycled history machines, > cavemen in faded blue jeans." Jimmy Buffett > > >************************************************************************ >**** Prof Tim Bell School of Earth Sciences James Cook University Townsville QLD 4811 Australia ph: +61 7 47814766 fax: +61 7 47251501 email: [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%