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Ah yes, I see, the minerals formed at high P without fluid and consequently remained unchanged at lower P. : )?. ----- Original Message ----- From: Tim Bell <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, November 04, 1999 11:30 PM Subject: Re: ultrahigh metamorphic rocks? > Sol & Eric > Dry extension did not occur in the Dabie Region of the Qinling. > Highpressure minerals are trapped as inclusion trails in garnet > porphyroblasts that formed during an early period of orogenesis and the > inclusion trails define about 3 sets of steep & shallow foliations. There > were two subsequent periods of garnet growth, each over a succession of > foliations with differently oriented intersection axes (FIAs), but a > consistent succession in time. Since for both the younger sets of axes > there is a succession of steep and shallow foliations preserved, orogenesis > was similar to any other compressional orogenic belt I have ever worked in. > Presumably the close by rocks with high pressure mineralogy still in the > matrix went through a similar history but were not retrogressed by it. > Perhaps all younger deformation simply partitioned around them? > Porphyroblasts reveal this happens routinely on a large outcrop and greater > scale. Why not for a whole package of rock, especially if it was surrounded > by weaker schists. > Cheers > Tim > > >Sol and all, > > Dry extension. > >Eric > > > > > > > >Talking of metamorphic rocks, does anybody know how ultrahigh metamorphic > >>rocks, as seen in the Dabie Shan China, are transported from mantle depths > >>back to the surface without undergoing extensive retrograde metamorphism or > >>even melting as a result of the rapid decrease in pressure? The ultrahigh > >>metamorphism must be related to continental collision but what is the > >>mechanism of relaxation that allows these rocks to move so rapidly towards > >>the surface? > >>Sol > >> > >> > >>*********************************** > >> > >>Solomon Buckman > >> > >>Department of Earth Science http://147.8.150.90/Sols%20Homepage.htm > >> > >>University of Hong Kong http://www.hku.hk/earthsci/rock.html > >> > >>Ph. 852-28571759, Fax 852-25176912 > > > 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] > > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%