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At 10:05 AM 20/11/2001 -0500, Bob Tracy wrote: >...how does our terminology constructively deal with a group >of rocks I've looked at in New York...? ... Thermometric calculations >indicate 1000 C+. >These rocks are very fine-grained... and in fact are partially melted >and metsomatized former pelitic-schist xenoliths... >in mafic to ultramafic cumulates at the base of a small Silurian >layered intrusion. Regional thermobarometry, however, indicates the >current erosion level represents a pressure of about 7 kbar. There >is no doubt whatsoever that these are contact-metamorphic rocks yet >they lie far outside the P-T range that any textbook indicates for >very high-T contact-metamorphic facies... Bob, Is it possible that much of the ~7kbar worth of exhumation happened after Middle-Ordovician regional metamorphism but before emplacement of the Silurian layered intrusion? Depending on the answer, a speculation in my 1978 paper may or may not still be tenable: "If the three geographically distinct metamorphic culminations in New England are in fact respectively of Ordovician, Devonian, and Pennsylvanian age, then the fact that all three of them appear to be more deeply eroded in the south invites speculation that the northward "tilting" that is reflected in the bathozonal pattern is post-Pennsylvanian throughout the area." (Am J Sci 278, 784). Cheers, Dugald Dugald M Carmichael Phone/V-mail: 613-533-6182 Dept of Geological Sciences and Geological Engineering Queen's University FAX: 613-533-6592 Kingston ON K7L3N6 E-mail: [log in to unmask]