I appreciate John Rosenfeld's comments, and especially his discussion
of the etymology of the expression "piezothermal array". However, I
am nearly certain that most physcisists, on hearing the term
"piezothermal array" will immediately think of a geotherm. And that
is exactly the connotation that we do NOT wish to place on the term.
We need a term that clearly specifies we are looking at an array of
P-T points in the 2-dimensional erosional surface ("piezothermal
field gradient"???).
But perhaps more to the point, the important revelation of the past
two decades is that the metamorphic field gradient (or whatever we
choose to call it) does NOT (necessarily) reflect a stable geotherm
at any point in time. I think this realization traces back to Oxburgh
and Turcott (1974) and England and Richardson (1977). Prior to that
time, interpretations of what we see today in the field (i.e. the
field gradient) were always related to crustal geotherms. Certainly
Turner (1981) makes this point. I think the idea of rock P-T paths
and evolving geotherms may have preceded these papers, but I don't
know of anything in print. Indeed, I have in my notes from a course
taught by John Rosenfeld in 1972 a picture of a rock P-T path that
was definitely not in the shape of a stable geotherm! So clearly John
was thinking about this!
Cheers to all and thanks again to John for an interesting and lively
discussion!
Frank
----------------------------------------------
Frank Spear
Professor and Chair
Department of Earth and Environmental Sciences, JRSC 1C25
Rensselaer Polytechnic Institute
Troy, New York 12180
Phone (office): 518-276-6103
(lab) : 518-276-4899
Fax: 518-276-6680
http://www.rpi.edu/dept/geo/spear/spear.html
