|
1 School of Geological Sciences, Kingston University, Penrhyn Road, Kingston-upon-Thames, Surrey KT1 2EE, UK p.treloar{at}kingston.ac.uk
2 Bayerisches Geoinstitut, Universitat Bayreuth, Postfach 101251, D-95440 Bayreuth, Germany Patrick.Obrien{at}uni-bayreuth.de
Although it has long been recognized that what ultimately drives metamorphism and metamorphic processes is heat, what was for long less certain is the distribution of heat within the crust, the type and location of the major heat sources and the rates of heat flux through crustal rocks. In early work a spatial link was established between the emplacement of igneous bodies and the metamorphism of their immediately adjacent country rocks. Widely described now as ‘contact metamorphism’ what needed addressing at that stage was the extent to which regional metamorphism itself might be a function of heat advected by igneous intrusions. Simply, are all ‘regional’ metamorphic terrains underlain by voluminous igneous plutons? In some of the earliest studied metamorphic terrains the highest temperature rocks are commonly associated with igneous rocks. Over a period of years, while George Barrow, Pentti Eskola and Cecil Tilley were developing the basis of modern metamorphic petrology (the facies concept and the concepts of metamorphic isograds, assemblages and zones) it became apparent that high-grade rocks are commonly spatially linked with igneous material, some of which would now be identified as former anatectic partial melts, but some of which, as in NE Scotland, include gabbroic plutons. In contrast, German petrologists in the early twentieth century developed an essentially baric approach to studies of regional meta-morphism. Here, rather than invoking magmatic heat advection as the driving force for regional metamorphism, the classification of epizonal, mesozonal and katazonal divisions stressed the change in metamorphic grade with structural depth. The
...
This 250-word extract was created in the absence of an abstract.
