ABSTRACT
When studying a suite of metamorphic rocks, especially those formed during orogenic metamorphism, the common occurrence of porphyroblasts and one or more tectonic fabrics provides valuable information concerning deformation–metamorphism interrelationships. When integrated with pressure and temperature estimates based on mineral assemblages and geothermobarometry, coupled with any age dates that may exist to date particular events in the region studied, such microstructural features can enable the construction of a pressure–temperature–time (P–T–t) path for individual rocks. This in turn can give important insights into aspects of crustal evolution, or metamorphic evolution in the vicinity of major igneous intrusions. Although the interpretations from porphyroblast–foliation relationships have excellent potential, the interpretation of porphyroblast inclusion trails and their relationships with external matrix fabrics in the rock have always been contentious topics. Different interpretations of the same textural and microstructural features have led to fundamental differences of opinion concerning the processes responsible for particular features observed and consequently the overall interpretations can vary greatly between different researchers. In Sections 5.1, 5.2 & 5.3, aspects of porphyroblast nucleation and growth were considered, and in Section 6.1 general aspects concerning mineral inclusions were discussed. This chapter concentrates on the various aspects of porphyroblast-foliation relationships, providing an introduction to the characteristic microstructural features observed, and providing an overview of the various points to take into consideration when making interpretations. The chapter highlights particular problem areas, where opinion is divided concerning the interpretation.
