Experimental simulation of contact metamorphism using natural quartzphyllite materials: advantages and pitfalls

Abstract

AbstractExperimental investigations on metamorphic processes can be viewed as an alternative forward modelling approach of the pressure–temperature–composition (P–T–X) evolution of a rock. To obtain results as close as possible to natural observations one can use natural rocks as starting materials. The disadvantage of this method is the complex chemical compositions of the rocks and therefore these whole-rock experiments need to be evaluated not only (1) in terms of their ability to reproduce the natural observations but also (2) in their ability to reproduce theoretical calculations. In this contribution high-T low-P experiments (550–780°C and 0.15–0.6 GPa) simulating contact metamorphism of metapelites at the rims of the Permian Brixen Granite and Klausen Diorite are evaluated with respect to the points discussed above. The agreement between the experimental results and the observed mineral assemblages and mineral compositions (plagioclase, biotite) from the contact aureoles is very good. Thermodynamic testing of the experiments showed, however, a variable match between observed and calculated assemblages, ranging from satisfactory to rather poor. Finally, observed and calculated mineral compositions showed a very poor match.Overall there is good agreement between the experiments and the natural observations, but theoretical calculations are still hampered by the complex nature of the starting materials.