Determining P–T paths from garnet zoning using a brute-force computational method

Abstract

Reconstructing metamorphic pressure–temperature (P–T) paths through petrographic textures, mineral assemblages, and compositions is fundamental to the understanding of orogenesis. We present a new method to derive the P–T path of a rock from mineral zoning. Using Perple_X (Connolly in Earth Planet Sci Lett 236(1–2):524–541, 2005) and a Matlab script, we forward model garnet zoning, parageneses, and mineral modes for an arbitrary set of possible P–T paths, and then compare the calculated results to mineral modes, textures, and zoning preserved in rocks. The best-fit P–T path is determined by comparing the calculated zoning to the measured zoning using the sum of squares. The results indicate that combining Mg#, Ca, and Mn zoning in garnet with mineral modes can yield precise constraints on the P–T path of a rock.