Using detrital garnet compositions to determine provenance: a new compositional database and procedure

Detrital garnet compositions can be used to help determine the provenance of sedimentary rocks. In this study a garnet compositional database consisting of more than 2500 wet chemical and electron microprobe analyses was compiled from the literature. For the garnets in the database the six principal garnet end-member compositions (pyrope, almandine, spessartine, uvarovite, grossular and andradite) were calculated. A multi-stage methodology was devised to match garnet compositions to source rocks, and a series of garnet provenance fields on ternary plots were identified. The method was tested using compositional data from detrital garnet studies in several areas where provenance has already been identified, with good results. The methodology was then used to assess the provenance of detrital garnets from Neogene sandstones of northern Sabah, Borneo for which provenance is unknown and in a region where there are few garnet analyses for comparison. Comparison of garnet compositions from possible sources on Palawan, Philippines and in Borneo combined with the ternary plots excludes some known garnet-bearing rocks as potential sources and suggests derivation of metamorphic and igneous garnets from Palawan during the Early Miocene.