*2.1. Sample Material*

Six polished thin sections from metamorphic rocks from southern West-Greenland were coated with Carbon and investigated with SEM (ZEISS SIGMA 300VP; Cambridge, UK), see below. In the light of this study, no cross-checks were performed on the optical microscope. More details about the geological history of the samples were published previously [37,41]. Table 1 presents the analytical details for the investigated samples and Supplementary 1 gives sample and outcrop images as well as rock and mineral compositions as analysed with Mineralogic.


**Table 1.** Analytical conditions for Mineral mapping. Mapping step size: three samples were mapped several times at different step sizes, see Section 3 (Examples of Applications) for details.

Samples 508599 and 508607 represent a finely layered volcanoclastic sediment collected from the Bjørnesund Supracrustal Belt (BSB). Hand specimen of sample 508599 is near-black with a slatey cleavage. It consists of quartz, andesine (plagioclase), biotite, amphibole, apatite, and pyrite. The rocks in the BSB were isoclinally folded at amphibolite facies conditions. The sample was collected close to an isoclinal fold core, and biotite in the sample clearly defines the shape of the fold and the foliation. Sample 508607 was collected from the same volcanoclastic unit in the RSB. However, in this sample contains quartz, anorthite, pale amphibole (anthophyllite based on field observations), biotite, and large garnets with inclusions of quartz, apatite, ilmenite, and rutile were grown over the main foliation.

Samples 521106 and 521111 show the reaction products between an ultramafic rock in contact with anorthosite or leucogabbro and intruded by a tonalite sheet. The anorthosite, leucogabbro and ultramafic rocks are part of the Fiskenæsset complex. The intruding tonalitic sheet causes a desilification reaction resulting in the formation of amphibole (anthophyllite, cummingtonite, gedrite or pargasite), phlogopite, and one or more aluminium-rich phases (cordierite, spinel, sapphirine and corundum (ruby)). Reaction temperatures are estimated to ca. 600 ◦C, using iso-chemical P–T-sections [36], with a gradient from lower granulite facies conditions in the western part of the Fiskenæsset complex to upper amphibolite facies close to the Inland ice sheet and in the southern part of the complex. The reaction occurred during the main folding phase in the region. Sample 521106 and 521111 are collected from Aappaluttoq, south of the village of Fiskenæsset, and here ruby is the main aluminium-rich phase resulting from the reaction. The sample consists of pale amphibole (gedrite), biotite, corundum, sapphirine, spinel, cordierite, anorthosite, hornblende, epidote, magnesite. Note that the peak mineral assemblage (gedrite, hornblende, ± biotite, cordierite, sapphirine; ca. 630 ◦C; 7 kbar [38]) does not contain quartz.

Sample 510152 represents a leucogabbro from the Fiskenæsset complex (Figure 1). The sample was collected in the southern part of the complex, where the complex lies in contact with the BSB. It consists of the minerals anorthite, Mg-rich hornblende, chromite and minor rutile. The amphibole in the sample is a result of deformation and metamorphism at amphibolite facies conditions, where it replaces pyroxene.

Sample 519923 is an amphibolite collected from the BSB. The hand specimen is dark green and finely foliated with a slatey cleavage. The minerals in the sample are distributed homogeneously, apart from tiny small faults filled with gouge and secondary minerals. Reactivated shear zones in the area accumulated gold in slightly enhanced concentrations. The sample contains anorthite, hornblende and the minor phases quartz, zoisite, rutile, sphene, apatite and zircon.

#### *2.2. Whole Rock Geochemistry*

Whole-rock geochemistry was carried out on a sample to characterize the bulk composition of these rocks. The analyses were carried out by Activation Laboratories (Actlab), Ancaster, ON, Canada, using their Research Lithium Metaborate/Tetraborate Fusion—ICP/MS analytical package. Samples 519923 was investigated, see Table 2. Both samples are described in more detail above.
