Metamorphic facies zonation in the Ronda peridotites: spectroscopic results from field and GER imaging spectrometer data

The Ronda peridotite massif and bordering marbles (Málaga province, southern Spain) are studied in Geophysical Environmental Research 63-channel Imaging Spectrometer data (GERIS). Reflectance spectra of weathered rock and soil samples form the basis for selecting endmembers for spectral unmixing of the GERIS data and mineral mapping by means of spectral angle mapping. Six spectral endmembers model the continuum reflectance of each pixel: three soil types (a peridotite soil, a limestone soil, and a spectrally quenched soil), green vegetation (and grass), senescent vegetation, and decayed vegetation. The spatial distribution of the soil endmembers shows that the spectrally quenched soil is restricted to an area near to the mylonitized contact zone between the marbles and the peridotites. Mineral mapping from GERIS data confirms the known metamorphic zonation of the Ronda peridotite body into a garnet-, spinel-, and a plagioclase-lherzolite facies related to the diapiric uprise of the ultramafics from the asthenosphere into the crust. A prograde series of minerals is mapped within the marbles grading from tremolite through diopside to fosterite near the peridotite contact. These mineral assemblages form typically along an isothermal decompression path related to contact metamorphism.