Application of Landsat-S TM imagery to mapping of the Giles Complex and associated granulites, Tomkinson Ranges, western Musgrave Block, central Australia

Application of Landsat-5 Thematic Mapper multispectral scanner data to the detailed mapping of the Tomkinson Ranges-Blackstone-Jameson region, western Musgrave Block, provides a test for spectral-lithological correlations in metamorphic-igneous terranes under the arid conditions of central Australia.  The terrane consists of ~1.3-1.5 Ga felsic/intermediate granulites metamorphosed at ~1.2 Ga and intruded by layered ~1.08 Ga mafic-ultramafic bodies of the Giles Complex and near-contemporaneous granites. Significant correlations are observed between Landsat-5 TM spectra, the reflectance patterns of iron oxide and clay-carbonate-dominated weathering surfaces and primary rock types. The weathering surfaces of gabbroic rocks are dominated by clay signatures, and those of felsic granulites, by mixed clay-iron oxide signatures. Iron oxides are well expressed by band ratio 5/4, log residual of bands 5 and 7, inverted log residual of band 1, and the iron oxide end member of pixel-unmixed images. Clay and/or carbonate are identified by high band ratio 5/7 partly masked by dry vegetation, high reflectance in the visible bands, high inverted log residuals of band 7, and the clay end member of pixel-unmixed images, and are effectively distinguished from green vegetation by the second principal component of (pc2[4/3, 5/7]).  Discrimination between carbonate and clay in the visible to infrared range is difficult, but calcrete banks along creeks are characterised by higher reflectance than clay. Quartz in weathered felsic rocks is commonly coated by clay and iron oxide, but abraded quartz in alluvial deposits and dunes shows high reflectance in combined bands [1+3+5+7]. As shown by field evidence, the remotel y sensed spectra allow discriminations between several lithologic types, including peridotite (commonly covered by calcrete and magnesite weathering crusts), orthopyroxenite (iron oxide-rich weathering), clinopyroxenite (weaker iron oxide signature than orthopyroxene), gabbro (clay [carbonate ]-dominated weathering), ferrogabbro (very strong iron oxide-rich weathering signature), anorthosite (strong clay/carbonate signature of weathering crusts), mafic granulites (iron oxide and silica-rich crusts), felsic granulites and granites (clay, iron oxide and silica-bearing weathering crusts), laterite (iron oxide-rich), calcrete (high reflectance, common along creeks), silcrete (very high reflectance), oxidised mafic source-derived alluvium (iron oxide-dominated), felsic source-derived alluvium (quartz and clay-dominated), clay pans and silty, in places ferruginous, dry lake (playa) deposits. The composition of small isolated bedrock outcrops is identified by the spectral signatures of derived detritus. Geologically useful discriminations include (1) separation of thin sills of anorthosite from host felsic granulites; (2) distinction between gabbro and derived mafic granulites (meta-gabbro); (3) distinction between ferrogabbro and gabbro; (4) separation between lateritic deposits and weathered gabbro. Pending field spectrometric measurements, these criteria can be applied in further mapping of the Musgrave Block and other metamorphic and igneous terranes in central Australia.

Tags: Earth Sciences, GA Publication, Journal, Published_External, SA, WA
Organization: Geoscience Australia Data