PART IV: GEOLOGICAL HISTORY OF THE AREA
The geological history of this area is clearly complex, and more work is required to elucidate several aspects of it. However it ie reasonable to suggest that the earliest event, of which evidence ie recognisable in the field, was sedimentation, on an earlier basement (possibly now represented by charnockites), in pre—Scourian times (probably 2,600 - 3,000 million years ago). During this time, in addition to deposition of arenaceous and argillaceous sediments, there were probably also lava flows. These rocks were metamorphosed (in the granulite facies), deformed and intruded by a tholeiitic magma, which differentiated to give layering phenomena. The layers were cut by dykes of doleritic or basaltic composition. Folding and granulite facies metamorphism (probably on a local scale) followed. Next, these rocks were intruded by granite pegmatites, then there was retrograding in the amphibolite facies and local migmatisation. A long period of erosion followed with intrusion of further olivine dolerite dykes (probably in the Eocene) and recent glaciation.
| Probable age | Rock unit | Rock types | Deformation, metamorphism etc |
| Tertiary (?Eocene) | 7. Doleritic dykes | Olivine dolerites | |
| Unconformity | |||
| Late Laxfordian (c1705 MA) | 6. Granite Pegmatites & Migmatites | Veins of granite pegmatite; migmatites | NNE-SSW cross-folding; retrograding of preceding rock types & migmatisation |
| 5. Central Amphibolites | Hornblendites; garnet-hornblende-pyroxene-feldspar assemblages | ||
| ? Early Laxfordian, ?Inverian, ?Scourian | 4. Igneous Complex | Anorthosites; garnet-pyroxene-hornblende-feldspar assemblages | NW-SE folding; ?local granulite facies metamorphism |
| ?NE-SW folding; granulite facies metamorphism | |||
| Pre-Scourian (2600-3000 MA) | 3. Rodel Amphibolites | Hornblendites; plagioclase-amphibolites; garnet-amphibolite | |
| 2. Finsbay Hornblendic Gneisses and Quartzites | Hornblende-quartz-biotite assemblages | ||
| 1. Rodel Metasediments | Quartzites; pelites; psammites; limestones; calc-silicate rocks; intermediate charnockite | ||
| ? | ? | ? |
The Geological Succession