Metamorphic Studies in Adula. The Central Alpine Adula Nappe is the largest of the Penninic basement nappes, and was subducted to between 60 and 80km depths in a south-directed subduction zone during the continental collision of Europe (Adula) and Africa in the Tertiary period. High pressures during subduction resulted in a regional eclogite facies metamorphism. Subsequent high-temperature metamorphism during decompression destroyed most of the high-pressure assemblages which were preserved mostly as relicts in mafic boudins and rare pelitic outcrops. High-pressure metabasic rocks show a regional variation in mineral assemblages consistent with increasing metamorphic pressures and temperatures from north to south. In the north of Adula high-pressure amphibolites preserve the assemblage garnet-barroisite/or glaucophane-epidote-quartz-rutile±clinozoisite±phengite±paragonite± carbonate±omphacite. The incidence of omphacite increases in these rocks from north to south and some high-pressure amphibolites show transitional characteristic towards eclogites. In central parts of Adula metabasic rocks preserve the eclogite facies assemblage garnet-omphacite-rutile±kyanite±amphibole±phengite±paragonite±carbonate ±clinozoisite/zoisite±quartz. The incidence of kyanite in eclogites increases from north to south while micas and amphiboles become less common. A sequence of four main phases of deformation affected all investigated parts of central and northern Adula but only the first two phases were associated with eclogite facies metamorphism. The first (Sorreda) phase of deformation was associated with the subduction of Adula and the prograde route into eclogite facies. The second (Zapport) phase of large scale isoclinal folding and development of the main foliation began under eclogite facies conditions and continued during decompression.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598248 |
| Date | January 2001 |
| Creators | Dale, J. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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