The pre-Mesozoic geological evolution of Graham Land, Antarctica
The exposed rocks of Graham Land, northern Antarctic Peninsula are almost entirely Mesozoic or Cenozoic in age. The existence of a pre-Mesozoic basement, however, has long been advocated and is of particular importance when considering reconstructions of the Antarctic Peninsula within Gondwana. Deta...
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | unknown |
| Published: |
1990
|
| Subjects: | |
| Online Access: | https://oro.open.ac.uk/64589/ https://oro.open.ac.uk/64589/1/253302%20%281%29.pdf https://oro.open.ac.uk/64589/2/253302.pdf https://doi.org/10.21954/ou.ro.0000fc4d |
| Summary: | The exposed rocks of Graham Land, northern Antarctic Peninsula are almost entirely Mesozoic or Cenozoic in age. The existence of a pre-Mesozoic basement, however, has long been advocated and is of particular importance when considering reconstructions of the Antarctic Peninsula within Gondwana. Detailed field mapping combined with geochronological studies have identified for the first time the pre-Mesozoic basement of Graham Land. It comprises: 1. Leppard Glacier Granite Gneiss: Silurian calc-alkaline granite gneiss cut by basaltic amphibolite sheets. Isochron ages obtained from these rocks of 426±12 and 10±15 Ma are the oldest known from Graham Land. 2 . Target Hill Banded Gneiss: Banded orthogneiss and paragneiss interpreted as a metamorphosed succession of sedimentary and volcanic rocks. 3 . Bildad Peak Amphibolite: Strongly sheared amphibolites and minor metapelite. 4 . Scar Inlet Metaplutonic Rock: Carboniferous plutonic rock predominantly of granitic composition. Trace element geochemistry of these units suggests that subduction beneath Graham Land occurred not only during the Mesozoic and Cenozoic but also during some of the Palaeozoic. Two geochemically distinct groups of calc-alkaline granite gneiss are present. Group I granite gneiss has a geochemistry similar to Mesozoic granites of Graham Land whereas low concentrations of certain minor and trace elements distinguish group II granite gneiss. Amphibolites in the Target Hill Banded Gneiss and the Leppard Glacier Granite Gneiss are relatively primitive and have MORB-like trace element characteristics. This indicates the influence of extensional processes during the mid-Palaeozoic. During the Carboniferous, the mid-Palaeozoic lithologies underwent amphibolite facies metamorphism which resulted in anatexis and granite emplacement. The timing of this metamorphism is constrained by Sm-Nd and Rb-Sr geochronology. A garnet-whole-rock age of 321±8 Ma for garnet cores dates the onset of metamorphism. A mixed gamet-whole-rock isochron age of 311±8 Ma is ... |
|---|