The age and origin of the Eastern Grampians Newer Granites
| Autor: | J. Hutchinson, T. N. Harrison |
|---|---|
| Rok vydání: | 1987 |
| Předmět: | |
| Zdroj: | Scottish Journal of Geology. 23:269-282 |
| ISSN: | 2041-4951 0036-9276 |
| DOI: | 10.1144/sjg23030269 |
| Popis: | Synopsis Four new Rb-Sr whole rock ages and initial ratios are reported for the Monadhliath (419 ± 4.7 Ma), Glen Gairn Phase II (403.9 ± 6.1), Kincardine, Water of Feugh (416.2 ± 9.9) and Kincardine, porphyritic Main granite (416.4 ± 4.1). These ages are representative of members of two newly recognised groups of Newer Granite in the Eastern Grampians: one group, emplaced at c. 415 Ma, is associated with relatively abundant dioritic precursors, whereas the other group was emplaced at c. 408 Ma and is not associated with any mafic precursors. These two groups cannot be distinguished on the basis of their strontium initial ratios. The two episodes of granitic magmatism are thought to represent the transition between subduction and strike-slip faulting during the very last stages of the Caledonian orogeny. The later group of granites are found at the intersection of pre-Caledonian basement lineaments with post-subduction strike-slip faults, and the introduction of mantle material into the root zones of these faults may have initiated melting in the lower crust and granite generation. The dioritic and the granitic rocks of the early group are considered to be partial melts of relatively mafic lower crustal material. The later group of granites are akin to A-type granites in their proposed source material (depleted granulitic lower crust) and tectonic setting, and an analagous situation to the Eastern Grampians has been recognised from the Western Cordillera of the United States. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|