Age and degree of metamorphism and time of nappe emplacement along the southern margin of the Damara Orogen/Namibia (SW-Africa) |
| |
| Authors: | Dr H Ahrendt Dr J C Hunziker Prof Dr K Weber |
| |
| Institution: | 1. Geol.-Pal?ont. Institut, Abt. Tektonik, University of G?ttingen, Goldschmidtstr. 3, D-3400, G?ttingen
2. Abt. f. Isotopen-Geologie, University of Bern, Erlachstr. 9, CH-3012, Bern
|
| |
| Abstract: | Along the southern margin of the Damara orogen age and degree of metamorphism were determined by means of K/Ar dating and illite crystallinity. The investigations include the following units: - The southwestern-most part of the east-west striking branch of the Damara orogen.
- The nappes of the Naukluft Mountains.
- The Nama-Group from north of the Naukluft Mountains to the Fish River in the south (including the western part of the Dwyka-Formation).
The metamorphism of the Naukluft nappes as well as the underlying Nama beds corresponds to the higher part of the anchi-zone and lower epi-zone. Between the Naukluft nappes and the folded Nama rocks adjoining the southeastern front of the nappes there is an obvious step from higher down to lower metamorphism. Further to the southeast the metamorphism in the Nama beds decreases continuously down to diagenesis. K/Ar age determinations were carried out on the three units mentioned above and also on the basement underlying the Nama sequence. Muscovites of this basement gave an age of about 1160 m. y. Determinations on white micas of the southern Damara belt, the Naukluft Mountains and the northern Nama basin define two isochrons with ages of 495 and 530 m. y The age of 530 m. y. represents the peak of metamorphism and the age of syncrystalline deformation. The age of 495 m. y. can be interpreted as a cooling age of the higher metamorphic rocks or as a dating of rejuvenation caused by a second post-crystalline deformation in parts of the Naukluft and Damara rocks. This age of 495 m. y. was also found in the mylonite of the main thrust plane of the Naukluft nappes and it represents the time of emplacement of the Naukluft nappes. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
