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Geological Society, London, Special Publications; 2008; v. 308; p. 69-90;
DOI: 10.1144/SP308.3
© 2008 Geological Society of London

Articles

Early Palaeozoic orogenic collapse and voluminous late-tectonic magmatism in Dronning Maud Land and Mozambique: insights into the partially delaminated orogenic root of the East African–Antarctic Orogen?

Joachim Jacobs1, Bernard Bingen2, Robert J. Thomas3, Wilfried Bauer3, Michael T. D. Wingate4 & Paulino Feitio5

1 Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway (e-mail: joachim.jacobs{at}geo.uib.no)
2 Geological Survey of Norway, 7491 Trondheim, Norway
3 British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
4 Geological Survey of Western Australia, 100 Plain Street, East Perth, W.A. 6004, Australia
5 Direcão Nacional Geologia, Maputo, Mozambique

The late tectonic history of the southern part of the Late Neoproterozoic–Early Palaeozoic East African–Antarctic Orogen (EAAO) is characterized by lateral extrusion, extensional collapse and large volumes of high-temperature A2-type granitoids. This late-tectonic igneous province covers an area more than 15 000 km2 of the EAAO in Dronning Maud Land (East Antarctica) and its northerly continuation as the Nampula Complex of NE Mozambique. The magmatic province is bounded in the north by the Lurio Belt. New secondary ionization mass spectrometry (SIMS) U–Pb analyses of zircons from two major late-tectonic granitoid intrusions from Dronning Maud Land indicate crystallization ages of 501±7 and 499±4 Ma, whereas a major extensional shear zone was dated at 507±9 Ma. New SIMS zircon U–Pb analyses of late-tectonic granitoid sheets and plutons from the Nampula Province indicate ages of 512±4, 508±4, 508±2 and 507±3 Ma. Consequently, the late-tectonic magmatism can be bracketed between c. 530 and 485 Ma. It started with small gabbro bodies emplaced at c. 530–520 Ma, culminated with the intrusion of major granite–charnockite plutons at c. 510–500 Ma and terminated with the introduction of small volumes of sheet-like granite at c. 485 Ma. The new dates demonstrate that extensional shearing and granitoid intrusion are synchronous, and that orogenic collapse and the magmatism are related. We ascribe the distribution, structural style, geochemical composition and age of the late magmatic province to a process of partial delamination of the orogenic root in the southern third of the EAAO. It remains to be tested whether there is a relationship between orogenic collapse–granitoid magmatism and south-directed escape tectonics in the southernmost EAAO.





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K. Shiraishi, D. J. Dunkley, T. Hokada, C. M. Fanning, H. Kagami, and T. Hamamoto
Geochronological constraints on the Late Proterozoic to Cambrian crustal evolution of eastern Dronning Maud Land, East Antarctica: a synthesis of SHRIMP U-Pb age and Nd model age data
Geological Society, London, Special Publications, 2008; 308: 21 - 67.
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