Rb-Sr Geochronology of the Region Between The Antarctic Peninsula and The Transantarctic Mountains: Haag Nunataks and Mesozoic Granitoids
- Garry D. Mckenzie
Published Online: 21 MAR 2013
Copyright 1987 by the American Geophysical Union.
Gondwana Six: Structure, Tectonics, and Geophysics
How to Cite
Millar, I. L. and Pankhurst, R. J. (1987) Rb-Sr Geochronology of the Region Between The Antarctic Peninsula and The Transantarctic Mountains: Haag Nunataks and Mesozoic Granitoids, in Gondwana Six: Structure, Tectonics, and Geophysics (ed G. D. Mckenzie), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM040p0151
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1987
Print ISBN: 9780875900643
Online ISBN: 9781118664483
Seventy-two new Rb-Sr whole-rock analyses are reported for Haag Nunataks, Mount Woollard, the Whitmore Mountains, the Pirrit and Nash hills, and Pagano Nunatak. For Haag Nunataks, three isochrons for gneisses and later aplogranite and microgranite sheets establish the age of crustal formation as 1000–1100 Ma. No other basement rocks of this age are known from the Antarctic Peninsula or Ellsworth Land. Results from the migmatite-pegmatite complex at Mount Woollard are inconclusive but do not suggest that this represents Precambrian crystalline basement. Provisional results for the Whitmore Mountains granites are compatible with crystallization of all components within error of a 182±5 Ma isochron for fine-grained microgranite, but variation in initial 87Sr/86Sr from 0.707 for porphyritic granites to 0.722 for the microgranite rule out simple crystal fractionation models which require a common parental magma. The granites of the Ellsworth-Thiel mountains ridge are well dated as Middle Jurassic by the new data: Pirrit Hills 173±3 Ma, Nash Hills 175±8 Ma, and Pagano Nunatak 175±8 Ma. Initial 87Sr/86Sr ratios of 0.707, 0.712, and 0.716, respectively, confirm that these are intracratonic S-type granites with a large crustal component involved in magma generation. The dolerite of Lewis Nunatak is shown by its Rb, Sr, and 87Sr/86Sr composition to be a member of the Jurassic Ferrar Supergroup.