Age and Ancestry of Metamorphic Rocks of the Daniels Range, Usarp Mountains, Antarctica
- Edmund Stump
Published Online: 16 MAR 2013
Copyright 1986 by the American Geophysical Union.
Geological Investigations in Northern Victoria Land
How to Cite
Adams, C. J. (1986) Age and Ancestry of Metamorphic Rocks of the Daniels Range, Usarp Mountains, Antarctica, in Geological Investigations in Northern Victoria Land (ed E. Stump), American Geophysical Union, Washington, D. C.. doi: 10.1002/9781118664957.ch2
- Published Online: 16 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875901978
Online ISBN: 9781118664957
- Geology—Antarctic regions—Victoria Land
Rubidium-strontium (Rb-Sr) whole-rock isochron and uranium-lead monazite ages are reported for metamorphic rocks, the Rennick Schists, and Wilson Gneisses (informal subdivisions of the Wilson Group) in the northern Daniels Range, Usarp Mountains, northern Victoria Land, East Antarctica. Rennick Schists, of both psammitic and pelitic type, yield Rb-Sr whole-rock isochron ages of 534±24 and 531±17 Ma, respectively (Cambrian), suggesting that early metamorphism predates Wilson Gneisses. The initial ratios are 0.7187±0.0009 and 0.7243±0.0009, respectively. Model ages based on averaged isochron data suggest that in sedimentary age, the Rennick Schists cannot be older than 1150 Ma, i.e., late Precambrian. Wilson Gneisses yield a Rb-Sr age of 490±30 Ma and U-Pb ages of 484–488 Ma, which indicate a Cambro-Ordovician age for these orthogneisses. They may be regarded as an early phase of the Granite Harbour Intrusives, a major plutonic phase of the Ross (Cambro-Ordovician) Orogeny in northern Victoria Land. The initial Sr isotope ratio for the Wilson Gneisses, 0.7205±0.0016, is high and indicative of an S type granitoid in which the sedimentary precursor is similar to psammitic type Rennick Schist, which during the Ross Orogeny would have had a similar mean 87SR/86Sr ratio. If the younger Granite Harbour Intrusives are less than 500 m.y. old, the initial Sr isotope ratios of selected granitoids from the northern Daniels Range (two diorites, five granodiorites, two leucogranites) must fall in the range of 0.709–0.715, which is significantly lower than the ratio for the Wilson Gneisses. This demonstrates that Granite Harbour Intrusives cannot be regarded as an end product of the anatexis of Rennick Schists that produced Wilson Gneisses.