Age and strontium‐isotope geochemistry of differentiated rocks from the newer Volcanics, MT Macedon Area, Victoria, Australia
作者:
E. J. Dasch,
D. J. Millar,
期刊:
Journal of the Geological Society of Australia
(Taylor Available online 1977)
卷期:
Volume 24,
issue 3-4
页码: 195-201
ISSN:0016-7614
年代: 1977
DOI:10.1080/00167617708728980
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
The Newer Volcanics Province of Victoria and South Australia consists of a major region of mainly alkaline basalts within which are two restricted areas containing strongly differentiated flow‐rocks. Typical alkalic basalts from this widespread province have K‐Ar ages from 4.5 to 0.5 m.y. and initial87Sr/86Sr ratios from 0.7038 to 0.7045. Contrastingly, in the Macedon area of differentiated lavas, flow compositions range from limburgite to soda trachyte, with K‐Ar ages from 6.8 to 4.6 m.y. and initial87Sr/86Sr ratios from 0.7052 to 0.7127. These differentiated rocks therefore are older, and some of them may have been contaminated by reaction with more radiogenic basement rocks during differentiation. Alternatively, the variation in initial Sr‐isotope composition may have resulted from varying isotopic composition of partial melts from the immediate source rocks. The most felsic of the differentiated rocks, soda trachyte, is extremely enriched with Rb relative to Sr; one of the three restricted outcrops of this rock (Camel's Hump) yields a total‐rock Rb‐Sr isochron age of 6.3 ± 0.6 m.y. with an initial87Sr/86Sr ratio of 0.7127. K‐Ar sanidine ages reported for the three outcrops of trachyte are identical to each other and to the Rb‐Sr isochron result.
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