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Precambrian rocks of Tasmania, Part II- Mt. Mary area

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Spry, A (1957) Precambrian rocks of Tasmania, Part II- Mt. Mary area. Papers and Proceedings of the Royal Society of Tasmania, 91. pp. 95-114. ISSN 0080-4703

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Abstract

The Mt. Mary area (S. lat. 42° 12', long. 145°50') is underlain almost entirely by rocks of Pre-Cambrian age, the exception being a small downfaulted block of Crotty (?) Sandstone, (Silurian). The Pre-Cambrian rocks are divided into three main groups. The oldest is the Joyce Group which consists of mica-garnet schists, quartzites and amphibolites. This is overlain unconformably by quartz schists, massive quartzites and phyllites of the Mary Group. Above these are quartzites. mica schists, garnet-mica schists and amphibolites of the Franklin Group. Igneous rocks are recognized as premetamorphic amphibolites (Older Basic Igneous Group) and post-metamorphic dolerites (Younger Basic Igneous Group). The sediments are broadly folded into the Mary Anticline. Tight, recumbent drag folds are abundant and are shown by all formations. Cleavage or schistosity, generally parallel to the bedding, is well developed in phyllites and schists. A regular, regional lineation plunges fiatly to the west and is cut by a sporadic lineation almost at right angles. Faulting is very abundant and makes the interpretation of the structure very difficult. Three sets of faults trend (in order of importance) at 120°, 10° and 60°-80°. The major faults are high angle reverse faults. There is some degree of structural control of the physiography. All rivers are superimposed and two streams show maturity in their central reaches due to resistant quartzites forming local base levels. There is evidence of rejuvenation of some rivers. Rocks of the Joyce and Franklin Groups are metamorphosed to garnet grade while the Mary Group is less altered. Selective metamorphism is demonstrated and is probably due to the favourable chemical and physical nature of the Joyce and Franklin Groups.

Item Type: Article
Keywords: Royal Society of Tasmania, RST, Van Diemens Land, natural history, science, ecology, taxonomy, botany, zoology, geology, geography, papers & proceedings, Australia, UTAS Library
Journal or Publication Title: Papers and Proceedings of the Royal Society of Tasmania
Page Range: pp. 95-114
ISSN: 0080-4703
Additional Information: Copyright Royal Society of Tasmania
Date Deposited: 24 May 2012 08:06
Last Modified: 18 Nov 2014 04:35
URI: http://eprints.utas.edu.au/id/eprint/13992
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