University of Tasmania
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Structure and petrology of the Raglan Range

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posted on 2023-05-26, 05:53 authored by Gee, Dennis
Raglan Range consists dominantly of pelitic schists, quartzites, and ortho-amphibolites generally of garnet grade. This is the Franklin Group, and overlies Mary Group phyllites of chlorite grade. All are Precambrian. Precambrian structures show a regional and systematic departure from homoaxiality due to a rotation 'about an axis trending 326 degrees (true), and plunging 24 degrees This is the expression of Tabberabberan folding. Unrolling about this axis reveals a uniformly gently dipping alternation of schist and quartzite over most of the area. Two Precambrian deformations are recognisable, here termed SI and S2. Associated with SI is the regional metamorphism producing chlorite, biotite, a amandine , kyanite in a zonal arrangement. The biotite isograd is taken as the upper limit of the Mary Group. S2 is accompanied by retrograde metamorphism and large scale recumbent folding, during which metamorphic zones were inverted, and the Franklin Group was transported over the Mary Group, possibly in a south-west direction. The Governor River Phyllite, herein defined, is a wide zone of dispersed movement associated with S2. Albite of metasomatic origin crystallised in the interval between SI and S2. Quartzites show R-tectonite micro-fabric. The quartz fabric is homogeneous, irrespective of tectonic position, hut the mica fabric is unrollable. Lineation in quartzite is due to the intersection of SI surfaces with an older surface, probably bedding. Lineation in schist is the intersection of the SI surfaces and axial surfaces related to the S2 folds. Approximately coaxial relationships between SI, S2 and the Tabberabberan folding permits a construction of a tectonic profile of the Raglan Range by axial projection. Lamprophyre dykes, probably Tabberabberan in age intrude the schists.


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