Quartz as indicator mineral in the Central Swiss Alps: the quartz recrystallization isograd in the rock series of the northern Aar massif |
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| Authors: | Hans Ulrich Bambauer Marco Herwegh Herbert Kroll |
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| Institution: | (1) Pmd*CRC, School of Earth Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia;(2) Present address: CSIRO Exploration and Mining, Australian Resources Research Centre, Bentley, WA, 6102, Australia;(3) Present address: Ballarat Goldfields Pty Ltd, 10 Woolshed Gully Drive, Ballarat, VIC, 3350, Australia |
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| Abstract: | Earlier observations on the deformation of rock-forming quartz during Alpine metamorphism that were made by Voll (1976) along
a traverse following the Reuss valley (Aar massif, Central Swiss Alps) are still relevant but can be explained in more modern
term. Voll found that a few kilometres south of the contact between the Aar massif and its sedimentary cover quartz has partly
undergone a combination of dynamic recrystallization and nucleation along grain boundaries and fractures at the expense of
the deformed parent grains. Further to the south, increasing grain growth of quartz under nearly static conditions is observed,
with polygonal grain shapes typical of annealed microfabrics. Comparable stages of recrystallization could be found in several
N–S traverses through the Aar massif so that “points of first occurrence” of newly formed quartz could be connected to define
a quartz recrystallization isograd. This isograd extents over 90 km through the northern Aar massif, following a course parallel
to the sanidine/microcline isograd but at a distance of 10–15 km further to the north. The evolution of the quartz microfabric
is discussed with respect to recent estimates of the T-t path of the Aar massif. |
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