New Zealand Journal of Geology and Geophysics abstracts
Uplift and exhumation of Alpine Schist, Southern Alps, New Zealand:
thermobarometric constraints
RODNEY H. GRAPES
Research School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
Abstract Thermobarometric estimates of early (D1) and late
(D2) metamorphic recrystallisation of Alpine Schist, Southern Alps of New
Zealand, define three polychronous piezothermic arrays: (1) 4.3-7.5 kbar and
260-370deg.C for chlorite and biotite-albite zone metagreywacke-semischist; (2)
5.2-9.2 kbar and 415-620deg.C for garnet and oligoclase zone schist, and (3)
5.4-6.6 kbar and 490-540deg.C for K-feldspar zone schist near the Alpine Fault.
The metamorphic arrays are used to develop a simple one-dimensional model to
explain metamorphism and uplift of the Alpine Schist in terms of a P-T-t(time)
loop. Evidence from retrograde albite (together with phengitic mica and
K-feldspar) in oligoclase zone schist implies an early (possibly Mesozoic)
schist uplift of 7-8 km corresponding to a temperature and pressure decrease of
c. 100deg.C and 2.0-2.3 kbar. Thermobarometric data from K-feldspar zone schist
suggests a further, possibly Late Cretaceous, uplift of 3-6 km giving a total
Mesozoic uplift of the Alpine Schist of between 10 and 14 km. The mylonitic
nature of the K-feldspar zone schists suggests that they may have
recrystallised along a mid-crustal decollement zone that was associated with
shear heating during late Cenozoic uplift amounting to 19-25 km along the
Alpine Fault. Late Cenozoic uplift of the schist was accompanied by tectonic
thinning, especially with respect to garnet and oligoclase zone schists, and
may be a function of the high rate of uplift in the central part of the Alps.
Keywords Alpine Schist; mineral thermobarometry; retrograde
plagioclase; uplift and exhumation; P-T-t(time) loop
New Zealand Journal of Geology and Geophysics, 1995, Vol. 38: 525-533
0028-8306/95/3804-0525 $2.50/0 (c) The Royal Society of New Zealand
1995
PDF file of entire paper: medium quality (1519K); (scanned from paper original: notes about this process)
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