Peak metamorphic temperature and thermal history of the Southern Alps (New Zealand).
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| Title: | Peak metamorphic temperature and thermal history of the Southern Alps (New Zealand). |
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| Authors: | Beyssac, O.1 Olivier.Beyssac@upmc.fr, Cox, S.C.2, Vry, J.3, Herman, F.4 |
| Source: | Tectonophysics. Apr2016, Vol. 676, p229-249. 21p. |
| Subjects: | Metamorphism (Geology), Thermochronometry, Cenozoic Era, Geologic faults |
| Geographic Terms: | Southern Alps/Kā Tiritiri o te Moana (N.Z.) |
| Abstract: | The Southern Alps orogen of New Zealand results from late Cenozoic convergence between the Indo-Australian and Pacific plates and is one of the most active mountain belts in the world. Metamorphic rocks carrying a polymetamorphic legacy, ranging from low-greenschist to high-grade amphibolites, are exhumed in the hanging wall of the Alpine Fault. On a regional scale, the metamorphic grade has previously been described in terms of metamorphic zones and mineral isograds; application of quantitative petrology being severely limited owing to unfavorable quartzofeldspathic lithologies. This study quantifies peak metamorphic temperatures (T) in a 300 × 20 km area, based on samples forming 13 transects along-strike from Haast in the south to Hokitika in the north, using thermometry based on Raman spectroscopy of carbonaceous material (RSCM). Peak metamorphic T decreases across each transect from ≥ 640 °C locally in the direct vicinity of the Alpine Fault to less than 330 °C at the drainage divide 15–20 km southeast of the fault. Thermal field gradients exhibit a degree of similarity from the southernmost to the northernmost transects, are greater in low-grade semischist than high-grade schist, are affected by folding or discontinuous juxtaposition of metamorphic zones, and contain limited information on crustal-scale geothermal gradients. Temperatures derived by RSCM thermometry are slightly (≤ 50 °C) higher than those derived by traditional quantitative petrology using garnet–biotite thermometry and THERMOCALC modeling. The age of RSCM T appears to be mostly pre-Cenozoic over most of the area except in central Southern Alps (Franz Josef–Fox area), where the amphibolite facies schists have T of likely Cenozoic age. The RSCM T data place some constraints on the mode of exhumation along the Alpine Fault and have implications for models of Southern Alps tectonics. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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