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| Titel |
Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hsüehshan range, Taiwan |
| VerfasserIn |
S. Kidder, J.-P. Avouac, Y.-C. Chan |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 4, no. 1 ; Nr. 4, no. 1 (2013-01-07), S.1-21 |
| Datensatznummer |
250001572
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| Publikation (Nr.) |
 copernicus.org/se-4-1-2013.pdf |
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| Zusammenfassung |
| The accuracy, reliability and best practises of Ti-in-quartz thermobarometry
(TitaniQ) in greenschist facies rocks have not been established. To
address these issues, we measured Ti concentrations in rutile-bearing samples
of moderately deformed, partially recrystallized quartzite and vein quartz
from the Hsüehshan range, Taiwan. The spread of Ti concentrations of
recrystallized grains in quartzite correlates with recrystallized grain
size. Recrystallized quartz (grain size ~100–200 μm) that
formed during early deformation within the biotite stability field shows a
marked increase in intermediate Ti-concentration grains (~1–10 ppm) relative to detrital porphyroclasts (Ti ~0.1–200 ppm).
Fine recrystallized quartz (~5% of the samples by
area, grain size ~10–20 μm) has a further restricted
Ti concentration peaking at 0.8–2 ppm. This trend suggests equilibration of
Ti in recrystallized quartz with a matrix phase during deformation and
cooling. Unlike previously documented examples, Ti concentration in the
quartzite is inversely correlated with blue cathodoluminescence. Deformation
was associated with a minimum grain boundary diffusivity of Ti on the order
of 10−22m2 s−1. Vein emplacement and quartzite recrystallization
are independently shown to have occurred at 250–350 °C and
300–410 °C, respectively, with lithostatic pressure of 3–4 kbar
(assuming a geothermal gradient of 25° km−1), and with hydrostatic
fluid pressure. Estimates of the accuracy of TitaniQ at these conditions
depend on whether lithostatic or fluid pressure is used in the TitaniQ
calibration. Using lithostatic pressure and these temperatures, the Thomas
et al. (2010) calibration yields Ti concentrations within error of
concentrations measured by SIMS. If fluid pressure is instead used,
predicted temperatures are ~30–40 °C too low.
TitaniQ has potential to yield accurate PT information for vein emplacement
and dynamic recrystallization of quartz at temperatures as low as
~250 °C, however clarification of the relevant
pressure term and further tests in rutile-present rocks are warranted. |
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