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| Titel |
Along strike variations of high temperature (350-500°C) thermal histories along the northern Andean margin of South America |
| VerfasserIn |
Andre Navin Paul, Richard Spikings, Alexey Ulyanov |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149755
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| Publikation (Nr.) |
 EGU/EGU2017-14137.pdf |
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| Zusammenfassung |
| High temperature thermochronometers (apatite U-Pb and muscovite 40Ar/39Ar; >350°C) are
used to constrain the thermal history of the long lived (>450 Ma) Pacific margin of northern
South America from the Triassic to the late Cretaceous. We acquired single grain apatite
U-Pb and muscovite 40Ar/39Ar dates from Triassic monzogranites and migmatites located
along a trench-parallel traverse spanning the Andes of Ecuador and Colombia. The
relationship between apatite U-Pb dates and their individual grain sizes suggests that Pb
was lost by thermally activated, volume diffusion. Apatite U-Pb dates, grain size
information and Pb-in-apatite diffusion parameters were then used to recover t-T histories
using mathematical inversion (E.g. Cochrane et al., 2014). The best fit t-T solutions
corroborate 40Ar/39Ar muscovite dates. All t-T solutions yield rapid post-anatexis
cooling during the Triassic. However, a sudden change in t-T topology occurs in the
northern Cordillera Real of Ecuador. Apatite U-Pb and muscovite 40Ar/39Ar dates
from southern Ecuador span between 70 to 130 Ma and 70 to 75 Ma respectively,
whereas the same techniques yielded dates of 220 to 160 Ma and 165 to 140 Ma, from
northern Ecuador and Colombia. The corresponding t-T paths reveal a period of
re-heating into the apatite Pb partial retention zone during the Early Cretaceous in
southern Ecuador, which is not observed towards the north. This is consistent with
previous tectonic interpretations for the N. Andes (Spikings et al., 2015), and is
interpreted to be due to increased amounts of extension, subsidence and heat flow in S.
Ecuador. The concordance between the best fit t-T paths obtained from the apatite
U-Pb data, and the muscovite 40Ar/39Ar dates supports the diffusion parameters of
Harrison et al. (2009) for Ar-in-muscovite, that yield closure temperatures higher than
400°C. We conclude that Pb-in-apatite closure temperature is slightly higher then
Ar-in-muscovite, supporting the closure temperature estimate of Harrison et al. (2009). |
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