 |
| Titel |
Towards continuous P-T paths? Multicalibration approach and application to subduction dynamics (Schistes Lustrés complex, France) |
| VerfasserIn |
Alexis Plunder, Philippe Agard, Benoît Dubacq, Christian Chopin |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050073
|
|
|
|
|
|
| Zusammenfassung |
| Our understanding of the dynamics of subduction zones chiefly depends on the precision of
metamorphic rock trajectories. Ideally, continuous P-T paths with a precision on the km-scale
or below would be needed to further constrain our knowledge of deformation, reequilibration
processes and element/fluid transfer along subduction zones. Thanks to improved
interconsistent thermodynamic databases, multiple thermodynamic softwares and analytical
tools, quantitative constraints on these metamorphic trajectories are indeed now accessible.
The question is, however: is this enough?... This contribution therefore attempts to (1)
critically evaluate the precision with which metamorphic P-T-t histories are retrieved today
and (2) discuss implications for processes taking place at the plates interface, in the
so-called subduction channel (Shreeve and Closs, 1986). We have compared and
combined P-T estimates using several independent approaches: from minerals assumed
to be in textural equilibrium (the classical approach), from electron microprobe
compositional maps (which significantly increases the number of analyses to choose
from), and from pseudosection modelling predictions. Multi-equilibrium calculations
were performed with Tweequ and Thermocalc, and pseudosections were built with
Perple_X and Theriak-Domino. These P-T estimates were in addition compared with
maximum temperatures deduced from the Raman spectroscopy of carbonaceous matter.
We have then applied these methods on a regional scale to study the metamorphic
evolution of the Liguro-Piemontese “Schistes Lustrés” paleo-accretionary complex
(SL; Haute Maurienne, W. Alps), whose good preservation should in principle
provide detailed insights into subduction dynamics. The different methods used here
yield the peak of pressure for the lower unit of the SL at the following conditions:
480°C-23kbar. They also allow us to constrain the retrograde path for both the
middle and lower SL units. The results show that P-T conditions can be determined
with a precision of ±0.5–1 kbar and ±20°C at best. The critical comparison of the
various methods also allows identifying which improvements could help refine,
in the near future, these thermobarometric estimates. In order to account for the
observed tectonic patterns, major lithological boundaries and the P-T and Tmax data
presented in this study, an interpretation of the tectonometamorphic evolution of
the SL complex is finally proposed. This evolution underlines the importance of
underplating processes and early structuration within the accretionary complex. |
|
|
|
|
|
|