『Abstract
We relate the high elevation of flat topography in the Eastern
Pyrenees to the resurrection of a mountain belt which prior to
〜12 Ma was a low-relief landscape, or peneplain, bevelling eroded
stumps of the Pyrenean compressional orogen. New apatite fission-track
and (U-Th)/He data together demonstrate the consistently young
age (<30 Ma) of mappable remnants of the peneplain irrespective
of their current elevations. An independent biochronology of micromammalian
assemblages collected from fissures in limestone pavements is
also presented and confirms the conclusion that all the relict
land surfaces have survived as islands of low erosion in this
high-energy mountain environment because of recent and perhaps
rapid post-deformation surface uplift. Imaging of lithospheric
structure beneath the Pyrenees based on geophysical modelling
suggests that topography in the Eastern Pyrenees is anomalously
elevated for crustal thicknesses of only 25-35 km, and that the
elevation is ascribable to thinning by thermal erosion of the
subcrustal lithosphere. uplift occurred after 12 Ma as a result
of lithospheric thinning, and was accompanied by volcanism and
crustal extension. it outpaced opportunities for denudation to
erode the uplifting peneplain entirely, even at its currently
observed maximum elevations of 2.4-2.9 km in the crest zone. Overall,
this study defines as example of nonequilibrium topography in
a region of past plate convergence where post-orogenic uplift
has been causing transient landscape response to thermally-driven
thinning of the lithosphere. It shows that compression and mountain
building do not always occur together: there can be compression
without mountain building and mountain building without compression.
Keywords: apatite fission-track; apatite helium dating; biochronology;
peneplain; topographic uplift; lithospheric thinning; Pyrenees』
1. Introduction
2. Study area: brief geology of the Pyrenees
3. Method
3.1. Biochronology of microfossils in surface karst fissure
fillings
3.2. Apatite thermochronology of basement rocks
4. Results
5. Discussion
5.1. Late Cenozoic palaeoelevation of the Pyrenean peneplain
5.2. Timing of differential peneplain uplift
5.3. Causes for the preservation of LRT in the present-day scenery
5.4. Alternatives to the raised peneplain theory?
6. Conclusion
Acknowledgements
Appendix A. Supplementary data
References