Exhumation as fast as subduction?
Exhumation as fast as subduction?
Geology (Boulder) (January 2001) 29 (1): 3-6
- absolute age
- Alps
- buoyancy
- Cenozoic
- Cottian Alps
- dates
- Dora Maira Massif
- Europe
- exhumation
- faults
- high pressure
- in situ
- inclusions
- ion probe data
- Italy
- marbles
- mass spectra
- metamorphic rocks
- metamorphism
- nesosilicates
- normal faults
- Oligocene
- orthosilicates
- P-T conditions
- P-T-t paths
- Paleogene
- Piedmont Alps
- Piemonte Italy
- pressure
- rates
- SHRIMP data
- silicates
- Southern Europe
- spectra
- subduction
- Tertiary
- titanite
- titanite group
- U/Th/Pb
- ultrametamorphism
- Western Alps
- Western Europe
We produced a pressure-temperature-time path in order to determine the exhumation rate of the deepest subducted Alpine rocks. In situ dating of peak-metamorphic titanite in an eclogite facies calc-silicate rock indicates that subduction to pressures of approximately 3.5 GPa was reached at 35.1+ or -0.9 Ma. Titanite formed during two decompression stages, at 1+ or -0.15 GPa and approximately 0.4-0.5 GPa, and yielded ages of 32.9+ or -0.9 Ma and 31.8+ or -0.5 Ma, respectively. Combining the age data and making assumptions about the conversion of pressure to depth yield mean exhumation rates of 3.4 cm/yr and 1.6 cm/yr. These rates imply that exhumation acted at plate tectonic speeds similar to subduction, and was significantly faster than erosion. We suggest that fast exhumation is driven by a combination of tectonic processes involving buoyancy and normal faulting.
