HR: 17:15h
AN: T24A-06    [Abstracts]
TI: Regional multi-thermochronometer long-term erosional flux estimates - a key to understanding development, maturity, and syn-convergent extension of the northern Apennine orogenic wedge.
AU: * Thomson, S N
EM: stuart.thomson@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06511 United States
AU: Brandon, M T
EM: mark.brandon@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06511 United States
AU: Zattin, M
EM: zattin@geomin.unibo.it
AF: Universita di Bologna, Dipartamento di Scienza della Terra e Geologico-Ambientali, Bologna, 40127 Italy
AU: Reiners, P W
EM: peter.reiners@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06511 United States
AU: Isaacson, P
EM: peter.isaacson@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06511 United States
AB: The northern Apennine orogenic wedge is one of several convergent orogens that exhibit syn-convergent extension. A number of geodynamic models have been proposed to explain this phenomenon, including slab retreat, slab detachment, orogenic collapse, and wedge underplating. However, no single model currently explains well all observed tectonic, geomorphic and geologic features in such orogens, as well as being able to couple mantle dynamics with critical wedge mechanics. Several key observations such models need to satisfy can be resolved by application of regional scale multi-chronometer thermochronology. This includes the regional pattern and history of erosional and tectonic denudation within the orogen, and by inference, the long-term record of erosional mass flux. Our investigation has yielded 143 new surface apatite (U-Th)/He (AHe) ages, including three age-elevation transects, as well as 11 new apatite fission track ages (AFT) and 13 AHe ages from three boreholes. Our results complement an existing regional database of about 160 AFT ages. We have constructed a thermal model to convert the closure temperature of each age to a closure depth and erosion rate to account for isotherm advection, cooling rate, and a 3D correction for topographic isotherm perturbation. Age elevation relationships and borehole profiles combining both AFT and AHe data show that long-term erosion rates have remained relatively steady at 0.5 to 0.7 mm/yr between about 8Ma and present. These rates are similar to regionally integrated erosion rates of 0.69 mm/yr and 0.63 mm/yr determined from the surface AFT and AHe ages, respectively. On a local scale, reset surface AFT and AHe data show a general trend of detrital ages, becoming reset and then increasing age from the prowedge (ca. 2-4 Ma) towards the core and retrowedge side (ca. 8-12 Ma) of the range. This is also reflected in the calculated erosion rates from both AFT and AHe ages that increase from rates of 0.2 to 1.2 mm/yr toward the core of the range, decreasing to more steady rates of 0.4-0.6 mm/yr on the extending retro-side of the orogen. These rates match reasonably well with a regional sediment yield estimated erosion rate of 0.77 mm/yr. The long-term erosional flux from the 100km wide orogen ca. 65km²/Myr. This compares to an accretionary flux of a ca. 10km section at a GPS determined rate of 3 mm/yr of ca. 30km²/Myr, implying that either the orogen has yet to reach flux steady-state, convergence rates were greater in the past, or that the orogen has increased in size.
DE: 1140 Thermochronology
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 9335 Europe
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: Fall Meeting 2005