Syn-orogenic extension is observed in numerous convergent orogens worldwide. A number of geodynamic models have been proposed to explain this phenomenon. However, no single model can presently explain all observed tectonic, geomorphic and geologic features. One quantifiable constraint for any geodynamic model is the regional pattern and history of erosional and tectonic denudation as determined from low-temperature thermochronology. For example, if extension is attributable to wedge underplating, then horizontal material flux across the orogen should be close to zero. This leads to a spatial pattern of ages from different low temperature thermochronometers closely reflecting independently determined surface exhumation rates. Alternatively, if extension is attributable to another cause (e.g. slab rollback, orogenic collapse, slab breakoff) where frontal accretion dominates, this will lead to significant horizontal material flux within the wedge. This results in an offset of reset thermochronometers with respect to highest erosion rates in the direction of convergence. To investigate this problem, we are undertaking a detailed regional low-temperature thermochronologic study in the northern Apennines of Italy - a classic example of an active orogenic wedge undergoing syn-convergent extension. Substantial pre-existing fission-track data are augmented by new apatite (U-Th)/He cooling ages from a total of over 300 samples across the orogen. Determination of current surface exhumation rates using tectonic geomorphologic methods are being carried out in conjunction with this study. Preliminary results provide new information on the timing, rates, and spatial variations of cooling (and by proxy denudation) that would not have been possible by applying each thermochronometer in isolation. A general trend of increasing total cooling and the age of onset of accelerated cooling is observed from the prowedge (ca. 2-4 Ma) towards the core and retrowedge side (ca. 8-12 Ma) of the range. Very young cooling ages (1-3 Ma) from the Alpi Apuane core complex disrupt this pattern and indicate that late Cenozoic detachment faulting contributed significantly to extension within the northern Apennine orogenic wedge. New data currently being obtained will enable a more detailed analysis of the spatial distribution of cooling ages and provide vital new constraints for the development of geodynamic models to explain the presence of syn-orogenic extension with convergent orogens.

A regional synthesis of low-temperature thermochronologic results from the Northern Apennines, Italy: a key to understanding syn-convergent extension and erosion in an orogenic wedge

ZATTIN, MASSIMILIANO;
2004

Abstract

Syn-orogenic extension is observed in numerous convergent orogens worldwide. A number of geodynamic models have been proposed to explain this phenomenon. However, no single model can presently explain all observed tectonic, geomorphic and geologic features. One quantifiable constraint for any geodynamic model is the regional pattern and history of erosional and tectonic denudation as determined from low-temperature thermochronology. For example, if extension is attributable to wedge underplating, then horizontal material flux across the orogen should be close to zero. This leads to a spatial pattern of ages from different low temperature thermochronometers closely reflecting independently determined surface exhumation rates. Alternatively, if extension is attributable to another cause (e.g. slab rollback, orogenic collapse, slab breakoff) where frontal accretion dominates, this will lead to significant horizontal material flux within the wedge. This results in an offset of reset thermochronometers with respect to highest erosion rates in the direction of convergence. To investigate this problem, we are undertaking a detailed regional low-temperature thermochronologic study in the northern Apennines of Italy - a classic example of an active orogenic wedge undergoing syn-convergent extension. Substantial pre-existing fission-track data are augmented by new apatite (U-Th)/He cooling ages from a total of over 300 samples across the orogen. Determination of current surface exhumation rates using tectonic geomorphologic methods are being carried out in conjunction with this study. Preliminary results provide new information on the timing, rates, and spatial variations of cooling (and by proxy denudation) that would not have been possible by applying each thermochronometer in isolation. A general trend of increasing total cooling and the age of onset of accelerated cooling is observed from the prowedge (ca. 2-4 Ma) towards the core and retrowedge side (ca. 8-12 Ma) of the range. Very young cooling ages (1-3 Ma) from the Alpi Apuane core complex disrupt this pattern and indicate that late Cenozoic detachment faulting contributed significantly to extension within the northern Apennine orogenic wedge. New data currently being obtained will enable a more detailed analysis of the spatial distribution of cooling ages and provide vital new constraints for the development of geodynamic models to explain the presence of syn-orogenic extension with convergent orogens.
2004
Abstracts
Thomson S.N.; Zattin M.; Brandon M.T.; Reiners P.W.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/15206
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