In active orogens spatial variations in exhumation rates are reflected by different cooling ages of single thermochronometers across the range, whereas temporal variations in exhumation rate are recorded in the age-elevation relationship (AER) of vertical transects. To a first order, slopes of the AER for each thermochronometer record the vertical velocity of samples relative to the relevant closure isotherm. Here we focus on the Northern Apennine chain, a tectonically active bimodal orogen characterized by paired contractional and extensional domains. We used fission-track and (U-Th)/He analysis on apatite to study vertical profiles sampled in the foredeep turbidite deposits of Oligocene-Miocene age at Mt. Cimone, Mt. Falterona and the Pratomagno ridge. The Mt. Falterona profile has been extended by using some samples from a nearby exploration well. The Pratomagno and Falterona profiles yield comparable exhumation rates, both showing an increase from values lower than 0.5 km/m.y. to values higher than 1 km/m.y. Maximum rates were reached at 3-4 Ma with subsequent exhumation apparently decreasing to rates lower than 1 km/m.y. The Cimone profile shows a significantly different exhumation history, with rates in the range of 0.3-0.4 km/m.y. at least until 3 Ma, followed by an apparent moderate increase in rates. These different exhumation histories can be explained in the light of the different structural setting of the sampled profiles. While the Pratomagno and Falterona profiles are located along the ridges of two of the Plio-Pleistocene intramontane basins that characterize the hinterland of the chain, the Cimone profile is close to the watershed and is not noticeably affected by extensional tectonics. Therefore, we propose that extensional tectonics was the likely cause of the pulse of the exhumation rates at 3-4 Ma detected in the Pratomagno and Falterona profiles. At present, a complete data set is available only for these three vertical transects, but we argue that an increase of exhumation rates is recorded in the AER from the ridges bordering all the intramontane basins and it is linked to the extensional tectonics of the basins themselves.
A multichronometer approach for unravelling the exhumation history of an active orogen: the example of the Northern Apennines (Italy) / Zattin M.; Brandon M.T.; Balestrieri M.L.; Reiners P.; Thomson S.N.. - ELETTRONICO. - (2004). (Intervento presentato al convegno 32nd International Geological Congress tenutosi a Firenze nel 20-28 Agosto 2004).
A multichronometer approach for unravelling the exhumation history of an active orogen: the example of the Northern Apennines (Italy)
ZATTIN, MASSIMILIANO;
2004
Abstract
In active orogens spatial variations in exhumation rates are reflected by different cooling ages of single thermochronometers across the range, whereas temporal variations in exhumation rate are recorded in the age-elevation relationship (AER) of vertical transects. To a first order, slopes of the AER for each thermochronometer record the vertical velocity of samples relative to the relevant closure isotherm. Here we focus on the Northern Apennine chain, a tectonically active bimodal orogen characterized by paired contractional and extensional domains. We used fission-track and (U-Th)/He analysis on apatite to study vertical profiles sampled in the foredeep turbidite deposits of Oligocene-Miocene age at Mt. Cimone, Mt. Falterona and the Pratomagno ridge. The Mt. Falterona profile has been extended by using some samples from a nearby exploration well. The Pratomagno and Falterona profiles yield comparable exhumation rates, both showing an increase from values lower than 0.5 km/m.y. to values higher than 1 km/m.y. Maximum rates were reached at 3-4 Ma with subsequent exhumation apparently decreasing to rates lower than 1 km/m.y. The Cimone profile shows a significantly different exhumation history, with rates in the range of 0.3-0.4 km/m.y. at least until 3 Ma, followed by an apparent moderate increase in rates. These different exhumation histories can be explained in the light of the different structural setting of the sampled profiles. While the Pratomagno and Falterona profiles are located along the ridges of two of the Plio-Pleistocene intramontane basins that characterize the hinterland of the chain, the Cimone profile is close to the watershed and is not noticeably affected by extensional tectonics. Therefore, we propose that extensional tectonics was the likely cause of the pulse of the exhumation rates at 3-4 Ma detected in the Pratomagno and Falterona profiles. At present, a complete data set is available only for these three vertical transects, but we argue that an increase of exhumation rates is recorded in the AER from the ridges bordering all the intramontane basins and it is linked to the extensional tectonics of the basins themselves.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
