Thermochronologic evidence for orogen-parallel variability in wedge kinematics during extending convergent orogenesis of the northern Apennines, Italy

Stuart N. Thomson, Mark T. Brandon, Peter W. Reiners, Massimiliano Zattin, Peter J. Isaacson, Maria Laura Balestrieri

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Abstract

Analysis of 146 new apatite (U-Th)/He ages, six new apatite fission-track ages, and 165 previously published apatite fissiontrack (AFT) ages from the northern Apennine extending convergent orogen reveals a significant along-strike change in post-late Miocene wedge kinematics and exhumation history. East of ~11°30'E, age patterns and age-elevation relationships are diagnostic of ongoing frontal accretion and slab retreat consistent with a northeastward-migrating "orogenic wave." Enhanced erosion rates of ~1 mm/yr over a period of ~3-5 Ma are recorded on the contractional pro-side of the orogen and ~0.3 mm/yr on the extending retro-side. West of ~11°30'E, ongoing exhumation has been restricted to the range core since at least ca. 8 Ma at rates of ~0.4 mm/yr increasing to ~1 mm/yr in the Pliocene (ca. 3 Ma) accompanied by post-Pliocene tilting and associated faulting. This pattern can be attributed to either continued convergence (but a switch in the transfer of material into the wedge to a regime dominated by underplating or out-of-sequence shortening), or a slowdown or cessation of frontal accretion and slab retreat with enhanced Pliocene uplift and erosion triggered by a deeper seated process such as lithospheric delamination, complete slab detachment, or slab tear. These findings emphasize that no single model of wedge kinematics is likely appropriate to explain long-term northern Apennine orogenesis and synconvergent extension, but rather that different lithospheric geodynamic processes have acted at different times in different lateral segments of the orogen.

Original languageEnglish (US)
Pages (from-to)1160-1179
Number of pages20
JournalBulletin of the Geological Society of America
Volume122
Issue number7-8
DOIs
StatePublished - Jul 1 2010

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ASJC Scopus subject areas

  • Geology

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