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Compression-to-extension record in the late Pliocene-Pleistocene Upper Valdarno Basin (Northern Apennines, Italy); structural and thermochronological constraints

Marco Bonini, Giovanna Moratti, Federico Sani and Maria Laura Balestrieri
Compression-to-extension record in the late Pliocene-Pleistocene Upper Valdarno Basin (Northern Apennines, Italy); structural and thermochronological constraints
Italian Journal of Geosciences (February 2013) 132 (1): 54-80

Abstract

We use new structural and apatite fission-track data together with apatite fission-track and (U-Th)/He data from literature to examine the tectonic evolution of the continental Upper Valdarno Basin, in the hinterland sector of the Northern Apennines fold-and-thrust belt. This basin is located in-between two structural ridges, the Chianti Mountains to the southwest and the Pratomagno to the northeast. In our interpretation, the Upper Valdarno Basin developed at ca. 3.4-3.3 Ma as pop-down synformal-shaped depression bounded and controlled by oppositely-verging thrust-related structures, namely the thrust system lifting the Chianti Mountains and the southwest-facing backfolds at the base of the Pratomagno. This evolution is compatible with the accelerated exhumation rates at 4-5 Ma documented through apatite fission-track data along both the Pratomagno and Chianti ridges. Shortening suffered by basin deposits is clearly manifested by the outcrop-scale reverse faults and thrust-related folds affecting the Late Pliocene sediments (Castelnuovo dei Sabbioni Synthem), which are well exposed in the Santa Barbara mine. These strongly folded deposits are overlain unconformable by Early Pleistocene sediments (Montevarchi Synthem), which display evidence for syn-depositional normal faulting. This suggests that the Upper Valdarno Basin experienced a phase of normal faulting that started at the base of Pleistocene (ca. 2.6-2.5 Ma) and likely produced the large southwest-dipping "Trappola Fault", which affects the southwestern margin of the Pratomagno displacing the earlier backthrusts and backfolds. Basin evolution can be thus basically framed into a two-phase history, with extensional tectonics superposed onto compressional structures that were deactivated by ca. 2.7 Ma. Being the Chianti Mountains part of the 250 km-long regional line of thrusts and thrust-related folds (the so-called "Tuscan Nappe front"), the results of this study may also involve regional implications, as they would also hint for the tectonic history of other sectors and basins settled along-strike this regional element.


ISSN: 2038-1719
EISSN: 2038-1727
Coden: BOGIAT
Serial Title: Italian Journal of Geosciences
Serial Volume: 132
Serial Issue: 1
Title: Compression-to-extension record in the late Pliocene-Pleistocene Upper Valdarno Basin (Northern Apennines, Italy); structural and thermochronological constraints
Affiliation: Istituto di Geoscienze e Georisorse, Florence, Italy
Pages: 54-80
Published: 201302
Text Language: English
Publisher: Societa Geologica Italiana, Rome, Italy
References: 112
Accession Number: 2013-033990
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N42°19'60" - N44°19'60", E09°40'00" - E12°25'00"
Secondary Affiliation: Universita degli Studi di Firenze, ITA, Italy
Country of Publication: Italy
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Societa Geologica Italiana. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201321
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