Faults linkage, damage rocks and hydrothermal fluid circulation: Tectonic interpretation of the Rapolano Terme travertines (southern Tuscany, Italy) in the context of Northern Apennines Neogene-Quaternary extension

Abstract

The tectonic history of Neogene-Quaternary extensional structures has been documented in the inner part of the Northern Apennines (Rapolano Terme area) from Quaternary travertines and faults relationships. In particular, structural studies, field mapping and tectono-stratigraphical considerations on the pre-Neogene, Pliocene and Quaternary units indicate two fault populations of different ages. The travertines, broadly exposed in the Rapolano Terme area, were related to hydrothermal fluid circulation and upwelling along the damage zones of Pleistocene normal faults. These structures were superimposed upon normal (mainly NNW-SSE and SW-NE oriented) and transtensional (mainly SW-NE oriented) faults, Early-Middle Pliocene in age, related to development of the Siena Basin. The age of such Pliocene normal and transtensional faults has been inferred on the basis of the relationships between tectonic elements and Pliocene deposits. In fact, Middle Pliocene marine sandy and gravelly sediments suture the faults. The Pleistocene normal faults (mainly SW-NE oriented) reactivated the oldest SW-NE transtensional faults, cut the NNW-SSE normal faults, and displaced Middle Pliocene marine deposits. Pleistocene-Holocene travertines and present-day thermal springs mainly occur at the intersection points between the Pleistocene SW-NE faults and the Pliocene NNW-SSE normal faults, or along the SW-NE Pleistocene normal faults. RIASSUNTOUn nuovo studio basato sull'analisi strutturale di faglie collegate con la tettonica distensiva noegenico-quaternaria, sulla realizzazione di un nuovo rilevamento geologico di dettaglio condotto nell'area di Rapolano Terme e sulla considerazione dei rapporti tettono-stratigrafici tra le faglie ed i depositi pliocenico-quaternari, ha permesso di individuare la presenza di una evoluzione articolata delle strutture collegate con la tettonica distensiva. In particolare sono state individuate due popolazioni di faglie sviluppate in età diversa. I travertini che affiorano ampiamente nell'area di Rapolano Terme sono collegati alla circolazione ed alla emergenza di fluidi idrotermali lungo le zone intensamente fratturate associate a faglie di età Pleistocenica. Queste strutture si sono sovrapposte a faglie normali (principalmente orientate NNW-SSE) ed a faglie transtensive (principalmente orientate SW-NE) di età Pliocenica inferioremedia, collegate con lo sviluppo del Bacino di Siena. La sovrapposizione delle due popolazioni di faglie e la loro parziale riattivazione è stata documentata dallo studio degli indicatori cinematici riconosciuti lungo i piani di alcune faglie. L'età pliocenica della prima popolazione di faglie è stata dedotta mediante l'analisi dei rapporti tra tettonica e sedimentazione nei depositi pliocenici. Infatti sedimenti del Pliocene medio suturano le faglie dirette e transtensive. Le faglie dirette di età Pleistocenica, principalmente orientate in direzione SW-NE, hanno riattivato le più antiche faglie transtensive ugualmente orientate ed hanno dislocato le faglie dirette principalmente o...

Travertine deposition and faulting: the fault-related travertine fissure-ridge at Terme S. Giovanni, Rapolano Terme (Italy)

“…The present thermal springs and the Pleistocene-Holocene travertine masses are mainly related to the activity of the second faults set, as fully discussed in Brogi (2004).…”

“…The extensional structures of the Rapolano area have been geometrically and kinematically described in several papers (Brogi 2002(Brogi , 2004Brogi et al 2002). PlioceneQuaternary extensional faults are the most important structures.…”

Tectonic control of tufa occurrences in the Podhale Synclinorium (Central Western Carpathians, southern Poland)

“…Travertines and tufas are con sid ered to be in di ca tors of tectonic ac tiv ity and can be used as a tool for iden ti fi ca tion of a nearby fault trace (Han cock et al, 1999;Brogi et al, 2012), of es ti mat ing the age of tec tonic ac tiv ity (Sibson, 1987;Altunel and Han cock, 1993;Han cock et al, 1999;Brogi et al, 2010) or of the per me abil ity of faults and as so ci ated brit tle struc tures (Brogi, 2004(Brogi, , 2012) that played a role as con duits of flu ids (Cain et al, 1996;Sibson, 1996Sibson, , 2000.…”

Travertine occurrences along major strike-slip fault zones: structural, depositional and geochemical constraints from the Eastern Anatolian Fault System (EAFS), Turkey

“…normal faulting and fracturing) and transtensional tectonic regimes (Altunel & Hancock, 1993a, 1993bAltunel & Karabacak, 2005;Brogi & Capezzuoli, 2009;Çakır, 1999;De Filippis et al, 2012;Faccenna et al, 2008;Hancock et al, 1999;Mesci, 2013). Faults and fracture network in these settings play an important role in the circulation and upwelling of hydrothermal fluids Brogi, 2004;Brogi & Capezzuoli, 2009;Faccenna et al, 2008;Uysal et al, 2007).…”

“…Most studies on the travertine-tectonic relationship are concentrated on extensional provinces (Altunel & Hancock, 1993a, 1993bAltunel & Karabacak, 2005;Brogi & Capezzuoli, 2009;Brogi, Capezzuoli, Alçiçek, & Gandin, 2014;De Filippis et al, 2012;Hancock et al, 1999;Renaut et al, 2013;Selim & Yanik, 2009;Uysal et al, 2007;Van Noten et al, 2013) where travertines are deposited at the tip zone of fault segments, in extensional stepover zones between fault segments (Çakır, 1999), at the intersection point of normal and strike-slip faults (Brogi, 2004;Brogi et al, 2012Brogi et al, , 2014 or along normal faults (Mesci, Gürsoy, & Tatar, 2008).…”