Non-final proof 35 The Geological Society of America Field Guide 28 2012 Deformation and fluid flow during underplating and exhumation of the Adria continental margin: A one-day field trip in the Alpi Apuane (northern Apennines, Italy) Giancarlo Molli* Dipartimento Scienze della Terra, Università di Pisa ABSTRACT This guide provides background information and an itinerary for a one-day field trip leaving Barga Garfagnana (Lucca) and crossing the Alpi Apuane toward Ver- silia. This field-trip route provides the opportunity to examine structures and strain features that record the underplating and exhumation of the Apuane metamorphic units. Special emphasis will given to the structures produced at the different scales in the Carrara marble, known throughout the world as a highly desirable building stone. The field trip will touch on the role of fluids, fluid-rock interaction, and defor- mation during underplating and subsequent exhumation of the region along major normal faults. *gmolli@dst.unipi.it Molli, G., 2012, Deformation and fluid flow during underplating and exhumation of the Adria continental margin: A one-day field trip in the Alpi Apuane (northern Apennines, Italy), in Vannucchi, P., and Fisher, D., eds., Deformation, Fluid Flow, and Mass Transfer in the Forearc of Convergent Margins: Field Guides to the Northern Apennines in Emilia and in the Apuan Alps (Italy): Geological Society of America Field Guide 28, p. 35–48, doi:10.1130/2012.0028(02). For permission to copy, contact editing@geosociety.org. ©2012 The Geological Society of America. All rights reserved. INTRODUCTION The Alpi Apuane region exposes the mid-crustal levels that characterize the internides of the northern Apennines orogen (Figs. 1A and 1B). The large-scale architecture of the moun- tain belt resulted from continental subduction of the Adria plate (since early Miocene) below the previously formed intraoceanic accretionary wedge made up of shallowly accreted Ligurian and sub-Ligurian units (Vannucchi et al., 2008; Molli and Malavie- ille, 2011). During continental subduction, parts of the Adria con- tinental margin were imbricated and incorporated into the wedge that formed the shallow crustal levels (e.g., the Tuscan Nappe), whereas other portions (exposed in the Alpi Apuane core) were underthrust to greater depths and metamorphosed. Early syn- contractional exhumation occurred within a sub-marine wedge during Miocene retreat of the Adria plate. This first exhumation occurred by combination of low-angle normal faulting in the upper parts of the prism coupled with ductile thinning related to formation of an antiformal stack in the lower parts. Starting from 5 Ma onward, the final exhumation of the Alpi Apuane occurred by a combined contribution of surface erosion and normal faulting. These processes combine to unroof an anti- formal nappe-stack with a core of metamorphic units surrounded by two elongated Neogene-basins (Fig. 1A), the eastern intra- montane Garfagnana and the partially marine western Lower Lunigiana–Versilia basins (Molli, 2008). GEOLOGICAL OVERVIEW OF THE ALPI APUANE The Alpi Apuane (NW Tuscany) is the largest tectonic win- dow in the northern Apennines where the deepest levels (Tuscan Metamorphic Units) of the belt are exposed.