Geology and Tectonic Setting of the Fornovolasco Area, Alpi Apuane (Tuscany, Italy)
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Journal of Maps ISSN: (Print) 1744-5647 (Online) Journal homepage: http://www.tandfonline.com/loi/tjom20 Geology and tectonic setting of the Fornovolasco area, Alpi Apuane (Tuscany, Italy) Diego Pieruccioni, Yuri Galanti, Cristian Biagioni & Giancarlo Molli To cite this article: Diego Pieruccioni, Yuri Galanti, Cristian Biagioni & Giancarlo Molli (2018) Geology and tectonic setting of the Fornovolasco area, Alpi Apuane (Tuscany, Italy), Journal of Maps, 14:2, 357-367 To link to this article: https://doi.org/10.1080/17445647.2018.1476985 © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps View supplementary material Published online: 03 Jun 2018. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tjom20 JOURNAL OF MAPS 2018, VOL. 14, NO. 2, 357–367 https://doi.org/10.1080/17445647.2018.1476985 Science Geology and tectonic setting of the Fornovolasco area, Alpi Apuane (Tuscany, Italy) Diego Pieruccioni , Yuri Galanti , Cristian Biagioni and Giancarlo Molli Department of Earth Sciences, University of Pisa, Pisa, Italy ABSTRACT ARTICLE HISTORY The study area is located in the Alpi Apuane (Tuscany, Italy), and extends between N 44° Received 13 December 2017 0′49.883′′–E 10°20′23.467′′ (SW corner) and N 44°2′53.403′′–E 10°23′19.175′′ (NE corner). The Accepted 12 May 2018 area shows a pile of tectonic units belonging either to the Apuane metamorphic complex, KEYWORDS and Tuscan Nappe, stacked during the Alpine orogeny. The latter is represented by a Metarhyolite; Paleozoic sedimentary Triassic-Miocene succession, and it is characterized by a large-scale east-dipping basement; Triassic monocline, with local excision of stratigraphic terms due to the occurrence of intra-unit low- metasiliciclastic rocks; angle normal faults. The Apuane metamorphic complex is formed by Paleozoic phyllites, Fornovolasco; Alpi Apuane; post-Variscan magmatic rocks (Fornovolasco Metarhyolite Fm.), and Mesozoic-Tertiary Italy metasedimentary formations. The 1:5000 scale geological map and the cross-sections illustrate the tectonic setting of the Fornovolasco area, resulting from the Tertiary tectono- metamorphic events. In the Fornovolasco area, small Tl-rich pyrite + magnetite ore bodies occur close to the contacts between the Paleozoic basement and the cover metasedimentary formations. 1. Introduction Carmignani et al. (1976) reported a detailed mapping of the area around the small pyrite + magnetite ore The Fornovolasco area is located in the Alpi Apuane deposit of ‘Cava del Ferro’ (Le Buge locality), whereas (NW Tuscany, Italy), where formations belonging to Pandeli, Bagnoli, and Negri (2004) focused their atten- the Tuscan Nappe and the Apuane metamorphic com- tion on the pre-Norian succession. plex outcrop. The latter consists of a Paleozoic base- In the present paper, the geological map of the For- ment and its Meso-Cenozoic metasedimentary cover novolasco area, resulting from a new geological survey (Figure 1), metamorphosed up to greenschist facies at the 1:5000 scale, is presented. The aim of this new conditions (Molli, Giorgetti, & Meccheri, 2002 and mapping is manifold. In particular, it aims to improve references therein). Traditionally, the study area has the knowledge about this sector of the Alpi Apuane been attributed to the so-called Stazzemese Slices, Staz- metamorphic complex, giving a reference framework zemese Parauthocton or Fornovolasco-Panie Unit (e.g. for both the pyrite + magnetite ore deposits and the Massa, 2007 and references therein). The attention of meter to decameter-sized metarhyolite lenses cropping several generations of geologists was focused on this out in the Fornovolasco area. sector of the Alpi Apuane, owing to the occurrence of several intriguing geological structures as well as ore deposits, mainly represented by pyrite ± baryte ± 2. Geological background iron oxide ore bodies. This type of mineralization is preferentially hosted within the Paleozoic basement The tectonic setting of the Alpi Apuane (Figure 1)is or close to the contact between the schists of the base- the result of two main tectono-metamorphic events ment and the Triassic metadolostone of the Grezzoni (D1 and D2 phases; Carmignani & Kligfield, 1990), Fm. (e.g. Carmignani, Dessau, & Duchi, 1976; Lattanzi, related to the deformation of the Adria continental Benvenuti, Costagliola, & Tanelli, 1994). margin during the continental subduction and the The first geological mapping of the Fornovolasco syn- to post-collisional exhumation (Molli, 2008; area dates back to Zaccagna (1894, 1926). Nardi Molli et al., 2002; Molli, Giorgetti, & Meccheri, 2000). (1961) compiled the first modern geological map of The D1 event, associated with underplating and the area, whereas further maps at 1:50,000 scale stacking of the tectonic units, developed a progressive were later published by Carmignani et al. (2000) and deformation in two stages (D1a and D1b in Molli & Puccinelli, D’Amato Avanzi, and Perilli (2016a). Meccheri, 2000; Molli & Vaselli, 2006) which CONTACT Cristian Biagioni [email protected] Supplemental data for this article can be accessed at doi:10.1080/17445647.2018.1476985 © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 358 D. PIERUCCIONI ET AL. Figure 1. (a) Geological sketch map (modified from Carmignani & Kligfield, 1990) and (b) cross-section across the Alpi Apuane massif. Equal area lower hemisphere stereograms show the poles of the main foliation (Sp), the stretching lineation (Lp), and the late crenulation cleavage (S2). Projected Coordinate System: Monte_Mario_Italy_zone_1. produced pervasive foliations (S1a and S1b) repre- 1978; Molli, 2008). According to several authors (e.g. senting the axial planes of isoclinal micro- to kilo- Fellin et al., 2007 and references therein), the peak metric-scale NE-vergent folds. This foliation is metamorphism was reached during the early D1 associated with a stretching lineation trending SW- phase, dated at ca. 27 Ma using K-Ar and NE and interpreted as the main transport direction 40Ar-39Ar techniques on white mica (Kligfield, Hunzi- of the tectonic units (Carmignani, Giglia, & Kligfield, ker, Dallmeyer, & Schamel, 1986); P-T conditions JOURNAL OF MAPS 359 were estimated at 350–450°C and 0.6 GPa (Molli (2004), it could be associated with the Middle Triassic et al., 2002 and references therein). marine furrow of the Punta Bianca I Cycle (Martini, The D2 event is associated with the exhumation of Rau, & Tongiorgi, 1986). the metamorphic units (e.g. Molli, 2012) and is related Due to the intense deformations, developed during to the development of different generations of folds the Alpine orogenesis, which characterize the studied and high-strain shear zones. As a result, a complex area, the ‘Fornovolasco schists’ are interpreted as a mega-antiform with Apenninic trending axis (NW- set of tectonic slices belonging to different litho-strati- SE) was produced (Carmignani & Kligfield, 1990). graphic units (e.g. Carmignani et al., 1976; Carmignani Non-cylindrical parasitic folds with sub-horizontal et al., 2000; Puccinelli et al., 2016a, 2016b) where the axial planar crenulations (S2) are related to this phase original stratigraphic relationships were completely and involved the transportation to the east on the east- obliterated. In the present work, the ‘Fornovolasco ern limb of the antiform and to the west on the western schists’ will be described following the stratigraphy side (Carmignani & Kligfield, 1990; Carmignani, Dis- proposed in the modern geological maps of the Alpi perati, Fantozzi, Giglia, & Meccheri, 1993; Carmignani, Apuane (e.g. Carmignani et al., 2000; Puccinelli et al., Fantozzi, Giglia, & Meccheri, 1993). The early stages of 2016a). the D2 phase were characterized by T higher than 250° C and, according to zircon fission track ages, dated back earlier than 11 Ma (Fellin et al., 2007). 3. Methods The latest stages of deformation, related to the final The geological map of the Fornovolasco area (Main exhumation and uplift of the metamorphic units, were Map – about 10 km2) was produced by means of a geo- characterized by the transition from a ductile to a logical survey at 1:5000 scale, relying on the classical brittle regime, with the formation of kink folds, low- tools of structural geology which joined together field and high-angle faults, and joint systems (Corti, Serena, and laboratory work with meso- and micro-structural Bonini, Sani, & Mazzarini, 2006; Molli et al., 2010; studies. The topographic base used for the Main Map Ottria & Molli, 2000 and references therein). The uplift was modified from the Carta Tecnica Regionale of and the final exhumation are testified by the apatite fis- the Tuscany Region at 1:10,000 scale. The geological – sion tracks dated at 2 6Ma(Abbate, Balestrieri, database was implemented using ESRI ArcGis 10.3 Bigazzi, Norelli, & Quercioli, 1994; Bigazzi, Di Pisa, and following the guidelines for the Geological Map Gattiglio, Meccheri, & Norelli, 1988), and by the occur- of Italy (1:50,000 scale; Artioli