Calabrian-Peloritan Arc’, Southern Italy: a Review
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J. geol. Soc. London, Vol. 141, 1984, pp. 137-145, 5 figs. Printed in Northern Ireland. Remnants of the Hercynian orogen along the ‘Calabrian-Peloritan arc’, southern Italy: a review P. Atzori, P. Ferla, A. Paglionico, G. Piccarreta & A. Rottura SUMMARY: Remnants of the Hercynian orogen, disturbed by Alpine tectonics, occur widely alongthe ‘Calabrian-Peloritan arc’. Indications of former oceanic conditions, for example Palaeozoic ophiolites and original deep water sediments, are lacking. Metamorphism developed under intermediate to low pressure conditions; the post-metamorphic plutonism appears to be morecompatible with intracontinental orogenic processes than with an active continental margin. The possible evolution of this segment of the Hercynian orogen is discussed. The ‘Calabrian-Peloritan arc’ is a complex structure, morphism in orderto understand the significance of made up of Palaeozoic. Mesozoic and Recent terrains Palaeozoicelements occurring along the Calabrian- which connect the NW-SE trending Apennines with Peloritanarc. Attention will befocused on the the E-W Maghrebide chain of Sicily (Fig. 1). The arc Hercynian magmatic and metamorphic events. results from the progressive bending and disruption of a previous continent-continent collisional belt (Scan- Pre-Hercynian events done1983). Current opinions are that the structure represents, either in total or in part (northern sector), A poly-metamorphic,pre-Alpine evolution has been a fragmenta of theCretaceous-Palaeogene Alpine suggested by someauthors for some tectonic units chain,made up of Pennineand Austro-alpine ele- cropping out along the Calabrian-Peloritan arc. The ments thrust on the Apennines in Early Miocene time poly-metamorphicinterpretation has been based on (e.g.Haccard etal. 1972;Scandone etal. 1974; mineralassemblages and textural features which Alvarez 1976; Amodio Morelli et al. 1976; Bonardi & suggestdifferent metamorphic imprints (e.g. Ferla Giunta1982; Zanettin Lorenzoni 1982; Scandone 1974; AmodioMorelli etal. 1976;Dubois 1976; 1983).There is noagreement, however, about the Paglionico & Piccarreta1978; Zanettin Lorenzoni origin of the arc (e.g. Amodio Morelli et al. 1976 and 1980).Unfortunately, there are no confirming references therein; Scandone 1979; Zanettin Lorenzo- geochronological data. Only one zircon age of 450 Ma ni1982), or onthe palaeogeography and structural (Schenk 1980, 1981) has been determined for granulite organization of some units. It has also been debated facies metabasites of the Polia-Copanello Unit (Serre, whether or not a Hercynianchain occurs in the Calabria),which is considered,according tothe Calabrian-Peloritanarc (e.g. Lorenzoni & Zanettin geophysicalcrustal models (Schwarz 1978; Schutte Lorenzoni1979; Bonardi et al. 1976,1980; Zanettin 1978),to be a fragment of Palaeozoiclower crust Lorenzoni 1982). (Schenk1980, 1981). This age was interpreted by ThePalaeozoic rocks cropping out along the arc Schenk(1980) as a minimum age for the magmatic consist of meta-sedimentary and meta-igneous litholo- crystallization of theprotolith. He also proposed a gies,ranging from low to very high metamorphic Caledonianmetamorphism prior to theHercynian gradegranuliteto(up facies) andgranitic- imprint(Schenk 1981). Besides the pre-Hercynian granodioritic plutonics with subordinate tonalites (e.g. metabasitesoccurring in the Polia-Copanello Unit, AmodioMorelli et al. 1976;Atzori etal. 19826; othermeta-igneous rocks affected by theHercynian D’Amico etal. 1982; Gurrieri etal. 1982).Nappe metamorphism,found along the Calabrian-Peloritan structures of Hercynianage have been described in arc,are augen-gneiss, tonalitic gneiss and amphibo- these terrains (e.g. Colonna etal. 1973; Atzori etal. lites,which might indicate pre-Hercynian magmatic 1977;Gurrieri etal. 1978;Lorenzoni & Zanettin activity. The meta-igneous rocks analysed so far range Lorenzoni 1979; Gurrieri et al. 1982), similar to those frombasic to acidic composition, comparable with generally occurring elsewhere in the European Hercy- those of magmaticproducts at modern converging nian orogen (e.g. Carmignani et al. 1978, 1980; Zwart plates(Atzori et al. 1982b).However, acomplete & Dornsiepen 1978; Weber 1981; Vai et al. 1982). The range of theserocks has not yet been analysed. Hercynian structural arrangement was greatly affected Fragments of maficlayered meta-gabbros, originally by theAlpine tectonics, which gave rise to complex intrudedinto a supra-crustal sequence of granulite nappestructures which obscure the Hercynian struc- faciesmeta-sediments plus meta-volcanics (Dubois ture. 1976; Moresi et al. 1978; Paglionico & Piccarreta 1978; The aim of this work is to synthesize the available Maccarrone et al. 1983),occur in the north-western data concerning the Palaeozoic magmatism and meta- Serre (Southern Calabria). They display calc-alkaline Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/141/1/137/4888119/gsjgs.141.1.0137.pdf by guest on 27 September 2021 138 P. Atzori et al. 0 AEOLIANISLANDS 0 FIG. 1. Location of the Calabrian-Peloritan arc: (1) Sedimentary terrain; (2) metamorphic terrain (pre-Alpine and Alpine) and sedimentary cover of the Stilo Unit; (3) meso-aluminous plutonites; (4) per-aluminous plutonites. featuresand overall similarities with the‘Main Peloritan Range (i.e. Longi-Taormina unit: Bonardi et Gabbro’ of the layered complex of the Ivrea zone in al. 1976;Southern Peloritan complex: Ferla 1974). thewestern Alps (Garuti et al. 1980).Since the Various sills and dykes with minor lavas and hyaloclas- layeredmeta-gabbroic rocks experienced Hercynian tites,contemporaneous with sedimentation of the metamorphism (Paglionico & Piccarreta 1978; Moresi tentaculitid-bearing limestones (Ferla 1978) of Middle et al. 1978; Schenk 1980, 1981), their age of emplace- Devonian age, display basic alkaline features compa- ment may be Hercynian or older. rableto ‘intraplate’ volcanics in extensional settings (Figs 2, 3; cf. Ferla 1978). The activity which followed Hercynian Magmatism unfortunately lacks any age data. A minimum age of LowerCarboniferous can beinferred, asthese Some Hercynian magmatic phases are recorded in the meta-volcanics,which range from basalts to dacites, Calabrian-Peloritan arc. The earliest phase preceded wereaffected by Hercynianmetamorphism. The theHercynian metamorphism and the latest one eruption may have been syn-orogenic in view of the followedit. The oldest pre-metamorphic magmatic association with graywackes and pelites. The chemistry activityhas been recognized so faronly inthe of the meta-volcanics is comparable with the modern Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/141/1/137/4888119/gsjgs.141.1.0137.pdf by guest on 27 September 2021 The 'Calabrian-Peloritan arc', southern Italy 139 0.1 0.05 ,-1- -. I I 0.01 t 0 000 0 Q 08 ope, 00 80 0.005 @,P I I 101 I SUB-ALKALINE ' I ALKALI I BASALT BASALT I l1' 11 l I1 II I Nb/Y I l I* Oll 0.5 1.0 5.0 10.0 FIG. 2. Zr/(Ti02 X 10') vs. NbiY plot (Winchester & Floyd 1976) relative to Hercynian meta-igneous rocks from Peloritani mountains. Circles. meta-volcanites (n = 35) associated with tentaculitid bearing limestones (Ferla 1978): dots, meta-igneous rocks (n = 81) associated with the overlying meta-psammites and meta-pelites (Atzori et al. 19824. orogenicextrusives (Figs 2, 3). In particular.these intrusions. Dykes of aplites. pegmatites and porphyries rocks display Zr values close to those of many modern cut the plutonics. The plutons were intruded into low- to active margin extrusives (Jakes & White 1972; Pearce medium-grade to high-grade metamorphics, generally C? Norry 1979), reaching contents as high as 300ppm at highcrustal levels. The intrusions cut across the in dacites.in Locally occurring meta-volcanics of regional structures discordantly in contrast with Pitch- rhyodaciticto rhyolitic composition have been inter- er's scheme (1979, p. 653) relative to the characteris- preted as products of localanatexis related to rising tics of the Hercynian orogen. The plutonics belong to calc-alkalinemagmas (Ferla 1978; Ferla & Azzaro twoseparate suites (e.g. Paglionico & Rottura1979; 1978;Atzori & Ferla1979). Insome Calabrian D'Amico et al. 1982):a meso-aluminous suite and a tectonic units (e.g. Bagni Unit and Longobucco Unit) per-aluminous suite (Fig. 4), the latter forming smaller composed of low-grademetamorphic rocks, dacitic, intrusions (cf. Lorenzoni et al. 1979;D'Amico et al. rhyodacitic and minor andesitic meta-volcanics (Gur- 1982; Del Moro et al. 1982). The meso-aluminous suite rieri et al. 1978;Ferla & Azzaro1978; Colonna & covers a surface of about 1700 km2, forming composite Simone1978; Colonna et al. 1982)are interbedded bodies with multiple intrusions, with meta-aluminous withmeta-arenites and meta-pelites and seem to be toper-aluminous composition (Fig. 4). characterized chemicallycomparable to those cropping out in the by frequent, possibly primary, muscovite and scarcity Peloritani area. The post-metamorphic magmatism is or absence of hornblende;biotite is theusual of Permo-Carboniferousage, from 295 f 2*Ma to ferromagnesian mineral (Crisci et al. 1980; Lorenzoni 270 f 5 Ma based on RbiSr whole rock and minerals et al. 1979; Gurrieri et al. 1982). The commonest rock ages and also U-Pb zircon ages according to Borsi & typesare granodiorites (70%) followed by tonalites Dubois (1968). Borsi et al. (1976), B. Wieland (pers. (20%) and a few granites (10%), all of which display comm. 1979), Schenk (1980) and Del Moroetal. (1982). calc-alkalineaffinities