MAPPING GEOLOGY MAPPING GEOLOGY ININ ITALYITALY

Editors

Giorgio PASQUARÈ*, Corrado VENTURINI**,with the assistance of

Gianluca GROPPELLI***

*Dipartimento di Scienze della Terra, Università degli Studi di Milano, Italia**Dipartimento di Scienze della Terra e Geologico-Ambientali, Università degli Studi di Bologna, Italia

***Istituto per la Dinamica dei Processi Ambientali Sezione di Milano, CNR Milano, Italia

Printed by

Authors

AIELLO, ANGELINO, ARUTA, ASIOLI, ASTORI, BAGGIO, BEHNCKE, BELTRANDO, BEN M’BAREK, BETTELLI, BETTS,BISTACCHI, BONOMI, BORRACINI, BOSI, BRANCA, BRUNI, BRUNAMONTE, BUCCIANTI, BUDILLON, CALAMITA,CALANCHI, CAPELLI, CARBONE, CARRARO, CASCIELLO, CATTANEO, CAVALLIN, CECCHI, CERRINA FERONI, CESARANO,CHIOCCI, CIBIN, CIPOLLARI, CIPRIANI, CISOTTO, COCCO, COLTELLI, COMERCI, COMPAGNONI, CONFORTI, CONTI,CORREGGIARI, COSENTINO, DALLAGIOVANNA, D’AMBROGI, D’ANTONIO, DAL PIAZ, D’ARGENIO, DE ALTERIIS, DEAMICIS, DE DONATIS, DEL BEN, DE LAURO, DEL CARLO, DE RITA, DI MARTINO, DINI, DI PAOLA, D’ISANTO, DISCENZA,DI STEFANO, DI VINCENZO, ESPOSITO, FABBRI, FELLIN, FERRARO, FERRELI, FORSTER, FUNICIELLO, GALLUZZO,GARUTI, GIARDINO, GILES, GIORDAN, GIORDANO, GOSSO, GRASSO, GROPPELLI, GROPPO, GUARNIERI, GUERRIERI,HILLS, HIRAJIMA, INNANGI, INSINGA, INNOCENTI, IORIO, JADOUL, LANDUZZI, LENTINI, LISTER, LUCCHESI, LUCCHI,MADONNA, MANISCALCO, MARCHETTI, MARRONI, MARSELLA, MARTELLI, MARTIN, MASSIRONI, MAZZA, MESSIGA,MESSINA, MICHETTI, MILIA, MOLISSO, MONTI, MORO, MORRA, MORTARA, NATOLI, NEBBIAI, NORINI, OTTRIA,PANDELI, PANDOLFI, PANINI, PANTALONI, PAPINI, PAPPONE, PAROTTO, PASQUALI, PASQUARÈ, PASSARO, PEDLEY,PELOROSSO, PELOSI, PENITENTI, POMPILI, PORFIDO, PRATURLON, RASPINI, REALE, REBAY, ROCCHI, RODANI, ROLFO,ROSSI, ROVERI, RUGGIERI, SACCHI, SALVI, SANTANTONIO, SARNACCHIARO, SCAMBELLURI, SENO, SERVA, SEVERI,SIRONI, SPALLA, STERLACCHINI, STURIALE, SURIAN, TALLONE, TAMAGNO, TAVIANI, TERRANOVA, TOMMASI,TONIELLI, TRANNE, TRINCARDI, TURELLO, VANOSSI, VANNUCCHI, VENTURINI, VILARDO, VIOLANTE, WESTERMAN,ZANCHI, ZUCALI.

A P A T - DIPARTIMENTO DIFESA DEL SUOLO - SERVIZIO GEOLOGICO D’ITALIADirettore responsabile: Leonello SERVA

REDAZIONE A CURA DEL Servizio Cartografico, Relazioni e Documentazioni di BaseDirigente: Norman ACCARDICoordinamento cartografico-editoriale: Domenico TACCHIA

Progetto grafico: Silvana FALCETTI & Corrado VENTURINI

Allestimento e realizzazione editoriale: Silvana FALCETTI, Mauro ROMA, Maria Luisa VATOVEC

Le cartografie sono state fornite dagli autori dei contributiCOPYRIGHT BY APAT - DIPARTIMENTO DIFESA DEL SUOLO

ROMA - 200

foglio “SORA 152” alla scala 1:100.000 - fotoritocco-le foto sono estrapolate da contributi del volume

Dedicated to the overlasting memory of Maddalena, and to our wives, Lilia and Maria Pia, with love

The volume is a collection of some of the mostrecent, geological and geomorphologic carto-graphic representations of key areas of theItalian territory and its evolution, illustrated bymeans of state-of-the-art methodologies, appro-priate to each site-specific geological condition;it contains 38 contributions, centred on areasthat are representative of the main geologicalaspects of the Italian territory. The initial page of each contribution features abackground image excerpted from a geographicAtlas of Italy dating back to the second half ofthe 19th Century; the back of the same pageshows the geological/geomorphologic map onwhich the contribution is based: This in order tocreate an ideal connection between two repre-sentations of the territory, separated by morethan 100 years of geological investigations.The main purpose of the present work is to com-bine data, cartographic representations and evo-lutive interpetations, with the related researchmethodologies. Moreover, this volume isintended to foster dialogue between experts inthe field of geological cartography, and serve asa didactic tool for Earth Science students andEarth scientists. We believe the above mentio-ned approach was agreed upon by all of the con-tributors of the present work, despite the inevi-table differences in style and expression.The first section of the volume provides a briefdescription of the geologic evolution of theItalian territory, and the final one contains aphysical map of Italy where the location of thestudied areas is indicated. Their cartographicrepresentation is the ultimate synthesis of themethodologies adopted and described by thecontributors.The contributions that compose the present volu-me are arranged following thematic areas, start-ing from the ones dedicated to the Quaternary(marine geology, geomorphology, neotectonicsand surface deposits analysis), to the ones relatedto recent and active volcanism, and then to stra-tigraphic, tectonic and kinematic topics relatedto the classic Apenninic Meso-Cenozoic succes-sions. Finally, the deformative features of diffe-rent Alpine basements are considered. A special conclusive section is dedicated to thecartographic illustration of two geosite case stu-dies, for which a graphical project targeted tothe lay public has been elaborated.Italy repre-sents a huge archive of geological conditionsand events, which, during the last 500 millionyears, left their undeletable signature in a verylimited crustal sector.Stratigraphic and deformative evidences, sedi-mentary and magmatic events, rotations andtraslations of lithospheric blocks, crustal stac-

king and doubling: A complicated geologicalevolution that is as compelling as a screenplayenriched with “coups de theatre” such as litho-spheric extensions, oceanizations, passive mar-gins turning into active margins, syn-sedimen-tary tectonic movements at different scales, Aand B subduction processes, collisional eventsgenerating fold-nappe orogens and thrust-and-fold belts, migrating foreland basins, fast-sprea-ding back-arc basins, superpositions of defor-mations related to different orogenetic proces-ses, reactivations of palaeostructures and spec-tacular topographic inversions. Metamorphicprocesses, exhumations of the deep crust andmagmatic processes linked to various geodyna-mic settings also played an important role inItaly’s geological evolution.Italy’s geomorphologic setting is the result of aseries of processes that, combined with ever-evolving geological conditions, contributed tothe shaping of the peninsula: A complex intert-wining of depositional and erosive features,both subaerial and submarine, originated by theQuaternary, glacial and post-glacial events thatinteracted, and interefered, with eustatic andisostatic movements, magmatic events and, lastbut not least, man-induced modifications of theterritory.All the above represents just a short summary ofItaly’s geology and geomorphology, which havenever ceased to charm both the experts and thelay public, attracted by a compelling geologicaltale, told by generations of Earth scientists.Basic geological knowledge is best representedand conveyed through geological and geomor-phologic, 2D, and state-of-the-art 3D maps.Italians have always prided themselves on theircartographic production. It all started back at thebeginning of Italy’s history as a unified country,when geological mapping studies were promp-ted by the need to represent landscape features,show the location of rivers and the distributionof mountainous areas, plan the siting of strategiccommunication and transportation infrastructu-res and individuate borders between countriesfor commercial and defense purposes.The first evidences of cartographic activity inItaly date back to the Roman Imperial age, whena huge and marvellous road-map (redrawn fromthe original in the High Middle Ages and after-wards named “Tabula Peutingeriana”) was com-pelled. Since then, the process of collection andelaboration of data has continued uninterruptedto our day. Two thousand years later, the Italian territoryhas still much to offer to the ones who are wil-ling to unveil its mysteries and search for cluesto its geological past.

9

INTRODUCTION

A SHORT OUTLINEOF THE GEOLOGY OF ITALY

The geologic makeup of Italy is characterisedby an extreme diversity of geologic featureswhich, since ancient times, have drawn theattention of Earth scientists from all over theworld. This peculiar geological setting is due toItaly’s location in the middle of theMediterranean Sea, where it was involved in thecomplex geodynamic processes derived fromthe long-lived, and ongoing, dynamic interac-tion between the European and African tectonicplates. These processes shaped the Italian penin-sula, charcaterised by a series of orogenic andmagmatic arcs, flanked by basins with differentstructural significance (Fig. 1).The earliest evidence found in Italy’s geologicrecord dates back to the tectonic processes rela-ted to the evolution of the Palaeozoic oceanknown as Palaeotethys and its margins, which,troughout Europe, led to the Caledonian andHercynian orogenies.In fact, some metasedimentary successions inSardinia and the Carnic Alps indicate aCaledonian age: In particular, Cambrian-Ordovician marine successions, mostly carbo-natic and terrigenous, which accumulated on anepicontinental passive margin, are exposed inSardinia, associated to basic and intermediatevolcanics, probably erupted during a concomi-tant rifting phase.The following, Hercynian palaeogeograhic andtectonic evolution is well documented in Italy,

mainly in Sardinia, in the Alps and theCalabrian-Peloritan Arc.The Sardinian basement, poorly affected byAlpine deformations, represents a classic exam-ple of Hercynian orogen, with a collisional beltcharacterised by significant crustal thickening,magmatism and metamorhism during theCarboniferous and the Devonian. The tectonicmakeup of Hercynian Sardinia is composed of astack of west-verging folds and thrusts, whoseemplacement was followed by a prolongedphase of intrusion of huge calcalkaline plutonicbodies and extrusion of alkaline and peralkalinevolcanics, related to the post-collisional exten-sion of the mountain belt (Fig. 2).In the Alpine belt, metamorphic basements dis-play almost everywhere an Hercynian overprintand evidences of volcanic activity. It is possibleto recognize polyphase metamorphic comple-xes, widely intruded by plutonic bodies whosechemical composition shows a temporal pro-gression from peraluminous to calcalkaline andfinally high-K calcalkaline character.The Calabrian-Peloritan basements displayvarious types of metamorphic sequences aswell, from weakly metamorphosed to amphibo-lite, granulite and migmatite facies. LateCarboniferous to Permian granitoids of calc-alcaline character occur.Among the Hercynian segments of the SouthernAlps, the succession exposed in the Carnic Alpsdeserves particular attention since, during theCarboniferous compressive phase, it was loca-ted in the external zone of the mountain belt.

10

Fig. 1 - The main geological and structural elements of the Mediterranean area.1) Neogene foredeeps. 2) Pannonian back-arc basin. 3) Neogene thrust belts. 4)

Cretaceous thrust belts. 5) Stable continental blocks. 6) Mediterranean continental crust.7) Mediterranean thinned continental crust. 8) Oceanic crust.

Therefore it displays non-metamorphic oranchimetamorphic features, and contains a richshallow-sea fauna of Late Ordovician to MiddleDevonian age.The Hercynian event ended with the settlementof a dextral transcurrence tectonic regime bet-ween Gondwana and Laurasia. In Italy, as wellas in several areas of Southern Europe, Permian-Carboniferous transtensions originated pull-apart basins, often continental and less fre-quently marine (Carnic Alps), located in sectorsof the Alps, Apennines and the Corsica-Sardiniablock.After the complex assembling of Pangea, thewhole central ad southern Europe was subject toa continental rifting regime that, starting in theEarly (-Late) Permian, led to the opening of anew Tethys Ocean between Gondwana andLaurasia.The future realm of the Italian territory was thencharacterised by a portion of the Tethys, knownas Ligurian-Piedmont Ocean, and by its mar-gins. The Ligurian oceanic floor was composedof peridotites intruded by gabbros and coveredby MORB tholeiites, radiolarites and pelagiclimestones. The passive margins of the oceanwere segmented into platforms and basinsduring most of the Mesozoic Era.In the Southern Alps, evidences of this particu-lar palaeogeographical setting are widepsreadand spectacular, especially in the Dolomites andthe Carnic and Giulian Alps. There the Permian-Carboniferous fluvial, lacustrine and marginalmarine depositional regime gave way, in theLate Permian and Triassic, to the sedimentationof evaporitic and terrigenous shallow-sea depo-sits and the build-up of huge organogenic, car-bonate bodies of Late Triassic age.During this geologic time interval, a high subsi-dence rate, coupled with extensive and transten-sive tectonic regime, caused the break-up ofperitidal platforms, fragmented in isolatedblocks, separated by deep basins infilled withterrogenous sediments and volcanic products. InJurassic time, the effects of the extensional tec-tonic activity became more marked, and furtheraffected the palaeogeographic articulation of thearea.In the central and southern Apennines, this kindof palaeogeographic conditions continuedduring the Cretaceous and most of the Tertiary:In fact, beside large carbonatic platforms suchas the Lazio-Abruzzo and Campania-Lucaniaones, spectacular slope-and by-pass marginsdeveloped, passing into deep pelagic basins likethe Umbria-Marche and the Molise-Sannioones.An event which played a major role in shapingthe present geologic setting of the Italian penin-sula, is represented by the abrupt change in therelative motion between Europe and Africa; inlate Cretaceous times, the two plates began con-verging towards each other, with minor exten-sional deformations, controlled by the samecompressional regime.This geodynamic reorganization led to the sub-stitution of passive margins, whic had long rep-resented key areas of the geologic evolution,with active margins. Along these convergingmargins, the Ligurian oceanic crust was almostcompletely consumed, with the exception of theJonian area whose oceanic crust continued itsnorthwestward suduction, also in Pliocene-Qaternary times, beneath the Calabrian Arc.

The above described processes led to the forma-tion of the Alpine and Apennine collisionalbelts, bounded by foreland basins, and to theopening of the Tyrrhenian back-arc basin whichwas preceded by the eastward drifting and coun-terclockwise rotation of the Sardinia-Corsicablock. The subsequent geodynamic evolutionled to the further fragmentation of the Africanforeland, with the separation between the Adriaand African plates and the rifting of the SicilianChannel.The Alps are composed of a stack of large tecto-nic nappes derived from the European andAfrican continental margins and the Tethyanoceanic lithoshpere, thrust towards the W, NWand N, over the European foreland. South of a amajor, lithospheric suture zone known asInsubric or Periadriatic Line, rise the SouthernAlps, dominated by south- and southwest-ver-ging thrust sheets, accreted toward the Adriaplate (Fig. 3).The Alps display a rough and steep topographywith high erosion and denudation rates and arecharacterised by a basement reaching high-grade metamorphic facies at the surface, a pro-cess of convergence that continued even afterthe collisional event, the development of outermolasse basins deformed by compressionalstructures, rather than extensional ones.The formation of the Alpine belt was extremelyarticulated, spanning the time between the lateCretaceous and the Neogene, and gave rise to atectonic architecture that, altough extremelycomplex in detail, reflects the expected piling-up of the palaeogeographic units forming theEuropean and African margins prior to their col-lision.Within this architecture it is still possibile torecognize the cylindristic models of the firstgeologists who studied the Alpine belt, amongwhom Emile Argand and Rudolf Staub, whoseremarkable intuitions date back to the beginningof the twentieth century. In spite of the impres-

11

Fig. 2 - The Hercynian orogenic belt in Sardinia.1) Post-Hercynian cover. 2) Intrusive complex. 3) Thrustbelt. 4) External fold belt.(After SERVIZIO GEOLOGICO NAZIONALE, 2001 - Mem. descrittivedella Carta Geologica d’Italia, Vol. LX, modified).

sive amount of subduction and obduction pro-cesses, of the great lateral displacement of ter-rains and of the tight alternation of divergingand converging structures, the palinspasticreconstructions carried out during the last cen-tury mostly recognize the longitudinal persist-ence of several palaeogeographic realms alongthe entire Alpine belt. Again, despite the tecto-nic and metamorphic deformations which stem-med from the Alpine collision and affected therock units derived from the previous palaeogeo-graphic setting there is a general agreement onthe main palaeogeographic-structural domainsforming the Alps. From the outer to the inner portions of the beltwe recognize: The European foreland; theHelvetic domain, belonging to the deformedEuropean margin; the Penninic domain, madeup of the ophiolitic remains of the Tethyanocean and its highly deformed and metamor-phosed margins; the Austroalpine domain,derived from the northern margin of the Africanforeland, tightly compressed against thePenninic tectonic units and overthrusted onthem; the Southalpine domain, composed of thedeformed margin of the Adria plate, andbackthrusted on it. There’s a general agreement on the recognitionof the oldest Alpine orogenetic movements inthe easternmost Austroalpine domain duringearly to middle Cretaceous. This orogenicphase produced also an eclogitic to Barrovianmetamorphism, commonly ascribed to the clo-

sure of a Triassic Vardar Ocean and subsequentcontinental collision in the Balkanic andCarpathian area.A widespread orogeny took place between thelate Cretaceous and the Eocene. The orogenicprocess began with the subduction of Ligurianoceanic lithosphere beneath the African margi-n’s accretionary wedge and ended with theEocene collision between Adria and Europe.The resulting accretionary wedge is represent-ed by the Penninic-Austroalpine core of theAlpine belt. The Penninic units include por-tions of the continental European lithosphere,fragments of the rifted European margin, as theBrianconnais realm basement nappes, ophioli-tic bodies and related Flysch-like sequencesand subduction melanges.The Austroalpine units, mainly derived fromthe Adria passive continental margin, consist ofa stack of cover and basement nappes overri-ding the Penninic ones, as clearly visible in thebeautiful Engadine and Tauern tectonic win-dows. Based on metamorphic imprints andoverprints it is possible to identify, within thePenninic and Austroalpine units, remnants oflithospheric slabs which were subducted todepths of at least 100 km and then rapidly exu-med in conditions of high thermal gradient(Barrovian-type collisional metamorphism).This phase ended when the Penninic units ofthe outer European margin were involved in thesubduction process, causing the commence-ment of a continent-continent collision.

12

Fig. 3 - Tectonic sketch-map of the Alps. 1) European foreland. 2) Jura fold belt. 3) Subalpine molasse. 4) Helvetic cover. 5) Helvetic basement. 6) Pennidic nappes. 7) Pennidic ophiolite-bearing nappes. 8) Pennidic Flysch nappes. 9) Austroalpine cover.10) Austroalpine basement. 11) Ivrea-Verbano Zone. 12) Southalpine cover.

13) Southalpine basement. 14) Paleogene intrusives. 15) Paleogene volcanics. 16) Perialpine Oligo-Miocene basins. 17) Po plain. 18) Pennidic front. 19) Main regio-nal faults (PA = Periadriatic Line). (After BISTACCHI & MASSIRONI, 2001 - In G. PASQUARÈ (Ed.):Tettonica recente e instabilità di versante nelle Alpi centrali, Cariplo-C.N.R., modified).

During the Oligocene the subduction of theEuroean continental lithosphere continued, pro-ducing intense deformations in the thickenedaxial sector of the Alpine belt, its isostatic riseand subsequent topographic and morphologicuplift of the orogen. The resulting, high erosion rate led to the depo-sition of huge volumes of turbiditic materials inthe external Helvetic-Dauphinois domains.From the late Oligocene onwards this realm wasaffected by very intensive tectonic deformationswith updoming of the European Variscan base-ment and decollement nappes in its sedimentarycover, wich reached the Alpine front with thePrealpine French-Swiss Klippens.During this phase, a portion of the materialsadded to the accretionary prism was carriedback and thrust toward the hinterland, formingthe Southern Alps. This huge, southern Alpineorogenic prism, is composed of a Variscan meta-morphic and plutonic basement and its Permo-Carboniferous and Mesozoic sedimentary cover,probably detached at the level of the Adriaticlower crust, nowadays exposed along the so-cal-led Ivrea-Verbano Zone. The overthrusting ofthis fold-and-thrust belt on the Adriatic crustended in the Messinian, and this testifies to thevery recent age of the post-collisional crustalshortening in the Alps. Because of the southal-pine orogeny the Alpine belt acquired the shapeof a gigantic pop-up between the fore-thrustsand back-thrusts, with molasse basins on eitherside.The diverging separation of the Southern Alpsfrom the main Alpine belt was controlled by theactivity of lithospheric faults such as thePeriadriatic (Insubric) one, along which a for-mer great dextral strike-slip movement wastaken up by main vertical displacements that, inturn, produced the larger uplift of the axial sec-tor of the belt with respect to the SouthernAlpine one (Fig. 4).At the same time, due to the laceration of theunderlying, stretched European lithosphere,significant volumes of calcalkaline magmas areproduced, with consequent emplacement of plu-tonic bodies along the Periadriatic Lineament.This magmatic activity can be ascribed to partialmelting of the lithospheric mantle previouslymodified during the main Alpine subductionphases.The Apennine mountain belt, despite its proxi-mity to the Alps, displays topographic, morpho-logic, chronologic, structural and geodynamicfeatures which are markedly different fromthose belonging to the Alpine model. Hoewever,the two orogens are connected, since the birthand evolution of the Apennines was the conse-quence and continuation of the same geodyna-mic process that originated the Alpine orogenicbelt.This connection is represented by the end of theEoalpine collisional phase and the onset of newgeodynamic processes in the westernMediterranean, such as the detachment of theSardinian-Corsican microcontinent from theIberia continental margin and the opening of theBalearic back-arc basin, the westward-dippingsubduction of the Adria plate and the inceptionof the Apenninic accretionary prism along itswestern margin.The geodynamic setting of the area, since thebeginning of the Oligocene, was characterisedby the progressive consumption of the Tethyan

sea floor, the development of new back-arcbasins among which (since Tortonian times) theTyrrhenian one, which was an event of para-mount importance in the geological history ofthe Apennines. The Tyrrhenian sea was opened as a result of asoutheastward rollback of subduction systemnear the margins of the Adriatic plate, providedthat the subduction rollback exceeded the rate ofconvergence. Moreover the Apenninic accretionary prism wascharacterised by different factors enabling agreat horizontal mobility like the shalloiw depthof the Moho, the high heat flux in its inner por-tions, and the deep, rapidly prograding forelandbasins. as a consequence of the above mentio-ned factors a thin-skinned thrusting developedwith the progressive and rapid accretion ofthrust sheets onto the Adriatic foreland in aregional subsidence regime, manteined by thepresence of the back-arc extension during thewhole Apenninic tectonic evolution.The opening of the Tyrrhenian Basin wasaccompanied by rotational drifting toward the Eand SE of the Apenninic accretionary prism,which acquired its sharp bending also becauseof the persistence of Tethyan oceanic crust in theJonian basin.Such process is attested by the presence of exo-tic fragments, of European and Alpine prove-nance within the palaeo-jonic melanges of theCalabrian arc, which connects the Apenninicbelt and the Sicilian-Maghrebide belt.The Apenninic accretionary prism was characte-rised by different factors enabling its great hori-zontal mobility like the shallow depth of theMoho, the high heat flux in its inner portions,and the deep, rapidly-prograding forelandbasins. Due to the presence of predominant sedi-mentary materials within the prism, thin-skin-ned thrusting could develop with the progressi-ve and rapid accretion of thrust sheets onto theAdriatic foreland in a regional subsidence regi-me, maintained by the presence of the wideTyrrhenian back-arc basin during the wholeApenninic tectonic evolution.A consequence of that is the limited participa-tion of the cristalline basement in the build-upof the orogenic prism. The final result of the geologic evolution of theApennines is a thrust-and-fold belt, markedlyconvex toward the Adriatic and Apulian fore-land, and characterised by remarkable geome-tric differences along the orogen’s longitudinalprofile, which are due to the superposition ofdifferent deformation styles and variable ratesof crustal shortening.This segmentation is mainly controlled by trans-versal discontinuities, also associated with anti-clokwise block rotations in response to possiblegeometric changes in the subduction processand in the rheologic behaviour of the involvedcrustal sectors.These transversal discontinuities display N-Sdirected dextral transcurrent movements in thecentral Apennines, and NW-SE directed sinistralmovements in Sicily. They control the differen-tial accretion of the main thrusts fronts on thePadanian-Adriatic-Apulian foreland, the Jonianbasin and the Hyblean platform. Among themost relevant transversal structures it is worthmentioning the Olevano-Antrodoco line (Fig.7), that acts also as an out-of-sequence thrustwhere pelagic sediments overthrust the

13

Fig. 4 - (After BISTACCHI & MASSIRONI, 2001 - In G.PASQUARÈ (Ed.): Tettonica recente e instabilità di ver-sante nelle Alpi centrali, Cariplo-C.N.R., modified).

Apenninic carbonate platform.In describing the geologic configuration of theApenninic belt, two structural, palaeogeogra-phic domains may be individuated:- The Internal Domain, mainly composed ofmagmatic and sedimentary successions derivedfrom the deformation of the Ligurian oceaniclithosphere during its descent underneath theAdriatic plate (coeval to the Cretaceous-EoceneEoalpine phase), and exhumed during the suc-cessive formation of the Apenninic orogenicprism;- The External Domain, represented by the riftedcontinental and passive margin sequences of theAdriatic and African platform, deformed at dif-ferent crustal levels during the Oligocene-Pliocene collisional process. The resultingimbricate thrust systems were emplaced withAdriatic and African vergence, overriding theoutermost foredeeps up to the Po-Apulian-Hyblean foreland. The Internal Domain is represented by theLigurian units, derived from the Tethyan Ocean.The most internal ones still preserve their ophio-litic substratum together with its volcanic andpelagic sedimentary cover. The external onesare represented by rocks originally covering the

Ligurian oceanic crust, detached from theirbasement and transported laterally. They containophiolitic blocks and ophiolite-rich debris flowsslided in the Ligurian basin during the lateCretaceous.These Ligurian Units, devoid of any recogniza-ble ophiolitic substratum, are widespread in theSouthern Apennines and in Sicily. Within thedeep-water sequences of Ligurian Units inCalabria and Basilicata, it is possible to observealso high-pressure subduction-related metamor-phic imprints followed, during the subsequentuplifting, by a green-schist facies re-equilibra-tion. Their exhumation occurred during theMiocene overthrusting of the Liguride accretio-nary wedge onto the continental margin of theSouthern Tethys (Figs. 5 and 6).During the Cretaceous and the Palaeogene, theLigurian basin was infilled by thick turbiditicsuccessions, both siliciclastic and carbonate, thelatter mainly represented by the HelminthoidFlysch.To the Internal Domain of the Apenninic-Maghrebide chain belongs also the so-called“Sicilide Complex”, a non-ophiolitic, deep-seasuccession of upper Cretaceous-lower Miocene,dominated by chaotic varicoloured shales.

16

Fig. 5 - Simplified geological map of the area visited on the field trip. The solid line showsthe trace of the line CROP 04. 26) Continental and subordinate coastal deposits; volca-nic rocks and volcaniclastic deposits (Holocene - Middle Pleistocene p.p.). 25)Terrigenous marine and paralic deposits filling the Bradano Trough and unconformableoverlying the Apennine Units (Middle Pleistocene p.p. - Lower Pleistocene). 24) Pliocenethrust-top deposits. 23) Calaggio Chaotic Complex (upper Messinian - lower Pliocene).22) Messinian - upper Tortonian thrust-top deposits (including the Braneta and Gessoso-Solfifera Formations). 21) Lower Messinian - upper Tortonian thrust-top deposits uncon-formably overlying the Sannio Unit (San Bartolomeo Formation). 20) Lower Messinian- upper Tortonian thrust-top deposits unconformably overlying the Matese Unit (SanMassimo sandstone). 19) Middle Miocene thrust-top deposits unconformably overlyingthe Alburno-Cervati and Monti della Maddalena Units (Castelvetere Formation). 18)Middle Miocene thrust-top deposits unconformably overlying the Sicilide Unit

(Gorgoglione Formation). 17) Lower Miocene thrust-top deposits unconformably overl-ying the North-Calabrian Unit (Albidona Formation). 16) North-Calabrian Unit(Palaeogene-Cretaceous). 15) Sicilide Unit (lower Miocene - Cretaceous). 14) Alburno-Cervati, Monti della Maddalena and minor Units derived from the Campania-Lucaniacarbonate platform (lower Miocene - Upper Triassic). 13) Sannio Unit (middle Miocene- lower Cretaceous). 12) Lagonegro Units (lower Cretaceous - Middle Triassic). 11)Matese Unit (upper Miocene - Upper Triassic). 10 Tufillo-Serra Palazzo Unit (upperMiocene - Palaeogene). 9) Daunia Unit (upper Miocene - Palaeogene). 8) Monte AlpiUnit (upper Miocene - Jurassic), including the overlying lower Pliocene thrust-top depo-sits (emergence of the Apulia - carbonate duplex system). 7) Cretaceous carbonates ofthe Murge foreland. 6) Faults, including normal faults and strike-slip faults. 5) Thrustflat. 4) Thrust ramp. 3) Anticline axis. 2) Syncline axis. 1) Caldera rim (Vulture Volcano).(After PATACCA et alii, 2000 with slight modifications).

The Ligurian Units were covered, after theirmain deformation phase, by piggy-back basinsfilled by marine and transitional clastic and eva-poritic sediments of Oligocene-Pliocene age,designed as Epi-Liguride sequences.The External Domain is characterised by sedi-mentary sequences of peritidal carbonate plat-form, pelagic carbonate platform and pelagicbasin, derived from the fragmentation of theAdriatic continental margin between theTriassic and the early Cretaceous, which wasconcomitant with the rifting and opening of theLigurian Tethys. The transitional areas betweenplatforms and basins represent a very clearexample of the Mesozoic rifting evolution andof the subsequent contractional tectonic inver-sion, becoming the preferred sites of the mainchanges in the structural style and of along-stri-ke kinematics (Fig. 7).Following the onset of plate convergence alongthe Apenninic margin, and beginning inOligocene time, in front of the external units aseries of deep foreland basins originated, infil-led with deep-water turbidite systems, entirelydeposited by turbidity currents and related gra-vity flows (Fig. 8).Within the External Domain, the deformationstyle is different in the southern and the northernsectors of the belt: The structure of the northernsector, characterised, at its back, by a limitedthinning of the Tyrrhenian crust, may be explai-ned in terms of a thick-skinned or inversion tec-tonic model that implies a certain degree ofbasement deformation and requires limited cru-stal shortening. The structure of the southernsector, characterised, at its back, by neoforma-tion of Tyrrhenian oceanic crust, is best explai-ned in terms of a thin-skinned model withdetachment of the sedimentary cover from thebasement and a larger tectonic tranport of theallochtonous sheets. The opening of the back-arc Tyrrhenian basinduring the Neogene caused the development ofwidespread extensional structures also along theinner sector of the belt. Such effects continued

17

Fig. 7 - Structural map of the Central Apennines.1) Pliocene-Quaternary marine and continental deposits.2) Pleistocene volcanic rocks. 3) Messinian evaporites.4) Neogene foredeep siliciclastic deposits. 5) Meso -

Cenozoic shallow-water limestones. 6) Meso - Cenozoicdeep-water limestones. 7) Thrust. 8) Fault. (After COSENTINO et alii, 2002 - Boll. Soc. Geol. It., Vol. spec.n.1, parte I, modified).

Fig. 6 - Interpreted line drawing of the line CROP 04. Colours as in Fig.5 ,with the exception of the North-Calabrian Unit, the Sicilide Unit and theAlbidona Formation that have been grouped. (After PATACCA & SCANDONE,2004. Geological transect across the Southern Apennines along the seismic lineCROP 04. 32nd Intern. Geol.Congr., Field Trip Guidebook vol. 1, P2).

18

also during the Pleistocene with the formationof wide intermountain basins in the central andnorthern Apennines, while in the southernApennines the extension processes caused theopening of peri-Tyrrhenian basins, subject tostrong structural control.Extensional tectonics favoured the onset ofwidespread volcanism in the Tyrrhenian penin-sular and insular areas, whose magmas reflectthe above illustrated geologic evolution (Fig. 9).Among the evidences of the relationship bet-ween magmatism and tectonics in the area, thereis the distribution of calcalkaline subduction-related magmatism, marked by a continuousmigration toward the east and south-east that fol-lows the Corsican-Sardinian and Apenninicblocks in their anticlockwise rotation.In the northern Tyrrhenian and Tuscany, calcal-kaline magmatism migrated southeastward bet-ween the late Miocene and the Quaternary,down to the Aeolian archipelago, today animportant site of volcanic activity.

Since Middle Pleistocene times, in Latium,Campania and, to a lesser extent, in Umbria andBasilicata, there has been a large diffusion ofpotassic and ultrapotassic volcanoes, some ofwhich (in Campania) are still active today. Thesevolcanoes’ genetic interpretation has been thetopic of intense debate, but today it seems that theprevailing opinion among publishers is that thesemagmas were generated in a mantle contaminatedby fluids possibly derived from the downgoingslab, i.e. in subduction-related environment.Several calcalkaline volcanic centres were acti-ve in Sardinia in Oligocene-Miocene times;today a few seamounts active in the central-sou-thern Tyrrhenian display a similar calcalkalinecomposition.In Sardinia, in the central-southern Tyrrhenian,in Sicily and the Sicily Channel, several volca-nic centers, among which Mt. Etna Volcano,during the Pliocene and the Quaternary eruptedNa-alkaline and transitional products bearingtypical intraplate geochemical signatures.

Fig. 9 - Distribution of Cenozoic and Quaternary volcanism incentral-southern Italy. (After PECCERILLO, 2002 - Boll. Soc. Geol. It.,Vol. spec. n.1, parte I).

Fig. 8 - Schematic relationships between the Apenninic thrust belt and its foreland duringthe foredeep stage. Ol) Olistostromes or megabreccias. bst) Basal massive siliciclastic

turbidites. ust) Upper pelitic siliciclastic turbidites. (After CENTAMORE et alii, 2002 - Boll.Soc. Geol. It., Vol. spec. n. 1, parte I, modified).