Showing papers in "Ofioliti in 2007"

Discovery of the oldest (upper ladinian to middle carnian) radiolarian assemblages from the bornova flysch zone in western turkey: implications for the evolution of the neotethyan izmir-ankara ocean

Abstract: Diverse upper Ladinian to middle Carnian radiolarian faunas have been obtained from different ribbon cherts blocks and tectonic slices of the Izmir- Ankara Suture Complex and the marginal sediments of the Tauride-Anatolide platform within the Bornova Flysch Zone, western Turkey. Four isolated samples with late Ladinian, early Carnian, late early Carnian, early middle Carnian ages and one continuous section with late Ladinian to late early Carnian age were considered. As a result of taxonomic studies, sixty-six taxa from different families were defined from these time intervals, definition of sixteen taxa remained in open nomenclature were given and one new species (Pseudostylosphaera mostleri) was determined. The radiolarian ages obtained indicate an upper Ladinian to upper lower Carnian deepening of the Middle Triassic Tauride-Anatolide carbonate platform. Combined with regional geological data this event is interpreted to reflect the initial opening of the Neotethyan Izmir-Ankara oceanic seaway.

Post-variscan mafic dikes from the late orogenic collapse to the tethyan rift: evidence from sardinia

Abstract: Dolerite dikes cut the Lower Paleozoic medium- to high-grade metamorphic basement, the Sardinia-Corsica batholith and the Stephanian - Autunian calcalkaline effusives (1st volcanic episode, according e.g. to Bonin, 1989; Cabanis et al., 1990) with a N-S trend and subvertical dip. Their occurrence is reported from several areas of Sardinia, from the N to the SE. The basic dikes are associated with diorite to rhyolite dikes having trends ranging from E-W to N-S. A late Triassic lamprophyric dike intruded the garnet-staurolite-kyanite micaschists near Mt. Nieddu and has a 40°N direction. Two 40Ar-39Ar age determinations for the dolerite dikes were carried out on amphibole. Ages between 253.8±4.9 and 248±8 Ma (Permian - Early Triassic) probably correspond to the emplacement interval. A continental within-plate geochemical signature, with prevalent tholeiitic to transitional (dolerites) and minor alkalic (lamprophyre) terms, has been determined. The relative LILE and REE enrichment compared with the MORBs and Nd isotopic ratios (4 bulk samples; initial 143Nd/144Nd ratios between 0.512529±0.000025 and 0.513143±0.000023) is consistent with a source in a sub-continental lithospheric mantle. The remarkable compositional and isotopic variability can be explained by the partial melting of a heterogeneous source. Crustal contamination variably affects some transitional dikes; the host Arzachena monzogranite probably represents the major contaminant source. On the whole, the geochemical data support an anorogenic geochemical affinity, in accordance with the extensional regional tectonics, for the Permo-Triassic dikes in Sardinia. The E-W emplacement patterns correspond to the major fractures and primarily R and RI structures associated with the late Variscan transcurrent-extensional E-W faults. The N-S emplacement trend is consistently associated with a generalized E-W extension of the Sardinian crust: in a predrift restoration it coincides with the patterns of extension between the European and Insubric crust at the beginning of the Tethyan rift. In Sardinia, the lamprophyre dike is significantly younger than the late Variscan alkaline volcanites and dikes of the rest of the Mediterranean domain (e.g. Eastern Provence: 278-264 Ma, 40Ar/39Ar isotope dating on feldspar from rhyolites and on plagioclase from mafic flow, Zheng et al., 1992; Western Pyrenean Axial Zone: 271-266 Ma, K-Ar isotope dating on kaersutite phenocrysts from mafic dikes, Debon and Zimmermann, 1993), in accordance with the diachronism of both the first and second volcanic episodes in different areas of the Mediterranean domain. The overlap between the calc-alkaline events and the volcanic and sub-volcanic alkalic event, is not exclusive to Sardinia and Corsica (e.g. the Pyrenees and Pan-African orogen).

OPHIOLITIC CHROMITITES FROM THE KAHRAMANMARAŞ AREA, SOUTHEASTERN TURKEY: THEIR PLATINUM-GROUP ELEMENTS (PGE) GEOCHEMISTRY, MINERALOGY AND Os-ISOTOPE SIGNATURE

Abstract: Mantle-hosted podiform chromitites from ophiolites of the Kahramanmaras area (south-eastern Turkey), have been investigated with ragard to the chromite composition, Platinum-group elements (PGE) concentration and mineralogy, as well as Os-isotope geochemistry. Chromitites vary from Al-rich to Cr-rich, however they indifferently display enrichment in Os-Ir-Ru over Rh-Pt-Pd, with concentrations of PGE lower than 510 ppb. Consistently, the most abundant Platinum-group minerals (PGM) are Ru-Os-Ir sulfides and alloys with subordinate Ir-Ru-Rh sulfarsenides and one grain of unidentified Pd-Sb phase. Textural relationships indicate that the PGM sulfides and alloys are mostly magmatic in origin, i.e. formed at high temperature prior to or concomitant with the crystallization of chromite, whereas the sulfarsenides and the Pd bearing minerals were formed during post-magmatic processes. The Kahramanmaras chromitites display relatively high Re/Os ratios, that coupled with error-chron calculated ages, point to a mixing of mantle-derived Os with Os from a source characterized by a relatively high radiogenic signature, possibly subduction-related fluids. If the genesis of the Kahramanmaras ophiolites is related to subduction, the concomitant presence of Al-rich and Cr-rich chromitites suggests chromite precipitation from melts varying in composition from MORB-like backarc basalts (Al-rich chromite) to boninites (Cr-rich chromite). The geochemical and mineralogical data indicate that most of the Kahramanmaras chromitites have low PGE potential, due to low PGE concentration, small size of the PGM grains, and predominance of Ru-Os-Ir over Rh-Pt-Pd. Only one sample from Elbistan, exceptionally, was found to have a pronounced positive Pt anomaly, up to 99 ppb, that is supported by identification of magmatic Pt specific phases. Genetic relationships of this chromitite with the others in the area are still unknown. This chromitite represents a potential target for Pt recovery, such that detailed study of the Pt mineralogy, distribution in the chromite ore, and identification of the magmatic sources of Pt, and the mechanisms of Pt concentration, may be useful tools to future exploration in the Kahramanmara` ophiolite.

Was the Valaisan basin floored by oceanic crust? Evidence of permian magmatism in the Versoyen Unit (Valaisan Domain, NW Alps)

Abstract: The Versoyen Unit (Western Alps) and its mafic rocks have been long considered the remnants of the oceanic crust that supposedly floored the Valaisan basin during the Cretaceous. Here we present U-Pb dating of zircons from a metaleucogabbro and a metagranite from the Versoyen Unit challenging this view. Magmatic zircon cores yield Permian ages of 267±1 and 272±2 Ma, respectively, which are interpreted as dating the crystallization of the magmas. Older inherited crystals and rare Cretaceous zircon rims (~110-100 Ma) are also present. The young rims are characterized by very high U and REE contents. We speculate that the Cretaceous ages are related to a thermal/fluid event possibly induced by the opening of the Valaisan basin. The proposed Permian age for the Versoyen magmatism, together with the lack of geochronological evidence for a Cretaceous oceanic crust in the Valaisan domain sensu stricto, may force to reconsider the oceanic nature of the Valaisan Basin. We propose a model in which the Versoyen Unit is unrelated to and pre-dates the extensional tectonics that led to the formation of the Valaisan Basin and the Cretaceous deposition of sediments on this Permian basement. The Permian ages for the Versoyen intrusives correlate with extensive Permian intra-plate magmatism related to lithospheric stretching prior to the break-up of Pangea. The Versoyen Unit becomes the most external Alpine terrane that displays traces of this Permian basic magmatism. Traces of Cretaceous magmatism are preserved in the more internal Chiavenna and Balma units, located in the Central and Western Alps, respectively. However, several lines of evidence suggest that such units may have been unrelated to the Valaisan Basin. Therefore, we propose a new palaeogeographic scenario for the western Tethys, where two independent basins, the Valaisan Basin and the Chiavenna/Balma Ocean, were located between the Brianconnais micro-Plate and the European Plate sensu stricto.

Age of the jurassic radiolarian chert formation from the zlatar mountain (sw serbia)

Abstract: Detailed micropaleontological research of the Jurassic siliceous rocks in the Pavlovic´a Brod locality, located on the eastern flanks of the Zlatar Mt. in the Internal Dinarides, adjacent to the Dinaridic Ophiolite Belt, was performed. According to the determined radiolarian associations, the investigated cherts and radiolarites are of Middle Jurassic age. Radiolarian 2-7 UAZ from late Aalenian to early Callovian have been determined for the first time.

Structural features of southern tuscany, italy

Abstract: The main structural features of Southern Tuscany are the result of post-collisional extensional tectonics which have affected the inner part of the Northern Apennines since the Early-Middle Miocene Geological analyses have shown that several deformational events are related to the development of extensional tectonics Geophysical studies suggest that a kinematically active mid-crustal shear zone is located at the present rheological boundary between the upper part of the crust, mainly characterized by brittle deformation, and the lower part, mainly characterized by ductile deformation The coexistence of extension with the compression tectonics, which affected the outer zone of the Northern Apennines, is explained as a result of the post-collisional evolution

Age and geochemistry of middle to late carnian basalts from the alakirçay nappe (antalya nappes, sw turkey): implications for the evolution of the southern branch of neotethys

Abstract: The geochemical features of spilitic basalts and the radiolarian fauna of associated pelagic sediments have been studied from two different sections of the Alakircay Nappe of the Antalya Nappes, SW Turkey. The first section in Cukurkoy is located in the eastern part of the Antalya Gulf and includes thick spilitic basalts, overlain by an alternation of mudstone, marl and pelagic cherty limestone. Radiolarian data from the cherty limestone in this unit reveals a middle Carnian age for this section. The second section in Yaylakuzdere is situated in the western part of the Antalya Gulf. In this section, thick pillow basalts are overlain by a succession of limestone/cherty limestone and shale beds. The age of the limestones interlayered with the pillow basalts was assigned to the late Carnian, whereas the basal part of the overlying cherty limestones was dated as latest Carnian/earliest Norian by conodont and radiolarian faunas. The pillow lavas in the Cukurkoy and Yaylakuzdere regions consist of within-plate type alkaline basalts and display multi-element pattern similar to typical oceanic island basalts (OIB). Low La/Yb, Zr/Y and La/Nb < 1 ratios are also indicative for an OIB-like deep mantle source. These alkaline basalts have not suffered interactions with a subducted slab and/or continental crust due to presence of high HFSE abundance, the lack of depletion in Nb and Ta that are characteristics of subduction and/or crustal contamination processes. Based on this data, it can be concluded that alkaline volcanism in these two regions of the Antalya Nappes have been probably generated by a small OIBtype mantle plume during the middle - late Carnian time interval, in the advanced stages of rifting of the Antalya Nappes successions in the southern branch of Neotethys. This data reveals the generation of a rift basin before middle Carnian for this ocean.

Neogene crustal shortening and basin evolution in tuscany (northern apennines)

Abstract: The structural studies carried out in the Northern Apennines during the last decade show that the Neogene tectonic evolution of this area is much more complex than the classical model which proposed a NE-directed shifting of the compressive front followed by lateral extension in the internal zone tied to the development of the Tyrrhenian basin. Recent structural data systematically collected both in the chain and in the sedimentary fill of the hinterland basins, allow us to propose an alternative model for the development of the basins and for the Neogene evolution of the whole Northern Apennines sector. In the central sector of the chain (Tuscan-Romagna Apennines), there is evidence of polyphase thrust reactivations and out-of-sequence thrusting. In the hinterland basins, compressive deformations usually occur in correspondence of thrust ramps and regional unconformities have been found. The timing of both thrust reactivations in the chain and of the major compressive phases affecting the hinterland basins (Radicondoli-Volterra, Baccinello, Velona and Siena-Radicofani basins) well correlates with the periods of magmatic quiescence and with the compressive phases detected in the external sector of the Northern Apennines (Padan-Adriatic foredeep). The presented data allow us to propose that compressive tectonics played a major role in the recent evolution of the Northern Apennines. The mechanism envisaged to explain this tectonic framework has been related to the piggyback emplacement (from the internal toward the external areas) of basement thrusts, that occurred since Miocene. The emplacement of basement thrusts likely caused the reactivation of cover thrusts, giving rise to out-of-sequence thrusting and affecting the development and/or deformation of the hinterland basins. This tectono-sedimentary evolution based on field analysis fits well with the recent reinterpretations of a deep seismic profile (CROP 03 line) hypothesising that basin development was strictly related to crustal shortening. In this frame, the extensional structures have been interpreted either as second-order features accommodating thrusting or as related to the Middle Pliocene and Quaternary extensional phases during which fault-controlled basins locally developed.

Geochemistry of sheeted dikes in the nain ophiolite (central iran)

Abstract: The Nain ophiolite is a highly dismembered ophiolite complex cropping out at the north of the Nain town to the west of central Iran. The igneous rocks of this complex consist of both mantle and crustal suites and include serpentinized peridotites, peridotites, harzburgites associated with dunite and lherzolite, pegmatitic and isotropic gabbros, plagiogranites, sheeted dikes and pillow lavas. Several pyroxenite, wehrlite and rodingite dikes are present in the ultrabasic rocks. The sheeted dikes include subalkaline basalts, basaltic andesites and andesites. Their magma was of sub-alkaline (low potassium tholeiite) type and they are chemically similar to island arc tholeiitic basalts. The N-MORB-normalized incompatible elements for the sheeted dike samples indicate depletion in most of the high field strength elements (HFSE). The concentrations of the large ion lithophile elements (LILE) in these rocks are all greater than those in the N-MORB. Significant chemical characteristics of the these rocks are the positive anomaly for Th and negative anomaly of Nb that are considered to represent a subduction zone component. The chondrite-normalized rare earth element (REE) patterns of these rocks show HREE enrichment and LREE depletion [(LaN/SmN)ave = 0.63]. Their geochmistry also shows that the primary melt derived from high degrees of partial melting of a mantle source previously depleted with respect to the source of mid-ocean ridge basalts, and were subsequently enriched by aqueous fluids driven off subducted oceanic lithosphere in an arcbasin setting. We conclude that the Nain ophiolite is a supra-subduction zone type ophiolite.

THE PLAGIOGRANITE - FeTi-OXIDE GABBRO ASSOCIATION OF VERNE (MONVISO METAMORPHIC OPHIOLITE, WESTERN ALPS)

Abstract: The Verne plagiogranite-FeTi-oxide gabbro association is exposed in the southern Basal Serpentinite Unit of the Monviso meta-ophiolite and consists of a tabular body (about 400 x 250 m wide and 70 m thick) of jadeite - quartz - bearing massive metaplagiogranite in primary contact with omphacite - garnet - rutile ± glaucophane eclogite (recrystallized FeTi-oxide gabbro). Albite - quartz - bearing leucocratic layers within the metaplagiogranite body are interpreted as late-magmatic dikes. Despite Alpine re-crystallization under eclogite-facies conditions, both the FeTi-oxide gabbros and the plagiogranites retain most of their primary geochemical features. Composition of the Verne FeTi-oxide gabbros (average Mg# = 31.8) is very similar to those of FeTi-oxide metagabbros from other units of the Monviso meta-ophiolite. Their REE chondrite-normalized patterns are characterized by the typical MORB depletion in LREE; two samples are between 10 and 13 times chondrite and display rather flat patterns; one sample (also having the highest contents in Ce and Zr) is about 100 times chondrite and displays a negative Eu anomaly. The plagiogranites (64.20 < SiO2 < 65.90 wt%, 7.23 < Na2O < 8.28, average Mg# = 19.1) are leucocratic, Fe-rich quartz diorites; the plagiogranite dikes (SiO2 = 70.85 wt%, FeOtot = 3.37 wt% and average Mg# = 17.3) are more differentiated trondhjemite varieties. All plagiogranites are Zr-enriched rocks lying along a typical MORB differentiation trend. Their REE chondrite-normalized patterns are also typical of MORB, ranging between 20 and 500 times chondrite. All samples display a negative Eu anomaly, ranging from weak to strong. The Verne association represents late stages of the plutonic activity within ultramafic oceanic crust and its occurrence can be modelled by fractional crystallization of an evolved tholeiitic magma, possibly of oceanic andesite composition. After fractional crystallization of the FeTi-oxide gabbros, the remaining liquid has a composition similar to those of the plagiogranites, suggesting that these formed essentially from direct crystallization of such a residual liquid. The trondhjemite dikes, being the most differentiated liquids, were probably emplaced through deformation-controlled, late-stage melt migration in the nearsolidified crystal mush of the plagiogranite.

The metasiliciclastic-carbonate sequence of the acquadolce unit (eastern elba island): new petrographic data and paleogeographic interpretation

Abstract: The Acquadolce Unit (upper part of Trevisan’s Complex II) consists of a phyllitic-quartzitic succession with calcschist and metagraywacke intercalations and a serpentinite wedge at the top This unit was generally correlated to the Dogger-Eocene metasediments of the Tuscan Paleozoic-Jurassic succession of the Apuan Alps but, more recently, has been attributed to the Ligurian or Piedmontese Domain (eg the “Schistes Lustres” of the Gorgona Island) In this paper we present a detailed petrographic study of both the Acquadolce Unit and the Metasedimentary Unit of the Gorgona Island In particular, we found significant mineralogical analogies between the lithotypes and tectono-metamorphic imprint of the two successions The hypothesis that the Acquadolce Unit can be ascribed to a “Schistes Lustres”-type succession is also supported by the relatively high-pressure (probably >8kbar) estimated for the D1 deformation phase of the Acquadolce Unit from the K-white mica composition The Acquadolce Unit is attributed to the metamorphic Ligurian-Piedmontese successions, allowing a redefinition of the main geological boundaries in the Tuscan Archipelago

Petrology and origin of plagiogranites from the dağküplü (eski̇şehi̇r) ophiolite along the i̇zmi̇r-ankara-erzi̇ncan suture zone, turkey

Abstract: The Izmir-Ankara-Erzincan Suture Zone (IAESZ) formed through the closure of the northern branch of the Neotethyan Ocean that once separated the Sakarya Continent and the Anatolide-Tauride Platform and the subsequent collision of these two continental blocks during Late Cretaceous-Paleocene time. Mafic-ultramafic rocks representing oceanic lithosphere, metamorphic sole rocks, and ophiolitic melange comprising oceanic and continental fragments and continental margin metamorphic and sedimentary rocks are preserved along the IAESZ. A northward dipping subduction zone developed within the Izmir-Ankara-Erzincan Ocean, a northern branch of Neotethyan Ocean, in the Early Cretaceous. The suprasubduction zone (SSZ) ophiolites formed in this intra-oceanic setting. The Dagkuplu Ophiolite was, like other ophiolite nappes in the region, thrust over the southern Anatolide-Tauride Platform. The Dagkuplu Ophiolite, exhibiting an incomplete and inverted ophiolite suite, consists mostly of refractory peridotites (harzburgite and dunite) representing mantle unit and lesser dunite and wehrlite cumulates, pyroxenites, and massive-layered gabbros. The plagiogranite volumetrically constitutes about 10% of the entire ophiolitic rocks. Petrographic and geochemical data suggest that plagiogranites were generated from TiO2-poor cumulate gabbros by fractional crystallization at a suprasubduction zone spreading center.

The island of elba - northern tyrrhenian sea aeromagnetic and gravity data

Abstract: The magnetic maps of the northern Tyrrhenian Sea show anomalies belonging to bodies with high magnetic susceptibility, distributed according to a north-south trend over arcuate belts from the Elba area towards N-NW. A qualitative analysis of the anomalies shows that, among the high amplitude and short wave length anomalies, submarine ophiolites and/or volcanics occur. The high frequency anomalies connected with the ophiolites show a complex pattern, justified in the tectonic context of the area. Two main belts of ophiolites are identified: the inner (western) belt lies between the Corsica basin and the Capraia, Elba, and Pianosa islands; the external (eastern) one lies between the Gorgona, Elba islands and the Tuscan coast line. The volcanics consist of magmatic bodies (Miocene-Quaternary). Magnetic anomalies with longer wavelength, lower amplitude and low susceptibility are attributed to the magnetic basement. Based on the interpretation of the magnetic and gravity data, an appraisal of the tectonics of this area is presented, where both oceanic (ophiolites) and continental affinity crustal units occur, locally intruded by Pliocene granodioritic stocks. The main SW-NE discontinuities, crossing the Elba ridge and extending to onshore Tuscany, complete the structural framework of this sector of the Tyrrhenian Sea and the contiguous northern Apennine domain, as the result of the Mio-Pliocene and Pleistocene tectonics.

GEOCHEMICAL SIGNATURE AND GEODYNAMIC SIGNIFICANCE OF AN Ag-Hg MINERALIZED DYKE SWARM IN THE NEOPROTEROZOIC INLIER OF IMITER - ANTI-ATLAS (MOROCCO)

Abstract: The Cryogynian basement of the Imiter Inlier and its volcanic cover are crosscut by an important swarm of mafic and felsic dykes. In the volcanic series, the dykes are oriented N-S to N70°E and emplaced within a E-W tensional stress field, whereas in the basement they are parallel to pre-existing planes (S0//S1) which vary in trend from N70°E to N90°E. Silver mineralization is closely associated with mafic dykes that behaved as mechanical traps, either due to their brittle structural behaviour or by behaving as a barrier to fluid flow. Two petrogenetic groups have been recognised in dyke rocks: the first group consists of basalts and basaltic-andesites, the second one corresponds to andesites, quartz-microdiorites, and keratophyres. Both groups are calc-alkalic and display geochemical features comparable to those of magmatic rocks from modern active continental margins and island arcs: large ion lithophile (LIL) element enrichments, high field strength (HFS) element depletion, and weakly fractionated rare earth element (REE) (La/Yb)N = 3.7 to 6.6) patterns. Constraints of the regional geology suggest that these rocks were associated with post-orogenic, post-Panafrican rifting and preclude any subduction activity at that time. Their nature and their chemical signature can be related to: (i) the existence of fragments of an older subducted crust, (ii) partial melting of a mantle contaminated during the orogenic Panafrican stages or (iii) contamination during ascent of mantle derived magmas by African crust.

2 - elba island a - introduction

Abstract: The geology of the Elba Island is very interesting for its structural complexity, for the relationships between Mio- Pliocene magmatism and tectonics and for its location between Corsica and Northern Apennines. In fact, it is the southwesternmost outcrop of the Northern Apennines chain. The first tectono-sedimentary events come back to the Palaeozoic. In fact, in the Palaeozoic basement are clearly recorded the Hercynian and, probably, also the Caledonian events. The Alpine sedimentary succession began during the Triassic and its tectonic evolution begins in Late Cretaceous - Early Tertiary and goes on until Late Miocene - Pliocene. The compressive movements started with the consumption of the Mesozoic Western Tethys (Liguria-Piedmont Basin), went up to the collision of European (Corsica) and Adriatic (Tuscany Domain) margins (Abbate et al., 1980, Boccaletti et al., 1980; Bortolotti et al., 2001a), and terminated with the successive polyphase deformations, which originated the Apennine orogenic chain. Trevisan (1950), proposed a geological frame of the Elba I. which, successively slightly modified by Barberi et al. (1967; 1969), which has been the geological starting-point for all successive studies. This model divides the nappe pile of the Island into five Complexes. New stratigraphical and structural data modify this frame. The new scheme we propose (Bortolotti et al., 2001a), comprises nine tectonic units, built up of Tuscan (Adria continental margin), Ligurian and Liguria-Piedmont (Jurassic-Eocene oceanic domains) successions, piled up with a very complex frame. This frame is complicated by post-orogenic extensional events, that produced the thinning of the Tuscan crust that underlies the Elba Units, the uplift of the Moho and the birth and evolution of the Tyrrhenian Basin (Boccaletti et al., 1985; Bartole et al., 1991; Bartole, 1995 cum bibl.; Carmignani et al., 1995). To this phase is linked the emplacement of the monzogranitic bodies and the formation of ore deposits and skarns. These latter constitute one of the best known geological features of the Island (Marinelli, 1975; Serri et al., 1991; Tanelli, 1977; 1983 cum bibl.).

New data on the age of the simoni melange, northern mirdita ophiolite nappe, albania

Abstract: In the Albanian sector of the Dinaric-Hellenic Chain, the ophiolites have been subdivided into two parallel belts: the Western Belt (WB) and the Eastern Belt, due to their different stratigraphical, petrological and geochemical characteristics: WB represents oceanic lithosphere generated at a mid-oceanic ridge (MOR ophiolites), EB represents an oceanic basin developed over a subduction zone (SSZ ophiolites) (ISPGJ-IGJN, 1990; Beccaluva et al., 1994; Bortolotti et al., 1996, and bibl. therein). EB overthrust westwards WB. The radiolarian cherts (Kalur Cherts) covering the volcanites of both the successions have the same ages, comprised between latest Bajocian-early Bathonian (UAZones 5 of Baumgartner et al., 1995) and middle Callovian-early Oxfordian (UAZones 8) (Chiari et al., 2004, and bibl. therein). Thin levels of radiolarian cherts intercalated in the basalts of EB have late Bajocian to latest Bajocian-early Bathonian ages (UAZones 4-5) (Chiari et al., 1994 and Chiari et al., 2004). A “blocks in matrix-type” sedimentary melange, the Simoni Melange, unconformably covers both the successions, indistinctly lying on the radiolarian cherts or on the upper portions of the underlying volcanites (Bortolotti et al., 1996; Carosi et al., 1996). It grades upwards to the Firza Flysch (latest Tithonian-Valanginian age after Shallo 1991; Gardin et al., 1996), a pelagic sediment with frequent ophiolitebearing polimict pebbly sandstones and mudstone intercalations. The melange includes blocks of different sizes (up to several hundred meters) of continental derived (predominant) and ocean derived rocks, in a shaly matrix. It can be interpreted as “syn-orogenic....deposited after the inception of ophiolite deformation” (Bortolotti et al., 1996). The age of the melange was indirectly determined, being comprised between middle Callovian-early Oxfordian, the more recent age found at the top of the Kalur Cherts (Marcucci and Prela, 1996), and the latest Tithonian-early Berriasian?, found at the base of the Firza Flysch (Gardin et al., 1996). The aim of this note is to present new biostratigraphical data that define a more precise age of the Simoni Melange, dating a cherty-silty level found at the top of the Kalur Cherts near the Lumi i Zi (northern Albania).

2 - elba island - c - western elba

Abstract: This part of the field trip (Fig. 1) is devoted to observe the main geological feature of western Elba: i- Mt. Capanne intrusion, a monzogranitic magmatic body with associate dike swarms and microgranite masses and, ii- its thermometamorphic aureole consisting of several types of hornfels after the ophiolite succession.

3 - southern tuscany - c - eastern sector of the volterra basin

Abstract: The geological setting of Southern Tuscany, where the Volterra Basin is located, is due to two different tectonic phases. The first one, compressional, is linked to the convergence and collision between the Adriatic Microplate and the European Plate and occurred from the Late Cretaceous to the Early Miocene. The second one is consequence of the extensional tectonic regime active since the Early-Middle Miocene (Carmignani and Kligfield, 1990; Jolivet et al., 1990; Bertini et al., 1992; Carmignani et al., 1994; 1995; Elter and Sandrelli, 1995a; Baldi et al., 1995; Dal Mayer et al., 1996). According to Elter and Sandrelli (1995a; 1995b), the extensional phase included two main events. During the first one, late Burdigalian to early Tortonian in age, there was a rapid uplift of the lithosphere, thickened during both the Alpine and Apenninic orogeneses. The lithosphere never reached the temperature necessary to generate calc-alkaline magmas(600°-650°, Sonder et. al., 1987). This event, was accompanied by “II phase folds” with both east and west vergence, by the emplacement of the Cretaceous Ligurian Units directly on the Triassic evaporites (“Serie ridotta”: Signorini, 1949; Trevisan, 1955; Giannini et al., 1971; Bertini et al., 1992; Decandia et al., 1993) and by the deposition of the Epiligurian Units. During the second extensional event, which started in the late Tortonian, a “thermal re-equilibration” associated to generation of anatectic magmas initiated in a thinned continental crust characterized by a high thermal flow (Table 1 in Elter and Sandrelli, 1995a). The extensional regime led also to the formation of graben and half-graben basins where thick sedimentary successions were deposited. These basins are laterally separated by WSW-ESE transverse lineaments (transfer zones Fig. 1). A different hypothesis on the geodynamic evolution of Southern Tuscany, considers that the first compressional phase acted until the end of the Neogene. In such a case, the sedimentary basins of western Tuscany would have formed as piggy-back or thrust-top basins (Bonini et al., 1994; Boccaletti et al., 1994; Bonini and Moratti, 1995; Boccaletti et al., 1997). During the field trip, we will visit the Volterra Basin between Spicchiaiola and Pignano. This area is particularly important because it lies on the western margin of the Middle Tuscany Ridge and recorded most of the depositional events which occurred in Southern Tuscany from Late Miocene to Pliocene. The four stops will illustrate some of the relationships between tectonics and sedimentation: Stop 1 - Transition from Turolian (upper Tortonian) lacustrine deposits to lower Messinian marine deposits in distal areas of the basin. A transgression affected different formations, highlighting discontinuities and disconformities. Stop 2 - Gypsum deposits formed during the salinity crisis which affected the Mediterranean Sea at the end of early Messinian. A debris flow interrupts the continuity of these deposits, suggesting synsedimentary tectonic activity. Stop 3 - Limestone deposits tilted down near a fault which formed before the deposition of Lower Pliocene marine sediments. This fact documents activity of the border fault between Early Pliocene and late Messinian. This portion of the basin was uplifted during late Messinian and subsided again during Early Pliocene. Stop 4 - The marine deposits of the Early-Middle Pliocene, very well developed in the Mazzolla-Volterra area, where they reach a thickness of about 1200 m. In the western area of Spicchiaiola-Pignano the Pliocene succession is, instead, thin and discontinuous. This difference in thickness is due to a synsedimentary normal fault.