Research program
Integrated methodologies (organic matter dispersed in sediments, fluid inclusions, clay mineralogy and geochemistry, fission tracks and U-Th/He ages) to unravel the tectonic/sedimentary burial and exhumation in the southern Apennines (Calabria-Lucania border) and eastern Sicily (sedimentary fold-and-thrust belt)
University Co-ordinator
Università degli Studi di CAMERINO -
SCIENZE DELLA TERRA - CAMERINO(MC)
Research Unit Leader
Maria Chiara INVERNIZZI
Description
This research program is focused on the ophiolite-bearing Ligurids units, particularly on the Frido Unit, characterized by medium-low grade metamorphic rocks, and on the non-metamorphic North-Calabrian Unit that crops out along the Calabria-Lucania border. These units are the remnants of the oceanic accretionary wedge. The area of southern Lucania where ophiolite-bearing units outcrop extends from Latronico and Castelluccio Inferiore (western boundary) to S.Costantino Albanese and Terranova del Pollino (eastern boundary). It makes up the most of the uplands, which broadens north of the Pollino Mts, forming a wide belt parallel to the carbonate ridge (Schiattarella, 1998). Within the belt, cover units prevail (Frido Unit and Nord-Calabrese Unit, sensu Bonardi et al., 1988), although significative volumes of serpentinite bodies and associated metabasite are also present.The goals of this research can be summarized as follows:- acquisition of quantitative data on the thermal history of the units that crop out along the Calabria-Lucania border with the aim to evaluate tectonic/sedimentary loads and exhumation age for these units by means of the combined use of different methodologies such as: fluid inclusions, fission tracks and U-Th/He ages, clay mineralogy, and, subordinately, organic matter maturity in sediments (in collaboration with the Roma Tre Research Unit). In fact, the best way to determine the thermal history and the regional metamorphism patterns of sedimentary successions involved in the chain building is a multi-disciplinary approach.- Validation of the utilized methods through systematic comparison between different methodologies and, when possible, through data correlation (in collaboration with Roma Tre Research Unit). Reaching this goal involves the use of these data to calibrate thermo-structural evolution models of the analyzed successions using suitable software.- Comparison among structural, mineralogical, geochemical, and geo-chronological features, as well as tectonic/sedimentary loads and exhumation rates of "inner" and "outer" domains of the southern Apennines. In fact, the sector we are proposing to investigate is located in a more "internal" position than other areas already studied through similar methodologies.METHODOLOGIESTo achieve their goal, the Camerino Research Unit will make use of the following methodologies: DETAILED GEOLOGICAL MAPPING AND STRUCTURAL (by optical microscopy, SEM, catodoluminescence) aimed to the recognition and characterization of the main tectonic contacts; microstructural analysis of fault rocks.FLUID INCLUSION ANALYSIS (F.I.) Fluid inclusions can be used to ascertain temperature and pressure conditions of mineral precipitation within the rocks; they also allow reconstructing the composition and origin of the fluid content of the inclusion and the modifications of these parameters during deformation history. Homogenization temperatures (Th) and melting temperature (Tm) of the fluid, calculated by microthermometric analysis, provide information on the inclusion's fluid density (and minimum trapping temperature of the inclusion) and on fluid composition. During data acquisition, the implicit limits of this kind of study will be taken into account: F.I. reduced size, possible "reopening" of the system and consequent thermal re-equilibration, volume variation of inclusions; they are predictable especially when "soft" minerals like gypsum and calcite are concerned (Goldstein & Reynols, 1994). F.I. studies during this project will be mainly aimed to minerals in syn- and post-tectonic veins. For some of the samples we will make use of cathodoluminescence. This technique allows highlighting mineral zoning so that it can be related to data from microthermometry. In this way, possible trends, temperature, and composition variations of fluids can be detected. A better reconstruction of the thermal history of tectonic units will be therefore achievable. FISSION TRACK (F.T.) ANALYSISThe F.T. dating method is based on the spontaneous fission of 238U, which causes a linear imperfection (or track) in the crystal. The number of tracks is proportional to the accumulation time and to 238U abundance. During the cooling of the rock, the F.T. "clock" starts when the closure temperature is reached (the closure temperature is defined as the temperature at which 50% of the tracks are stable). The method is more frequently applied on apatite (Tc = 100±10°C) and zircon (Tc = 250±40°C). There is a temperature range in which a track size reduction occurs (partial annealing zone, PAZ). It spans from about 60 to 120°C for apatite. The measurement of fission tracks length in apatite supplies information on temperatures reached by the minerals and, more in general, on the thermal history. Therefore, it is possible to evaluate heating episodes or variations in the cooling rates. A quantitative study of these phenomena can be dealt with specific software that yields the time-temperatures evolution.- U-Th/He AGE ANALYSISThe U-Th/He thermo-chronological method represents a natural complement of the F.T. method. Recently, it has been demonstrated that the U-Th/He can represent a new thermo-chronometer that provides information even on lower temperatures (closure temperature in apatite is ca. 75±5°C). U-Th/He age analysis was one of the oldest radiometric methods tested for the absolute dating of rocks, but it's been discarded because of the very likely helium diffusion with increasing temperature. From laboratory helium diffusion experiments, we have that with increasing temperature helium ages show a similar pattern to the F.T. ages, but in a zone between 40° and 80°C. The two zones do not overlap; apatites may reside at temperatures where fission-tracks are stable while helium diffuses. Helium ages can significantly narrow the range of the possible thermal histories and can represent an independent control on the paths derived from F.T. length modeling or from other parameters.CLAY MINERALS ANALYSIS- Mineralogical analyses will be carried out by X-ray Diffraction (XRD). The estimation of the abundances of minerals in the bulk samples and in the less than 2 micron fraction will be obtained by means of SIROQUANT and LINKFIT software. A Scanning Electron Microscopy (SEM) will be also used to characterise some mineralogical phases better; - The prograde sequence of minerals usually observed to occur in regularly repeating sequences as a function of metamorphic grade (i.e. smectite -> illite/smectite (I/S) mixed layers -> illite -> muscovite and smectite-> chlorite/smectite (C/S) mixed layers ->chlorite), will be monitored by XRD and computer modelling. The NEWMOD software will be used; The clay minerals reaction progress will be measured by: a) Clay minerals crystallinity. It will be defined by XRD and will be calibrated on the Crystallinity Index Standards scale to avoid inter-laboratory problems; b) Illite polytypes and K-white mica b cell dimension. The former will be identified by XRD and the latter will be calculated from a regression equation by obtaining high quality Atomic Emission Microscopy (AEM) to avoid interference from detrital mica. Measurement of the b dimension by XRD technique using dioctahedral mica (060) reflections will also be performed; c) Size and strain measurement. Crystal size and strain measurements of clay minerals will be carried out by the W-A-B method of XRD peak profile analysis, modified and coded in the MADMASTER computer program;d) Chemical and isotopic composition. Major, trace, and rare earth elements will be detected by X-Ray Fluorescence and Neutron Activation. The radiogenic and stable isotopes (Nd, Pb and O isotopes and K/Ar and Rb/Sr) will be determined in the clay fraction.PHASES OF THE RESEARCHThis research will be divided into four phases:Phase 1 (Duration: 1 month) – Critical review of bibliography and available data Phase 2 (Duration: 4 months) - Geological-structural survey, mesostructural analysis, collection and stratigraphic signature of samplesThe sampling we are proposing is to be performed on different cover lithologies with different structural conditions along some discontinuous transects (given the outcropping conditions of the area and complex structural geometries); sampling areas fall within S. Severino Lucano, S. Costantino Albanese, and Viggianello topographic maps. The following terrains will be analyzed in detail:- the Frido Unit (like in Bonardi et al., 1988), made up of basic and ultrabasic rocks, metabasites, quartzites, slates, and calc-silicates; they comprise most of the reference section described by Vezzani (1969);- the Episcopia and San Severino tectonic mélanges, made up of ophiolitic rocks (serpentinite-rich blocks), and blocks of continental crust immersed in a serpentine-phyllosilicate matrix overlying the Frido Unit;- terrains from the North-Calabrian Units (Upper Jurassic-Upper Oligocene), tectonically overlying the Frido Unit; This is also an ophiolitic but not metamorphic suite, such as:a) Timpa delle Murge Formation, made up of a few meters of radiolarites and silica-rich shale; the passage to the overlying formation is marked by the appearance of quartzarenites within the shale;b) the Crete Nere Formation, made up of alternating layers of quartzarenites and dark, organic matter-rich, grey shale;c) the Saraceno Formation, made up of calcareous turbidites, often silicized, with the siliciclastic fraction increasing upwards, dated back to Upper Eocene-Upper Oligocene.Phase 3 (Duration: 12 months) – Sample preparation, Laboratory analyses, first interpretation of resultsSample preparation (double-polished sections), petrographic and microthermometric analyses on fluid inclusions, as well as microstructural and SEM investigations on fault rocks, will be carried out at the laboratories of the Department of Earth Sciences and at the "Centro Grandi Apparecchiature" of the Camerino University. For cathodoluminescence analysis the labs of the University of Paris XI (Orsayterre ) will instead be used; they are scientifically collaborating since a few months ago.Taking into account the investigated lithologies and tectonic units, we believe it is necessary to collect nearly 30 samples for the Calabria-Lucania border. Furthermore, ca. 10 samples will be analyzed, as a support to Roma Tre Research Unit for the study of a transect in eastern Sicily.Preparation and analysis of samples for fission tracks will be performed at the laboratory of the Earth and Geological/Environmental Sciences Department of the Bologna University. The irradiation phase will be carried out at the Union College Labs (Schenectady, NY, USA), which are already collaborating. Considering also the support of the Roma Tre Reserch Unit for this methodology (4 samples), we believe a total number of 20 samples would be suitable.From apatite concentrates of nearly 10 samples among those prepared in Bologna, we will select some inclusion-free grains and will determine their 4He content at the "Istituto di Geoscienze e Georisorse – CNR", in Pisa. Once collected, they will be analyzed by the ICP-MS of the Pisa University Earth Science Department for U and Th determination.Sample preparation and mineralogical analyses on bulk and <2 micron fractions by X-ray Diffraction (XRD) will be carried out mainly in the IMAA-CNR laboratories, in Tito Scalo, Potenza, and in the Mineralogy Dept., at the Natural History Museum (London, UK), with which there is an ongoing fruitful collaboration. Chemical analyses will be carried out in the X-Ral laboratories (Canada). A Scanning Electron Microscopy (SEM), available in the IMAA-CNR laboratories will also be used to characterize some mineralogical phases better. High-quality Atomic Emission Microscopy (AEM) analyses of mica, as well as measurements of the b dimension by XRD technique, using dioctahedral mica (060) reflections, will be also performed. Data interpretation will lead to the definition of low-grade metamorphic patterns. Chemical-isotopic composition (major, trace, rare earth elements, and Nd, Pb, O, K/Ar and Rb/Sr isotopes) of bulk and clay fractions will be detected by X-Ray Fluorescence and Neutron Activation in the above mentioned laboratories. About 100 samples will be selected for mineralogical analyses. After having performed the mineralogical characterization of these samples, we will select the most suitable samples for chemical-isotopic analyses.Furthermore, the Roma Tre Research Unit will perform organic matter maturity analysis on about 20 samples.Phase 4 (Duration: 5 months) – Comparison and integration of obtained data. Final elaboration of the thermo-structural evolution model of the studied sections. Synthesis for the Calabria-Lucania border and comparison to adjacent sectors. In this phase we will focus mainly on calibration by acquired data of thermostructural software-generated models. This will allow reconstructing the tectonic/sedimentary loads of the studied sections and times and rates of exhumation. In particular, fission tracks data modelling is a typical "inverse" problem, since the thermal history of each single analyzed sample is reconstructed in laboratory. In this phase we will use the AFTSolve computer program that accepts both data measured at the microscope (single crystal age, lengths) and geological constraints (stratigraphic age, present temperature, thermal events, etc.). The software uses the Monte Carlo algorithm to randomly generate "synthetic" thermal histories. After several thousand simulations, we choose the thermal history whose parameters (age, lengths) are statistically more similar to those measured at the microscope. The software also provides an evaluation of organic matter maturity, expressed as Ro. This evaluation is very useful since it allows a comparison with organic matter thermal maturity, generally well correlated to other inorganic indicators used in this research. For some significant sectors we will have the chance to collaborate with the Roma Tre Research Unit that will guarantee for the thermal-structural modelling through the Bmod-1D software.
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