RICERCA ITALIANA     

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)

Università degli Studi Roma Tre

Abstract

The aim of this research program is to define the THERMAL EVOLUTION of some of the main tectonic units of the APENNINE-MAGHREBIAN OROGEN. They are exposed in the SOUTHERN APENNINE and EASTERN SICILY, and lie in different structural positions in the orogenic wedge. The investigations will put NEW QUANTITATIVE CONSTRAINTS to define a model of GEODYNAMIC EVOLUTION of the orogen.
The research will be focussed on the study of:
- sedimentary and metamorphic successions that are related to the Ligurian Complex exposed in the Southern Apennine, at the Calabria-Lucania border;
- the sedimentary portion of the fold-and-thrust belt that crops out in Eastern Sicily, from the inner Sicilide Units to the external units, and the related syn-sedimentary successions.
In detail, investigations will concern:
- the area to the North of the Pollino mountain chain (Calabria-Lucania border) on the Frido Unit, belonging to the metamorphic complex, and on the non-metamorphic North-Calabrian Unit; sampling transects will be located in areas comprised in S. Severino Lucano, S. Costantino Albanese, and Viggianello topographic maps.
- a North-South transect through the sedimentary fold-and-thrust belt in Eastern Sicily between S.Agata di Militello and Ramacca villages (from Nebrodi Mts. to the North, to Iblei Mts. to the South).
The proposed methodological approach is multisciplinary and was originally developed for hydrocarbon exploration purposes (BASIN ANALYSIS). Nevertheless, it has been recently adopted to solve structural issues in orogenic belts in order to provide constraints to define magnitudes and rates of orogenic shortening and exhumation.
This strategy will be applied to both study areas to create mono- and bi-dimensional THERMO-STRUCTURAL MODELS by means of software applications (e.g., Basin Mod1D, Get 1, and SEbe3, AFTsolve) that jointly elaborate data from stratigraphic-structural, thermometric, thermo-barometric, and thermo-chronologic databases. This objective will be achieved thanks to:
- Quantifying maximum sedimentary and/or tectonic load the studied successions underwent. This is obtained by using geothermometers based on the OPTICAL STUDY OF THE ORGANIC MATTER DISPERSED IN SEDIMENTS; X-RAY DIFFRACTION STUDY OF CLAY MINERALS -substantiated by SEM analysis- and FISSION TRACK STUDIES.
- Defining EXHUMATION RATES AND MAGNITUDES of exposed successions through the acquisition of thermo-chronological data based on FISSION TRACK ANALYSIS and U-Th/He DATING.
- Defining GEOMETRY AND KINEMATICS of main TECTONIC CONTACTS in the study areas. At the Calabria-Lucania border, one of the contacts is between the metamorphic Frido Unit and the non-metamorphic North-Calabrian Unit. In Eastern Sicily, other contacts we want to characterize are those realized by the overthrusting among different tectonic units. This will be achieved by FIELD GEOLOGICAL SURVEY and MESO- and MICRO-STRUCTURAL ANALYSIS. With this aim, we will widely perform MICROTHERMOMETRIC ANALYSIS OF FLUID INCLUSIONS in quartz and calcite (together with cathodoluminescence analysis). These crystals are from vein systems that will be investigated for geometric and kinematic significance.
Comparing STRUCTURAL, ORGANIC PETROGRAPHIC, MINERALOGICAL, GEOCHRONOLOGICAL, and subordinately GEOCHEMICAL (derived from chemical analysis by X-ray fluorescence; neutronic activation; and isotopic analysis of clay fraction) features of deep-sea units from internal domains to those of external domains of Southern Apennine and Eastern Sicily.
The whole data set will provide a synthetic model that accounts for the thermo-structural evolution in the Southern Apennine and Eastern Sicily. All the collected data will be compared and integrated with the data set available for the surrounding areas in order to define adequately the geodynamic evolution of this important sector of the Apennine-Maghrebian belt orogenic wedge. <<<

Principal Investigator

Sveva CORRADO Università degli Studi ROMA TRE

Research Objectives

This research program's PRIMARY GOAL is reconstructing and comparing the THERMAL EVOLUTION of sedimentary and low/medium metamorphic grade successions of the Liguride complex, exposed at the Calabria-Lucania border in southern Apennine, of the sedimentary portion of Eastern Sicily's fold-and-thrust belt, and of related syn-orogenic successions.
The goal will be achieved by creating THERMO-STRUCTURAL MODELS by means of software applications (e.g., Basin Mod1D, Get1, SEbe3, AFTSolve) that jointly elaborate data from stratigraphic-structural and paleo-thermometric databases. The knowledge from the study of the examined units' thermal evolution will be then integrated with that on the Apennine-Maghrebian orogenic system. This will allow to put new constraints for the definition of a geodynamical evolution model of the orogen.

The achievement of the primary goal will derive from the accomplishment of the following SPECIFIC OBJECTIVES:
1. Quantifying maximum BURIAL hence maximum SEDIMENTARY and/or TECTONIC LOAD the studied successions underwent. This is obtained by using geothermometers based on clay minerals, on maturity indicators of the organic matter dispersed in sediments and on fission tracks. These indicators allow constraining the burial maximum temperatures. In this context we will attempt a direct correlation. The parameters are: vitrinite reflectance (Ro%, Stach et al., 1982); Thermal Alteration Index (Staplin, 1969); composition of illite/smectite and clorite/smectite mixed layers (Pollastro, 1990; 1993); illite crystal size distributions(Crystal Size Distribution, CSD, Drits et al., 1998); clay minerals crystallinity index calibrated on the CIS scale (Crystalinity Index Standard scale), illite polytypes percentage distribution (1Md-1M-2M1; Austin et al, 1989), annealing degree in fission tracks (Gleadow et al., 1983).
2. Defining RATES and EXHUMATION PROCESSES of exposed successions through the acquisition of thermo-chronological data based on fission track analysis (Gleadow et al., 1983) and U-Th/He dating (House et al., 1999); they allow a detailed monitoring of the cooling history between different temperature intervals.
3. Defining GEOMETRIC and KINEMATIC RELATIONSHIPS among main tectonic-stratigraphic units in the two study areas through the study of their TECTONIC CONTACTS. They include the contacts between the low/medium metamorphic grade Frido Unit and the non-metamorphic north-Calabrian Unit at the Calabria-Lucania border, and those realized by the overthrusting of different tectonic-stratigraphic units in Eastern Sicily. This will be achieved by field geological survey and meso- and, to a lesser extent, micro-structural analysis. In this context, the THERMAL EVOLUTION OF TECTONIC UNITS will be quantified through microthermometric analysis of fluid inclusions in minerals (quartz and calcite). They derive from vein systems whose geometric and kinematic significance has been investigated (also through cathodoluminescence analysis). These analyses will be integrated with data selected from available maps in order to draw structural maps and viable sections.
4. COMPARING STRUCTURAL, PETROGRAPHIC, ORGANIC, MINERALOGICAL, GEOCHRONOLOGICAL, and subordinately GEOCHEMICAL features of deep-sea units pertaining to internal domains to those of more external domains of southern Apennine and Eastern Sicily.

In summary, this research project aims to the INTEGRATION OF DIFFERENT EARTH SCIENCES DISCIPLINES and METHODOLOGIES that converge into BASIN ANALYSIS. This is an essential strategy for tackling a complex scientific issue like the structuring of the Apennine-Maghrebian orogen in southern Italy. The aim is also to point out the need of a global vision of geological processes both at regional and worldwide scale. This will lead to the creation of a reference "basin maturity chart" for the studied areas and, in general, for the study of sedimentary basins involved in the structuring of an orogen. Finally, quantifying paleo-thermal features and better defining geometric and kinematic features in southern Italy - releasing the results to the scientific community - will provide an important contribution to petroleum exploration in Italy.

Cited references
Austin G.S., Glass H.D. & Hughes R.E., 1989. Resolution of the polytype structure of some illitic clay minerals that appear to be 1Md. Clay and Clay Minerals, 37, 128-134.
Drits, V.A., Eberl, D.D., & Srodon, J., 1998. XRD measurement of mean thickness, thickness distribution and strain for illite and illite/smectite crystallites by the Bertaut-Warren-Averbach techniques. Clay and Clay Minerals, 46, 38-50.
Gleadow A.J.W., Duddy I.R. & Lovering J.F., 1983. Fission track analysis: a new tool for the evaluation of thermal histories and hydrocarbon potential. Austral. Petrol. Expl. Ass. J., 23, 93-102.
House M.A., Farley K.A. & Kohn B.P., 1999. An empirical test of diffusion in apatite: borehole data from the Otway basin, Australia. Earth Planet. Sci. Lett., 170, 463-474.
Pollastro R.M., 1990. The illite/smectite geothermometer - concepts, methodology and application to basin history and hydrocarbon generation. In Nuccio, F., Barker, C.E., eds., "Application of thermal maturity studies to energy exploration". SEPM Rocky Mountains section 1-18.
Pollastro, R.M., 1993. Considerations and applications of the illite/smectite geothermometer in hydrocarbon-bearing rocks of Miocene to Mississippian age. Clays and Clay Minerals, 41, 119-133.
Stach, E., Mackowsky, M.-Th., Teichmüller, M., Taylor, G.H., Chandra, D., Teichmüller, R., Murchinson, D.G., Taylor, G.H., Zierke, F., 1982. Stach's Textbook of Coal Petrology. Berlin Gebrüder Borntraeger.
Staplin F. 1969. Sedimentary organic matter, organic metamorphism and oil and gas occurrence. Bull. Can. Petr. Geol., 17, 47-66. <<<

First Results

Assessment of available data; further focusing on:
- open issues;
- major interest areas for the geological-structural investigation and sampling.Expected partial results for this phase of the project are:
• definition of geometric and kinematical features of the main structural elements delimitating the different investigated stratigraphic-structural units;
• preliminary elaboration of new meso-structural data acquired along the tectonic contacts and their integration to available databases;
• construction of preliminary geological-structural sketches and maps and geological sections;
• stratigraphic-structural samples contextualization.At the end of this phase laboratory analysis results will be available. Analytical tables, plots and - when needed - photos will be produced. The following specific papers will be also provided:
- frequency histograms of fluid inclusions microthermometry, subdivided by tectonic unit and deformation event; Tm/Th diagrams for identifying inclusions populations containing different fluids;
- Ro% frequency histograms and correlation table between Ro% and T.A.I. data;
- XRD patterns; illite crystal size distribution frequency diagrams and correlation tables of different mineralogical parameters;
- time-temperature paths and distribution of fission tracks lengths in the different investigated units;
- updates to the sediment's thermal evolution indicators database.In this phase we will integrate the results from different fields within a single, synthetic evolutionary scheme. In particular, the expected results are the following:
1. Correlation scheme of organic matter maturity data, clay mineralogy, fission tracks, U-Th/He dating and fluid inclusions, geochemical data.
2. Thermo-structural evolutionary models of studied successions calibrated by thermal evolution parameters (time vs. depth, thermal maturity vs. depth diagrams etc.).
3. Geological-structural sections (for significant time stages), including the reconstruction of the tectonic and/or sedimentary loads evolution and analytical thermal evolution data, for Eastern Sicily.
4. Geological-structural schemes of the two investigated areas, including the distribution of analytical data, the tectonic/sedimentary loads values, and the magnitudes and rates of exhumation.
5. Mainly methodological, and to a lesser extent, regional publications on national and international journals. <<<

Timescale

24 months

National and international background

In the last 30 years, the thermal and burial history quantitative reconstruction of sedimentary successions that make up fold-and-thrust belts represents one of the major goals in the interdisciplinary researches of basin analysis (Allen & Allen, 1993 and references therein, Dorè et al., 1993). This type of research includes the integration of stratigraphic, structural, petrographic, and petrophysic data (for example, thickness of sedimentary successions and distribution of lithofacies, style and kinematics of deformation, composition and geotechnical features of lithotypes) (Van Hinte, 1978) with thermal evolution data from both inorganic fraction analysis (e.g., fission tracks, fluid inclusions, clay mineralogy and geochemistry, U-Th/He dating) and of the sediment's organic fraction (e.g., organic matter maturity) (Sholle & Schluger, 1979). Since the early 70s, using multidisciplinary databases of this kind, researchers proposed a number of modelling strategies for sedimentary sequences of undeformed basins; this also encouraged the study of thermal regime perturbations occurring in sedimentary units involved in orogenic processes (Lerche, 1990). In the beginning, these researches produced one-dimensional models (Furlong & Edman, 1984; Oxburgh & Turcotte, 1974); later, more refined two-dimensional models were created (Endignoux & Wolf, 1990; Shi & Wang, 1987; Grigo & Schmalholz, 2003) that also allow defining the entity of the tectonic and sedimentary load and determining the history of exhumation in chain areas (e.g., Zattin et al. 2000 and references therein). Therefore, on one hand, the improvement of subsurface seismic exploration technology and of rock deformation systems modelling led to a better quality in reconstructing the processes on the whole crust scale. On the other hand, basin analysis techniques - developed especially under the urge of oil exploration (Tissot & Welte, 1978; Gauter, 1986), are today a powerful tool for understanding geological structures and for reconstructing rock bodies once in the chain and now removed by erosion and/or tectonics. Thanks to these methods, the above-surface portions of geological sections, once usually drawn as dashed lines, have now become more consistent. However, we have to point out that the application limits of each technique show the importance of calibration and integration among these different methods; many international research groups have been working in this direction for years (Heroux et al., 1979, Green et al., 1986, Naeser & McCulloh, 1988, Hurford, 1990).

In recent years, this integrated approach has been successfully applied in some sectors of the Italian peninsula, particularly on the Apennine-Maghrebian orogen (among others: Failla & Mezzetti, 1987; Reinhardt, 1990; Corrado, 1995; Di Bucci et al., 1996; Corrado et al., 1998; 2002; 2003; Abbate et al. 1999; Zattin et al. 2000; 2002; Ventura et al., 2001; Cerrina Feroni et al., 2001; Aldega et al. 2003a, b; Balestrieri et al., 2003; Botti et al., 2003; Calamita et al., 2003). These studies provided the foundation for defining orogenic shortening magnitude and rates and the amount of exhumation in large sectors of the chain. They also contributed to the definition of the orogenic wedge's geometry time evolution. Anyway, few are the contributions where more than a couple of thermal parameters have been used. They have also been used for different purposes than those we are proposing. For example, clay mineralogy has been adopted for defining correlations between compositional variations and geotechnical parameters (Amicarelli et al., 1977; Burragato et al., 1986), for climate evolution studies (Mattias et al., 1992; Balenzano et al., 1993), and for assessing the pre-orogenic setting of sedimentary basins (Belviso et al., 1977; Mostardini et al., 1988; Cavalcante et al., 2001). Only in south-central Apennines clay mineralogy has been used to obtain not only paleo-environmental but also diagenetic indicators. Mineralogical changes linked to progressive burial allowed reconstructing the thermal history of well known sedimentary sequences exposed in the chain and to constrain the magnitude of tectonic loads they underwent in the past (Di Bucci et al., 1996; Corrado et al., 1998; Schiattarella et al., 2003). On the other hand, the study of organic matter has been since now aimed to the definition of the oil potential of some strategic sector (e.g., Reutter et al., 1983; 1991; Mostardini et al. 1988; Scotti, 2003); to a lesser extent only, it has been used to solve strictly geological-structural issues (e.g., Botti et al., in press; Cerrina Feroni et al., 2001). The study of fission tracks concentrated essentially on the northern portion of the Apennine (Abbate et al. 1999; Zattin et al. 2000; 2002; Ventura et al., 2001), although some notable results are available for the Calabrian arc (Thomson, 1998; Rossetti et al., 2001).
In summary, for what concerns the Apenninic sector (Calabrian arc aside), data about exposed units emphasize a higher degree of sediment thermal evolution in northern and southern Apennine than in the central. Moving across vertical sections, from lower to higher structural units and from inner to outer zones, a general reduction of thermal maturity is observable in the Northern Apennines (Reutter et al., 1983; Zattin et al. 2000), though several local anomalies are present (Reutter et al., 1991; Botti et al., 2003). Data about Central Apennines are less abundant (Corrado, 1995; Corrado et al., 2003; Calamita et al., 2003) and suggest lower tectonic load and subsequent exhumation. Southern Apennine's data are limited to the Lucanian area of the chain and indicate a high thermal maturity of Lagonegro successions (Aldega et al., 2003a); lower readings are evident in the more internal Apennine carbonate platform (Aldega et al., 2003b), whereas the buried Apulian carbonate platform shows varying figures from surface (Corrado et al., 2002) and subsurface (Scotti, 2003) data.
Therefore, for most of the southern Apennine and Sicily, we do not have an abundant quantity of data about thermal evolution of sediments and low-medium metamorphic rocks.
On the other hand, the large amount of available geophysical, stratigraphic, and deep well data, allowed to thoroughly define the age and geometry of the orogenic system. Hence it was possible to reconstruct the tectonic evolution of the external portion of the chain (Patacca et al., 1990; Carbone et al., 1991; Hippolyte et al., 1994, 1995; Cello & Mazzoli, 1998; Monaco et al., 1998; Menardi Noguera & Rea, 2000; Ghisetti & Vezzani, 2002; Catalano et al., 1996; Bello et al., 2000; Lentini et al.; 1994; 1996; 2000; Doglioni et al., 1999; Patacca & Scandone, 2001). These studies proved the existence of a complex thrust system with variable senses of transport ranging from northeast to south. The coeval evolution of differential uplifts and of modes and rates of exhumation is partially documented, at least in southern Apennine (Rossetti et al., 2001 and references therein; Aldega et al., 2003a; Schiattarella et al., 2003 and references therein). However, the data have not been yet integrated in a coherent pattern from inner to outer sectors of the chain. In these terms, acquiring new knowledge about thermal evolution of units involved in the structuring of the chain appears essential to the creation of a unique evolutionary model. But some issues are still strongly disputed, including the evaluation of orogenic shortening magnitudes and deformation rates; the paleogeographic reconstructions depicting the pre-orogenic stage those models imply and the evaluation of the subsequent exhumation are also central topics of the scientific debate.

In this context, a crucial point in southern Apennine is the need of refining the information on the internal units exhumation's starting times and on the evaluation of its magnitude. In fact, a syn-convergence exhumation hypothesis is well accepted (Wallis et al., 1993; Knott, 1994). It implies the application of a tectonic exhumation model based on extension in a sub-critical triangular wedge with uniform dip (Platt, 1986). Nevertheless, its occurrence in a pre- or syn-collisional moment is strongly debated. Some authors (Wallis et al., 1993; Knott, 1994) suggest it happened at an early stage, during the pre-collision phase (Upper Eocene?), whereas Mazzoli (1998) prefers an exhumation associated to syn-collisional extension. Bonardi et al. (1993) join the debate, starting from new data on the Frido Formation's top (Upper Oligocene). This implies to shift the exhumation to younger ages, in agreement to Rossetti et al. (2001), who state the exhumation of high-pressure and low-temperature rocks have occurred between 30 and 14 m.y..
The Ligurides exposed at the Calabria-Lucania border, that lies north of the Pollino chain, form a belt parallel to the carbonate mountain range (Schiattarella, 1998). They are well suited for a contribution to this debate based on the multidisciplinary approach we are proposing. Ligurian rocks -once constituting the oceanic accretionary prism- can be separated into two groups, each pertaining to a different tectono-metamorphic unit (Cello & Mazzoli, 1998). The first is made of ophiolite-bearing metamorphic rocks and match up mainly to the Frido Fm., as shown in Amodio-Morelli et al. (1976). The second is represented by ophiolitic non-metamorphic rocks mostly matching to the North-Calabrian Unit of Bonardi et al. (1988) and to the Calabrian-Lucanian Flysch unit defined by Monaco et al. (1991). At the Calabria-Lucania border the Frido Formation and the North-Calabrian Unit predominate. Outcrops of serpentine-rich bodies and the associated metabasites are in many places volumetrically significant. During Miocene, the Ligurides overthrust the carbonate platform units (Campania-Lucania or Apenninic Platform). They normally are the geometrically highest units of the southern Apennine's fold-and-thrust belt. Anyway, shallow water Mesozoic carbonates are locally thrust out-of-sequence on Ligurian Units, as along the northern front of the Pollino chain (Schiattarella, 1998). Plio-Quaternary brittle tectonics is, finally, responsible for the dissecting of the different units at the Calabria-Lucania border (Schiattarella, 1998 and references therein; Cello & Mazzoli, 1998), whose structural setting appears therefore much complicated.

Finally, for what concerns the Sicilian orogen, the research will focus only on the sedimentary chain portion exposed in Eastern Sicily. The complete structure is made up of the Calabrian-Peloritan arc's southern tip, the sedimentary fold-and-thrust belt, the foredeep, and the Iblean Plateau. They formed between Eocene and Quaternary during the Alpine orogenesis. But just in Eastern Sicily we can find optimal exposures for monitoring the tectonic and/or sedimentary burial history along regional transects. Here it is possible to observe an orogen's typical tectono-stratigraphic units, from the more internal to the more external ones. This portion of the chain is made of south-verging thrust sheets made up of different Meso-Cenozoic stratigraphic successions. They are deposited along the African paleomargin. The Sicilide Complex, from internal zones, is associated to those units. In the northernmost portions (Nebrodi Mts.) it outcrops as extensive thrust sheets. It has been observed far to the south in strong allochthony. These successions are generally overlain by younger siliciclastic deposits of diverse geodynamical meaning (Catalano et al., 1996). In brief, two main contractional deformation phases are responsible for the main geometries of the chain (Bello et al., 2000): the first took place between Upper Oligocene and Lower Miocene when the development of low-angle thrusts caused the overlapping of the allochthonous units on the Iblean Unit; the second phase dates back to Upper Miocene-Pliocene and involved the Iblean Unit. It completely modified the allochthonous unit's geometry by the simultaneous formation of minor thrusts and back-thrusts within them. They generated the structural depressions that form the syn-tectonic basins.
So the thrust sheets geometry is accompanied by the deposition of large syn- and post-orogenic siliciclastic successions, which provides the timing of the deformation's progression toward the foreland. Orogenic geometries (Carbone et al., 1991; Lentini et al., 1994; 2000) and the derived pre-orogenic paleogeographic reconstructions suggest the presence of remarkable tectonic cover, now totally or partially eroded; the cover was achieved by the overthrusting of more internal units -which show high orogenic shortening and contractional deformation rate- on outer ones (e.g. Monte Judica Unit).
Such features make this region an anomalous case if compared to other orogenic belts in the world (e.g., Tozer et al., 2002) and to other sectors of the Apennine (e.g., Butler et al., in press). Furthermore, the otherwise rich and detailed geologic literature about the subject shows some ambiguities about the quantification of the two aspects; the uncertainty is inherent to the classical approach generally used in the study of the area (Bianchi et al., 1987). The proposed research is based on the application of the integrated basin analysis approach. This will provide independent and additional constraints to validate existing geometric and kinematic models. <<<