Introduction
Reconstructing paths and rates of exhumation in orogens is one of the main goals in defining their kinematics. Traditional contributions to this topic have been provided by classical geochronological techniques when dealing with the inner portions of orogens. The advent of fission tracks studies since the early sixties allowed to date-enabled dating of the last portion of exhumation paths at shallow crustal levels thanks to low closure temperatures of zircon and apatite (respectively about 240 and 110°C). Furthermore, the improvement of knowledge about He diffusion in apatite allowed the development in the last 10 years of a new technique that provides quantitative constraints to the very final last path of exhumation down to 40°C. As a matter of fact, apatite fission track (AFT) and apatite (U–Th)/He [hereafter (AHe)] are the most widespread thermochronometers for investigating the tectonic and climate-driven interactions for durations of heating and cooling in excess of 106 years within the top few kilometers of the crust (e.g., Ehlers and Farley, 2003; Reiners and Brandon, 2006). These techniques are also widely used for investigating burial conditions in sedimentary basins in different tectonic settings and in the external portions of orogens (namely fold and thrust belts) that are, par excellence, the sites devoted to hydrocarbons genesis and accumulation, where maximum burial amounts (due to either sedimentary loading or overthusting) never exceed a few kilometers. In these settings, the reconstruction of burial and exhumation processes is a crucial issue for petroleum exploration. Low temperature thermochronology is then generally coupled with paleothermal indicators - as a combined approach can provide information on both time and extent of burial and cooling evolution. Among the existing paleothermal indicators, the most widespread is vitrinite reflectance that provides detailed resolution in diagenesis and very low grade metamorphism as it increases irreversibly with temperature and depth (Dow, 1977; Stach et al., 1982). Other organic matter thermal indicators derived from fluorescence colours and thermal alteration of palinomorphs (Staplin, 1969) and pyrolisis (Tissot and Espitalié, 1975) may be used to strengthen vitrinite data. Paleo-thermal indicators from clay mineralogical assemblages, measured by X-ray diffraction, such as Kübler Index (Kübler, 1967) and illite content in mixed layer illite-smectite (I-S) may be used for reconstructing maximum burials as well (Pollastro, 1993). Although each approach has its own advantages, in general clay mineral and organic maturity indicators are complementary or at least compensate each other where they cannot be applied singularly. The integration of vitrinite reflectance and illite content in I-S may provide important pieces of information on heating rates that cannot be provided by a single indicator (Hillier et al., 1995 for review; Aldega et al., in press for applications).
The main purpose of this paper is to provide, for the first time, an updated database of thermal and thermochonological indicators for the Italian Apennines fold-and thrust belt with special regard to sedimentary units (Figs. 1-5). It may represent a robust starting point for validating structural and geodynamic models that include modelling of the vertical movements within the orogen. This database, organized in ArcGIS platform, gathers most of the data from samples with known location and sampling coordinates, collected in the last fifteen years along four representative regional sections of the Apennines, with contributions provided in the eighties on organic thermal maturity in the Northern Apennines (Reutter, 1980; 1983; 1991). Other available mineralogical data used to detect diagenetic and low-grade metamorphic stages of different tectonic units in Northern (e.g., Leoni et al., 1996; Carosi et al., 1999; 2003, Dellisanti et al., 2008) and Southern Apennines (Perri et al., 2008) and in Sicily (Barbera et al., 2009) were not added in the database for the lack of sampling coordinates.
Figure 1. Distribution of paleo-thermal and thermo-chronological along the Apennines and Sicily
Digital Elevation Model of the Italian peninsula showing the distribution of vitrinite reflectance, Kübler Index, illite content in mixed layers I-S, apatite and zircon fission tracks and U/Th-He data along the Apennines and Sicily. Simplified main geological features from APAT (2004). Coordinates in UTM European Datum 1950 33N. Traces of cross-sections of Fig.6 are shown.
Figure 2. Distribution of organic matter thermal maturity data along the Apennines and Sicily
Digital Elevation Model of the Italian peninsula showing vitrinite reflectance data distribution along the Apennines and Sicily. Simplified main geological features from APAT (2004). Coordinates in UTM European Datum 1950 33N.
Figure 3. Distribution of illite content in mixed layers I-S along the Apennines and Sicily
Digital Elevation Model of the Italian peninsula showing the distribution of illite content in mixed layers I-S along the Apennines and Sicily. Simplified main geological features from APAT (2004). Coordinates in UTM European Datum 1950 33N.
Figure 4. Distribution of Kübler Index data along the Apennines
Digital Elevation Model of the Italian peninsula showing the distribution of Kübler Index data along the Apennines. Boxes define study areas which are not included in the database for the lack of sampling coordinates. Simplified main geological features from APAT (2004). Coordinates in UTM European Datum 1950 33N.
Figure 5. Distribution of thermo-chronological data along the Apennines and Sicily
Digital Elevation Model of the Italian peninsula showing the distribution of apatite and zircon fission tracks and U/Th-He dating along the Apennines and Sicily. Simplified main geological features from APAT (2004). Coordinates in UTM European Datum 1950 33N.