Integration of Thermal and Thermochronological Constraints in Thermal Modeling of Fold-and-Thrust Belts: The Case History of the Eastern Sicily Wedge
Lea Di Paolo¹, Luca Aldega², Maria Laura Balestrieri³, Sveva Corrado¹, and Valerio Olivetti¹
¹Dipartimento di Scienze Geologiche, Università degli Studi “Roma Tre”, Roma, Italy
²Dipartimento di Scienze della Terra, Sapienza Università di Roma, Roma, Italy
³C.N.R., Istituto di Geoscienze e Georisorse, Sezione Firenze, Firenze, Italy
The reconstruction of burial and exhumation history of sedimentary rocks provides important time-temperature constraints to unravel thrust belt dynamics. The used multidisciplinary approach, based on the integration of different thermal and thermo-chronological methodologies allowed us to decipher the maximum paleo-temperatures and the exhumation rates of the sedimentary successions constituting the Eastern Sicily fold-and-thrust belt.
Thermal and thermochronogical constraints indicate that the structural and stratigraphic Units constituting the Sicilian Orogen are divisible in two levels of thermal maturity: a less evolved level that records limited sedimentary burial and minor heating and a more evolved level tectonically buried and exhumed.
The lower level of thermal maturity is characterized by (1) R0 mixed layer illite-smectite with an illite content < 60% (%I in I-S), (2) vitrinite reflectance < 0.5% (VRo%), (3) vitrinite reflectance values derived from FTIR analysis < 0.5% (VRoeq. %) in the immature stage of hydrocarbon generation and early diagenetic conditions (Aldega et al., 2007; 2011; Corrado et al., 2009), (4) no resetting of apatite fission tracks and cooling ages higher than ca. 144 Ma.
This level of thermal maturity consists of sedimentary rocks belonging to the shallower structural units of the Sicilide accretionary prism and the Numidian Flysch foredeep, and of siliciclastic rocks of thrust-top and normal fault-controlled basins. Organic and inorganic thermal indicators records early diagenetic conditions and immature stage of hydrocarbon generation and suggest that sedimentary burial never exceeded 2 km.
The higher level of thermal maturity is characterized by (1) R1 and R3 mixed layer illite-smectite with an illite content in the range of 60-85%, (2) vitrinite reflectance values between 0.61 and 0.96%, (3) AFT ages ranging between 37 and 6 Ma totally or partially annealed (Thomson, 1994; Aldega et al., 2007; 2011; Corrado et al., 2009; Olivetti et al, 2010; Di Paolo et al., 2012). This level of thermal maturity includes rocks from the crystalline units and their sedimentary cover, the deepest structural units of the Sicilide accretionary prism and the Numidian Flysch foredeep and the Africa passive margin units. As opposed to rocks of the lower level of thermal maturity, all samples were affected during Oligocene-Miocene times, by maximum temperatures higher than the AFT total annealing temperature. Therefore, ages indicate time of cooling through the isotherm ~110°C dating the exhumation of previously tectonically buried successions. For the Peloritani Units, AFT are totally annealed with two clusters of ages. The older group shows an average age of 25 Ma pre-dating the early thrust top deposits and the younger group indicates ages (8 Ma) which post-date the early thrust-top deposits. U-Th/He ages constrain the last stage of exhumation recording the time of cooling through the isotherm ~70°C with values of 19 Ma for the first group of data and 3 Ma for the second one (Olivetti et al., 2010).
For the Sicilide units, AFT show a cooling age ranging between 21 and 17 Ma (Corrado et al., 2009). Burial modeling of the Africa passive margin units cropping out in the frontal part of the Apenninic-Maghrebian fold-and thrust belt, indicate a tectonic burial of 2.4-3.2 km during middle Miocene times and subsequent exhumation mainly in the Late Pliocene times (Di Paolo et al., 2012).
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Aldega, L., Corrado, S., Di Paolo, L., Somma, R., Maniscalco, R., and Balestrieri, M.L., 2011, Shallow burial and exhumation of the Peloritani Mts. (NE Sicily, Italy): Insight from paleothermal and structural indicators: Geological Society of America Bulletin, v. 123, p. 132-149.
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AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012