A collaboration between researchers from the National Institute of Geophysics and Volcanology (INGV), Sapienza University of Rome, and the University of Roma Tre has made it possible to develop an innovative model to reconstruct the evolution of mountain ranges.

This is the finding of the study “Magnetic fabric as a marker of thermal maturity in sedimentary basins: A new approach for reconstructing the tectono‐thermal evolution of fold‐and‐ thrust‐belts”, recently published in the scientific journal ‘Tectonics’.

In order to establish the age and transformations of mountain ranges, geoscientists examine the thermal maturity of sediments, i.e. the heating to which the rocks and, in particular, certain indicators in them - such as clay minerals and wood chips - have been subjected over geological time.

“The thermal maturity of sediments reflects the degree of evolution of organic matter and the transformations of clay minerals during burial diagenesis”, says Chiara Caricchi, INGV researcher and first author of the paper. “Such thermal maturity is influenced by factors such as temperature and time, and is a fundamental concept for understanding the formation of energy resources such as oil and natural gas”.

Diagenesis is a geological process involving the chemical, physical and biological changes that sediments undergo after their deposition and before their lithification, i.e. their transformation into rock. This process takes place at relatively low temperatures (up to about 200 °C) and moderate pressures (2-3 bar) and can last millions of years.

The reliability of a reconstruction of the evolution of mountain ranges depends on the number of usable thermal indicators, which are not always available. Researchers from INGV, Sapienza and Roma Tre have identified a new potential indicator based on the geometric characteristics of the particles that make up a rock and their mutual orientation relationships. This information is obtained from a property, the so-called ‘anisotropy of magnetic susceptibility’ (AMS), which refers to the tendency of minerals to predominantly arrange themselves in planes perpendicular to the direction of deposition and subsequent sediment compaction. This process occurs when sediments are progressively covered by other, more recent deposits and then carried deep into the crust, where they are subjected to increasing temperatures and pressures, only to re-emerge on the surface during the formation of mountain ranges.

“Our analysis aims to answer the question ‘To what depth were the analysed sediments buried before being brought to the surface by the Apennine formation?’, i.e. ‘To what maximum temperatures were they subjected?’, explains Leonardo Sagnotti, INGV researcher and co-author of the paper. “The AMS is a property that is measured in paleomagnetism laboratories with dedicated instrumentation and relates the variability of magnetic susceptibility to the direction in which it is measured, which depends - in turn - on the preferential orientation of the minerals that make up the sediment”.

“Our study focused on the northern Apennines, in an area between Umbria and Tuscany, where we took samples of mutually consistent sediments for AMS and X-ray diffraction analyses”, adds Luca Aldega, researcher at Sapienza University of Rome and co-author of the paper. “The data from the analyses indicate that the AMS of these clay sediments can be put in direct correlation with deposition and compaction processes, as suggested by thermal maturity indicators, thus reflecting sediment evolution during sedimentary and/or tectonic burial”.

“This observation allowed us to calibrate a model based on a linear correlation between the AMS parameter and the palaeothermal indicators that can be successfully applied to define thermal maturity levels in sedimentary basins, overcoming the limitations of classical methods and constraining the diagenesis conditions of sedimentary successions on a time scale”, points out Massimo Mattei, a researcher at the University of Roma Tre and co-author of the paper.

Further future research in this direction may be useful to improve the definition of correlation in case of advanced stages of thermal maturity and highly deformed sedimentary successions.

References

C. Caricchi, L. Aldega, L. Sagnotti, F. Cifelli, S. Corrado, M. Mattei, Magnetic Fabric as a Marker of Thermal Maturity in Sedimentary Basins: A New Approach for Reconstructing the Tectono-Thermal Evolution of Fold-and-Thrust-Belts, Tectonics, Tectonics (2024) DOI: https://doi.org/10.1029/2024TC008530

Further Information

Luca Aldega

Department of Earth Sciences

luca.aldega@uniroma1.it