The regional contribution to the geo-neutrino signal at Gran Sasso National Laboratory (LNGS) was determined based on a detailed geological, geochemical and geophysical study of the region. U and Th abundances of the main lithotypes belonging to the Mesozoic and Cenozoic sedimentary cover were analyzed. Sedimentary rocks were grouped into four main "Reservoirs" based on similar paleogeographic conditions and mineralogy, leading to comparable U and Th contents. Basement rocks do not outcrop in the area. Thus U and Th in the Upper and Lower Crust of Valsugana and Ivrea-Verbano areas were analyzed. Irrespective of magmatic or metamorphic origin lithotypes were subdivided into a mafic and an acid reservoir, with comparable U and Th abundances. Based on geological and geophysical properties, relative abundances of the various reservoirs were calculated and used to obtain the weighted U and Th abundances for each of the three geological layers (Sedimentary Cover, Upper and Lower Crust). Using the available seismic profile as well as the stratigraphic records from a number of exploration wells, a 3D modelling was developed over an area of 2°x2°. This allows to determine the volume of the various geological layers and eventually integrate the Th and U contents of the whole crust beneath LNGS. On this base the local contribution to the geo-neutrino flux was calculated and added to the contribution given by the rest of the world, obtaining a Refined Reference Model prediction for the geoneutrino signal in the Borexino detector at LNGS: S(U) = (28.7 ± 3.9) TNU and S(Th) = (7.5 ± 1.0) TNU. An excess of about 4 TNU was previously obtained by Mantovani et al. (2004) based on general, worldwide assumptions. The considerable thickness of the sedimentary rocks, almost prevalently represented by carbonate, U- and Th-poor rocks is responsible for this difference. Thus the need of a detailed integrate geological study is underlined by this work, if the usefulness of geo-neutrino flux for the global U and Th distribution within the various Earth's layers (Crust, Mantle and Core) and tectonic settings wants to be thoroughly exploited.
U and Th content in the Central Apennines continental crust: a contribution to the determination of the geo-neutrinos flux at LNGS.
COLTORTI, Massimo;BORASO, Riccardo;MANTOVANI, Fabio;MORSILLI, Michele;FIORENTINI, Giovanni;RIVA, Alberto;TASSINARI, Renzo;CHUBAKOV, Viacheslav
2011
Abstract
The regional contribution to the geo-neutrino signal at Gran Sasso National Laboratory (LNGS) was determined based on a detailed geological, geochemical and geophysical study of the region. U and Th abundances of the main lithotypes belonging to the Mesozoic and Cenozoic sedimentary cover were analyzed. Sedimentary rocks were grouped into four main "Reservoirs" based on similar paleogeographic conditions and mineralogy, leading to comparable U and Th contents. Basement rocks do not outcrop in the area. Thus U and Th in the Upper and Lower Crust of Valsugana and Ivrea-Verbano areas were analyzed. Irrespective of magmatic or metamorphic origin lithotypes were subdivided into a mafic and an acid reservoir, with comparable U and Th abundances. Based on geological and geophysical properties, relative abundances of the various reservoirs were calculated and used to obtain the weighted U and Th abundances for each of the three geological layers (Sedimentary Cover, Upper and Lower Crust). Using the available seismic profile as well as the stratigraphic records from a number of exploration wells, a 3D modelling was developed over an area of 2°x2°. This allows to determine the volume of the various geological layers and eventually integrate the Th and U contents of the whole crust beneath LNGS. On this base the local contribution to the geo-neutrino flux was calculated and added to the contribution given by the rest of the world, obtaining a Refined Reference Model prediction for the geoneutrino signal in the Borexino detector at LNGS: S(U) = (28.7 ± 3.9) TNU and S(Th) = (7.5 ± 1.0) TNU. An excess of about 4 TNU was previously obtained by Mantovani et al. (2004) based on general, worldwide assumptions. The considerable thickness of the sedimentary rocks, almost prevalently represented by carbonate, U- and Th-poor rocks is responsible for this difference. Thus the need of a detailed integrate geological study is underlined by this work, if the usefulness of geo-neutrino flux for the global U and Th distribution within the various Earth's layers (Crust, Mantle and Core) and tectonic settings wants to be thoroughly exploited.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
