Rend. Online Soc. Geol. It., Suppl. n. 1 al Vol. 31 (2014)
© Società Geologica Italiana, Roma 2014
CONGRESSO SGI-SIMP 2014
Formation and accumulation of Messinian evaporites in the Caltanissetta Basin
(Sicily) by “supercritical out-salting”: reasons for a Tethys serpentinite connection
Carbone S.1, Scribano V.*1 & Manuella F.C.2
1. Dipartimento di Scienze Biologiche, Geologiche e Ambientali (DBGA), Università degli Studi di Catania. 2. Via Dell'Oro, 137 – Catania.
Corresponding email: scribano@unict.it
Keywords: Evaporite, Supercritical fluids, Serpentinites, Sicily.
Vai (2003) suggested that the area presently occupied by Sicily was a deep marine basin belonging to the ultra-slow
spreading Ionian-Tethys Ocean, Early Permian in age. The study of the Hyblean xenolith suite and the reappraisal of
geophysical data (Manuella et al., 2013) indicate that the unexposed basement of the Hyblean-Pelagian foreland
consists of serpentinized peridotites and minor gabbros, suggesting the existence of oceanic core complex structures
(Scribano et al., 2006). Accordingly, the abundance of serpentinites in the oceanic roots of Sicily and its offshore areas
hints at the presence of huge amounts of water and evaporite-like salts (probably about 10.5 kg of salts per m3 of
serpentinized peridotite) in the Tethys basement of Sicily, as a result of the seawater-driven serpentinization (Manuella,
2011). Regarding the Caltanissetta Depression, a thick succession of evaporites (Gessoso-Solfifera Group) was
deposited in a Miocene marine basin, during Messinian. The most popular climate evaporite theory suggests that deep
salt water basins, having restricted communication with the open ocean, dried out and filled up several times, forming a
thick sequence of salts. This explanation may be realistic for a salt thickness of few tens of meters (Hovland et al.,
2014). Differently, the Caltanissetta succession consists of 250 m of outcropping gypsum and carbonates and about
1000 m of buried chlorides. Therefore, we put forward the hypothesis that supercritical fluids, deriving from the
massive dehydration of serpentinites due to a geothermal rise, may have remobilized the buried Triassic evaporites as
saline brines (supercritical out-salting model; Hovland et al., 2014), during Messinian. These saturated brines were
emplaced as hot “geysers” forming hypersaline ponds at the sea bottom (Hovland et al., 2014), as presently observed in
the numerous deeps in the Red Sea floor.
Hovland M., Rueslatten H. & Johnsen H.K. 2014. Buried hydrothermal systems: the potential role of supercritical
water, “ScriW”, in various geological processes and occurrences in the sub-Surface. Am. J. Anal. Chem., 5, 128-139.
Manuella F.C. 2011. Vein mineral assemblage in partially serpentinized peridotite xenoliths from Hyblean Plateau
(Southeastern Sicily, Italy). Per. Mineral., 80, 247-266.
Manuella F.C., Carbone S., Brancato A. & Gresta S. 2013. A crustal–upper mantle model for southeastern Sicily (Italy)
from the integration of petrologic and geophysical data. J. Geodyn., 66, 92-102.
Scribano V., Sapienza G.T., Braga R. & Morten L. 2006. Gabbroic xenoliths in tuff-breccia pipes from the Hyblean
Plateau: insights into the nature and composition of the lower crust underneath Southeastern Sicily, Italy. Mineral.
Petrol., 86, 63-88.
Vai G. 2003. Development of the palaeogeography of Pangaea from Late Carboniferous to Early Permian. Palaeog.
Palaeocl. Palaeoecol., 196, 125-155.
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