Origin of Saponite-Rich Clays in A Fossil Serpentinite-Hosted Hydrothermal System in The Crustal Basement of The Hyblean Plateau (Sicily, Italy)

Abstract

A diapiric intrusion of clays in the Carlentini Formation (Tortonian) was discovered in a quarry at S. Demetrio High (Hyblean Plateau, Sicily, Italy). Seven clay samples were analyzed by different analytical methods, including X-ray powder diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, to determine the composition and mechanism of formation (sedimentary vs. hydrothermal) of these clays. Ferric saponite, carbonates (calcite and traces of ankerite), quartz, pyrite, and zeolites (phillipsite and harmotome) were detected using XRD and FTIR. This mineral assemblage, dominated by Fe-rich saponite, and the abundance of light rare-earth elements (LREE), Eu, fluid-mobile elements (FME > 10 × primordial mantle: Li, Be, B, As, Sb, Pb, U, Ba, Sr, Cs), and other incompatible elements (Zr = 169 ppm, Nb = 46 ppm, Th = 11 ppm, on average) imply that S. Demetrio clays precipitated from a mixture of hot Si-rich hydrothermal fluids (350–400°C) and cold seawater. The evidence is in accord with the affinity of clays for hydrothermally modified mafic and ultramafic rocks, forming the Hyblean lower crust, based on multi-element comparisons, and on the occurrence of trace amounts of chrysotile 2Mc1 and sepiolite. The association of long-chain aliphatic-aromatic hydrocarbons (intensity ratios I2927/I2957 > 0.5) with hydrothermal clays, the lack of fossils, and the similarity of the IR absorption bands with those of organic compounds detected previously in some metasomatized Hyblean gabbroic xenoliths suggest a possible abiogenic origin of hydrocarbons via a Fischer-Tropsch-type reaction. The S. Demetrio clay diapir was emplaced at shallow crustal levels in the Late Miocene as a consequence of the interaction, at a greater depth, of an uprising basalt magma and the products of an early, serpentinite-hosted hydrothermal system.

Asbestiform sepiolite coated by aliphatic hydrocarbons from Perletoa, Aosta Valley Region (Western Alps, Italy): characterization, genesis and possible hazards

“…8, magnification; Table 3), where no bands of sepiolite should appear. These bands are consistent with those sometimes observed in literature on gabbroid or serpentinized/carbonated mantlederived ultramafic xenoliths as well as saponite-rich clays originated from hydrothermal serpentinitic systems (Ciliberto et al, 2009;Sciré et al, 2011;Manuella et al, 2012) and attributed to (C-H) of saturated aliphatic hydrocarbons. Their presence can therefore be related to the organic film which fills the interstices among different fibres, possibly inducing the 'opening' of bigger parallelograms into thinner units as hinted by TEM (see Fig.…”

Metasomatizing effects of serpentinization-related hydrothermal fluids in abyssal peridotites: new contributions from Hyblean peridotite xenoliths (southeastern Sicily)

“…5b, c) are similar to those of abyssal serpentinites that underwent interactions with melts (MRI). However, the same patterns of Hyblean peridotites are close to those of hydrothermal sediments from the MAR (Dias and Barriga, 2006) A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 31 and St. Demetrio hill (northern Hyblean Plateau; Table A2; Manuella et al, 2012). This similarity suggests that the enrichment in LREE and other trace elements in Hyblean peridotites may be ascribed to a possible interaction with hydrothermal fluids, hence supporting the importance of serpentinization and related hydrothermalism in accordance with Frisby et al (2016a,b).…”

“…To achieve this objective, we have considered the complete dataset of 21 whole-rock analyses of Hyblean peridotites (Table A1), and compared them to hydrothermal clays from the St. Demetrio hill ( Fig. 1; Table A2; Manuella et al, 2012), abyssal peridotites (Paulick et al, 2006), and hydrothermal sediments from the MAR (Rainbow and Saldanha serpentinite-hosted vents; Dias and Barriga, 2006). We also report comparisons of trace element compositions of Hyblean serpentines with those of abyssal serpentines from the MAR and SWIR (Augustin et al, 2012;Frisby et al, 2016a,b;Kodolányi et al, 2012;Rouméjon et al, 2015), along with hydrothermal fluids from the Rainbow (36° 14′ N) and…”

“…The study of this stratigraphic succession allowed Manuella et al (2012) to discover a diapirical intrusion of hydrocarbon-bearing clays. The authors reported that these clays are mainly formed by Fe-rich saponite, with scarce amounts of chrysotile 2M c1 and sepiolite.…”

“…The authors reported that these clays are mainly formed by Fe-rich saponite, with scarce amounts of chrysotile 2M c1 and sepiolite. Based on mineralogical and geochemical data, Manuella et al (2012) concluded that the St. Demetrio clays, and the associated abiotic hydrocarbons, originated in an ancient hydrothermal system in the fossil oceanic basement of the Hyblean Plateau.…”