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Manuella, F. C.
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Manuella, F. C.
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- PublicationRestrictedThe Hyblean xenolith suite (Sicily): an unexpected legacy of the Ionian–Tethys realm(2015-07)
; ; ; ; ;Manuella, F. C. ;Scribano, V.; University of Catania ;Carbone, S.; University of Catania ;Brancato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;; ; The extensive study of a great number of deep-seated xenoliths from Tortonian tuff-breccia pipes in the Hyblean area (Sicily) revealed the following fundamental evidence: (1) typical continental crust rocks are completely absent in the entire xenolith suite; (2) mantle ultramafics are more abundant than gabbroids; (3) sheared oxide–gabbros, closely resembling those from oceanic fracture zones, are relatively common; (4) secondary mineral assemblages, compatible with alteration processes in serpentinite-hosted hydrothermal systems, occur both in peridotites and gabbros. Among the products of this hydrothermal activity, organic compounds, having abiotic origin via Fischer–Tropsch synthesis, occur in some hydrothermally altered gabbro and ultramafic xenoliths, as well as in hydrothermal clays. Moreover, the U–Pb dating of hydrothermal zircon grains, hosted in a xenolith of metasomatized tectonic breccia, indicated an Early–Middle Triassic age of the fossil hydrothermal system. Another line of evidence for the oceanic nature of the Hyblean–Pelagian basement is the complete absence of continental crust lithologies (granites, felsic metaigneous, and metasedimentary rocks) in outcrops and in boreholes, and the oceanic affinity of the Tertiary volcanic rocks from the Hyblean Plateau and the Sicily Channel (Pantelleria and Linosa Islands), which lack of any geochemical signature for continental crust contamination. A reappraisal of existing geophysical data pointed out that serpentinites form the dominant lithologies in the lithospheric basement of the Hyblean–Pelagian area down to a mean depth of 19 km, which represents the regional Moho considered as the serpentinization front, marking the transition from serpentinites to unaltered peridotites. On these grounds, we confirm that Hyblean xenoliths contain mineralogical, compositional, and textural evidence for tectonic, magmatic, and hydrothermal processes indicating the existence of fossil oceanic core complexes, in the geotectonic framework of the Paleo–Mesozoic, ultra-slow spreading, Ionian–Tethys Ocean forming the present Ionian–Hyblean–Pelagian domain.276 58 - PublicationOpen AccessNew evidence for the serpentinization of the Palaeozoic basement of southeastern Sicily from joint 3-D seismic velocity and attenuation tomographyIn this study, we derived the first 3-D P-wave seismic attenuation images (QP) as well as new 3-D VP and VP/VS models for the crust in southeastern Sicily.We used a large data set of local seismic events occurring in the time span 1994–2013. The results of this tomographic study have important implications on the seismic behaviour of the region. Based on velocity and attenuation images, we identified distinct volumes characterized by different fluid content, which correlate well with seismicity distribution. Moreover, the obtained velocity and attenuation tomographies help us to provide a more complete picture of the crustal structure of the area. High VP, high QP and high VP/VS values have been obtained in the crustal basement, below a depth of 8 km, and may be interpreted as due to the presence of serpentinized peridotites. Accordingly, the new model for the degree of serpentinization, retrieved from VP values, shows that the basement has an average serpentinization value of 96 ± 3 vol.% at 8 km, decreasing to 44 ± 5 vol.% at about 18–20 km. Our joint interpretation of geophysical and petrophysical evidence suggests that the nature and composition of the Hyblean upper lithosphere may differ from accepted and longestablished geological models, which consider this lithospheric block a continuation of the Africa continental plate.
242 235 - PublicationRestrictedReply to “Comments on the paper “A crustal-upper mantle model for southeastern Sicily (Italy) from the integration of petrologic and geophysical data” by Manuella et al. (2013)”(2014)
; ; ; ; ;Manuella, F. C.; Dipartimento di Scienze Biologiche, Geologiche e Ambientali - Università di Catania ;Brancato, A.; Dipartimento di Scienze Biologiche, Geologiche e Ambientali - Università di Catania ;Carbone, S.; Dipartimento di Scienze Biologiche, Geologiche e Ambientali - Università di Catania ;Gresta, S.; Dipartimento di Scienze Biologiche, Geologiche e Ambientali - Università di Catania; ; ; We reply to the comments of Beccaluva et al. (2013) on the paper “A crustal-upper mantle model for southeastern Sicily (Italy) from the integration of petrologic and geophysical data” by Manuella et al.(2013). We entirely reject their speculative comments and strongly confirm our viewpoint on the aged oceanic nature of the lithospheric basement of southeastern Sicily and its offshore area.306 90 - PublicationRestrictedReply to “Comment on Manuella et al. ‘The Hyblean xenolith suite (Sicily): an unexpected legacy of the Ionian–Tethys realm’ by Beccaluva et al. (2015)”(2015-09)
; ; ; ; ;Manuella, F. C. ;Scribano, V.; University of Catania ;Carbone, S.; University of Catania ;Brancato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;; ; In our paper (Manuella et al. 2015), which arose from our 30-year-long research on the Hyblean xenoliths, we discussed an exhaustive dataset retrieved from the literature. We concluded that the unexposed basement of southeastern Sicily and neighboring areas consists of a remnant of the Paleo–Mesozoic Ionian–Tethyan oceanic lithosphere. Our viewpoint is opposite to the most popular theory that the Hyblean–Pelagian foreland domain is part of the Africa continental plate. We acknowledge some comments by Beccaluva et al. (2015) since they prompted us to explicit some background information given as implicit in our paper and hence to reaffirm with more emphasis fundamental aspects of our research, strongly confirming our previous conclusions.198 54