New constraints on the origin of the ophiolitic rocks within sinorogenic turbiditic sequences at Cilento region (southern Italy)

Mafic igneous rocks (pillow lavas and gabbros) embedded as olistoliths within Miocene turbiditic sequences crop out in the Cilento area at the Mount Centaurino (Campania region, Southern Italy). The concentration of major oxides, as well as trace element ratios (Nb/Yb, Nb/Ta, Th/Nb) and the chondrite-normalized Rare Earth Elements (REE) patterns suggest a tholeiitic character with Mid Oceanic Ridge Basalts (MORB) affinity. The chemical composition of pillow lavas is consistent with magmas generated by 10% degrees of non-modal fractional partial melting, of a spinel-bearing MORB-type asthenospheric mantle. Regarding gabbros, the calculated composition of parental melts in equilibrium with the clinopyroxenes show a wide compositional range, and there are very different from the pillow basalts of the Mount Centaurino, suggesting that the clinopyroxenes might have derived from more evolved melts compared to those that produced the basalts. The origin of these olistoliths is not yet understood. Here we suggest that these rocks represent fragment of a dismantled accretionary wedge embedded during the deposition of the Cilento group sedimentary successions in a thrust top basin

Dynamics of large pyroclastic currents inferred by the internal architecture of the Campanian Ignimbrite

Large ignimbrites are the product of devastating explosive eruptions that have repeatedly impacted climate and life on global scale. The assemblage of vertical and lateral lithofacies variations within an ignimbrite sheet, its internal architecture, may help to determine how the parental pyroclastic current evolves in time and space. The 39 ka Campanian Ignimbrite eruption, vented from Campi Flegrei caldera, laid down a thick ignimbrite over an area of thousands of km2. A detailed reconstruction of the vertical and lateral variation of the seven lithofacies recognised in the ignimbrite medial sequence constrains the behaviour of this event. The pyroclastic current flowed over a wide area around Campi Flegrei without depositing (bypass zone), and inundated a huge area during most of the paroxysmal, waxing phase, emplacing a mainly incipiently- to strongly- welded ignimbrite. Following this waxing phase, the leading edge of the current retreated back towards the source as the current waned, impacting a progressively smaller area and leaving an unconsolidated ash and lapilli deposit, later lithified. Our study illustrates how large pyroclastic currents can evolve in time and space and the importance of both internal (eruptive and transport mechanisms) and external (topography, surficial water and rain) factors in governing their behaviour

Eruption History and Depositional Processes of the Campanian Ignimbrite Based on its Lithofacies Architecture

Large ignimbrites are the product of high-temperature pyroclastic density currents (PDCs) spreading over vast regions and representing one of the most devastating natural catastrophes in human history. We present a detailed examination of the ignimbrite sequence, emplaced from 10 to 80 km from the source area, of the Campanian Ignimbrite (CI) eruption, a caldera-forming Plinian event, occurred 39 ka ago, whose PDC spread over a huge area from Campi Flegrei (Italy). The CI sequence comprises seven lithofacies based upon the different sedimentary structures: 1) massive tuff or lapilli tuff; 2) diffuse-stratified tuff; 3) fines-poor lithic lapilli tuff; 4) pumice-rich lapilli tuff; 5) lenses of pumice lapilli; 6) cross-stratified tuff; 7) accretionary lapilli-bearing. Three main vertical facies association have been identified: a) fines-poor lithic lapilli to diffuse stratified or massive or inverse graded; b) cross-stratified or diffuse stratified to massive or normal- to inverse-graded; c) massive to inverse graded. These vertical variations define a dominant trend during which the concentration into the boundary layer was progressively increasing, at a fixed point, and records the increasing importance of fluid-escape condition with time. Distribution of lithofacies in the different units shows a remarkable lack of lateral variation at regional scale. This suggests an overall uniform behavior of the PDC. A temporal evolution, from traction- to granular- or fluid-escape- dominated mechanisms, records unsteadiness conditions and contrast with persistent lateral facies reflecting an overall uniform behavior of the current. Stratigraphical and chemical evidences indicate the presence of a bypass zone around the caldera

New constraints on the origin of the ophiolitic rocks within sinorogenic turbiditic sequences at Cilento region (southern Italy)

Mafic igneous rocks (pillow lavas and gabbros) embedded as olistoliths within Miocene turbiditic sequences crop out in the Cilento area at the Mount Centaurino (Campania region, Southern Italy). The concentration of major oxides, as well as trace element ratios (Nb/Yb, Nb/Ta, Th/Nb) and the chondrite-normalized Rare Earth Elements (REE) patterns suggest a tholeiitic character with Mid Oceanic Ridge Basalts (MORB) affinity. The chemical composition of pillow lavas is consistent with magmas generated by 10% degrees of non-modal fractional partial melting, of a spinel-bearing MORB-type asthenospheric mantle. Regarding gabbros, the calculated composition of parental melts in equilibrium with the clinopyroxenes show a wide compositional range, and there are very different from the pillow basalts of the Mount Centaurino, suggesting that the clinopyroxenes might have derived from more evolved melts compared to those that produced the basalts. The origin of these olistoliths is not yet understood. Here we suggest that these rocks represent fragment of a dismantled accretionary wedge embedded during the deposition of the Cilento group sedimentary successions in a thrust top basin