The Tyrrhenian back－arc basin and subduction of the Ionian lithosphere

A deep, narrow, and distorted Benioff zone, plunging from the Ionian Sea towards the southern Tyrrhenian basin, is the remnant of a long and eastward migrating subduction of eastern Mediterranean lithosphere. From Oligocene to Recent, subduction generated the Western Mediterranean and the Tyrrhenian back-arc basins, as well as an accretionary wedge constituting the SouthernAoenninic Arc.In the Tyrrhenian Sea, stretching started in late Miocene and eventually produced two small oceanic areas: the Vavilov Plain during Pliocene (in the centralsector) and the Marsili Plain during Quaternary (in the southeastern sector). They are separated by a thicker crustal sector, called the Issel Bridge. Back-arc exten-sion was rapid and discontinuous, and affected a land locked area where continental elements of various sizesoccurred. Discontinuities in extension were mirrored bychanges in nature of the lithosphere scraped off to form the Southern Apenninic Arc. Part of the tectonic units of the southern Apennines, accreted into the wedge from late Miocene to Pliocene, had originally been laid down on thinned conti-nental lithosphere, which should constitute the deep portion of the present slab. After Plio-cene, only Ionian oceanic lithosphere wassubducted, because the large buoyancy of thewide and not thinned continental lithosphere of Apulia and Africa (Sicily) preserved the seelements from roll back of subduction. After Pliocene, the passively retreating oceanic slabhad to adjust and distort according to the geometry of these continental elements.The late onset of arc volcanism in respect to the duration of extension in the Tyrrhenian-Ionian system may find an expla-nation considering an initial stage of subduc-tion of thinned continental lithosphere. The strong Pleistocene vertical movements that occurred in the whole southeastern system(subsidence in the back-arc basin and upliftin the orogenic arc) may instead be related to the distortion of the oceanic slab.

Geophysical mapping of Vercelli Seamount： Implications for Miocene evolution of the Tyrrhenian back arc basin

Since the Tortonian, the geodynamic evolution of the Tyrrhenian Sea has been driven by an eastward roll-back of the entire Apennine subduction system, triggering distinct episodes of back-arc basin formation with spots of oceanic crust. Major structural differences are observed between northern and southern portions of the Tyrrhenian Sea, reflecting two distinct evolution stages of the Ionian slab retreat. In the central portion of the Tyrrhenian Sea, the seafloor morphology is characterized by a set of magmatic intrusions and structural highs associated to an Ee W magnetic lineament along the 41 st geographical parallel. The Vercelli seamount represents one example of structural highs correlated to Miocene magmatic episodes along the 41 st parallel zone. In this study, we discuss the results of new high resolution magnetic data and morphological mapping of the Vercelli seamount acquired during the VER2010 cruise. The seamount represents the relict part of a granitic intrusion emplaced during the Tortonian phase of Tyrrhenian rifting. Tectonic and deep-sea erosive processes have jointly modified the seamount structure that can be observed nowadays. Cumulative gradient analysis highlights an asymmetric morphology of the flanks as a result of erosive action of opposite water mass gyres which modelled the southern portion of the seamount. The joint interpretation of magnetic and bathymetric datasets identifies a high magnetized source laying close to the base of the seamount and located in correspondence to a small basin. This structure has been modelled as a post-Tortonian lava sequence emplaced between structural highs in correspondence of Ne S elongated flat sedimentary basin.Modelling of new geophysical data highlights the relationship between crustal setting and magnetic evidences of the central Tyrrhenian Sea, providing a new interpretation of the 41 st magnetic lineament.

Magnetic Theory and Applications in the Naples Bay (Southern Tyrrhenian Sea, Italy): Magnetic Anomaly Fields and Relationships with Morpho-Structural Lineaments

Magnetic theory and application to a complex volcanic area located in Southern Italy are here discussed showing the example of the Gulf of Naples, located at Southern Italy Tyrrhenian margin. A magnetic anomaly map of the Gulf of Naples has been constructed aimed at highlighting new knowledge on geophysics and volcanology of this area of the Eastern Tyrrhenian margin, characterized by a complex geophysical setting, strongly depending on sea bottom topography. The theoretical aspects of marine magnetometry and multibeam bathymetry have been discussed. Magnetic data processing included the correction of the data for the diurnal variation, the correction of the data for the offset and the leveling of the data as a function of the correction at the cross-points of the navigation lines. Multibeam and single-beam bathymetric data processing has been considered. Magnetic anomaly fields in the Naples Bay have been discussed through a detailed geological interpretation and correlated with main morpho-structural features recognized through morpho- bathymetric interpretation. Details of magnetic anomalies have been selected, represented and correlated with significant seismic profiles, recorded on the same navigation lines of magnetometry. They include the continental shelf offshore the Somma-Vesuvius volcanic complex, the outer shelf of the Gulf of Pozzuoli offshore the Phlegrean Fields volcanic complex, the relict volcanic banks of Pentapalummo, Nisida and Miseno, the Gaia volcanic bank on the Naples slope, the western slope of the Dohrn canyon, the Magnaghi canyon’s head and the magnetic anomalies among the Ischia and Procida islands.

The sedimentary dynamics of Sabellaria alveolata bioconstructions (Ostia,Tyrrhenian Sea, central Italy)

Sabellaria alveolata(Linnaeus 1767)is a polychaete able to build bioconstructions of different thickness,size and patchiness,in intertidal and subtidal environments.Its biological features have been the object of numerous studies worldwide.The worm reefs are formed by millions of tubes built by sand and shells(whole or in fragments)bonded together with a strong glue produced by the worm itself.Hence,Sabellaria alveolata represents a sedimentological asset for the coastal protection,since it contributes to create natural barriers against storm waves and erosion,and supplies the beach with new sandy deposits.This work shows a multidisciplinary approach to studying a bioconstruction of Sabellaria alveolata along the Latium coast(Ostia,Tyrrhenian Sea,central Italy),proposing image analysis as a novel technique to investigate worm reefs,along with classical sedimentological/ecological tools.The Sabellaria bioconstructions have been analysed at different scales of observation,suggesting the more appropriate strategies to develop a reliable model illustrating the different growth steps of these bioconstructions.

Shoreline evolution and modern beach sand composition along a coastal stretch of the Tyrrhenian Sea, southern Italy

This contribution focuses on a multidisciplinary research showing the geomorphological evolution and the beach sand composition of the Tyrrhenian shoreline between Capo Suvero promontory and Gizzeria Lido village(Calabria,southern Italy). The aim of the geomorphological analysis was to reconstruct the evolutionary shoreline stages and the present-day sedimentary dynamics along approximately 6 km of coastline. The results show a general trend of beach nourishment during the period 1870–2019. In this period, the maximum shoreline accretion value was estimated equal to + 900 m with an average rate of + 6.5 m/yr. Moreover, although the general evolutionary trend is characterized by a remarkable accretion, the geomorphological analysis highlighted continuous modifications of the beaches including erosion processes. The continuous beach modifications occurred mainly between 1953 and1983 and were caused mainly by human activity in the coastal areas and inside the hydrographic basins. The beach sand composition allowed an assessment of the mainland petrological sedimentary province and its dispersal pattern of the present coastal dynamics. Petrographic analysis of beach sands identified a lithic metamorphi-clastic petrofacies, characterized by abundant fine-grained schists and phyllites sourced from the crystalline terrains of the Coastal Range front and carried by the Savuto River. The sand is also composed of a mineral assemblage comparable to that of the Amato River provenance. In terms of framework detrital constituents of QFL(quartz:feldspars:aphanitic lithic fragments) and of essential extraclasts, such as granitoid:sedimentary:metamorphic phaneritic rock fragments(Rg:Rs:Rm), sand maturity changes moderately from backshore to shoreface, suggesting that transport processes had a little effect on sand maturity. Moreover, the modal composition suggests that the Capo Suvero promontory does not obstruct longshore sand transport from the north. Indeed, sands displaced by currents driven by storm-wave activity bypass this rocky headland.

Planktonic foraminifera as bio-indicators for monitoring the climatic changes that have occurred over the past 2000 years in the southeastern Tyrrhenian Sea

A high-resolution integrated study has been performed in a super-expanded marine record(sedimentation rate spanning from 11 cm/100 years to 20 cm/100 years)from the continental shelf area of the southeastern Tyrrhe­nian Sea.Planktonic foraminiferal distribution illustrates 6 major environmental changes during the past 2000 years:(i)the Roman Period-Dark Age transition(from herbivorous-opportunistic to carnivorous species);(ii)the Dark Age-MCA transition(from carnivorous to herbivorous-opportunistic species);(iii)the Medieval Clas­sic Anomaly-Little Ice Age transition(a further and definitive change from carnivorous to herbivorous-opportunistic species);(iv)the period during the Maunder event between approximately 1720 AD and 1740 AD(turnover from the carnivorous planktonic foraminifer Globigerinodes ruber to the herbivorous-opportunistic planktonic foraminifer Turborotalita quinqueloba);(v)the Industrial Period(dominance of herbivorous-opportunistic planktonic foraminifera);and(vi)the Modern Warm Period at approximately 1940 AD(the last turnover in favor of herbivorous-opportunistic planktonic foraminifers,associated with an increase in benthic foraminifera).Our studies lead us to link this latter feature to an anthropogenic impact associated with the dam­ming of Sele River(Salerno Gulf)at 1934 AD,which induced a change in the sediment input with a strong de­crease in coarse-grained fraction and a probable alteration in nutrient supply.Theδ^(18)O_(G.ruber) record of the past 2000 years shows the alternation of warm/wet and cold/dry events related to the Roman Period,the Dark Age,the Medieval Classic Anomaly,the Little Ice Age,the Industrial Period and the Modern Warm Period.The 5 ev­identδ^(18)O_(G.ruber) oscillations(between approximately 1325 AD and 1940 AD)coincide with the 5 minima in the solar activity record(Wolf,Spörer,Maunder,Dalton and Damon events).

西地中海的弧后盆地

地中海是太平洋之外弧后盆地较为发育的海区。巴利阿里海盆和第勒尼安海盆是西地中海两个位置相邻、互有成因联系的弧后盆地。海盆莫霍面埋深分别为 1 2～ 1 5km和 1 0 km,热流密度分别为 1 0 0 m W/m2和 2 0 0 m W/m2 ,发育有大洋型磁条带异常 ,大洋钻探和拖网取样均采到了拉斑玄武岩。较之巴利阿里海盆 ,第勒尼安海盆更富年青性。两弧后盆地的成生演化是与欧洲板块与非洲 -阿普利亚板块的相互作用息息相关的。中新世 ,随着非洲 -阿普利亚板块向西、西北俯冲 ,科西嘉、撒丁裂离欧洲大陆 ,巴利阿里海盆被打开 ;上新世 ,阿普利亚微板块进一步俯冲 ,导致亚平宁与科西嘉、撒丁之间的裂离 ,形成第勒尼安海盆。