Comparative Analysis of the Sedimentary Cover Units of the Jurassic Western Tethys Ophiolites in the Northern Apennines and Western Alps (Italy): Processes of the Formation of Mass-Transport and Chaotic Deposits during Seafloor Spreading and Subduction Zone Tectonics

The Jurassic ophiolites in the Northern Apennines and the Western Alps represent fossil mid-ocean ridge (MOR) oceanic lithosphere that formed in the Mesozoic Ligurian-PiedmontOcean Basin (LPOB). Their sedimentary covers include chaotic rock units containing ophiolite-derived material. The processes of formation and the lithostratigraphic position of these chaotic units in theWestern Alps remain amatter of debate, unlike their counterparts in theNorthern Apennines. This is because of pervasive tectonic deformation and high-pressure metamorphism that affected their internal structure during collisional tectonics. A comparative analysis of these chaotic units in bothmountain belts reveals the nature of processes involved in their formation. Chaotic deposits of gravitational origin occur both below and above the extrusive sequences in the ophiolites. They represent synextensional, hyperconcentrated deposits associated with the seafloor-spreading evolution of the LPOB lithosphere during Middle and Late Jurassic times. Mass transport deposits (MTDs) occur as intercalations within turbiditic sequences above the ophiolites. They represent syncontractional submarine slides that occurred on frontal accretionary prism slopes during the Late Cretaceous-Paleocene closure of the LPOB. The results of our comparative analysis imply that (1) the structure-stratigraphy of the chaotic deposits and MTDsof theNorthernApennines can be used as a proxy to better identify their metamorphosed and highly deformed counterparts in the Western Alps, (2) sedimentological processes associatedwith slow-spreadingMORtectonics and accretionary prismdevelopment in convergentmargin tectonics contributed to the sediment budgets of the cover sequences, and (3) magmatic, tectonic, and sedimentological processes that occurred during the formation of the Jurassic oceanic lithosphere and its sedimentary cover in the LPOB were remarkably uniform and synchronous.

Automated summary

The chaotic rock units in the Northern Apennines and Western Alps, representing Jurassic ophiolites, were influenced by tectonic deformation and high-pressure metamorphism during formation, leading to debates on their lithostratigraphic position. A comparative analysis of these units revealed the nature of processes involved in their formation and suggested that they can be used as proxies for identifying metamorphosed counterparts. The sedimentological processes associated with slow-spreading MOR tectonics and accretionary prism development were found to contribute to sediment budgets, indicating uniform and synchronous processes in the formation of Jurassic oceanic lithosphere in the LPOB.