Abstract
Basaltic crust is present in the oceans and marginal seas. Oceanic accretion from inception to ending may be usefully recognized in small basin setting like the Tyrrhenian. Alternating episodes of strong and moderate extensional tectonics characterized the small Tyrrhenian opening. Hyperextension (drifting) of late-Miocene and latemost Pliocene age was followed by Pliocene and Late Quaternary moderate extension (rifting). Early hyperextension (~7.5–6.3 Ma) acted in the submerged margin of Hercynian Sardinia. Sardinia offshore, E-directed low-angle faults were accompanied by MORB-like volcanism of non linear shape in the shallow Vavilov plain - inherited segment of alpine-age orogen. Late hyperextension (~1.9–1.7 Ma) acted along the central N-S lineament of Vavilov plain, former metamorphic core complex. At the lineament northern side, E-dipping detachment faulting exposed serpentinized peridotite. At the other side, Vavilov volcano was faulted and its east flank tilted westwards. At the same time, volcanism with affinity to transitional MORB induced opening of Marsili basin. The drift episodes were characterized by absence or scarcity of volcanic activity on the conjugated emerged margins. The rift episodes (respectively ~5–1.9 Ma, and ~1/0.8 Ma-Recent) saw growth of major north-south trending volcanoes in bathyal area as intense volcanic activity developed on the continental margins.
Highlights
Oceans are thought to originate following continental rupture
Positive magnetization and foram assemblage of ooze directly overlying basement indicate that east-dipping detachment linked to mantle exposure occurred in the latemost Pliocene (LmP) - Olduvai subchron, ~1.9–~1.7 Ma
Regarding the nature of Tyrrhenian igneous basement, some authors[12] suggest that the area floored by peridotite is larger than that showing basalt compostion[6]. The former view may imply that Tyrrhenian opening was mainly forced by extensional tectonics and the latter by magmatic activity
Summary
The basalt - peridotite lineament of Vavilov plain. Regarding the nature of Tyrrhenian igneous basement, some authors[12] suggest that the area floored by peridotite is larger than that showing basalt compostion[6]. LmP hyperextension along the Vavilov plain tectonic line accompanied by rhyolitic volcanism from Palmarola might announce inception of Vavilov-Marsili basaltic crust rapid subsidence. Such event was preceded by basin formation linked to high-angle faulting affecting basaltic plain and margins’ continental crust. On the Sardinia margin, ODP Site 654 drilled lava flow interbedded in Pliocene-Quaternary sedimentary sequence[10] (Fig. 1) It is a basaltic andesite of LmP age, and is analogous to some subaerial Pliocene manifestations of intraplate affinity from Sardinia[29]. The anomalies associated with deep-seated basaltic crust have low intensity (up to 200 nT11) and shapes which are almost rounded or poorly elongated (diffusional spreading linked to strong extension and low-angle faults (the drillsites DSDP 373 and ODP 650; see inset -a- of Fig. 3). Vavilov seamount and the over-fed Marsili seamount may be considered to be a “sui-generis” southeastward migrated sequence of N-S oriented axes of spreading
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