Crustal thinning in the northern Tyrrhenian Rift: Insights from multichannel and wide‐angle seismic data across the basin

Abstract

Extension of the continental lithosphere leads to the formation of rift basins or rifted continental margins if breakup occurs. Seismic investigations have repeatedly shown that conjugate margins have asymmetric tectonic structures and different amount of extension and crustal thinning. Here we compare two coincident wide-angle and multichannel seismic profiles across the northern Tyrrhenian rift system sampling crust that underwent different stages of extension from north to south and from the flanks to the basin center. Tomographic inversion reveals that the crust has thinned homogeneously from~24 km tõ 17 km between the Corsica Margin and the Latium Margin implying a β factor of~1.3-1.5. On the transect 80 km to the south, the crust thinned from~24 km beneath Sardinia to a maximum of~11 km in the eastern region near the Campania Margin ( β factor of~2.2). The increased crustal thinning is accompanied by a zone of reduced velocities in the upper crust that expands progressively toward the southeast. We interpret that the velocity reduction is related to rock fracturing caused by a higher degree of brittle faulting, as observed on multichannel seismic images. Locally, basalt flows are imaged intruding sediment in this zone, and heat flow values locally exceed 100 mW/m 2 . Velocities within the entire crust range 4.0-6.7 km/s, which are typical for continental rocks and indicate that significant rift-related magmatic underplating may not be present. The characteristics of the pre-tectonic, syn-tectonic and post-tectonic sedimentary units allow us to infer the spatial and temporal evolution of active rifting. In the western part of the southern transect, thick postrift sediments were deposited in half grabens that are bounded by large fault blocks. Fault spacing and block size diminish to the east as crustal thinning increases. Recent tectonic activity is expressed by faults cutting the seafloor in the east, near the mainland of Italy. The two transects show the evolution from the less extended rift in the north with a fairly symmetric conjugate structure to the asymmetric margins farther south. This structural evolution is consistent with W-E rift propagation and southward increasing extension rates.

Seismic Oceanography in the Tyrrhenian Sea: Thermohaline Staircases, Eddies, and Internal Waves

“…The seismic data were acquired as part of the MEDOC‐2010 survey (Ranero & The MEDOC Team, ), completed in April–May 2010, with the Spanish vessel R/V Sarmiento de Gamboa. It was a project designed to address the geological formation of rifted tectonic margins by utilizing both refraction and reflection seismology (e.g., Moeller et al, ; Prada et al, ). Seismic acquisition parameters are shown in Table S1 in Supporting Information S1.…”

Spatial variations of magmatic crustal accretion during the opening of the Tyrrhenian back‐arc from wide‐angle seismic velocity models and seismic reflection images

“…In the Northern Tyrrhenian, extension slowed down to finally end in the Early‐Middle Pliocene (Fig. b), although some deformation occurred during Pleistocene time (Zitellini et al ., ; Trincardi & Zitellini, ; Bartole, ), forming as a result a N‐S trending system of normal fault blocks within an ~18–25 km thick continental crust (Moeller et al ., , ).In contrast, in the Central Tyrrhenian, higher extension rates led to crustal break‐up and mantle exhumation (Prada et al ., , ).…”

“…The MEDOC Wide‐Angle seismic ( WAS ) and Multichannel seismic ( MCS ) lines are represented with black and red lines respectively. Transects MEDOC 1/A‐B (Moeller et al ., ) and MEDOC 2/C‐D (Moeller et al ., ) report the crustal structure of the Northern Tyrrhenian, while transects MEDOC 4/E‐F (Prada et al ., ) and MEDOC 6/G‐H (Prada et al ., ) provided crustal information of the central region. The data from MCS CROP line M28B and the coincident WAS MEDOC transect M‐N are used in this study to infer the crustal structure of the southwestern region of the Tyrrhenian Basin.…”

“…Recent results from geophysical data acquired in 2010 during the MEDOC experiment conducted with the Spanish Research Vessel (R/V) Sarmiento de Gamboa and Italian R/V Urania, and available basement sampling information have shown that the tectonic structure in the Central Tyrrhenian Basin is more complex than previously thought (Prada et al ., ). The data show that the northern Tyrrhenian is underlain by continental crust (Moeller et al ., , ), but the central region is largely floored by magmatic rocks and exhumed mantle (Prada et al ., , , ). The basement under the Cornaglia and Campania Terraces (Fig.…”

The Zuccale Fault, Elba Island, Italy: A new perspective from fault architecture

“…At larger scale, geophysical data [ Moeller et al ., ] indicate that crustal extension in the northern Tyrrhenian Sea significantly decreases from south to north (i.e., from latitude 41°N to the Tuscan shelf). Furthermore, there is no evidence of low‐angle fault geometries in seismic reflection profiles, and the total fault displacement is entirely distributed among high‐angle faults [ Moeller et al ., ].…”