PRIN 2017_2017KY5ZX8 Oceanic Megatransforms: a New Class of Plate Boundaries-Resp. Marco Ligi (DTA.AD003.403)

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Area progettuale

Struttura responsabile del progetto di ricerca

Istituto di scienze marine (ISMAR)

Responsabile di progetto

MARCO LIGI
Telefono: 051-6398882
E-mail: marco.ligi@bo.ismar.cnr.it

Abstract

Oceanic transform plate boundaries consist of a single, narrow (a few km wide) strike-slip seismic zone offsetting two mid-ocean ridge segments. However, we define here a new class of oceanic transform boundaries (megatransforms), with broad complex multifault zones of deformation, similar to some continental strike-slip systems. Examples are the Romanche transform, where the MAR is offset by a lens-shaped, 900 km-long, >120 km-wide sliver of deformed lithosphere bound by two major transform valleys, and the 750 km-long, 120-km-wide Andrew Bain transform on the SWIR. We propose a research Project aimed at assessing tectonic, magmatic and geodynamic processes acting at these long-offset slow-slip transforms. In order to investigate mechanisms explaining their formation and evolution in space and time, and to examine accretionary processes occurring at their ridge intersections, we plan to do fieldworks at the equatorial MAR just south of its intersection with the Romanche, where we have identified large areas with mantle rocks exposed on the seafloor; and at 8° N where the Doldrums transform offsets the ridge axis by ~600 km and may represent an evolutionary stage of megatransforms.

Obiettivi

We propose to investigate mechanisms leading to the formation of megatransforms and their evolution in space and time, and to examine the magmatism generated at their RTIs. Megatransform RTI's are ideal sites to investigate mantle and deep lithospheric accretionary processes because the strong decrease of magmatic crust production due to an enhanced cold edge effect. The resulting mantle exhumation and reduction in the extent of melting allows to detect chemical variability of the mantle source, melt transport and extraction beneath mid ocean ridges. Our proposal addresses five major issues: 1) detailed geological and geophysical study of the eastern Romanche RTI and of the Doldrums transform to unravel their evolution through time. 2) a petrological-geochemical study of crustal and mantle rocks to determine how megatransform systems affect mantle upwelling and melting; 3) a petrological-microstructural study of exhumed deepest rocks to assess the extent of melt/fluid rock interactions; 4) detection of basalt- and ultramafic-hosted hydrothermal fields; 5) geodynamic theoretical modelling to assess megatransforms evolution through time and the interplay with mantle processes

Data inizio attività

03/11/2019

Parole chiave

Oceanic transform faults, Mid-ocean ridges, Seismicity

Ultimo aggiornamento: 15/06/2025