Breaking up continents at magma-poor rifted margins: a seismic v. outcrop perspective

Abstract

The breakup of continents at magma-poor rifted margins is a complex, yet little understood process accounting for intricate interactions between tectonic and magmatic processes. Whereas high resolution seismic data may resolve the first order architecture of Ocean Continent Transitions (OCT), direct access to rocks remains limited to deep sea drilling. In this study, we combine seismic observations from the East Antarctica margin (Geoscience Australia Survey 228) with field observations from the Bracco-Levanto area (Northern Apennine/Italy), representing modern and fossil examples of ultra-distal magma-poor rifted margins respectively. The combination of detailed structural mapping and petrological studies from fossil examples with architectural features observed in seismic sections from present day OCTs enables to bridge the different observation scales. Field evidence indicates that the magmatic budget is not zero, as magma is present throughout the exhumation process. Extensional detachment faults that exhumed serpentinised mantle and deep-seated gabbro intrusions are truncated by later high-angle normal faults, which most likely acted as feeders for the emplacement of massive syn-extensional basalts. These observations suggest a polyphase tectonic and magmatic evolution of the ultra-distal margin prior to the formation of first oceanic crust, which can be studied in detail only by combining seismic and outcrop observations.