WP2: Ultra-slow Oceanic Spreading – understanding the structure and evolution of the Gakkel Ridge
Work package leaders: Rolf B. Pedersen (UiB) and Carmen Gaina (CEED, UiO)
Contributions from: Cedric Hamelin (UiB), Kuvvet Atakan (UiB), Johannes Schweitzer (NORSAR)
The present day geological frontier between Eurasia and North America, two major tectonic plates, runs through the Eurasian Basin along the Gakkel Ridge (previously known as Nansen cordillera). Along this divergent plate boundary, seafloor spreading is taking place, creating new oceanic lithosphere. Gakkel Ridge started its activity with an intermediate spreading rate in the Late Paleocene-Early Eocene (e.g. Glebowsky et al. 2006), but regional tectonic events forced this system to slow down in the Late Eocene (around 43-40 Ma) and in the Oligocene (around 30 Ma) (e.g. Gaina et al. 2015). Presently, it is the slowest mid-ocean ridge on Earth, with a full spreading rate decreasing eastward from 14.6 mm/yr to 6 mm/yr (e.g. Jokat et al. 2003; Savostin et al. 1984; Dick et al. 2003).
Ocean ridges spreading at less than 20 mm.yr-1 have been far less studied than their fast spreading counterparts and the first comprehensive descriptions of the ultraslow-spreading class of ocean ridges had to wait until the last decade (Dick et al. 2003; Jokat et al. 2003). The effect of such slow spreading on oceanic lithosphere accretion was projected to produce on-axis colder thermal regime, therefore impeding magma generation. In this scenario, Gakkel Ridge should have sparse volcanism due to low extents of mantle melting, very little hydrothermal activity and a dominance of exhumed peridotites over basalts (Dick 1989). However, published data from Gakkel Ridge have now challenged this prediction and provided new insights into the structure and development of ultraslow spreading centers (e.g. Jokat et al. 2003; Jokat and Scmidt-Aursch 2007). Current knowledge indicates that the present-day ridge is segmented into contrasting amagmatic and volcanic sections (e.g. Michael et al. 2003) and is characterized by an uneven lithosphere-asthenosphere boundary (Schlindwein and Schmid 2016). Despite its ultra-slow spreading tectonic regime, Gakkel Ridge seems to show a large range in magma supply and a remarkable occurrence of hydrothermal sites.
Identify the geology, architecture and evolution of Gakkel Ridge and its flanks. It examines how variations of volcano-tectonic processes are influencing the oceanic lithosphere accretion at such ultra-slow spreading. Using modern deep-sea exploration technology, we aim to produce unprecedented detailed pictures of the seafloor, coupled with high-resolution sampling of the ridge. These new data combined with direct observations by ROV (Remotely Operated Vehicle) are an opportunity to study the interplay between faults, volcanism, hydrothermal circulation and life. Another key objective of this work package is to understand the evolution of the plate boundary within the Eurasia Basin through time, and construct a comprehensive model of this basin since the Eocene. Integrating new and published geophysical data will be critical in order to succeed in the task of linking our knowledge about the Eurasian Basin basement morphology and sedimentary deposits to variations in the Arctic paleo-bathymetry and paleoclimate.