Challenging our understanding of the early evolutionary history of transform margins using a revised, high-resolution model of the Fram Strait, North-eastern Atlantic Ocean.
Authors: Hill Catherine , Webb Peter , Masterton Sheona 
Published: February 2023

The Fram Strait (North-eastern Atlantic Ocean) developed along a narrow transform margin that separates the Arctic Basin in the north from the Atlantic Basins in the south. The transform margin developed from the Miocene to Present Day and provided the first oceanic gateway between the Arctic Basin and the Atlantic Basins, allowing the ventilation of a previously closed Arctic Basin and a dramatic shift in global ocean circulation. Existing tectonic models are over-simplified and do not account for new data acquired from 2017 onward. Understanding the tectonic complexity of the Fram Strait and reconciling the fine details in a globally robust plate model is critically important for global ocean circulation models but may also provide an important insight into the development of paleo-transform margins further back in time. &#160;Potential fields data provide a particularly useful screening tool, especially at high latitudes where sea-ice makes the acquisition of seismic and well data more difficult. Detailed analysis of the structural and crustal architecture of the Fram Strait was conducted using potential fields data for structural mapping, 2D gravity and magnetic models, and 3D inversions for depth-to-basement and depth-to-Moho; these all combine for a new, high-resolution, tectonic model for the region. The results reveal the geometries of ocean basins under transtension, where the ultra-slow and non-volcanic opening have no currently established thermal driver. The crust is low-density and formed by faulting, exhumation and serpentinization of deeper mantle layers.&#160; This mode results from tectonically forced opening where transtension accommodates plate motion at established offset spreading ridges to the north in the Arctic Basin and to the south in the North-eastern Atlantic Ocean.&#160;&#160;Of particular importance is the arrangement of early fracture zones and the location of bathymetric ridges, which illustrate the segmented nature of early transform margins and variability of crustal type and evolution within individual segments. This variability has dramatically affected paleo-bathymetry and, therefore, has exerted significant control on ocean circulation and sediment transport.&#160;&#160;An incomparable advantage of globally available gravity and magnetic data is the ability to draw upon global analogues when investigating new or frontier areas. Analogues can be made between conjugate margins, but also between different systems around the planet. Younger, developing tectonic systems may provide important insights into the early evolution of more complicated areas, where poly-phase tectonic histories may have since matured or been subsequently overprinted. The Fram Strait model shares similarities with other examples of global transform margins, such as the Equatorial Atlantic. This provides an opportunity to re-examine the crustal architecture and structural relationships within other transform margin settings, using the Fram Strait as an analogue for early opening history.&#160;&#160;