Active Plate Boundaries

Significant modification of the Earth’s landscape and interior occurs at active plate boundaries, where slow convergent movements deform the edges of tectonic plates. Studies at NGU focus on dynamic lithospheric processes at both modern and ancient active plate boundaries.
Map with present-day subduction zones. The colours show the age of the oceanic crust from Mueller et al. (Gcubed 9, 2008). Image modified from Buiter et al. (Solid Earth 4, 2013).

Convergent movements occurring at active plate boundaries modify the Earth’s surface and internal structure of the deforming lithosphere. During convergence between an oceanic and continental plate, the denser oceanic plate sinks beneath the more buoyant continental plate. This process, known as subduction, is responsible for abundant volcanic activity and the strongest recorded earthquakes on Earth. During convergence between two continental plates of similar density (continental collision), neither plate is able to sink and large mountain ranges form as the tectonic plates thicken to accommodate convergence.

At short time scales (< 100 to 10,000 years), subduction is associated with earthquakes, volcanic eruptions and erosion, which slowly modify landscapes and often present significant risk to large populations. Over longer time scales (10,000 to > 100 million years), the cumulative effect of these processes may produce large topographic features such as the modern Himalayan mountain range and Andes volcanic mountain chain. In Norway past episodes (400-500 million years before present) of both subduction and continental convergence are responsible for the formation of the Norwegian Caledonian Mountains.

At NGU, processes at convergent plate boundaries are examined through field studies of ancient plate boundaries within Norway and computer simulations of subduction and continental convergence. These studies consider processes ranging from deformation at microscopic scales to the forces controlling convergence over 1000’s of km. The goals of these studies include identification of mineral resources, natural hazard mitigation, assessment of long-term fault behaviour and interpretation and visualisation of prior tectonic events.

Skjematisk tverrsnitt gjennom en subduksjonssone.
Schematic cross-section through a subduction zone