MORGen: an Algorithm to Compute Spreading Centre and Transform Geometries from Simple Initial Plate Boundaries and Euler Rotations

Abstract

The age structure of the global ocean floor is a key feature in paleogeographic reconstructions, which in turn forms the quantitative basis for Earth System Science. However, much of the ocean floor in paleogeographic reconstructions has been lost to subduction. The age structure of such lost ocean floor is constructed from the reconstructions of adjacent continents, using the relative rotations, around Euler poles to predict the geometry of spreading centres and transform faults. Building such mid-ocean ridge features in paleogeographic reconstructions is laborious, as it requires redrawing of ridge-transform systems upon every Euler pole shift in the model. In this paper, we present the Mid-Ocean Ridge Generator (MORGen) algorithm, based on pyGPlates. MORGen reduces the laborious task by automating the drawing of mid-ocean ridge geometries from geometrically simple plate boundary input assuming ridge-perpendicular spreading and adjusts ridge geometries in a simplest-scenario fashion by gradually adjusting ridge orientation and transform fault length upon Euler pole shifts, inspired by observations from the modern sea floor. The code takes as input curved line features, representing approximate divergent plate boundaries, and a set of Euler poles. These are then converted into spreading centre-transform geometries. Upon Euler pole shifts, the geometries are adjusted to fit the set of small circles and great circles dictated by the new Euler pole. For studies of paleo-environment and paleo-oceanography MORGen can be used in combination with other algorithms for full reconstructions of ocean floors, including their age, bathymetry, and roughness. For in-situ preserved ocean floor, the paleo-age distribution can be reconstructed directly in high resolution from geophysical and geological data from the modern ocean floor and MORGen would not normally be the option of choice. In cases where models contain ocean floor that has now been subducted, MORGen straightforwardly facilitates mid-ocean ridge geometry reconstruction. To illustrate how well the MORGen algorithm reproduces real ocean floor age structure, we show a synthetic ridge evolution for the South Atlantic and Southern Oceans and compare this to geophysically constrained ocean floor geometry. In addition, we show examples of use cases where direct (re)construction of mid ocean ridges is not possible: now-subducted ocean basins in the Mediterranean region and an ocean in a future supercontinent scenario.