The research conducted in the Thetford Mines ophiolite represents the first magnetic fabric (anisotropy) study to quantify complete tectonic obliteration of original magmatic fabrics in an ophiolite. There have been many publications that have documented and described the evolution of magnetic fabrics in deformed sedimentary rock successions, but very few have addressed deformation-related fabrics in igneous successions and none in an important ophiolite. Results show that magnetic fabrics in all components of the main Thetford Mines ophiolite (serpentinized mantle rocks, gabbros, dykes and lavas), that formed by distinctly different magmatic processes, share the same fabric that reflects structurally-controlled crystallographic preferred orientations of iron-rich phases. Fabrics have consistent NW-SE oriented minimum anisotropy axes and steeply plunging NE maximum axes, and most likely developed during the Acadian orogeny in response to regional NW-SE shortening. This suggests complete obliteration of earlier magmatic fabrics during orogenesis. In contrast, gabbros in the south of the ophiolite retain a magnetic fabric parallel to compositional layering, suggesting that primary fabrics may survive locally in low strain zones. Importantly, consideration of anisotropy data from individual overprinted sites could lead to erroneous interpretations, as the tectonic fabric has anisotropy axes aligned coincidentally with magmatic morphologies such as dike margins in some cases. This emphasizes the need for caution during analysis of magnetic fabric data in complexly deformed terranes.
The additional component of training in the Oman ophiolite has yielded data that are still being analysed by the Fellow, but preliminary interpretations indicate that: (i) remanence directions within different levels of the northern massifs of the ophiolite have been highly rotated in a clockwise sense since formation of the ophiolite in the Cretaceous, consistent with previous studies; but (ii) that this rotation did not start during magmatic construction of the crust (as previously suggested), as different levels in the lava sequences record identical rotations when analysed using a net tectonic rotation approach. This is in contrast to previously published results from these rocks. These results therefore overturn c. 20 years of acceptance of these earlier interpretations, and remove the need for progressive rotation of the ophiolite during seafloor spreading, simplifying the reconstruction of the regional evolution of the world’s largest ophiolite.
There are no socio-economic impacts or wider societal implications of the project.
