THE ARCHEAN ECLOGITE PARADOX
Seminars
Semester 2
Orogenic eclogites are definitive hallmarks of subduction, yet they are nearly absent from the Archean rock record despite growing evidence for early horizontal tectonics. This paradox raises a critical question: did Archean eclogites fail to form, or did they simply fail to exhume? Using thermomechanical models, we demonstrate that orogenic eclogites can indeed form during Archean terrane accretion, as the subducting slab provides sufficient advective cooling for eclogitization. However, their subsequent exhumation is fundamentally hindered. The rheological weakness of the hot Archean lithosphere inevitably triggers rapid, shallow slab break-off, driving the deep-mantle recycling of the vast majority of the eclogitic crust. Furthermore, convergence-driven crustal deformation remains highly diffuse and dominated by steep, vertical shear zones rather than the localized thrust faults required for upward transport, thereby trapping any surviving fragments at depth. Validated by geological observations from the Superior Craton, our results indicate that the scarcity of Archean eclogites is not evidence against early horizontal tectonics. Instead, it is a direct mechanical consequence of hot accretionary dynamics that strongly favored deep recycling over exhumation.
For additional information, please contact Ms. Yu Chenying, yuchy3@connect.hku.hk.