Advances in plate tectonics: interdisciplinary approaches to understanding the separation of continents and initiation of subduction zones at GeoPRISMS primary sites

Abstract:

Two of the fundamental components of plate tectonics are the separation of continents, leading to new ocean basins, and the initiation of subduction zones, which facilitate recycling of the Earth’s outer shell into its interior. Many aspects of subduction initiation and continental breakup remain elusive; thus, these processes were identified as critical science targets by the Subduction Cycles and Deformation (SCD) and Rift Initiation and Evolution (RIE) initiatives within the GeoPRISMS community.

Here we highlight results from the Eastern North American Margin (ENAM) and the Puysegur Margin (PM), which were designated as GeoPRISMS primary sites to spark collaborative efforts and acquire novel datasets to investigate continental breakup and subduction initiation, respectively. Our analysis focuses on active-source and passive seismic imaging from these regions complemented by other geophysical data (e.g. magnetics, gravity) and geologic, petrologic, and geodynamic observations and models.

New findings along the ENAM show that initial rifting and magmatism was limited and occurred in discrete pockets influenced by pre-existing orogenic boundaries. Magmatism throughout rift evolution can be explained by moderately elevated mantle potential temperatures but did not involve a mantle plume. Low extension rates and thick inherited lithosphere delayed final breakup despite the presence of mantle melts and new igneous crustal accretion. Along the PM, initial extension stretched continental crust and created new oceanic lithosphere farther south, while later dextral strike-slip juxtaposed these terranes at a restraining bend. Subsequent subduction initiation was assisted by these inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of tectonic activity.

These outcomes highlight common themes between the SCD and RIE initiatives and suggest that tectonic inheritance (e.g. structure and composition) and weakening mechanisms (e.g. melts/volatiles) may be the principal factors controlling the evolution of the lithosphere at developing plate boundaries. GeoPRISMS and MARGINS demonstrate the success of community-driven science and the legacy of these programs has made significant contributions to our understanding of the Earth.