Supercontinent Reconstructions as of 2014: Advances and Challenges

Abstract:

Dynamic models of supercontinent assembly and dispersal should strive to emulate kinematic histories obtained from the geologic record; but the breakup of Pangea and initial assembly of Amasia, at 200-0 Ma, are the only phases of an alleged "cycle" that are known with good precision. Pre-Mesozoic reconstructions (i.e., 95% of Earth history) must rely on typically non-unique geological comparisons between extant continental fragments, guided by sparse paleomagnetic data from those blocks. Pangea assembly and evolution (500-200 Ma) are known in broad terms, but uncertainties of order 10-20° arc distance are common. The transition from Rodinia breakup to incipient Pangea assembly (Gondwana amalgamation; 700-500 Ma) is the least understood interval of global kinematics from the past two billion years, with uncertainties occasionally nearing 90°, and raising the geophysical specters of non-dipole geomagnetic field geometries and/or rapid true polar wander oscillations. Various Rodinia reconstructions (900-700 Ma) share many common features, but they are upheld by a rather lean dataset, by comparison to Pangea. The assembly stage of Rodinia (1300-900 Ma) derives its substantial uncertainty from questions concerning not only the supercontinent's end-configuration as noted above, but also the reconstruction of its predecessor Nuna (1600-1300 Ma), which has made much recent progress though likewise based on relatively limited data. Nuna's assembly phase (2000-1600 Ma) is a fruitful frontier for global reconstruction hypotheses at their earliest stages of development. Older intervals (2700-2000 Ma) will likely soon yield some insights into whether an earlier possible supercontinent, Kenorland, may have existed; but gaining even a broad outline of its reconstruction will be hard-fought, probably over decades, against dwindling Archean preservation. Today's geodynamic modelers of supercontinental episodicity should consider these noteworthy uncertainties as they assess whether their models are "Earth-like." Explorations into neglected corners of parameter space may shed light not only onto possible dynamic evolutions of exoplanets, but perhaps also to our own planet in deep time.