Thermo-compositional structure of the north-eastern Canadian Shield from Rayleigh wave dispersion analysis as a record of its tectonic history

Abstract

The thermal and compositional structure of lithospheric keels underlying cratons, which are stable continental cores formed during the Precambrian, is still an enigma. Mapping lithospheric temperatures and compositional heterogeneities is essential to better understand geodynamic processes that control craton formation and evolution. Here we investigate the northeastern part of North America which comprises the Superior Craton, the largest Archean craton in the world, and surrounding Proterozoic belts. We model Rayleigh-wave dispersion curves from a previous study, which were regionalized based on cluster analysis. Next, we perform a grid search for sub-crustal thermal and compositional structures that are consistent with the average dispersion curve for each cluster. We apply constraints on crustal structure and use thermodynamic methods to map thermo-compositional structures into seismic velocity. In agreement with previous studies, most regions require concentrations of metasomatic minerals over certain depth intervals to fit the seismic profiles. Our results further require vertical as well as lateral variations in compositional and thermal structures, which appear to reflect different stages of formation and modification of the lithosphere below the region, with distinct structures found under Archean cores, Archean/Paleoproterozoic collision belts, mid-late Proterozoic collision belts, and zones affected by rifting.

Lithospheric Formation and Evolution of Eastern North American Continent

“…A variety of mechanisms have been proposed for the seismically observed MLDs within North America. One hypothesis is that the craton was formed at (at least) two stages, with the top 100–150 km representing the Archean lithosphere and the lower part formed at a later stage (e.g., Altoe et al., 2020; Eeken et al., 2020; Foster et al., 2020; Petrescu et al., 2017; Yuan & Romanowicz, 2010). Another mechanism is that the entire craton was formed during the Archean, but its lower part was later modified by subduction‐derived metasomatism (e.g., Boyce et al., 2016; Boyce et al., 2019).…”

Thermo‐Compositional Structure of the South American Platform Lithosphere: Evidence of Stability, Modification, and Erosion

“…Emerging from this work and a few previous studies (Altoe et al, 2020;Boyce et al, 2019;Eakin, 2021;Eeken et al, 2020;Gilligan et al, 2016;Liddell et al, 2018) is the conclusion that the lithospheric mantle below the continental platform holds more of a record of its previous tectonic history than often assumed. The seismic data we use have more lateral resolution than the most recent thermo-compositional analyses by Finger et al (2021) and with the combination of dispersion curves and geoid we are able to better evaluate the variation in composition with depth.…”

“…The thermo-chemical structure of the mantle below each of the groups is estimated by performing a grid-search for a set of forward models that fit the dispersion curves, topography, and geoid anomalies within their uncertainties. The general approach used in this study follows the methods of Altoe et al (2020) and Eeken et al (2018); Eeken et al (2020), with an extension to fit density-sensitive data. The approach can be divided into four basic steps (Figure 4).…”

A Thermo‐Compositional Model of the African Cratonic Lithosphere

“…For example, OPX may also decrease with melt depletion under certain temperature and pressure conditions (Baker, 1994). Moreover, the possible existence of Eclogite, as found in the Superior Craton (Altoe et al., 2020), is not considered in our approach. In any case, the amount of Eclogite in a cratonic mantle should not be significant.…”