Plate-tectonic evolution of the Earth: bottom-up and top-down mantle circulation

Abstract

Abstract:Intense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below low-pressure solidi of dry peridotite, basalt, and granite, ϳ1300, ϳ1120, and ϳ950°C, respectively. At less than half their T solidi, rocky materials existed as thin lithospheric slabs in the near-surface Hadean Earth. Stagnant-lid convection may have occurred initially but was at least episodically overwhelmed by subduction because effective, massive heat transfer necessitated vigorous mantle overturn in the early, hot planet. Bottom-up mantle convection, including voluminous plume ascent, efficiently rid the Earth of deep-seated heat. It declined over time as cooling and top-down lithospheric sinking increased. Thickening and both lateral extensional + contractional deformation typified the post-Hadean lithosphere. Stages of geologic evolution included (i) 4.5-4.4 Ga, magma ocean overturn involved ephemeral, surficial rocky platelets; (ii) 4.4-2.7 Ga, formation of oceanic and small continental plates were obliterated by return mantle flow prior to ϳ4.0 Ga; continental material gradually accumulated as largely sub-sea, sialic crust-capped lithospheric collages; (iii) 2.7-1.0 Ga, progressive suturing of old shields + younger orogenic belts led to cratonal plates typified by emerging continental freeboard, increasing sedimentary differentiation, and episodic glaciation during transpolar drift; onset of temporally limited stagnant-lid mantle convection occurred beneath enlarging supercontinents; (iv) 1.0 Ga-present, laminar-flowing asthenospheric cells are now capped by giant, stately moving plates. Near-restriction of komatiitic lavas to the Archean, and appearance of multicycle sediments, ophiolite complexes ± alkaline igneous rocks, and high-pressure-ultrahigh-pressure (HP-UHP) metamorphic belts in progressively younger Proterozoic and Phanerozoic orogens reflect increasing negative buoyancy of cool oceanic lithosphere, but decreasing subductability of enlarging, more buoyant continental plates. Attending supercontinental assembly, density instabilities of thickening oceanic plates began to control overturn of suboceanic mantle as cold, top-down convection. Over time, the scales and dynamics of hot asthenospheric upwelling versus lithospheric foundering + mantle return flow (bottom-up plume-driven ascent versus top-down plate subduction) evolved gradually, reflecting planetary cooling. These evolving plate-tectonic processes have accompanied the Earth's thermal history since ϳ4.4 Ga.Résumé : Un intense dégagement de matières volatiles et une différentiation selon la densité chimique faisait partie de l'accrétion de planétésimaux à la Terre primordiale. Ces processus ont grandement diminué après le refroidissement et la solidification d'un océan primitif de magma. Vers 4,3 ou 4,2 Ga, il existait des océan...

Constraining the Time Interval for the Origin of Life on Earth

“…If CO2 subduction occurred early, it could have continued to remove CO2 from the atmosphere until the partial pressure was well below 1 bar, which is about the pressure required to maintain a clement climate on Earth. However, there is still no consensus as to when these plate-tectonic processes began (Maruyama et al 2017, Ernst et al 2016, Shirey et al 2008). Ernst et al (2016) argue, that the Earth's surface was covered by crustal platelets by 4.4 Ga, and that episodic deep mantle-and plume-driven subduction began as early as 4.4-4.0 Ga.…”

“…However, there is still no consensus as to when these plate-tectonic processes began (Maruyama et al 2017, Ernst et al 2016, Shirey et al 2008). Ernst et al (2016) argue, that the Earth's surface was covered by crustal platelets by 4.4 Ga, and that episodic deep mantle-and plume-driven subduction began as early as 4.4-4.0 Ga. They reason that the terrestrial heat budget requires overturn of platelets during that time, since conduction is much less efficient than convectionadvection at transferring heat.…”

Did the transition to plate tectonics cause Neoproterozoic Snowball Earth?

“…Nevertheless, it is increasingly clear that Earth went through major tectonic changes in Neoproterozoic time (e.g. Brown, 2010;Ernst, Sleep, & Tsujimori, 2016;Hawkesworth, Cawood, & Dhuime, 2016). It is worth further considering whether this was when plate tectonics as defined above began.…”

Gravitational Potential Energy per Unit Area as a Constraint on Archean Sea Level

“…Regarding Archean sea level, many have argued that little continental crust stood above it (e.g., Arndt, 1999;Ernst et al, 2016;Flament et al, 2008;Lee et al, 2017;McCulloch & Bennett, 1994). Buick et al (1995), however, reported an angular unconformity that they associated with subareal erosion and deposition, overlain by a tuffaceous sandstone that they correlated with nearby sedimentary rock containing zircons dated at 3.46-3.47 Ga.…”