Potassic, high-silica Hadean crust

Abstract

Understanding Hadean (>4 Ga) Earth requires knowledge of its crust. The composition of the crust and volatiles migrating through it directly influence the makeup of the atmosphere, the composition of seawater, and nutrient availability. Despite its importance, there is little known and less agreed upon regarding the nature of the Hadean crust. By analyzing the Sr/Sr ratio of apatite inclusions in Archean zircons from Nuvvuagittuq, Canada, we show that its protolith had formed a high (>1) Rb/Sr ratio reservoir by at least 4.2 Ga. This result implies that the early crust had a broad range of igneous rocks, extending from mafic to highly silicic compositions.

The142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present

“…In a brief literature survey, the initiation of the Wilson cycle was proposed to have been around 3.0 Ga based on diamond inclusions (36), while the initiation of plate tectonics was similarly proposed to have been relatively recent (∼3.0 Ga) based on inferences about the evolution of composition of the upper crust (37). Meanwhile, the investigation of titanium isotopes of shales (38) suggests that plate tectonics must have been initiated more than 3.5 Ga. Another study (39) has proposed high silica content in the early crust based on Rb/Sr ratios, suggesting that the early Earth was capable of forming continental crust within <350 My of solar system formation. Such a scenario would push the initiation of plate tectonics as early as 4.2 Ga.…”

Titanium isotopes as a tracer for the plume or island arc affinity of felsic rocks

“…titanium isotopes | plume | island arc | magma differentiation | plate tectonics T he onset of plate tectonics is still highly debated due to the fragmentary geologic record for the early Earth. The proposed onset time of plate tectonics in literature has ranged from >4.2 to 0.85 billion years ago (Ga), and the emergence of the felsic continental crust has been usually considered as a major proxy to trace plate tectonics in the past (1)(2)(3)(4)(5)(6)(7)(8). Nonetheless, the validity of such a criteria to trace the onset of plate tectonics has been frequently questioned based on the fact that both plume (tholeiitic) and island arc (mainly calc-alkaline) settings are able to produce rocks of intermediate to felsic compositions (9)(10)(11).…”

Ideas and perspectives: Development of nascent autotrophic carbon fixation systems in various redox conditions of the fluid degassing on early Earth

“…The deep hydrocarbon generation in seismically active satellites manifested as the significant concentrations of hydrocarbons, including methane on their surface. For example, there is a prevalence of methane on Titan and Enceladus (the satellites of Saturn; Tobie et al, 2006;Bouquet et al, 2015) and on Europa (the satellite of Jupiter; e.g., . Additionally, high concentrations of methane are assumed to be present on early Mars (Oehler and Etiope, 2017).…”

“…With increasing alkalinity (alkaline slope) of igneous rocks, the different hydrocarbons invariably appear in fluid inclusions (Potter and Konnerup-Madsen, 2003;Nivin et al, 2005). The high content of potassium in the high-silica Hadean crust (Boehnkea et al, 2018) indicates the depth of magmatism and its hydrocarbon specificity.…”