Archean continental crust formed by magma hybridization and voluminous partial melting

Abstract

Archean (4.0–2.5 Ga) tonalite–trondhjemite–granodiorite (TTG) terranes represent fragments of Earth’s first continents that formed via high-grade metamorphism and partial melting of hydrated basaltic crust. While a range of geodynamic regimes can explain the production of TTG magmas, the processes by which they separated from their source and acquired distinctive geochemical signatures remain uncertain. This limits our understanding of how the continental crust internally differentiates, which in turn controls its potential for long-term stabilization as cratonic nuclei. Here, we show via petrological modeling that hydrous Archean mafic crust metamorphosed in a non-plate tectonic regime produces individual pulses of magma with major-, minor-, and trace-element signatures resembling—but not always matching—natural Archean TTGs. Critically, magma hybridization due to co-mingling and accumulation of multiple melt fractions during ascent through the overlying crust eliminates geochemical discrepancies identified when assuming that TTGs formed via crystallization of discrete melt pulses. We posit that much Archean continental crust is made of hybrid magmas that represent up to ~ 40 vol% of partial melts produced along thermal gradients of 50–100 °C/kbar, characteristic of overthickened mafic Archean crust at the head of a mantle plume, crustal overturns, or lithospheric peels.

Petrology, geochemistry, and zircon U–Pb‐Lu–Hf isotopes of granitoids from the Ivindo Basement Complex of the Souanké Area, Republic of Congo: Insights into the evolution of Archean continental crust

“…The range of TTG compositions observed in nature is controlled by the bulk chemistry of the protolith and the P–T conditions of melt equilibration during partial melting (Moyen, 2011). During melt loss, the initial trace‐element concentrations, which are related to host minerals in the source rocks, influence the enrichment and depletion of elements such as REE, Sr, Y, Nb, and Ta in resulting melt fractions (Hernández‐Montenegro, Palin, Zuluaga, & Hernández‐Uribe, 2021; Moyen, 2011; Moyen & Stevens, 2006). Moreover, variable fluid availability at distinct crustal depths can generate melts with similar trace‐element patterns to average TTG compositions.…”

The versatility of petrological modeling: Thermobarometry of high‐pressure metabasites from the Renge and Sanbagawa belts and phase evolution during warm subduction at Nankai

“…In the case of forward modeling, petrological calculations can be performed along a sequence of P-T points to determine paragenesis along a given P-T-X path. Therefore, it is possible to explore and evaluate the mineralfluid-melt evolution of different lithologies along different trajectories and shed light on important geological processes such as slab devolatilization, hydrothermal alteration of the oceanic floor, water transport to the mantle through time, intermediate-depth seismicity, and crustal formation and growth, just to mention some examples (Baxter & Caddick, 2013;Condit et al, 2020;Hern andez-Montenegro et al, 2021; Hern andez-Uribe, Hern andez-Montenegro, et al, 2020; Hern andez-Uribe, Kendrick & Yakymchuk, 2020;Konrad-Schmolke et al, 2011;Walters et al, 2020;among other examples).…”

A comparative study of two-phase equilibria modeling tools: MORB equilibrium states at variable pressure and H2O concentrations

“…While not considered in our present study, the use of the HPx-mb16 model to study fractional crystallization or any other open-system process would be relatively laborious for this task with the current software available (i.e., Theriak-Domino, Perple_X, and THERMOCALC), although several works using these software have succesfully modeled open-system processes (e.g., Yakymchuk and Brown, 2014;Kendrick and Yakymchuk, 2020;Stuck and Diener, 2020;Johnson et al, 2021;Hernández-Montenegro et al, 2021) Furthermore, it is important to note that recent comparative study assessing the robustness of the Green et al (2016) clinopyroxene and amphibole a-X relations shows discrepancies between the phase equilibria calculations and natural rocks in the proportions and compositions (Forshaw et al, 2019;Santos et al, 2019); yet, our comparisons with the experiments show that the difference in proportions are not as significant as suggested in those This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change.…”