¹Hitoshi Miura
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116317]
¹Graduate School of Science, Nagoya City University, Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya, 467-8501, Aichi, Japan
Copyright Elsevier

In this study, we propose a novel numerical method to simulate the growth dynamics of an olivine single crystal within an isolated, multicomponent silicate droplet. We aimed to theoretically replicate the solidification textures observed in chondrules. The method leverages the phase-field model, a well-established framework for simulating alloy solidification. This approach enables the calculation of the solidification process within the ternary MgO–FeO–SiO2 system. Furthermore, the model incorporates the anisotropic characteristics of interface free energy and growth kinetics inherent to the crystal structure. Here we investigated an anisotropy model capable of reproducing the experimentally observed dependence of the growth patterns of the olivine single crystal on the degree of supercooling under the constraints of two-dimensional modeling. By independently adjusting the degree of anisotropies of interface free energy and growth kinetics, we successfully achieved the qualitative replication of diverse olivine crystal morphologies, ranging from polyhedral shapes at low supercooling to elongated, needle-like structures at high supercooling. This computationally driven method offers a unique and groundbreaking approach for theoretically reproducing the solidification textures of chondrules.

¹Alexei V. Ivanov
Earth and Planetary Science Letters 647, 119058 Link to Article [https://doi.org/10.1016/j.epsl.2024.119058]
¹Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, 128 Lermontov Street, Irkutsk 664033, Russia
Copyright Elsevier

It is frequently proposed that large bolide impacts and voluminous volcanic eruptions may be responsible for environmental catastrophes. In the conventional approach, the potential causes and consequences are matched using an age-versus-age plot, with preferential ages selected for comparison. This approach inevitably results in a one-to-one correlation, which may be misleading. To address this issue, a novel statistical metric, named concordance, has been proposed which accounts for the possibility of age coincidence resulting from random processes (i.e. bad luck coincidence). The available and updated geochronological datasets of bolide impacts, large igneous provinces, CO2-concentration peaks in the atmosphere, mass extinctions, ocean anoxic events, and climatic optima and thermal highs were subjected to a comparison in terms of their concordance. The most significant discovery is the correlation between the ages of mass extinctions and those of giant bolide impacts (crater diameter >40 km), as well as volcanism of continental large igneous provinces and CO2-concentration peaks in the atmosphere. The severity of mass extinctions appears to be dependent upon the number of simultaneously occurring causes. The most pronounced Late Maastrichtian (∼66 Ma) and Changhsingian (∼252 Ma) mass extinctions were likely caused by a combination of factors, including the simultaneous occurrence of volcanism of continental large igneous provinces, giant bolide impact and CO2-concentration rise in the atmosphere. Conversely, the ages of large igneous provinces, bolide impacts and CO2-concentration peaks are not correlated, indicating that these three causes were not interdependent.