Subliquidus rheology of basalt from the 2018 Lower East Rift Zone Kilauea eruption: isothermal vs. dynamic expression

Soldati, A.; Houghton, B. F. und Dingwell, D. B. (2021): Subliquidus rheology of basalt from the 2018 Lower East Rift Zone Kilauea eruption: isothermal vs. dynamic expression. In: Chemical Geology, Bd. 581, 120363

Abstract

The dynamic effects of temperature and strain rate on rheology of crystal-bearing magma are investigated. We conducted high-temperature rheometry experiments in both isothermal and dynamic crystallization regimes and recovered textural data for the isothermal runs. We propose a framework for the parameterization of magma rheology, via an equation describing how the rheological cutoff temperature (the temperature at which magma stops flowing) varies as a function of cooling rate and strain rate. This equation may be used to inform rapid response in effusive crises. Cooling rate has the larger effect, with higher cooling rates yielding lower cutoff temperatures;higher strain rates yield higher cutoff temperatures. Textural analyses reveal differences in crystal aspect ratios, such that higher cooling rates produce only subequant crystals, whereas lower cooling rates also produce a second, higher aspect ratio crystal population. We identify this textural variation as the physical cause for the dependence of cutoff temperature on cooling rate. Plain language summary: As lava cools, it crystallizes. Eventually, this crystallinity becomes so high that the lava can no longer advance. The temperature at which the crystals lock up the lava is called the rheological cutoff temperature. This depends, in principle, on the crystallization pathway, which is influenced by both the cooling rate and the strain rate of the lava flow. We conducted rheological experiments on 2018 Kilauea lavas along different crystallization pathways. We determined that higher cooling rates (5 degrees C/min) yield cooler cutoffs (983-1058 degrees C), and higher strain rates (8 s(-1)) yield hotter cutoffs (1058-1093 degrees C). Moreover, the cooling rate affects the cutoff temperature more than the strain rate. Through a complementary set of experiments, we found that the physical cause for the dependence of the cutoff temperature on the cooling rate is crystal aspect ratio (length/width). At any given crystallinity, crystals with a higher aspect ratio interact more, and lock at higher temperatures. Higher cooling rates produce only crystals with an aspect ratio of 1, whereas lower cooling rates produce higher aspect ratio crystals as well. Therefore, lava which has cooled more slowly, which crystallizes higher aspect ratio crystals, has a higher rheological cutoff temperature.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geographie
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 0009-2541
• Sprache: Englisch