Catastrophically fast: basalt magma chambers grow much faster than expected

hot magma

The basaltic magma is low in potassium and sodium but rich in iron, calcium and magnesium.

A new study makes an unexpected discovery.

Geologists from Wits University in Johannesburg (Professor Rais Latypov and Dr Sofya Chistyakova) were part of an international team of researchers who unexpectedly discovered that basaltic magma chambers can grow incredibly rapidly – in months or years. years – making these chambers remarkable intrusive equivalents of the caldera – forming eruptions related to the Great Igneous Provinces. The groundbreaking study was recently published in the journal Scientists progress.

Minimum vertical placement rate

Numerical simulations indicate that the minimum vertical emplacement rate for the Skaergaard magma chamber in Greenland is of the order of several hundred to a few thousand m/year. Credit: University of the Witwatersrand

Professor Rais Latypov says: “The vertical rate at which magma chambers expand via the emplacement of magma is highly debated. Based on high-precision zircon dating and surface deformation measurements, most plutons would currently be emplaced very slowly (a few cm/year). However, such slow rates are difficult to reconcile with the existence of large, well-differentiated intrusions that only seem to form if the emplacement rates are very high. A key question we tried to answer is what rate of magma emplacement is needed to keep the growth chamber fully molten? »

Rais Latypov, Catherine Annen and Sofya Chistyakova

Professor Rais Latypov, Dr Catherine Annen and Dr Sofya Chistyakova (from right to left). Credit: University of the Witwatersrand

The researchers used a new approach to answer this question, using the iconic Skaergaard Intrusion in Greenland, which began to crystallize from all margins inwards only after it was completely filled with nearly crystal-free magma.

“This fundamental physical constraint provides a unique opportunity to estimate the minimum rate of magma emplacement that was required to maintain the Skaergaard magma body in a largely molten state (<<1% crystals) while reaching its current size. “, says Dr. Sofya. Chistyakova from the Wits University School of Geosciences.

The researchers used numerical simulations to calculate the conditions necessary for the formation of such a massive, crystal-free magma chamber and found that the Skaergaard intrusion must have occurred within decades or even months/weeks. Vertical growth rates must have been on the order of hundreds to thousands of meters per year, which equates to volumetric flows on the order of tens to hundreds of cubic kilometers per year. This means that the volumetric flow that fed Skaergaard was several orders of magnitude higher than currently recognized basaltic magma chamber growth rates.

The researchers proposed that the Skaergaard and possibly other stratified intrusions could be considered plutonic equivalents of super-eruptions (or catastrophic intrusions) that develop via extremely rapid emplacement of magma in the crust, producing magmatic chambers completely melted in a few weeks/months to tens/hundreds of years maximum.

“In other words, we suggest that some layered mafic intrusions may represent the plutonic analogues of volcanoes related to large igneous provinces that are responsible for erupting huge volumes of flooded basalts on the Earth’s surface,” Latypov says.

Reference: “Catastrophic growth of totally melted magma chambers in months or years” by Catherine Annen, Rais Latypov, Sofya Chistyakova, Alexander R. Cruden and Troels FD Nielsen, September 23, 2022, Scientists progress.
DOI: 10.1126/sciadv.abq0394

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