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 have unexpectedly discovered that basaltic magma chambers can grow incredibly quickly — in months to years — making these chambers remarkable intrusive equivalents of caldera-forming eruptions connected with the Large Igneous Provinces. The groundbreaking study was recently published in the journal Science Advances.
Professor Rais Latypov says “The vertical rate at which magma chambers grow via magma emplacement is highly debated. Based on high-precision zircon dating and surface deformation measurements, most plutons are currently thought to be emplaced very slowly (a few cm/year). Such slow rates are, however, difficult to reconcile with the existence of large, well-differentiated intrusions which appear to form only if emplacement rates are very high. A key question we tried to address is which rate of magma emplacement is required to keep the growing chamber entirely molten?”
The researchers utilized a novel approach to answer this question, using the iconic Skaergaard intrusion in Greenland, which began crystallizing from all margins inwards only after it had been entirely 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 keep the Skaergaard magma body in a largely molten state (<<1% crystals) while growing to its current size,” says Dr. Sofya Chistyakova from the School of Geosciences at Wits University.
The researchers used numerical simulations to calculate the conditions necessary for the formation of such a massive crystal-free magma chamber and discovered that the Skaergaard intrusion must have occurred within a few decades, if not months/weeks. Vertical growth rates must have been in the hundreds to thousands of meters per year, equating to volumetric flow rates in the tens to hundreds of cubic kilometers per year. This means that the volumetric flow rate that fed Skaergaard was several orders of magnitude greater than the currently recognized basaltic magma chamber growth rates.
The researchers proposed that the Skaergaard and possibly other layered intrusions can be viewed as plutonic equivalents of super-eruptions (or catastrophic intrusions) that grow via extremely rapid magma emplacement into the crust, producing totally molten magma chambers in a matter of a few weeks/months to maximum dozens/hundreds of years.
“In other words, we suggest that some layered mafic intrusions may represent the plutonic analogs of the Large Igneous Provinces-related volcanoes that are responsible for eruptions of enormous volumes of flood basalts on the Earth’s surface,” says Latypov.
Reference: “Catastrophic growth of totally molten magma chambers in months to years” by Catherine Annen, Rais Latypov, Sofya Chistyakova, Alexander R. Cruden and Troels F. D. Nielsen, 23 September 2022, Science Advances.