A Martian meteorite that landed in Morocco in 2011, has provided the first chemical evidence for convective activity within the mantle of Mars.
By studying the crystals of olivine (a typical mantle mineral in terrestrial planets) in the Tissint meteorite, scientists were able to provide new insights into the Martian magma chamber from which this rock originated. The researchers, led by Nicola Mari from the University of Glasgow, concluded that vigorous crystal convection driven by a huge internal heat caused the unusual patterns seen in this roughly 574 million-year-old meteorite. The existence of magma convection on Mars, coupled with its lack of plate tectonics, suggests that the Red Planet could still be volcanically active, the study authors say.
On Mars’ surface, the presence of olivine, a magnesium iron silicate, is thought to be evidence for the planet’s cold and dry conditions, as water is known to weather the mineral. However, down in the mantle of terrestrial planets like Earth, olivine is found in abundance. But it was the irregularly spaced bands of phosphorous in the olivine crystals that formed in the so-called Tissnit magma chamber which gave away its turbulent trips in Mars’ mantle, tens of kilometers below the surface.
The process that produces these bands, called solute trapping, occurs “when the rate of crystal growth exceeds the rate at which phosphorus can diffuse through the melt,” Mari told IFLScience. “Thus the phosphorus is obliged to enter the crystal structure instead of 'swimming' in the liquid magma.”
Published in Meteoritics and Planetary Science, Mari’s study explains that the rapid formation of olivine crystals that gave rise to the phosphorous bands was thanks to a vigorous convection current in the Tissint magma chamber. “Olivines were moved from the bottom of the chamber (hotter) to the top (cooler) very rapidly – to be precise, this likely generated cooling rates of 15-30°C per hour,” Mari explained.
Using the larger of the two olivine populations present in the Tissint meteorite as a “thermometer”, the authors were also able to determine that the Tissint magma source reached a temperature of 1,680 °C (3,056 °F), and the local Martian mantle a temperature of 1,560 °C (2,840 °F) when the crystals were first formed, over half a billion years ago. In fact, the latter figure is consistent with the ambient mantle temperature of Earth between 4 to 2.5 billion years ago.
However, unlike Earth, Mars has not been shown to have terrestrial-style plate tectonics – which if present may act in dissipating some of this heat from the mantle. Therefore, Mars’ internal warmth (which drives the volcanic convection currents) could have been retained for longer than Earth. Which begs the question, is there still a possibility for volcanic activity on Mars?
“I really think that Mars could be a still volcanically active world today, and these new results point toward this,” Mari said. “We may not see a volcanic eruption on Mars for the next 5 million years, but this doesn't mean that the planet is inactive. It could just mean that the timing between eruptions on Mars and Earth is different, and instead of seeing one or more eruptions per day, as on Earth…we could see a Martian eruption every n-millions of years.”
With the first findings from NASA’s InSight Mission revealed earlier this year, future discoveries below the Martian surface could shed more light on the planet’s volcanic past.
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