'FELSIC materials' find on MARS could rewrite Red Planet's history A group of researchers have found evidence of large granite deposits on the surface of Mars, an indication that the Red Planet may be more volcanically active than originally believed. The research group from the Georgia Institute of Technology said that it has found evidence of volcanic feldspar on the martian surface, an …
AFAIK the only way that happens is if Mars is solid all the way through.
OTOH that would also seem to kill any sort of magnetic field (no molten nickel iron to generate a current), but Mars does have one (although IIRC it's not very strong).
So a Mars with no volcanoes ever would be a very surprising beast.
thumbs up for the analysis.
It wouldn't necessarily need to be solid all the way through. The top (eg) 500 km could be solid, with a more liquid core. Such a crust would likely be too thick for plate tectonics. In my limited understanding, such a situation could be relatively common for a cooling planet.
"OTOH that would also seem to kill any sort of magnetic field...but Mars does have one."
According to the usual source, "Mars has no evidence of a current structured global magnetic field, observations show that parts of the planet's crust have been magnetized, and that alternating polarity reversals of its dipole field have occurred in the past"
'AFAIK the only way that happens is if Mars is solid all the way through.'
Not at all. The Earth is solid with the exception of the Outer Core - but it convects. Venus doesn't have plate tectonics because it has an enormously thick, strong lithosphere; but its density and size suggests it *should* have a convecting interior.
Mars did have primitive plate tectonics. It shows magnetic striping similar to that on the Earth's ocean floors and the Valles Marineris is a tectonic boundary. The mystery is why plate tectonics did not develop as fully on Mars as they have on Earth. By the time we know tectonics were going on Earth (there is still some debate about them in the first 600Ma of the Earth's history), Mars's interior would have been hot enough to support tectonism, but many of the features we associate with tectonics on Earth are absent on Mars.
More likely, the outer core is more in a plastic state than fluid state. That would halt the currents that would create the dynamo effect.
It would also account for the apparent thick lithosphere. It just cooled off a bit quicker, less mass and all.
And of course, one less impact than Earth had, which tended to melt everything all over again.
''A felsic igneous rock, granite is normally formed on earth as the result of volcanic activity and other tectonic phenomena. ''
Granite is not the result of volcanic activity. It is a plutonic rock formed at depth; it can be created by fractionating a more primitive magma, or, it can be created by depressurising deeply-buried crustal rocks.
Without a surface mission it will be hard to say if the rocks are indeed granite and have been exposed by erosion or faulting; or if they are corresponding felsic volcanic rocks that were erupted on to the surface. If the latter, it will be interesting, as it is a new rock type for Mars and it will imply magma was in existence long enough at relatively shallow depths to undergo fractionation. Similar felsic eruptions occur here on Earth, such as the Öræfajökull in Iceland, which has produced the amazing rhyolite and obsidian landscape of Landmannalaugur despite being source by quite primitive Mantle-derived basalts.
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