Also, the follow on from this was that this led to the ceasing of mantle convection which ended the possibilities of plate tectonics? Could somebody more knowledgable than I perhaps outline a theory of why this is?
In addition if mantle convection has ceased, than when do we think it stopped being active?
Analysis shows that 4.5 billion years ago - when Mars was forming along with the rest of the solar system - two distinct "reservoirs" formed in the mantle - the "Enriched Reservoir" (ER) and the "Depleted Reservoir" (DR). The ER had high ratios of lanthanum/ytterbium and $^{87}$Sr/$^{86}$Sr, and a low ratio of samarium/neodymium. The DR had the opposite ratios.
Eventually, meteorites known as shergottites formed, mixtures of both of these reservoirs. A graph (which I'd insert here, but I'm unsure of the copyright on it) entitled "Heterogeneous Martian Mantle" illustrates how these meteorites have a wide range of composition compared to rocks from Earth. This provides compelling evidence for a heterogeneous Martian mantle.
At the moment, I can't find enough information to answer the follow-up part, though the convection certainly did stop.
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