I agree dangineer.
Much of Mercury does appear much too old to be from a remnant core of a former gas giant.
Also as I said, there would have been volcanism from the heat generated from the core, mantle, crust seperation, then perhaps a slightly later episode when the core itself differentiated.
Mercury is not a core of a former gas giant, in fact IMO all evidence points to Mercury being more or less the same size & mass since formation, in the inner regions of the protoplanetary nebula.
About 40% of Mercury is covered by lava plains, most of the rest is fairly heavily cratered (though not unformily). Also there appears to be a region of 30% of the surface being generaly smoother, with a similar amount being heavily cratered, suggesting that perhaps Mercury was one Sun synhronous, i.e did at one time keep the same side facing the Sun, with the smoother terrain being the former trailing side & the more cratered area leading??
If we are going down the erroneous route of Mercury once being a core of a former gas giant (IMHO), than why not suppose that Venus, Earth & Mars are also exposed cores of former gas giants???
It does not stand up to closer scrutiny.
Andrew Brown.