Very many thanks for the highly constructive points raised! Please note that I raise these here as highly speculative stipulations and as a sort of brainstorming attempt and I do not see - at least for now any evidence - of geological activity. Yet, I wish to raise further detailed points for your consideration.)
I'm enclosing a very typical scenery of glacier-shaped rocks and boulders from Greenland. Even volcanic rocks, as hard they may be, are impacted and subjected to the milling of ice domes from above (if rocks were covered by one). I have seen many volatile structures on that region (unlike the Svalbard) that do not appear in any way round but look like a frozen in time, a still frame. The overall appearance is similar to water-flooding impacted strata of the Grand Canyon region, not an ice sheet gourged one. For me, the region has perhaps undergone strong isostatic uplift, but it was impacted by water floods, Jokullhaups, turning it to the Grand Canyon of Greenland. It is not geomorphic according to the ice sheet planing, if it were the volcanic mountains would have a distinctive smooth rise facing the direction ice sheet had flowed, with steep rear sides.
Source of these floods would then be Jokullhaups.
The volatile structures preserved is, therefore, suggestive to me that the rocks were hot when the ice sheet was forming (and hence expelling the local ice development unlike elsewhere). As Jokullhaups periodically discharged water and lahar, the loose, slushy stratum eroded rapidly.
If so, then the volcanic incursion is associated with the Central Greenland's subsidence when the ice dome was being deposited onto the Precambrian granites across Greenland. Thus, the incursion of magma is a result of ice sheet compressing subglacial magma reservoir and driving a partial melting of asthenosphere beneath the glaciating region - with the partial melting breakdown products being driven out here near this edge area of Greenland continental plate (where plate's weaknesses are greatest). The only option is for me to go and collect more volatile rock structure evidence which would dispel the idea of ice having carved out this peculiar area. That's a future project for me and these expeditions are costly!
There are earthquakes and the Nantortalik hot spring. I suspect that there must be more hot springs hidden beneath ice sheet as the faults are myriad. Hot springs could be behind some of the subglacial heat anomalies are found in various parts of Greenland. Today more pressurized water is fed into subglacial faults by water from moulins that are becoming increasingly active over perimetrical subglacial bedrock. Moulins one day number in millions over perimeter shield.
I expect the volcanic region (potentially) evolving to the Mascarene volcanism. A two-phase volcanism where a low viscosity, vast lava floods are followed by a long non-active interval to the previous episodes of vast effusive volcanic eruptions. Then a smaller secondary episode re-emerges a new bout of different type of volcanism which shatters the old crust and causes mountain incursions to pierce the old, lava field by the extremely high viscosity (cool) secondary lavas. This renewal of eruptivity thus shatters the solidified ('extinct') flat lava volcano field. The secondary volcanism in the Mascarene volcanos had so high viscosity that many eruptions caused vertically rising lava floods (like a toothpaste comes out of the tube when it is pointed upwards).
In the Mascareane volcanism, the force of high viscous rock oozing through flat lava field was so great that nearly all secondary volcanoes go vertigo through the plain, lava rising vertically skyward. Even parts of the old solidified lava crust sitting as a tip of the newly oozing highly viscous lava with the old solid blocks of lava becoming a mushroom-like 'hat' shapes for the volcano, i.e. Peter Both 'hat' cap.
https://upload.wikimedia.org/wikipedia/commons/b/b3/Pieter_Both%2C_mountain.jpg These vertical formations rising from flat lava landscapes.
The question is of course how solid is the high viscous incursion and whether such incursions could make way up once Greenland ice sheet melts. What drives high viscous lava up is not exactly clear but some disassociation of gases must have happened, maybe further afield, pressure change reverberated from nucleating lavas elsewhere to make cool rocks to cause secondary Mascarene eruptivity. In the case of deglaciation, this could be the secondary trigger, whereas the low viscous eruptivity would have been the primary trigger, a forming ice sheet.
It is my view that the secondary Mascarene volcanism was driven by gaseous disassociating within low viscous magmas in long distance, perhaps when the hot spot was already transiting from Mauritius to nearby Reunion. Events in Iceland and/or deep partial melting in asthenosphere under Greenland could be the source to force old cool lavas in Greenland once the ice sheet mass balance losses become large enough to create Mauritian style new volcanic life on the old volcanic region.
By the way, whilst climbing to study Mount Lepus I came also across old continental blocks of rock embedded in these high viscous plumes of semi-solid rocks that had broken through the primary plain of solidified lavas and seabed. (Only years after people theorized this sunken continent.)
