That pic is blocks of water ice crust. The water-ice has been disrupted into blocks that are now almost buried by weaker kinds of ice (nitrogen, carbon monoxide). The closer you go to the edge of Sputnik Planum in that part of Pluto, the more numerous the projecting blocks of water-ice; presumably the N2/CO ice is thicker towards the centre of Sputnik Planum.

Thank-You Professor...I have very limited knowledge of our Solar Systems Moons or Planets (I wish I'd have studied more about these back at school) but I do know I get excited every time we receive data such as this from various projects & missions (and we've had so many great one's lately)

I can only think that most (including yourself) back at mission control could hardly believe their eyes at what they were seeing on both Pluto & Charon, which to my eyes seemed to have been far more interesting than perhaps we could have imagined...and the detail!!! the detail is simply wonderful.

A Wikipedia link for you folks out there (below) this would seem to be a very interesting place to explore if ever possible in the future.
en.wikipedia.org/wiki/Sputnik_Planum