The short answer is: no, not a bannable offence in itself.
The longer answer: Funcom will only take action in extreme cases of griefing. Such as players completely blocking access from the starting spawn points into the rest of the game. Or blocking access to bosses which hold a keystone fragment which is necessary to complete the game goal of removing your bracelet and leaving the exiled lands permanently on that character.
The obelisks are not necessary for playing the game or achieving the ultimate goal of removing your bracelet therefore blocking them is not extreme enough in itself to warrant a ban.
Your server (1130) I believe is a PvP server … therefore it is on the players of that server to deal with the blocking buildings and the players creating them by yourselves. Harsh but the reality of playing on the official Funcom servers as Funcom does not offer a typical hands-on moderation on them.
Official Funcom statement on harassment and griefing on official servers:
https://forums.funcom.com/t/harassment-and-griefing-issues/15950