You may not receive all of the tectonic fragments needed for this quest on one run through the zone. (Note: When I did this quest, I killed the Stones of Thudos even though they were non-aggro, before I killed the mobs near them. I received more than enough tectonic fragments to complete the quest.)
Proceed through the rest of the zone and kill the Council of Four at ( 1340, 784, 39 ) Copy/waypoint 1340, 784, 39
Note that you cannot log out during this zone. If you do, the Stones of Thudos in the zone will respawn, preventing you from opening any door leading higher. (As of July 24, 2021, it is possible to re-enter the zone an hour later, access every level; find the Portal to the Heart of Thudos and complete the quest.)
Use the Portal to Heart of Thudos that appears at ( 1501, 784, 42 ) Copy/waypoint 1501, 784, 42.
Click on The Thudos Corestone at ( -216, 113, 160 ) Copy/waypoint -216, 113, 160 to cleanse the The Thudos Corestone of the errant elemental aspects.