Method 1[]
According to this site, the Grand Canyon has a volume of 4.17 trillion meters^3. Converting it to cubic centimeters makes it 4.17*10^18 cm^3.
Half of that is: 4.17*10^18 / 2 = 2.085*10^18 cm^3
In the image shown above, the debris were small that a lot of small debris are even smaller than the repulsors itself. So let's use v. fragmentation:
2.085*10^18 cm^3 * 69 = 1.43865*10^20 joules or 34.384 gigatons of TNT (Island Level)
Method 2[]
According to the Wikipedia, Grand Canyon is 446 km long, is 29 km wide and has a depth of 1.9 km. Multiplying them (v = l*w*h) will contribute into a volume of 24575 km^3. Converting it to cubic centimeters makes it 2.46*10^19 cm^3.
Half of that is: 2.46*10^19 / 2 = 1.23*10^19 cm^3
In the image shown above, the debris were small that a lot of small debris are even smaller than the repulsors itself. So let's use v. fragmentation:
1.23*10^19 cm^3 * 69 = 8.49*10^20 joules or 202.916 gigatons of TNT (Large Island Level)
Update:[]
The original calculation used the maximum amount of width. The average width according to Wikipedia; (6.4 km + 29 km) then divided by 2 is 17.7 km.
(446 km * 17.7 km * 1.857 km) / 2 = 7.329*10^18 cm^3
7.329*10^18 cm^3 * 69 = 5.057*10^20 joules or 120.865 gigatons of TNT (still Large Island Level)
Conclusion[]
So either Island Level or Large Island Level AP for one of Iron Man's weaker armors. Not to mention his Extremis armor is far stronger and more advanced. Personally, I prefer Method 2.