read matrix

I would like to read 9 sub-matrices from a 16*16 matrix.

A [0,0] [6][6] B [0,6] [6][4] C [0,10] [6][6]

D [6,0] [6][6] E [6,6] [6][4] F [6,10] [6][6]

G [12,0] [4][6] H [12,6] [4][4] I [12,10] [4][6]

Does anyone knows a function which automatically reads the matrices if I define the starting point? later if I can read the sub-matrices I want to create a [3][3] matrix with the means.