I understand that you want to concatenate all the 35 3-D matrices to a 4-D matrix and also want to take the mean across the data from all the 35 files.
The solution to this is to use "cat" function and the "mean" function. Example code snippet on how to use "cat" and "mean" for your situation is shown below.
a = ones(320,104,1457);
b = ones(320,104,1457);
c = cat(4,a,b);
d = mean(c,4);
So, like this you can concatenate all the 35 files which you have by using a loop.
