How to find min or max in constant time using infinite # processors?
I managed to solve this so hoping it's alright to answer your own question.
Initialize to all elements off, an $n$ bit vector $A$ having a 1:1 mapping with the $n $ numbers. Compare each number against every other number on $n \choose 2$ processors. Each processor switches the bit corresponding to the smaller of its two elements to 1. Assumption is that the processors can do concurrent writes to $A$. The bit in $A$ remaining off denotes the maximum element.

This is $\Theta(1)$ (constant time) as the depth of the computational graph is independent of the number of elements. The work required is however $\mathcal {O(n^{2})}$.