Incremental accumulator by subvectoring
To code in a more functional style, break it down starting with the smallest pieces.  I would do it like this:

(defn head-accum [n coll]
  (reduce + (take n coll)))

(defn tail-accum [n coll]
  (reduce + (drop n coll)))

(defn pair-accum [n coll]
  [ (head-accum n coll)
    (tail-accum n coll) ] )

(defn all-pair-accum [coll]
  (let [n-vals (count coll) ]
    (for [split-val (range 1 n-vals) ]
      (pair-accum split-val coll))))

(println (all-pair-accum (range 11)))

;=&gt; ([0 55] [1 54] [3 52] [6 49] [10 45] [15 40] [21 34] [28 27] [36 19] [45 10])