Can anyone see what is wrong with my transpose function in F#?

Given a list of tuples, where each tuple consists of 3 integers, transpose the list recursively so that the "rows" and "columns" are swapped. The result will be a list of lists.

So for example:transpose [ (1, 2, 3); (11, 12, 13) ]=> [ [1; 11]; [2; 12]; [3; 13] ]

So I tried:

   let rec transpose LT =      match LT with      | [] -> [[], [], []]      | (a, b, c) :: tail ->         let rest = transpose tail         match rest with         | [d; e; f] -> [a::d; b::e; c::f]

but is getting the error:

All elements of a list must be implicitly convertible to the type ofthe first element, which here is ''a list * 'b list * 'c list'. Thiselement has type ''d list'.

at the list of lists [a::d; b::e; c::f]

Can anyone tell me what I'm missing or what I'm doing wrong?