Okay so this is something that I came across as I was writing my canons and analyzing the harmony to try to figure out which canon is best for my symphony. There is a section in one of my canons where the harmony seems to be outside of the key. Now I did get this sort of thing in another canon where I had a C power chord and then the rest of it was dissonant. But here, I seem to be getting something which is not only out of key but not all that related to the key. The key I am doing these canons in is Bb major.
My first instinct was that it was an F major chord in second inversion but without the root because of the key being Bb major. This though did not make sense. So then I decided on it being A minor. But then I started questioning myself because there is no E natural to make it clear that it is A minor and the C and the A are a sixth apart. So then I thought maybe it is A diminished without the tritone since it lands on Bb major 1.5 measures after the last statement of the chord in that section but once again it did not make sense. The tritone is what makes it sound diminished. Without the tritone, it seems wrong to call that chord A diminished.
So is the harmony in that section that I circled A minor or is it F major? And yes, the second line is a second up from the first line and delayed by 1.5 measures. If the harmony in the section I circled is indeed A minor, why did I get non-diatonic harmony out of a completely diatonic melody?