a question for phonologie

I have one question for people who understand something more as me about
phonology.
I will like to know about the sounds noted in Romanian with "ã" and "î"
or "â"

If /ã/ seems to be an /a/ then what about the second one, this strange
/â/ or /î/ ?
Is this sound a evolution of /ã/ kind of /a/ > /ã/ > /â/ or is this one
an evolution of /i/, kind of /i/ > /î/ ?

many thanks in advance,
Alex