Starting Elo is 1000 for 1v1 and team games.
But if you already have a 1v1 rating, than it will be used to adjust your team game rating. Same is true if you have already a team game rating. It will be used as starting point for 1v1.
The main issue is that team game ratings are for some reason inflated. Everyone gets more points than the loose. Based on the graphs 1350 TG Elo = 1000 1v1 Elo. TG rating is inflated by around 350 already and still inflate even further.
The question: Why do we gain more points than we loose, is still unanswered for me. I asked the same question in my own thread (Analyses of the ratings - Spotting the issues). No one really answered that question. I hope the devs know the answer and also know the fix. Otherwise ranked team games will be dead very quickly.