GLOBAL MARKETS-Growth worries grip stocks, oil markets

* Oil prices hit two-year lows* Investors wait for Fed minutes* Treasury bond prices up, dollar extends gains(Adds U.S. market open, changes byline, changes dateline, previously LONDON, recasts lead)By Yasmeen AbutalebNEW YORK, Oct 8 (Reuters) - An index of global equities hit a six-month low and oil prices slumped again on Wednesday, as investors reduced positions in riskier assets amid concerns