EMERGING MARKETS-Latam markets sink on Ukraine, China worries

(Recasts; adds quotes, context on Petrobras; updates prices) By Asher Levine SAO PAULO, April 15 (Reuters) - Latin American stocks and currencies dropped on Tuesday, with investor concerns over escalating tensions in Ukraine and potentially weaker growth in key trade partner China sapping enthusiasm for emerging market assets. The MSCI Latin American stock index posted its biggest one-day drop in nearly three months, while nearly every currency in the region weakened against the U.S.