NEW YORK (Reuters) - Oil prices lurched 5 percent lower on Monday to their lowest since January, taking global benchmark Brent below $50 a barrel as weak factory activity in China deepened a commodity-wide rout. Growing concerns over excess global oil supplies, heavy selling in pumped-up gasoline futures and technically driven momentum trading knocked prices to within a few dollars of the six-year lows touched at the start of this year. U.S. crude had already fallen 21 percent in July, its worst month since 2008 amid mounting evidence of an expanding global glut and a stock market collapse in China,...