GLOBAL MARKETS-Trade tensions hit stocks, while oil craters on supply fears

* GRAPHIC-World FX rates in 2018: http://tmsnrt.rs/2egbfVh * Trump OKs $50B in tariffs as China vows retaliation * European, emerging market stocks down more than 1 percent each * Oil down 3 pct on prospect for higher output (Updates with afternoon trading) By Nick Brown NEW YORK, June 15 (Reuters) - Share prices extended their slide across the globe in U.S. afternoon trading on Friday after U.S. President Donald Trump announced new tariffs on Chinese goods, while oil p