In metals, gold tumbled $37.80, or 2.3%, to $1,602 a troy ounce.

Volatility lurched 6.2% higher as tracked by the CBOE's VIX, while the yield on the 10-year U.S. Treasury slumped 0.073-percentage point to 1.845%. The breadth of the selling was wide, with more than seven declining shares trading hands on the New York Stock Exchange for each advancing share. 

Greek Worries Flare Up

Elections over the weekend in Greece saw the two mainstream political parties there failing to hold a combined majority in parliament. The PASOK and New Democracy parties had been critical players in drafting agreements with eurozone leadership on implementing deficit-cutting measures in exchange for bailout funds needed to avoid a default. 

Reeling from the painful economic consequences of the austerity measures, votes were distributed between PASOK, New Democracy and several other parties, all of which are trying to push for their own policies.