Slashed outlooks from Nvidia Corp and Symantec Corp knocked chipmakers lower on Thursday, raising questions about demand for technology components and igniting a broad selloff.

Both companies cut expectations for the next quarter, giving additional weight to concerns that the economy was growing at a slower pace than initially anticipated and leading investors to reset their growth expectations for the second half.

Nvidia Corp was down 9.8 percent to $9.14, and Symantec Corp, the world's No. 1 security software maker, fell 11.7 percent to $12.95.

Expectations in the marketplace are particularly aggressive for tech as a whole in terms of consensus expectations, said Greg Woodard, portfolio strategist with Manning & Napier Advisors, Inc. in Fairport, New York. The rate of change is probably much lower than what's currently baked into these higher-than-expected growth stocks.

The Dow Jones industrial average <.DJI> dropped 78.10 points, or 0.74 percent, to 10,419.78. The Standard & Poor's 500 Index <.SPX> dropped 10.52 points, or 0.95 percent, to 1,095.61. The Nasdaq Composite Index <.IXIC> dropped 29.65 points, or 1.31 percent, to 2,234.91.

The PHLX semiconductor index <.SOXX> fell 2.8 percent, its largest percentage decline in nearly two weeks, taking the index near its 200-day moving average. The 200-day average, now near 348, served as resistance on July 20.

A close below 347 or 345 would imply we're heading back down to the bottom of the (recent) range, said Craig Peskin, co-head of technical analysis research at Concept Capital in New York.

The index has been in a 324-377 range since early May and hit a five-week closing high just below 370 on Monday.

Exxon Mobil Corp , the S&P's largest company by market capitalization, fell 0.5 percent to $60.61 despite reporting stronger-than-expected quarterly profit.

Consumer staples also fell, with the S&P consumer staple index falling 1.5 percent after results and a lowered outlook from Kellogg Co . Kellogg Co fell 5 percent to $48.95.

So far, 60 percent of companies in the S&P 500 have reported quarterly earnings. Of those, 75 percent beat expectations and earnings have grown 35.1 percent year-over-year, according to Thomson Reuters Proprietary Research.

But forecasts for the third and fourth quarters, which investors are using as a barometer for the economic recovery, have frequently missed the mark.

Earnings are looking good but confidence in the future is missing, said Gail Dudack, chief investment strategist at Dudack Research Group in New York.

The S&P 500 remained below its 200-day moving average, breaking it only briefly after failing to close above on Wednesday. It also remained slightly below its 50 percent Fibonacci retracement. The 200-day moving average and Fibonacci retracements are seen by many investors as a key measure of market direction.

(Reporting by Matthew Lynley; Additional reporting by Leah Schnurr, Rodrigo Campos and Chuck Mikolajczak; Editing by Kenneth Barry)

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