By Carla Mozee

Major Latin American equity markets finished mixed Thursday, with benchmarks in Brazil and Argentina finding strength from surges in prices for crude oil and metals in the wake of the U.S. Federal Reserve's plan to pump up the money supply.

Argentina's Merval rose 1.2%, with Buenos Aires-listed shares of Brazilian oil giant Petroleo Brasileiro up 3.5%, Petrobras Energia (PZE) up 2.5% and Tenaris (TS), maker of steel tubes for use in the oil industry, higher by 3.8%.

The stocks benefited from a 7% jump in crude-oil futures to above $51 a barrel for their best closing level in nearly four months.

In the metals market, silver rallied nearly 13% to $13.445 an ounce and copper for May delivery surged 5.3% to $1.8075 a pound.

Commodities as tracked by the Reuters/Jefferies CRB Index (CRB) gained 5.3%.

The prospect that the ailing U.S. economy may soon find firmer ground boosted prices for natural resources. The U.S. Federal Reserve surprised the markets Wednesday when it said it will buy $300 billion in longer-term Treasury bonds and purchase more mortgage-backed securities.

The central bank "promised everything and more that the Fed can do to stabilize the economy and banks," wrote Sherry Cooper, chief economist at BMO Capital Markets, in a note. "As well, the Fed committed to keeping the overnight rate at 0-to-25 basis points for an extended period of time. It doesn't get more aggressive than that."

Petrobras (PBR) shares traded in Sao Paulo climbed 3.4% as oil prices surged. Also, the company may begin drilling in Cuba's coast within about a year, according to a Dow Jones Newswire report, citing Brazilian Mines and Energy Minister Edison Lobao.

Lobao also told the news agency on Wednesday that Brazil is considering joining the Organization of Petroleum Exporting Countries, but the move would be the right one only if Brazil becomes an oil exporter.

Brazil's Bovespa index rose 0.8% to 40,453.43 with help from steel stocks. Usiminas climbed 6.4%, Vale (RIO) rose 1.3%, and Gerdau (GGB) picked up 0.4%.

Investors also assessed minutes from last week's meeting of Brazilian central bankers, at which they cut the key Selic rate to 11.25%.

The overall tone of the minutes was "relatively dovish, in line with the 150 [basis points] interest rate cut," wrote analysts who cover Latin America at Barclays Capital Research.

"The most important dovish hints are the evaluation that domestic demand is adjusting considerably (the meeting was one day after the dismal 4Q09 GDP release), that activity weakness will probably be persistent, and that this should contain inflation."

Barclays analysts backed their forecast for another rate cut of 150 basis points on April 30, "but recognize that the pace of cuts could be lowered."

On Friday, Mexican central bankers will release their decision on interest rates. Analysts expect the Bank of Mexico to cut its benchmark rate by 25 basis points to 7.25%, according to a Dow Jones Newswire survey.

Mexico's IPC lost an earlier advance to close down 0.1%.

Most metals stocks showed strength. Industrias Penoles shares rose 3% and copper miner Grupo Mexico rose 1.3%.

Cemex shares fell 1.2% ahead of the cement maker's first-quarter results due after market close.

Moody's on Thursday downgraded the senior notes of the company's Rinker Materials unit to B2 from B1. The ratings agency also said it will subsequently withdraw the rating based on its "belief that on a go-forward basis it will lack the appropriate information to effectively assess the creditworthiness of Rinker, and its parent, Cemex."

Cemex has been working with its bankers to restructure about $14.5 billion in debt, much of its Cemex accumulated when it purchased Rinker in 2007.

In Santiago, the IPSA index shed 0.4% at 2,502.52.