* Power to leave in Feb 2018, no successor named
* 'Consistent with long-term succession plan' - Chmn
* Shares drop 4.2 pct to lowest in nearly a month (Adds details on Power's tenure, share move)
Sept 15 (Reuters) - The world's fourth-biggest iron ore miner Fortescue Metals Group FMG.AX said on Friday that Chief Executive Neville Power will step down in February next year, a surprise announcement that didn't name a successor and sent shares sharply lower.
The stock was off 4.2 percent by 0230 GMT at A$5.57, its lowest in nearly a month, after opening weakened on commodity price concerns as investors digested news of Power's departure just a few weeks after steering the miner to a record final dividend on annual profit that more than doubled. Australian benchmark index was off about 0.9 percent.
"This is consistent with our long-term succession plan," Chairman Andrew Forrest said in the statement disclosing Power's departure. The statement didn't say when Fortescue will name its next CEO.
Appointed as CEO in July 2011, mining industry veteran Power has overseen a quadrupling in the company's production to 170 million tonnes per year, the company's website shows.
Since Power took the helm, the company's revenue has risen 55 percent to $8.4 billion, and its market value now stands at about A$18 billion ($14.39 billion).
The move is the second top management change at the miner to be announced this year. Fortescue appointed Elizabeth Gaines as its chief financial officer in January this year. ($1 = 1.2511 Australian dollars)