UPDATE 1-SocGen deputy CEO unexpectedly leaves after disagreement

(Updates with details)

PARIS, March 14 (Reuters) - France's Societe Generale said on Wednesday its deputy chief executive in charge of investment banking activities, Didier Valet, was leaving the group "following a divergence of approaches regarding management of a specific legal matter".

The bank did not give any more details in its statement about the legal matter and said Valet resigned in order to preserve the bank's "general interests".

The "divergence of approaches" related to investigations over the suspected rigging of the London interbank offered rate (Libor), a key interest rate used in contracts worth trillions of dollars globally, a source familiar with the matter said.

SocGen is one of several banks to be caught up in investigations into the rigging of Libor around the time of the global financial crisis. U.S. authorities charged two former SocGen managers in August with taking part in a scheme to manipulate the global U.S. dollar Libor benchmark.

"It's the biggest thing to happen in the group since the departure of Jean-Pierre Mustier," an insider said of Valet's departure, referring to what happened in 2008 when Mustier, head of the investment bank at the time of the Jerome Kerviel trading scandal, quit. Mustier is currently CEO of Italy's Unicredit.

"Didier Valet succeeded in transforming the corporate and investment banking activities, building a profitable and sustainable model," SocGen said.

Valet, a close and long-time ally of chief executive Frederic Oudea, started his career at SocGen in 2000 and was chief financial officer of the bank from 2000 to 2007. He had been at the head of investment banking activities since 2012.

Under Valet, the bank has worked on making investment bank revenue less volatile by increasing the share of fixed income activities versus equities.

The bank said his replacement would be announced shortly. (Reporting by Maya Nikolaeva; Editing by Leigh Thomas and Mark Potter)