By Jack Kimball and Helen Murphy
BOGOTA (Reuters) - Colombian President Juan Manuel Santos announced on Thursday he replaced his finance minister, in a move that surprised financial markets, and named current Energy Minister Mauricio Cardenas to take over running Latin America's fourth-largest economy.
At the midpoint of his four-year term, Santos late on Wednesday asked all 16 ministers to resign, including Finance Minister Juan Carlos Echeverry, setting the stage for a cabinet shuffle aimed at shoring up his slumping approval ratings.
It was not immediately known when Cardenas, who holds a doctorate in economics from the University of California at Berkeley, would take on his new role.
Santos, after naming Cardenas, said he was "designed for finance minister." Cardenas previously held ministerial posts in economic development and transport.
Among other posts that also may be changed in the coming days are education, health, interior, agriculture and defence, according to government sources.
"Cardenas is an extremely well known and respected economist, with fiscally sound ideas, so from a market perspective this will be well received," said Alberto Bernal, head of research for Bulltick Capital Markets in Miami.
"What's more important now for the market is the political makeup for the entire Santos cabinet."
Santos did not say who would be the next minister of mines and energy. Echeverry will be nominated for a top role in the International Monetary Fund, Santos said.
The 61-year-old Santos has been under pressure from a constant stream of criticism from former President Alvaro Uribe and a growing number of attacks by leftist rebels, denting his once commanding popularity.
Some analysts said Defence Minister Juan Carlos Pinzon could be on the list of those leaving after a rise in guerrilla assaults, coupled with the perception that security was getting worse.
Santos, credited with some of the biggest blows to the rebels, accuses foes of using attacks by rebels as a "political weapon" and dismisses claims by Uribe and his followers that he is failing on security.
Once an investment pariah as drug-trafficking insurgents kidnapped, killed and attacked rural areas with bombs, Colombia has seen a dramatic turnaround in the last decade, attracting record foreign investment.
(Editing by Sandra Maler and Leslie Adler)
