Context : The so-called lithium depletion boundary ( LDB ) provides a secure and independent tool for deriving the ages of young open clusters .

Aims : In this context , our goal is to determine membership for a sample of 147 photometrically selected candidates of the young open cluster IC 4665 and to use confirmed members to establish an age based on the LDB .

Methods : Employing the FLAMES multi-object spectrograph on VLT/UT2 , we have obtained intermediate-resolution spectra of the cluster candidates .
The spectra were used to measure radial velocities and to infer the presence of the Li i 670.8 nm doublet and H \alpha emission .

Results : We have identified 39 bona fide cluster members based on radial velocity , H \alpha emission , and Li absorption .
The mean radial velocity of IC 4665 is found to be V _ { rad } = -15.95 \pm 1.13 km/s .
Confirmed cluster members display a sharp transition in magnitude between stars with and without lithium , both in the I _ { m } vs .
I _ { m } - z and in the K _ { s } vs .
I _ { C } - K _ { s } diagrams .
From this boundary , we deduce a cluster age of 27.7 ^ { +4.2 } _ { -3.5 } \pm 1.1 \pm 2 Myr .

Conclusions : IC 4665 is the fifth cluster for which an LDB age has been determined , and it is the youngest cluster among these five .
Thus , the LDB is established from relatively bright stars still in the contracting pre-main sequence phase .
The mass of the boundary is M _ { \ast } = 0.24 \pm 0.04 M _ { \odot } .
The LDB age agrees well with the ages derived from isochrone fitting of both low and high mass , turn–off stars , a result similar to what is found in the slightly older NGC 2547 .