Adjustable guide vane for a turbine, and method for producing an adjustable nozzle assembly

The invention relates to an adjustable diffuser for a turbine, particularly for a turbine (2) an exhaust gas turbocharger, having a carrier ring (10) comprising a plurality of the support ring (10) rotatably mounted vanes (11), and with a contoured ring (12), wherein the support ring (10) opposite coaxial axially arranged, such that the guide vanes (11) are rotatably positioned between the support ring (10) and the contour ring (12). According to the invention, the contour ring (12) on a first ring portion (17) and a second ring portion (18), which movements relative to each other are formed executable.