We report here the first results of a multi-wavelength campaign focussing on magnetospheric accretion processes within the close binary system V4046Â Sgr , hosting two partly-convective classical TÂ Tauri stars of masses \simeq 0.9Â { M } _ { \odot } Â and age \simeq 12Â Myr . In this paper , we present time-resolved spectropolarimetric observations collected in 2009 September with ESPaDOnS at the Canada-France-Hawaii Telescope ( CFHT ) and covering a full span of 7Â d or \simeq 2.5 orbital/rotational cycles of V4046Â Sgr . Small circularly polarised Zeeman signatures are detected in the photospheric absorption lines but not in the accretion-powered emission lines of V4046Â Sgr , thereby demonstrating that both system components host large-scale magnetic fields weaker and more complex than those of younger , fully-convective cTTSs of only a few Myr and similar masses . Applying our tomographic imaging tools to the collected data set , we reconstruct maps of the large-scale magnetic field , photospheric brightness and accretion-powered emission at the surfaces of both stars of V4046Â Sgr . We find that these fields include significant toroidal components , and that their poloidal components are mostly non-axisymmetric with a dipolar component of 50-100Â G strongly tilted with respect to the rotation axis ; given the similarity with fields of partly-convective main-sequence stars of similar masses and rotation periods , we conclude that these fields are most likely generated by dynamo processes . We also find that both stars in the system show cool spots close to the pole and extended regions of low-contrast , accretion-powered emission ; it suggests that mass accretion is likely distributed rather than confined in well defined high-contrast accretion spots , in agreement with the derived magnetic field complexity .