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HARPS spectra with signal-to-noise ratios S/N > 600 at 6000 A were analysedwith MARCS model atmospheres to obtain 1D LTE abundances of C, O, Na, Mg, Al,Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y for 72 nearby solar-type stars withmetallicities in the range -0.3 < [Fe/H] < +0.3 and ASTEC stellar models wereused to determine stellar ages from effective temperatures, luminositiesobtained via Gaia DR2 parallaxes, and heavy element abundances. The resultingage-metallicity distribution appears to consist of two distinct populations: asequence of old stars with a steep rise of [Fe/H] to about +0.3 dex at an ageof ~7 Gyr and a younger sequence with [Fe/H] increasing from -0.3 dex to about+0.2 dex over the last six Gyr. Furthermore, the trends of several abundanceratios, [O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar agesplit into two corresponding sequences. The [Y/Mg]-age relation, on the otherhand, shows no offset between the two age sequences and has no significantdependence on [Fe/H], but the components of a visual binary star, zetaReticuli, have a large and puzzling deviation. The split of the age-metallicitydistribution into two sequences may be interpreted as evidence of two episodesof accretion of gas onto the Galactic disk with a quenching of star formationin between. Some of the [X/Fe]-age relations support this scenario but otherrelations are not so easy to explain, which calls for a deeper study ofsystematic errors in the derived abundances as a function of [Fe/H], inparticular 3D non-LTE effects.

High-precision abundances of elements in solar-type stars. Evidence of two distinct sequences in abundance-age relations