Heavy element accumulation and stellar mass assembly are fundamental processes in the formation and evolution of galaxies. However, the key elements that govern them, such as gas accretion and outflow, are not fully understood. This is especially true for luminous and massive galaxies, which usually suffer strong feedback as massive outflows and large-scale gas accretion triggered by galaxy interactions. Using a sample of 77 luminous infrared (IR) galaxies, we derive chemical abundances using new diagnostics based on nebular IR lines, which peer through their dusty medium and allow us to include the obscured metals. In contrast to optically based studies, our analysis reveals that most luminous IR galaxies remain close to the mass–metallicity relation. Four galaxies with extreme star formation rates (>60 M_⊙ yr⁻¹) in their late-merger stages show strongly depressed metallicities (12 + log(O/H) ≈ 7.7–8.1) along with solar-like N/O ratios, indicative of gas mixing processes and suggesting the action of massive infall of metal-poor gas in a short phase, eventually followed by rapid enrichment. These results challenge the classical gas equilibrium scenario applied to main-sequence galaxies, suggesting that chemical enrichment and stellar-mass growth in luminous IR galaxies likely occur via mergers, driving these galaxies out of chemical equilibrium.

重元素积累和恒星质量聚集是星系形成和演化的基本过程。然而，控制它们的关键因素，例如气体吸积和流出，尚不完全清楚。对于发光星系和大质量星系来说尤其如此，它们通常会受到星系相互作用引发的大规模流出和大规模气体吸积的强烈反馈。使用 77 个发光红外 (IR) 星系的样本，我们使用基于星云红外线的新诊断方法推导出化学丰度，这些红外线可以透过它们的尘埃介质进行观察，使我们能够将被遮挡的金属包括在内。与基于光学的研究相比，我们的分析表明，大多数发光红外星系仍然接近质量-金属丰度关系。四个在合并后期具有极端恒星形成率（>60  M _⊙  yr ^-1 ）的星系显示出强烈降低的金属丰度（12 + log(O/H) ≈ 7.7–8.1）以及类似太阳的 N/O 比率，表明气体混合过程，并表明贫金属气体在短时间内大量流入，最终迅速富集。这些结果挑战了应用于主序星系的经典气体平衡情景，表明发光红外星系中的化学富集和恒星质量增长可能通过合并发生，从而使这些星系脱离化学平衡。