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<p>Petit-spot volcanoes, occurring due to plate flexure, have been reported globally. As the petit-spot melts ascend from the asthenosphere, they provide crucial information of the lithosphere–asthenosphere boundary. Herein, we examined the lava outcrops of six monogenetic volcanoes formed by petit-spot volcanism in the western Pacific. We then analyzed the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msup><mi/><mn mathvariant="normal">40</mn></msup><mi mathvariant="normal">Ar</mi><msup><mo>/</mo><mn mathvariant="normal">39</mn></msup><mi mathvariant="normal">Ar</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="49pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="1b3028ccc4b469916ef2e4ca2dcca302"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-15-167-2024-ie00001.svg" width="49pt" height="15pt" src="se-15-167-2024-ie00001.png"/></svg:svg></span></span> ages, major and trace element compositions, and <span class="inline-formula">Sr</span>, <span class="inline-formula">Nd</span>, and <span class="inline-formula">Pb</span> isotopic ratios of the petit-spot basalts. The <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msup><mi/><mn mathvariant="normal">40</mn></msup><mi mathvariant="normal">Ar</mi><msup><mo>/</mo><mn mathvariant="normal">39</mn></msup><mi mathvariant="normal">Ar</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="49pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="644829f092a7f46da57c485ba10d080e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-15-167-2024-ie00002.svg" width="49pt" height="15pt" src="se-15-167-2024-ie00002.png"/></svg:svg></span></span> ages of two monogenetic volcanoes were ca. 2.6 Ma (million years ago) and ca. 0 Ma. The isotopic compositions of the western Pacific petit-spot basalts suggest geochemically similar melting sources. They were likely derived from a mixture of high-<span class="inline-formula"><i>μ</i></span> (HIMU) mantle-like and enriched mantle (EM)-1-like components related to carbonatitic/carbonated materials and recycled crustal components. The characteristic trace element composition (i.e., <span class="inline-formula">Zr</span>, <span class="inline-formula">Hf</span>, and <span class="inline-formula">Ti</span> depletions) of the western Pacific petit-spot magmas could be explained by the partial melting of <span class="inline-formula">∼</span> 5 % crust bearing garnet lherzolite, with 10 % carbonatite flux to a given mass of the source, as implied by a mass-balance-based melting model. This result confirms the involvement of carbonatite melt and recycled crust in the source of petit-spot melts. It provides insights into the genesis of tectonic-induced volcanoes, including the Hawaiian North Arch and Samoan petit-spot-like rejuvenated volcanoes that have a similar trace element composition to petit-spot basalts.</p>