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<p>The North Pamir, part of the western syntax of the India–Asia collision zone, preserves remnants of a poorly understood Paleozoic intra-oceanic subduction zone. To constrain the age of this ancient ocean floor, we analyzed calcite phases in vesicular basalt and basaltic volcanic breccia with <span class="inline-formula">U</span>–<span class="inline-formula">Pb</span> geochronology using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Dating of radial fibrous to equant spary calcite yielded three meaningful Visean–Serpukhovian ages. Rare-earth elements and yttrium (REE <span class="inline-formula">+</span> <span class="inline-formula">Y</span>) data reveal that the basaltic host rock of the calcite and oxidizing seawater are major sources of trace elements during calcite precipitation. <span class="inline-formula">U</span>–<span class="inline-formula">Pb</span> ages seem to be independent of REE <span class="inline-formula">+</span> <span class="inline-formula">Y</span> concentrations. Our results demonstrate the potential of calcite dating to constrain the age of ancient ocean floors. We challenge the hypothesis that a continuous early Paleozoic Kunlun Terrane extended from northern Tibet into the North Pamir.</p>