The Loch Bà ring-dyke and the associated Centre 3 granites represent the main events of the final phase of activity at the Palaeogene Mull igneous complex. The Loch Bà ring-dyke is one of the best exposed ring-intrusions in the world and records intense interaction between rhyolitic and basaltic magma. To reconstruct the evolutionary history of the Centre 3 magmas, we present new major- and trace-element, and new Sr isotope data as well as the first Nd and Pb isotope data for the felsic and mafic components of the Loch Bà intrusion and associated Centre 3 granites. We also report new Sr, Nd and Pb isotope data for the various crustal compositions from the region, including Moine and Dalradian metasedimentary rocks, Lewisian gneiss, and Iona Group metasediments. Isotope data for the Loch Bà rhyolite (⁸⁷Sr/⁸⁶Sr_i = 0.716) imply a considerable contribution of local Moine-type metasedimentary crust (⁸⁷Sr/⁸⁶Sr = 0.717–0.736), whereas Loch Bà mafic inclusions (⁸⁷Sr/⁸⁶Sr_i = 0.704–0.707) are closer to established mantle values, implying that felsic melts of dominantly crustal origin mixed with newly arriving basalt. The Centre 3 microgranites (⁸⁷Sr/⁸⁶Sr_i = 0.709–0.716), are less intensely affected by crustal assimilation relative to the Loch Bá rhyolite. Pb-isotope data confirm incorporation of Moine metasediments within the Centre 3 granites. Remarkably, the combined Sr–Nd–Pb data indicate that Centre 3 magmas record no detectable interaction with underlying deep Lewisian gneiss basement, in contrast to Centre 1 and 2 lithologies. This implies that Centre 3 magmas ascended through previously depleted or insulated feeding channels into upper-crustal reservoirs where they resided within and interacted with fertile Moine-type upper crust prior to eruption or final emplacement.

LochBà环堤和相关的3号花岗岩代表了古近纪马尔火成岩复合体活动最后阶段的主要事件。巴赫环堤是世界上最裸露的环形侵入体之一，记录着流纹岩浆岩和玄武质岩浆之间的强烈相互作用。为了重建中心3岩浆的演化历史，我们提出了新的主要元素和痕量元素，以及新的Sr同位素数据，以及尼斯湖Bà侵入体及相关中心的首个Nd和Pb同位素数据3个花岗岩。我们还报告了该地区各种地壳成分的新的Sr，Nd和Pb同位素数据，包括Moine和Dalradian沉积沉积岩，Lewisian片麻岩和Iona Group沉积沉积物。海湾流纹岩的同位素数据（⁸⁷ Sr /⁸⁶ Sr _i  = 0.716）暗示了局部的Moine型沉积沉积壳（⁸⁷ Sr / ⁸⁶ Sr = 0.717-0.736）的贡献很大，而海湾巴基镁铁质包裹体（⁸⁷ Sr / ⁸⁶ Sr _i  = 0.704-0.707）更加接近成熟地幔值，表明主要是地壳起源的长英质熔体与新到的玄武岩相混合。中心3个微 花岗岩（⁸⁷ Sr / ⁸⁶ Sr _i = 0.709–0.716 ）相对于LochBá流纹岩，受地壳吸收的影响较小。铅同位素数据证实了Moine沉积物在3号中心花岗岩中的结合。值得注意的是，与中心1和2岩性相比，结合的Sr–Nd–Pb数据表明，中心3岩浆没有记录到与潜在的路易斯阶片麻岩基底的相互作用。这意味着中心3岩浆通过先前已枯竭或绝缘的进料通道上升到上地壳储层，在那里它们在喷发或最终沉积之前就驻留在肥沃的Moine型上地壳中并与之相互作用。