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The limitations of many in situ microsampling techniques, especially when applied to isotopic analyses, may result in lower measurement precision and limit the ability to compare different isotope systems within the same phase or the same isotope system between phases. High‐precision, combined and complementary isotopic measurements are typically limited to whole‐rock samples or mineral separates at the expense of textural context. We demonstrate that laser ablation instruments could offer an effective, non‐mechanical alternative to micro‐milling for delineating and extracting single crystals, interstitial phases, and sub‐crystal scale features from soluble‐resin thick sections for column chromatography and high precision ID‐TIMS measurement. Systematic testing demonstrated that both modern and legacy laser instruments are capable of ablating through plagioclase, pyroxene and fused glass to depths of 200 μm. Modern instruments offer software benefits to identifying optically‐indistinct petrographic features, chemical zoning and avoiding alteration phases by using overlain high‐resolution datasets. Extracting delineated targets of varying geometry was achieved under binocular microscope using common mineral‐separation tools. Analysis of RM glass used as mineral proxies indicate (a) no significant thermal aureole on ablated margins that could affect measured parent‐daughter ratios, (b) no elevated risk of contamination compared with traditional mineral separation techniques, (c) excellent blanks for low‐yield analyses and (d) high‐precision ID‐TIMS results (87Sr/86Sr and 143Nd/144Nd) for sub‐100 ng Sr loads and sub‐10 ng Nd loads.

A sequence of eight poikilitic anorthosite layers (labeled 1 to 8), within the Upper Main Zone in the eastern lobe of the Bushveld Complex, are exposed along a road-cut, 5.3 km northeast of the town of Apel, Limpopo Province. The anorthosite layers are meter-scale in thickness (0.4 to 10 m), have sharp contacts and are defined on the size and shape of pyroxene oikocrysts they contain. The anorthosite sequence is bounded by typical Main Zone gabbronorites. Euhedral, zoned primocrystic laths of plagioclase (An62.5-80.6; 0.2 to 4 mm long) are morphologically identical throughout the anorthosite sequence and define a moderate to strong foliation that is typically aligned parallel to the plane of layering. Interstitial clinopyroxene and orthopyroxene typically occur as large (0.8 to 80 cm) oikocrysts enclosing numerous partly rounded plagioclase chadacrysts. Rarely, orthopyroxene appears as subophitic crystals enclosing few and significantly smaller (0.08 to 0.4 mm), equant plagioclase inclusions. Detailed plagioclase and pyroxene mineral compositions for layers 2 to 5 show minimal variations within layers (0.1 to 2.3 mol% An and 0.7 mol% Mg#), whereas compositional breaks occur between layers (0.5 to 3.8 mol% An and 1.3 mol% Mg#). In layers 2 to 5, the An-content of plagioclase cores and the Mg# of both clinopyroxene and orthopyroxene crystals decrease by 2.5 mol%, 8.6 mol% and 13.0 mol% upwards, respectively. Bulk-rock incompatible trace element concentrations and patterns are similar for all analyzed anorthosite layers indicating that they are related to the same parental magma. However, bulk-rock major element oxides (e.g. Al2O3, TiO2, K2O) and atomic Mg# become more evolved upwards, consistent with magmatic differentiation. Based on the consistent plagioclase crystal morphologies and relatively constant chemistries within each anorthosite layer, we propose that each layer was formed by the intrusion of a plagioclase slurry. The upwards-evolving mineral chemistries, bulk-rock major element oxides and atomic Mg# suggests that each plagioclase slurry injection, that yielded an anorthosite layer, was derived from a slightly more fractionated parental magma prior to emplacement.

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