Petrogenesis of mafic microgranular enclaves in the Lingshan granitic intrusion, eastern South China: new insights from X-ray CT analysis and macro elemental mapping

This study investigates mafic microgranular enclaves (MMEs) within the Lingshan granite (Jiangxi Province, South China) through an integrated approach combining traditional geochemistry, macro-X-ray fluorescence (MA-XRF) mapping, and X-ray computed tomography (X-CT). Zircon U-Pb ages and Hf isotopes indicate that the MMEs share similar crystallization ages and isotopic ratio with their host granite. X-CT imaging reveals similar short-axis and long-axis mineral orientations (biotite, hornblende, magnetite, ilmenite and some heavy minerals) between MMEs and host rock, supporting flow alignment of mafic magma globules within the felsic melt (globules of a more mafic magma injected into the felsic magma and subsequently mingled and mixed with it) rather than a restite, or early cumulate origin (the mineral orientations of MMEs in these models are nearly impossible to be consistent with those of the host granite.). Whole-rock geochemistry exhibits non-linear trace element trends, which are inconsistent with simple magma mixing but rather an example of the chaotic nature of the mixing process. MA-XRF mapping further demonstrates enrichment of Fe, Mn, Ti, Y, Nb, and Ca alongside depletion of Sr, K, and Rb in MMEs, attributed to diffusion-driven exchange. The hybridization process weakened the A-type signature of the host granite, implying that some I-type granites may derive from A-type precursors, primarily through magma mixing. Notably, MMEs may sequester some critical ore-forming elements (e.g., Nb, Ta), potentially suppressing the metallogenic potential of the host granite. These findings may provide new constraints on magma differentiation processes and related mineralization mechanisms in South China's granitic systems.