<p>Amphibole clusters commonly occur in mafic magmatic enclaves (MMEs) and their aggregation mechanisms provide insights into physical processes of magma mixing. This study uses electron backscatter diffraction (EBSD) to examine the formation of amphibole clusters in MMEs from the Sanguliu monzogranitic pluton in East China. The amphibole clusters appear as loose to dense aggregates and range in size from 2 to 5&#xa0;mm. EBSD results reveal that approximately 40% of neighboring-paired grains exhibit preferred orientation with inter-grain misorientation angle of &lt; 5° or 180°, driven by interfacial energy minimization. This indicates aggregation via synneusis, i.e., suspending grains collide, then rotate to minimize interfacial energy and sinter. Intra-grain misorientation (&gt; 5° up to 12°) and kinked boundaries are attributed to plastic and brittle deformation induced by crystal crowding. Individual grains range in length from ∼0.1 to 0.5&#xa0;mm and show bright and dark domains in BSE images. The bright and dark domains have distinct Al/Si ratios, similar to amphibole in the diabase dyke intruding the pluton and in host monzogranite, respectively, indicating crystallization from both mafic and felsic magmas. The amphibole clusters are thus interpreted to form in a hybrid boundary layer between ascending mafic mushy magmas and overlying felsic mushy magmas in the shallow crust. A Rayleigh number of ~ 9.4 × 10⁷ implies chaotic convection within the layer, facilitating amphibole movement, impingement, rotation and aggregation. This study demonstrates that crystallographic and chemical records of amphibole clusters in MMEs bear insightful information for chaotic mushy magma mixing in a hybrid boundary layer.</p>