The Microstructural Record of Convection in the Little Minch Sill Complex, Scotland

Abstract Detailed microstructural analysis of three basaltic sills the Little Minch Sill Complex demonstrates that convection leaves a detectable signature in fully solidified bodies. The presence dense clusters equant grains olivine and clinopyroxene central parts can only be accounted for if they formed were enlarged while suspended convecting magma, with delayed settling to sill floor. An associated stratigraphic invariance plagioclase grain shape is consistent growth magma. These indicators demonstrate during solidification was vigorous long-lived 135-m-thick picrodolerite-crinanite unit (PCU) composite Shiant Isles Main likely short-lived PCU Creagan Iar sill. In contrast, Meall Tuath weak short-lived: this varies height, indicative primarily situ nucleation at magma-mush interface, kept overlying magma all fractionated solidification, permitting driven by instability an upper thermal boundary layer. comparative vigour longevity due their emplacement above earlier, still-hot, intrusion, resulting highly asymmetric cooling.