Partial melting, melt collection and transport in the Swakane Gneiss, North Cascades crystalline core, Washington.

摘要

This study focused on partial melting and melt ascent in middle to deep crust. The Swakane Gneiss records the highest pressure and temperature conditions (650--725°C/10--12 kbar) in the Cascades core, yet it is one of the youngest metamorphic units, with a protolith age of 73 Ma. Following burial, the Swakane Gneiss was subjected to partial melting by 68 Ma. Initial melt migration occurred parallel to the dominant foliation during which time strain gradients controlled migration from intergranular melt pockets to relatively lower stress sites. With increasing melt volume, the locally-derived melts were subsequently intruded into higher levels of the Swakane Gneiss as cm-scale dikes and sills, and 10 to 100 meter sheets and stocks. Stress gradients caused by heterogeneous strain, and tectonic stress controlled the emplacement of the leucogranitic intrusions, and local anisotropies e.g. foliation, folds, and shear zones had minimal effects on their ascent.