50. Plate tectonics, the segmented Laramide Slab, deformation, and large scale K- and Si-metasomatism

Deformation, caused by the down-going segmented Laramide Slab under southern California, created shear zones in the Sierra Nevada batholith, in the Mojave-Salinia arc segment, and in eastern California. In these shear zones, the plagioclase crystals in primary quartz diorite plutons were deformed and microfractured so that introduced K caused some of them to be replaced by K-feldspar. Broken mafic silicates were also replaced by quartz. As a consequence of the K- and Si-replacements, the quartz diorites in the shear zones were converted into metasomatic granodiorite, quartz monzonite, or granite. Myrmekite is a clue to the metasomatism. In other parts of the world where K is available and where primary mafic igneous rocks are sheared, K-metasomatism that produces K-feldspar and myrmekite can be expected