Red Hill Syenite

The rock complex is between 197-199 million years old, dated to the Early Jurassic epoch, making it one of the oldest sections of the White Mountain magma series.

The six units of the Red Hill Syenite all contain primarily alkali feldspar, with many rocks displaying perthitic igneous texture.

The primary mafic mineral is calcic amphibole, or ferrohastingite, and the feldspars show a coarse, braided exsolution pattern.

The Garland Peak Syenite consists of >15% mafic minerals (needle-shaped amphibole and biotite), 2-6% quartz, 8-15% plagioclase, and 60-70% perthitic feldspar (microperthite).

Igneous rocks display a variety of textures that can indicate the temperature and speed of magma cooling, among other things.

Textures from early cooling stages display plastic deformation, as they occurred when there was high liquid content in the magma chamber, which allows for crystal movement without breakage.

[4] Red Hill holds researchers' interest as they seek to determine how rocks with such different compositions formed from the same magma.

Although rock suites that display discontinuous compositions are often interpreted to have formed from different parent magmas, Red Hill was thought to have formed from the same magma chamber due to geochemical similarities between all syenitic units as well as the concentric formation of the units.

They also found geochemical patterns in amphiboles from the Garland Peak Syenite that are not easily explained by the theory of Red Hill having a single magma source.