Figure 96

Deformation and metamorphic reactions in polyphase rocks

Figure caption

Deformation and metamorphic reactions

granodiorites / anorthosites

96

Granodiorite mylonite deformed at low to mid greenschist conditions; pure quartz layers are stronger than mixed phase matrix.

Overview of a granodiorite mylonite. The monophase layers of quartz are more competent (pinch and swell structures, boudinage) than the fine-grained mixture of albite + epidote + quartz + white mica matrix. Photo 97 (plane polarized light) shows that quartz forms more or less pure, monophase layers. This competence reversal between quartz and feldspar-dominated layers indicates that the matrix has not deformed by intracrystalline plasticity, because quartz (which is dynamically recrystallized, and thus deformed by crystal plastic mechanisms) forms the mechanically stronger aggregates, and pure albite at these temperatures deforms by brittle fracturing.

		Deformation and metamorphic reactions in polyphase rocks
		Figure caption

	Deformation and metamorphic reactions	granodiorites / anorthosites


96		Granodiorite mylonite deformed at low to mid greenschist conditions; pure quartz layers are stronger than mixed phase matrix. Overview of a granodiorite mylonite. The monophase layers of quartz are more competent (pinch and swell structures, boudinage) than the fine-grained mixture of albite + epidote + quartz + white mica matrix. Photo 97 (plane polarized light) shows that quartz forms more or less pure, monophase layers. This competence reversal between quartz and feldspar-dominated layers indicates that the matrix has not deformed by intracrystalline plasticity, because quartz (which is dynamically recrystallized, and thus deformed by crystal plastic mechanisms) forms the mechanically stronger aggregates, and pure albite at these temperatures deforms by brittle fracturing.