Experimental feldspar

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Experimentally deformed feldspar aggregates

TOP

1-

Experimentally deformed quartz aggregates

2-

Naturally deformed quartz-rich rocks

3-

Experimentally deformed feldspar aggregates

4-

Naturally deformed feldspar rocks

5-

Experimentally deformed quartzo-feldspathic rocks

6-

Naturally deformed quartzo-feldspathic rocks

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Experimentally deformed pyroxenite and diabase

8-

Deformation and metamorphic reactions in polyphase rocks

Experimentally deformed feldspar aggregates

Starting material / cataclastic flow / regime 1

Introduction

The photos in this chapter illustrate the full transition from brittle faulting to macroscopically ductile cataclastic flow (distributed microcracking and grain-scale faulting) to crystal plasticity (crack-free dislocation creep), which occurs with increasing temperature and pressure. The field of cataclastic flow is especially well developed in feldspar aggregates (it does not occur at all in quartz aggregates), due to the two excellent cleavages in this mineral. One photo illustrates the effects of previous brittle faulting on later high temperature deformation. Although there is evidence from naturally deformed rocks that feldspars show the same 3 dislocation creep regimes as quartz, characterized by distinct mechanisms of dynamic recrystallization, so far we have only been able to achieve the lowest temperature 'regime 1' in laboratory experiments, before being cut off by melting. Thus that is the only type of dislocation creep microstructure illustrated in this chapter; for microstructures characteristic of higher temperature regimes, see Chapter 4 (Naturally Deformed Feldspar Rocks).
It is important to mention that in nature, the deformation of feldspars at conditions appropriate for the low temperature 'regime 1' dislocation creep almost always involves the additional complexity of chemical change. Recent experiments have been done to investigate the microstructures produced in such cases, but they are not included here; for natural examples, see Chapter 8 (Deformation and Metamorphic Reactions in Polyphase Rocks).
All of the samples illustrated in this chapter have been deformed in axial compression, at constant strain rate, but several photos illustrate the microstructures developed under shear, which occurs around the corners of the top piston as it moves down into the sample at high strain.

further reading

3		Experimentally deformed feldspar aggregates
3

TOP	1-	Experimentally deformed quartz aggregates	2-	Naturally deformed quartz-rich rocks
	3-	Experimentally deformed feldspar aggregates	4-	Naturally deformed feldspar rocks
	5-	Experimentally deformed quartzo-feldspathic rocks	6-	Naturally deformed quartzo-feldspathic rocks
	7-	Experimentally deformed pyroxenite and diabase	8-	Deformation and metamorphic reactions in polyphase rocks

Experimentally deformed feldspar aggregates		Starting material / cataclastic flow / regime 1

		Introduction The photos in this chapter illustrate the full transition from brittle faulting to macroscopically ductile cataclastic flow (distributed microcracking and grain-scale faulting) to crystal plasticity (crack-free dislocation creep), which occurs with increasing temperature and pressure. The field of cataclastic flow is especially well developed in feldspar aggregates (it does not occur at all in quartz aggregates), due to the two excellent cleavages in this mineral. One photo illustrates the effects of previous brittle faulting on later high temperature deformation. Although there is evidence from naturally deformed rocks that feldspars show the same 3 dislocation creep regimes as quartz, characterized by distinct mechanisms of dynamic recrystallization, so far we have only been able to achieve the lowest temperature 'regime 1' in laboratory experiments, before being cut off by melting. Thus that is the only type of dislocation creep microstructure illustrated in this chapter; for microstructures characteristic of higher temperature regimes, see Chapter 4 (Naturally Deformed Feldspar Rocks). It is important to mention that in nature, the deformation of feldspars at conditions appropriate for the low temperature 'regime 1' dislocation creep almost always involves the additional complexity of chemical change. Recent experiments have been done to investigate the microstructures produced in such cases, but they are not included here; for natural examples, see Chapter 8 (Deformation and Metamorphic Reactions in Polyphase Rocks). All of the samples illustrated in this chapter have been deformed in axial compression, at constant strain rate, but several photos illustrate the microstructures developed under shear, which occurs around the corners of the top piston as it moves down into the sample at high strain.

		further reading