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Ductile Fractures in Geological Materials

 

Roberto Weinberg, Monash University, Australia

 

 

 

Ductile fractures: see Eichhubl's papers for more on ductile fractures in geological materials and full references
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Ductile fractures in mafic pillows in granite

 

 

Ductile fractures
Ductile fractures
Irregular cracks inside a mafic pillow found within granite at the Ota Complex in Corsica, interpreted to result from magma shrinkage during cooling within the colder granitic magma. Ductile fractures formed by the coallescence of pores (from Bluhm and Morrisey, 1965, in Eichhubl and Aydin (2003).

 

Ductile fractures in vesicle walls

 

 

Ductile fractures in vesicle walls
 Ductile fractures in vesicle walls
Irregular cracks on the inside of a vesicle resulting from vesicle expansion electron microscope image by Susan Aarburg. Comparison to the shrinkage cracks of Mungall et al. (1996).

 

Ductile fractures Ductile fractures
Figure 13a. Lil-Lappo, Finnish archipelago. Irregular, zig-zagging tonalite-filled fractures in two different orientations in hornblende-cumulate, possibly formed as a result of segregation of interstitial melt. Figure 13b.

 

Ductile fractures
 Ductile fractures
Figure 14a. Stop between Brändöharum and Påvskär, Finnish archipelago. Magma mingling resulting in irregular fractures repeatedly splitting (mid-left-hand side). Figure 14b. Stop between Brändöharum and Påvskär. Right-angle fractures filled with granite in monzonite.

 

Ductile fractures
  Ductile fractures
Figure 15a. Lövgrund, Finnish archipelago. Ductile fractures in migmatite following mode II fractures. Figure 15b. Enlinge island, Finnish archipelago.

 

Damage in front of fracture tips

 

 

leucosome in fracture
leucosome in fracture
Leucosome filled fractures in high-grade rocks on Mt Hay, Central Australia. Detail showing the outward expansion of leucosome filled cracks.

 

 

damage around fracture tips, from Eichhubl
Damage around fracture tips in Eichhubl (2004, Geol. Soc. London, Sp. Publ. 231). a) side-lobe damage (from Evans and Blumentahl, 1984); b) frontal damage. Side-lobe damage (a) is characteristic of ductile fracturing in metal and ceramics dependent on shear stress, and frontal damage (b) is characteristic of brittle opening-mode fracturing, dependent on normal stress.