Previous   |    Close   |    Next

Table T6. Microstructure of gabbroic rock.

Plagioclase Olivine Pyroxene Physical state
1 No or minor crystal-plastic deformation microstructures (e.g., deformation twins, undulose extinction) No deformation microstructures ± local undulose extinction and/or local subgrain development
No deformation microstructures Primarily magmatic
a Random shape orientation      
b Preferred shape orientation      
2 <30% fine-grained recrystallized matrix; deformation twins and subgrain boundaries may be present Common subgrain boundaries and undulose extinction No deformation microstructures ± minor crystal-plastic deformation microstructures Crystal-plastic ± magmatic
3 >30% recrystallized matrix; deformation twins, subgrain boundaries, and undulose extinction common; moderate shape-preferred orientation; strong crystallographic-preferred orientation Elongated aggregates of neoblasts Kinked grains; common to extensive recrystallization Crystal-plastic
4 Strongly bimodal grain size distribution; localized fine-grained neoblasts, polygonal neoblasts, sutured neoblasts Closely spaced subgrain boundaries; pervasive undulose extinction; extensive neoblasts Bent/kinked porphyroclasts; localized recrystallization Crystal-plastic
5 Common intracrystalline microfractures associated with very fine grained neoblasts; extensive kinked and deformation twinned grains; pervasive undulose extinction; may contain hydrothermal alteration mineral assemblages Same as plagioclase Same as plagioclase Semibrittle
6 Intra-/intercrystalline microfractures and cataclastic bands; extensive kinked and deformation twinned grains; pervasive undulose extinction Same as plagioclase Same as plagioclase Brittle/Cataclastic

Previous   |    Close   |    Next   |    Top of page