Table T6. Microstructure of gabbroic rock.
| Textural group |
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 |
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