gabbro
/ˈɡabrəʊ
/noun (plural gabbros) [mass noun] Geology
A dark, coarse-grained plutonic rock of crystalline texture, consisting mainly of pyroxene, plagioclase feldspar, and often olivine: a house of gabbro [count noun]: olivine gabbros...
- Permian and Triassic plutonic complexes comprise monzonite, granite, granodiorite or tonalite with minor gabbro and diorite.
- The highest core recovery occurs in the massive olivine gabbro, which contain lower densities of fractures and are generally undeformed.
- Contacts between plutons of gabbro or hybrid rock and granite are commonly marked by net-vein complexes.
Derivatives
gabbroic
- The plutons are composed of medium - to coarse-grained, porphyritic quartz monzonite, quartz syenite and granite, together with smaller amounts of equigranular gabbroic and monzonitic rocks.
- Of far less importance are occurrences in gneisses and amphibolites, in small plutons derived from syenitic and gabbroic magmas, and in certain contact-metamorphic rocks.
- This is based on preservation of original gabbroic textures and occurrence of intergranular coesite in UHP rocks.
gabbroid
- The enclaves in the mentioned basaltoids represent peridotites, pyroxenites and gabbroid rocks.
- Hess's hypothesis on the serpentinite composition of the lower oceanic crust was confirmed by serpentinite and gabbroid fragments dredged from some fracture zones.
- Following, or partly during, their amalgamation, the terranes of the Arabian shield were covered by younger Neoproterozoic volcanic and sedimentary rocks and intruded by relatively undeformed granitoid and subordinate gabbroid rocks.
Origin
Mid 19th century: from Italian, from Latin glaber, glabr- 'smooth'.