metagabbro

Metagabbro is a metamorphic rock that represents the metamorphosed equivalent of gabbro, a coarse-grained mafic intrusive igneous rock dominated by plagioclase feldspar and pyroxene. It forms when gabbro is subjected to regional or contact metamorphism, causing recrystallization and textural change while largely preserving the original chemical composition and mineralogy.

The textures of metagabbro are typically granoblastic or weakly foliated. Mineral assemblages reflect the metamorphic grade: at lower to intermediate grades, plagioclase and pyroxene (or amphibole) dominate, with possible minor biotite. Under higher-grade conditions, granulite or amphibolite facies assemblages may include garnet, hornblende, orthopyroxene, or clinopyroxene, and accessory minerals such as rutile or ilmenite. Metamorphism can also introduce alteration minerals such as chlorite or epidote at lower grades.

Occurrence and significance: Metagabbro is commonly found in metamorphic belts and in association with ophiolitic complexes where original gabbroic bodies were subjected to deformation and heating during tectonic processes. As a coarse-grained, mafic rock, it provides information about crustal differentiation, metamorphic conditions, and the thermal history of the belts in which it occurs. Geochronology on metagabbro samples can help date metamorphic events and related tectonic phases.

Distinguishing features: metagabbro preserves igneous textures of plagioclase and pyroxene with metamorphic recrystallization. It is distinguished from magnetite-rich or quartz-rich metamorphic rocks by its felsic-to-mafic mineral balance and plagioclase-pyroxene composition, which remains recognizable despite recrystallization.