Gabbro - Geology Is The Way

Gabbro

Gabbro is a plutonic igneous rock and the intrusive counterpart of basalt. The name ‘gabbro’ derives from the Italian town of Gabbro (Rosignano Marittimo, Tuscany) and was first coined by the Italian geologist Tozzetti in 1768. Tozzetti used the term to refer to a suite of ophiolitic rocks. Only in 1809, the German geologist Christian Leopold von Buch, restricted the use of this term to plagioclase – clinopyroxene-bearing rocks (although he actually described metagabbros). Gabbros consist of calcic plagioclase (>An50), clinopyroxene (augite, diopside), and iron oxides (ilmenite, magnetite). Olivine, hornblende, orthopyroxene, and spinel may be present as accessory minerals and can constitute important, rock-forming phases in some varieties of gabbros. Plagioclase is generally comprised between 35 and 65% of the rock volume. Gabbros may also contain small amounts of quartz, indicating oversaturation in silica, or feldspathoids, present in silica-undersaturated gabbros. Additional details about the classification of gabbros are available at the page below.

• Classification of gabbros – Gabbroid rocks are a large family of plutonic rocks that contain almost exclusively plagioclase as the only felsic mineral, hence plotting close to the P vertex of the QAPF classification diagram (quartz < 5% and plagioclase > 90% feldspars). The relatively simple classification through the QAPF diagram hides, however, the true complexity of these rocks, which may contain variable proportion… Read More »Classification of gabbros

GabbroPlutonic igneous rockFelsic minerals:• Ca-plagioclaseMafic minerals:• pyroxene• olivine

QAPF classification:Q = 0 – 5%Plagioclase/feldspars > 90%Colored varieties:• leucogabbro (M < 35%)• melagabbro (M > 65%)Other varieties: quartz gabbro, foid-bearing gabbro, olivine gabbro, hornblende gabbroExtrusive equivalent: basalt

Gabbros have also been classified based on their grain size, which is very variable in nature. Very coarse-grained varieties, showing crystals larger than several centimeters, are known as pegmatoid gabbro. On the other hand, fine-grained varieties have been called microgabbro, diabase, or dolerite – three terms that are considered synonyms in the present literature.

Gabbro is a fundamental constituents of ophiolite sequences and of the deeper part of the oceanic crust. It is also common in association with lower crustal rocks, as gabbros intrude at the base of the crust, and in rift areas, where mafic magma ascends within the crust. Mafic complexes, like layered intrusions, contain gabbro as a product of cumulus processes.

References Cox, K. G. (Ed.). (2013). The interpretation of igneous rocks. Springer Science & Business Media. Le Bas, M. J., & Streckeisen, A. L. (1991). The IUGS systematics of igneous rocks. Journal of the Geological Society, 148(5), 825-833. Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press. Streckeisen, A. (1976). To each plutonic rock its proper name. Earth-science reviews, 12(1), 1-33. Wilson, D. S., Teagle, D. A., Alt, J. C., Banerjee, N. R., Umino, S., Miyashita, S., … & Ziegler, C. (2006). Drilling to gabbro in intact ocean crust. science, 312(5776), 1016-1020.

See alsoGabbro – Sandatlas.orgGabbro – Alexstrekeisen.it

Search for... Igneous Minerals Quartz Alkali Feldspar Plagioclase Feldspathoids Biotite Muscovite Amphibole Pyroxene Olivine Andalusite Tourmaline Garnet Calcite Igneous Textures Porphyritic Crystal shape Plutonic Rocks Classification of plutonic rocks Classification of gabbros Classification of ultramafic rocks Granite Quartzolite and quartz-rich granitoid Alkali feldspar granite Granodiorite Tonalite Syenite Alkali feldspar syenite Foid syenite Foid monzosyenite Monzonite Monzodiorite and monzogabbro Foid monzodiorite and foid monzogabbro Gabbro Foid diorite and foid gabbro Foidolite Lamprophyres Igneous Bodies Dike Sill Magmatic enclaves and magma mingling/mixing Xenolith and xenocrystal Do you like this page?

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