Gabbro

Definition

Gabbro is a coarse-grained igneous rock formed from the slow crystallization of magma beneath the Earth's surface. It is primarily composed of plagioclase feldspar and pyroxene, which gives it a dark color. Gabbro is significant as it is often found in oceanic crust and plays a critical role in understanding mid-ocean ridges and rift valleys, where tectonic processes create new oceanic crust through volcanic activity.

5 Must Know Facts For Your Next Test

1. Gabbro forms from magma that cools slowly beneath the Earth's surface, allowing larger crystals to develop compared to rapidly cooled rocks like basalt.
2. It is commonly found in oceanic crust, especially at mid-ocean ridges where tectonic plates diverge.
3. The mineral composition of gabbro typically includes around 60-70% plagioclase feldspar and 10-20% pyroxene, along with minor amounts of olivine and other minerals.
4. Gabbro can provide insights into the history of tectonic activity and the processes that form oceanic crust.
5. It is an important rock type for understanding the geothermal gradient and the processes occurring at divergent plate boundaries.

Review Questions

• How does gabbro differ from basalt in terms of formation and characteristics?
  • Gabbro differs from basalt primarily in its formation process and grain size. Gabbro is formed from the slow cooling of magma beneath the Earth's surface, resulting in a coarse-grained texture with larger crystals, while basalt forms when lava cools rapidly at or near the surface, leading to a fine-grained texture. This difference highlights the varying cooling rates and environments where these rocks are created, with gabbro typically found in deeper crustal settings.
• Discuss the role of gabbro in the formation of oceanic crust at mid-ocean ridges.
  • Gabbro plays a crucial role in the formation of oceanic crust at mid-ocean ridges, where tectonic plates are pulling apart. As magma rises from the mantle to fill the gap created by diverging plates, it begins to cool slowly beneath the surface, forming gabbro. This process contributes to the building of new oceanic crust, and studying gabbro provides insights into the thermal and compositional aspects of these dynamic environments.
• Evaluate the significance of gabbro in understanding tectonic processes related to rift valleys and mid-ocean ridges.
  • Evaluating gabbro's significance reveals its essential role in understanding tectonic processes at rift valleys and mid-ocean ridges. The presence of gabbro indicates areas of active magma intrusion and solidification, which are vital for studying how new crust is formed and how tectonic plates interact. Furthermore, by analyzing gabbro's mineral composition and formation conditions, geologists can infer historical geological events and predict future tectonic activity, contributing to our broader knowledge of Earth's geology.

Related terms

Basalt: A fine-grained igneous rock that forms when lava cools quickly at or near the Earth's surface, often found in volcanic regions.

Magma: The molten rock material found beneath the Earth's surface, which can solidify to form igneous rocks like gabbro and basalt.

Mid-Ocean Ridge: An underwater mountain range formed by plate tectonics, where new oceanic crust is created through volcanic activity, often associated with gabbro formation.