Britannica
Sources used in this answer
How does the upper gabbro layer differ from the lower gabbro layer?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
oceanic crust
A cross section of Earth's outer layers, from the crust through the lower mantle.
In the context of oceanic crust geology, the upper and lower gabbro layers represent different portions of the magma chambers that feed volcanic activity on the seafloor. They differ primarily in their structure and composition:1
- Upper Gabbro Layer: This layer is characterized by an isotropic, or uniform, structure. In certain locations, it may contain pods of plagiogranite, which is a rock type more enriched in silica than gabbro.1
- Lower Gabbro Layer: This layer exhibits a stratified, or layered, structure and is believed to represent the floor or sides of the magma chamber. This structure is referred to as cumulate, as the layers form through the sedimentation of minerals out of the liquid magma. Chemically, these layers contain less silica but are richer in iron and magnesium than the upper gabbro. Olivine, an iron-magnesium silicate, is a common mineral found in this lower section.1