A geological anachronism
The volcanic rocks of Gorgona Island are a geological puzzle. They are komatiites, a rare type of ultramafic lava defined by a magnesium oxide (MgO) content of over 18%. This composition requires immense heat to form, with eruption temperatures reaching 1,600°C. Such conditions were common during the Archean Eon, billions of years ago, when the Earth's mantle was significantly hotter. Nearly all known komatiites are found in Archean-era rock formations, 2.5 billion years or older.
The Gorgona komatiites defy this timeline. Radiometric dating places their formation in the Late Cretaceous period, approximately 89-90 million years ago. This makes them the youngest known komatiites on Earth, providing a rare record of mantle processes that have otherwise ceased. Their existence suggests that pockets of the deep mantle have retained the intense heat of the early Earth for eons, capable of producing these unusual lavas long after the planet's average internal temperature dropped. These rocks are part of the Caribbean Large Igneous Province, an oceanic plateau formed by a massive mantle plume event.
Crystalline signatures of extreme heat
One of the most distinctive features of komatiites is a crystalline structure called spinifex texture. This pattern consists of long, slender, blade-like crystals of the mineral olivine that are often arranged in crisscrossing sheaves. The texture is named after the spiky Triodia spinifex grass of Australia, which it resembles.
This unique structure is a direct result of the lava's physical properties and cooling process. Komatiite lava was extremely fluid—having a viscosity similar to water—and erupted at very high temperatures. The spinifex texture formed as the top layer of the lava flow cooled rapidly against the air or water, creating a steep thermal gradient. Large, skeletal olivine crystals nucleated on this chilled crust and grew downwards into the hotter, still-molten interior of the flow, forming the characteristic acicular plates that can sometimes reach up to a meter in length. On Gorgona, the komatiite flows are typically one to three meters thick and display layers of this remarkable texture.