The discovery of this volcano on the far side of the moon raises many questions

On Earth, granite is a very common rock. They are found just about everywhere and for good reason, the continental crust is mainly composed of these silica-rich volcanic rocks. However, this would be a very terrestrial peculiarity, as granites are almost absent from the other telluric planets of the solar system. However, the absence of this rock outside the Earth can be explained quite easily. The production of granite indeed requires very specific conditions.

Granite, a typical terrestrial igneous rock

Thus magma composed of granite can be formed either by the amalgamation of continental crustal rocks during tectonic collision, or by the amalgamation of mantle rocks. If in the first case we will get a magma liquid directly from the granite composition (granite fusion gives magma), then in the second case the resulting liquid will be, first of all, from the basalt composition. The granitic composition will be obtained only at the end of a long process of magma differentiation, in several stages. The chemical composition of the magma will gradually evolve as it cools and the gradual crystallization of different minerals. Thus, many rocks of different mineral composition would be able to form from the same primary magma. This is called magma chain. Granite is at the end of this series. In all cases, the process results in the concentration of radioactive elements in the granitic magma. Crystallization of the granite then requires very slow cooling of the magma deep in the crust. Therefore, granite is a plutonic rock, not a flat rock.

Water and Plate Tectonics: Necessary Components for the Formation of Granites

On Earth, the formation of a liquid granite would be favored by the presence of large amounts of water, which would favor the melting process of the rock. However, water is mainly brought to the depth by tectonic processes, in particular by subduction zones. We better understand, in fact, why granite is so frequent on Earth and almost absent elsewhere.

However, we must say “almost” absent, because small samples of granite have already been found outside our planet, especially on the surface of the Moon, without being able to clearly explain their origin yet. The hypothesis was that this was a narrative phenomenon, and lunar geology and geodynamics do not allow large granite plutons to be created.

A massive granite object has been discovered on the far side of the Moon

An idea undermined by the recent discovery of a majestic granite object on the far side of the Moon. It was microwave frequency data obtained by the Chang’e-1 and Chang’e-2 probes orbiting China that helped pinpoint an abnormally hot area beneath the surface of what scientists believe is an ancient volcano known as Compton-Belkovich.

This anomaly in heat flux can be linked to a high concentration of radioactive elements. For scientists, this could only be a sign of a huge granite object with a diameter of 50 kilometers, resembling a bathtub. On Earth, batholiths usually attest to the past existence of very large volcanic systems, such as the Half-Dome of Yosemite Park.

A “wet” moon, or is it just a very hot moon?

The startling discovery of such a granitic unit on the Moon necessarily raises questions and requires either a review of the processes that could lead to the formation of granite in the absence of water (which would involve very high temperatures), or consideration of the presence of water within the Moon. crust at the time of its formation. The batholiths had already formed very early in the history of the Moon, 3.5 billion years ago. The results of the study have been published in the journal nature.