The volcanic island of Anjouan in the southwest Indian Ocean is home to a strange geological mystery. The inhabitants of the island and geologists are more than surprised to find a type of rock that should not be on this island.
The island emerged in an ocean basin, when tectonic plates diverged and magma rose and cooled, turning into basalt that formed the island. Thus, in Anjouan, quartz sand grains collected in river deltas before the quartzite was compressed over time. sedimentary rock quartzite, a type of sandstone, is not expected to be found. The island’s basalt does not contain quartz, and the island itself is too young to form a large river delta. Still, geologists report finding abundant quartzite on the island for perhaps more than a century.
Geologists have reported unusual rocks that may have been quartzite in 1900, though with poor documentation to know for sure. In 1969, a large “sandstone” formation was found on the island near the town of Tsembehou and later determined to be quartzite. Then in 2017 the French geologist Patrique Bachèleryfound more quartzite in a nearby ridge. Lamont-Doherty Earth Observatory geochemist of Columbia University, who set out a few years later Cornelia Class began his research. Class and his team did indeed find quartzite in just minutes and confirmed that there was an abundance of quartzite along the ridge.
In a Columbia University press release, Class said, “This is against plate tectonics.” he said and added: “Quartzite bodies do not belong to volcanic islands.”
Islanders told Class that they always found these rocks, used them to sharpen their knives, and showed them where they could find more quartzite. By creating a map of the quartzite on the island, Class calculated the amount of quartzite. almost half a mountain found it was.
There is no definite explanation yet as to how the quartzite was found on this island. A piece of quartzite from the continental crust may have deposited itself in the ocean basin and then risen 4,000 meters above the seafloor by igneous basalt, but Class said in an interview with Live Science that the chemistry of the island’s basalt rocks did not show a relationship with the continental crust.something we thought was impossible but really here and when we find something like this we need to explain” he described.
Tests to determine the age of the quartzite will help determine when it has accumulated. It may be possible that this island was the only volcanic island in the world that stood with a continent on it after the collapse of the ancient continent Gondwana.
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