On a small island in between Madagascar and the east coast of Africa, researchers have actually found a mom lode of rocks that should not exist.
The island is made from igneous, volcanic rock that comes from the oceanic crust. However the secret rocks originate from continental crust– more particularly, from a river delta or beach.
” It does not appear like anything that might have formed on an island like that,” stated Cornelia Class, a geochemist at the Lamont-Doherty Earth Observatory at Columbia University. [See Images of the Odd Rocks on This African Island]
Moneyed by a National Geographic Society grant, Class just recently led a clinical exploration to the island, directed by spread reports of the light, sandy rock, which is called quartzite. She and her associates discovered that the secret is bigger than they understood. In reality, it comprises half of a mountain.
Anjouan island is among the Comoro Islands. It’s a rugged, 163- square-mile (424 square kilometers) station in the Indian Ocean, abundant in greenery and house to around 277,000 individuals. Anjouan formed similar to the Hawaiian Islands It includes the remains of a guard volcano, which gushed and exuded lava that slowly developed from the sea bottom.
Considering that a minimum of the 1900 s, geologists have actually reported discovering some really nonvolcanic rocks on Anjouan. In the 1980 s, a French group recorded some spread protrusions of quartzite. In 1991, Class saw a couple of pieces herself while dealing with her doctoral research study on the islands.
” All those years, it has actually troubled me that I didn’t comprehend how those rocks arrived,” she informed Live Science. [Photos: The World’s Weirdest Geological Formations]
Quartzite merely should not be on Anjouan. The island beings in an ocean basin. Such basins form as tectonic plates pull apart, permitting lava from the mantle to roil up, harden and form brand-new crust. Due to this procedure, Class stated, the rocks from ocean basins are basaltic: dark, magnesium- and iron-rich rocks of the sort that comprise the Hawaiian Islands or the renowned outcrops of Devils Postpile in California
Continental plates, on the other hand, are made from less-dense, lighter-colored granitic rocks. Shift zones in between oceanic and continental crust can hold both kinds of rock, however Anjouan does not match those areas.
” There is absolutely nothing there that might form a quartzite,” Class stated.
And yet, when Class and her associates surveyed Anjouan on the National Geographic-funded journey in September in 2015, they discovered even more quartzite than anybody had actually ever recorded on the island prior to.
” It’s nearly half a mountain,” Class stated.
A Columbia University post about the journey recorded the look for the quartzite The scientists went back to websites where earlier geologists had actually found pieces of the light-colored rock. Fieldwork is difficult on the island, Class stated, due to the fact that whatever is covered with a thick layer of greenery and soil.
And, the scientists quickly discovered, residents utilize the quartzite patches as knife-sharpeners. As an outcome, pieces of quartzite that have actually toppled down in streambeds and rivers have actually been silently moved to towns and workshops throughout the years, leaving geologists less ideas about where to browse.
As the researchers treked around the town of Tsembehou, however, they discovered increasingly more pieces of quartzite, even big stones and outcrops of the compound. Ultimately, they bushwhacked up a neighboring knife-edge ridge called Habakari N’gani and discovered that its upper reaches were almost completely quartzite.
Class and her group are now gathering their information to map the quartzite and to design its real size. Today, the presence of the rock at this area is mysterious. Sometimes, such as Madagascar, continental crust can wind up in the middle of an ocean basin due to the fact that a portion of continent– mantle, crust and all– breaks off and wanders away. However the chemistry of Anjouan’s volcanic rocks does not show any association with an entire bundle of continental crust.
In some way, the crustal quartzite wound up in the ocean basin and was raised in addition to the volcanic rocks some 13,120 feet (4,000 meters) from the seabed.
Describing this secret will need more details, Class stated. A very first concern is to determine how old the quartzite is, which would assist researchers determine where it stemmed. (Class thought East Africa or Madagascar.) More geochemical measurements of the volcanic rocks that comprise the remainder of the island would assist clarify the island’s geological history also, she stated.
” This is what nature presents, in some cases,” she stated. “It’s something we think about difficult, however then we discover it, and when we discover it, we need to describe it.”
Initially released on Live Science