Magnetism of Himalayan rocks reveals the mountains’ complex tectonic history
- macmalmil
- Dec 9, 2020
- 2 min read
Earth's magnetic field locks information into lava as it cools into rock. Millions of years later, scientists can decipher this magnetic data to build geologic timelines and maps
We might now have a better understanding of the Earth's magnetic field, keep on reading to find out...
Official report
By Craig Robert Martin, Massachusetts Institute of Technology
November 3, 2020
Retrieved from https://theconversation.com/global/topics/rocks-10597
Breathing quickly in the thin mountain air, my colleagues and I set down our equipment. We’re at the base of a jagged outcrop that protrudes upwards out of a steep gravel slope.
The muffled soundscape of the spectacular Himalayan wilderness is punctuated by a military convoy roaring along the Khardung-La road below. It’s a reminder how close we are to the long-disputed borders between India, Pakistan and China which lie on the ridgelines just a few miles away.
This area also contains a different type of boundary, a narrow sinuous geological structure that stretches along the length of the Himalayan mountain range. Known as a suture zone, it’s only a few kilometers wide and consists of slivers of different types of rocks all sliced together by fault zones. It marks the boundary where two tectonic plates fused together and an ancient ocean disappeared.
Our team of geologists traveled here to collect rocks that erupted as lava more than 60 million years ago. By decoding the magnetic records preserved inside them, we hoped to reconstruct the geography of ancient landmasses – and revise the story of the creation of the Himalayas.
Sliding plates, growing mountains
Tectonic plates make up the surface of Earth, and they’re constantly in motion – drifting at the imperceptibly slow pace of just a few centimeters each year. Oceanic plates are colder and denser than the mantle beneath them, so they sink downward into it at subduction zones.
At a subduction zone, two tectonic plates collide, with one slowly sliding beneath the other.
The sinking edge of the ocean plate drags the ocean floor along behind it like a conveyor belt, pulling the continents toward each other. When the entire ocean plate disappears into the mantle, the continents on either side plow into each other with enough force to uplift great mountain belts, like the Himalayas.
Geologists generally thought that the Himalayas formed 55 million years ago in a single continental collision – when the Neotethys Ocean plate subducted under the southern edge of Eurasia and the Indian and Eurasian tectonic plates collided.
But by measuring the magnetism of rocks from northwest India’s remote and mountainous Ladakh region, our team has shown that the tectonic collision that formed the world’s largest mountain range was actually a complex, multi-stage process involving at least two subduction zones.
Research is a way to find meaning for everything, some come at a dead end, but trying will never get us nowhere for we will always have something new to learn.
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