Imagine you’re on a tremendously heavy vehicle running into another. Well, you don’t have to imagine it, you are on such a vehicle, a tectonic plate running into, over, or under another one. Motions of the 15 or so major plates move us vast distances over times and create earthquakes and volcanoes. The fastest moving plate carries India into southern Asia. It has already bumped up the towering Himalayas.
While most plates are rather slow, moving relative to each other at about 1.5 cm per year, India is racing at 18 cm (7 inches) per year. You can almost watch it move. You also expect many earthquakes and large ones, to boot. In a human lifetime of 70 years the cumulative motion is about 1.3 meters, while several meters of motion suddenly slipping can generate a great quake. Hao Zhu and colleagues at universities in China and Singapore recently studied why India’s motion became so fast about 65 million years ago. The short answer is that deep sediments accumulated on the edges of the Indian plate. The sediments rather lubricate the plate’s dive under Eurasia. Since no one can poke around at the depths of the collision, Zhu and colleagues analyzed magma, fluid rock reaching toward the surface (as in volcanoes). The signature of the sediment vs other rock is in the abundance of isotopes of chemical elements. Neat tools!
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
Source: Nature 14 Nov. 24, pp. 359 ff.
