What do tectonic plates form

The third type of plate boundary occurs where tectonic plates slide horizontally past each other. This is known as a transform plate boundary. As the plates rub against each other, huge stresses can cause portions of the rock to break, resulting in earthquakes. Places where these breaks occur are called faults. A well-known example of a transform plate boundary is the San Andreas Fault in California. Virgin Islands. Home Ocean Exploration Facts What features form at plate tectonic boundaries?

Download citation. Published : 06 April Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Advanced search. Skip to main content Thank you for visiting nature. Download PDF. Subjects Geology Geophysics Mathematics and computing Physics. Continual diving of crust into mantle is sufficient to explain formation of plate boundaries.

Increasing interest in therapy implications of epigenetics Investigation faults Japanese stem-cell researcher Calorie restriction makes monkeys live longer after all.

References 1 Bercovici, D. Authors Jessica Morrison View author publications. Rights and permissions Reprints and Permissions. About this article Cite this article Morrison, J. Copy to clipboard. Today, the planet has eight major plates defined as those with areas over 20 million square kilometers and dozens of minor plates between 1 million and 20 million square kilometers and microplates less than 1 million square kilometers.

While some plates are composed solely of oceanic or continental crust, most major plates contain portions of both. While continental crust that is billions of years old still exists on Earth's surface, most oceanic crust is less than million years old Ma.

Older oceanic crust, which is more dense than continental crust, has long since been recycled in the process of subduction. Credit: U. Geological Survey. Mantle convection is driven by temperature differences between the hot interior and the gradually cooling outer layers of the planet. Cooler, denser material sinking down into the mantle is thought to be the primary driver of circulation, while hotter, less dense material rising to the surface in the form of mantle plumes and upwellings provides a secondary driver.

The forces generated by these vertical movements result in horizontal shifts of the tectonic plates at the surface at rates of about a few centimeters per year. One of the big questions about the onset of plate tectonics is how subduction got started. Geologists think that the lithosphere of the pretectonics Earth existed as a single plate that covered the whole planet.

Massive forces would have been needed to break this single lithosphere into multiple plates and to initiate plates descending into the mantle. Minerals in lithospheric slabs restructure as slabs descend into the mantle, releasing water and increasing the slabs' densities.

The dense, downgoing slabs pull on the parts of the plates still at the surface, driving plate tectonics. Some subducting slabs stall at the transition zone, while others descend toward the core-mantle boundary.

Credit: both: K. Cantner, AGI. The forces involved are incredible. Modern plate tectonic movement is driven primarily by the descent of the subducting limb of a plate, called a slab, pulling the rest of the plate down behind it. The momentum of the massive sinking slabs overcomes the friction generated by the upper mantle adjacent to the slabs as they descend. But it raises a chicken-and-egg question.

If plate tectonics is primarily driven by the forces generated by downgoing slabs, how could tectonics have gotten started before there were subducting slabs? It may have to do with heat. Since continental crust is not dense enough to be pulled into the mantle by subduction, it is moved around on Earth's surface through a cycle of supercontinent formation and breakup. Today, temperatures in the mantle hover around 1, degrees Celsius. But numerical models by Jun Korenaga , of Yale University, and colleagues indicate that about 3 billion years ago, the mantle was hotter by about to degrees.

These extreme temperatures — as hot as 1, degrees Celsius — had a profound effect on the early crust: Computer models from Gerya published in Nature in suggest that the hotter temperatures of early Earth may have made for weaker, more easily broken plates. That heat would have also created a very different mantle environment. But while this hotter and weaker scenario could have helped initiate the process, strength is required to sustain it, van Hunen says.

Tomographic imagery of the low-angle subduction of the Farallon Plate green beneath North America. The Farallon Plate began subducting under the North American Plate during the Jurassic, and is thought to have been completely overrun by about 50 million years ago.

The fate of its remnant slabs as they descended into the mantle may explain several features of the overlying continent, including the rise of the Rockies and the activity of the New Madrid Seismic Zone. The colors show anomalies in rigidity, which correlate with temperature anomalies. Green and blue represent relatively cooler regions, and orange and red represent hotter regions.

Empirical data are also needed to calibrate models, and to answer questions about what happens to slabs once they start subducting: Where do they go, and how has this process changed over time?