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Last Updated: Monday, 10 May, 2004, 11:49 GMT 12:49 UK
Image reveals Mars' active past
Acheron Fossae
The geological faults have disrupted an impact crater
Europe's Mars Express probe has sent back detailed images of a region of the Red Planet that was shaped by intensive continental plate activity.

Continental plate, or tectonic, activity is responsible on Earth for continental drift, the formation of ocean basins and earthquakes.

These tectonic forces are believed to have since ceased on the Red Planet.

The image shows curving faults, up to 1,700m deep, which opened up in Mars' Acheron mountain range.

The region, known as Acheron Fossae, marks the northern edge of the Tharsis plateau and is 1,000 kilometres north of the enormous Olympus Mons volcano, the tallest volcano in the Solar System.

Rift zone

It is part of a network of fractures that radiate out from the "Tharsis bulge", an area of regional uplift where intense volcanic activity once occurred.

The faults in the images were created by this uplift process: cracks in the crust formed when hot material rising from deep in the Martian mantle pushed the overlying lithosphere, or surface layers of rock, upward.

Acheron Fossae
The region was shaped by intense tectonic activity
When the stresses became too great, the brittle crust on top of the lithosphere broke along zones of weakness.

The Acheron Fossae region could be similar to rift zones on Earth, such as the Rift Valley in East Africa, where continental plates spread apart.

Geologists call Acheron Fossae a "Horst and Graben" system. When several parallel faults form, the block of crust between them drops down, forming a "graben".

The remnants of the pre-existing topography are called the "horsts". This faulting pattern disrupted some older impact craters at the site.


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