When one continent grinds slowly into another and the rocks in between (whether marine or terrestrial) are slowly crushed and thrust upwards, the resulting tectonic forces create huge networks of faults as the rocks crack, along with subsidiary mountain ranges as the stresses redistribute though the landmasses.
The main ranges are created by giant thrust faults, when huge slabs of rock (called nappes after the French for tablecloth) detach from the underlying layers along a weaker layer of rock and push up over the continents. At roughly right angles to these, subsidiary faults redistribute stress through the surrounding plate as it heaves and groans up a new mountain range and its surrounding landscape pattern. Try shoving your tablecloth across the table as if your hand was a continent and you will quickly see how the stress patterns distribute, even though cloth is a very different material to rock. The Piquiang fault is located in Xinjian province, China, on the fringes of the mighty Tien Shan, and is picked out wonderfully by the varying colours and origins of the lightly tilted sedimentary rocks smiling up at the camera. Far to the south, India is crashing into Asia, and a whole clump of mountain chains across the continent continue to grow. The Himalaya are the best known, but many other chains are growing further inland, including the Hindu Kush, Altai, and Pamirs, petering out into rolling hills and ridges such as those of Burma, Vietnam and northern Thailand.
The fault trends northwest, and is a strike slip one like the San Andreas, where blocks of rock are sliding past each other as Asia shudders. Running for some 70km, at the point where it reveals itself so clearly in the photo, it is crossing some colourful sedimentary rocks that pick it out perfectly through their beautiful 3 km offset. The bottom layers are greyish cream limestones, deposited in shallow Cambrian and Ordovician seas (542-443 million years or Ma). The sea subsided in the Silurian (443-420Ma), becoming a deeper marine oxygen poor environment, represented by the darker grey and green layers of sandstone in the middle of the sandwich. Their colour is due to unoxidised iron, that tells us the chemistry of the depositional environment.
In the following Devonian period (419-359Ma) the land rose above the waves again. The grains in the red sandstones sitting above the marine sediments are covered in a fine patina of rust giving the rocks their colour. They were originally deposited in rivers just as land plants were beginning to take over the shaping of the landscape. Other rocks were deposited on top, but have now been removed by erosion.
Their current geological adventure involves being gently tilted upwards into parallel brightly coloured ridges some 1200 metres high in the Keping Shan thrust belt. Like many mountain chains, these peaks have had multiple rises and falls. They first formed some 300 million years ago when the Tarim block (a chunk of Australia) came crashing in. During the Mesozoic era (252 to 66 million years ago), several chains of volcanic islands collided with Asia, remobilising the faults and pushing new peaks upwards each time, only to be eroded in their turn.
And 80 million years back, the current ongoing collision started, bringing about the third incarnation of this mountain range, as new stresses push through the same old deep geological weak points in the underlying continental structures.
Further photos of the region from space: http://earthobservatory.nasa.gov/IOTD/view.php?id=82853
