Altiplano Uplift

29 Oct 2016

The topography of the central Andes is the subject at http://phys.org/print396589441.html ... geologists have been investigating why so much uplift has occurred in that region since the end of the Pleistocene - uplift on a scale contrary to the mainstream consensus regards how long these processes take. For example, it is widely recognised that  Lake Titicaca was a coastal lagoon but now it is elevated at several thousand feet.

The altiplano plateau is a high, and dry region, a vast plain punctuated by some spectacular volcanoes. A study in the Oct 25th issue of Nature Communications has used remote sensing data and computer simulation to model how they think a huge dome of magma lies beneath the Altiplano. They have declared this explanation is the cause of the elevation. The dome sits over an active magma body and this has the effect of thickening the crust due to the repeated injections of magma from below. The dome, they say, is the Earth's response to the low density magma chamber pumping up from below. Hence, they are shifting blame from uplift (which would be anomalously too rapid) on to the magma chamber. It is quite a clever way to erase the problem and they point to Plate Tectonics as one of the reasons why this is happening - the South American plate is overriding the oceanic plate (so we are provided with two hypothesis and some computer gymnastics to arrive at the solution). Does a magma chamber exist below the Altiplano? One can imagine a magma dome may do and it seems this research follows on from previous claims of the dome's existence by the same team a year or so ago.  

In contrast, geologist Peter M James, in his book on crustal deformation, says the equator during the Cambrian epoch ran along the line of the Rockies and the Andes. In addition, in the Late Pleistocene the North Pole was in the sea off the NW coast of Greenland and as a result of geoid change the equatorial bulge, sea levels were much higher. The equator, he says, was situated in a line from close to Lake Titicaca, crossing the present equator in the Gulf of Guinea and Cameroon, and ran north of the present equator in East Asia. Hence, sea levels on the coast below Titicaca would have been much higher suggesting there might be no reason to evoke an exotic solution and normal uplift may account for subsequent raising of the altiplano (in association with lower sea levels as the waters of the equatorial bulge shifted northwards).