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Monday, 14 November 2011

Geological controls in Torres del Paine

People seemed to like those pics of Torres del Paine -- so here are two more.  Thanks to Rob for pointing out that the geology is quite complex here -- and it's plain that it has played a considerable role in determining the "shape of the land" following more intensive glaciation.

In the top photo you can see that there is a "cap" of dark-coloured rock on the pinnacles, and also a darker-coloured rock in the foreground.  The rocks in these areas are Cretaceous sedimentaries -- shales, mudstones, conglomerates etc.  In Miocene times these rocks were invaded by an igneous intrusion called a laccolith -- and the rocks here are granidiorites, gabbros and other complicated rock types.  Outside the edges of this intrusion there are also gabbros and diorites which were intruded slightly earlier in the form of sills.  The main intrusive band is seen in the part of the upper photo caught in the sunlight and slit by the big V-shaped gash.

I'm not sure of the geology in the lower photo -- but what impresses me here is the extraordinary degree of smoothing and glacial moulding of the "shoulder" beyond the lake.  Vast amounts of ice have come down here -- probably over the col to the top left of the photo.

2 comments:

Anonymous said...

Laccoliths are large bodies of igneous rock -so cooling times will be millions of years and at a depth of 10s kilometres below.

BRIAN JOHN said...

Quite so. What matters here (with the igneous rock sandwiched between layers of sedimentaries) is the resistence or coherence of the rock with respect to glacial processes and to periglacial processes (frost shattering and scree formation) after the glacier has melted away. Those incredibly steep rock faces in the igneous zone are intriguing...