Day 13 - Argentina 2025: Parque Bi-Nacional Patagonia

I have had a humbling day, in which I, but a tiny human being, have been awed by the grandeur of the surrounding landscape. The folks here in the region have been working for years to have their surroundings named a national park, partly for conservation purposes and partly to attract ecotourism to the region. Finally, in the last couple of years, four or five separate areas received national park status, and the cluster of these areas is what here is called the Parque Bi-Nacional Patagonia. It is quite commendable that Argentinians and Chileans worked together on this matter, so the unofficial borders of the park extend across both nations.

At the core of the park is the enormous Lago Buenos Aires, which is twice as large as Lake Geneva. The lake cuts across the international border and extends deep into Chile (where it is called Lago General Carrera). The lake has undoubtedly been shaped by glaciers, but it is fairly deep (400 to 450 m), so it likely started like a tectonic graben that cuts across the Cordillera. Why would that be? Well, if you look at a plate tectonics map of this part of the world, you will see that due west of the lake is the triple junction, where the Nazca, Antarctic, and South American plates meet. In the parlance of geology is where a spreading ridge meets a subduction zone, so a shallow graben could well be the expression of the subducted oceanic ridge. Personally, I think that to the south the triple junction breaks into a transform fault that extends to Tierra del Fuego, but I may be the only person who thinks so.

The scale of the lake, the Andes, and volcano-sedimentary apron to the east is hard to grasp, so I just drove the first 100 km of a 500 km loop, stunned by the complexity of the rock units exposed in the mountain front. Here and there I felt pretty confident I could see stratigraphic relations, structural deformation, a volcanic neck, or a hydrothermally altered pluton, but for the most part I had to shake my head, thinking of the poor geologists who had to map and make sense of the colorful puzzle confronting me. Oh, and those mountains are high, steep, and stern, and I am convinced that to entice them to yield up their secrets will require  lot of walking and detailed mapping. Maybe I should bring my Field Geology class here (cackle, cackle, cackle).