Published in 1974, the 4th Special Publication of the Geological Society of London aimed to give a comprehensive overview of the “Mesozoic-Cenozoic orogenic belts”, as they were understood and sketched by this time. Below, I confront sections on the Himalaya (from book’s chapter by Augusto Gansser, in fact coming from his 1964 book) with sections of the Andes (from the chapter on the Central Andes by Rupert William Rutland).
This reveals the limited understanding of Andean structure and tectonics in the seventies, when compared to a typical collisional orogen like the Himalayas. Note that the most recent [active] faults on the Andean section are drawn extremely steep; many are sketched as normal faults; and they limit blocks affected by vertical tectonism. This bears very little resemblance with an orogenic wedge that would result from the shortening of the whole crust, as was already proposed for the Alps or the Himalaya ! Hopefully, from the middle of the eighties, important thrusts, and large fold and thrust belts were progressively discovered and described in the Andes: look for example to the first structural geological sections of the famous Aconcagua fold and thrust belt by Victor Ramos, published in 1985-88.
However, a good crustal-scale view of the typical subduction orogen, namely the Central Andes, came decades after our understanding of collisional mountain belts. Just think to the Alps sketched by E. Argand in the 1910’s, and of course to Gansser’s Himalayan sections. And even now the primary vergence of the Andes belt (east-, west-, bi-vergent) is lively discussed.
- Gansser A., 1974, Himalaya. Geol. Soc. London Spec. publ., 4, 267-278.
- Rutland, R.W.R., 1974, Andes. Geol. Soc. London Spec. publ., 4, 733-743.
- Ramos, V.A., 1988, The tectonics of the central Andes, 30 to 33°S latitude. Geol Soc Am. Spec. pap., 218, 31-54.
