There are two staggered mountain ranges running the length of Costa Rica. The northern consists of a chain of young volcanoes, many of them active. The southern range is the uplifted core of an earlier volcanic chain, now eroded to expose the intrusive rocks of the former magma chamber. This range, the Sierra de Talamanca, contains Cerro Chirripo, the highest peak in Costa Rica at 12,300 feet (3819 m). Chiripo was high enough to support glaciers during the Pleistocene and has a number of cirques. It can snow there occasionally, and it has also snowed at the summits of Irazu and Turrialba, both around 11,000 feet.
If you like ancient rocks, like I do, Costa Rica is pretty bland. It's your basic volcanic arc geology. The oldest rocks are around 180 million years old and are chunks of uplifted ocean floor called ophiolites. Various marine sedimentary rocks overlie the ophiolites and are in turn covered by younger volcanic rocks and recent deposits. The Sierra de Talamanca exposes the eroded roots of a former volcanic chain. Major volcanism ceased in southern Costa Rica around 8 million years ago and the intrusive rocks are mostly younger than 5 million years.
The process of subduction would have resulted in metamorphism but there are almost no metamorphic rocks at the surface in Costa Rica. They are probably still buried deep in the crust.
Created 18 January 2008, Last Update 14 December 2009
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