treated as part of the Northern Andes. The Leeward Antilles islands Aruba, Bonaire, and Curaçao, which lie in the Caribbean Sea off the coast of Venezuela, were formerly thought to represent the submerged peaks of the extreme northern edge of the Andes range, but ongoing geological studies indicate that such a simplification does not do justice to the complex tectonic boundary between the South American and Caribbean plates. Geology The Andes are a Mesozoic–Tertiary orogenic belt of mountains along the Pacific Ring of Fire, a zone of volcanic activity that encompasses the Pacific rim of the Americas as well as the Asia-Pacific region. The Andes are the result of tectonic plate processes, caused by the subduction of oceanic crust beneath the South American Plate as the Nazca Plate and South American Plate converge. These processes were accelerated by the effects of climate. As the uplift of the Andes created a rain shadow on the western fringes of Chile, ocean currents and prevailing winds carried moisture away from the Chilean coast. This caused some areas of the subduction zone to be sediment starved, causing excess friction and an increased rate of compressed coastal uplift. The main cause of the rise of the Andes is the compression of the western rim of the South American Plate due to the subduction of the Nazca Plate and the Antarctic Plate.To the east, the Andes range is bounded by several sedimentary basins, such as Orinoco, Amazon Basin, Madre de Dios and Gran Chaco, that separate the Andes from the ancient cratons in eastern South America. In the south, the Andes share a long boundary with the former Patagonia Terrane. To the west, the Andes end at the Pacific Ocean, although the Peru-Chile trench can be considered their ultimate western limit. From a geographical approach, the Andes are considered to have their western boundaries marked by the appearance of coastal lowlands and a less rugged topography. The Andes Mountains also contain large quantities of iron ore located in many mountains within the range. The Andean orogen has a series of bends or oroclines. The Bolivian Orocline is a seaward concave bending in the coast of South America and the Andes Mountains at about 18° S. At this point, the orientation of the Andes turns from Northwest in Peru to South in Chile and Argentina. The Andean segment north and south of the Orocline have been rotated