Regional crustal thickness and precipitation in young mountain chains

AUTOR(ES)
FONTE

National Academy of Sciences

RESUMO

Crustal thickness is related to climate through precipitation-induced erosion. Along the Andes, the highest mountains and thickest crust (≈70 km) occur at 25° south, a region of low precipitation. Westerly winds warm passing over the Atacama Desert; precipitation is modest in the High Andes and eastward over the Altiplano. Severe aridity, hence low erosion rates, helps to account for the elevated volcanogenic contractional arc and high, internally draining plateau in its rain shadow. Weak erosion along the north-central arc provides scant amounts of sediment to the Chile–Peru Trench, starving the subduction channel. Subcrustal removal might be expected to reduce the crustal thickness, but is not a factor at 25° south. The thickness of the gravitationally compensated continental crust cannot reflect underplating and/or partial fusion of sediments, but must be caused chiefly by volcanism-plutonism and contraction. Contrasting climate typifies the terrane at 45° south where moisture-laden westerly winds encounter a cool margin, bringing abundant precipitation. The alpine landscape is of lower average elevation compared with the north-central Andes and is supported by thinner continental crust (≈35 km). Intense erosion supplies voluminous clastic debris to the offshore trench, and vast quantities are subducted. However, the southern Andean crust is only about half as thick as that at 25° south, suggesting that erosion, not subcrustal sediment accretion or anatexis, is partly responsible for the thickness of the mountain belt. The Himalayas plus Tibetan Plateau, the Sierra Nevada plus Colorado Plateau, and the Japanese Islands exhibit analogous relationships between crustal thickness and climate.

ACESSO AO ARTIGO

Documentos Relacionados