H漫画

Regional variations in the chemical composition of Miocene-to-Recent volcanic rocks from the Central Andes are investigated on the basis of 260 chemical analyses compiled from the literature in addition to 25 new analyses for 5 trace elements. Correlations are established between major and trace element compositions and other variables such as distance from the eruptive centres from the Peru-Chile trench or crustal thickness, using the computer and multigraphic techniques.

Among the most striking correlations are the confirmation of the previously established continent-ward increase of K₂O for all rock types, a surprising negative correlation of Na₂O with distance from the trench in one large segment of the Cordillera and the positive correlation of Li, U and Rb with crustal thickness.

Comparisons are also made between Andean rocks and those of island arcs and other tectonic regimes.

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Supervisor: Marcos Zentilli