Abstract
A study of approximately 300 samples of basic to intermediate lavas of Mesozoic and Tertiary age from five profiles across the Andes of central Chile (25°30′–35°S) shows that the ascribed “normal” geochemical trends transverse to this active continental margin and, with time (up to the Miocene), are oversimplified or reversed. The Jurassic-Paleogene lavas show no clear trend towards more evolved compositions in the east (away from the paleotrench), nor with time. There are even indications that the crust was thicker towards the south during part of the Mesozoic, contrary to the present situation. The tectonic evolution during the Jurassic-Early Cretaceous is characterized by episodic changes in the subduction regime, expressed among other things by a recurring non-organic shoshonitic fissure volcanism. The Late Cretaceous history constitutes a transition to the Cenozoic development with calcalkaline volcanic rocks erupting from central volcanoes in a caldera-graben setting.
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