Production of Jurassic Rhyolite by Anatexis of the Lower Crust of Patagonia

PANKHURST, R.J; RAPELA, C.W.

EARTH AND PLANETARY SCIENCE LETTERS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1995 vol. 134 p. 23 - 36

0012-821X

The mid-Jurassic Marifil and Chon Aike volcanic rocks of Patagonia are part of one of the largest silicic igneous province known. Rb-Sr geochronology indicate eruptive ages of 175-190 Ma for tghe Marifil complex (mostly Toarcian-Aalenian). The majority of the rocks are isotopically uniform, with initial 87Sr/86Sr  = 0.7067 +- 0.0003 and EpNd = -4 +-2. Primary magmas of andesitic compositionwere generated by partial melting of mafic "Grenvillian" lower crust, identifiel byn depleted-mante  model ages of 1150-1600 Ma. Lower crustal piroxene-granulite  xenoliths can be modelled as a residual source, although they may be alternatively b co-genetic cumulates. The dacite-rhyolite suite formed by cristal-liquid fractionation processes from the primary andesites: involving multistage crystallization and re-melting during magma ascent, with the later stages of evolution being explicable by fractional crystallization of plagioclase, amphibole and accesory minerals. The province represents large-scale cristal reworking associated with the unique tectonic environment of Gondwana break-up.