Middle Triassic trachytic lava flows associated with coeval dyke swarm in the North Patagonian Massif: A postorogenic magmatism related to extensional collapse of the Gondwanide orogen

GONZÁLEZ, SANTIAGO N.; GRECO, GERSON A.; SATO, ANA M.; LLAMBÍAS, EDUARDO J.; BASEI, MIGUEL A.S.; GONZÁLEZ, PABLO D.; DÍAZ, PABLO E.; GONZÁLEZ, SANTIAGO N.; GRECO, GERSON A.; SATO, ANA M.; LLAMBÍAS, EDUARDO J.; BASEI, MIGUEL A.S.; GONZÁLEZ, PABLO D.; DÍAZ, PABLO E.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017 vol. 75 p. 134 - 143

0895-9811

The Marifil Volcanic Complex is an extended volcanic and pyroclastic unit that has been included in the Chon Aike large igneous province. The Marifil Volcanic Complex is mainly composed of rhyolites, dacites, rhyodacites and minor andesites. The latter are common in the base of the unit. The acidic part of this unit has been dated between 192 Ma to 151 Ma (Early to Middle Jurassic) by K-Ar, Ar-Ar and Rb-Sr methods, but for the andesites no reliable age is available. Published K-Ar age data range from 221 Ma to 173 Ma. In this research we provide an U-Pb crystallization age of 247.22 ± 0.46 Ma for an andesite that covers Permian granitoids and which is covered by rhyolitic ignimbrites from the Marifil Volcanic Complex. We also describe the stratigraphic relations, the petrographic characteristics and geochemistry of these andesitic rocks. We propose to include the Triassic, trachytic to trachyandesitic (mesosilicic) magmatic rocks into the Monasa Formation, name used previously for basal basaltic to andesitic rocks from the Marifil Volcanic Complex. The Monasa Formation is distinguishable from the Marfil Volcanic Complex basis on age, composition and genesis. The Monasa Formation is correlated with other magmatic units similar in composition, age and stratigraphic position all over the North Patagonian Massif. We consider these magmatic rocks as an expression of a Triassic postorogenic extension in the North Patagonian Massif.