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Geochemical features of southern Andes Quaternary volcanics between 41°50′ and 43°00′S

By
Leopoldo López-Escobar
Leopoldo López-Escobar
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Michio Tagiri
Michio Tagiri
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Mario Vergara
Mario Vergara
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Published:
January 01, 1991

Basaltic samples from the volcanic centers Hualaihué, Hornopirén, and Michinmahuida (southern region of the Southern Volcanic Zone of the Andes), and one rhyolite sample from the resurgent dome of the Chaitén volcano, neighbor of Michinmahuida volcano, were analyzed for major and trace elements and for Sr-, Nd-, Pb-, and O-isotope compositions.

Basaltic samples are, in general, similar to basaltic rocks from the central region (37 to 41°15′S) of the southern Andes Quaternary volcanic front (SAQVF) in major and trace elements and Sr-, Nd-, and O-isotopic compositions. However, basaltic rocks from the southern region (41°15′ to 46°S) of the SAQVF have more variable Pb-isotope ratios than the central region ones. These ratios are similar to those of basaltic rocks from the northern region (33 to 37°S), even when both regions differ significantly in crustal thickness.

In spite of being located in an area of presumably thin continental crust, the Chaiten rhyolite, which is the only rhyolite reported in the southern region of the SAQVF, has higher Sr- and lower Nd-isotopic ratios than basalts. These ratios are similar to those of rocks from the northern region (33 to 37°S) of the SAQVF, where the continental crust is thick. This rhyolite also has higher Pb- and O-isotopic ratios than its neighbour the Michinmahuida basalt, but is notably depleted in medium rare-earth elements (MREE), heavy rare-earth elements (HREE), Sr, Eu, Ti, Zr, and Hf. Also, it is similar to rhyolites from the northern region of the SAQVF in the abundances and ratios of incompatible trace elements.

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GSA Special Papers

Andean Magmatism and Its Tectonic Setting

Russell S. Harmon
Russell S. Harmon
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Carlos W. Rapela
Carlos W. Rapela
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Geological Society of America
Volume
265
ISBN print:
9780813722658
Publication date:
January 01, 1991

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