Skip to Main Content
Book Chapter

Recent lavas from the Andean volcanic front (33 to 42°S); Interpretations of along-arc compositional variations

By
Daniel R. Tormey
Daniel R. Tormey
Search for other works by this author on:
Rosemary Hickey-Vargas
Rosemary Hickey-Vargas
Search for other works by this author on:
Frederick A. Frey
Frederick A. Frey
Search for other works by this author on:
Leopoldo López-Escobar
Leopoldo López-Escobar
Search for other works by this author on:
Published:
January 01, 1991

Along the volcanic front of the Southern Volcanic Zone of the Andes between 33°S and 42°S the continental crust increases in thickness from south to north, and erupted lavas define several along-arc geochemical trends. These geochemical trends are the integrated effects of processes occurring in the subducted oceanic crust, the overlying mantle, and the continental crust. Major- and trace-element abundances and isotopic ratios are used to distinguish the effects of crustal and mantle processes. In the relatively thin crust region south of 37°S, lavas evolve dominantly by low-pressure crystallization and incorporate insignificant amounts of continental crust. Abundance ratios of most incompatible elements and isotopic ratios in these lavas reflect components derived from the mantle and subducted oceanic crust. Compared to basalts from north of 37°S, basalts from 37 to 42°S have higher CaO but lower Na2O and incompatible element contents. These differences are consistent with a north to south increase in degree of mantle melting, perhaps controlled by variable fluxing from the subducted slab (Rb/Cs ratios decrease from north to south), or variations in the thickness of the mantle column that undergoes melting (thicker crust in the north leads to a thinner mantle column and lower degree of melting). In the thicker crust region north of 37°S crustal contamination exerts a greater control on lava compositions. In the interval from andesite to rhyolite, upper crustal contamination causes Rb, Cs, and Th enrichment and isotopic variability. The evolution from basalt to basaltic andesite in this region occurs in the lower crust and crustal contamination causes enrichment in Rb, Cs, and Th and increased La/Yb. The most probable lower crustal protolith for the contaminant is a young, arc-derived garnet granulite.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

Andean Magmatism and Its Tectonic Setting

Russell S. Harmon
Russell S. Harmon
Search for other works by this author on:
Carlos W. Rapela
Carlos W. Rapela
Search for other works by this author on:
Geological Society of America
Volume
265
ISBN print:
9780813722658
Publication date:
January 01, 1991

References

Related

Citing Books via

Related Articles
Related Book Content
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal