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Bulletin of Volcanology

, Volume 50, Issue 5, pp 287–303 | Cite as

The Nevados de Payachata volcanic region (18°S/69°W, N. Chile)

I. Geological, geochemical, and isotopic observations
  • G. Wörner
  • R. S. Harmon
  • J. Davidson
  • S. Moorbath
  • D. L. Turner
  • N. McMillan
  • C. Nyes
  • L. Lopez-Escobar
  • H. Moreno
Article

Abstract

Subduction-related volcanism in the Nevados de Payachata region of the Central Andes at 18°S comprises two temporally and geochemically distinct phases. An older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late Miocene age. The Pleistocene to Recent phase (≤0.3 Ma) includes the twin stratovolcanoes Volcan Pomerape and Volcan Parinacota (the Nevados de Payachata volcanic group) and two small centers to the west (i. e., Caquena and Vilacollo). Both stratovolcanoes consist of an older dome-and-flow series capped by an andesitic cone. The younger cone, i. e., V. Parinacota, suffered a postglacial cone collapse producing a widespread debris-avalanche deposit. Subsequently, the cone reformed during a brief, second volcanic episode. A number of small, relatively mafic, satellitic cinder cones and associated flows were produced during the most recent activity at V. Parinacota. At the older cone, i. e., V. Pomerape, an early dome sequence with an overlying isolated mafic spatter cone and the cone-forming andesitic-dacitic phase (mostly flows) have been recognized. The two Nevados de Payachata stratovolcanoes display continuous major- and trace-element trends from high-K2O basaltic andesites through rhyolites (53%–76% SiO2) that are well defined and distinct from those of the older volcanic centers. Petrography, chemical composition, and eruptive styles at V. Parinacota differ between pre- and post-debris-avalanche lavas. Precollapse flows have abundant amphibole (at SiO2 > 59 wt%) and lower Mg numbers than postcollapse lavas, which are generally less silicic and more restricted in composition. Compositional variations indicate that the magmas of the Nevados de Payachata volcanic group evolved through a combination of fractional crystallization, crustal assimilation, and intratrend magma mixing. Isotope compositions exhibit only minor variations. Pb-isotope ratios are relatively low (206Pb/204Pb = 17.95–18.20 and208Pb/204Pb = 38.2–38.5);87Sr/86Sr ratios range 0.70612–0.70707,143Nd/144Nd ratios range 0.51238–0.51230, andγ18OSMOW values range from + 6.8%o to + 7.6%o SMOW. A comparison with other Central Volcanic Zone centers shows that the Nevados de Payachata magmas are unusually rich in Ba (up to 1800 ppm) and Sr (up to 1700 ppm) and thus represent an unusual chemical signature in the Andean arc. These chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components. Primary mantle-derived melts, which are similar to those generated by subduction processes throughout the Andean arc, are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface. These magmas subsequently evolve at shallower levels through assimilation-crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast.

Keywords

Late Miocene Basaltic Andesite Cinder Cone Eruptive Style Crustal Assimilation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • G. Wörner
    • 1
  • R. S. Harmon
    • 2
  • J. Davidson
    • 3
  • S. Moorbath
    • 4
  • D. L. Turner
    • 5
  • N. McMillan
    • 6
  • C. Nyes
    • 5
  • L. Lopez-Escobar
    • 7
  • H. Moreno
    • 7
  1. 1.Institut für MineralogieRuhr Universität BochumBochumGermany
  2. 2.Dept. of Geological SciencesSouthern Methodist UniversityDallasUSA
  3. 3.Department of Geological SciencesUniversity of MichiganAnn ArborUSA
  4. 4.Department of Earth SciencesOxfordUnited Kingdom
  5. 5.Geophysical InstituteUniversity of AlaskaFairbanksUSA
  6. 6.Department of Geology and GeographyEastern Illinois UniversityCharlestonUSA
  7. 7.Departamento de Geologia y GeophisicaUniversidad de ChileSantiagoChile

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