Stable isotopes evidence of recycled subduction fluids in the hydrothermal/volcanic activity across Nicaragua and Costa Rica

A. Ramírez-Leiva, R. Sánchez-Murillo*, M. Martínez-Cruz, H. Calderón, G. Esquivel-Hernández, V. Delgado, C. Birkel, E. Gazel, G. E. Alvarado, C. Soulsby

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


The Central America volcanic front provides a unique opportunity to study hydrothermal inputs and their interaction and mixing with modern meteoric waters. The objectives of this study were to: a) characterize the isotopic composition (δ18O, δ2H, d-excess, and lc-excess) of hydrothermal/volcanic systems, b) analyze the influence of kinetic fractionation and meteoric water inputs in the isotopic composition of hydrothermal waters, and c) estimate the ‘andesitic water’ contribution (recycled subduction fluids) within the volcanic front of Nicaragua and Costa Rica. Hydrothermal evaporation lines are described as: δ2H = 4.7·δ18O − 13.0 (Costa Rica) and δ2H = 2.7·δ18O − 31.6 (Nicaragua). These regressions are significantly (p < 0.001) deviated from their respective meteoric water lines: δ2H = 7.6·δ18O + 7.4 (Costa Rica) and δ2H = 7.4·δ18O + 5.2 (Nicaragua). The greater rainfall inputs in Costa Rica with respect to Nicaragua, resulted in the attenuation of the evaporative effect as observed in the strong bimodal distribution of the hydrothermal waters, which can be divided in fluids: a) isotopically-close to meteoric conditions and b) isotopically-altered by the interaction with recycled subduction fluids and kinetic fractionation. The latter is clearly depicted in the significantly (p < 0.001) low d-excess and lc-excess median values between Costa Rica (+ 5.10‰ − 5.25‰) and Nicaragua (− 2.42‰ − 10.65‰), respectively. Poor correlations between δ18O/δ2H and the elevation gradient emphasize that the contribution of recycled subduction fluids and subsequent surface kinetic fractionation are the main drivers of the isotopic departure from the orographic distillation trend captured in the rainfall isoscapes. End-member mixing calculations resulted in a significant difference (p < 0.001) between the mean ‘andesitic water’ contribution to the hydrothermal systems of 15.3 ± 10.8 (%, ± 1σ) (Nicaragua) and 19.7 ± 10.3 (%, ± 1σ) (Costa Rica). The spectrum of ‘andesitic water’ contribution largely reflects the degree of mixing with isotopically ‘pre-shifted’ recycled subduction fluids. The latter is supported by previous strong evidence of mantle-derived N2/He contributions across the volcanic front of Nicaragua and Costa Rica.

Original languageEnglish
Pages (from-to)172-183
Number of pages12
JournalJournal of Volcanology and Geothermal Research
Early online date1 Sept 2017
Publication statusPublished - 1 Oct 2017

Bibliographical note

This project was supported by International Atomic Energy Agency grants COS7005 (Ensuring Water Security and Sustainability of the Central Valley of Costa Rica) and CRP-19747 to RSM under the initiative “Stable isotopes in precipitation and paleoclimatic archives in tropical areas to improve regional hydrological and climatic impact models” and the Research Office of the Universidad Nacional of Costa Rica through grants SIA-0482-13, SIA-0378-14, and SIA-0101-14. The authors would also like to thank the IsoNET initiative funded by the University of Costa Rica Research Council and the recent sampling help from OVSICORI (Universidad Nacional, Heredia, Costa Rica) and Instituto Costarricense de Electricidad (San José, Costa Rica). We also thank the Programme on Water Resources of the International Atomic Energy Agency for granting access to stable isotope archives of Costa Rica and Nicaragua. A complete database is provided in the supplemental materials.


  • Central America volcanic front
  • Groundwater mixing
  • Hydrothermal systems
  • Isotopic fractionation
  • Recycled subduction fluids


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