Preliminary geochemical characterization of volcanic and geothermal fluids discharged from the Ecuadorian volcanic arc.

In Ecuador, magmatism results from the subduction of the Nazca Plate beneath the North Western part of South America. North of 2.5°S, the Ecuadorian Quaternary volcanic arc is characterized by about 60 volcanoes distributed along three different parallel NNE-striking chains. Many of these volcanoes are potentially active or currently in activity displaying associated geothermal fields. South of this latitude, no active arc is present in Ecuador.
Few geochemical studies of the discharged fluids in this region have been attempted, mainly related to geothermal exploration. Nevertheless, a complete study of the fluids of the volcanic arc is lacking.
The aim of this work is to present the first systematic geochemical characterization of discharged fluids from the entire Ecuadorian volcanic arc. In order to achieve this objective, 56 samples of thermal and cold waters, as well as 32 dissolved and 27 bubbling gases, were collected from North to South across the arc and analyzed for determination of the main geochemical parameters.
A chemical study reflects the physical and chemical processes undergone by these cold and thermal waters during their circulation through the different host rocks.
The chemistry of the dissolved gases, are characterized by He and CO2 contents, 2 to 3 orders of magnitude higher than the ASW values implies very active gas-water interaction processes.
Moreover, both dissolved and bubbling gases isotopic signature shows a wide compositional range, with Helium ranging between 0.1 to 7.12 R/Ra and carbon ranging from -1.75 to -10.50 13C(TDIC) vs PDB standard. Such isotopic features may be related to the presence of at least two distinct end-members: mantle and crustal..
Helium, Nitrogen, Carbon, Oxygen and Deuterium isotopic signatures will help us to identify and characterize the main end-members of fluids involved in Ecuador’s continental arc-volcanism.
Moreover, on the basis of the chemistry of thermal waters and associated bubbling gases the characteristics and the potential resources of the different geothermal fields are being investigated.

Aspden, J.A., Fortey, N., Litherland, M., Viteri, F. and Harrison, S.M., 1992a. Regional S-type granites in the Ecuadorian Andes: Possible remnants of the breakup of western Gondwana. Journal of South American Earth Sciences, 6(3): 123-132.
Aspden, J.A., Harrison, S.H. and Rundle, C.C., 1992b. New chronological control for the tectono-magmatic evolution of the metamorphic basement, Cordillera Real and El Oro Province of Ecuador. Journal of South American Earth Sciences, 6(1-2): 77-96.
Aspden, J.A. and Litherland, M., 1992. The geology and Mesozoic collisional history of the Cordillera Real, Ecuador. Tectonophysics, 205(1-3): 187-204.
Barckhausen, U., Ranero, C.R., von Huene, R., Cande, R. and Roeser, H.A., 2001. Revised tectonic boundaries in the Cocos plate off Costa Rica: Implicatios for the segmentation of the convergent margin and for plate tectonic models. Journal of Geophysical Research, 106: 19207-19220.
Beate, B. et al., 2001. Mio-Pliocene adakite generation related to flat subduction in southern Ecuador: The Quimsacocha volcanic center. Earth and Planetary Science Letters, 192: 561-570.
BGS-CODIGEM, 1998. Geologic map of the Western Cordillera of Ecuador between 0°-1°S, Quito.
Calahorrano, A., Sallarès, V., Collot, J.-Y., Sage, F. and Ranero, C., 2008. Nonlinear variations of the physical properties along the southern Ecuador subduction channel: Results from depth-migrated seismic data. Earth and Planetary Science Letters, 267: 453-467.
Capasso G & Inguaggiato S (1998) A simple method for the determination of dissolved gases in natural waters: An application to thermal waters from Vulcano island.: Applied Geochem., v. 13, p. 631-642.
Cosma, L. et al., 1998. Pétrographie et géochimie des unités magmatiques de la Cordillère Occidental d'Equateur (0°30'S): implications tectoniques. Bulletin de la Société Géologique de France, 169(6): 739-751.
Goosens, P.J. and Rose, W., 1973. Chemical composition and age determination of tholeiitic rocks in the Basic Igneous Complex, Ecuador. Geological Society of America Bulletin, 84: 1043-1052.
Hein, R.J. and Yeh, H.-W., 1983. Oxygen-isotope composition of secondary silica phaes, Costa Rica Rift, Deep Sea Drilling Project Leg 69. Deep Sea Drilling Project Initial Reports, 69: 423-429.
Hughes, R. and Pilatasig, L., 2002. Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador. Tectonophysics, 345: 29-48.
Inguaggiato, S., Pecoraino, G., and D'Amore, F., 2000, Chemical and isotopical characterization of fluid manifestations of Ischia Island (Italy).: J.Volcanol.Geoth.Res., v. 99, p. 151-178.
Inguaggiato S., Rizzo A (2004) Dissolved helium isotope ratios in ground-waters: a new technique based on gas-water re-equilibration and its application to Stromboli volcanic system. Appl Geochem 19:665-673
Inguaggiato S, Taran YA, Grassa F, Capasso G, Favara R, Varley N, Faber E (2004b) Nitrogen isotopes in thermal fluids of a forearc region (Jalisco Block, Mexico): evidence for heavy nitrogen from continental crust. Geochem Geophys Geosyst 5:Q12003
Inguaggiato S, Martin-Del Pozzo AL, Aguayo A, Capasso G, Favara R (2005) Isotopic, chemical and dissolved gas constraints on spring water from Popocatepetl (Mexico): evidence of gas-water interaction magmatic component and shallow fluids. J Volcanol Geotherm Res 141:91-108
Inguaggiato S., F. Grassa, G. Capasso, R. Favara, A. Rizzo, Y. Taran (2006) Simultaneous determination of 36Ar and N2 content together with d15N values in gas samples: examples from different arc-related volcanic systems AGU Fall Meeting 2006.V33A-0638
Jaillard, E. et al., 2004. Stratigraphy of the late Cretaceous-Paleogene deposits of the cordillera occidental of central Ecuador: geodynamic implications. Journal of South American Earth Sciences, 17(1): 49-58.
Kellogg, J.N. and Vega, V., 1995. Tectonic development of Panama, Costa Rica, and the Columbian Andes : Constraints from global positioning system geodetic studies and gravity. In: P. Mann (Editor), Geologic and Tectonic Development of the Caribbean Plate Boundary in Southern Central America. Geological Society of America Bulletin, Boulder, Colorado, pp. 75-86.
Lapierre, H. et al., 2000. Multiple plume events in the genesis of the peri-Caribbean Cretaceous oceanic plateau province. Journal of Geophysical Research, 105(B4): 8404-8421.
Lavenu, A. et al., 1992. New K-Ar age dates of Neogene and Quaternary volcanic rocks from the Ecuadorian Andes : implications for the relationship between sedimentation, volcanism, and tectonics. Journal of South American Earth Sciences, 5(3-4): 309-320.
Lebrat, M., Megard, F., Dupuy, C. and Dostal, J., 1987. Geochemistry and tectonic setting of pre-collision Cretaceous and Paleogene volcanic rocks of Ecuador. Bulletin of the Geological Society of America, 99(4): 569-578.
Litherland, M., Aspden, J.A. and Jemielita, R.A., 1994. The metamorphic belts of Ecuador, Overseas memoir 11. British Geological Survey.
Lonsdale, P., 1978. Ecuadorian subduction system. The American Association of Petroleum Geologist Bulletin, 62(12): 2454-2477.
Lonsdale, P. and Klitgord, K.D., 1978. Structure and tectonic history of the eastern Panama Basin. Geological Society of America Bulletin, 89: 981-999.
Luzieux, L.D.A., Heller, F., Spikings, R., Vallejo, C. and Winkler, W., 2006. Origin and Cretaceous tectonic history of the coastal Ecuadorian forearc between 1[deg]N and 3[deg]S: Paleomagnetic, radiometric and fossil evidence. Earth and Planetary Science Letters, In Press, Corrected Proof.
Marty, B., Jambon, A., 1987. C/3He in volatile fluxes from the solid earth: implications for carbon geodynamics. Earth Planet. Sci.Lett. 83, 16–26.
Michaud, F. et al., 2005. Fields of multi-kilometer scale sub-circular depressions in the Carnegie Ridge sedimentary blanket: Effect of underwater carbonate dissolution? Marine Geology, 216: 205-219.
O'Connor, J.M., Stoffers, P., Wijbrans, J.R. and Worthington, T.J., 2007. Migration of widespread long-lived volcanism across the GalápagosVolcanic Province: Evidence for a broad hotspot melting anomaly? Earth and Planetary Science Letters, 263: 339-354.
Pennington, W.D., 1981. Subduction of the eastern Panama Basin and seismotectonics of northwestern South America. Journal of Geophysical Research, 86(B11): 10753-10770.
Reynaud, C., Jaillard, E., Lapierre, H., Mamberti, M. and Mascle, G., 1999. Oceanic plateau and island arcs of southwestern Ecuador:their place in the geodynamic evolution of northwestern South America. Tectonophysics, 307: 235-254.
Sano, Y., Marty, B., 1995. Origin of carbon in fumarolic gas from island arcs. Chem. Geol. 119, 265–274.
Somers, C. et al., 2005. Miocene adakitic intrusions in the Western Cordillera of Ecuador, 6th International Symposium on Andean Geodynamics (ISAG 2005), Barcelona, pp. 679-680.
Toro, J. and Jaillard, E., 2005. Provenance of the Upper Cretaceous to upper Eocene clastic sediments of the Western Cordillera of Ecuador: Geodynamic Implications. Tectonophysics, 399(1-4): 279-292.
Trenkamp, R., Kellogg , J.N., Freymueller , J.T. and Mora, H.P., 2002. Wide plate margin deformation, southern Central America and northwestern South America, CASA GPS observations. Journal of South American Earth Sciences, 15: 157-171.
Varekamp, J.C., Kreulen, R., Poorter, R.P.E., Van Bergen, M.J., 1992. Carbon sources in arc volcanism, with implications for the carbon cycle. Terra Nova 4, 363– 373.
Witt, C. et al., 2006. Development of the Gulf of Guayaquil (Ecuador) during the Quaternary as a response to the Norht Andean Block tectonic escape Tectonics, 25: TC3017, doi: 10.1029/2004TC001723.