journal of volcanology and geothermal research 141 (2005) 91 – 108.pdf

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Isotopic, chemical and dissolved gas constraints on spring water

from Popocatepetl volcano (Mexico): evidence of gaswater

interaction between magmatic component and shallow fluids

S. Inguaggiatoa,*, A.L. Martin-Del Pozzob, A. Aguayob, G. Capassoa, R. Favaraa

aIstituto Nazionale di Geofisica e Vulcanologia Sezione di Palermo, via Ugo La Malfa, 153, Palermo, 90146, ItalybInstituto de Geofisica UNAM, Ciudad Universitaria, Mexico DF, 04510 Mexico

Received 5 February 2004; accepted 1 September 2004

Abstract

Geochemical research was carried out on cold and hot springs at Popocatepetl (Popo) volcano (Mexico) in 1999 to identify a

possible relationship with magmatic activity. The chemical and isotopic composition of the fluids is compatible with strong gas

water interaction between deep and shallow fluids. In fact, the isotopic composition of He and dissolved carbon species is

consistent with a magmatic origin.

The presence of a geothermal system having a temperature of 801008 C was estimated on the basis of liquid

geothermometers. A large amount of dissolved CO2in the springs was also detected and associated with high CO 2 degassing.

D 2004 Elsevier B.V. All rights reserved.

Keywords: popocatepetl volcano; helium isotope composition; carbon isotope composition; dissolved gases; gaswater interaction

1. Introduction

Popocatepetl (Popo) is a large andesitic stratovol-

cano (5452 m) near Mexico City, which has been

erupting since December 1994. The fumarolic activityincreased in the early 1990s and culminated in ash

eruptions at the end of 1994 and in early 1995. Since

1996, a consecutive series of crater domes have been

formed and destroyed explosively. During the previous

eruptive activity (19181925), a small dome also grew

on the crater floor.

Popo is potentially dangerous because of its

explosive eruptive history and because millions of

people live within 60 km of the volcano. A geo-physical and geochemical monitoring network is

maintained by UNAM-CENAPRED in order to

evaluate changes in the eruptive activity.

Popo forms the southern part of the Sierra Nevada

complex which includes the older volcano, Iztaccihuatl

(Izta). The present-day Popo cone is also built on an

older volcano that was destroyed in a Bezymmiany-

type event (Robin and Boudal, 1987). To the south of

0377-0273/$ - see front matterD 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.jvolgeores.2004.09.006

* Corresponding author. Fax: +39 91 6809449.

E-mail address: [email protected] (S. Inguaggiato).

Journal of Volcanology and Geothermal Research 141 (2005) 91108

www.elsevier.com/locate/jvolgeores


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Fig.

1.

Locationmapofsampledsprings.

S. Inguaggiato et al. / Journal of Volcanology and Geothermal Research 141 (2005) 9110892


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Popo, directly at the foot of the volcano, Cretaceous

limestones and granodioritic stocks crop out.

Several geochemical investigations have been

carried out over the past years on the volcanicproducts and fluid emissions of Popo. On the basis

of sulfur isotope data from the fumaroles, and the

CO2 and S budget of the volcano, Goff et al. (1980)

hypothesized a minor assimilation of Cretaceous

evaporitic wall rocks by the volcanic products of

Popo, which is consistent with leachate studies of

recent volcanic ash (Armienta et al., 1998).

Recent CO2and SO2budget estimates highlight the

large amount of gas emitted by Popo volcano (Love et

al., 1998; Delgado-Granados et al., 2001), which

therefore represents one of the largest contributor ofvolcanic gases to the atmosphere. Spring water has

been monitored for the last 13 years to detect changes

related to the magmatic activity (Aguayo and Martin

del Pozzo, 1994; Martin-Del Pozzo et al., 2002a).

Recently, studies have been aimed at characterizing the

isotopic composition and type of interaction between

the volcanic gases and the spring water (Inguaggiato et

al., 1999, 2001; Martin-Del Pozzo et al., 2002b).

On the basis of the previous geochemical studies,

two different interpretations have been formulated

regarding the circulation of fluids at Popo and the

possible interaction between shallow waters and

deep fluids of magmatic origin. In keeping with the

first interpretation, based on the chemical composi-

tion of major, minor, and trace elements of the

spring waters (Werner et al., 1997), each spring

maintains a relatively constant composition over

time, and this suggests that there is no interaction

between spring waters and volcanic fluids.

Whereas, as indicated by second interpretation

(Inguaggiato et al., 1999, 2001; Martin-Del Pozzo et

al., 2002a,b), based on the chemical and isotopic

composition of both water and dissolved gases, thereis a strong interaction between deep magmatic fluids

and the cold spring waters circulating into the Popo.

The aim of this paper is to investigate the

interaction processes between rocks, water, and deep

gases at Popo volcano and explain the f luid

circulation within the volcano. In order to reach this

goal, in 1999 we studied 11 cold springs located near

Popo and Izta volcanoes, as well as three hot springs

to the south of Popo (Fig. 1). The cold springs on

Popo are located between 7 and 22 km from the

crater at altitudes between 3600 and 1900 m a.s.l.

The hot springs, as well as the two springs from Izta

were sampled for comparison. The hot springs,

located about 40 km from the volcano at about1000 m above sea level, were included in order to

identify their possible relation either with the

volcano or with the regional fault system. Previous

reconnaissance and sampling allowed us to decide

which springs were the most representative springs

for this study. All samples of water and dissolved

gases were analyzed for major and minor element

compositions as well as for noble gas isotopes

(3He/4He and 4He/20Ne ratios) and stable isotopes

(d34S, d13C, d18O, and dD).

2. Analytical methods

Groundwater samples were collected in poly-

ethylene bottles for laboratory analyses while tem-

perature, conductivity, and pH were determined

directly in the field. Alkalinity was analyzed by

titration with HCl 0.1 N, whereas major and minor

elements were determined in the laboratory using a

Dionex 2000i ion chromatograph with an accuracy

ofF2%. A Dionex CS-12 column was used for the

cations (Li, Na, K, Mg, Ca) and a Dionex AS4A-SC

column for the anions (F, Cl, Br, NO3, SO4). The

content of SiO2 was ascertained utilizing spectro-

photometric method based on yellow silicamolib-

date complex read at a wavelength of 650 nm.

Gases were analyzed using a Perkin Elmer 8500

gas-chromatograph equipped with a 4-m-long Car-

bosieve S II column and Ar as the carrier gas.

Helium, H2, O2, N2 and CO2 were measured by

means of a TCD detector while CH4 and CO were

determined through a FID detector coupled with a

methanizer. The detection limits were about 3 ppmvol. for He, 2 ppm vol. for H2 and 0.5 ppm vol. for

CO and CH4. The content of dissolved gas was

analyzed by the method described by Capasso and

Inguaggiato (1998) and Capasso et al. (2000) which

is based on the equilibrium partition of gas species

between a liquid and a gas phase after introduction

of a host gas into the sample.

Analyses of the dissolved He isotopic composition

were performed using the methodology proposed by

Inguaggiato and Rizzo (2004), which is based on

S. Inguaggiato et al. / Journal of Volcanology and Geothermal Research 141 (2005) 91108 93


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isotope equilibrium between liquid and host gas

phases. The 3He/4He ratios were measured by a

VG-5400TFT double collector (accuracy F1%) and4He /20Ne ratios by a VG Masstorr FX quadruple

mass spectrometer (accuracy F5%).

The d13C of Total Dissolved Inorganic Carbon

(TDIC) and the d18O of H2O of spring waters were

analyzed by a Finnigan Delta Plus mass spectrometer.

Carbon isotopic values are expressed in dx vs. PDB,

with an accuracy of 0.2dx. Oxygen isotopic values areexpressed in dx vs. V-SMOW with an accuracy of

0.2dx. In particular, the chemical and physical

stripping of CO2 from the water samples was carried

out to determine the isotope ratios of TDIC, using the

Table 1

Chemical and isotopic composition of the water

Sample Date Altitude pH Electrical

conductivity

T Ca Mg Na K F Cl NO3 SO4 HCO3 SiO2 dD

(H2O)

d18O

(H2O)

d34S

(SO4)POPO

RIO Feb-99 8.2 152 18.1 8.4 6.0 12.3 3.0 0.29 8.8 2.5 18.3 64.1 44.5 78.0 11.0 n.d.TO Feb-99 2060 6.9 176 13.5 9.7 8.2 13.4 2.9 0.25 9.2 2.0 24.3 70.2 45.8 81.5 11.4 9.6AG Feb-99 2100 6.6 209 15.2 9.9 9.5 21.5 3.5 0.51 11.6 4.4 18.2 94.6 48.8 80.0 11.4 8.2AX Feb-99 1920 6.1 633 16.8 35.4 41.1 56.3 7.1 0.55 25.1 5.7 38.5 378 62.3 83.0 12.0 8.8SB Feb-99 2200 6.7 176 13.1 10.2 6.6 16.8 2.0 0.51 8.9 3.8 11.8 94.6 41.5 80.0 11.6 n.d.TG Feb-99 2140 6.9 202 17.1 9.7 7.8 20.0 3.7 0.80 9.7 9.9 20.5 88.5 43.6 82.0 11.5 6.7TL Feb-99 3620 7.4 72 7.6 4.7 2.0 6.7 2.5 0.13 2.1 1.3 3.3 42.7 54.0 79.0 11.5 n.d.AX Nov-99 5.9 680 19.1 39.9 43.3 65.8 7.8 0.76 21.9 2.0 37.7 421 n.d. n.d. 11.5 n.d.

IXTA

SP Feb-99 7.6 142 14.4 7.7 7.0 11.4 2.3 0.19 8.4 3.9 7.9 70.2 38.0 75.0 11.0 n.d.ZM Feb-99 7.8 113 8.7 9.2 3.0 6.2 2.9 0.21 7.9 5.7 14.0 39.7 51.6 84.0 12.0 6.5

CUAUTLA

AH Feb-99 1290 6.2 2443 26.2 411 122 112 11.0 3.50 192 21.8 1048 677 58.4 72.0 10.4 16.6IX Feb-99 1150 6.9 3088 51.5 495 77 326 14.7 4.31 564 20.7 1303 214 57.0 65.0 9.6 17.5AH Nov-99 6.3 1250 26.4 486 127 114 12.9 1.90 81 3.3 1225 833 n.d. n.d. n.d. n.d.

IX Nov-99 6.6 3400 52.1 516 87 372 28.5 3.61 585 7.8 1489 226 n.d. n.d. n.d. n.d.

AT Nov-99 1250 6.8 710 36.6 302 66.6 65.5 6.3 1.71 31 4.6 992 201 56.0 64.0 9.3 16.3

The values are expressed in mg/l. Temperature in 8C and electrical conductivity in AS/cm. The isotopic values are expressed in per mil vs. V-

SMOW for deuterium and oxygen and in per mil vs. CDT for Sulphur. Altitudes are expressed in m. n.d.=not determined.

Fig. 2. Temperature vs. TDS values of sampled springs.



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method proposed by Favara et al. (2002). Analytical

results are reported inTables 1 and 4.

3. Geochemical framework

The chemical and isotopic compositions of the

sampled water are reported in Table 1. Almost all

the springs have low salinity and low outlet

temperatures which suggests a low degree of

waterrock interaction. Only the southern springs

(i.e. AH, AT and IX samples) have relatively high

salinity and T (Fig. 2). The Langelier Ludwig

diagram (Fig. 3a) shows that many samples fall in

the bicarbonatealkalineearth field except for theAH, AT and IX springs, located further south of

Popo, which fall in the chloridesulphatealkaline

earth field. The relative SO4, Cl and HCO3 contents

of groundwaters (Fig. 3b) show that the collected

samples fall into two groups: one rich in HCO3(samples from the flanks of Popocatepetl) and the

other rich in SO4 (southern samples: AH, IX and

AT). Moreover, these two groups show different

SO4/Cl ratios, while the southern samples show

relatively high SO4/Cl ratios that are probably

linked to leaching of sedimentary gypsum.Conversely, the groundwater from the flanks of

Popocatepetl shows relatively low SO4/Cl ratios,

which are probably linked to the influence of

volcanic sources, such as volcanic gases that seep

through the volcano and interact with the rain-water

that feeds the springs (Martin-Del Pozzo et al.,

2002a). Alternatively, these low SO4/Cl ratios could

result from leaching of recently erupted ashes.

4. Waterrock interaction

4.1. Saturation index and geothermometer

The chemical composition and dissolved salt

content in natural water result from the interaction

betwee n wat er, gas and hos t roc k. Chemical

equilibrium between water and rocks is not always

attained since it depends on many chemical and

thermodynamic conditions. In order to check

whether equilibrium had been reached or not, the

saturation index regarding possible mineral phases

present in the host rocks was calculated for eachspring. Said index in relation to a given mineral

phase is defined as the logarithm of the ratio

between the ion activity product (I.A.P.), relative to

the mineral phase, and the corresponding solubility

product (Ksp):

S:I: log I:A:P:=Ksp 1

Computations were performed by means of the

WATEQP program (Appelo, 1988) (Table 2). An

aqueous solution is usually considered saturated by

Fig. 3. (a) LangelierLudwig diagram showing that all sampled

springs fall in bicarbonateearthalkaline field except the southern

samples (AH-AT-IX) that fall in chloridesulphatealkalineearth

field. (b) Triangular plot HCO3ClSO4. All the samples are shared

in two HCO3and SO4-rich groups.



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a given mineral phase when the S.I. ranges between

+5% and 5% of log Ksp (Jenne et al., 1980).Saturation indexes calculated for quartz, chalcedony,

calcite, gypsum and fluorite at outlet T, P are

plotted in Fig. 4a and b. All the samples are slightly

over-saturated as regards quartz and chalcedony but

almost all are under saturated as regards the other

mineral phases, except for samples AH, IX and AT

that are close to being saturated by the considered

minerals. This excludes the possibility that the water

samples from the flanks of Popocatepetl interact

with carbonate minerals.

The deep temperature of the aquifer feeding the

southern springs was estimated by several geo-

thermometers. These water geothermometers are

based on the following theoretical assumptions: (a)

the water and host rock are in equilibrium which

implies that the water is saturated by the mineral

phases governing the geothermometer; and (b)during the ascent towards the surface, the waters

did not undergo re-equilibration nor did they mix

with shallow fluids.

Deep temperatures at depth of the aquifer feeding

the southern springs were calculated by the quartz

geothermometer without any vapor loss (TQC,

Fournier, 1973), and chalcedony solubility. Equili-

brium temperatures obtained by these geothermom-

eters are about 120 8C for quartz and 80 8C for

chalcedony (Fig. 5).

The two geothermometers for waters flowing in

carbonate and evaporite aquifers (Marini et al.,

1986; Chiodini et al., 1995) provide deep temper-

atures (about 100 8C) consistent with the silicageothermometers (Table 3).

Fig. 4. Saturation index diagrams: (a) gypsumcalcite; (b) fluorite

quartz. These diagrams highlight that all sampled springs are

slightly over-saturated with respect to quartz and that only the

southern samples are close to the saturation with respect to gypsum,

fluorite and calcite.

Table 2

Saturation indexes table: saturation indexes calculated with respect

to (Quartz, Chalcedony, Calcite, Gypsum and Fluorite) at outletP,T

conditions

Sample Calcite Gypsum Fluorite Quartz Chalcedony

RIO 0.55 3.02 2.45 0.65 0.14TO 1.79 2.84 2.46 0.74 0.23AG 1.95 2.98 1.85 0.74 0.23AX 1.45 2.32 1.42 0.82 0.32SB 1.89 3.13 1.8 0.7 0.19TG 1.66 2.93 1.5 0.66 0.15TL 1.85 3.91 3.17 0.91 0.4SP 1.19 3.4 2.78 0.64 0.13ZM 1.24 3.04 2.52 0.87 0.36AH 0.15 0.34 0.72 0.65 0.2IX 0.35 0.22 0.63 0.19 0.2AT 0.00 0.27 0.41 0.71 0.25

Computation were performed by means of the WATEQP program

(Appelo, 1988).



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4.2. H, O and S stable isotopes

The dD and d18O isotopic data of the water

samples are plotted in Fig. 6 together with the

world meteoric water line (Craig, 1961) and the

local meteoric water line (Cortes et al., 1997). This

graph shows that all the water samples fall between

the two meteoric water lines, suggesting that the

spring waters are of meteoric origin or, at least,

controlled largely by meteoric recharge (Martin-Del

Pozzo et al., 2002a). Furthermore, the samples do

not show any isotopic shift in oxygen due to water

rock exchange. This suggests that the southern

waters come from low-temperature relatively

bdynamicQ geothermal reservoirs, characterized by

short residence time, as suggested by Giggenbach

(1991).

The isotopic composition of sulfur is plotted

against the total concentration of SO4 of the spring

waters in Fig. 7, along with the isotopic composi-

tion of the Cretaceous marine evaporites, and

PopoTs crater fumaroles. The samples fall into two

main groups: (a) one characterized by a high SO4content (10001300 mg/l) and high isotopic values,

close to 17 vs. CDT; and (b) another one with a

very low SO4 content (1439 mg/l) and relatively

low isotopic values, close to 8 vs. CDT.

The first group is related to the leaching of

Cretaceous evaporite beds underlying the southernarea, which are expected to have an average 734S

value of 15.6x (Nielsen et al., 1991), which is very

close to the isotopic values of S in these springs.

Furthermore, as previously discussed, these springs

are in equilibrium with gypsum. The second group

is probably related to volcanic SO2 that interacts

with the meteoric-waters soaking the Popo edifice.

The isotopic value of S in the fumaroles adsorbed

from alkaline traps is 3.35F0.92 (Goff et al., 1980).

This value is higher than that of the mantle sulphur

Fig. 5. Silica content vs. outlet T of sampled springs. Assuming equilibrium with chalcedony solubility, a process of cooling starting from about

80 8C, has been hypothesized for Cuautla springs.

Table 3

Estimated equilibrium temperatures computed by several liquid

geothermometers

Sample T-

vent

T-

Chalcedony

T-

Quartz t

TCa

Mg

TSO4

FHCO3

Cuautla

AH 26.2 80 132 75 98

IX 51.5 78 120 105 100

AT 28.7 78 130 52 99

The temperature is expressed in 8C.



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and is probably to be referred to the assimilation of

evaporite rocks by the magma (Goff et al., 1980).

The S isotopic values of the second group of

springs, ranging from 6.2x to 9.8x, are slightly

more positive than those of the fumaroles. This can be

explained at least in two ways: shallow contamination

with sulfur of evaporitic origin or fractionation

processes between SO2

and dissolved SO4

(Sakai,

1968). Considering that the SO4contents in the spring

waters from Popo are very low (14 to 39 mg/l), the

addition of very small amounts of evaporitic S would

be sufficient to move the isotopic composition of S

from 3.35 (average crater fumarole value) towards the

values found in the springs.

5. Gaswater interaction

5.1. Dissolved gas contents

Dissolved gases in spring water are a useful tool

for understanding gaswater interactions. High

mobility in addition to different solubility makes

gases excellent geochemical tracers. The amount

Fig. 6. dD vs. d18O diagram. The World Meteoric Water Line, and the Local Meteoric Water Line are also shown.

Fig. 7. d34S values vs. SO4 content of sampled springs. The values of the magmatic and evaporitic end-members are also indicated.



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and type of dissolved gases have been successfully

used in geochemical investigations to solve hydro-

logical, geothermal, and volcanological problems

(Dyck, 1976; Capasso et al., 2000, 2001; Inguag-giato et al., 2000; Taran et al., 2002; Carapezza et

al., 2004).

The chemical composition of the dissolved gases

in almost all the samples of the Popo spring water

shows high gaswater interaction (Table 4). In fact,

the amount of dissolved CO2 measured in the

spring waters (up to 336 cm3 STP/l) is several

orders of magnitude higher than that of water in

equilibrium with the atmosphere. Furthermore, high

concentrations of helium (up to 5104 cm3 STP/l)

were also detected in the southern springs (Fig. 8).The relative amounts of dissolved O2, N2, and CO2,

are shown in Fig. 9. All the samples have O2/N2ratios lower than the atmosphere and show different

N2/CO2 ratios, with a minimum of 0.03 to 0.10 for

samples AX and AH. These samples have a CO2partial pressure of up to 0.5 atm. Three groups of

samples can be identified in this graph: CO2dominated samples (AH and AX) that fall close to

CO2 vertex; samples with intermediate N2/CO2ratios, between 1.5 and 0.6; N2-rich samples (ZM,

SP, TL) that fall relatively close to the N2 vertex

(N2/CO2 ratio around 2.6); The chemical composi-

tion of the dissolved gases does not reflect the

geographic distribution of the sampled springs (i.e.

Popo flanks vs. southern area) and is related to

different degrees of gaswater interaction andvarying gas contents and composition. The IX and

Table 4

Chemical and isotopic composition of dissolved gases

Sample Data He H2 O2 N2 CO CH4 CO2 Log

(C/3He)

d13C

(CO2)

R/Ra He/

Ne

R/Racorr.

Diss. gases

POPO

TO Feb-99 1.6e04 b.d.l. 0.1 15.2 b.d.l. 5.63e04 9.9 11.1 19.6 1.11 0.62 1.37AG Feb-99 7.6e05 b.d.l. 0.2 13.6 b.d.l. b.d.l. 17.2 11.5 14.3 1.14 0.51 1.51AX Feb-99 7.2e05 b.d.l. 0.3 9.9 b.d.l. 3.38e04 336.6 12.3 6.9 1.78 0.60 2.63AX Jun99 n.d. b.d.l. 2.0 11.6 1.7e03 3.22e03 301.4 n.d. n.d. n.d. n.d. n.d.AX Nov-99 n.d. 3.5e04 0.1 15.3 7.8e05 n.d. 244.7 n.d. 7.2 n.d. n.d. n.d.SB Feb-99 n.d. b.d.l. 0.3 18.1 2.5e05 1.38e04 19.7 n.d. 15.6 n.d. n.d. n.d.TG Feb-99 1.6e04 b.d.l. 0.1 14.4 b.d.l. 3.10e04 11.4 11.2 22.1 1.02 0.66 1.30TL Feb-99 1.5e04 b.d.l. 0.1 14.4 b.d.l. 1.07e03 5.6 10.9 21.4 1.12 0.71 1.46

IXTA

SP Feb-99 4.9e05 b.d.l. 0.2 14.2 1.4e04 8.26e03 5.4 11.6 22.9 1.06 0.89 1.25ZM Feb-99 n.d. b.d.l. 1.1 11.1 n.d. 1.82e04 4.3 n.d. 17.5 n.d. n.d. n.d.

CUAUTLA

AH Feb-99 4.8e04 b.d.l. 0.1 16.5 1.84e04 3.25e02 398.9 12.5 7.8 2.74 6.43 2.84AH Jun99 n.d. 1.4e03 0.6 11.5 b.d.l. 7.29e03 284.6 n.d. n.d. n.d. n.d. n.d.AH Nov-99 n.d. b.d.l. 0.3 29.2 b.d.l. 1.64e02 302.0 n.d. 8.1 n.d. n.d. n.d.

IX Feb-99 n.d. 4.6e04 2.8 11.9 1.2e04 6.88e02 17.4 n.d. n.d. n.d. n.d. n.d.IX Nov-99 4.8e04 b.d.l. 2.9 12.7 b.d.l. 1.89e02 25.8 11.9 8.3 1.34 2.41 1.43AT Feb-99 1.8e04 b.d.l. 0.1 16.2 n.d. 2.50e02 15.0 11.4 12.0 1.17 1.69 1.36AT Jun99 2.4e04 b.d.l. 1.5 18.0 3.2e04 1.06e02 31.1 n.d. n.d. n.d. n.d. n.d.AT Nov-99 n.d. b.d.l. 1.2 12.6 b.d.l. b.d.l. 20.0 n.d. n.d. n.d. n.d. n.d.

A.S.W. 4.55e05 ***** 6.6 12.3 ***** ***** 0.3 1 0.286 1

Bubb. gases

IX Feb-99 290.0 5.0 5.0 90.5 1.4 6.30E+03 3.0 n.d. 9.9 n.d. n.d. n.d.IX Nov-99 366.0 9.0 0.3 92.0 b.d.l. 7.96E+03 9.0 8.1 8.5 1.48 55.28 1.48

The chemical values are expressed in cm3 STP/l for dissolved gases. The chemical values of bubbling gases are expressed in ppm vol for He,

H2, CO and CH4and in vol.% for O2, N2and CO2. The isotopic values are expressed in per mil vs. PDB for Carbon isotope and as R /Ra(where

Ra=1.36106) for Helium isotope. b.d.l.=below detection limits. n.d.=Not determined.



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AT samples are also characterized by high quantities

of dissolved He, with up to 366 ppm in the

equilibrated free gas phase. Two explanations can

be given for the origin of the dissolved gases in the

samples that plot relatively close to the N2 vertex:

(a) the chemical composition of the pristine gas is

N2-dominated with a high He content;

(b) the chemical composition of the pristine gas is

CO2-dominated; during ascent towards the surface it

loses CO2through water interaction. This is caused by

the high solubility coefficient of CO2, a n d a s a

consequence, the residual gas is enriches in the low-

solubility components such as He, CH4and N2.

5.2. Isotopic composition of dissolved gases

The helium and carbon isotopic compositions of

the dissolved gases in groundwater give useful

information about the origin of the gases and the

physico-chemical processes they undergo during

their rise towards the surface (Sano and Wakita,

1985; Nakai et al., 1997; Marty et al., 1994;

Capasso et al., 1997; Inguaggiato et al., 2000;

Inguaggiato and Rizzo, 2004; Capasso et al., 2004).

Moreover, because of their different mobility and

chemical reactivity, these gases can highlight differ-

ent degrees and kinds of interaction with shallow

fluids.

Helium is a non-reactive, chemically inert gas that

has low solubility in water, i.e. only 9 cm3/l STP when

the He partial pressure is equal to 1 atm. Furthermore,

it does not undergo any significant chemical or

isotopic modifications during its interaction with

shallow fluids, at least in the absence of diffusive

effects (Jahne et al., 1987; Chiodini et al., 2000).On the contrary, CO2 is a highly soluble and

chemically reactive gas that undergoes large chemical

and isotopic modifications when interacting with

shallow fluids. These modifications strongly depend

on the temperature and pH of the groundwater.

5.2.1. Carbon

To better define the origin of carbon, it is important

to consider that the isotopic composition of TDIC is

the result of the following chemical and isotope mass

Fig. 8. CO2vs. He contents of dissolved gases in the sampled springs. The ASW (Air Saturated Water) values are also reported for comparison.

Fig. 9. Relative amounts of dissolved of CO2, N2and O2. The ASW

values are also reported for comparison.



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balance, where M stands for molarity, and the activity

of CO3 is considered negligible for pHb8.3:

d13

CTDIC d

13

CCO2aq4

MCO2aq

d13CHCO34MHCO3 =MTDIC 2

MTDIC MCO2aq MHCO3 3

By utilizing the enrichment factors ea and eb(Mook et al., 1974; Deines et al., 1974),

ea d13CHCO3 d

13CCO2g 9552=TK24:1 4

eb d13CCO2aq d

13CCO2 g 0:91

0:0063*106

=T2

k 5Eq. (2) can be written as follows:

d13CCO2g d

13CTDIC eb*MCO2aq=MTDIC

ea*MHCO3=MTDIC 6

In this way, we can calculate the d13C value of the

pristine CO2 gas interacting with the groundwater

(Inguaggiato et al., 2000) the obtained values are

reported inTable 4.

The d13C computed values have been justified

utilizing two different models:

(1) Two end-members mixing (magmaticorganic):the d13C computed values have been plotted inFig. 10

against the total content of dissolved inorganic carbon.

Thed13CCO2g of the Popo crater area (Goff et al., 1980)

has also been reported for comparisons sake. A

theoretical mixing-curve between magmatic and

organic end-members was constructed considering

values of6.5x with 35 mmol of TDIC and 25xwith 1 mmol of TDIC, respectively. All the analytical

data for the water-samples fall along a theoretical

mixing-curve that strongly supports this hypothesis.

(2) A Rayleigh-type fractionation process by CO2removal: this hypothesis implies that the deep gas is

CO2-rich (9095 vol.%). In this case, the CO 2content

in the bubbling gas phase is the result of strong CO2removal caused by dissolution in the deeper aquifer.

This process virtually enriches the gain mixture in the

less-soluble components such as He and CH4. In a

situation like this, we can model a Raleigh-typefractionation process that removes about 95% of CO 2from the pristine gases and moves the original isotope

composition of Carbon towards the more negative

values. The isotope C value of pristine CO2, which

interacts with a deep aquifer, can be calculated by

using the following relation (Inguaggiato et al., 2000):

d13CCO2res 1000d

13CCO2ini *fa1 1000 7

where f is the fraction of the CO2 remaining in the

system, a stands for the isotopic fractionation factor

between HCO3 (aq) and CO2 (g), and subscripts res andini refer to residual and initial, respectively. The results

of this theoretical process, which has two different

starting values for the carbon isotope composition

Fig. 10. d13CCO2 gvs. TDIC plot. A theoretical mixing-curve between magmatic and organic end-members was constructed considering the

values of6.5x with 35 mmol of TDIC and 25x with 1 mmol of TDIC, respectively.



12/18

(+2x, 6x) at two different temperatures (30 and508C, which is approximately theoutlet temperature of

springs IX and AT) are shown inFig. 11.According to

this type of process, the possible initial values of CO2for IX and AT samples range around +2. These

theoretical values are compatible with CO2 of carbo-

nate origin, considering that IX and AT springs are in

equilibrium with carbonate minerals sediments (see

above), which outcrop in this zone. The possible initial

value of CO2 for all the remaining samples is 6,which is compatible with a different degree of

magmatic CO2removal (0.15bfb0.85).

To investigate and support the existence of this

selective CO2dissolution process, we also modelized

the chemical effect linked to this process. During aselective CO2-dissolution in the groundwater, the less

soluble gases, as He, undergo a virtually process of

enrichment producing a change in the He/CO2ratio. In

graph ofFig. 12,the He/CO2ratio has been plotted vs.

the isotopic composition of CO2. This diagram high-

lights the good inverse correlation between these two

parameters showing a increase of He/CO2ratio and a

decrease ofd13CCO2g, confirming the existence of this

process. Only the AT and IX sample values lie out of

this trend, probably because of the different starting

point of isotopic CO2 value (+2) and also for the

differences in outlet temperatures.

5.2.2. HeliumThe isotope composition of dissolved He ranges

from 1.37 to 2.63 (R/Racorr.; R a=1.39106), which

indicates a magmatic contribution. Fig. 13shows the

isotopic composition of CO2 gas vs. the He isotopic

composition. The AX and AH samples show the

highest He isotope ratios (around 3 R/Ra) which

suggests that there is a high input of He, clearly of

magmatic origin. The remaining samples show values

ranging from 1.2 to 1.5R/Ra. The IX sample is the only

one in which we also sampled the bubbling gas phase.

It is characterized by a N2-dominant composition, lowCO2content (about 9%) and high He and CH4content

(366 and 7960 ppm vol, respectively). The isotopic

composition of the He of free gas (R/Racorr.=1.48)

confirms the value measured in the dissolved gas (R/Racorr.=1.43) which indicates that there is a good cor-

respondence between free and dissolved gases while

supporting the hypothesis of a significant deep, magma

or mantle contribution for this gas. The theoretical

amount of dissolved He in the IX spring, recalculated

from the He bubbling gas (30104 cm3/l), is

Fig. 11. d13CCO2 resgasvs. residual fraction (f). Theoretical Rayleigh-type fractionation process with two different starting values of carbon

isotope composition (+2x and6x) at two different temperatures (30 and 50 8C).



13/18

compatible with the measured amount of dissolved

helium (8104 cm3/l) this also indicates that a partialchemical equilibrium between the dissolved and free

gas phases for this gas has been reached.

Assuming that the isotopic values of He are not

influenced by shallow interaction processes, and by

coupling this information with the carbon isotope

composition, a non-linear isotopic mixing of two

component end-members could be hypothesized to

explain the origin of the deep gases and the processesthey underwent. So as to test this last hypothesis, we

used the equation proposed byLangmuir et al. (1978):

if bMQ and bOQ are two end-members containing

different amounts of a given compound C and if IC

represents the isotopic ratio of C, it is possible to

calculate the isotopic value of the mixture S, ISC, by

utilizing the following equation:

ICS ICMXMyI

CO 1y

=XMyXO 1y 8

where ISC is the isotopic value of mixing, XM and

XO are respectively the contents of C in M and O,the magmatic and organic end-members, and y is

the molar fraction of end-member M in the mixture.

Fig. 12. d13CCO2 gas vs. He/CO2 ratio of dissolved gases showing a inverse correlation between these two parameters.

Fig. 13. d13CCO2 gas vs. 3He/4He diagram. Theoretical mixing lines of two components, organic and magmatic end-members, considering

different values ofK(0.1 to 100) are plotted along with a pair of isotopic values (He and C) of the sampled springs ratio of dissolved gases

showing a inverse correlation between these two parameters.



14/18

To calculate the isotopic composition of two

elements (C and He) in a binary mixture, we need

to write Eq. (8) twice (for two different isotope), and

solve both of the (Langmuir et al., 1978) relationswith respect to y. The following equation is thus

obtained:

aICS bICS I

HeS cI

HeS d 0 9

where, in our case, a=IMC*CMHe OIO

C*COHeM;

b=C OHeMCMHeO; c=IOHe*CMHeOIM

He*COHeM;

d=IOC*IM

HeCOHeMIMC IHeO CMHeO.

To define the shape of the mixing line, we can use anew constant K=(C/He)O/(C/He)M. When K=1, b=0,

then the mixing line is a straight-line. On the contrary

whenKN1 orb1, the mixing line is a hyperbola andthe

curve increases for KH1 or Kb1. In Fig. 13, the

Fig. 14. (a) R/Ravs. log C/3He values for the sampled springs and fluids from other parts of the world including two Mexican volcanoes

(Ceboruco and Colima (data from Taran et al., 2002). (b) d13CCO2 gas vs. log C/3He. springs ratio of dissolved gases showing a inverse

correlation between these two parameters.



15/18

theoretical mixing-line between organic and magmatic

end-members, considering different values ofK (1 to

100), has been plotted together with the pair of isotopic

values (He and C) of the sampled springs. A theoreticalmixing-curve was constructed considering values of

6.5x of carbon and 6 R /Raof He for the magmaticend-member, and values of25x of carbon and 1 R /Ra for organic end-member. The origin of He in the

organic end-member was mainly supposed to be of

recycled atmospheric origin. The sample points, which

fall along mixing lines with Kvalues ranging between

10 and 100, strongly support the hypothesis of a non-

linear mixing between magmatic and organic end-

members for these samples.

To better clarify the origin of these gases and theprocesses that they underwent during the ascent

towards the surface, the log of the C/3He ratio is

plotted vs. the isotopic composition of both He and C

(Fig. 14; Marty and Jambon, 1987; Varekamp et al.,

1992;Sano and Marty, 1995).

In Fig. 14a, the R/Ra vs. log C/3He values of the

sampled springs are plotted together with data from

other parts of the world including the two Mexican

volcanoes Ceboruco and Colima (data from Taran et

al., 2002).

All the sampled waters show log C/3He values

ranging between 10.8 and 11.6, withR/Ravalues above

1 and below 3, which are consistent with pristine

mantle deep fluids contaminated by carbon addition

linked to continental crust end/or carbonate sediments.

The higher R/Ravalues of AX and AH support the

hypothesis of a more He-mantle contribution for these

samples that could be referred to many causes: different

hydrological system, different tectonic system (magni-

tude and/or distance to fault), etc.

In the same graph, the analytical values of gaseous

phase of IX (IX bubbling) have been plotted. This point

shows the sameR/Ravalue but with a very different logC/3He ratio caused by selective CO2 removal processes

that virtually increase the He content. If we consider

that the CO2content decreases by about one order of

magnitude (90 to 9 vol.%) and consequently that the He

increase is of the same magnitude, the restored log

C/3He for these samples is 10.1 which is compatible

with mantle origin. The log C/3He differences observed

in the free and dissolved IX sample strongly support the

importance of the investigation of both phases which

give us a complete picture of both the shallow

interaction processes and the relative modifications of

thepristinechemical composition.

Fig. 14b highlights the scattering of the d13C

isotopic composition, caused by mixing or fractiona-tion processes of the original fluids (magmatic or

carbonate origin) through interaction with shallow

fluids. Moreover, the IX bubbling shows that neither

also for carbon in this sample underwent any isotope

fractionation process between free and dissolved IX

phases.

6. Discussion

Since Popo volcano has gone beyond the immaturestage, it should be characterized by the presence of a

geothermal system linked to the volcano.

Previous studies hypothesized the absence of a

geothermal system inside the Popo volcanic system,

based on the absence of diffuse soil degassing from its

flanks (Varley and Armienta, 2001; Varley and Taran,

2003) and on the lack of evidences regarding

interaction processes between deep magmatic fluids

and the groundwaters circulating in the volcano

(Werner et al., 1997).

The results obtained in the course of the present

geochemical studies in question contradict these

previous studies and confirm the hypothesis put

forward by Inguaggiato et al. (1999, 2001) and

Martin-Del Pozzo et al. (2002a,b), wherein spring

waters carry the signature of magmatic processes.

The different interpretations regarding the interac-

tion processes between deep magmatic fluids and

shallow fluids are probably linked to a different

geochemical approach. The investigated area is huge

and a large number of areas are difficult to access

especially with heavy scientific equipment. This makes

it extremely difficult to make a methodical survey ofdiffuse soil degassing. Due to the insufficient number

of measurements and the non-uniform distribution of

the aerial coverage, the geochemical interpretation

probably does not truly reflect the real degassing

situation. As a comparison, the diffuse degassing

studies of a Mt. Etna show anomalous zones with high

fluxes on its flanks located only in a few points that

represent a very small surface of the total area and are

hard to find (Giammanco et al., 1998a,b). For these

reasons, it is very likely that on the Popo flanks, there



16/18

are zones with anomalous degassing that still have to be

identified and monitored. Instead, the geochemical

approach used in our work, on the contrary, was based

on the study of the dissolved gases in the groundwaterscirculating in the volcanic edifice. The main advantage

of this approach is that the chemical and isotopic

characteristics of the dissolved gases in spring waters

result from the overall deep degassing gathered by the

dynamic system along several rising pathways. On the

contrary, soil degassing has to be seen as a relic of deep

degassing after the interaction with groundwater.

To support this, the amount of CO2dissolved in the

aquifers of Popo area has been preliminarily estimated

considering a mean of total dissolved carbon of 10

mmol/l (this work) and a mean of annual rainfall ofabout 2 km3 (SPP, 1981; Cortes et al., 1997; CNA,

2001; Martin-Del Pozzo et al., 2002a) referred to a

surface of 800 to 3000 km2 (Popo cone onlyentire

area covered by the Popo deposits, respectively).

Therefore, an average amount of total dissolved CO2ranging approximately from 1 to 2 Mt/a has been

estimated for the groundwaters circulating in the Popo

area.

This value represents about the 10% of total

amount of CO2 emitted from the plume of Popo

volcano (14.536.5 Mt/a) as estimated fromDelgado-

Granados et al. (1998).

Furthermore, the geochemical approach employed

byWerner et al. (1997)did not allow them to identify

the chemical interaction processes occurring between

deep and shallow fluids, as the authors collected and

analyzed water samples for major and minor compo-

nents but did not investigate the chemical and isotope

composition of the dissolved gases. The Popo springs

show a very low salt content resulting from low

waterrock interaction, whereas the only way to

identify gaswater interaction is to investigate the

dissolved gas species.In fact, the high CO2and He contents measured in

the spring-samples, coupled with the respective iso-

topic compositionsclearly of magmatic origin

indicate a high gaswater interaction between deep

CO2-rich gases and shallow fluids. This process lowers

the pH of water and makes it more aggressive

promoting dissolution of sublimates and ash compo-

nents (Martin-Del Pozzo et al., 2002b). The possible

sources that determine the chemical composition of

springs-water are: (a) input of strongly acid magmatic

fluids (HF, HCl, H2S, and SO2); (b) sublimate

remobilization, ash solubilization, reaction with pyro-

clastic rocks; and (c) input of weak acidic magmatic

gases, mainly CO2.Process (a) can be ruled out because of the very

low salinity, low temperature, and not very acid pH of

the waters; the processes of group (b) are all possible

considering the low amount of dissolved salt in the

springs that is quite often less than 200 mg/l; process

(c) is very probable and well supported because the

quantity of dissolved carbon dioxide in the water is

very high (up to 336 cm3/STP liter) and its isotopic

composition suggests a magmatic origin. Moreover,

the isotopic composition of dissolved He also

supports a magmatic component in the waters.Despite the large difference in the chemical compo-

sition of the hot springs in the south with respect to

those located on the flanks of the volcano (i.e. linked to

different interacting lithologies), the isotopic character-

ization of the dissolved gases indicates a common

volcanic origin for the southern AH hot spring and the

ones located on the Popo flanks. However, further

researches are necessary in order to understand the

origin and possible mechanisms that determine the

chemical and isotopic composition of IX and AT

springs. Nevertheless, based on the isotopic composi-

tion of He and C of the dissolved gases, a connection

with volcanic activity cannot be ruled out.

7. Conclusions

The geochemical investigation carried out on the

dissolved gas species in this work highlights the

following aspects:

(1) The chemical and isotopic composition of the

Popo springs suggests that they discharge waters of

meteoric origin that have undergone limited waterrock interaction processes This is also in line with the

low salinity and temperature values that confirm our

previous studies (Martin-Del Pozzo et al., 2002a,b).

(2) High contents of magmatic gases (He and CO 2mainly as revealed by the chemical and isotopic

fingerprints) are present as dissolved gases in the cold

groundwaters located on the flanks of Popocatepetl;

(3) The flanks of the volcano release large amounts

of CO2 which have been detected as dissolved gases

in the groundwater, indicating the presence of



17/18

important CO2 magma degassing. This is supported

by the estimated amount of CO2 released from the

Popo flanks effectuated by coupling the information

of volume of Popo groundwater and the amount oftotal carbon dissolved.

(4)The hot water (AH spring) emerging at about 40

km to the south of Popos crater is probably the only

surface manifestation of the geothermal system (i.e.

estimated temperature about 80100 8C) located

beneath the volcano. Further research on Cuautlas

thermal springs will help to clarify its origin.

(5)The characteristics of the IX and AT springs are

probably linked to both regional tectonic structures

and/or the volcanic activity of Popocatpetel. Even

though the isotopic composition of C suggests aprobable carbonate origin for these gases, the isotopic

composition of He reveals the presence of a mantle

component.

In conclusion, the chemical and isotopic composi-

tions of the water and dissolved gases in the Popo

springs have given us insight into the mechanism and

degree of interaction between the deep magmatic

fluids and shallow groundwaters.

Acknowledgments

Authors wish to thank DGAPA (PAPIIT), Inter-

cambio Academico (UNAM) and Istituto Nazionale di

Geofisica e Vulcanologia Palermo for financing the

research, as well as L. Marini, P.M. Nuccio and Y.

Taran for their critical review and constructive com-

ments for improving the manuscript. Ramon Espinasa,

Fabiola Mendiola, Humberto Saenz, Francisco Sainz,

Rita Fonseca, Miguel Angel Butron and Fernando

Aceves assisted in field sampling and processing.

Furthermore, we are indebted to Andrea Rizzo and

Fausto Grassa for their isotopic analytical support.

References

Aguayo, A., Martin del Pozzo, A.L., 1994. Variaciones en los

Manantiales de los Volcanes Popocatepetl y Colima. Colima

Volcano International Meeting, p. 56. (abstracts).

Armienta, M.A., Martin Del Pozzo, A.L., Espinasa, R., Cruz, O.,

Ceniceros, N., Aguayo, A., Butron, M.A., 1998. Geochemistry

of Ash Leachates durino the 19941996 activity of Popocatepetl

Volcano. Appl. Geochem. 13 (7), 841850.

Appelo, C.A.J., 1988. WATEQP program. Instituut Voor Aardwe-

tenschappen, Vrije Universitei Amsterdam.

Capasso, G., Inguaggiato, S., 1998. A simple method for

determination of dissolved gases in natural waters. An

application to thermal waters from Vulcano Island. Appl.

Geochem. 13 (5), 631642.

Capasso, G., Favara, Inguaggiato, S., 1997. Chemical features and

isotopic composition of gaseous manifestations on Vulcano

Island (Aeolian Islands, Italy): an interpretative model of fluid

circulation. Geochim. Cosmoch. Acta 61 (16), 34253440.

Capasso, G., Favara, R., Inguaggiato, S., 2000. Interaction between

fumarolic gases and thermal groundwaters at Vulcano Island

(Italy): evidences from chemical composition of dissolved gases

in waters. J. Volcanol. Geotherm. Res. 102 (34), 3093180.

Capasso, G., DAlessandro, W., Favara, R., Inguaggiato, S., Parello,

F., 2001. Interaction between the deep fluids and the shallow

groundwaters on the vulcano island (Italy). J. Volcanol.

Geotherm. Res. 108 (14), 189200.Capasso, G., Carapezza, M.L., Federico, C., Inguaggiato, S., Rizzo,

A., 2004. The 20022003 eruption at Stromboli volcano (Italy):

precursory changes in the carbon and helium isotopic compo-

sition of both fumarole gases and thermal waters. Bull.

Volcanol. (in press).

Carapezza, M.L., Inguaggiato, S., Brusca, L., Longo, M., 2004.

Geochemical precursors of the activity of an open-conduict

volcano: Stromboli 20022003 eruptive events. Geophys. Res.

Lett. 31, L07620.

Cortes, A., Durazo, J., Farvolden, R., 1997. Studies of Isotopic

hydrology of the basin of Mexico and vicinity: annotated

bibliography and interpretation. J. Hydrol. 198, 346 376.

Chiodini, G., Frondini, F., Marini, L., 1995. Theoretical geother-

mometers and PCO2 indicators for aqueous solutions comingfrom hydrothermal systems of mediumlow temperature hosted

in carbonate-evaporite rocks:application to the thermal springs of

the Etruscan Swell, Italy. Appl. Geochem. 10, 337346.

Chiodini, G., Cioni, R., Guidi, M., Magro, G., Marini, L., Raco, B.,

2000. Gas chemistry of the lake Piccolo of Monticchio, Mt.

Vulture, in December 1996. In: Villari, L. (Ed.), Data related to

eruptive activity, unrest phenomena and other observations on

the Italian active volcanoes 196: miscellaneous. Acta Vulcan-

ologica, vol. 12, pp. 139142.

CNA (Commission Nacional de Agua), 2001. www.inegi.gob.mx.

Craig, H., 1961. Isotope variation in meteoric waters. Science 133,

17021703.

Deines, P., Langmuir, D., Herman, R.S., 1974. Stable carbon isotope

ratio and the esistence of a gas phase in the evolution of carbonate

groundwaters. Geochim. Cosmochim. Acta 38, 1147 1164.

Delgado-Granados, H., Piedad Sanchez, N., Galvan, L., Julio, P.,

Alvarez, J.M., Cardenas, L., 1998. CO2 flux measurements at

Popocatepetl volcano: II. Magnitude of emissions and signifi-

cance (abstract). EOS Trans., AGU 79 (45), 926 (Fall Meeting

Suppl.).

Delgado-Granados, H., Cardenas Gonzalez, L., Piedad Sanchez, N.,

2001. Sulfur dioxide emission rate, passively degassing erupting

volcano. J. Volcanol. Geotherm. Res. 108, 107120.

Dyck, W., 1976. The use of helium in mineral exploration.

J. Geophys. Explor. 5, 320.

http://www.inegi.gob.mx/http://www.inegi.gob.mx/http://www.inegi.gob.mx/


18/18

Favara, R., Grassa, F., Inguaggiato, S., Pecoraino, G., Capasso, G.,

2002. A simple method to determine the d 13C of total dissolved

inorganic carbon. Geofis. Int. 41 (3), 313320.

Fournier, R.O., 1973. Silica in thermal waters: laboratory

and field investigations. Proceedings, International Sympo-

sium on Hydrogeochemistry and Biogeochemistry, Tokyo.

Clark, Washington, DC, vol. 1, pp. 122129.

Giammanco, S., Inguaggiato, S., Valenza, M., 1998a. Soil and

fumarole gases of Mount Etna: geochemistry and relations with

volcanic activity. J. Volcanol. Geotherm. Res. 81, 297 310.

Giammanco, S., Gurrieri, S., Valenza, M., 1998b. Anomalous soil

CO2 degassing in relation to faults and eruptive fissures on

Mount Etna (Sicily, Italy). Bull. Volcanol. 60, 252259.

Giggenbach, W.F., 1991. Isotopic composition of geothermal water

and steam discharges. Application of Geochemistry in Geo-

thermal Reservoir Development. UNITAR, pp. 253 273

(F. DAmore coordinator).

Goff, F., Janik, C.J., Delgado, H., Werner, C., Counce, D.,Stimac, J.A., Siebe, C., Love, S.P., Williams, S.N., Fischer,

T., Johnson, L., 1980. Geochemical surveillance of magmatic

volatiles at Popocatepetl volcano, Mexico. Geol. Soc. Am.

Bull. 110, 695710.

Inguaggiato, S., Rizzo, A., 2004. Dissolved helium isotope ratio in

ground-waters: a new technique based on gaswater re-

equilibration and its application to Stromboli volcanic system.

Appl. Geochem. 19, 665673.

Inguaggiato, S., Martin Del Pozzo, A.L., Aguayo, A., Garcia, E.,

Espinasa, R., Favara, R., Capasso, G., 1999. Popocatepetl

volcano (Mexico): preliminary geochemical characterization of

volcanic fluids and comparison with Italian volcanic systems

(Etna, Vulcano). Abstract book V32A-14, AGU Fall Meeting,

San Francisco, December.Inguaggiato, S., Pecoraino, G., DAmore, F., 2000. Chemical and

isotopical characterization of fluid manifestations of Ischia

Island (Italy). J. Volcanol. Geotherm. Res. 99, 151178.

Inguaggiato, S., Capasso, G., Favara, R., Martin Del Pozzo, A.L.,

Aguayo, A., 2001. Waterrock interaction processes at Popoca-

tepetl volcano, Mexico. In: Rosa Cidu, A.A. (Ed.), Proceeding

of the Tenth International Symposium on bWaterrock Inter-

actionQ, WRI-10/Villasimius/Italy/1015 July 2001. Water Rock

Interaction, vol. 2. Balkema Publishers, pp. 859862.

Jahne, B., Heinz, G., Dietrich, W., 1987. Measurements of

the diffusion coefficients of sparingly soluble gases in

water. J. Geophys. Res. 92 (C-10), 1076710776.

Jenne, E.A., Ball, J.W., Burchard, J.M., Vivit, D.V., Barks, J.H.,

1980. Geochemical modeling: apparent solubility controls on

Ba, Zn, Cd, Pb and F in waters of Missouri tri-State mining

area. In: Heniphill, D.D. (Ed.), Trace Substances in Environ-

mental Health, vol. 14. University of Missouri, Columbia, pp.

353361.

Langmuir, C.H., Vocke, R.D., Hanson, G.N., Hart, H.R., 1978. A

general mixing equation with applications to Icelandic basalts.

Gunter FaurePrinciples of Isotope Geology, Earth Planet. Sci.

Lett., vol. 37. John Wiley and Sons, pp. 380392.

Love, S.P., Goff, F., Counce, D., Siebe, C., Delgado, H., 1998.

Passive infrared spectroscopy of the eruption plume at

Popocatepetl volcano, Mexico. Nature 396, 563567.

Marini, L., Chiodini, G., Cioni, R., 1986. New geothermometers for

carbonate-evaporite geothermal reservoirs. Geothermics 15,

7786.

Martin-Del Pozzo, A.L., Aceves, F., Espinasa, R., Aguayo, A.,

Butron, M.A., Inguaggiato, S., Morales, P., Cienfuegos, E.,

2002a. Influence of volcanic activity on spring water chemistry

at Popocatepetl Volcano, Mexico. Chem. Geol. 190, 207 229.

Martin-Del Pozzo, A.L., Inguaggiato, S., Aceves, F., Saenz, H.,

Aguayo, A., 2002b. Spring Water and CO2 interaction at

Popocatepetl Volcano, Mexico. Geofis. Int. 41 (3), 345351.

Marty, B., Jambon, A., 1987. C/3He in volatile fluxes from the solid

earth: implications for carbon geodynamics. Earth Planet. Sci.

Lett. 83, 1626.

Marty, B., Trull, T., Lussiez, P., Basile, I., Tanguy, J.C., 1994. He,

Ar, O, Sr and Nd isotope constraints on the origin and evolution

of Mount Etna magmatism. Earth Planet. Sci. Lett. 126, 2339.

Mook, W.G., Bemmerson, J.C., Steverman, W.H., 1974. Carbon

isotope fractionation between dissolved bicarbonate and gaseouscarbon dioxide. Earth Planet. Sci. Lett. 22, 169176.

Nakai, S., Wakita, H., Nuccio, P.M., Italiano, F., 1997. MORB-type

neon in an enriched mantle beneath Etna, Sicily. Earth Planet.

Sci. Lett. 153, 57 66.

Nielsen, H., Pilot, J., Grinenko, L.N., Grinenko, V.A., Lein, A.Yu.,

Smith, J.W., Pankina, R.G., 1991. Litospheric sources of

sulphur. In: Krouse, H.R., Grinenko, V.A. (Eds.), SCOPE

43Stable isotopes: natural and anthropogenic sulfur in the

environment. Wiley, Chichester, pp. 65 132.

Robin, C., Boudal, C., 1987. A gigantic Bezymianny-type event at

the beginning of modern Volcan Popocatepetl. J. Volcanol.

Geotherm. Res. 31, 115130.

Sano, Y., Marty, B., 1995. Origin of carbon in fumarolic gas from

island arcs. Chem. Geol. 119, 265274.Sano, Y., Wakita, H., 1985. Geographical distribution of3He/4He in

Japan: implications for arc tectonics and incipient magmatism.

J. Geophys. Res. 90, 87298741.

Sakai, H., 1968. Isotopic properties of sulphur compounds in

hydrothermal processes. Geochem. J. 2, 2949.

SPP, 1981. Carta de climas. Secretaria de Programmacion y

Presuppuesto, Mexico City.

Taran, Y., Inguaggiato, S., Varley, N.R., Capasso, G., Favara, R.,

2002. Helium and carbon isotopes in thermal waters of the

Jalisco Block, Mexico. Geofis. Int. 41, 459466.

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, 363373.

Varley, N.R., Armienta, A., 2001. The absence of diffuse

degassing at Popocatepetl volcano (Mexico). Chem. Geol.

177, 157173.

Varley, N.R., Taran, Y., 2003. Degassing processes of Popocatepetl

and Volcan de Colima, Mexico. In: Oppenheimer, C., Pyle,

D.M., Barclay, J. (Eds.), Volcanic Degassing. Geol. Soc.

London Spec. Publ. 213, 263280.

Werner C., Janik C.J., Goff F., Counce D., Johnson L., Siebe C.,

Delgado H., Williams S., Fischer T., 1997. Geochemistry of

summit fumerole vapors and flanking thermal minerals waters at

Popocatepetl volcano, Mexico. Los Alamos National Labora-

tory. Series report LA-13289-MS, 33 pp.


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