<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>0016-7169</journal-id>
<journal-title><![CDATA[Geofísica internacional]]></journal-title>
<abbrev-journal-title><![CDATA[Geofís. Intl]]></abbrev-journal-title>
<issn>0016-7169</issn>
<publisher>
<publisher-name><![CDATA[Universidad Nacional Autónoma de México, Instituto de Geofísica]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S0016-71692005000100039</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[Chemical and isotopic study of thermal springs and gas discharges from Sierra de Chiapas, México]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Nencetti]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Tassi]]></surname>
<given-names><![CDATA[F.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Vaselli]]></surname>
<given-names><![CDATA[O.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
<xref ref-type="aff" rid="Aaf"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Macías]]></surname>
<given-names><![CDATA[J. L.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Magro]]></surname>
<given-names><![CDATA[G.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Capaccioni]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Minissale]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Mora]]></surname>
<given-names><![CDATA[J.C.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Università degli Studi di Firenze Department of Earth Sciences ]]></institution>
<addr-line><![CDATA[Florence ]]></addr-line>
<country>Italy</country>
</aff>
<aff id="Af2">
<institution><![CDATA[,CNR Institute of Geosciences &amp; Earth Resources ]]></institution>
<addr-line><![CDATA[Florence ]]></addr-line>
<country>Italy</country>
</aff>
<aff id="Af3">
<institution><![CDATA[,UNAM Institute of Geophysics ]]></institution>
<addr-line><![CDATA[Mexico City D.F.]]></addr-line>
<country>Mexico</country>
</aff>
<aff id="Af4">
<institution><![CDATA[,CNR Institute of Geosciences &amp; Earth Resources ]]></institution>
<addr-line><![CDATA[Pisa ]]></addr-line>
<country>Italy</country>
</aff>
<aff id="Af5">
<institution><![CDATA[,Università degli Studi di Urbino Institute of Volcanology and Geochemistry ]]></institution>
<addr-line><![CDATA[Urbino ]]></addr-line>
<country>Italy</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>03</month>
<year>2005</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>03</month>
<year>2005</year>
</pub-date>
<volume>44</volume>
<numero>1</numero>
<fpage>39</fpage>
<lpage>48</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S0016-71692005000100039&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S0016-71692005000100039&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S0016-71692005000100039&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="en"><p><![CDATA[ABSTRACT Thermal water and gas discharges south-east of El Chichón volcano, Mexico are associated mainly with NW-SE oriented fault systems. Spring discharges include i) waters with Na-Cl composition and TDS&gt;3000 mg/L; ii) waters with Ca-SO4 composition and TDS values between 1400 and 2300 mg/L; iii) waters with Na-Cl composition and TDS of 800 to 2400 mg/L and sulphate content up to 650 mg/L and iv) waters with Ca-HCO3 composition and low salinity (TDS &lt;250mg/L). Most of these waters are associated with free-gas discharges of N2 (up to 93 % by vol.), CO2 (2.4 to 31.2 % by vol.) and Ar (up to 1.25 % by vol.) with a predominant meteoric origin. H2S is present only in gas samples collected at El Azufre (up to 1.1 % by vol.). The &#948;13C CO2 values are always below -9.7% (PDB) and suggest a partially biogenic origin for CO2. Chemical and isotopic features of spring discharges indicate that fluid circulation in the Sierra de Chiapas is mainly regulated by meteoric waters that tend to infiltrate the upper and middle-Cretaceous carbonate units up to the lower Cretaceous-upper Jurassic evaporitic formations (by López-Ramos, 1982). The latter provide the main source of the species in solution. No evidence for high-to-medium enthalpy systems at depth beneath the Sierra de Chiapas has been found.]]></p></abstract>
<abstract abstract-type="short" xml:lang="es"><p><![CDATA[RESUMEN La Sierra de Chiapas localizada en el Sureste de México, se caracteriza por la presencia de descargas de gas y agua. La mayoría de los manantiales termales se asocian a rocas volcánicas Terciarias a lo largo de fallas regionales con orientación NO-SE. Las descargas termales se dividen en cuatro grupos: i) aguas con composición Na-Cl y Sólidos Disueltos Totales (SDT) &gt;3000 mg/L; ii) aguas con composición Ca-SO4 y valores de SDT entre 1400 y 2300 mg/L; iii) aguas con composición Na-Cl, bajos contenidos de SDT (800 2400 mg/L) y un contenido de sulfato alto (hasta 650 mg/L) y iv) aguas con una composición Ca-HCO3 y salinidad baja (SDT &lt;250mg/L). La mayoría de estas aguas están asociadas con descargas de gas compuestas por N2 (hasta 93 % en vol.), CO2 (2.4-31.2 % en vol.) y Ar (hasta 1.25 % en vol.) con origen predominantemente meteórico. H2S aparece únicamente en las muestras de gas colectadas en El Azufre (hasta 1.1 % en vol.). Los valores de &#948;13C-CO2 comúnmente inferiores a -9.7% (PDB) sugieren un origen parcialmente biogénico del CO2. Los parámetros químicos e isotópicos de los manantiales indican que la circulación de fluidos en la Sierra de Chiapas se regula principalmente por la infiltración de aguas meteóricas en rocas carbonatadas del Cretácico medio-tardío hasta las formaciones evaporíticas del Jurásico tardío-Cretácico temprano. Estas últimas representan la fuente principal de las especies en solución de las aguas. No se encontraron evidencias de la presencia de sistemas con entalpías medias a altas por debajo de la Sierra de Chiapas.]]></p></abstract>
<kwd-group>
<kwd lng="es"><![CDATA[Isótopos]]></kwd>
<kwd lng="es"><![CDATA[química de manantiales]]></kwd>
<kwd lng="es"><![CDATA[Chiapas]]></kwd>
<kwd lng="es"><![CDATA[México]]></kwd>
<kwd lng="en"><![CDATA[Isotopes]]></kwd>
<kwd lng="en"><![CDATA[chemistry]]></kwd>
<kwd lng="en"><![CDATA[thermal springs]]></kwd>
<kwd lng="en"><![CDATA[water]]></kwd>
<kwd lng="en"><![CDATA[Chiapas]]></kwd>
<kwd lng="en"><![CDATA[Mexico]]></kwd>
</kwd-group>
</article-meta>
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