Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas
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Auteurs : Silvia Gonzalez ; Graham Sherwood ; Harald Böhnel ; Elisabeth SchneppSource :
- Geophysical Journal International [ 0956-540X ] ; 1997-07.
Abstract
13 lava flows of known age (ages from 14C dating), which have been erupted in the last 30000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 1022 A m2. Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.
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DOI: 10.1111/j.1365-246X.1997.tb00999.x
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<record><TEI wicri:istexFullTextTei="biblStruct"><teiHeader><fileDesc><titleStmt><title>Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas</title><author><name sortKey="Gonzalez, Silvia" sort="Gonzalez, Silvia" uniqKey="Gonzalez S" first="Silvia" last="Gonzalez">Silvia Gonzalez</name><affiliation><mods:affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: bessgonz@livjm.ac.uk</mods:affiliation></affiliation></author><author><name sortKey="Sherwood, Graham" sort="Sherwood, Graham" uniqKey="Sherwood G" first="Graham" last="Sherwood">Graham Sherwood</name><affiliation><mods:affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: bessgonz@livjm.ac.uk</mods:affiliation></affiliation></author><author><name sortKey="Bohnel, Harald" sort="Bohnel, Harald" uniqKey="Bohnel H" first="Harald" last="Böhnel">Harald Böhnel</name><affiliation><mods:affiliation>Instituto de Geofisica, UNAM, Del. Coyoacan, CP 04510 Mexico DF, Mexico</mods:affiliation></affiliation></author><author><name sortKey="Schnepp, Elisabeth" sort="Schnepp, Elisabeth" uniqKey="Schnepp E" first="Elisabeth" last="Schnepp">Elisabeth Schnepp</name><affiliation><mods:affiliation>Institut für Geophysik der Westfälischen Wilhems-Universität, Correnstrasse 24, 48149 Münster, Germany</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:524FF0CF0963A71743E66C701FFF649472936847</idno><date when="1997" year="1997">1997</date><idno type="doi">10.1111/j.1365-246X.1997.tb00999.x</idno><idno type="url">https://api.istex.fr/document/524FF0CF0963A71743E66C701FFF649472936847/fulltext/pdf</idno><idno type="wicri:Area/Istex/Corpus">001C25</idno><idno type="wicri:explorRef" wicri:stream="Istex" wicri:step="Corpus" wicri:corpus="ISTEX">001C25</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a">Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas</title><author><name sortKey="Gonzalez, Silvia" sort="Gonzalez, Silvia" uniqKey="Gonzalez S" first="Silvia" last="Gonzalez">Silvia Gonzalez</name><affiliation><mods:affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: bessgonz@livjm.ac.uk</mods:affiliation></affiliation></author><author><name sortKey="Sherwood, Graham" sort="Sherwood, Graham" uniqKey="Sherwood G" first="Graham" last="Sherwood">Graham Sherwood</name><affiliation><mods:affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: bessgonz@livjm.ac.uk</mods:affiliation></affiliation></author><author><name sortKey="Bohnel, Harald" sort="Bohnel, Harald" uniqKey="Bohnel H" first="Harald" last="Böhnel">Harald Böhnel</name><affiliation><mods:affiliation>Instituto de Geofisica, UNAM, Del. Coyoacan, CP 04510 Mexico DF, Mexico</mods:affiliation></affiliation></author><author><name sortKey="Schnepp, Elisabeth" sort="Schnepp, Elisabeth" uniqKey="Schnepp E" first="Elisabeth" last="Schnepp">Elisabeth Schnepp</name><affiliation><mods:affiliation>Institut für Geophysik der Westfälischen Wilhems-Universität, Correnstrasse 24, 48149 Münster, Germany</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Geophysical Journal International</title><title level="j" type="abbrev">Geophys. J. Int.</title><idno type="ISSN">0956-540X</idno><idno type="eISSN">1365-246X</idno><imprint><publisher>Blackwell Publishing Ltd</publisher><pubPlace>Oxford, UK</pubPlace><date type="published" when="1997-07">1997-07</date><biblScope unit="volume">130</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="201">201</biblScope><biblScope unit="page" to="219">219</biblScope></imprint><idno type="ISSN">0956-540X</idno></series><idno type="istex">524FF0CF0963A71743E66C701FFF649472936847</idno><idno type="DOI">10.1111/j.1365-246X.1997.tb00999.x</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0956-540X</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract">13 lava flows of known age (ages from 14C dating), which have been erupted in the last 30000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 1022 A m2. Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.</div></front></TEI><istex><corpusName>oup</corpusName><author><json:item><name>Silvia Gonzalez</name><affiliations><json:string>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</json:string><json:string>E-mail: bessgonz@livjm.ac.uk</json:string></affiliations></json:item><json:item><name>Graham Sherwood</name><affiliations><json:string>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</json:string><json:string>E-mail: bessgonz@livjm.ac.uk</json:string></affiliations></json:item><json:item><name>Harald Böhnel</name><affiliations><json:string>Instituto de Geofisica, UNAM, Del. Coyoacan, CP 04510 Mexico DF, Mexico</json:string></affiliations></json:item><json:item><name>Elisabeth Schnepp</name><affiliations><json:string>Institut für Geophysik der Westfälischen Wilhems-Universität, Correnstrasse 24, 48149 Münster, Germany</json:string></affiliations></json:item></author><subject><json:item><value>magnetic mineralogy</value></json:item><json:item><value>Mexico</value></json:item><json:item><value>palaeointensity</value></json:item><json:item><value>palaeomagnetism</value></json:item><json:item><value>Quaternary</value></json:item><json:item><value>secular variation</value></json:item></subject><language><json:string>unknown</json:string></language><originalGenre><json:string>research-article</json:string></originalGenre><abstract>13 lava flows of known age (ages from 14C dating), which have been erupted in the last 30000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 1022 A m2. Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.</abstract><qualityIndicators><score>10</score><pdfVersion>1.4</pdfVersion><pdfPageSize>612 x 827.759 pts</pdfPageSize><refBibsNative>true</refBibsNative><keywordCount>6</keywordCount><abstractCharCount>1664</abstractCharCount><pdfWordCount>9435</pdfWordCount><pdfCharCount>61358</pdfCharCount><pdfPageCount>19</pdfPageCount><abstractWordCount>253</abstractWordCount></qualityIndicators><title>Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas</title><refBibs><json:item><author><json:item><name>L.M. Alva-Valdivia</name></json:item><json:item><name>J. Urrutia Fucugauchi</name></json:item></author><host><volume>77</volume><pages><first>155</first></pages><issue>46</issue><author></author><title>EOS, Trans. Am. Geophys. 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E-mail:bessgonz@livjm.ac.uk</affiliation></author><author xml:id="author-2"><persName><forename type="first">Graham</forename><surname>Sherwood</surname></persName><email>bessgonz@livjm.ac.uk</email><affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</affiliation></author><author xml:id="author-3"><persName><forename type="first">Harald</forename><surname>Böhnel</surname></persName><affiliation>Instituto de Geofisica, UNAM, Del. Coyoacan, CP 04510 Mexico DF, Mexico</affiliation></author><author xml:id="author-4"><persName><forename type="first">Elisabeth</forename><surname>Schnepp</surname></persName><note type="biography">*Now at: NLFB Grubenhagen, Rotenkirchen, Einbeck 1, D-37574, Germany.</note><affiliation>*Now at: NLFB Grubenhagen, Rotenkirchen, Einbeck 1, D-37574, Germany.</affiliation><affiliation>Institut für Geophysik der Westfälischen Wilhems-Universität, Correnstrasse 24, 48149 Münster, Germany</affiliation></author></analytic><monogr><title level="j">Geophysical Journal International</title><title level="j" type="abbrev">Geophys. J. Int.</title><idno type="pISSN">0956-540X</idno><idno type="eISSN">1365-246X</idno><imprint><publisher>Blackwell Publishing Ltd</publisher><pubPlace>Oxford, UK</pubPlace><date type="published" when="1997-07"></date><biblScope unit="volume">130</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="201">201</biblScope><biblScope unit="page" to="219">219</biblScope></imprint></monogr><idno type="istex">524FF0CF0963A71743E66C701FFF649472936847</idno><idno type="DOI">10.1111/j.1365-246X.1997.tb00999.x</idno></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>1997</date></creation><abstract><p>13 lava flows of known age (ages from 14C dating), which have been erupted in the last 30000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 1022 A m2. Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.</p></abstract><textClass><keywords scheme="keyword"><list><head>Key words</head><item><term>magnetic mineralogy</term></item><item><term>Mexico</term></item><item><term>palaeointensity</term></item><item><term>palaeomagnetism</term></item><item><term>Quaternary</term></item><item><term>secular variation</term></item></list></keywords></textClass></profileDesc><revisionDesc><change when="1997-07">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/document/524FF0CF0963A71743E66C701FFF649472936847/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus oup" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0"</istex:xmlDeclaration><istex:docType PUBLIC="-//NLM//DTD Journal Publishing DTD v2.3 20070202//EN" URI="journalpublishing.dtd" name="istex:docType"></istex:docType><istex:document><article article-type="research-article"><front><journal-meta><journal-id journal-id-type="hwp">gji</journal-id><journal-id journal-id-type="publisher-id">gji</journal-id><journal-title>Geophysical Journal International</journal-title><abbrev-journal-title>Geophys. J. Int.</abbrev-journal-title><issn pub-type="ppub">0956-540X</issn><issn pub-type="epub">1365-246X</issn><publisher><publisher-name>Blackwell Publishing Ltd</publisher-name><publisher-loc>Oxford, UK</publisher-loc></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.1111/j.1365-246X.1997.tb00999.x</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group></article-categories><title-group><article-title>Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Gonzalez</surname><given-names>Silvia</given-names></name><xref ref-type="aff" rid="au1"><sup>1</sup></xref></contrib><contrib contrib-type="author"><name><surname>Sherwood</surname><given-names>Graham</given-names></name><xref ref-type="aff" rid="au1"><sup>1</sup></xref></contrib><contrib contrib-type="author"><name><surname>Böhnel</surname><given-names>Harald</given-names></name><xref ref-type="aff" rid="au2"><sup>2</sup></xref></contrib><contrib contrib-type="author"><name><surname>Schnepp</surname><given-names>Elisabeth</given-names></name><xref ref-type="aff" rid="au3"><sup>3</sup></xref><xref ref-type="author-notes" rid="fn1">*</xref></contrib><aff id="au1"><label>1</label>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:<email>bessgonz@livjm.ac.uk</email></aff><aff id="au2"><label>2</label>Instituto de Geofisica, UNAM, Del. Coyoacan, CP 04510 Mexico DF, Mexico</aff><aff id="au3"><label>3</label>Institut für Geophysik der Westfälischen Wilhems-Universität, Correnstrasse 24, 48149 Münster, Germany</aff></contrib-group><author-notes><fn id="fn1" fn-type="other"><label>*</label><p>Now at: NLFB Grubenhagen, Rotenkirchen, Einbeck 1, D-37574, Germany.</p></fn></author-notes><pub-date pub-type="ppub"><month>7</month><year>1997</year></pub-date><volume>130</volume><issue>1</issue><fpage>201</fpage><lpage>219</lpage><history><date date-type="accepted"><day>7</day><month>3</month><year>1997</year></date><date date-type="received"><day>7</day><month>3</month><year>1997</year></date></history><permissions><copyright-year>1997</copyright-year></permissions><abstract><title>Summary</title><p>13 lava flows of known age (ages from <sup>14</sup>C dating), which have been erupted in the last 30000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 10<sup>22</sup> A m<sup>2</sup>. Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.</p></abstract><kwd-group><title>Key words</title><kwd>magnetic mineralogy</kwd><kwd>Mexico</kwd><kwd>palaeointensity</kwd><kwd>palaeomagnetism</kwd><kwd>Quaternary</kwd><kwd>secular variation</kwd></kwd-group></article-meta></front></article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>Palaeosecular variation in Central Mexico over the last 30000 years: the record from lavas</title></titleInfo><name type="personal"><namePart type="given">Silvia</namePart><namePart type="family">Gonzalez</namePart><affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</affiliation><affiliation>E-mail: bessgonz@livjm.ac.uk</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Graham</namePart><namePart type="family">Sherwood</namePart><affiliation>School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. E-mail:bessgonz@livjm.ac.uk</affiliation><affiliation>E-mail: bessgonz@livjm.ac.uk</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Harald</namePart><namePart type="family">Böhnel</namePart><affiliation>Instituto de Geofisica, UNAM, Del. Coyoacan, CP 04510 Mexico DF, Mexico</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Elisabeth</namePart><namePart type="family">Schnepp</namePart><affiliation>Institut für Geophysik der Westfälischen Wilhems-Universität, Correnstrasse 24, 48149 Münster, Germany</affiliation><description>*Now at: NLFB Grubenhagen, Rotenkirchen, Einbeck 1, D-37574, Germany.</description><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article"></genre><originInfo><publisher>Blackwell Publishing Ltd</publisher><place><placeTerm type="text">Oxford, UK</placeTerm></place><dateIssued encoding="w3cdtf">1997-07</dateIssued><copyrightDate encoding="w3cdtf">1997</copyrightDate></originInfo><physicalDescription><internetMediaType>text/html</internetMediaType></physicalDescription><abstract>13 lava flows of known age (ages from 14C dating), which have been erupted in the last 30000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 1022 A m2. Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.</abstract><note type="footnotes">Now at: NLFB Grubenhagen, Rotenkirchen, Einbeck 1, D-37574, Germany.</note><subject><genre>Key words</genre><topic>magnetic mineralogy</topic><topic>Mexico</topic><topic>palaeointensity</topic><topic>palaeomagnetism</topic><topic>Quaternary</topic><topic>secular variation</topic></subject><relatedItem type="host"><titleInfo><title>Geophysical Journal International</title></titleInfo><titleInfo type="abbreviated"><title>Geophys. J. Int.</title></titleInfo><genre type="journal">journal</genre><identifier type="ISSN">0956-540X</identifier><identifier type="eISSN">1365-246X</identifier><identifier type="PublisherID">gji</identifier><identifier type="PublisherID-hwp">gji</identifier><part><date>1997</date><detail type="volume"><caption>vol.</caption><number>130</number></detail><detail type="issue"><caption>no.</caption><number>1</number></detail><extent unit="pages"><start>201</start><end>219</end></extent></part></relatedItem><identifier type="istex">524FF0CF0963A71743E66C701FFF649472936847</identifier><identifier type="DOI">10.1111/j.1365-246X.1997.tb00999.x</identifier><recordInfo><recordContentSource>OUP</recordContentSource></recordInfo></mods></metadata><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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