Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe- and Mg-rich Wehrlites
Identifieur interne : 000222 ( Istex/Corpus ); précédent : 000221; suivant : 000223Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe- and Mg-rich Wehrlites
Auteurs : N. Raffone ; G. Chazot ; C. Pin ; R. Vannucci ; A. ZanettiSource :
- Journal of Petrology [ 0022-3530 ] ; 2009-02.
Abstract
Mantle xenoliths enclosed in the Plio-Quaternary alkaline basalts from Bou Ibalrhatene, Middle Atlas, Morocco, are characterized by a wide range of lithological and chemical heterogeneity, consistent with metasomatism of their lithospheric mantle source. Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO2-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere–asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central–Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). The majority of the mantle sectors beneath the NE–SW volcanic alignment associated with the Trans-Moroccan fault system consist of rejuvenated lithosphere formed by small-scale, shallow-mantle upwelling and accretion of asthenospheric material since late Cretaceous or Eocene times.
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DOI: 10.1093/petrology/egn069
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Raffone</name><affiliation><mods:affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</mods:affiliation></affiliation><affiliation><mods:affiliation>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: raffone@crystal.unipv.it</mods:affiliation></affiliation></author><author><name sortKey="Chazot, G" sort="Chazot, G" uniqKey="Chazot G" first="G." last="Chazot">G. Chazot</name><affiliation><mods:affiliation>Institut Universitaire Européen de La Mer, UniversitÉ de Bretagne Occidentale, UMR 6538, Place Copernic, F-29280, Plouzane, France</mods:affiliation></affiliation></author><author><name sortKey="Pin, C" sort="Pin, C" uniqKey="Pin C" first="C." last="Pin">C. Pin</name><affiliation><mods:affiliation>Laboratoire de Géologie—UMR 6524, Université Blaise Pascal, 5 Rue Kessler, F-63038, Clermont-Ferrand Cedex, France</mods:affiliation></affiliation></author><author><name sortKey="Vannucci, R" sort="Vannucci, R" uniqKey="Vannucci R" first="R." last="Vannucci">R. Vannucci</name><affiliation><mods:affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</mods:affiliation></affiliation><affiliation><mods:affiliation>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</mods:affiliation></affiliation></author><author><name sortKey="Zanetti, A" sort="Zanetti, A" uniqKey="Zanetti A" first="A." last="Zanetti">A. Zanetti</name><affiliation><mods:affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Journal of Petrology</title><idno type="ISSN">0022-3530</idno><idno type="eISSN">1460-2415</idno><imprint><publisher>Oxford University Press</publisher><date type="published" when="2009-02">2009-02</date><biblScope unit="volume">50</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="197">197</biblScope><biblScope unit="page" to="249">249</biblScope></imprint><idno type="ISSN">0022-3530</idno></series></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0022-3530</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract">Mantle xenoliths enclosed in the Plio-Quaternary alkaline basalts from Bou Ibalrhatene, Middle Atlas, Morocco, are characterized by a wide range of lithological and chemical heterogeneity, consistent with metasomatism of their lithospheric mantle source. Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO2-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere–asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central–Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). The majority of the mantle sectors beneath the NE–SW volcanic alignment associated with the Trans-Moroccan fault system consist of rejuvenated lithosphere formed by small-scale, shallow-mantle upwelling and accretion of asthenospheric material since late Cretaceous or Eocene times.</div></front></TEI><istex><corpusName>oup</corpusName><author><json:item><name>N. 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Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO2-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere–asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central–Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). 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Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org</p></availability><date>2009-02-26</date></publicationStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe- and Mg-rich Wehrlites</title><author xml:id="author-0000" corresp="yes"><persName><forename type="first">N.</forename><surname>Raffone</surname></persName><email>raffone@crystal.unipv.it</email><affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><affiliation>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation></author><author xml:id="author-0001"><persName><forename type="first">G.</forename><surname>Chazot</surname></persName><affiliation>Institut Universitaire Européen de La Mer, UniversitÉ de Bretagne Occidentale, UMR 6538, Place Copernic, F-29280, Plouzane, France</affiliation></author><author xml:id="author-0002"><persName><forename type="first">C.</forename><surname>Pin</surname></persName><affiliation>Laboratoire de Géologie—UMR 6524, Université Blaise Pascal, 5 Rue Kessler, F-63038, Clermont-Ferrand Cedex, France</affiliation></author><author xml:id="author-0003"><persName><forename type="first">R.</forename><surname>Vannucci</surname></persName><affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><affiliation>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation></author><author xml:id="author-0004"><persName><forename type="first">A.</forename><surname>Zanetti</surname></persName><affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation></author><idno type="istex">056E3EEC1E822785FC05C03E37BAFBFF55E8B28C</idno><idno type="DOI">10.1093/petrology/egn069</idno><idno type="ArticleID">egn069</idno></analytic><monogr><title level="j">Journal of Petrology</title><idno type="pISSN">0022-3530</idno><idno type="eISSN">1460-2415</idno><idno type="PublisherID">petroj</idno><idno type="PublisherID-hwp">petrology</idno><imprint><publisher>Oxford University Press</publisher><date type="published" when="2009-02"></date><biblScope unit="volume">50</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="197">197</biblScope><biblScope unit="page" to="249">249</biblScope></imprint></monogr></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2009-02-26</date></creation><abstract><p>Mantle xenoliths enclosed in the Plio-Quaternary alkaline basalts from Bou Ibalrhatene, Middle Atlas, Morocco, are characterized by a wide range of lithological and chemical heterogeneity, consistent with metasomatism of their lithospheric mantle source. Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO2-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere–asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central–Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). The majority of the mantle sectors beneath the NE–SW volcanic alignment associated with the Trans-Moroccan fault system consist of rejuvenated lithosphere formed by small-scale, shallow-mantle upwelling and accretion of asthenospheric material since late Cretaceous or Eocene times.</p></abstract><textClass><keywords scheme="keyword"><list><item><term>Original Papers</term></item></list></keywords></textClass><textClass><keywords scheme="keyword"><list><head>keywords</head><item><term>lithospheric mantle</term></item><item><term>metasomatism</term></item><item><term>wehrlites</term></item><item><term>trace elements</term></item><item><term>Sr–Nd isotopes</term></item><item><term>Morocco</term></item><item><term>mantle xenoliths</term></item></list></keywords></textClass></profileDesc><revisionDesc><change when="2009-02-26">Created</change><change when="2009-02">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/document/056E3EEC1E822785FC05C03E37BAFBFF55E8B28C/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus oup" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="utf-8"</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">petrology</journal-id><journal-id journal-id-type="publisher-id">petroj</journal-id><journal-title>Journal of Petrology</journal-title><issn pub-type="ppub">0022-3530</issn><issn pub-type="epub">1460-2415</issn><publisher><publisher-name>Oxford University Press</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.1093/petrology/egn069</article-id><article-id pub-id-type="publisher-id">egn069</article-id><article-categories><subj-group><subject>Original Papers</subject></subj-group></article-categories><title-group><article-title>Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe- and Mg-rich Wehrlites</article-title></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name><surname>Raffone</surname><given-names>N.</given-names></name><xref ref-type="aff" rid="AFF1"><sup>1</sup></xref><xref ref-type="aff" rid="AFF2"><sup>2</sup></xref><xref ref-type="corresp" rid="COR1">*</xref></contrib><contrib contrib-type="author"><name><surname>Chazot</surname><given-names>G.</given-names></name><xref ref-type="aff" rid="AFF3"><sup>3</sup></xref></contrib><contrib contrib-type="author"><name><surname>Pin</surname><given-names>C.</given-names></name><xref ref-type="aff" rid="AFF4"><sup>4</sup></xref></contrib><contrib contrib-type="author"><name><surname>Vannucci</surname><given-names>R.</given-names></name><xref ref-type="aff" rid="AFF1"><sup>1</sup></xref><xref ref-type="aff" rid="AFF2"><sup>2</sup></xref></contrib><contrib contrib-type="author"><name><surname>Zanetti</surname><given-names>A.</given-names></name><xref ref-type="aff" rid="AFF1"><sup>1</sup></xref></contrib></contrib-group><aff id="AFF1"><sup>1</sup>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</aff><aff id="AFF2"><sup>2</sup>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</aff><aff id="AFF3"><sup>3</sup>Institut Universitaire Européen de La Mer, UniversitÉ de Bretagne Occidentale, UMR 6538, Place Copernic, F-29280, Plouzane, France</aff><aff id="AFF4"><sup>4</sup>Laboratoire de Géologie—UMR 6524, Université Blaise Pascal, 5 Rue Kessler, F-63038, Clermont-Ferrand Cedex, France</aff><author-notes><corresp id="COR1">*Corresponding author: Nicola Raffone, Dipartimento di Scienze della Terra, Università di Pavia and CNR–IGG, Sezione di Pavia, via Ferrata 1, I-27100, Pavia, Italy. Telephone: <phone>0039 0382 985842</phone>. Fax: <fax>0039 0382 985890</fax>. E-mail: <email>raffone@crystal.unipv.it</email></corresp></author-notes><pub-date pub-type="ppub"><month>2</month><year>2009</year></pub-date><pub-date pub-type="epub"><day>26</day><month>2</month><year>2009</year></pub-date><volume>50</volume><issue>2</issue><fpage>197</fpage><lpage>249</lpage><history><date date-type="received"><day>21</day><month>6</month><year>2008</year></date><date date-type="accepted"><day>21</day><month>11</month><year>2008</year></date></history><permissions><copyright-statement>© The Author 2009. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org</copyright-statement><copyright-year>2009</copyright-year></permissions><abstract><p>Mantle xenoliths enclosed in the Plio-Quaternary alkaline basalts from Bou Ibalrhatene, Middle Atlas, Morocco, are characterized by a wide range of lithological and chemical heterogeneity, consistent with metasomatism of their lithospheric mantle source. Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO<sub>2</sub>-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere–asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central–Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). The majority of the mantle sectors beneath the NE–SW volcanic alignment associated with the Trans-Moroccan fault system consist of rejuvenated lithosphere formed by small-scale, shallow-mantle upwelling and accretion of asthenospheric material since late Cretaceous or Eocene times.</p></abstract><kwd-group><kwd>lithospheric mantle</kwd><kwd>metasomatism</kwd><kwd>wehrlites</kwd><kwd>trace elements</kwd><kwd>Sr–Nd isotopes</kwd><kwd>Morocco</kwd><kwd>mantle xenoliths</kwd></kwd-group></article-meta></front></article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe- and Mg-rich Wehrlites</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>Metasomatism in the Lithospheric Mantle beneath Middle Atlas (Morocco) and the Origin of Fe- and Mg-rich Wehrlites</title></titleInfo><name type="personal" displayLabel="corresp"><namePart type="given">N.</namePart><namePart type="family">Raffone</namePart><affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><affiliation>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><affiliation>E-mail: raffone@crystal.unipv.it</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">G.</namePart><namePart type="family">Chazot</namePart><affiliation>Institut Universitaire Européen de La Mer, UniversitÉ de Bretagne Occidentale, UMR 6538, Place Copernic, F-29280, Plouzane, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">C.</namePart><namePart type="family">Pin</namePart><affiliation>Laboratoire de Géologie—UMR 6524, Université Blaise Pascal, 5 Rue Kessler, F-63038, Clermont-Ferrand Cedex, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">R.</namePart><namePart type="family">Vannucci</namePart><affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><affiliation>Dipartimento di Scienze Della Terra, Università di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">A.</namePart><namePart type="family">Zanetti</namePart><affiliation>CNR–Istituto di Geoscienze E Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article"></genre><subject><topic>Original Papers</topic></subject><originInfo><publisher>Oxford University Press</publisher><dateIssued encoding="w3cdtf">2009-02</dateIssued><dateCreated encoding="w3cdtf">2009-02-26</dateCreated><copyrightDate encoding="w3cdtf">2009</copyrightDate></originInfo><physicalDescription><internetMediaType>text/html</internetMediaType></physicalDescription><abstract>Mantle xenoliths enclosed in the Plio-Quaternary alkaline basalts from Bou Ibalrhatene, Middle Atlas, Morocco, are characterized by a wide range of lithological and chemical heterogeneity, consistent with metasomatism of their lithospheric mantle source. Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO2-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere–asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central–Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). The majority of the mantle sectors beneath the NE–SW volcanic alignment associated with the Trans-Moroccan fault system consist of rejuvenated lithosphere formed by small-scale, shallow-mantle upwelling and accretion of asthenospheric material since late Cretaceous or Eocene times.</abstract><subject><genre>keywords</genre><topic>lithospheric mantle</topic><topic>metasomatism</topic><topic>wehrlites</topic><topic>trace elements</topic><topic>Sr–Nd isotopes</topic><topic>Morocco</topic><topic>mantle xenoliths</topic></subject><relatedItem type="host"><titleInfo><title>Journal of Petrology</title></titleInfo><genre type="journal">journal</genre><identifier type="ISSN">0022-3530</identifier><identifier type="eISSN">1460-2415</identifier><identifier type="PublisherID">petroj</identifier><identifier type="PublisherID-hwp">petrology</identifier><part><date>2009</date><detail type="volume"><caption>vol.</caption><number>50</number></detail><detail type="issue"><caption>no.</caption><number>2</number></detail><extent unit="pages"><start>197</start><end>249</end></extent></part></relatedItem><identifier type="istex">056E3EEC1E822785FC05C03E37BAFBFF55E8B28C</identifier><identifier type="DOI">10.1093/petrology/egn069</identifier><identifier type="ArticleID">egn069</identifier><accessCondition type="use and reproduction" contentType="copyright">© The Author 2009. 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