Crustal contamination of Late Neogene basalts in the Dien Bien Phu Basin, NW Vietnam: Some insights from petrological and geochronological studies

Ewa Koszowska, Anna Wolska, Witold Zuchiewicz, Nguyen Quoc Cuong, Z. Pécskay

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Early Pliocene (Zanclean) basalts in the Dien Bien Phu pull-apart basin in NW Vietnam, associated with the presently sinistral Dien Bien Phu Fault Zone, have been dated by the K-Ar method at 4.4-4.9 and 5.4-5.2 Ma. Rapid migration of basaltic magma to the surface in the Dien Bien Phu Fault Zone may be due to Pliocene transtension of the crust in this region, resulting from asthenospheric upwelling induced by lateral displacement of the mantle. The basalts are moderately phyric ( <10%) and consist of olivine (hyalosiderite), plagioclase (bytownite-labradorite) and orthopyroxene (bytownite-labradorite) phenocrysts, and a fine-grained crystalline matrix (olivine-hortonolite, plagioclase-labradorite, clinopyroxene-pigeonite and augite, K-feldspar). The presence of Fe-rich olivine and orthopyroxene phenocrysts indicates that the basalts are SiO2-saturated/oversaturated olivine tholeiites which formed under water-undersaturated conditions. The Dien Bien Phu basalts contain both mantle-derived (pyroxenites, dunites, gabbros) and crustal (sillimanite/mullite + Mg-Fe spinel), wallrock xenoliths, indicative of crustal contamination during the ascent of the basaltic magma. The basalts show selective enrichment in some mobile elements (K, Rb, Sr and Th), a feature considered to be a result of metasomatism. These rocks, classified on the basis of their normative composition as quartz tholeiites, could represent primary olivine tholeiites/basalts, in which the geochemical signatures were modified by the processes of contamination.

Original languageEnglish
Pages (from-to)1-17
Number of pages17
JournalJournal of Asian Earth Sciences
Volume29
Issue number1
DOIs
Publication statusPublished - Jan 15 2007

Fingerprint

crustal contamination
Neogene
basalt
olivine
labradorite
basin
orthopyroxene
fault zone
plagioclase
Pliocene
magma
mantle
porcellanite
pigeonite
transtension
pull apart basin
augite
sillimanite
metasomatism
spinel

Keywords

  • Dien Bien Phu Fault Zone
  • Geochronology
  • Late Tertiary
  • Petrology
  • Within-plate basalts

ASJC Scopus subject areas

  • Earth-Surface Processes
  • Geology

Cite this

Crustal contamination of Late Neogene basalts in the Dien Bien Phu Basin, NW Vietnam : Some insights from petrological and geochronological studies. / Koszowska, Ewa; Wolska, Anna; Zuchiewicz, Witold; Cuong, Nguyen Quoc; Pécskay, Z.

In: Journal of Asian Earth Sciences, Vol. 29, No. 1, 15.01.2007, p. 1-17.

Research output: Contribution to journalArticle

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abstract = "Early Pliocene (Zanclean) basalts in the Dien Bien Phu pull-apart basin in NW Vietnam, associated with the presently sinistral Dien Bien Phu Fault Zone, have been dated by the K-Ar method at 4.4-4.9 and 5.4-5.2 Ma. Rapid migration of basaltic magma to the surface in the Dien Bien Phu Fault Zone may be due to Pliocene transtension of the crust in this region, resulting from asthenospheric upwelling induced by lateral displacement of the mantle. The basalts are moderately phyric ( <10{\%}) and consist of olivine (hyalosiderite), plagioclase (bytownite-labradorite) and orthopyroxene (bytownite-labradorite) phenocrysts, and a fine-grained crystalline matrix (olivine-hortonolite, plagioclase-labradorite, clinopyroxene-pigeonite and augite, K-feldspar). The presence of Fe-rich olivine and orthopyroxene phenocrysts indicates that the basalts are SiO2-saturated/oversaturated olivine tholeiites which formed under water-undersaturated conditions. The Dien Bien Phu basalts contain both mantle-derived (pyroxenites, dunites, gabbros) and crustal (sillimanite/mullite + Mg-Fe spinel), wallrock xenoliths, indicative of crustal contamination during the ascent of the basaltic magma. The basalts show selective enrichment in some mobile elements (K, Rb, Sr and Th), a feature considered to be a result of metasomatism. These rocks, classified on the basis of their normative composition as quartz tholeiites, could represent primary olivine tholeiites/basalts, in which the geochemical signatures were modified by the processes of contamination.",
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