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| Titel |
Mantle xenoliths from Central Vietnam: evidence for at least Meso-Proterozoic formation of the lithospheric mantle |
| VerfasserIn |
Peter Proßegger, Theodoros Ntaflos, Lukáš Ackerman, Christoph Hauzenberger, Tuan Anh Tran |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132287
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| Publikation (Nr.) |
 EGU/EGU2016-12781.pdf |
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| Zusammenfassung |
| Intraplate Cenozoic basalts that are widely dispersed along the continental margin of East Asia belong to the
Western Pacific “diffuse” igneous province. They consist mainly of alkali basalts, basanites,rarely nephelinites,
which are mantle xenolith-bearing, potassic rocks and quartz tholeiites. The volcanism in this area has been
attributed to the continental extension caused by the collision of India with Asia and by the subduction of the
Pacific Ocean below Asia.
We studied a suite of 24 mantle xenoliths from La Bang Lake, Dak Doa district and Bien Ho, Pleiku city in the
Gia Province, Central Vietnam. They are predominantly spinel lherzolites (19) but spinel harburgites (3) and two
garnet pyroxenites are present as well. The sizes of the xenoliths range from 5 to 40 cm in diameter with medium
to coarse-grained protogranular textures.
Whole rock major and trace element analyses display a wide range of compositions. The MgO concentration
varies from 36.0 to 45.8 wt% whereas Al2O3 and CaO range from 0.63 to 4.36 wt% and from 0.52 to 4.21 wt%
(with one sample having CaO of 6.63 wt%) respectively. Both CaO and Al2O3 positively correlate with MgO
most likely indicating that the sampled rocks were derived from a common mantle source experienced variable
degrees of partial melting.
Mineral analyses show that the rock forming minerals are chemically homogeneous. The Fo contents of olivine
vary between 89.2 and 91.2 and the Mg# of orthopyroxene and clinopyroxene range from 89 to 92 and 89 to 94
respectively. The range of Cr# for spinel is 0.06-0.26.
Model calculations in both whole rock and clinopyroxenes show that lithospheric mantle underneath Central
Vietnam experienced melt extractions that vary between 2-7, 12-15 and 20-30%.
The majority of the primitive mantle-normalized whole rock and clinopyroxene REE patterns are parallel to each
other indicating that clinopyroxene is the main repository of the trace elements. Clinopyroxenes are divided into
two groups: group A with concave upwards REE and (La/Yb)N < 1 suggesting various degrees of melt extraction
and group B with (La/Yb)N ranging between 1 and 10. The group B in a mantle normalized trace element diagram
shows negative Pb and Sr anomalies compared to their neighbour elements, which together with the general
absence of hydrous phases, suggest variable interaction with percolating silicate melt(s).
The primitive-mantle normalized highly siderophile element (HSE) concentration pattern show almost no
fractionation among Ir, Ru and Pt with only slight depletion in Os suggesting very limited effect of metasomatism
on the HSE contents. On the other hand, most of the samples display clear Re addition from the percolating melts
preventing calculation of reliable rhenium depletion ages (TRD). However, one sample with depleted Pd and Re
signature yield TRD of 1.0 Ga which can be interpreted as a minimum SCLM stabilization age in this area.
Mantle xenoliths from Central Vietnam range from fertile to depleted compositions partly affected by metasomatic
silicate melts. Re-Os isotopic composition reveals a Meso-Proterozoic minimum stabilization age of the
lithospheric mantle. |
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