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| Titel |
In situ SIMS oxygen isotope analysis of olivine in the Tibetan mantle
xenoliths |
| VerfasserIn |
Zhidan Zhao, Di-Cheng Zhu, Dong Liu, Xuanxue Mo |
| 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 |
250130670
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| Publikation (Nr.) |
 EGU/EGU2016-10960.pdf |
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| Zusammenfassung |
| Although the mantle-derived xenoliths from Lhasa terrane provide a means of directly
investigating the mantle underlying the southern part of the plateau, they were rarely found in
the region. The only case of mantle xenoliths came from the Sailipu ultrapotassic volcanic
rocks, erupted at ∼17 Ma, which have indicated that the subcontinental mantle of southern
Tibetan Plateau is hot and strongly influenced by metasomatism (Zhao et al., 2008a, b; Liu et
al., 2011). A further study by Liu et al.(2014) of in-situ oxygen isotope of olivine crystals in
Sailipu mantle xenoliths identify a metasomatized mantle reservoir that interpreted
as the sub-arc lithospheric mantle, with anomalously enriched oxygen isotopes
(δ18O=8.03). Here we present oxygen isotopes data on the Sailipu mantle xenolith olivines,
using different method of sample preparation. Mantle xenoliths (less than 1 cm
in diameter) together originally with their host volcanic rocks were prepared in
epoxy adjacent to grains of a San Carlos olivine intralaboratory standard and then
polished to a flat and smooth surface. Oxygen isotope compositions of olivines
occurs both in mantle xenolith and as phenocryst in the host rock, were analyzed
in situ using CAMECA SIMS-1280 ion microprobe at the Institute of Geology
and Geophysics, Chinese Academy of Sciences. We also performed traditional
oxygen isotope analysis on three olivine phenocrysts separates from the host lava.
Our new data show: (1) The mantle xenolith olivines have typical mantle oxygen
isotopic composition (δ18O=4.8-8.0‰ with average of 5.5±0.2‰ n=105) with
variety Fo#(78-90), (2) Oxygen isotopes of situ olivine phenocrysts in the Sailipu
lavas (δ18O=7.1-9.2‰ Fo#=70-84, n=66), are similar to that of the whole rock
(δ18O=7.0-9.4‰ Fo#=64-74, n=8, Zhao et al., 2009), and three olivine phenocryst grains
(δ18O=7.2-7.8); (3) The intralaboratory standard of San Carlos olivine can be a
suitable standard using for analyzing olivines with Fo not only around 90, but also as
low as Fo of 70; (4) In olivine crystals in mantle xenolith, the oxygen isotopes in
rim (δ18O=6.96-7.98‰ Fo#=78-82) significantly shift to high δ18O values that
similar to their neighboring lava olivine phenocrysts (δ18O=8.03‰ Fo# =80).
These data suggest that the oxygen isotopes in mantle xenolith olivines are more
stable during the processes of metasomatism. The mantle xenolith may have been
metasomatized by the host lava, in addition to other enriched reservoir in the sub-arc mantle.
[Financially supported by the NSF of China, grants 41273044, 41225006, 41230209,
41130314].
References:
[1] Zhao Z, et al., 2008a. Acta Petrologica Sinica, 24 (2): 193-202
[2] Zhao Z, et al., 2008b. Geochimica et Cosmochimica Acta, 72, 12 (Supp.): A1095
[3] Zhao Z, et al., 2009. Lithos, 113: 190-212
[4] Liu C-Z, et al., 2011, Geology, 39, 923-926
[5] Liu C-Z, et al., 2014, Geology, Scientific Report, 4, 4232; DOI:10.1038/srep04232 |
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