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| Titel |
Mantle Sources and Tectonic Affinities of the Accreted Basalts in Southern
Taiwan |
| VerfasserIn |
Hsin-Yu Chen, Huai-Jen Yang, Yun-Hsin Liu, Kuo-Fang Huang, Eiichi Takazawa |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250139265
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| Publikation (Nr.) |
 EGU/EGU2017-2467.pdf |
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| Zusammenfassung |
| Accreted basalts provide critical information on mantle nature, tectonic evolution, and mass
transport in convergent boundaries. In this study, nineteen accreted basalts from southern
Taiwan on the convergent boundary between Eurasia and Philippine Sea plates were
analyzed for element concentrations as well as Sr, Nd, Hf, and Pb isotope ratios to
investigate their petrogenetic and tectonic significance. All the samples contain > 2%
L.O.I., reflecting post-magmatic alteration. The invariability of REE and HFSE
abundances relative to the L.O.I. content indicates that these two element groups
remained intact after magmatic processes. In contrast, Rb, Sr, and Ba were relatively
mobile as indicated by the scatterings in the concentration plots of La versus these
three elements. Pb is also mobile but to a lesser extent; therefore, Pb isotope ratios
generally reflect characteristics of mantle sources. The Pb and Nd isotope ratios and
REE patterns classify the samples into derivation from the N-MORB, E-MORB,
and OIB sources. REE simulations showed that the N-MOEB-like high-HREE
samples were evolved melts after 30–40% crystal fractionation from a primary melt
generated by ∼20% melting with residual spinel in a source having La and Ce
abundances 1.33 and 1.23 times higher than those of the DMM-HS source, respectively.
The N-MORB-like low-HREE samples were similarly generated, however, from
a relatively depleted source with residual garnet, implying heterogeneity in the
N-MORB source. The two E-MORB-like samples required high extents of LREE
enrichment in their sources; specifically, 3.1 and 5.5 times for the La relative to the
DMM-HS source for the flat and LREE-enriched patterns, respectively. They, therefore,
cannot be derived from the N-MORB source by lower melting degrees, reflecting
the role of enriched sources. If the OIB-like samples were generated by ∼10 %
melting with residual garnet, their mantle source should have LREE and MREE
concentrations higher than those of the DMM-HS source by factors of ∼9 and ∼2,
respectively. There is no geochemical similarity between these accreted basalts and the
ocean floor basalts from the so-called “Taiwan Sea” or “Huatung Basin” in the
south and southeast of Taiwan. The OIB-like samples have Pb–Nd–Hf isotopic
systematics showing an affinity to the overriding Philippine Sea floor, whereas all but one
N-MORB-like samples, on the basis of the TiO2–P2O5 discrimination plot, were
considered as representatives of the subducting South China Sea basalts. The occurrence
of hornblende phenocrysts and hornblende-containing nodules in the exceptional
N-MORB-like sample is suggestive for an arc origin from the Philippine Sea plate.
Accordingly, it is inferred that the dominance of an affinity to the subducting plate for the
N-MORB basalts in the accretionary prism can be indicative of the subduction polarity. |
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