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| Titel |
Geochemical, zircon U-Pb and Hf isotopic study on metabasalt in the Cathaysia Block: Implications of Paleozoic migmatization of Precambrian crustal and mantle materials in South China |
| VerfasserIn |
Wen Zeng, Hanwen Zhou, Zheng-Xiang Li, Ian C. W. Fitzsimons, Zengqiu Zhong, Hua Xiang, Rui Liu, Song Jin |
| 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 |
250140935
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| Publikation (Nr.) |
 EGU/EGU2017-4390.pdf |
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| Zusammenfassung |
| Metamorphic rocks scattered in northeastern Cathaysia Block experienced upper-amphibolite
to granulite facies metamorphism. This study focuses on the mafic metamorphic rocks
(including biotite-amphibolite and amphibolite) found in migmatite. The whole
rock geochemical characteristics of ten mafic metamorphic rock samples suggest
that their protoliths are subalkaline basalts, including tholeiites and calc-alkaline
basalts resemble those in E-MORB, within-plate and volcanic-arc tectonic settings.
Eighty zircon grains from three representative samples (samples FJ39-1, FJ61-3
and FJ125-4) were picked for geochronology analyses. Cathodo-luminescence
images show that most zircons are elongated subhedral to eueuhedral crystals with
oscillatory zoning. Some of them are surrounded by thin, homogeneous luminescent
overgrowth rims, which may present a later thermal event. LA-ICP-MS analyses indicate
that most analyzed zircon grains have high Th/U ratios (0.16–1.41, n = 69) and
yield U–Pb zircon ages of 444 ± 3 Ma (FJ39-1), 445 ± 2 Ma (FJ61-3), 448 ± 3
Ma and 473 ± 4 Ma (FJ125-4), respectively for each sample. The Hf model ages
calculated for these zircons ranges from ∼3613 to ∼853 Ma with ɛHf(t) values
from -20.0 to +7.1; zircons with model ages of 1121–853 Ma show positive ɛHf(t)
values (+0.2 – +7.1). This implies that the protoliths of the mafic metamorphic rocks
contain diverse basalts erupted in various tectonic settings during the Precambrian,
rather than being Ordovician new crustal addition. The data suggest that there could
be an Archaean basement component in the Cathaysia Block and the basement
possibly had crustal additions during the Meso- to Neoproterozoic. The zircon
U-Pb ages of the mafic metamorphic rocks are the same as those of leucosomes
(471 ± 4 Ma and 445 ± 3 Ma). The metamorphic P-T conditions are constrained
by the zircon Ti-content thermometer, the Amp-Pl thermobarometer and mineral
stability fields of titanite and garnet to be 722–779 ºC and 8–9 kbar. It suggests that
the metamorphic rocks were products of tectonothermal events in the Cathaysia
Block during the Ordovician, i.e. the Wuyi-Yunkai orogeny. We conclude that at
least two episodes of high-grade metamorphism occurred during the Wuyi-Yunkai
orogeny in the Cathaysia Block, one at ca. 470 Ma and the other at ca. 445 Ma. |
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