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| Titel |
1.0 Ga Ophiolite on North Margin of the Yangtze Craton Clarifies South China's Amalgamation with Rodinia |
| VerfasserIn |
Timothy Kusky, Songbai Peng, Lu Wang |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049545
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| Zusammenfassung |
| We report the presence of a Grenvillian ophiolite on the northern margin of the Yangtze craton, drastically changing current ideas about South China’s position in plate reconstructions of the Rodinia supercontinent. Strongly deformed pillow lavas, isotropic and layered metagabbro, diabase dikes, serpentinized dunite and harzburgite with podiform chromite are dated at circa 1000 Ma (U-Pb zircon). The ophiolite is structurally dismembered and thrust over the Proterozoic shelf sequence that covers the north margin of the Yangtze craton, and overrode a conglomerate-wildflysch unit shed from the ophiolite and a magmatic arc terrane. The youngest clasts in the conglomerate are circa 861-813 Ma (U-Pb zircon), giving a maximum age for ophiolite emplacement. The fine-grain layered amphibolites exhibit TiO2 = 1.14%-1.48%, slightly depleted-flat type REE curves with no obvious Eu anomalies, (La / Yb) N = 0.87-1.12, average La / Nb, Ce / Zr, Zr / Nb, Zr / Y, Ti / Y are respectively 1.04,0.15,18.78,2.53,290.51, and the average Nb / Th is 9.88. These features show that these amphibolites are N-MORB type tholeiites typical of mid-ocean ridge tectonic settings. The metagabbro has typical cumulate textures, flat REE distributions and obvious positive Eu anomalies. The REE characteristics of serpentinized dunites show a U-shape of slight loss of middle REE, representing cumulates metasomatized by LREE slightly enriched mantle. All these features indicate that the metamafic-ultramafic rocks from the Proterozoic Miaowan Formation form a structurally dismembered ophiolite resting above an ophiolitic mélange, sitting on top of the Proterozoic shelf sequence on the Yangtze craton. The discovery of the Proterozoic Miaowan ophiolite supplies important evidence for the existence of a Neoproterozoic oceanic basin on the north margin of the Yangtze craton, and demonstrates that the Yangtze craton first collided with Rodinia on its northern margin, with subsequent accretion of the Cathyasia block on the southern margin of the craton. |
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