Journal
INTERNATIONAL JOURNAL OF EARTH SCIENCES
Volume 106, Issue 5, Pages 1469-1486Publisher
SPRINGER
DOI: 10.1007/s00531-015-1282-z
Keywords
Metaigneous rocks; Lancang Group; Late Ordovician; Proto-Tethyan evolution; SW Yunnan
Categories
Funding
- China Natural Science Foundation [41190073, 41372198]
- National Basic Research Program of China [2014CB440901]
- Natural Environment Research Council [NE/J021822/1]
- Fundamental Research Fund for the Central Universities
- NERC [NE/J021822/1] Funding Source: UKRI
- Natural Environment Research Council [NE/J021822/1] Funding Source: researchfish
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SW Yunnan of China constituted part of the northern margin of Gondwana facing the proto-Tethys ocean in the early Paleozoic. However, the evolution of the region and its relationship with the accretionary orogenism have been poorly established. This paper reports a set of new zircon U-Pb age data and whole-rock major oxides, elemental and Sr-Nd isotopic data for early Paleozoic metavolcanic rocks from the previously defined Lancang Group and reveals the development of an Ordovician suprasubduction zone in SW Yunnan. Zircon U-Pb ages of 462 +/- 6 and 454 +/- 27 Ma for two representative samples indicate eruption of the volcanic rocks in the Late Ordovician. Geochemical data for the metavolcanic rocks together with other available data indicate a calc-alkaline affinity with high Al2O3 (13.04-18.77 wt%) and low TiO2 (0.64-1.00 wt%). They have Mg-numbers ranging from 62 to 50 with SiO2 of 53.57-69.10 wt%, compositionally corresponding to the high-Mg andesitic rocks. They display enrichments in LREEs and LILEs with significant Eu negative anomalies (delta Eu = 0.20-0.33), and depletions in HFSEs, similar to arc volcanic rocks. Their initial Sr-87/Sr-86 ratios range from 0.721356 to 0.722521 and epsilon Nd(t) values from -7.63 to -7.62 with Nd model ages of 2.06-2.10 Ga. Integration of ages and geochemical data with available geological observations, we propose the presence of Ordovician magmatism related to proto-Tethyan evolution in SW Yunnan and the metaigneous rocks formed in an island-arc setting. They were part of a regional accretionary orogen that extended along the northern margin of Gondwana during Neoproterozoic to early Paleozoic period.
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