Zircon U-Pb age, Hf isotopic composition of the Bulangshan Ordovician granite in the Menghai area, southwestern Yunnan Province, and its tectonic significance

SUN Zaibo; HU Shaobin; ZHOU Kun; WANG Yunxiao; LIU Guichun; WU Jialin; ZHAO Jiangtai

2018 Vol. 37, No. 11

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SUN Zaibo, HU Shaobin, ZHOU Kun, WANG Yunxiao, LIU Guichun, WU Jialin, ZHAO Jiangtai. Zircon U-Pb age, Hf isotopic composition of the Bulangshan Ordovician granite in the Menghai area, southwestern Yunnan Province, and its tectonic significance[J]. Geological Bulletin of China, 2018, 37(11): 2044-2054.

Citation:

SUN Zaibo, HU Shaobin, ZHOU Kun, WANG Yunxiao, LIU Guichun, WU Jialin, ZHAO Jiangtai. Zircon U-Pb age, Hf isotopic composition of the Bulangshan Ordovician granite in the Menghai area, southwestern Yunnan Province, and its tectonic significance[J]. Geological Bulletin of China, 2018, 37(11): 2044-2054.

Zircon U-Pb age, Hf isotopic composition of the Bulangshan Ordovician granite in the Menghai area, southwestern Yunnan Province, and its tectonic significance

1.
Yunnan Institute of Geological Survey, Kunming 650216, Yunnan, China
2.
Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization, Ministry of Natural Resources, Kunming 650061, Yunnan, China
3.
Department of Natural Resources of Yunnan Province, Kunming 650224, Yunnan, China

Received Date: 10 March 2018

Revised Date: 02 May 2018

Publish Date: 15 November 2018

Abstract

Abstract

The LA-ICP-MS U-Pb dating of the zircon from the Bulangshan granite in the Menghai area of Yunnan Province was carried out. The weighted average age of the granite ²⁰⁶Pb/²³⁸U was 458.5±3.0Ma (n=21, MSWD=2.3), suggesting that the Bulangshan granite was not formed in Late Yanshanian period as originally thought, but was produced in Middle-Late Ordovician. The zircon ε_Hf(t) of the samples range from -2.4 to 0.9 with an average of -0.9. The t_DMC of the crustal model vary from 1.41Ga to 1.58Ga with a weighted average of 1.49Ga. It is inferred that the original rock was probably the second cloud (quartz) schist. The geochemical characteristics of the rock indicate that the granite has high SiO₂ (75.79%~77.56%), high alkali (K₂O+Na₂O=7.39%~8.42%), medium-high potassium (K₂O/Na₂O=1.23~1.95), and low MgO (0.14%~0.27%) and CaO(0.05%~0.64%). Aluminum supersaturated index A/CNK values range from 1.02 to 1.27, and the rock is a high-potassium-calcium-alkali-strong over-aluminum S-type granite. The total amount of rare earth elements in the rocks appears to be transition from LREE enrichment to a flat"gull"type, with a strong negative Eu anomaly and δEu values ranging from 0.03 to 0.14. There exists significant enrichment of elements such as Rb, Th, Nd, and Ta and significant loss of Ba, Sr, P, and Ti in the original mantle standard trace element spider pattern. Combined with regional geological data, the authors hold that the formation of the rock mass may be related to the following factors:the subduction of the original Tethys Ocean and the Paleo-Tethys Ocean expanded into basins, the area was under the condition of intense compression, and the continued intracontinental subduction and collision would continuously increase the regional crust and led to regional equilibrium gravity uplift, which caused deep crust materials to migrate upward after heating and decompression and partial melting.
- Bulangshan granite /
- Ordovician /
- original Tethys /
- zircon U-Pb age /
- Hf isotope /
- Menghai

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