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Geoscience ›› 2018, Vol. 32 ›› Issue (04): 727-738.DOI: 10.19657/j.geoscience.1000-8527.2018.04.09

• Petrology • Previous Articles     Next Articles

Zircon U-Pb Geochronology and Geochemistry of Granitic Mylonites in Fengqing, Yunnan Province

WANG Hong(), CONG Feng(), LI Zaihui, WANG Hailin   

  1. Chengdu Center, China Geological Survey, Chengdu,Sichuan 610081, China
  • Received:2017-05-14 Revised:2017-11-26 Online:2018-08-10 Published:2018-09-19
  • Contact: CONG Feng

Abstract:

Based on field investigations, new data on the geochronology, petrology and geochemistry of the Fengqing granitic mylonites (north of Lincang batholith) located in southern Sanjiang region are presented. LA-ICP-M zircon U-Pb dating of two Fengqing granitic mylonites are yielded Triassic ages of (223.3 ±0.50) Ma, and (231.9 ±1.8) Ma, much younger than the previously conceived Proterozoic age. Geochemical analyses show that the granitic mylonites are peraluminous (A/CNK=1.54-1.75),high-K calc-alkaline, with low Na2O/K2O ratio. The rocks are enriched in light rare earth elements (LREE), and depleted in heavy rare earth elements(HREE), with distinct negative Eu anomalies( Eu/Eu*=0.27-0.58). The rocks contain low Cr and Ni contents, high Rb, Th, U and Sm contents, and low Zr, Hf and Ti contents. The biotite granodioritic mylonite, compared to the younger granopegmatitic mylonite, is more enriched in Ni, Fe, Mg, Ca and REE. This may reflect the products of co-magmatic fractionation. The Fengqing granitic mylonites and Lincang granite are broadly coeval and geochemically similar, and they show a transitional contact of brittle-ductile shearing in the field. This indicated that the granitic mylonite is part of the Lincang granite before shearing in the Lancangjiang fault zone, rather than being the previously-conceived Proterozoic Damenglong high-grade metamorphic rocks.

Key words: zircon U-Pb geochronology, geochemistry, granitic mylonite, Fengqing,Yunnan Province

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