Genesis of Lamprophyres from Machangqing, Western Yunnan: Constraints from Geochemistry, Geochronology and Sr-Nd-Pb-Hf Isotopes
详细信息
- 责任者：Jia Liqiong (School of Earth Sciences and Resources ; China University of Geosciences ; Beijing 100083 ; China) ; Mo Xuanxue
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(4)
- 关键词：煌斑岩 ; lamprophyres ; 云南 ; Yunnan Province
- 页码：p.1247-1260
- 图表：illus., 4 tables, 59 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Lamprophyres occur as early and late dykes in Machangqing, western Yunnan. The early lamprophyres are mostly kersantons and the late are minettes. Zircon LA-MC-ICP-MS U-Pb dating yields an age of 33.77±0.11Ma, which indicate lamprophyres are the product of middle stage magmatic process of Machangqing complex and early pulse of Cenozoic magmatism in the Jinshajiang-Ailaoshan fault belt. Geochemically, the lamprophyres have high values of potassium (K2O/Na2O=2.88~4.60), alkaline (K2O+Na2O=6.40%~7.55%) and Mg#(74.3~76.9) and are enriched in large ion lithophile elements (K, Rb, Ba) and LREEs and depleted in the high field strength elements (Nb, Zr, P) and HREEs. The isotopes of lamprophyres are characterized by high (87Sr/86Sr)i (0.707406~0.706506) , low εNd(t) (-1.78~-7.64) but enriched radioactive Pb (208Pb/204Pb=38.87~39.35, 207Pb/204Pb=15.6390~15.6431, 206Pb/204Pb=18.6579~18.8093) . The ratios of 176Hf/177Hf range from 0.282712 to 0.282864, with εHf(t) values varying from -1.4 to 4.0. The εNd(t) and εHf(t) values show a Nd-Hf decoupling feature. Based on the geochemistry, isotopes and the regional tectonic evolution history, the lamprophyres were derived from EMII produced by an interaction between the Jinshajiang oceanic crust and the mantle peridotite while the heat was provided by the upwelling asthenosphere. The Jinshajiang-Ailaoshan fault belt is likely to act as migration channels for magmatic emplacement.