Study on the origin and rock-forming simulation experiments of aquamarine-bearing pegmatites of Ailaoshan, Yunnan, China
- 出版年：2007
- 作者：LI ZhaoLin LI Wen；JI JunFeng；WANG YinXi；SHI GuiYong
- 单位1：Department of Earth Sciences,Zhongshan University
- 单位2：The Stae Key Laboratory for Mineral eposits Research,Nanjing University
- 语种：英文
- 作者关键词：Pegmatite；Metamorphic anatexis；Fluid inclusions；Isotope Geochemistry；Trace elements geochemistry；Simulation experiments；Ailaoshan
- 起始页：39
- 总页数：14
- 刊名：岩石学报
- 是否内版：否
- 刊频：月刊
- 创刊时间：1985
- 主办单位：中国矿物岩石地球化学学会；中国科学院地质与地球物理研究所
- 电子信箱：Ihzd@ public.tpt.tj.cn
- 卷：23
- 期：1
- 期刊索取号：P350.66357
摘要
The Ailaoshan aquamarine-bearing pegmatites are associated with Proterozoic metamorphic rocks in the southem portionof the Ailaoshan fault-folded complex. The gem-bearing pegmatite mineralization zones of the region occur in areas generally consistentwith the regional tectonic trend. The pegmatites are found in metamorphic rocks, migmatites and in the inner/outer contact zones ofgneissoid granites.
The Rb-Sr isochron drawn for the pegmatites is 26～31Ma,(i.e.in Himalayan).The homogenization temperatures of melt andliquid inclusions in minerals vary from 185to 920℃, which are comparable to the inclusions observed in banded migmatites andptygmatic quartz veins in the surrounding metamorphic rocks.
The mineralization fluids of the pegmatite were rich in HCO**3 and CO**2, and their compositional assemblages are comparable tometamorphic fluids. Results of H, O, C, Si etc. isotopic analyses and REE, and Be analyses indicates that the sources ofmineralization components that formed the pegmatites are closely associated with metamorphic fluids and the enclosing metamorphicrocks.
A pegmatite structure simulation experiment was conducted at high temperature and pressure (840℃ and 1,500×105Pa.),withvarious metamorphic rock samples in a water-rich and volatile-rich environment. When the liquidus was reached, the temperature wasgradually decreased at the rate of 5～10℃/day over a time period of three months. SEM energy-dispersive spectrum analyses wereperformed on the experimental products. A series of pegmatoid textures were observed including zonal texture, megacryst texture, drusycavities, crystal druses, and vesicular texture along with more than ten types of minerals including plagoclase, microcline, quartz andbiotite. Different metamorphic rock melts generated different mineral assemblages. Experiment results revealed that the partial melting ofmetamorphic rocks could form melts similar to pegmatite magmas.
Based upon the geological characteristics, geochemistry, and pegmatite texture simulation experimental results, it is concludedthat the mineralization components of Ailaoshan aquamarine-bearing pegmatites came from metamorphic rocks. The petrogenetic modelfor the origin of pegmatites is related to ultrametamorphism and metamorphic anatexis.
The Rb-Sr isochron drawn for the pegmatites is 26～31Ma,(i.e.in Himalayan).The homogenization temperatures of melt andliquid inclusions in minerals vary from 185to 920℃, which are comparable to the inclusions observed in banded migmatites andptygmatic quartz veins in the surrounding metamorphic rocks.
The mineralization fluids of the pegmatite were rich in HCO**3 and CO**2, and their compositional assemblages are comparable tometamorphic fluids. Results of H, O, C, Si etc. isotopic analyses and REE, and Be analyses indicates that the sources ofmineralization components that formed the pegmatites are closely associated with metamorphic fluids and the enclosing metamorphicrocks.
A pegmatite structure simulation experiment was conducted at high temperature and pressure (840℃ and 1,500×105Pa.),withvarious metamorphic rock samples in a water-rich and volatile-rich environment. When the liquidus was reached, the temperature wasgradually decreased at the rate of 5～10℃/day over a time period of three months. SEM energy-dispersive spectrum analyses wereperformed on the experimental products. A series of pegmatoid textures were observed including zonal texture, megacryst texture, drusycavities, crystal druses, and vesicular texture along with more than ten types of minerals including plagoclase, microcline, quartz andbiotite. Different metamorphic rock melts generated different mineral assemblages. Experiment results revealed that the partial melting ofmetamorphic rocks could form melts similar to pegmatite magmas.
Based upon the geological characteristics, geochemistry, and pegmatite texture simulation experimental results, it is concludedthat the mineralization components of Ailaoshan aquamarine-bearing pegmatites came from metamorphic rocks. The petrogenetic modelfor the origin of pegmatites is related to ultrametamorphism and metamorphic anatexis.
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