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东准噶尔贝勒库都克铝质A型花岗岩的厘定及意义
The determination of Beilekuduke aluminous A-type granites in east Junggar,Xinjiang
【摘要】 初步研究表明,长期以来被认为S型花岗岩的贝勒库都克黑云母花岗岩应为铝质A型花岗岩。该岩体以富硅(SiO2=75.25%~76.67%)和碱(Na2O+K2O=8.08%~8.97%),贫镁(MgO=0.02%~0.18%)和钙(CaO=0.39%~0.89%),氧化指数变化较大(W=0.02~0.15)以及高FeOT/MgO比值(12.71~84.51,平均34.55)为特征。其K2O>Na2O,NK/A=0.86~0.95(平均0.92),A/CNK=0.97~1.02(>0.95),属偏铝-过铝质钙碱-弱碱性岩石。在微量元素和稀土元素组成上,岩石富Ga、Zr和Hf等高场强元素,亏损Ba、Nb、Sr等元素。10000Ga/Al比值(2.97~4.20)均大于A型花岗岩的下限值(2.6),明显高于I型和S型花岗岩的平均值(分别为2.10和2.28)。在Zr、Ce、Nb对10000Ga/Al以及FeOT/MgO对(Zr+Nb+Ce+Y)、SiO2等A型花岗岩多种判别图上,投影点均落在A型花岗岩区,而与高分异的I、S型花岗岩明显不同。这些特征表明,贝勒库都克黑云母花岗岩与国内外铝质A型花岗岩(如福建沿海、东西准噶尔和澳大利亚Lachlan褶皱带铝质A型花岗岩)十分相似。在Nb-Y-Ce、R1-Ga/Al和R1-R2构造环境判别图上,显示出造山后花岗岩的特征。贝勒库都克铝质A型花岗岩的厘定,不仅对探讨卡拉麦里地区地壳物质组成及构造演化有着重要的地质意义,还为我国新疆北部寻找与铝质A型花岗岩有关的锡矿资源开辟了方向。
【Abstract】 The Beilekuduke biotite granites in the study area have long been thought to be of S-type.Nevertheless,the preliminary research conducted by the authors shows that biotite granites are actually typical aluminous A-type granites,which have the following characteristics:enriched silica(SiO2=75.25%~76.67%) and alkali(Na2O+K2O=8.08%~8.97%),low magnesium(MgO=0.02%~0.18%) and calcium(CaO =0.39%~0.89%),obvious variation of oxidation index(W=0.02~0.12),high FeOT/MgO ratio(12.71~84.51,34.55 on average).K2O>Na2O,NK/A=0.86~0.95(0.92 on average),A/CNK=0.97~1.02(higher than 0.95),thus belonging to sub-aluminous-ultra-aluminous calc-alkali-weak-alkali rocks.In trace element and REE characteristics,the rocks are enriched in HFSE(such as Ga,Zr and Hf) and depleted in Ba,Nb and Sr.10 000 Ga/Al ratios(2.97~4.20) are exclusively higher than the lower limit value of the A-type granites(2.6),obvious higher than average values of I-,S-type granites(2.1 and 2.28,respectively).In Zr,Ce,Nb versus 10 000 Ga/Al and FeOT/MgO versus(Zr+Nb+Ce+Y),SiO2 diagrams,the samples fall into the area of A-type granites,and are obviously different from things of I-,S-type granites.The above characteristics show that Beilekuduke biotite granites are very similar to such typical aluminous A-type granites in the world as aluminous A-type granites in the coastal area of Fujian Province,in west and east Jungaar and in the Lachlan fold belt of southeastern Australia.In Nb-Y-Ce,R1-Ga/Al and R1-R2 tectonic diagrams,they belong to post-orogenic granites.The determination of the Beilekuduke typical aluminous A-type granites not only has geological significance in the study of the crust material composition and tectonic evolution in Kalamaili area but also opens up a new orientation in looking for tin resources related to aluminous A-type granites in northern Xinjiang.
【Key words】 aluminous A-type granite; geochemistry; geological significance; Beilekuduke; east Junggar;
- 【文献出处】 岩石矿物学杂志 ,Acta Petrologica Et Mineralogica , 编辑部邮箱 ,2009年01期
- 【分类号】P588.121
- 【被引频次】39
- 【下载频次】617