西准阿克巴斯陶铝质A型花岗岩厘定及意义

THE DETERMINATION AND ITS SIGNIFICANCE OF AKEBASITAO ALUMINOUS A-TYPE GRANITES IN WEST JUNGGAR, XINJIANG

岩石学和元素地球化学研究表明,阿克巴斯陶岩体属铝质A型花岗岩.该岩体以富硅(SiO2=74.51%～78.39%)、富碱(Na2O+K2O=7.87%～8.53%)和铝(Al2O3=11.8%～13.33%)、贫镁(MgO=0.15%～0.46%)、贫钙(CaO=0.45%～1.02%)和磷(P2O5=0.01%～0.06%),氧化指数变化较大(W=0.22～0.57),高<FeO>t/MgO比值(2.76～9.24,平均5.83)为特征.其K2O>Na2O,NK/A=0.60～0.68,A/NCK=1.00～1.06,均大于1,属弱过铝质岩石.微量和稀土元素组成上,岩石富高场强元素(Zr和Hf等),亏损Ba,Nb,Ta,Y等元素.Zr+Nb+Ce+Y元素组合平均值(368.3×10-6)大于A型花岗岩下限值(350×10-6).在<FeO>t/MgO-Zr+Nb+Ce+Y和Rb/Ba-Zr+Ce+Y两类地球化学判别图解上均落入A型花岗岩区.δEu为0.038～0.130,铕强烈亏损,稀土分布曲线为"V"字型.上述特征表明,阿克巴斯陶岩体与国内外铝质A型花岗岩十分相似.在Nb-Y-Ce、AR-R1和R1-R2构造环境判别图上,显示出后造山花岗岩特征.阿克巴斯陶铝质A型花岗岩的厘定,对探讨西准噶尔地区构造演化问题具有重要意义.

The results of studies on petrology and elemental geochemistry show that Akebasitao granites are Aluminous A-type granites.Which characterized by enrichment of silicon （SiO2=74.51%～78.39%）、alkali（Na2O＋K2O=7.87%～8.53%） and aluminous（Al2O3=11.8%～13.33%） 、 low magnesium（MgO=0.15%～0.46%） 、 calcium （CaO=0.45%～1.02%） and phosphor（P2O5=0.01%～0.06%）,oxidationindex change obvious（W=0.22～0.57）,highFeOt/MgO ratio（2.76～9.24,average is 5.83）.K2ONa2O,NK/A=0.60～0.68,A/NCK=1.00～1.06,all bigger than 1,belongs to sub-aluminous rocks.Study by trace element and REE,enrichment of HFSE（such as Zr and Hf）,defect Ba,Nb,Ta,Y.The assorted average of Zr＋Nb＋Ce＋Y （368.3×10-6） lagerer than A-type granites lower limit value（=350×10-6）.In figure FeOt/MgO-（Zr＋Nb＋Ce＋Y） and Rb/Ba-Zr＋Ce＋Y,the sample drop to A-type granites area.δEu is 0.038～0.13,Eu is strongly depleted,the REE distribution patterns is＂V＂type.From the above characters,Akebasitao granites very similar to aluminous A-type granites all of world（such as aluminous A-type granites in the coastal area of Fujian Province,West、East Jungaar）.On tectonic figure Nb-Y-Ce、AR-R1 and R1-R2,belongs to post-orogenic granite.Determinations of the Akebasitao aluminous A-type granites have important significance of research tectonic evolution in West Junggar.