内蒙古敖汉旗晚侏罗世满克头鄂博组火山岩地球化学特征及构造背景分析

内蒙古敖汉旗满克头鄂博组火山岩是一套酸性火山熔岩及火山碎屑岩。主量元素分析显示Si O2为69.76%~76.04%,K2O为4.48%~6.78%,Na2O+K2O为7.63%~9.44%,表明满克头鄂博组流纹岩具有高钾钙碱性岩石的特征。LREE/HREEE为10.46~15.87,稀土配分曲线呈轻稀土富集的右倾模式,δEu值为0.10~0.51,负异常明显;富集大离子亲石元素Rb、Th、U、K、Pb,贫Ba、Sr;亏损高场强元素P、Nb、Ta、Ti。说明满克头鄂博组火山岩属低Ba—Sr酸性火山岩,是下地壳基性火山岩部分熔融,并发生了斜长石、角闪石源区残留或分异结晶而形成的。满克头鄂博组火山岩具有A型花岗岩特征,其形成的动力学机制为蒙古—鄂霍茨克洋闭合造山后的岩石圈伸展环境。

Geochemical characteristics and tectonic setting of volcanic rocks in Late Jurassic Manketou'ebo Formation from Aohan banner,Inner Mongolia

Volcanic rocks of Manketou'ebo Formation in Aohan banner，Inner Mongolia are mainly composed of a series of acid lava and volcaniclastic rocks． Analysis of major elements shows that the SiO 2 content is 69. 76% ～76. 04%，K 2 O is 4. 48% ～6. 78%，and Na 2 O + K 2 O is 7. 63% ～9. 44%，suggesting the volcanic rocks belong to high- K calc- alkaline series． LＲEE/HＲEE ranges from 10. 46 to 15. 87，and the ＲEE distribution pattern reveals that the volcanic rocks are enriched in light earth rare elements with strong negative Eu anomaly (δEu = 0. 10 ～ 0. 51)． The characteristics of trace elements suggest the volcanic rocks rich in LILE (e.g.，Ｒb，Th，U，K，Pb) and depleting in HFSE (e.g.，Nb，Ta，Ti)． These characteristics are almost in accord with the low Ba - Sr acid volcanic rocks，indicating that there are residual remain or crystal fractionation of plagioclases and amphiboles during the formation of volcanic rocks． The volcanic rocks of Manketou'ebo Formation possess the characters of A- type granites and formed by the effect of the extensional environment caused by the closure of Mongolia- Okhotsk．