内蒙古北山地区咸水沟一带早石炭世红柳园组火山岩地球化学、锆石U-Pb年龄及Hf同位素特征

Geochemistry, zircon U-Pb ages and Hf isotopes of the Early Carboniferous Hongliuyuan volcanic rocks in Xianshuigou,Beishan area, Inner Mongolia

内蒙古北山地区咸水沟一带红柳园组火山岩岩性为细碧岩、玄武岩、流纹岩,具双峰式岩浆组合特征。基性岩稀土元素总量∑REE(包括Y元素)变化于123×10^(-6)~217×10^(-6)之间,轻稀土明显富集((La/Yb)_N=2.42~4.74)。在原始地幔标准化的蛛网图中,Nb、Ta、Ti元素明显亏损;具有高的Th/Nb比值(3.14~10.2)和低的Nb/La比值(0.3~0.7<1);Mgo和Cr、Ni总体呈正相关关系,反映了橄榄石±辉石的结晶分异作用。细碧岩ε_(Hf)(t)值变化于6.0~11.5,表明岩浆来源于亏损地幔,两阶段模式年龄(T_(DM2)=631~982 Ma)明显大于其结晶年龄,结合ε_(Hf)(t)值揭示出岩浆源区受到地壳物质混染的可能。流纹岩具有向强过铝质岩石过渡趋势(A/CNK=1.08~1.32),稀土元素总量∑REE(包括Y元素)较高(133×10^(-6)~383×10^(-6)),轻稀土明显富集((La/Yb)_N=4.5~8.0),Eu负异常强烈(δEu=0.1~0.5);Ga/Al比值(10 000*Ga/Al=1.8~4.2)较高,具A型花岗岩特征。其下部细碧岩LA-ICP-MS锆石U-Pb测年表明其形成年龄为359.9±1.4 Ma。咸水沟红柳园组基性岩的形成表明北山地区在石炭纪早期幔源岩浆活动非常强烈,这些幔源岩浆的底侵导致了浅部地壳发生脱水熔融形成具有A型花岗岩特征的酸性火山岩。地质与地球化学特征表明,咸水沟红柳园组火山岩形成于裂谷构造背景。

The volcanic rocks of spilite, basalt and rhyolite from the Hongliuyuan formation in Xianshuigou area, Beishan area, Inner Mongolia show Bi-model magma combination features. The total rare earth element （REE, including element Y）of basic volcanic rocks range from 123×10-6-217×10-6, and the light rare earth elements exhibit distinctly enrichment （（La/Yb） N=2.42- 4.74）. In the primitive mantle standardized spider diagram, elements Nb, Ta and Ti are obviously defective, meanwhile, the samples have relatively high Th/Nb values （3.14 - 10.2） and low Nb/La ratios （0.3 -.0.7〈1 ）. The positive correlates between MgO and Cr and Ni reflect the crystallization differentiation of Olivine＋Pyroxene. The values of spilite are 6.0 to 11.5, which are lower than the contemporary deficit mantle, and two-stage model ages （TDM2=631 - 982 Ma） are obviously higher than their formation ages, suggesting the magma source is contaminated by the crust materials. The rhyolite shows the tendency of transformation to strongly peraluminous rock （A/CNK=1.08 - 1.32）. The total rare earth elements （including Y） of the rhyolite are relatively high （133 × 10.6 - 383 × 10-6）, and with an enrichment of light rare earth element （ （La/Yb）N=4.5 - 8.0） and strong Eu negative anomaly （SEu=0,1 - 0.5）. At the same time, the rhyolite has relatively high Ga/A1 ratios （10 000＊Ga/AI=1.8 - 4.2）, which possess the features of A-type granite. The zircon U-Pb ages defined the lower spilite formation time is 359.9± 1.4 Ma. The formation of the Hongliuyuan basic rocks in the Xianshuigou area indicate a strong magmatic activity in the Beishan region, and the intrusion of this mantle originated magmatic caused the dehydration fusion of shallow crust and formed the felsic volcanic rocks with some features of A-type granite. The geological and geochemical characteristics of the Hongliuyuan volcanic rocks reflect these rocks formed in a rift tectonic setting.