内蒙古霍林河地区晚石炭世本巴图组火山岩年代学、地球化学特征及构造背景

The chronology,geochemical characteristics and tectonic setting of the volcanic rocks in the Benbatu Formation of Huolinhe area,Inner Mongolia

在内蒙古东部霍林河地区晚古生代地层中厘定出一套火山岩,其LA-ICPMS锆石U-Pb年龄为(313.7±3.5)Ma,时代归属晚石炭世。岩石学、岩石地球化学特征表明:研究区本巴图组火山岩主要由安山岩、玄武安山岩组成,属准铝质碱性系列岩石,SiO2含量52.83%~54.76%,具较高的Al2O3含量(17.43%~20.79%),Ti O2含量(0.97%~1.41%)较低,Na2O(3.74%~4.21%)>K2O(2.37%~3.02%)。稀土总量(ΣREE)较高,为46.78×10^-6~124.36×10^-6,轻稀土(LREE)富集(42.57×10^-6~109.06×10^-6),重稀土(HREE)较富(4.21×10^-6~15.30×10^-6);LREE/HREE值为6.04~10.43,轻、重稀土分馏较强,(La/Yb)N值为6.32~14.56,在球粒陨石标准化稀土元素配分图上呈现出左高右低的右倾型分配模式;富集大离子亲石元素(Rb、Ba、K、Pb、Sr)和轻稀土元素,亏损高场强元素(Nb、Ta、Ti)和重稀土元素。岩浆来源于俯冲流体交代的地幔楔部分熔融;具岛弧及大陆边缘弧构造环境的特征,形成于板块边缘的消减带,主要与古亚洲洋板块的俯冲作用有关。

In this study, the authors determined a set of volcanic rocks in the Late Paleozoic strata at Huolinhe area, Inner Mongolia.The age of zircon U-Pb isotope based on LA-ICP-MS analysis is(313.7 ± 3.5)Ma, suggesting Late Carboniferous. The characteristics of petrography and petrogeochemical indicate that the Benbatu Formation consists of andesite and andesitic basalt rocks and belongs to aluminous rocks of alkalic series. The SiO2 values are 52.82%-54.76%, with higher Al2 O3 content(17.43%-20.79%) and lower TiO2 content(0.97%-1.41%);Na2 O(3.74%-4.21%)>K2 O(2.37%-3.02%). In addition, rare earth elements(ΣREE) are between 46.78×10^-6 and 124.36×10^-6, light rare earth elements(LREE) are enriched(42.57×10^-6-109.06×10^-6), and heavy rare earth elements(HREE) are relatively enriched(4.21 × 10^-6-15.30×10^-6). The ratios of LREE/HREE are 6.04-10.43,suggesting obvious fractionation of light and heavy rare earth elements. The ratios of(La/Yb)Nare 6.32-14.56, exhibiting rightinclined shape high on the left and low on the right on the chondrite-normalized REE patterns. Large ion lithophile elements(Rb,Ba, K, Pb, Sr)and LREE are enriched whereas high field-strength elements(Nb, Ta, Ti, P)and HREE are depleted. Magma came from mantle wedge partial melting with underthrust fluid metasomatism. These rocks are characterized by structural environment of island arc and continental edge arc and were formed along the subduction zone at the edge of the plate and related to Paleoasian Ocean subduction.