内蒙古赤峰地区晚泥盆世双峰式火山岩地球化学特征与板内伸展事件

发布时间：2018-07-27 10:33

【摘要】：内蒙古赤峰敖汉旗一带的朝吐沟组火山岩由变玄武岩、变流纹岩组成,是一套典型的"双峰式"火山岩组合。采用LA-ICP-MS锆石U-Pb测年方法,获得了流纹岩的锆石206Pb/238U加权平均年龄分别为(359±1)Ma和(360±1)Ma,形成于晚泥盆世法门期。火山岩的Si O2含量分布在46.24%~56.6%和77.59%~85.75%,分别属于变玄武岩(玄武安山岩)和变流纹岩。变玄武岩(玄武安山岩)轻稀土元素弱富集而重稀土元素略亏损,(La/Yb)N=2.4~8.76,有弱Eu负异常,富集大离子亲石元素和高场强元素,Nb、Ta、Ti有明显负异常,87Sr/86Sr初始比值为0.705076~0.707770,具有高的正εNd(t)值(+0.51~+4.90)和年轻的模式年龄TDM(964~1090 Ma),推断其源于遭受地壳物质混染的亏损地幔;变流纹岩富硅、钾和钠,贫镁,具有轻稀土元素富集而重稀土元素略亏损,(La/Yb)N=7.07~11.07,有强烈的Eu负异常(δEu=0.12~0.43),Ti、P、Sr、Ba相对强烈亏损,Nb、Ta亏损,Rb、Th、U、K相对富集;其87Sr/86Sr初始比值为0.713757~0.739647,εNd(t)值为-1.75~+2.54),和年轻的模式年龄TDM(846~1156 Ma);多数锆石的εHf(t)为-2.3~+6.9,年轻的模式年龄TDM(707~1074 Ma),具有A型花岗岩的特征,推测其来源为新元古代时新生的年轻陆壳。综合前人区域研究成果、地球化学特征,朝吐沟组"双峰式"火山岩形成于晚泥盆世板内伸展构造背景。
[Abstract]:Chaotugou formation volcanic rock in Aohanqi area of Chifeng Inner Mongolia is composed of metabalts and rhyolite and is a typical "bimodal" volcanic assemblage. Using LA-ICP-MS zircon U-Pb dating method, the zircon 206Pb/238U weighted mean ages of rhyolite are (359 卤1) Ma and (360 卤1) Ma, respectively, which were formed in the late Devonian Famen period. The content of Sio _ 2 in volcanic rocks is 46.24% and 77.595.75, belonging to Black Tortoise andesite and rhyolite, respectively. The Black Tortoise andesite is weakly enriched in light rare earth elements and slightly depleted in heavy rare earth elements, and (La/Yb) 2.4m 8.76, with weak EU negative anomalies. The enrichment of large ion lithophile element and high field strength element NbTa-Taitti has obvious negative anomalies. The initial ratio of 87s r-86Sr is 0.705076 / 86Sr 0.707770, with a high positive 蔚 Nd (t) value (0.51-4.90) and a young model age of TDM (964m 1090 Ma),). It is derived from the depleted mantle affected by the mixing of crustal materials, and the rhyolite is rich in silicon. Potassium and sodium are poor in magnesium. They are rich in light rare earth elements and slightly depleted in heavy rare earth elements. (La/Yb) N is 7.07 ~ 11.07, and there is a strong negative EU anomaly (未 Eu=0.12~0.43). The initial ratio of 87Sr/86Sr is 0.713757 / 0.739647 and the 蔚 Nd (t) value is -1.75 ~ 2.54), and the young model age TDM (846 ~ 1156 Ma);), the 蔚 Hf (t) of most zircons is -2.3 ~ 6.9, and the young model age TDM (70771074 Ma),) is characterized by A-type granite, which presumably originated from the Neoproterozoic young continental crust. Based on the results of previous regional studies and geochemical characteristics, the "bimodal" volcanic rocks of Chaotugou formation were formed in the late Devonian intraplate extensional tectonic setting.
【作者单位】：中国地质调查局天津地质调查中心;
【基金】：国家自然科学基金(41572172) 中国地质调查局项目(1212011121078)联合资助~~
【分类号】：P542;P588.14

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