【摘要】：內(nèi)蒙古赤峰敖漢旗一帶的朝吐溝組火山巖由變玄武巖、變流紋巖組成,是一套典型的"雙峰式"火山巖組合。采用LA-ICP-MS鋯石U-Pb測年方法,獲得了流紋巖的鋯石206Pb/238U加權(quán)平均年齡分別為(359±1)Ma和(360±1)Ma,形成于晚泥盆世法門期�；鹕綆r的Si O2含量分布在46.24%~56.6%和77.59%~85.75%,分別屬于變玄武巖(玄武安山巖)和變流紋巖。變玄武巖(玄武安山巖)輕稀土元素弱富集而重稀土元素略虧損,(La/Yb)N=2.4~8.76,有弱Eu負(fù)異常,富集大離子親石元素和高場強(qiáng)元素,Nb、Ta、Ti有明顯負(fù)異常,87Sr/86Sr初始比值為0.705076~0.707770,具有高的正εNd(t)值(+0.51~+4.90)和年輕的模式年齡TDM(964~1090 Ma),推斷其源于遭受地殼物質(zhì)混染的虧損地幔;變流紋巖富硅、鉀和鈉,貧鎂,具有輕稀土元素富集而重稀土元素略虧損,(La/Yb)N=7.07~11.07,有強(qiáng)烈的Eu負(fù)異常(δEu=0.12~0.43),Ti、P、Sr、Ba相對強(qiáng)烈虧損,Nb、Ta虧損,Rb、Th、U、K相對富集;其87Sr/86Sr初始比值為0.713757~0.739647,εNd(t)值為-1.75~+2.54),和年輕的模式年齡TDM(846~1156 Ma);多數(shù)鋯石的εHf(t)為-2.3~+6.9,年輕的模式年齡TDM(707~1074 Ma),具有A型花崗巖的特征,推測其來源為新元古代時新生的年輕陸殼。綜合前人區(qū)域研究成果、地球化學(xué)特征,朝吐溝組"雙峰式"火山巖形成于晚泥盆世板內(nèi)伸展構(gòu)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 鹵1) Ma and (360 鹵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.
【作者單位】： 中國地質(zhì)調(diào)查局天津地質(zhì)調(diào)查中心;
【基金】：國家自然科學(xué)基金(41572172) 中國地質(zhì)調(diào)查局項目(1212011121078)聯(lián)合資助~~
【分類號】：P542;P588.14

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