中国地质2017，Vol.44Issue(2)：371-388,18.DOI:10.12029/gc20170212
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
Geochemical characteristics and intraplate extension of Late Devonian bimodal volcanic rocks in Chifeng area of Inner Mongolia
摘要
Abstract
The volcanic rocks of the Chaotugou Formation in Chifeng area of Inner Mongolia consist of meta-basalts and meta-rhyolites and exhibit typical"double peaks", with the SiO2 content being 46.24%-56.6%and 77.59%-85.75%respectively. Zircon LA-ICP-MS U-Pb dating of rhyolite yielded U-Pb ages of(359±1)Ma-(360±1)Ma, which represent the time of crystallization of the volcanic rocks. The volcanic rocks were formed in late Devonian Famennian age. Geochemically,meta-basalts (or basaltic andesites) are characterized by enriched LREE, depleted HREE, slightly negative Eu, Nb, Ta, Sr and Ti anomalies and high abundances of LILE and HFSE, with the (La/Yb)N ratios from 2.4 to 8.76, and the 87Sr/ 86Sr initial values from 0.705076 to 0.707770;in addition, they have relatively high positiveεNd(t)values (+0.51 to+4.90) and relatively young TDM (964-1090 Ma) ages. The mafic rocks might have resulted from the mixture of depleted mantle with crustal source. Meta-rhyolites are generally characterized by rich silicon, alkali and poor magnesium. They are characterized by enriched LREE, depleted HREE, noticeable negative Eu (δEu 0.12-0.43), Nb, Ta, Sr, P and Ti anomalies, relatively high U, Th and rather low Ba, Sr, Ti and P;the (La/Yb)N ratios are from 7.07 to 11.07, 87Sr/86Sr initial values are high (0.713757-0.739647), negativeεNd(t) values are low (-1.75 to+2.54) , and TDM ages are relatively young (846-1156 Ma);besides, most zircons have the positiveεHf(t) values (-2.3 to+6.9) and relatively young TDM ages (707-1074 Ma ). The felsic rocks show an A-type affinity and might have come from a juvenile crustal source. According to their geochemistry and previous regional geological studies, the late Devonian volcanic rocks are basalts and rhyolites, suggesting a typical bimodal volcanic rock association and implying an extensional setting.关键词
晚泥盆世/双峰式火山岩/伸展构造背景/内蒙古赤峰Key words
Late Devonian/bimodal volcanic rocks/extensional setting/Chifeng area分类
天文与地球科学引用本文复制引用
孙立新,张云,李影,张永,任邦方,张天福..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[J].中国地质,2017,44(2):371-388,18.基金项目
国家自然科学基金(41572172)和中国地质调查局项目(1212011121078)联合资助.Supported by Programs of National Natural Science Foundation (No. 41572172) and China Geological Survey (No. 1212011121078). （41572172）
