华北地块北缘泥盆纪岩浆活动及其构造背景

晚古生代—早中生代岩浆岩广泛分布在华北地块北缘，构成了沿华北地块北缘呈近东—西向分布的上千公里的岩浆岩带。泥盆纪岩浆岩作为其中的组成部分，虽然分布范围不及石炭—二叠纪岩浆岩广泛，但近十多年来随着研究工作的深入，越来越多的泥盆纪岩浆岩被发现，其构造背景及意义也逐渐引起重视。对华北地块北缘近年来发现的泥盆纪岩浆活动进行总结分析表明，泥盆纪岩浆活动时限在400~360 Ma左右，其中碱性侵入岩和基性—超基性侵入岩时代主要集中在400~380 Ma之间，沿华北地块北缘自东向西均有分布；火山岩则主要集中在400 Ma和360 Ma，主要分布在华北北缘东段的赤峰地区。泥盆纪侵入岩在岩石组合上以碱性杂岩及碱性花岗岩为主，其次为二长闪长岩、基性—超基性杂岩。泥盆纪火山岩则以变质流纹质火山岩—次火山岩—火山碎屑岩及变质玄武安山岩、玄武岩（斜长角闪岩）为主，总体上具有双峰式岩石组合特征。综合研究该地区构造演化历史及泥盆纪岩石组合、弱构造变形特征、岩石地球化学与同位素地球化学组成等，认为泥盆纪岩浆活动的形成与白乃庙岛弧和华北地块在晚志留世发生弧—陆碰撞后的伸展背景有关。华北北缘泥盆纪岩浆岩带的形成对于认识古生代期间地壳增生过程、方式及古亚洲洋最终闭合时间有重要科学意义。 

DEVONIAN MAGMATISM IN THE NORTHERN MARGIN OF THE NORTH CHINA BLOCK AND ITS TECTONIC SETTING

Late Paleozoic-early Mesozoic magmatic rocks are widespread along the northern margin of the North China Block and constitute an east-west belt that is about one thousand kilometers long. As a part of the late Paleozoic-early Mesozoic magmatic belt, the distribution of the Devonian magmatic rocks is not common as that of the Carboniferous-Permian magmatic rocks. However, in recent years, more and more Devonian magmatic rocks have been identified and their geological background and tectonic implications have been much more attractive than before. Our research in combined with previously published results indicate that the Devonian magantism along the northern North China Block occurred mainly during 400~360 Ma. Among them the Devonian alkaline intrusive rocks and mafic-ultramafic intrusive rocks are distributed along the northern North China Block from Guyang to Chifeng areas and their emplacement occurred mainly during 400~380 Ma. The Devonian volcanic rocks are mainly distributed in Chifeng area in the eastern part of the northern North China Block and their eruption occurred during two peaks at 400 Ma and 360 Ma, respectively. The Devonian intrusive rocks consist mainly of monzonite, syenite and alkaline granite with minor monzodiorite and mafic-ultramafic rocks. The Devonian volcanic rocks are composed mainly of metamorphic rhyolitic rocks and metamorphic basaltic andesite, metabasalt (plagioclase amphibolite) and exhibit characteristics of bimodal volcanic rocks. Rock association, weak deformation fabrics, and geochemical and isotopic characteristics of the Devonian magmatic rocks, as well as the tectonic evolution history suggest that formation of the Devonian magmatic rocks in the northern North China Block is related to post-collisional extension after arc-continental collision between the Bainaimiao arc and the northern North China Craton during the latest Silurian. The Devonian magmatic rocks identified from the northern North China Block in recent years are of great significance to better understand the continental crustal growth of the northern margin of North China Block during late Paleozoic period and timing for final closure of the Paleo-Asian ocean.