【作者】 李晓勇；

【导师】 范蔚茗；

【作者基本信息】 中国科学院研究生院（广州地球化学研究所） ， 构造地质学， 2003， 博士

【摘要】 论文通过对燕山地区中生代火山岩，特别是中基性火山岩，进行详细而系统的岩石学、主微量元素地球化学特征和Sr-Nd同位素组成特征的研究，主要取得了以下研究成果： 1 燕山地区中生代(J-K)火山岩为一套钙碱性-高钾钙碱性-橄榄安粗岩系列岩石。中基性火山岩稀土配分模式为富集LREE的右倾型，富集LILE(如K、Ba)，Sr变化较大、亏损HFSE(如Nb、Ta)。在中酸性火山岩系列中，张家口组火山岩表现出中等-强烈的Eu负异常和不同程度的Sr、Ti、P负异常；东岭台组火山岩表现出富集LREE和平坦的HREE的稀土配分模式，Nb／Ta分馏，高Zr／Sm比值。在Sr-Nd同位素组成上，中基性火山岩为中等富集的Sr和低的Nd同位素比值；中酸性火山岩的Sr同位素比值总体较中基性岩高且变化大，类似华北陆块下地壳岩石的同位素组成特征。 2 燕山地区早侏罗世中基性火山岩来自于早期俯冲交代的古老岩石圈地幔部分熔融作用，俯冲交代作用可能与早期古亚洲洋闭合事件有关；晚侏罗世中基性火山岩更多来自于类似于EMI型地幔源区的部分熔融作用，俯冲交代成分贡献很弱；早白垩世基性火山岩则来自于EMI型地幔源区的部分熔融作用。燕山地区中酸性火山岩则来源于地壳，与玄武质岩浆底侵作用关系密切。 3 燕山地区火山岩源区组分在时空上具有一定的演化规律：在时间上，从早期俯冲交代地幔及EMI的参与，经中期以EMI占主导及极少量俯冲交代组分的阶段，演变到晚期以EMI为主，可能有少量软流圈贡献的组分，再到晚白垩世以软流圈为主。古亚洲洋俯冲板块对古老岩石圈的交代作用在岩石圈减薄和置换过程中起了很重要的作用。在空间上，燕山地区中基性火山岩熔融地幔源区与邻区华北陆块和兴蒙造山对比表现出过渡的性质：从鲁西→燕山地区→兴蒙造山带，源区具有由华北陆块EMI型古老岩石圈地幔→EMI+／-俯冲交代组分→向俯冲交代岩石圈地幔转变的特征。 4 燕山地区特有的相对“易熔”的岩石圈性质，所处的特殊的构造位置及发育的深大断裂，可以较好的解释该地区发生贯穿整个中生代的火山活动和构造变形的可能性。 5 燕山地区岩浆活动与构造事件有较好的偶合关系，其构造岩浆活动可能是板块相互作用和深部岩石圈活动的共同结果。更多还原

【Abstract】 On the basis of detailed and systematic studies on the petrography, major and trace elements and Sr-Nd isotopic data of Mesozoic volcanic rocks, especially the mafic volcanic rocks in Yanshan area, we successfully studied the deep processes related to magma generation and their relationship with shallow-level tectonic evolution. The major conclusions are summarized as below.1. The Mesozoic volcanic rocks in Yanshan area comprise a wide spectrum of rock types including calc-alkaline, high-K calc-alkaline and shoshonitic lava. All mafic rocks show significant enrichment in LREE, LILE and depletion in HFSE with variable Sr anomalies. Among the felsic rocks, samples from the Zhangjiakou Formation (Fm.) are characterized by moderately to strongly Eu anomalies, and variable negative anomaly of Sr, Ti and P, whereas samples from the Donglingtai Fm. exhibit enriched LREE and flat HREE patterns with Nb/Ta fractionation and high Zr/Sm ratios. All of the mafic samples have age-corrected moderate enriched Sr and enriched Nd isotopic ratios and the felsic rocks span larger range in the initial Sr and Nd isotopic ratios than mafic volcanics, similar to isotopic compositions of lower crust of North China Block.2. Early Jurassic mafic volcanic rocks in Yanshan area were derived from decompression melting of an ancient continental lithospheric mantle, which had been previously metasomatized by subducted slabs during the closure of Paleo-Asian Ocean; the mantle source of late Jurassic mafic volcanic rocks were contributed by dominant EMI and insignificant subducted Metasomatic components; Early Cretaceous mafic volcanic rocks were derived from decompression melting of an ancient continental lithospheric mantle (EMI). With regard to the basaltic lavas, the felsic rocks resulted from partial melting of continental crust, which closely related to basaltic underplating.3. The mantle source for the Mesozoic mafic volcanic rocks in Yanshan area exhibit transition character in space and time: the mantle source components vary from subduction-related metasomatic components and EMI components throughdominant EMI components and slight subduction-related metasomatic components to EMI components; spatially, mantle source of the volcanic rocks show a regular variation trend from an enriched lithospheric mantle with EMI-like signatures in the western Shandong province through EMI and/or subduction-related metasomatic components in Yanshan area to subduction-related metasomatic lithospheric mantle in the Hinggan-Mongolian Orogen.4. The relative fertile lithospheric characters of Yanshan area, unique plate tectonic situation and developed deep faults can explain reasons of the volcanism and tectonic events in Yanshan area throughout the Mesozoic.5. The Mesozoic volcanism in Yanshan area temporarily and spatially corresponds with the regional tectonic events, which might be a consequence of deep lithospheric processes and multi-plate interaction.更多还原