【作者】 叶浩；

【导师】 赵越； 张拴宏；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2014， 博士

【摘要】 华北克拉通是地质研究的热点地区,国内外学者就这一地区早前寒武纪克拉通化和中-新生代的克拉通破坏问题开展了大量的研究工作,取得了许多重要的研究成果。华北克拉通北缘具有漫长的大陆边缘演化历史,近年来的主要研究成果是对该地区晚古生代构造格架的廓清,但是对华北北缘中生代早期构造背景的认识还存在一定争议。中生代早期是华北克拉通北部古亚洲洋关闭,进入板内造山阶段的重要转折时期。深入研究该时期华北北缘地壳深部岩浆活动与浅部构造变形有助于更好的理解两大陆块拼合之后构造体制转变的深部背景,以及浅部地质与深部壳、幔及岩石圈、软流圈之间是如何相互作用的。本文主要开展了以下几个方面的研究工作：(1)以华北北缘早中生代不同时期火山岩为研究对象,运用锆石U-Pb测年、岩石地球化学等手段,对火山岩喷发时代、岩石成因及其反映的深部构造过程进行了研究；(2)对蓟县盘山地区和北京西山地区中生代早期构造变形的时代进行同位素年代学限定；(3)以冀东晚三叠世都山复式岩基为例,研究其侵位变形和岩石成因,从不同角度认识华北北缘中生代早期深部和浅部地质过程。通过本论文的研究,取得一些新的认识及进展,主要包括以下几个方面：1.除大量侵入岩外,华北克拉通北缘中生代早期发育两套火山岩组合：二叠纪末-早三叠世火山岩形成时代介于245-255Ma,主要为流纹质岩石；中-晚三叠世火山岩形成于228-238Ma,主要为安山质岩石和少量流纹岩。早期火山岩可能是通过古老下地壳熔融并分离结晶形成的,而晚期火山岩则可能是软流圈地幔上涌,引起岩石圈地幔和古老下地壳熔融混合之后形成的。2.盘山岩体侵位造成了周缘向斜(府君山向斜、庄果峪向斜和水峪向斜)的形成并明显改造了早期区域近东西向褶皱。在盘山岩体北侧的红石坎背斜和西大峪向斜的两翼可以观察到褶皱的花岗斑岩岩席,它们分别给出214±3Ma和213±2Ma的锆石U-Pb年龄。盘山岩体是一个典型的复式岩体,已发表的SHRIMP U-Pb数据给出206Ma的加权平均年龄,代表峰期年龄,而狼家峪单元稍早,为210Ma。因此,区域褶皱变形的时代在210-213Ma之间。蓟县断裂明显错断和改造了君山向斜和庄果峪向斜,并被盘山岩体穿刺,因此蓟县断裂的活动发生在210Ma前后,并可能延续到大约206Ma。3.北京西山青白口背斜南翼奥陶系灰岩被“南大岭组”火山岩以微角度不整合覆盖,根据背斜核部顺层闪长玢岩床和“南大岭组”安山质凝灰岩的锆石U-Pb定年将青白口背斜隆起的起始时代限定在170～177Ma。但从整个盆地边缘来看,早侏罗统地层与下伏地层之间的角度不整合不明显,仅在局部地区发育。因此北京西山中生代早期构造变动并不强烈,其主要构造格局在燕山期形成。4.都山复式岩基包括南部变形较强的的都山岩体和北部弱变形的大石柱岩体。新获得的锆石LA-ICP-MS U-Pb年龄结果显示都山岩体和大石柱岩体侵位时代在误差范围内一致(～220Ma)。岩体变形特征初步调查表明都山岩体可能是通过主动膨胀方式侵位的,记录了区域晚三叠世挤压构造背景。而岩石学研究表明都山岩基是在岩石圈伸展体制下形成的,因此,华北北缘中生代早期构造体制在时间和深度上存在解耦,挤压构造应力可能在岩石圈伸展后很长一段时间内仍在上地壳或地表持续作用,显示了时间上的滞后性。更多还原

【Abstract】 The North China Craton (NCC) has become a hotspot of geological research and attracted more and more researchers from both domestic and abroad. A lot of studies have been carried out on Precambrian cratonization and Phanerozoic decratonization processes, and much progress has been achieved. The northern margin of NCC has a long continental margin history from Mesoproterozoic to Late Paleozoic. Recent researches on the northern margin of the NCC have been mainly focused on the late Paleozoic tectonic events. However, the tectonic setting during the early Mesozoic is still in dispute.Early Mesozoic period is a key stage after closure of the Paleo-Asian Ocean and the northern margin of the NCC entered into an intra-plate tectonic setting. Therefore, studying the early Mesozoic magmatism and deformation in the northern NCC is of great importance to understanding the geodynamic processes after the final closure of the Paleo-Asian Ocean and amalgamation between the Mongolian arc terranes and the NCC along the Solonker suture.The main contents of this thesis include:(1) Zircon U-Pb dating, whole rock geochemical and isotopic analysis and in-situ zircon Lu-Hf analysis were performed on contrasting latest Permian-Triassic volcanic rock suites from the northern NCC;(2) Based on field profile observation and isotopic dating, Early Mesozoic deformation in the Panshan area and the Western Hills of Beijing were established;(3) Petrogenesis and emplacement deformation of the Dushan composite batholith was studied in order to better understand the geological setting of the northern NCC during the Early Mesozoic time.The main advancements achieved from the thesis are as follows:1. There are two contrasting volcanic rock suites in the northern NCC during the latest Permian-Triassic. The earlier volcanic rock suite erupted during the latest Permian to Early Triassic at ca.245～255Ma and was composed of rhyolitic rocks. The later suite erupted during the Middle to Late Triassic at ca.228～238Ma and composed of andesitic rocks and minor rhyolitic rocks. Geochemical and isotopic data revealed that the latest Permian to Early Triassic volcanic rocks were likely produced by fractional crystallization of ancient lower crustal-derived magmas. However, the Middle to Late Triassic suites is mainly derived from lithospheric mantle and ancient crust, with minor involvement of asthonospheric mantle.2. The intrusion of the Panshan composite pluton resulted in formation of the U-shaped synclines (e.g. the Fujunshan syncline, the Zhuangguoyu syncline and the Shuiyu syncline). On the map scale, the U-shaped synclines obviously superimpose on the earlier regional east-west trending Malanyu anticlinorium fold. There are two folded granitic porphyry sheets in both Hongshikan anticline and Xidayu syncline in the western plunging zone of the Malanyu anticlinorium. Zircon U-Pb dating for these granitic porphyry sheets yield214±3Ma and213±2 Ma, respectively. The Panshan composite pluton emplaced during the late Triassic, with peak at about206Ma. The Langjiayu unit emplaced earlier, at about210Ma. Therefore, regional folding time can be constrained between210～213Ma. The Jixian thrust fault truncates the Fujunshan syncline and the Zhuangguoyu syncline, and then intruded by later emplacement of the Panshan composite pluton. The Jixian thrust fault may activate simultaneously with the intrusion of the Panshan pluton, and may last to～206Ma.3. On the southern limb of the Qingbaikou anticline (dome) in the Western Hills of Beijing, there is an angular unconformity between the upper Nandaling Formation and the lower Ordovician limestone. By dating the bed parallel dioritic sills in the core of the Qingbaikou anticline and andesitic tuff from the Nandaling Formation, the initial deformation time of the Qingbaikou anticline can be constrained between170～177Ma. Considering that the angular unconformity beneath the Nandaling Formation is local and it is parallel unconformity between lower Jurassic strata and underlying formations at most area of the Western Hills of Beijing, we proposed that the Early Mesozoic deformation is relatively weak in the Western Hills of Beijing.4. The Dushan composite batholith consists of the southern deformed Dushan pluton and the northern undeformed Dashizhu pluton. New zircon LA-ICP-MS U-Pb data indicate that the Dushan pluton and the Dashizhu pluton have the same emplacement ages within the limit of error. Deformation analysis on the Dushan pluton show that it formed by stoping and expansion in a contraction tectonic stress field during its emplacement. However, petrogenesis studies the Dushan composite batholith and the alkaline complexes in the northern NCC reveals that they were formed in a lithospheric scale extension setting, with upwelling of asthonosphere mantle. Therefore, the deep and superficial process may have decoupled during the early Mesozoic time in the northern margin of the NCC, and contraction deformation may last for a long time after closure of the Paleo-Asian Ocean.更多还原