【作者】 钟长汀；

【导师】 邓晋福；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2006， 博士

【摘要】 华北克拉通北缘中段古元古代花岗岩可分为埃达克质(adakitic)花岗岩、赞岐状岩(sanukitoids)、Closepet花岗岩、富Nb辉长岩、黑云母花岗岩-正长岩和强过铝(SP)花岗岩等。这些花岗岩在区域上成带状分布:埃达克质花岗岩-赞岐状岩组合主要分布于固阳-武川断裂南北两侧,赞岐状岩和Closepet花岗岩组合主要分布于固阳-武川断裂与大青山山前断裂之间,SP型花岗岩主要分布于大青山山前断裂南侧,少量分布于乌拉山哈达门沟一带。此外,还发育有古元古代变中基性火山岩。这些变中基性火山岩原岩主要为玄武岩、安山岩和英安岩。部分变中基性火山岩地球化学特征显示具有镁质安山岩(MA,MgO≈6%)、埃达克岩和富Nb玄武岩(NEB, 7 <Nb<20×10-6)/高Nb玄武岩(HNB,Nb>20×10-6)的岩石化学特征。地球化学模型显示,埃达克质花岗岩形成于俯冲作用早期板片熔融,为基性岩在含石榴石角闪岩相和榴辉岩相过渡条件下发生熔融,石榴子石和角闪石在残留相保留。在大青山,高压麻粒岩可能就是其残留体。赞岐状岩(sanukitiods)是由于埃达克质岩浆在其上升过程中和地幔橄榄岩进行混染,由于其地幔物质的加入,使其Mg质和过渡元素Cr、Ni等元素也显著增加。在俯冲作用的中晚期由于地壳物质的加入,使其钾质含量、大离子亲石元素增加,形成Closepet花岗岩。被埃达克质岩浆交代的地幔橄榄岩的熔融形成富Nb玄武岩(NEB)熔浆,在其未喷出地表时则形成富Nb辉长岩。黑云母花岗岩,主要是深熔花岗岩;正长花岗岩-二长花岗岩,属A型花岗岩。SP花岗岩是原地、半原地地壳物质熔融的产物。地球化学特征显示,南部SP花岗岩具有澳大利亚拉克伦造山带的特点,是一热(>875℃)环境形成,其原岩主要为成熟度不高的杂砂岩为主,同时还有少量粘土岩。是碰撞峰期后岩石圈伸展的产物。利用SHRIMP和TIMS方法,在华北克拉通北缘中段取得了如下年龄:埃达克质花岗岩,2435±16Ma;赞岐状岩(sanukitoids),2426±41Ma;Closepet花岗岩,2416～2330Ma年龄;富Nb辉长岩,1845±14Ma;SP花岗岩具有两组年龄:凉城-和林格尔一带1904~1933Ma;乌拉山SP花岗岩,2438±43Ma～2231±17Ma。在原一直认为是中太古代~新太古代的变质火山岩(乌拉山群)取得1953~1967Ma的锆石U-Pb SHRIMP年龄(王惠初等,未刊资料)。深熔黑云母花岗岩锆石U-Pb同位素也显示两组年龄:2277-1953Ma和1853~1803Ma。通过对本地区古元古代埃达克质花岗岩-赞岐状岩(sanukitoids)-Closepet花岗岩,黑云母花岗岩、SP花岗岩和正长岩地球化学特征、同位素年代学研究,认为华北克拉通北缘古元古代发生了和现代俯冲作用机制一样的俯冲作用,并认为本区古元古代存在2期造山作用,其时限分别为～2.3Ga和~1.9Ga。这些花岗岩代表古元古代华北克拉通北缘从俯冲、碰撞造山、造山后抬升和伸展作用不同阶段的岩浆岩组合。通过研究认为华北克拉通克拉通化开始于～2.3Ga,最终完成时间约1.9Ga。吕梁运动(~1.9Ga )在本区是一次重要的造山作用,该造山运动时间(2.3~1.9Ga)和其后的裂解(1.84~1.74Ga)作用时间,和Clumbia超大陆的汇聚和裂解时限基本一致。本研究从岩浆岩在造山带演化,研究了华北克拉通古元古代造山作用从俯冲-碰撞造山-造山后抬升和伸展过程。为研究华北前寒武纪构造演化,确定Columbia超大陆的性质,吕梁运动的性质等方面具有重要的意义。更多还原

【Abstract】 The PaleoProterozoic granitoids are generally classified into six types as adakitic granitoids,sanukitiods, Closepet type granitoids, Nb-enriched gabbros (NEG), Biotite-bearing granites and stronglyperaluminous granites in the central segment of North China craton (CSNCR). The adakitic granitoids andsanukitoids are occrenced northern and southern region along the Guyang-Wuchuan fault;sanukitoids andClosepet-type granites are occreenced middle region between Guyang-Wuchuan fault and Daqingshanmountain front fault;and strongly peralumious (SP) granitoids are mainly occenced south region alongJining-Liangcheng-Helingeer-Helanshan Mountain. Furthermore, they are usually company with themetamorphic intermedial-basic volcanic rocks as basalts and andesites, sometimes dacites. The some ofmetamorphic volcanic rocks are chemically characterized by relatively high MgO content and transitionmetals element (such Cr and Ni), and depleted in high field strength element (HFSE). They are like adkites,Nb-reriched basalts (NEB, 7 <Nb<20×10-6)/high Nb basalts (HNB, Nb>20×10-6) and magnesian andesites(MA, MgO≈6%).Adakites are generally suggested producing slab melt in the early collision. Geochemical modellingshows that the source of adakites cannot be ultramafic but rather basaltic in composition. This implies thatadakitic magmas are produced by melting of a basaltic source transformed into garnet-bearing amphiboliteor eclogite such that garnet±hornblende could be residual phases. In Daqingshan area, the high-pressuregranulite may be the residual phases. Sanukitoids genesis model was proposed that an adakitic melt risingthrough peridotite is able to assimilate olivine, resulting in a “hybridised slab melt”. Which increased speedMg#, Cr and Ni in melt. Closepet-type granite is commonly late-to post-kinematic and generally associatesthe matter of crustal, which increased K and other LILE. And the Nb-enriched gabbros (NEGs) aresuggested that intruded on low crustal from the melt of peridotite hybridesed adakitic melt. Biotite-bearinggranites (BBG) are mostly anatectic granites, monzogranites and syenogranite are A-type granite.According to SHRIMP and TIMS, we have attained lots of ages for different kinds granitoids in NCR:adakitic granitoid is 2435±16Ma;sanukitoids are 2426±41Ma;Closepet granites are 2416~2330Ma;andNEG is 1845±16Ma. The SP granites are 1904 to 1933 Ma in south, but that is 2231Ma to 2438Ma in thenorth. And, the BBG and A-type granite are two stages (2277-1953Ma and 1853~1803Ma). However,Wanghuichun et al. (unpublished data) has obtained U-Pb zircon SHRIMP age for Wulashan amphibolitesuggested as middle to new Archean in past literature from the southwest of Guyang that are1953~1967Ma.Base on the geochemistry, petrology and geochronology of the Paleoproterozoic granitoids, wesuggested that subduction bearing an analogy to modern plate has taken on the Paleoproterozoic in NCR.We suggested it has two orogenic episodes, which are ~2.3Ga and ~1.9Ga. And adakitic granitoids/adkties,sanukitoids/HMA, closepet-type granites and other granites are producted with the process of subduction –collision – orogeny – uplift – extension. After studying the magma rock assemblage, we suggested thecraton time is started in ~2.3Ga, and finished in ~1.9Ga. Lüliang movement (~1.9Ga) is very importantorogenics in CSNCR, which orogenic movement time (2.3~1.9Ga) and post-orogenic cracking time(1.84~1.74) are similar to the converging and cracking time of Columbia suppercontinent. It is significantlyto studying the crustal evolution, the characteristics of Lüliang movement and paleoproterozoic Columbiasuppercontinent.更多还原