【作者】 刘金霖；

【导师】 王建；

【作者基本信息】 吉林大学 ， 地球化学， 2014， 博士

【摘要】 华北东部在奥陶纪存有厚达200km、以方辉橄榄岩为主的岩石圈根。到了新生代，前奥陶纪冷的、厚的岩石圈已被厚度为100km、新鲜而饱满的大洋型地幔所替代，岩石圈的去根、减薄这一事实已得到广泛认同，但在减薄机制等问题上仍存有很大争议。华北克拉通东北缘龙岗—长白山—宽甸地区及东北造山带阿尔山—柴河地区的新生代玄武岩中存有大量的地幔橄榄岩捕掳体，通过对这些捕掳体进行详细的岩相学、岩石地球化学特征的研究，可以揭示不同构造环境的陆下岩石圈地幔性质，通过对不同研究区地幔性质的对比讨论可以反演其陆下岩石圈地幔的不同演化历史与形成机制，这对探讨华北克拉通东部地区陆下岩石圈地幔性质转变的相关机制有重要的借鉴意义。本文选用了相关的先进实验测试技术对华北克拉通东北缘和东北造山带橄榄岩捕掳体全岩的主、微量元素以及矿物主、微量元素进行了分析测试，对分析结果进行了详细的岩石学及地球化学研究，并运用研究区陆下岩石圈地幔的氧化—还原状态参与讨论。研究结果表明，华北克拉通东北缘陆下岩石圈地幔以新生的大洋型地幔为主，其岩石圈地幔的氧逸度值与受软流圈影响的地幔相似，岩石圈地幔形成机制很可能是中生代以来，西太平洋板块和蒙古—鄂霍茨克洋板块分别向东和向南的复合俯冲作用，使得华北克拉通东北缘古老的岩石圈失衡、拆沉，取而代之的是下面热而饱满的软流圈物质的底劈、上涌，且太平洋板块自东向西的俯冲作用是岩石圈地幔拆沉的根本性因素。而东北造山带阿尔山—柴河地区保有相当量的古老地幔残余，表明其不存在类似华北克拉通东北缘地区对原生岩石圈地幔强烈的破坏和改造过程。更多还原

【Abstract】 It is one of the important scientific problems of deep Earth dynamicsto conduct inversion for the evolutionary history of the continentallithosphere. The changes have occurred in the nature, thickness andthermal state of the eastern lithosphere of North China Craton sincePaleozoic. Compared with the cratons in other areas of the world, NorthChina Craton reflects its own differences, and many geologists have fewcontroversies for the cognizance of this geological event. However,different points of view still exist in the time, mechanism and deepprocess of the occurrence of the great change. The previous studiesusually took the marginal areas of North China Craton as the studyhotspots, while the northeastern margin of North China Craton is close toPacific subduction plate and northeast orogenic belt, and obviously thestudy work on the nature of the mantle of the subcontinental lithosphereof the northeast orogenic belt similarly has important significance. Inview of this, in this paper, in addition that the peridotite xenoliths of theCenozoic basalts in Kuandian, Longgang and Changbai Mountain areas of the northeastern margin of North China Craton were selected as thestudy objects, we also selected the spinel phase peridotite xenoliths inAer-Chaihe area of northeast orogenic belt Daxinganling as the studyobject, conducted the studies on the nature and evolutionary process ofthe subcontinental lithosphere mantle under different tectonicenvironments through the detailed petrology and geochemistry as well asthe redox state (O2) of the mantle in the study area, and carried out thedetailed comparative study on the formation mechanism.The chemical characteristics of the major elements of the wholerock and minerals in the study area show that, the nature of the mantle ofthe northeastern margin of North China Craton overall is dominated bythe nascent oceanic mantle, while the Aer-Chaihe lithosphere mantleretains more remnants of ancient mantle. The equilibrium temperature ofthe study area also shows the following heterogeneity: The equilibriumtemperature of the peridotite in Longgang-Changbai Mountain-Kuandian areas of the northeastern margin of North China Craton is low,being close to the equilibrium temperature of the peridotite in Changleand Shanwang areas of eastern North China Craton; the equilibriumtemperature range of the mantle peridotite in Aer-Chaihe area is similarto the equilibrium temperature range of the peridotite in Hebi area ofHenan of North China Craton; both lherzolite and harzburgite have thedistinctions of high temperature and low temperature, the minority lowtemperature samples present the characteristics of the lithosphericmantle which accepts transformation; while the high temperaturelherzolite samples are speculated to be the results after the interactionbetween asthenosphere and lithosphere.The characteristics of the trace elements of the clinopyroxene in thestudy area show that, the overall partial melting degree of thenortheastern margin of North China Craton is similar to the low partial melting degree experienced by the nascent and full-type peridotite inShanwang area, besides, the northeastern margin of North China Cratonexperienced the metasomatism of low degree, and the metasomaticmedium was the silicate fluid/melt. The data of the Aer-Chaihe areashow that, the partial melting degree of most samples in the study area issimilar to that of the refractory and defective Hebi peridotite, showinghigh partial melting degree. The discussions about the metasomatism ofthe Aer-Chaihe study area show that, the metasomatic process of thestudy area is relatively complex, the main bodies of its metasomaticmedium are silicate fluids/melts, very few samples have the metasomaticresidues of carbonate melt and the metasomatic characteristics ofwater-rich fluids, and it is speculated that the water-rich fluids comefrom the deep asthenosphere, while not from the influence of the ancientsubduction slabs.The results of the discussions about the redox state of the mantle inthe study area show that, the range value of the oxygen fugacity (O2) ofthe subcontinental lithosphere mantle of the northeastern margin of NorthChina Craton is equivalent to the range value of the oxygen fugacity ofthe subcontinental lithosphere mantle affected by the asthenosphere, andit is speculated that the formation of the nascent mantle in the study areais related to the activities of the asthenosphere. However, the Aer-Chaihearea has a considerable number of the transition samples of thegarnet-spinel phase. After discussions, it is thought that, the oxygenfugacity calculated by using the peridotite samples which do not reach themineral chemical equilibrium (spinel-garnet transition samples) is invalid,and it cannot truly reflect the redox state of the mantle in the study area.The content characteristics of the pro-copper and pro-iron elementsof the subcontinental lithosphere mantle in Longgang-ChangbaiMountain-Kuandian areas of the northeastern margin of North China Craton show that, the sulfides are not the main occurrence matters ofPGE, while the alloys, silicate minerals and oxides are more inclined tobe the occurrence matters of PGE. The low content of Cu, S and PGEmay indicate that compared with other areas inside North China Craton,the nature of the mantle of the northeastern margin of North ChinaCraton is characterized by heterogeneity.After the discussions were conducted for the formation mechanismof the mantle in the study area, it is thought that, the respectivelyeastward and southward composite subduction of western Pacific plateand Mongolia-Okhotsk oceanic plate result in the imbalance anddelamination of the ancient lithosphere of the northeastern margin ofNorth China Craton, while cause the diapir and upwelling of the hot andfull asthenosphere substances below, thereby leading to the formation ofthe nascent lithosphere mantle of the northeastern margin of North ChinaCraton. Besides, the eastward and westward subduction of westernPacific plate is the fundamental factor of the delamination of thelithosphere mantle. However, the processes which are similar to thedestruction and transformation of the northeastern margin of North ChinaCraton for the protogenetic lithosphere mantle do not exist in thelithosphere mantle of the Aer-Chaihe area. The phenomenon that thestudy area retains a considerable number of ancient lithosphere mantleshow that the evolutionary history of the lithosphere mantle of theAer-Chaihe area significantly differs from the destruction and activationprocesses experienced by the northeastern margin of North China Craton.更多还原