【作者】 公王斌；

【导师】 胡健民；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2014， 博士

【摘要】 华北克拉通是中国大陆面积最大的克拉通,同时也是世界上最古老的克拉通之一,经历了多阶段复杂的前寒武纪构造演化过程,记录了几乎所有地球早期的重大地质事件,包括陆壳的巨量生长、地球环境的突变和构造体制的转变等。对于华北克拉通前寒武纪构造演化,虽然前人提出了多种不同的模型,但是对古元古代末华北克拉通发生的碰撞造山事件及中元古代约1.80Ga开始的伸展裂解事件已基本达成共识。而古元古代末构造变形特征由挤压向伸展的转换时期也是华北克拉通前寒武纪构造演化的关键阶段,对其进行研究具有重要意义：首先,前人对碰撞造山之后至伸展裂解之前约1.85-1.80Ga构造变形及构造演化的研究很少,制约了对华北克拉通古元古代构造格局与演化及构造体制的认识；其次,中元古代之后华北整体处于相对稳定的地台状态,古元古代构造演化奠定了华北克拉通中-新元古代成矿的构造格局；第三,古元古代可能是前寒武纪构造体制由非板块构造体制向现代板块构造体制的转换期,该时期构造变形特征的研究可确定该时期华北克拉通是否受板块构造所控制。华北克拉通西部由多个块体沿碰撞造山带拼合而成,这种稳定的刚性块体与活动造山带的组合,可为认识古元古代华北克拉通构造变形特征及构造体制提供重要信息。前人研究表明古元古代造山带中发育的一系列韧性剪切变形带多形成于古元古代末,基本一致的形成时间表明这些韧性剪切带可能具有成因联系,是研究古元古代末华北克拉通碰撞造山后构造变形的理想对象。本文在前人研究的基础上,以构造分析为主线,通过野外地质调查、室内显微分析、锆石U-Pb测年、变形矿物Ar-Ar测年等方法,对华北克拉通西部鄂尔多斯地块西缘、北缘及东缘韧性剪切带的变形特征及变形时间进行了系统研究。其中北缘乌拉山-大青山韧性剪切带走向近EW,以右行走滑剪切为主；西缘宗别立剪切带走向近NE-NEE,上盘自SE向NW逆冲；东缘贺兰山雪岭剪切带走向近NE-NNE,上盘自NW向SE逆冲,具有弱的左行走滑剪切分量。变形矿物40Ar/39Ar及同构造花岗质脉体测年结果表明以上剪切带均形成于1.85-1.80Ga。相似的变形时间表明这些几何学与运动学特征不同的韧性剪切带具有成因联系。构造分析显示鄂尔多斯地块西缘宗别立韧性剪切带向NE方向的延伸很可能与北缘乌拉山-大青山韧性剪切带相连,构成鄂尔多斯地块的西北边界：吕梁山雪岭剪切带向NE延伸可能与恒山杂岩中的朱家房左行走滑剪切带相连,构成鄂尔多斯地块的东界。根据剪切带的变形时间、几何学和运动学特征,这些剪切带共同限定鄂尔多斯地块在古元古代末约1.85-1.80Ga可能发生了向SW方向的构造挤出。现代板块构造体制中,碰撞造山之后会发生不同程度的陆内构造活动,表现为陆内造山、陆内造盆和微陆块的横向和纵向逃逸等。古元古代末华北克拉通西部鄂尔多斯地块向SW挤出是否表现为陆内变形,可限定该时期华北克拉通是否受板块构造体制所控制,而这又取决于鄂尔多斯地块与周缘块体的关系。鄂尔多斯地块的北缘及东缘受古元古代造山带所限,分别与阴山地块和东部陆块相接。而古元古代末鄂尔多斯地块西缘是否与阿拉善地块相连仍存在争议,本文通过阿拉善地块东北缘毗邻华北克拉通的狼山地区新元古代狼山群的锆石测年分析,及阿拉善与华北克拉通前寒武纪沉积岩的碎屑锆石年龄组成特征对比和岩浆岩锆石年龄对比等,限定了二者具有相似的构造-热事件,即古元古代末华北克拉通西缘与阿拉善地块相连,表明鄂尔多斯地块西缘为陆内环境。鄂尔多斯地块西南缘是否与其他大陆相连决定是否存在块体向SW运动的空间,鄂尔多斯地块西南部发育的中元古界长城-蓟县系,以砂岩为主,未见与燕辽裂谷系、熊耳裂陷槽相似的裂谷相关火山岩,其碎屑锆石U-Pb年龄组成特征与华北克拉通前中-新元古代沉积岩一致,反映其物源均来自华北克拉通内部,表明该区不存在中元古代裂谷,据此推测古元古代华北克拉通西南缘不与其他大陆相连,存在鄂尔多斯地块向西南方向挤出的空间。本文研究表明,古元古代末华北克拉通西部鄂尔多斯地块西缘、北缘及东缘均为陆内环境,而西南缘不与其他大陆相连,约1.85-1.80Ga发生了以鄂尔多斯地块向应力较小的SW向挤出为主的陆内构造变形。该研究成果填补了华北克拉通1.85-1.80Ga构造变形及构造演化研究的空白,古元古代晚期华北克拉通所经历的碰撞造山事件及之后的陆内变形共同表明该时期华北克拉通已经受板块构造体制的控制。古元古代华北克拉通的碰撞造山及陆内变形均与哥伦比亚超大陆的聚合过程有关,由此可进一步推断在哥伦比亚超大陆聚合过程中,碰撞造山之后也可能存在广泛的横向及纵向的块体逃逸。更多还原

【Abstract】 The North China Craton (NCC) is the largest craton in the China continent, and is one of the oldest cratonic blocks in the world. The NCC experienced multiple tectonic events and complex Precambrian tectonic evolution and record most of the significant tectonic events happened in the early history of the world, including the enormous crustal growth, the great oxygen event and the tectonic regime inversion from pre-plate tectonics to plate tectonics.The definition of Paleoproterozoic continent-continent collisional and orogenic events and the Mesoproterozoic extension rifting events initiated at about1.80Ga have been accepted by most of the researchers although various models have been postulated about the Precambrian tectonic evolution of the North China Craton (NCC). It is significant to study the characteristics of structural deformation and tectonic evolution of the NCC in the late for the following reasons. Firstly, the structural deformation and tectonic evolution between the orogeny at about1.85Ga and the rifting initiated at about1.80Ga been scarely studied, which have limited the understanding of the tectonic framework, evolution and mechanism of the NCC in the Paleoproterozoic. Secondly, the tectonic evolution in the late Paleoproterozoic controlled the tectonic framework of Meso-to Neo-proterozoic. Thirdly, the most important is the Paleoproterozoic might be the period of the tectonic regime inversion from pre-plate tectonics to plate tectonics, the study of the characteristics of structural deformation in the late Paleoproterozoic is helpful for confirming whether the NCC was controlled by the plate tectonic regim.The western part of the NCC is composed by several blocks which amalgamated along the collision orogenic belts, the combination of stable rigidity blocks and active orogenic belts could provide significant informations for understanding the characteristics of structural deformation and tectonic regim.A series of large scale ductile shear zones developed in the Paleoproterozoic orogenic belts in the NCC. Previous studies have shown that these ductile shear zones formed in the late Paleoproterozoic. The similar deformation ages indicate that the ductile shear zones might be genetically correlated, and are significant for studing the post orogeny structural deformation of the NCC.The characteristics and deformation ages of the ductile shear zones developed in the west, north and east margin of the Ordos block have been studied systematically through field investigation, mircro-structural analysis, zircon U-Pb dating and deformed mineral Ar-Ar dating. On the north margin of the Ordos block, the E-W trending Wulashan-Daqingshan ductile shear zone is characterized by dextral strike-slip shearing kinematics. On the west margin, the NE-NEE trending Zongbieli ductile shear zone is characterized by top-to-the-NW thrusting kinematics. On the east margin, the NE trending Xueling ductile shear zone is characterized by top-to-the-SE thrusting accompanied by sinistral strike-slip shearing. The40Ar-39Ar ages of deformed minerals from mylonites and LA-ICP-MS U-Pb dating results of zircons from syn-tectonic anatectic granites reflected that the ductile shear zones surrounding the Ordos block deformed between1.85and1.81Ga. The geometry, kinematics and geochronology characteristics of these ductile shear zones might defined the possible southwestward extrusion of the Ordos block in the late Paleoproterozoic (about1.85-1.80Ga).The extruded Ordos block was bounded on the northwest by the Zongbieli ductile shear zone which extended to the NE and connected with the Wulashan-Daqingshan ductile shear zone, and on the east by the Xueling ductile shear zone which extended to the NE and connected with the sinistral ductile shearing Zhujiafang shear zone.Under the modern palte tectonic mechanism, intracontinental tectonic movements including the intracontinental orogeny, intracontinental basining and the lateral and vertical extrusion of micro blocks would be initiated after the collision orogenic event. Whether the NCC was controlled by the plate tectonic mechanism was depended on the definition of intracontinent movement of the Ordos block in the late Paleoproterozoic, which was depended on the relationships of the Ordos block with its sorrunding blocks. The Yinshan block and Eastern block were connected to the Ordos block on the north and east, respectively. However, the relationship between the NCC and the Alax block in the late Paleoproterozoic was controversial and analysed by this work. Analysis of the zricon U-Pb dating results of the Langshan Group located at the neighbouring of the northeast margin of the Alax block and north margin of the NCC, and comprision of the detrital zircon U-Pb age compositions of the Precambrian sedimentary rocks developed in the Alax block and the NCC indicated that both of which have experienced similar tectonothermal events, which means that the Alax block was connected to the west margin of the NCC in the late Paleoproterozoic, and the west margin of the Ordos block was an intracontinental environment. And if there was space for the extrusion of the Ordos block depending on whether the NCC was connected with other blocks on the southwest margin. The Mesoproterozoic Changcheng-Jixian group developed in the southwestern part of the Ordos block is composed mainly by sandstones, and no rift related volcanic rocks similar to the Yanliao rift system and the Xiong’er rift system have been founded. Detrital zircon U-Pb age composition of the Changcheng-Jixian group in the southwestern part of the Ordos block was similar to which of the Meso-to Neo-proterozoic sedimentary rocks in the NCC, which indicated that the detritus were from the interior of the NCC. Both of this evidences indicated that no Mesoproterozoic rift system has developed in the southwest margin of the NCC. The conclusion of southwest margin of the NCC was not joined with other continents in the late Paleoproterozoic could be inferred, which offered the space of the extrusion.The west, north and east margin of the Ordos block in the western part of the NCC were in the intracontinental environment in the late Paleoproterozoic, whereas it was not connected with other blocks on the southwest margin. The western part of the NCC experienced intracontinental deformation represented by the SW extrusion of the Ordos block after the orogenic events at about1.85Ga. The results of this work defined the structural deformation and tectonic evolution of the NCC after the Paleoproterozoic orogeny at about1.85and before the Mesoproterozoic rifting at about1.80Ga. The combination of the orogenic events in the Paleoproterozoic and the post-orogenic intracontinent deformation indicated that the NCC has been controlled by the plate tectonic mechanism in the Paleoproterozoic. The structural deformation and tectonic evolution of the NCC in the Paleoproterozoic was correlated with the amalgamation of the Columbia supercontinent, which indicated that lateral and vertical extrusion of blocks might have happened after the orogeny in the Columbia super continent.更多还原