综合华北克拉通西部陆块阴山地块、孔兹岩带和鄂尔多斯地块基底正、副片麻岩以及鄂尔多斯地块现代河流沙锆石U-Pb和Hf同位素资料,并根据最新获得的鄂尔多斯基底及盖层继承碎屑锆石U-Pb年龄及Hf同位素统计分析揭示,该陆块存在古、中太古代陆壳物质,自新太古代以来先后发生了新太古代～2.7Ga、2.55～2.45Ga以及古元古代2.2 ～ 2.0Ga和1.95～ 1.85Ga等多期构造热事件.由基底和盖层中各类岩石中获得的～2.5Ga锆石的εHf(t)多为正值,Hf陆壳模式年龄(tDMC)介于2.9 ～2.6Ga之间(峰值～2.75Ga),阴山地块存在～2.7Ga的岩石,鄂尔多斯地块基底有～2.7Ga继承锆石记录,证明新太古代存在一期重要的陆壳生长.2.55～2.45 Ga的岩浆活动在西部陆块不同地质单元基底岩石中均有记录,出现大量壳源花岗岩和幔源岩浆侵入及麻粒岩相变质作用,它们的锆石εHf(t)值由负到正变化大,Hf陆壳模式年龄(tDM)除少数接近岩浆活动年龄外,多数明显高于它们的形成年龄,指示了强烈的陆壳再造和一定陆壳生长,岩石组合及地球化学特征反映了汇聚挤压转为伸展环境,类似于华北陆块～2.5Ga广泛的岩浆变质事件及构造背景,揭示了不同陆块碰撞拼合而后转为伸展的构造演化过程.古元古代2.2 ～2.0Ga期间,沿鄂尔多斯地块北部及东部边缘出现大洋俯冲消减有关的陆缘弧花岗岩类,它们的锆石εHf(t)和tDMC值变化范围很大,表明在古元古代中晚期鄂尔多斯地块基底仍发生有陆壳增生和再造.此后在1.95～1.85Ga期间,沿鄂尔多斯地块北部的孔兹岩带和东部的中部构造带均发生顺时针P-T演化轨迹的变质作用,证明～1.95 Ga鄂尔多斯地块相继与北部阴山地块和东部陆块碰撞拼合为一体,至～ 1.85Ga发生陆壳抬升与伸展、发生陆壳物质减压熔融的强烈混合岩化和大量S型花岗岩形成,其后发生镁铁质岩墙侵入,标志着华北陆块最终克拉通化完成.%The new zircon U-Pb geochronological and in-situ Hf isotopic data from the detrital zircons of the Ordos basement paragneisses and cover sandstones,combined with previous zircon U-Pb geochronology and Hf isotopic data from the Yinshan Block,Khondalite Belt and Ordos Block in the Western Block of the North China Craton (NCC),reveal that there were Paleo-mid Archean crustal materials in West Block,which underwent several tectonic-thermal events of ～2.7Ga,2.55 ～ 2.45Ga,2.2 ～2.0Ga and 1.95～ 1.85Ga from Neoarchean to Paleoproterozoic,respectivly.Of Which,most of ～ 2.5Ga zircons from the various rocks in the basement and covers have positive εHf(t) values and wide range of Hf crust model ages (tD~M) from 2.6Ga to 2.9Ga with a peaking at 2.75Ga.In addition,the ～2.7Ga gneisse have been found in Yinshan Block and ～2.7Ga crustal materials have been also recognized in Ordos basement.All indicate an important juvenile crustal growth at 2.8 ～ 2.7Ga.Aboundent crust-and mantle-derived magmatism widely occurred in the basement of West Block during 2.55 ～ 2.45Ga,and they recorded a nearly coeval granulite facies metamorphism.Their εHf(t) values varies from negative to positive,and most t~M are evidently older than their forming ages and minor have the same,suggesting an extensive reworking associated with some juvenile crustal growth at ～2.5Ga.Their rock assemblages and geochemical fetures indicate a transition of tectonic setting from compression to extention during later Neoarckean-early Paleopreterozoic,much similar to those occurred widely within eastern North China Craton,implying an evolution processes from convergence to extention followed by the collision-amalgamation of the serveral micro-continental blocks.An oceanic plate subduction occurred along both of the northern and eastern margins to the Ordos Block in the 2.2 ～ 2.0Ga,and numerous arc-related granitoids Chad been formed.Their zircons have various εHf (t) from negative to positive values and wide range of tDMC,indicating continuous juvenile crustal growth and reworking of Ordos basement during midle-later Paleoperoterozoic.After that,the metamorphism with a clockwise P-T path occurred during 1.95 ～ 1.85Ga along the Khondalite Belt and Trans-North China Orogen,representive of the continent-continent collisional belts along which Ordos and Yinshan Block as well as Eastern Block amalgamated to form an uniform basement of North China Craton at ～ 1.95Ga,and then continental crust uplifted and extend at ～ 1.85Ga,resulting in magamatization and S-type granitic formation due to the decompression partial melting of crustal materails,which followed aboundent mafic dyke intrusion within all North China Craton,indicating completely final cratonilazition.
展开▼
