辽西医巫闾山地区瓦子峪变质核杂岩的厘定(英文)

以前未被发现的辽西医巫闾山地区瓦子峪变质核杂岩主要由一条向西倾的低角度正断层———瓦子峪拆离断层组成 ,它将由早白垩世沉积岩和火山岩组成的上盘与糜棱岩化和未变形的下盘分开。瓦子峪拆离断层 (以前称之为孙家湾—稍户营子断裂 )位于变质核杂岩的西侧 ,倾角 10～ 4 0°,构造标志指示向北西方向 (约 2 90°)剪切。与早白垩世地壳伸展相伴生的下盘糜棱岩剪切方向也是北西向 ,这与瓦子峪拆离断层运动相关。已经发表的和未发表的锆石U Pb年龄、40 Ar/3 9Ar热年代学和上盘阜新盆地中生物地层的时代研究表明 ,地壳伸展和变质核杂岩形成时代为早白垩世 (约 12 7～ 116Ma)。我们未发现以前文献报道的医巫闾山是一对称的变质核杂岩的任何证据。瓦子峪变质核杂岩以及WNW侧的拆离断层的厘定会加深我们对华北克拉通早白垩世伸展作用的理解和认识 ,下一步的研究重点包括野外构造研究以确定拆离断层和下盘糜棱岩的空间展布 ,进一步采集样品以研究变质核杂岩的地质 /热年代学和变质核杂岩范围内的岩体成因。我们认为瓦子峪变质核杂岩的形成是太平洋板块边界重组、早白垩世岩浆作用致使地壳升温 ,从而导致经造山作用而加厚的地壳垮塌的结果。

The newly discovered Waziyu metamorphic core complex, Yiwulü Shan, western Liaoning Province, Northwest China

The previously undiscovered Waziyu metamorphic core complex in the Yiwulü Shan,a mountain range in western Liaoning Province,consists of a master,west-dipping,low-angle normal fault,the Waziyu detachment,that separates a hanging wall of dominantly Early Cretaceous sedimentary and volcanic units from a footwall of mylonitic and non-mylonitic units.Exposures of the Waziyu detachment fault (previously called the Sunjiawan-Shaohuyingzi fault) along the western flank of the range have dips of 10～40° and excellent kinematic indicators that give consistent top-to the west-northwest sense of shear (ca.290°).Mylonitic units in the footwall associated with Early Cretaceous crustal extension yield the same top-to the west-northwest sense of shear and are kinematically related to the Waziyu detachment fault.The timing of extension and metamorphic core complex development in the Yiwulü Shan is broadly constrained as Early Cretaceous (ca.127～116 Ma) by published and unpublished U-Pb geochronology,40Ar/39Ar thermochronology,and stratigraphic age determinations based upon biostratigraphy in the hanging wall supradetachment Fuxin basin.We have found no evidence for a symmetrical Yiwulü Shan mcc as reported in earlier literature.Recognition of the Waziyu mcc and its WNW-rooting detachment fault adds to our understanding of the extensional behavior of the North China crust.Future work in the Yiwulü Shan should include field-based structural studies to define the spatial extent of both the detachment fault and the kinematically related footwall mylonites,collection of additional samples for geo/thermochronology,and petrologic studies of the plutons within the range.We attribute formation of the Waziyu metamorphic core complex to collapse of an orogenically thickened crust that was facilitated by thermal weakening due to Early Cretaceous magmatism and paleo-Pacific plate boundary reorganization.