北京周口店太平山南坡晚古生代碎屑锆石U-Pb年代学
Detrital Zircon Geochronology of Late Paleozoic Strata from Southern Hillside of Taiping Hill in Zhoukoudian Area, Beijing and Their Tectonic Implications

为了探讨华北板块北缘晚古生代的隆升历史和古亚洲洋的闭合过程，利用碎屑岩的锆石U-Pb年代学、Hf同位素和锆石微量元素组成对北京周口店太平山南坡晚石炭世－早二叠世地层进行物源分析，并判定源区的大地构造背景.5件样品的碎屑锆石U-Pb年龄主要分布在3个时代：显生宙(285～425 Ma)、古元古代(1 700～2 450 Ma)和新太古代(2 500～2 747 Ma).前寒武纪的锆石年龄主要集中在2.5 Ga和1.8 Ga，与华北克拉通的前寒武纪基底岩石相似.显生宙的锆石年龄主要集中在 308～297 Ma，最年轻的峰值年龄在299～291 Ma，在误差范围内与地层沉积年龄相似，因此这些最年轻的碎屑锆石属于早二叠世同沉积锆石.29颗同沉积锆石的Hf同位素结果显示，原始176Hf/ 177Hf比值介于0.282 021～0.282 318， εHf ( t )值介于-20.1～-9.6.显生宙锆石的年龄谱特征以及Hf同位素组成与内蒙古隆起同期的岩浆锆石特征十分相似，因此显生宙碎屑锆石可能来源于内蒙古隆起，并伴随有少量来自北侧兴蒙造山带南部的早古生代岛弧碎屑的输入.二叠纪同沉积锆石的微量元素特征表明锆石结晶的岩浆源区具有大陆岛弧的构造属性.上述数据表明：(1)华北板块北缘在晚石炭世－早二叠世为活动大陆边缘；(2)晚古生代古亚洲洋向华北北缘的持续俯冲消减导致了内蒙古隆起的快速隆升；(3)古亚洲洋闭合的时间应晚于早二叠世.
The Late Paleozoic siliciclastic rocks outcrop in the southern hillside of Taiping hill, Zhoukoudian area. In order to trace sediment provenance and unravel the tectonic evolution of the North China craton and its surrounding plates, U-Pb dating and Hf isotopic analyses were performed on detrital zircons from this succession. U-Pb ages of five samples can be divided into three groups: Phanerozoic (285-425 Ma), Paleoproterozoic (1 700-2 450 Ma) and Neoarchean (2 500-2 747 Ma). Precambrian zircons show obvious age peaks at 2.5 Ga and 1.8 Ga, which are similar to those of basement rocks of the North China Craton. Phanerozoic zircons from five samples are predominantly distributed in the range of 308-297 Ma, with the youngest peaks varying from 299 to 291 Ma. U-Pb ages of the youngest zircons are consistent with the Early Permian depositional age, suggesting that these zircons are synsedimentary detritus. Characteristics of age spectra of the Phanerozoic zircons are similar to those of coeval igneous rocks outcropped in the Inner Mongolia paleo-uplift to the north, which suggests the source of Phanerozoic zircons. The 176Hf/ 177Hf andεHf ( t ) values of 29 synsedimentary zircons range from 0.282 021 to 0.282 318 and -20.1 to -9.1, respectively, which are consistent with those of active arc rocks in the Inner Mongolia paleo-uplift, rather than the Xing-Meng orogenic belt. Minor detritus from the Early Paleozoic arc rocks in the southern orogen of the Xing-Meng Orogen also flowed into the basin. Trace elements of Early Permian synsedimentary zircons are characterized by those of zircons crystallized in the environment of continent arc and active continental boundary. The results suggest that: (1) the northern margin of the North China craton was an Andean-type continental margin during the Late Carboniferous to Early Permian period, (2) rapid rise of the Inner Mongolia paleo-uplift was attributed to the subduction of Paleo-Asian ocean under the