Stop 27. 铁堡清水河（N38°53′53″ E113°43′46″）
［内容］：“铁堡不整合”，阜平杂岩的混合片麻岩，年龄2.51～2.50Ga，上部板峪口组长石石英岩中的碎屑锆石年龄：2.51-2.30Ga；接触界面观察描述、产状测量，
In the riverbank near Tiebu village [Lat. 38° 53' 40"; Long.113° 43' 39"], we can observe one of the classic localities in Chinese geological literature; the so-called Tiebu ’Unconformity‘. It is traditionally described as the contact between the Fuping ’Group‘ and the overlying Wutai ’Group‘. The Fuping rocks have been described as belonging to the Longquanguan augen gneisses (Tian et al., 1996). The Wutai portion is considered to be part of the Banyukou ’Formation‘  and, as such, is thought to represent the basal part of the Wutai succession.

The Wutai rocks consist of a 20 cm thick unit of biotite schist overlain by quartzfeldspar-biotite metasediment with clasts of pink arkose at the base. This unit shows upward depletion in biotite over about one meter and passes into a feldspathic quartzite. However, bedding planes are locally marked by muscovite. Zircons obtained from a sample of quartzite (95-PC-64), collected one meter from the basal contact, show a spread of ages from ca 2700 to 2510 Ma. The fact that the youngest grains give an age younger than the felsic volcanics from the so-called ’Middle‘ Wutai (see stop 17) means that this unit cannot be the base of the Wutai sequence (Cawood et al., 1998).

    Two samples were collected from the Fuping gneisses: sample 95-PC-65 from the grey gneiss and sample 95-PC-66 from the pink granite phase (Wilde et al., in prep.). Sample 95-PC-65 contains three discrete suites of zircon (Fig. 47). The oldest four grains define a 207Pb/206Pb age of 2763±10 Ma. These are the oldest crystals known from either the Fuping or Hengshan Complexes and are interpreted to be xenocrysts incorporated in the igneous protolith to the grey gneiss. The largest population of 12 zircons define a 207Pb/206Pb age of 2660±7 Ma, taken to represent the crystallisation age of the igneous protolith. In addition, a group of 6 zircons give a 207Pb/206Pb age of 2534±10 Ma. This is similar to the age of granitic rocks elsewhere in the Fuping Complex (Guan et al., 2002; Zhao et al., 2002) and in the Hengshan and Wutai Complexes (see above). It is also overlaps within error the age of Sample 95-PC-66. This, however, contains discordant zircons and has a rather imprecise upper intercept age of ~2525 Ma. We interpret the younger zircons in sample 95-PC-65 as resulting from growth during emplacement of the extensive pink granitic layers.

  The contact between the metasediments and the underlying gneiss is tectonic at this location. Whether there was an original unconformable relationship is unclear although, as discussed above, based on the age of the youngest detrital zircons, it is not possible for this quartzite unit to represent the base of the Wutai sequence. Approximately 2 km further upstream, a 5 meter-wide unit of quartzite is totally enclosed within Fuping grey gneisses, clearly indicating tectonic interleaving.

Stop 28. 新路沟
[内容]：糜棱岩化花岗岩和龙泉关剪切带；

龙泉关剪切带研究认识：
    龙泉关剪切带几何学：龙泉关剪切带分割太古宇阜平杂岩和西部的太古宇五台杂岩的重要地质界线（图III-19，III-20）（张进江等，2006）。该剪切带内主体岩性为一套低角闪岩相的眼球状片麻岩、浅粒岩和少量的斜长角闪岩，前人称之为龙泉关群。近年来研究表明这些岩石的原岩主体为变质的花岗质岩石，其中残留了部分表壳岩（刘树文，1995；刘树文等，1997）。这些正副变质岩石经历了强烈的构造变形，产生了不同程度的糜棱岩化作用，形成了眼球状或条带状糜棱岩化片麻岩，应变集中部分形成了典型的糜棱岩（李江海等，1991；许荣华等，1995；唐先梅等，1997）。

龙泉关剪切带变形期次与运动学：龙泉关韧性剪切带糜棱面理倾向NWW-W ，构造面理倾角低缓，总体倾角为0～40°，龙泉关剪切带内共发育3 期线理，最早一组为矿物拉伸线理，由矿物的定向排列，如云母和角闪石及矿物的定向拉伸形成(如石英和长石) 。该期线理为透入性线理，发育于各岩石单元内部，形成龙泉关剪切带的主导线理，统计倾伏向为N60°W 左右，代表剪切带的主期变形；第2 、3 期线理为非透入性线理，仅发育于劈理面，表现为热擦痕，由机械刻痕和水热矿物纤维形成，其中第2期向北倾伏，第3 期向SWW 倾伏，两者可能代表后期的垮塌（赵兰等，2006）。


Stop 29. 灵境乡回龙底村北偏西1km (38°52′15.5″N, 113°31′7.6″E)
[内容]： 东冶亚群叠层石

Stop 30. 回龙底 (N38°53′56″, E113°31′09″)
[内容]： 滹沱群内基性火山岩

Stop 31. 横岭两组基性岩墙（N38°53′56″ E113°31′09″）