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    Provenance of Meso- to Neoproterozoic cover sediments at the Ming Tombs, Beijing,North China Craton An integrated study of U–Pb dating and Hf isotopic measurement of detrital zircons and whole-rock geochemistry [查看] YushengWan、DunyiLiu、WeiWang、TianruiSong、AlfredKröner、ChunyanDong、HongyinZhou、XiaoyanYin
    The North China Craton (NCC)was subjected to an extensional regime after the Lüliangmovement at ~1.8 Ga and then was covered by an extensive Meso- to Neoproterozoic sedimentary succession, namely the Changcheng,Jixian and Qingbaikou Groups in ascending order. We report age spectra for detrital zircons and monazites, Hf isotopic systematics of detrital zircons, and whole-rock chemical and Nd isotopic compositions for sediments from the succession in the Ming Tombs area, Beijing, one of the typicalMeso- to Neoproterozoic areas in the NCC.Detrital zircons of six sedimentary samples have two distinct age peaks at ~2.52 Ga and ~1.85 Ga. There are some detrital zircons at 2.4–2.0 Ga but none at 2.3 Ga and only a few N2.7 Ga. The detrital zircon age spectra change with time. Sediments in the lower succession (Changcheng Group) and in the upper successions (Jixian and Qinbaikou Groups) are dominated by significant detrital zircon populations of late Neoarchean and late Paleoproterozoic ages, respectively. The ~2.5 Ga detrital zircons of the ChangchengGroup have εHf(2.5 Ga) values and tDM(Hf) model ages mainly ranging from −2 to +7 and 2.8 to 2.7 Ga, respectively. Detrital monazites of a sample fromthe JixianGroup exhibit amajor age peak between 1.95 and 1.80 Ga with somedata between 2.0 and 1.95 Ga. The sedimentary rocks of the Changcheng Group are characterized by high K2O contents (mostly 7.09–15.20%) and insignificant Eu anomalies (Eu/Eu*=0.71–1.16). They have tDM(Nd) model ages ranging from 2.70 to 2.43 Ga, being older than the tDM(Nd) ages (2.11 and 1.99 Ga) of sedimentary samples from the Qingbaikou Group. Based on a comparison with ages for the early Precambrian (N1.8 Ga) basement of the NCC, it can be concluded that (1) the sediments of theMeso- to Neoproterozoic coverwere undoubtedly derived fromthe NCC itself or once neighboring terranes; (2) variations in the detrital zircon age spectra from the lower to the upper successions reflect provenance evolution in that the lower crustal late Paleoproterozoic rockswere exposed at the surface after the upper crustal late Neoarchean rocks had already been eroded.
    NEW U-Pb AND Hf ISOTOPIC DATA CONFIRM ANSHAN AS THE OLDEST PRESERVED SEGMENT OF THE NORTH CHINA CRATON [查看] DUNYILIU、SIMONA.WILDE、YUSHENGWAN、JIASHANWU、HONGYINZHOU、CHUNYANDONG、XIAOYANYIN
    ABSTRACT. The Anshan area in the northeastern part of the North China Craton contains the oldest known rocks in China. Rocks with ages of 3.8 Ga are present in three trondhjemite-dominated gneiss complexes, referred to as the Baijiafen, Dongs-han and Shengoushi complexes. The oldest material identified in these complexes has weighted mean 207Pb/206Pb ages of 3800 5 Ma, 3794 4 Ma and 3777 13 Ma,respectively. In addition, younger geological events at 3680 19 Ma, 3620 23 Ma, and 3573 21 Ma have been identified, recording the emplacement of several generations of trondhjemite. A biotite schist of possible supracrustal origin contains a zircon population with a weighted mean 207Pb/206Pb age of 3723 17 Ma and is cut by a 3620 Ma trondhjemite, implying formation prior to3.62 Ga. TDM(Hf) model ages for the zircons range from 3256 to 4264 Ma, but are mostly 3.9 Ga, indicating that significantly older crust was not present in the source region of the trondhjemitic magmas.
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