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Wan Y.,Chinese Academy of Geological Sciences | Wan Y.,State Key Laboratory of Geological Process and Mineral Resources | Ho K.,CSIC - National Museum of Natural Sciences | Liu D.,Chinese Academy of Geological Sciences | And 3 more authors.
Chemical Geology

The Chilungshan andesite belongs to the Chilung Volcano Group in northern Taiwan and constitutes the western end of the island chains of the Ryukyu arc. Chemically it is a normal, medium-K calc-alkaline andesite. SHRIMP dating of magmatic zircons yielded an emplacement 206Pb/ 238U age of 1.04±0.06Ma with ε Hf(t) of 6.1 to 13.4 and δ 18O of 5.02 to 6.28‰. The zircons contain inherited cores and felsic to andesitic silicate-melt (glass) inclusions besides apatite, quartz, K-feldspar, biotite, garnet, Fe-Mg minerals (pyroxene or hornblende) and plagioclase with variable An values. Plagioclase phenocrysts also contain quartz, K-feldspar and felsic melt inclusions. This study confirms the presence of micro-scale heterogeneity in the andesite as a result of mixing between mantle-derived and continental material. Contamination of continental crust occurs either within the magma chamber at a medium to deep crustal level and/or during dehydration and melting of a subducted oceanic slab and overlying sediments in an island-arc environment. © 2011 Elsevier B.V. Source

Wan Y.,Chinese Academy of Geological Sciences | Wan Y.,State Key Laboratory of Geological Process and Mineral Resources | Liu D.,Chinese Academy of Geological Sciences | Nutman A.,Chinese Academy of Geological Sciences | And 5 more authors.
Journal of Asian Earth Sciences

Near Anshan city in the North China Craton, the oldest rocks in Asia (≥3300. Ma) have been thoroughly documented at two localities (Baijiafen and Dongshan). In this paper we report the full geological context for more ancient rocks from a third Anshan locality - the polyphase migmatite Shengousi Complex. SHRIMP U-Pb zircon dating indicates a protracted tectono-magmatic history for the Shengousi Complex: The oldest recognised component is banded trondhjemitic gneiss (3773 ± 6. Ma), which is veined by strongly deformed granitic pegmatite. These occur with a second generation of trondhjemitic rocks (3454 ± 8 and 3448 ± 9. Ma). The next generation of plutonic rocks is a composite suite of iron-enriched mafic dykes (3332 ± 6 and 3331 ± 8. Ma) with broadly coeval felsic veins (3311 ± 4. Ma). Finally there was intrusion of monzogranite (3129 ± 6. Ma). Strong deformation has generally brought these 3773-3129. Ma plutonic phases into close concordance to form banded rocks. However, locally cross-cutting relationships are preserved in small lower strain domains, that give a relative chronology agreeing with the absolute zircon U-Pb chronology. All of this complex history is recorded in a single. <50. m wide outcrop.Some of the. <3600. Ma rocks of the Shengousi Complex contain 3780-3730 and 3660-3600. Ma inherited zircon xenocrysts. The stronger prominence of 3660-3600. Ma components distinguishes the Shengousi Complex from the Baijiafen and Dongshan complexes, where components of this age are rarer. One possibility is that at 3660-3600. Ma, the Shengousi Complex was at a deeper crustal level than the Baijiafen and Dongshan complexes, and underwent migmatisation at that time.The ~3450. Ma igneous phases discovered in the Shengousi Complex are new ages for igneous rocks in the Anshan area. The Precambrian geology of the Anshan area is thus marked by polyphase Eoarchaean orthogneisses, the newly recognised ~3450. Ma phases, widespread 3360-3300 magmatic activity, found in association with Mesoarchaean plutonic rocks and the Neoarchaean Anshan Group and Palaeoproterozoic Liaohe Group metasedimentary rocks. This shows that the geology of the Anshan area has a strong similarity with the Narryer Gneiss Complex of Western Australia, which contains the polyphase Eoarchaean Meeberrie gneisses, the 3490-3440. Ma Eurada gneiss association, ~3300. Ma granites and migmatisation, and is intercalated with younger Precambrian metasedimentary rocks of different ages containing Hadean detrital zircons. No other ancient gneiss complexes in the world show such a close match in their history with the Anshan area rocks. This means that the Anshan area is prospective for locating new occurrences of Hadean crustal components intercalated with younger sedimentary rocks. © 2012 Elsevier Ltd. Source

Wan Y.,Chinese Academy of Geological Sciences | Wan Y.,Beijing Center | Wan Y.,State Key Laboratory of Geological Process and Mineral Resources | Dong C.,Chinese Academy of Geological Sciences | And 13 more authors.
Precambrian Research

At the end of the Neoarchean continental evolution, voluminous syenogranites were emplaced in the North China Craton, together with other magmatic rocks (trondhjemite-tonalite-granodiorite (TTG), monzogranite, diorite, gabbro). Syenogranites are widely distributed in Anshan-Benxi, Qinhuangdao and western Shandong, and also occur in southern Jilin, northern Liaoning, northwestern Hebei and central Henan. Based on geological relationships, degree of metamorphism, deformation and magmatic zircon ages, two phases of syenogranite magmatism are recognized. Rocks produced during the first phase show a gneissic texture and were formed between 2.53 and 2.52Ga and locally comprise abundant TTG. Rocks of the second phase cut late Neoarchean TTG and supracrustal rocks, display a massive structure, and mainly formed between 2.52 and 2.50Ga. All syenogranites share the same features in major element compositions, being high in SiO2 and low in CaO, total FeO, MgO, TiO2 and P2O5. However, they are different in trace and REE compositions and can be subdivided into three types. (1) Type 1 shows a large variation in total REE contents, low (La/Yb)n ratios, strong negative Eu*/Eu anomalies and Ba depletion; (2) Type 2 is similar to Type 1 but has higher (La/Yb)n ratios. (3) Type 3 shows a large variation in total REE and (La/Yb)n ratios and significantly do not show strongly negative Eu*/Eu anomalies and Ba depletion. Whole-rock Sm-Nd isotopic compositions show large variations in εNd(t) values and tDM(Nd) modal ages, ranging from -9.49 to -4.72 and 3.70 to 3.25Ga (Type 1), 0.55-1.03 and 2.77-2.71Ga (Type 2) and -2.35 to 1.23 and 2.93-2.66Ga (Type 3), respectively. Hf isotopic compositions of zircons from three samples have εHf(t) values and tDM1(Hf) ages of 0.7-7.2 and 2.84-2.56Ga (Type 1), 2.6-7.4 and 2.74-2.56Ga (Type 2) and 2.1-6.3 and 2.76-2.60Ga (Type 3). It is concluded that syenogranites were generated by melting of continental crust with different mean crustal residence ages, and most of them were emplaced during the second phase (2.52-2.50Ga) in an extensional tectonic regime. The formation of these voluminous syenogranites marks a tectono-magmatic event resulting in stabilization of the North China Craton at the end of the Neoarchean. © 2011 Elsevier B.V. Source

Wan Y.,Chinese Academy of Geological Sciences | Wan Y.,Beijing Center | Wan Y.,State Key Laboratory of Geological Process and Mineral Resources | Liu D.,Chinese Academy of Geological Sciences | And 10 more authors.
Gondwana Research

The North China Craton (NCC) was subjected to an extensional regime after the Lüliang movement at ~1.8Ga 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 typical Meso- to Neoproterozoic areas in the NCC. Detrital zircons of six sedimentary samples have two distinct age peaks at ~2.52Ga and ~1.85Ga. There are some detrital zircons at 2.4-2.0Ga but none at 2.3Ga and only a few >2.7Ga. 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 ~2.5Ga detrital zircons of the Changcheng Group have εHf(2.5Ga) values and tDM(Hf) model ages mainly ranging from -2 to +7 and 2.8 to 2.7Ga, respectively. Detrital monazites of a sample from the Jixian Group exhibit a major age peak between 1.95 and 1.80Ga with some data between 2.0 and 1.95Ga. 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 2.43Ga, being older than the tDM(Nd) ages (2.11 and 1.99Ga) of sedimentary samples from the Qingbaikou Group. Based on a comparison with ages for the early Precambrian (>1.8Ga) basement of the NCC, it can be concluded that (1) the sediments of the Meso- to Neoproterozoic cover were undoubtedly derived from the 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 rocks were exposed at the surface after the upper crustal late Neoarchean rocks had already been eroded. © 2011 International Association for Gondwana Research. Source

Wang X.,Wuhan University | Jiao Y.,Wuhan University | Du Y.,Wuhan University | Ling W.,State Key Laboratory of Geological Process and Mineral Resources | And 6 more authors.
Journal of Geochemical Exploration

The rare earth element (REE) behavior and the related Ce anomalies of two profiles in bauxite of the Xinmo Syncline from Wuchuan-Zheng'an-Daozhen (WZD) area (Northern Guizhou, China) have been studied. The bauxite has diaspore as its main ore mineral, with lesser amounts of boehmite. Clay minerals, including kaolinite, chlorite, illite and smectite, are a minor mineral constituent. Furthermore, a significant Ce-bearing mineral parisite (Ce2Ca(CO3)3F2) is found near the bottom of the profiles. The bauxites have flat HREE (Er-Lu) shape relative to NASC, with variable weak depletion to weak enrichment patterns of LREE (La-Nd) and MREE (Sm-Ho) across the profiles. Strong positive Ce-anomalies (normalized to NASC) are also noticeable in the uppermost part of the profiles. Mass balance calculations suggest that an obvious fractionation exists among different REE and LREE are more mobile than HREE during the leaching process. In addition, the samples collected along a vertical profile show that a downward increase for the REE concentration and a remarkable enrichment of REE are found at the basement of the bauxite deposits. A similar downward increase trend is also observed in the values of LaN/YbN and GdN/YbN. The above characteristics show that the REE losses caused by leaching decreased gradually from the top to the bottom of the profile. The higher mobility of LREE in the profile might be due to differences in the stabilities of the original REE-bearing minerals during leaching process. The REE enrichment at the basement of bauxite deposits is attributed to the increase of pH around the parent rock as well as the presence of mineral ligands during bauxitization. The value of [Ce/Ce*]NASC decreased downwards, and increased again near the bottom of the profile. The positive Ce-anomaly in the uppermost part of the profile has been attributed to the redox change of Ce3+ to Ce4+ and the consequent precipitation of cerianite (CeO2). A decrease in the oxidation state downwards causes the decrease of the value of [Ce/Ce*]NASC. The formation of parisite near the bottom of the profile leads up to the increase in the value of [Ce/Ce*]NASC again. The precipitation of parisite may occur via reactions between the fluoride complexes (CeF2+ or CeCO3F0) and Ca2+ and HCO3 -. © 2013 Elsevier B.V. Source

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