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    SHRIMP Zircon U-Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains [查看] YUShengqiang、LIUShuwen、TIANWei、LIQiugen、FENGYonggang
    Abstract：Henglingguan and Beiyu metamorphic granitoids，distributed in the northwest of the Zhongtiaoshan Precambrian complex，comprise trondhjemites and calc-alkaline monzogranites，displaying intrusive contacts with the Archean Zhaizi TTG gneisses．And the Beiyu metamorphic granitoids consist mainlY of trondhjemites，distributed at the core of the Hujiayu anticline fold．New SHRIMP zircon U-Pb dating data show that the weighted mean207Pb/206Pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc-alkaline monzogranites and Beiyu meta morphic trondhjemites．respectively，and reveal ～2600 Ma inherited core in magmatic zircons．Whole-rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calcalkaline monzogranites belong to the metaluminous medium-and high-pota ssium calc-alkaline series．These rocks are characterized by relatively high total alkali contents (Na20+K20，up to 9.08％)，depleted Nb，Ta，P and Ti，and right-declined REE patterns with m oderate to high LREEs/HREEs fractionation (the mean ratio of(La/Yb)n= 25)．The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb．Th and K anomalies in the multi-element spider diagrams normalized by primi tive mantle．Sm-Nd isotopic data reveal that these granitoids have initial Nd(f)=-12 to +24 and Nd depleted mantle model ages of TMD= 2622 Ma-2939 Ma．A11 these geoc hemical features indicate that these granitoids were form ed in an continent-marginal arc and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and，howbeit，the Henglingguan metamorp hic calc-alkaline monzogranites derived from recycling of materials in the ancient crust under a continent-marginal arc．The granitic magma underwent contami nation and fractional crystallization during their formation.
    SHRIMP U-Pb zircon dating from Sulu-Dabie dolomitic marble, eastern China constraints on prograde, ultrahigh-pressure and retrograde metamorphic ages [查看] F.L.LIU、A.GERDES、J.G.LIOU、H.M.XUE、F.H.LIANG
    Laser Raman spectroscopy and cathodoluminescence (CL) images show that zircon from Sulu-Dabie dolomitic marbles is characterized by distinctive domains of inherited (detrital), prograde, ultrahighpressure(UHP) and retrograde metamorphic growths. The inherited zircon domains are darkluminescent in CL images and contain mineral inclusions of Qtz + Cal + Ap. The prograde metamorphic domains are white-luminescent in CL images and preserve a quartz eclogite facies assemblage of Qtz + Dol + Grt + Omp + Phe + Ap, formed at 542–693℃and 1.8–2.1 GPa. In contrast, the UHP metamorphic domains are grey-luminescent in CL images, retain the UHP assemblage of Coe + Grt + Omp + Arg + Mgs + Ap, and record UHP conditions of 739–866℃ and >5.5 GPa. The outermost retrograde rims have dark-luminescent CL images, and contain low-P minerals such as calcite, related to the regional amphibolite facies retrogression. Laser ablation ICP-MS trace-element data show striking difference between the inherited cores of mostly magmatic origin and zircon domains grown in response to prograde, UHP and retrograde metamorphism. SHRIMP U-Pb dating on these zoned zircon identified four discrete 206Pb/238U age groups: 1823–503 Ma is recorded in the inherited (detrital) zircon derived from various Proterozoic protoliths, the prograde domains record the quartz eclogite facies metamorphism at 254–239 Ma, the UHP growth domains occurred at 238–230 Ma, and the late amphibolite facies retrogressive overprint in the outermost rims was restricted to 218–206 Ma. Thus, Proterozoic continental materials of the Yangtze craton were subducted to 55–60 km depth during the Early Triassic and recrystallized at quartz eclogite facies conditions. Then these metamorphic rocks were further subducted to depths of 165–175 km in the Middle Triassic and experienced UHP metamorphism, and finally these UHP metamorphic rocks were exhumed to midcrustal levels (about 30 km) in the Late Triassic and overprinted by regional amphibolite facies metamorphism. The subduction and exhumation rates deduced from the SHRIMP data and metamorphic P–T conditions are 9–10 km Myr)1 and 6.4 km Myr)1, respectively, and these rapid subduction–exhumation rates may explain the obtained P–T–t path. Such a fast exhumation suggests that Sulu-Dabie UHP rocks that returned towards crustal depths were driven by buoyant forces, caused as a consequence of slab breakoff at mantle depth.
    Report on 3.4 Ga SHRIMP Zircon Age from the Yuntaishan Geopark in Jiaozuo, Henan Province [查看] GAOLinzhi、ZHAOTing、WANYusheng、ZHAOXun、MAYinsheng、YANGShouzheng
    Using the reported new U-Pb age with the Sensitive High-Resolution Ion hlicroprobe (SHRIRIP-II), zircon U-Pb ages were obtained from two samples of K-feldspar felsic paragneiss and K-feldspar gneissoid trondhjemite on the southern margin of the Taihang hlountains in the North China Craton. The protolith of the K-feldspar felsic paragneiss is argillaceous-sandy clastic sedimentary rock, probably deposited in the Neoarchean. Most of the detritus zircons show heavy loss of Pb. Five spots of zircons near the upper point, yield a weighted mean 207Pb/206Pb age of 3399±8 Ma, representing an age of the sedimentary source. Two groups of zircons from the K-feldspar gneissoid trondhjemite give weighted mean 207Pb/206Pb ages of 2511±13 Ma and 2735±16 Ma respectively. The former represents the emplacement time of the pluton, while the latter is interpreted as the age of the inherited zircons. The new data support that the Archean geological body in the central zone has an affinity with those from the eastern block of the North China Craton.
    Petrogenesis and significance of the Hongshan syenitic pluton,South Taihang zircon SHRIMP U-Pb age,chemical compositions and Sr-Nd isotopes [查看] ZhouLing、ChenBin
    The Hongshan syenitic pluton(South Taihang)is mainly made up of hornblende syenite and minor granite.SHRIMP zircon dating yields a U-Pb age of 135±2.7Ma for the emplacement of the pluton,while biotite Rb-Sr isotopic data give an isochron of 120.3±2.4Ma.Hongshan syenites show low silica,hig alkalis and LILE such as Sr,and exhibit negligible Eu anomalies or slightly positive anomalies in the REE patterns.The syenites show quite enriched isotopic compositions with Isr from 0.7052 to 0.7102 and Nd(t)from -7.5 to -11.1.Petrogenesis of the pluton can be that partial melting of an enriched lithospheric mantle gave birth to an alkali basaltic magma,whcih subsequently underplated in the lower crust and experienced a coupled factionation of ferromagnesian phases like pyroxene and hornblende and minor(＜10%)contamination of lower continental crust,producing the Hongshan syenites that partially evolved into granite through combined fractionation of hornblende and feldspar.Our data are not in agreement with a previours model that the syenites originated melting of lower crust in a thickened crust circumstance,and thus do not support the speculation of "East China Plateau"in the Mesozoic
    Paleoproterozoic Potassic Granitoids in the Sushui Complex from the Zhongtiao Mountains,Northern China Geochronology,Geochemistry and Petrogenesis [查看] TIANWei1、LIUShuwen、ZHANGHuafeng
    Abstract: Paleoproterozoic potassic granitoids in the southern Sushui Complex from the Zhongtiao Mountains yielded SHRIMP zircon U-Pb ages of 1968–1944 Ma. Lithologically, the potassic granitoid series consists chiefly of monzodiorite, quartz monzonite and syenogranite. Their trace elements and Sm-Nd isotope characteristics indicate that they were derived from partial melting of Archean TTG rocks in an overthickened continental crust. Petrogenesis of this potassic granitoid series implies a collisional environment within the Trans-North China Orogen in the Paleoproterozoic, which supports a tectonic model of Eastern and Western Continental Blocks being amalgamated in the Paleoproterozoic.
    Metamorphism in the Central Zone of the North China Craton SHRIMP U-Pb dating of zircon from metamorphic rocks in the Lushan area, Henan Province [查看] YushengWan、SimonA.Wilde、DunyiLiu、ChangxiuYang、BiaoSong、XiaoyanYin
    This paper reports SHRIMP zircon U–Pb dating of Precambrian supracrustal and granitic rocks from the Lushan area, Henan Province, in the southern portion of the Central Zone (also referred to as the Trans-North China Orogen) of the North China Craton. A graphite–garnet–sillimanite gneiss (Sample TW0006/1) of the Shangtaihua F Group gives a range of inherited zircon ages from 2.73 to 2.26 Ga and a metamorphic zircon age of 1.84±0.07 Ga. A garnet-bearing gneissic granitoid (Sample TWJ358/1), which is considered to intrude the Shangtaihua F Group, gives a magmatic zircon age of 2.14±0.02 Ga and a metamorphic zircon age of ¨1.87 Ga. The metamorphic zircon ages of 1.87–1.84 Ga obtained in this study indicate that an important tectonothermal event occurred at the end of the Paleoproterozoic in the Lushan area. This supports the southern continuation of a Central Zone in the North China Craton that workers have recently considered to result from continent–continent collision. It is also evident that the Shangtaihua FGroup_ was formed during the Paleoproterozoic (between 2.26 and 2.14 Ga), and not during the Archean, as previously considered.
    Implications based on the first SHRIMP U-Pb zircon dating on Precambrian granitoid rocks in North Korea [查看] GuochunZhao、LinCao、SimonA.Wilde、MinSun、WonJongChoe、SanzhongLi
    Precambrian basement rocks in North Korea consist of supracrustals and granitoid rocks, of which the former comprise the late Archean Nangrim Group and the Paleoproterozoic Jungsan andMachollyong Groups, whereas the latter include four major types: grey TTG gneisses, garnet/sillimanite-bearing (S-type) granites,massive porphyritic granites, and hornblende-bearing granites. SHRIMP U–Pb zircon geochronology, combined with cathodoluminescence (CL) imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the Precambrian history of North Korea and its relations toNorth China. SHRIMP U–Pb zircon analyses on two grey gneiss samples (PO501 and K14) reveal that they were emplaced at 2538±14 Ma and 2636±49 Ma,respectively, and metamorphosed at 2462–2433 Ma. These data, for the first time, confirm the existence of late Archean rocks in the Korean Peninsula.Moreover, one grey gneiss sample (K14) contains several zircons with ages of 3.1–3.4Ga, suggesting possiblemiddle Archean crust in North Korea. Rocks with such ages are widely distributed in North China, implying that North China and North Korea have similarArchean basement.One grey gneiss sample (R53) yielded a SHRIMP zircon age of 1933±12Ma, indicating that some grey gneisses in North Korea formed during the Paleoproterozoic. Two garnet- and/or sillimanite-bearing S-type granite samples gave 207Pb/206Pb ages of 1908±31Ma and 1903±49Ma, interpreted to reflect the time ofmetamorphismof the Paleoproterozoic Jungsan and Machollyong Groups since these S-type granites are considered to be derived fromthe partialmelting of pelitic rocks fromthese groups. The∼1.9Gametamorphic event has also been revealed in Paleoproterozoic rocks in South Korea and NorthChina. SHRIMP zircon data also show that massive porphyritic monzogranites inNorth Korea evolved over a protracted interval from1865Ma to 1843Ma. Similaraged porphyritic monzogranites are also found in North China and South Korea, and their origin is considered to be related to a posttectonic extensional event of regional extent. The last phase of Precambrian magmatism recognized in North Korea is Grenvillian-aged,represented by the hornblende-bearing granite that yields a SHRIMP zircon age of 1195±4Ma, and is considered to be the source rock of the adjacent Yushulazi Group (North China) that contains numerous 1.1–1.2 Ga old detrital zircons.
    Evidence for w1.8 Ga extension of the Eastern Block of the North China Craton from SHRIMP U–Pb dating of mafic dyke swarms in Shandong Province [查看] GuitingHou、YulinLiu、JianghaiLi
    A large mafic dyke from the NNW-trending dyke swarms in the Eastern Block of the North China Craton was dated by SHRIMP U-Pb age analysis. This dyke occurs near Mt. Taishan in Shandong Province; it cuts Neoarchean tonalite, adamellite and diorite plutons. Two types of zircons were found in the dyke. Type 1 zircons were inherited from the host rocks and gave a SHRIMP U-Pb age of 2544±24 Ma with a weighted mean 207Pb/206Pb age of 2523±18 Ma. Type 2 zircons were crystallized from the dyke magma and yielded a concordant SHRIMP U-Pb age of 1830±17 Ma with a weighted mean 207Pb/206Pb age of 1837±18 Ma, indicating that the large dyke at Taishan was emplaced at w1830 Ma. The mafic dyke swarm provides evidence of a phase of extension in the Eastern Block of the North China Craton at w1.8 Ga This dyke has a similar age to dyke swarms in the Western Block and in the Central Orogen Belt of the North China Craton. This lithospheric extension, led to the opening of the Yanliao and Zhongtiao aulacogens. The similar ages and orientations of w1.8 Ga dyke swarms throughout the North China Craton demonstrate that at that time the Eastern and Western blocks were united and that the amalgamated craton experienced widespread extension.
    Dating of prograde metamorphic events deciphered from episodic zircon growth in rocks of the Dabie-Sulu UHP complex,China [查看] DunyiLiu、PingJian、AlfredKröner、ShutongXu
    The timing of ultra-high pressure (UHP) metamorphism has been difficult to determine because of a lack of age constraints on crucial events, especially those occurring on the prograde path. New Sensitive High-Resolution Ion Microprobe (SHRIMP) U–Pb age and rare-earth element (REE) data of zircon are presented for UHP metamorphic rocks (eclogite, garnet peridotite, garnet pyroxenite, jadeite quartzite and garnet gneiss) along the Dabie–Sulu UHP complex of China. With multiphase metamorphic textures and index mineral inclusions within zircon, the Dabie data define three episodes of eclogite-facies metamorphism, best estimated at 242.1±0.4 Ma, 227.2±0.8 Ma and 219.8±0.8 Ma. Eclogite-facies zircons of the Sulu UHP complex grew during two major episodes at 242.7±1.2 and 227.5±1.3 Ma, which are indistinguishable from corresponding events in the Dabie UHP complex. A pre-eclogite metamorphic phase at 244.0±2.6 Ma was obtained from two Sulu zircon samples which contain low pressure–temperature (plagioclase, stable below the quartz/Ab transformation) and hydrous (e.g., amphibole, stable below ∼ 2.5 Gpa) mineral inclusions. In terms of Fe–Mg exchange of trapped garnet–clinopyroxene pairs within zircon domains, we are able to determine the Pressure–Temperature (PT) conditions for a specific episode of metamorphic zircon growth. We suggest that mineral phase transformations and associated dehydration led to episodic eclogite-facies zircon growth during UHP metamorphism(∼ 2.7 Gpa) began at 242.2±0.4 Ma (n=74, pooling the Dabie–Sulu data), followed by peak UHP metamorphism (N∼ 4 Gpa) at227.3±0.7 Ma (n=72), before exhumation (b∼ 220 Ma) to quartz stability (~ 1.8 Gpa). The Dabie–Sulu UHP metamorphism lasted for about 15 Ma, equivalent to a minimum subduction rate of 6 mm/year for the descending continental crust.
    Mesozoic Multi-phase Magmatism and Gold Mineralization in the Early Precambrian North China Craton, Eastern Hebei Province, China SHRIMP Zircon U-Pb Evidence [查看] LAICHENGMIAO、YUMINQIU、WEIMINGFAN、ANDFUQINZHANG
    The early Precambrian North China craton (NCC) in eastern Hebei Province (also known as the Jidong area) was intruded by granitic batholiths and plutons spatially associated with gold deposits. No consensus has been reached regarding timing and tectonic setting of the gold deposits, chiefly due to the lack of reliable geochronological data. The gold deposits in the district are localized by NE-striking faults within granite plutons and/or nearby Archean amphibolites, as well as in Proterozoic sedimentary rocks. Gold mineralizations in the area are characterized by quartz (± albite) veinand sulfide-disseminated styles; both types of ores have relatively low sulfide contents (<10 vol%) and similar sulfide mineral assemblages dominated by pyrite + chalcopyrite + pyrrhotite + galena + sphalerite, locally with molybdenite, tellurides, and bismuthinoids. The alterations around the gold lodes include K-feldspathization, sericitization, silicification, chloritization, and sulfidation. Previous fluid inclusion data from all the deposits of the district show that the mineralizing fluids are characterized by relatively high salinities (3 to 17 wt% NaCl equiv.), H2O-CO2 ± CH4, N2 solutions, with CO2 contents in the inclusions ranging from 5 to 40 mol%. Fluid inclusion homogenization temperatures are between 240 and 400°C, and estimates of the trapping pressures vary significantly from 0.5 to 3.7 kbar. Stable isotope (O, H, S, C, and Pb) data from these deposits indicate a major magmatic component in the mineralizing fluids and the ore-forming materials, with a partial contribution by Archean host rocks, suggesting that these deposits are basically intrusion-related. SHRIMP zircon U-Pb geochronology of the gold-hosting granitic intrusions, in combination with previous Ar-Ar and Rb-Sr dates on hydrothermal minerals (e.g., sericite), indicates that there was no Archean gold mineralization, but instead suggests that at least three episodes of granitic magmatism and associated gold mineralization took place during the Mesozoic. The first episode occurred in the Late Triassic at ~222 Ma, with emplacement of the Dushan granite batholith (223 ± 2 Ma), Sanjia granite porphyry (222 ± 4 Ma), and the Baizhangzi granite (222 ± 3 Ma). This episode of magmatism and gold mineralization was coeval with collision of the NCC with the South Mongolian block in the north along the Solonker suture and with the Yangtze craton in the south along the Dabie-Sulu suture. The second episode took place in the Early Jurassic, with emplacement of the Qingshankou granite (199 ± 2 Ma), and the third episode occurred in the Middle Jurassic, with intrusion of the Yuerya (~ 175 Ma) and Niuxinshan (172 ± 2 Ma) and granites. These two events are about 25 and 45 Ma later than the collision of the NCC with other continental blocks in a post-collisional environment.
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