Zircon SHRIMP dating of sodium alkaline rocks from Maomaogou area of Huili County in Panxi, SW China and its geological implications

Alkalinerocksareoftenassociatedwithextensionaltectonicsandregardedasthecharacteristicproductsoc-curringincontinentalmarginsorriftzones[1].Theywereusuallygeneratedindeep-large-faultzoneandcloselyconnectedwithbasic/ultrabasicrocksinspace.Therefore,alkalinerocksareofsignificanceintectonicpetrology.Atthebeginningofthe1980s,geologicalandgeophysicalstudieswereperformedinPanzhihua-Xichangpaleo-riftzone(Panxiriftzone).However,thesestudiesonlyin-volvedgeologyandpetrochemistryoftheMaomaogouringalkalic…     

Mineralizing age of the Rushan lode gold deposit in the Jiaodong Peninsula：SHRIMP U-Pb dating on hydrothermal zircon

Knowledge of the mineralizing timing is fundamen-tal to understand the genesis of mineral deposits, and ex-act time spectrum of mineralization is essential to com-prehending the relationship among the genesis of en-dogenic hydrothermal deposits, regional tectonic-magma-tism event and the geodynamics of mineral deposits. The Jiaodong or eastern Shandong gold province islocated in the southeastern margin of the North Chinacraton, and belongs to the Mesozoic circum-Pacific oro-genic gold system…     

4.1 Ga old detrital zircon in western Tibet of China

4.1 Ga old detrital zircon was found by SHRIMP U-Pb dating for quartz schist from Buring County in western Tibet, Southwest China. This is the oldest zircon U-Pb age found in China so far. The detrital zircon is a zircon of magmatic origin because its Th/ U ratios are 0.76 to 0.86. Two dates older than 4.0 Ga were measured only in one grain. U-Pb ages of 35 measured spots in 24 zircons can be subdivided into 6 groups, corresponding to at least 6 episodes of magmatic activity in the target area. The present results provide an important geochronological constraint on the geological evolution of Qinghai-Tibet Plateau.     

Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS

Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively fiat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.     

In situ U-Pb dating of xenotime by laser ablation （LA）-ICP-MS

Xenotime is an ideal mineral for U-Th-Pb isotopic dating because of its relatively high U and Th contents, but typically low concentration of common Pb. These characteristics, and the fact that it is widespread throughout various types of rocks, suggest that the U-Th-Pb dating of xenotime has broad applications. Studies of U-Pb dating on xenotime by ion microprobe (such as SHRIMP) have increased in recent years, whereas studies by laser ablation (LA)-ICP-MS are still rare. In this study, we developed a technique for U-Pb dating of xenotime using the 193 nm ArF laser-ablation system and Agilent 7500a Q-ICP-MS. To evaluate the reliability of our method, a xenotime standard, BS-1, was analyzed and calibrated against another xenotime standard, MG-1. The weighted mean 206 Pb/ 238 U ages of 510.1 ± 5.2 Ma (2 n = 21), 509.8 ± 4.3 Ma (2 n = 21) and 510.0 ± 4.6 Ma (2 n = 21) were obtained using beam diameters of 16, 24 and 32 m, respectively. These ages are identical to those determined by ID-TIMS method (weighted mean 206 Pb/ 238 U age of 508.8 ± 1.4 Ma), which supports the reliability of our LA-ICP-MS method. We also analyzed xenotimes in leucogranites from South Tibet and granites from Xihuashan in southern China, and obtained accurate and precise ages. Nevertheless, we observed systematic differences in Pb/U fractionation among xenotime, monazite and zircon. The matrix-effect resulted in either under-correction or over-correction of fractionation, and thus led to inaccurate ages. Thus, a matrix-matched material is required for U-Pb dating of xenotime by LA-ICP-MS.     

陕南铜厂闪长岩体的成岩、成矿时代及其地质意义

铜厂闪长岩体位于扬子地台北缘勉县-略阳-阳平关三角地块区域内, 主要由闪长岩、石英闪长岩和花岗闪长岩组成。LA-ICPMS 和 SHRIMP 锆石U-Pb 同位素定年结果表明铜厂闪长岩体存在 3 个侵位结晶阶段: 早期阶段的闪长岩形成于 879 ±7 Ma; 中期阶段的石英闪长岩形成于 848±5 ～840±7 Ma, 含矿钠长岩脉于 834±7 Ma侵位结晶, 与中期阶段石英闪长岩侵位时代在误差范围内一致; 晚期阶段花岗闪长岩形成于 824±5 Ma。这些新的年代学数据表明铜厂闪长岩体及其相伴生的大型铜厂铜矿形成于晋宁期, 而不是古生代, 揭示了扬子地台北缘存在重要的新元古代早期岩浆活动, 与 Rodinia 超大陆的裂解事件在时间上( 860 ～750 Ma) 基本一致, 是Rodinia 超大陆事件在扬子地台北缘的重要响应。     

江西南部版石盆地火山岩SHRIMP锆石U-Pb年龄及其地质意义

应用SHRIMP锆石U-Pb定年方法,对江西南部三南-寻乌火山岩带版石盆地原鸡笼嶂组凝灰岩和原版石组流纹岩开展年代学研究.结果表明,凝灰岩SHRIMP锆石U-Pb年龄为(142.5±1.3)Ma,流纹岩SHRIMP锆石U-Pb年龄为(131.4±1.3)Ma.根据新的国际地层表,晚侏罗世与早白垩世的界线划在(145.5...     

Zircon U-Pb SHRIMP ages of eclogites from the North Qilian Mountains in NW China and their tectonic implication

TheNorthQilianMountainsattheboundarybe-tweenGansuandQinghaiProvincesareafamousCaledo-nianplatesuturezoneinthenorthwesternChina.Thissuturezoneis80to100kmwideandextendsintheNWdirectionparalleltotheNorthQaidamUHPbeltinthesouth[1,2].Itconsistspredominantlyofophiolite,island-arccomplexandhigh-presuremetamorphicrocks[38],andshowstypicalfeaturesofPacific-type[9](orB-type)sub-ductionzone.Spatially,thehigh-pressurerockscanbesubdividedintohigh-gradeblueschistbeltandlow-gradeblueschistbelt[5,6].Th…     

Paleoproterozoic lower crust beneath Nushan in Anhui Province： Evidence from zircon SHRIMP U-Pb dating on granulite xenoliths in Cenozoic alkali basalt

Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, and have been subjected to granulite-facies metamorphism at 1915 27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported. Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.     

Mixing events between the crust- and mantle-derived magmas in Eastern Kunlun: Evidence from zircon SHRIMP Ⅱ chronology

Granitoidswidelyoccurincontinentalcrustandareusuallygeneratedinresponsetocontinentalgrowthandassociatedcrust-mantleinteraction.Granitoidscanbepro-ducedthroughdifferentways,ofwhichmagmamixinghasdrawnspecialattentionbecauseofitsprofoundbear-ingsoncrust-mantleinteractionandcontinentalgeody-namics[1].Themostdistinctfeatureforgranitoidsformedbymagmamixingisprobablytheoccurrenceofmaficmicrogranularenclaves(MMEs).Sofar,originforMMEsisstillhotlydebated,andavailablehypothesesconsidertheMMEsas(1)ref…     

SHRIMP U-Pb zircon geochronology and its implications on the Xilin Gol Complex,Inner Mongolia,China

The Xilin Gol Complex was referred to the meta-morphic rocks exposed near Daqing Pasturage, east of Xilinhot, for the first time by the Hebei Geological Survey in 1958[1]. Similar metamorphic rocks have been increas-ingly identified in the Xilin Gol-Xiwuqi-Balinyouqi re-gion since then. They all are collectively grouped into the Xilin Gol Complex and considered as a part of the Bao- yintu Group (Pt1by)[1]. However, the timing of its deposi-tion and subsequent deformation and metamorphi…     

Identification of Mesoproterozoic zircons in a Triassic dolerite from the Liaodong Peninsula,Northeast China

Evolution of mantle and crust in all blocks of China and their relationship with the surrounding blocks are re-lated to amalgamation and breakup of the supercontinents. Studies on the Mesoproterozoic Grenvillian orogeny and the configuration of Neoproterozoic Rodinia provide the most important advances to the ideas of continental crustal growth and configuration of plates[1,2]. Recent studies show that there are geological records of assembly and breakup of Rodinia in the Cathaysia and Yang…     

Zircon SHRIMP U-Pb dating of meta-diorite from the basement of the Songliao Basin and its geological significance

Located in the east portion of the North Orogenic Belt, the Songliao Basin is bounded by the Da Hinggan Mountains in the west, the Xiao Hinggan Mountains in the north, the Zhangguangcai Range in the east, and the North China Craton (NCC) in the south (Fig…     

内蒙古中部宝力高庙组长英质火山岩U-Pb-Hf同位素特征及其地质意义

锆石SHRIMP U-Pb定年结果显示: 内蒙古中部白音乌拉地区原宝力高庙组的流纹岩形成时代为300.0±2.9 Ma, 属晚石炭世; 青格勒宝拉格地区原宝力高庙组的凝灰岩结晶年龄为159.6±1.4 Ma, 并获得 3颗捕获锆石的年龄分别为291.8±3.4, 304.0±3.3和734.7±9.2 Ma, 应属于晚侏罗世满克头鄂博组。锆石LA-MC-ICP-MS Hf同位素分析显示: 流纹岩锆石ε_Hf(t) 值为+10.5~+12.9, T_DM^C值为493~645 Ma; 凝灰岩岩浆锆石ε_Hf(t)值为+10.1~+13.1, T_DM^C值为369~563 Ma。研究结果表明, 流纹岩源于晚古生代新生地壳的重熔并混入少量老地壳物质, 凝灰岩源于晚古生代地壳的熔融。Hf同位素特征显示晚古生代流纹岩和中生代凝灰岩源于相似的源区, 揭示了晚古生代的一次重要的增生事件, 并且在约160 Ma时期发生过地壳的再造。结合前人的研究成果表明, 兴蒙造山带在约300 Ma时处于古亚洲洋演化过程中岛弧向碰撞后伸展环境的转换时期, 在约160 Ma受到蒙古?鄂霍茨克构造域的影响。     

SHRIMP zircon U-Pb dating for subduction-related granitic rocks in the northern part of east Junggar, Xinjiang

A great deal of studies have recently devoted to the Central Asian orogenic belt (CAOB). Some of the studies have proposed that CAOB is a tectonic frame ofcomplex mosaic fragments, link of multiple suture zone and mountain-basin coupling, and has undergon…     

SHRIMP U-Pb zircon geochronology of granulites at Rimana （Southern Tibet） in the central segment of Himalayan Orogen

TheCenozoicHimalayanorogenisimportantinun-derstandingcontinentaldynamicprocesses.Lowercrustal,high-grademetamorphicrockshaverecentlybeendiscov-eredinNamcheBarwaandParmir,i.e.therespectivere-gionsofeasternandwesternsyntaxisoftheorogen[1—4].Eclogitesthatunderwentgranulite-faciesmetamorphismhaverecentlybeenreportedintheCadaareatotheeastofMountEverestinthecentralsegmentoftheHimalayanorogen[5].WiththehelpofthegeologicalsurveyofDing-gyeCountyandChentangSheets(scale1︰250000),high-pressuremafic…     

The recognizing of ca. 1.95 Ga tectono-thermal eventin Kongling nucleus and its significance for the evolution of Yangtze Block, South China

Some 1.95 Ga metamorphism of high-grade Archean rocks in Kongling terrain, continental nucleus of Yangtze Block, South China, are recognized by Sm-Nd dating. This event is further confirmed by the ages of single zircon SHRIMP U-Pb and K-Ar analyses of TTG and (or) paragneisses, and intrusions of potassic-granitic batholith in the region. The coincidence in period between the high-grade metamorphism in the Kongling area and the creation of major basement rocks of its neighborhoods of the Yangtze Block around the Kongling Archean nucleus makes it a favorable explanation for their tectonic connections that, in the whole Yangtze Block there was some tectono-thermal event of ca. 2.0—1.8 Ga, which resulted in the formation of unitive Yangtze basement.     

SHRIMP U-Pb zircon age of the Jinbaoshan ultramafic intrusion, Yunnan Province, SW China

SHRIMP U-Pb zircon dating gives ages of 260.6± 3.5 Ma and 260.7± 5.6 Ma for serpentinised wehrlite and plag-hornblendite in the Jinbaoshan ultramafic intrusion, respectively. The results indicate that the Jinbaoshan intrusion was emplaced at ca.260 Ma and contemporaneous with the Emeishan continental flood basalts (ECFB), similar to other mafic-ultramafic intrusions of the Emeishan large igneous province (LIP). The new ages provide a geochronological constraint on the origin of the Jinbaoshan ultramafic intrusion. It confirms that the Jinbaoshan ultramafic intrusion belongs to the Emeishan LIP that formed at ca. 260 Ma. Supported by Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-111), National Natural Science Foundation of China (Grant Nos. 40573020 and 40773033) and National Basic Research Program of China (Grant No. 2007CB411408)     

Lower boundary age of the Nanhua System and the Gucheng glacial stage: Evidence from SHRIMPⅡ dating

After the disintegration of the pro-Sinian System, the choice of the stratotype section of the newly established Nanhua System and determination of its lower boundary age have been one of the most important problems in Neoproterozoic stratigraphy[1—3]. In the Yangtze Gorge area in Yichang of Hubei Province where the standard section of the pro-Sinian System is located, the newly established Nanhua System consists only of the Nantuo formation (tillite) and the Liantuo Formation with tuf-…     

Finding of Neoproterozoic （～775 Ma） magmatism recorded in metamorphic complexes from the North Qilian orogen： Evidence from SHRIMP zircon U-Pb dating

The Qilian Mountain is considered a part of the Cen- tral Orogenic Belt of China[1]. The Central Orogenic Belt of China, extending for a distance of about 4000 km long in the E-W direction from the east coast west- ward through the mainland China all the …