SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications

The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower val-ley of the Yangtze River,is one of the important vol-canic basins in East China. Volcanic rocks in the Jin-niu Basin are distributed mainly in the Majiashan Formation,the Lingxiang Formation and the Dasi Formation,consisting of rhyolite,basalt and basaltic andesite,(trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively,in which the Dasi volcanism is volumet-rically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indi-cate that there exist a large amount of magmatic zir-cons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128 ± 1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios,this age is considered to represent the crystallization time of the Dasi volcan-ism. The volcanic rocks in the Dasi,Majiashan and Lingxiang Formations share similar trace elementand REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geol-ogy,it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Creta-ceous,just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also sug-gested for tectonic regime in this region in the Cre-taceous Period.     

SHRIMP U-Pb zircon geochronology of Yangfang aegiriteaugite syenite in Wuyi Mountains of South China and its tectonic implications

In addition to the wide spread peraluminous granites, some alkaline or alkali-rich intrusive rocks were recently observed in the Wuyi Mountains. The Yangfang aegiriteaugite syenites in the Wuyi Mountains are strongly enriched in light rare earth elements (LREE), K, Ba, Ga, Zr and Y. What is more, differentiations of REE are obvious. In addition, the Yangfang aegiriteaugite syenites have also some characteristics similar to A-type granite. Zircons are selected from the Yangfang aegiriteaugite syenites for Sensitive High-Resolution Ion Microprobe (SHRIMP-Ⅱ) U-Pb geochronology study. 15 analyses give concordant 206Pb/238U ages in a narrow range of 233—249 Ma, which correspond to a single age population with a weighted mean 206Pb/238U age of 242 4 Ma, which records the crystallization time of the aegiriteaugite syenites. It is suggested that: (1) there were early Triassic peralkaline intrusive rocks in South China; (2) the early Indosinian extension event was probably active in local area, South China. This discovery provides a new insight for farther understanding of 揑ndosinian orogeny in South China.     

Ages and tectonic significance of the collision-related granite porphyries in the Lhunzhub Basin, Tibet, China

The Paleocene collision-related granite porphyries are identified for the first time along the western margin of the Lhunzhub Basin, Tibet. SHRIMP U-Pb zircon analysis indicates that the granite porphyries were emplaced at 58.7±1.1 Ma (MSWD = 0.79) during the Indo-Asian continental collision. The granite porphyries are peraluminous and high in K, belonging to the calc-alkaline to high-K calc-alkaline series. They are relatively enriched in LILE, Th and LREE and depletion in Ba, Nb, P and Ti, characterized by LREE-enriched patterns with slightly to moderately negative Eu anomalies. These Paleocene granite porphyries are interpreted as the products generated by partial melting of the pre-existing arc crustal rocks caused by the increase of pressures and temperatures during the crustal shortening at the early stages of the Indo-Asian continental collision since 65 Ma. Despite inherited geochemical features and tectonic settings of the arc protoliths, they are significantly different from the volcanic rocks of the Dianzhong Formation within the Linzizong Group and the Miocene granite por- phyries in the Gangdise belt.     

LA-ICP-MS U–Pb geochronology of detrital zircons from the Zhaochigou Formation-complex in the Helan Mountain and its tectonic significance

This paper carries out studies about LA-ICPMS U–Pb dating and Hf isotopic compositional analysis for detrital zircons in two metasedimentary samples that were taken from the Zhaochigou Formation-complex in the Helan Mountain.The results show that the Zhaochigou Formation-complex formed*1.96 Ga,and it is a part of the Khondalite Series that is widespread in the North China Craton(NCC).The age spectrum of the detrital zircons indicates that the Zhaochigou Formation-complex shared the same provenance with the eastern edge of the Khondalite Series.Products of ancient magmatic activities within the Khondalite Belt may be the major source for the sedimentary materials that formed the Khondalite Series.Our age-dating results suggest that the Khondalite Series in the NCC may have experienced two stages of metamorphism,as the early stage occurred during 1.96–1.95 Ga,and the later stage occurred at about 1.87 Ga.The Hfisotopic data indicate that the Western Block of the NCC endured a stage of crustal growth at 2.5–2.3 Ga.     

U-Pb dating of zircons from quartz diorite and its enclaves at Tongguanshan in Anhui and its petrogenetic implication

The Tongling area, Anhui Province lies in the centralpart of the Cu-Fe-Au mineralization belt of the Mid-dle-Lower Yangtze River region, and hosts the highestincidence of this mineralization belt. Geotectonically, theTongling area is located at the middle of the Lower Yang-tze fold belt in the Yangtze block. Silurian to Triassicshallow marine carbonatite and a few semi-abyssal sili-ceous rocks, continental-ocean arenites are the dominantoutcropping strata. A series of NE trending fold s…     

SHRIMP U-Pb zircon dating on Nyainqentanglha granite in central Lhasa block

The Nyainqentanglha granite, a batholith with an area of 1500 km^2 in the central Lhasa block, comprises mainly medium-fine-grained biotite monzonitic granite and medium-coarse-grained biotite monzonitic granite. Their contact relationship suggests that the medlum-fine-grained biotite monzonitic granite was crystallized earlier than the medium-coarse-grained monzonitic granite. A SHRIMP U-Pb dating on zircons from representative samples of the batholith shows that the crystallization age of the medium-fine-grained biotite monzonitic granite is 18.3 Ma and that of the medium-coarse-grained monzonitic granite is 11.01 Ma. The emplacement and crystallization of the Nyainqentanglha granite, the youngest granite batholith ever known inside the Lhasa block, have a close relationship with the collisional orogeny, crustal thickening, plateau uplifting,E-W crustal extension and have a dynamic genetic relationship with the crustal partial melting.     

秦皇岛柳江盆地混合花岗岩的锆石U-Pb定年

目的确定秦皇岛柳江盆地基底混合岩的年龄。方法在锆石阴极荧光内部结构研究的基础上,进行LA-ICP-MS锆石原位U-Pb定年。结果获得柳江盆地基底混合岩化作用发生的年代为2570-2 560 Ma。结论冀东地区华北地台的基底在2 560 Ma的晚太古代已经发育成熟。     

SHRIMP zircon U-Pb geochronology of Indosinian granites in Hunan Province and its petrogenetic implications

The structure, magmatism and sedimentation within the South China Block (SCB) related to the Indosinian Orogeny had attracted considerable attention since De-prat[1] and Fromagat[2] proposed the “Indosinian move-ment” based on two unconformities between Pre-Norian and Pre-Rhaetian during Triassic in Vietnam. However, Indosinian tectonic evolution of the SCB has been long debated[3―6]. Some researchers believed that the compli-cated structure-magmatism-sedimentation within the SCB w…     

U-Pb dating of zircon grains from the ore-bearing plagioclase amphibolite in the Dashuigou Te deposit

The Dashuigou Te deposit is a unique independent one found in the world, and hosted in the plagioclase arnphibolite. The upper intercept age of single zircon from the arnphibolite can be considered to be the crystallization age of the source-rock of the amphibolite (tholeiitic basalt), while the lower intercept is nearly consistent with the time of the tectono-thermal event.     

LA-ICP-MS zircon U-Pb dating for high-pressure basic granulite from North Qinling and its geological significance

Inrecentyears,discoveriesofhightoultrahighpressuremetamorphicrocksatthenorthandsouthsidesoftheQinlingGroupinthenorthernpartoftheQinlingMountains(hereafterNorthQinling)haveattractedfocusattentionofgeologistsworldwide.Thenorthhigh-pressure(HP)metamorphicbelt,distributedintheareafromGuanpotoShuanghuaishunorthwardtoShizipin,LushCountyinHenanProvince,consistsmainlyofeclogiteoutcroppedaslenticularmassesofdifferentsizesinthegneissesoftheQinlingGroupclosetothesouthsideofZhuyangguan-Xiaguanfault…     

Comparison of SHRIMP U-Pb dating of monazite and zircon

Monazite dating is an important technique in geochronological studies. However, monazite U-Pb dating by SHRIMP is much less popular than zircon in geochronological applications. This paper compares the results of SHRIMP U-Pb dating of monazites and zircons separated from two granite samples, indicating that monazite SHRIMP U-Pb dating at the Beijing SHRIMP Centre is feasible and provides identical results within error.     

SHRIMP U-Pb zircon dating for Qiashikansayi granodiorite, the Northern Altyn Tagh Mountains and its geological implications

The Qiashikansayi granodiorite is foliated resulting in a granodioritic gneiss. Its geochemical features, such as alumina saturation index(A/CNK) of 0.81-0.99, Na2O/K2O values>1, TiO2 contents <1.0%, LREE enrichment with high fractionation factors, weakly negative or no Eu anomalies, and significant Ba and Ti negative anomalies, suggest that it is similar to a typical island arc pluton. The trace elements of the Qiashikansayi granodiorite are plotted in the island arc field in the tectonic setting discrimination diagrams as well. Cathodoluminescence images demonstrated that the zircons have clear rhythmic crystallized zoning, without any remnant core and new crystallized rim, suggesting the zircons be magmatic ones. Their U and Th contents vary in the range of 574-870 μg/g, and 279-556μg/g respectively, with the Th/U ratio in the range of 0.52-0.68. SHRIMP zircon U-Pb dating yielded the 481.5±5.3 Ma age for the intrusion of the granodiorite, which is coeval with the island arc volcanic rocks in the no     

The existing time of Sihetun vertebrate in western Liao- ning, China---Evidence from U-Pb dating of zircon

In different opinions, the stratigraphic time of the feathered dinosaurs and early birds in Sihetun and its neighboring areas in Beipiao, western Liaoning is appointed to different epoches of eras, such as Late Jurassic, Early Cretaceous and Late Jurassic-Early Cretaceous. Even the recently dating data are still very different. This note first reported the U-Pb age of (125.2±0.9) Ma of zircon separated from tuff of Sihetun vertebrates horizon. The age reveals that Sihetun vertebrate belongs to Early Cretaceous. The method is more objective, because of the strong ability of disturbance resistance and high U-Pb blocking temperature of zircons.     

甘肃北祁连武威地区莲花山花岗岩体的单颗粒锆石U-Pb年龄及其地质意义

在1:25万武威幅区域地质调查中对北祁连莲花山花岗岩体进行了调查研究,通过高精度单颗粒锆石U-Pb同位素测年,获得w(206Pb)/w(238U)表面年龄统计权重平均值为426±15 Ma,属加东晚期.岩石化学和地球化学特征表明莲花山岩体属钙碱性系列,少量为高钾钙碱性系列.σ=0.6~2.3,A/CNK=0.81~1.04,ΣREE=68.58~188.76,LREE/HREE=2.80~5.09,δEu=0.60~0.87.研究表明莲花山岩体形成于陆陆碰撞造山阶段后期,可能形成于加厚地壳的部分熔融.