辽北新宾?苇子峪地区太古宙花岗质岩石的形成年代、成因及其地质意义

辽北新宾?苇子峪地区的花岗质岩石主要由英云闪长质?奥长花岗质片麻岩和二长花岗岩?正长花岗岩岩体等组成。为确定其形成年代及成因, 对这些花岗质岩石进行锆石U-Pb-Hf同位素和全岩地球化学分析。锆石LA-ICP-MS U-Pb同位素定年结果表明这些花岗质岩石均形成于新太古代, 英云闪长质和奥长花岗质片麻岩的岩浆结晶年龄分别为2588±4 Ma (MSWD=1.3)和2587±6 Ma (MSWD=1.8), 二长花岗岩?正长花岗岩则侵位于2555±4 Ma (MSWD=0.51)。全岩地球化学和锆石Lu-Hf同位素研究表明, 英云闪长质?奥长花岗质片麻岩形成于俯冲板片的部分熔融, 其原始岩浆在上升过程中受到地幔楔岩石的交代; 而二长花岗岩?正长花岗岩中一部分岩浆起源于变质杂砂岩的部分熔融, 其余形成于以变质玄武岩与变质沉积岩为主要成分的混合源区的部分熔融。结合近年的研究成果, 认为新宾?苇子峪地区的新太古代花岗质岩石可能形成于活动大陆边缘的动力学背景。     

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…     

Single zircon LAM－ICPMS U－Pb dating of Guidong complex （SE China） and its petrogenetic significance

Because of the strong effects of the Caledonian and Indosinian orogenies and Yanshanian magmatism since early Paleozoic time, different types of granites and ore deposits occur widely in the Nanling region of SE China[1]. The Guidong complex is situated at the border between the South Jiangxi—North Guangdong post-Caledonian orogenic belt and the Hercynian-Indosinian belt, which is constrained by an E-W regional deep fault (Guidong-Da- dongshan deep fault) and therefore is elongated nea…     

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling,northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2.The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions.The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite,whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite.There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata,forming an ore-rich belt around the batholith.Based on zircon LA-ICP-MS U-Pb ages,the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma(MSWD = 2.49),with slightly earlier magmatic activity at 243.0 ± 5.8 Ma(MSWD = 2.62).The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma(MSWD = 1.44).The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma(MSWD = 11.3).Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period.These new results together with previous isotope data,suggest that South China underwent not only the well-known Yanshanian mineralization event,but also a widespread Indosinian metallogenic event during the Mesozoic period.Therefore,South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.     

江南隆起（九岭）多阶段构造演化的花岗岩记录

以江南隆起九岭花岗岩体为研究对象,应用激光剥蚀等离子体质谱(LA-ICP-MS)锆石U-Pb定年技术,得到该花岗岩侵入年龄为853～811Ma.自晋宁期以来,九岭地区依次经历了加里东、印支及燕山等多阶段构造演化.通过花岗岩地球化学及构造图解分析,可知江南隆起九岭多阶段构造演化环境各不相同.晋宁期(929-810 Ma)花岗岩体落入岛弧与碰撞的过渡环境;而加里东期(439-411 Ma)花岗岩体具板内汇聚环境特点;燕山期(158-118 Ma)花岗岩形成于同碰撞兼火山弧构造环境.     

^40Ar／^39Ar dating of Daqingshan thrust

The Daqingshan thrust system is an important part of the western segment of the Mesozoic Yinshan-Yanshan orogenic belt. Therefore, much attention has been paid to the thrusts due also to their large-scale and entirely devel-oped structural elements and typical structural styles. Studies and progress have been concentrated on the ge-ometry, kinematics, dating and dynamic mechanism of the thrust and thrusting. To date, there have been no reliable published isotopic data, however, on the dating…     

Triassic U-Pb age for zircon from granites in the Tonghua area and its response to the Dabie-Sulu ultrahigh-pressure collisional orogenesis

Single-grain zircon U-Pb dating was carried out to constrain the emplacement timing of granitic plutons at Chaxinzi, Xiaoweishahe and Longtou in the Tonghua area, south of Jilin Province. The results show that these plutons formed in the Triassic with ages of 203—217 Ma. Geological and geochemical characteristics indicate that the plutons are composed of quartz diorite and granite. The former was derived from partial melting of mafic lower crust, whereas the latter originated from thickened crust with garnet as the residue in the source. It appears that protoliths of these two types of granitits are different although they have the same emplacement age. Considering that these plutons are petrologically different from the coeval granites in the Xingmeng (Xing‘an-Mongolian) to Jihei (Jilin-Heilongjiang) orogenic belt in the north, it is suggested that their formation was related to the Dabie-Sulu ultrahigh-pressure collisional orogenesis since their ages are only 10—20 Ma younger than timing of the ultrahigh-pressure metamorphism, but comparable to that of the first rapid exhumation of the ultra-high-pressure metamorphic rocks and the emplacement of the post-collisional granites.     

Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China

The Miaoershan uranium(U)ore field in northeastern Guangxi is one of the important granite-related U deposits in south China and is closely related to the Douzhashan U-bearing granite.The Douzhashan granite contains primary U-rich accessory minerals,including monazite(UO2=0.98-1.75 wt%)and xenotime(UO2=1.48-6.14 wt%).Primary monazite and xenotime yield chemical ages of 231±28 Ma and 230±38 Ma by electron microprobe analysis and U-Pb isotopic ages of 220±6 Ma and 211±7 Ma by laser ablation-inductively coupled-mass spectrometry respectively.These ages demonstrate that the Douzhashan granite formed during the period of Indosinian magmatic activity.Back scattered electron imaging shows that monazite and xenotime are commonly altered to assemblages of low-U synchisite and apatite,which was associated with loss of U to hydrothermal fluids.U-Th-Pb analyses of secondary apatite yielded a chemical age of 136±17 Ma,which corresponds to the timing of Cretaceous-Tertiary crustal extension in south China.We suggest that the heat and CO2required for mineralization was the result of Yanshanian crustal extension,and that this triggered the breakdown of U-rich accessory minerals in the Douzhashan U-bearing granite.Uranium remobilization from the Douzhashan granite provided materials for mineralization within the granite and/or surrounding country rocks.Therefore,a combination of Indosinian compression and Yanshanian extensional overprint produced the hydrothermal U deposits associated with the Douzhashan granite.     

SHRIMP zircon U-Pb ages of Kalatongke No. 1 and Huangshandong Cu-Ni-bearing mafic-ultramafic complexes,North Xinjiang,and geological implications

In Xinjiang, northwestern China, there are some veryimportant magmatic Cu-Ni sulfide deposits hosted by ma-fic-ultramafic complexes. In addition to the Jingbulake inwestern Tianshan and the Xingdi in northeastern Tarimblock, the others are concentrated in the Kalatongke andHuangshan-Jingerquan mafic-ultramafic complex beltsand two largest Cu-Ni sulfide deposits occur in the Kala-tongke No.1 and Huangshandong complexes. In the pastdecade, a great number of researches have been conductedfo…     

西藏洞中拉铅锌矿床石英斑岩锆石U-Pb年代学研究

探讨西藏洞中拉铅锌矿区的石英斑岩岩体归属.通过详细的地质填图,并采用LAICPMS锆石U-Pb法年龄测定技术,对石英斑岩进行年代学研究.通过石英斑岩样品中单颗粒锆石22个样品点的分析,得到其206 Pb/238U的加权平均年龄为126.9±1.1 Ma,MSWD=0.96.这一结果否认了这套岩石单元属于始新世林子宗群帕...     

北祁连西段熬油沟——-二只哈拉达坂蛇绿岩的形成环境和时代

熬油沟蛇绿岩是北祁连造山带西段最具代表性的蛇绿岩残片之一。运用SHRIMPⅡ锆石U-Pb法, 对北祁连造山带西段的熬油沟和二只哈拉达坂两地出露的细粒辉长岩和粒玄岩进行了精确同位素测年。采自熬油沟剖面的细粒辉长岩样品 ²⁰⁶Pb/²³⁸U年龄数据分布在一个很小的范围(490~508 Ma), 其加权平均年龄为501±4 Ma (MSWD=1.09); 采自二只哈拉剖面的粒玄岩样品年龄值稍小, ²⁰⁶Pb/²³⁸U加权平均年龄为495±4 Ma (MSWD=0.98)。结合详细的野外调查、矿物化学和地球化学研究, 认为熬油沟?二只哈拉达坂蛇绿岩构造破坏严重, 其中基性岩浆岩代表早?中寒武世的北祁连洋壳。与新元古界朱龙关群碳酸盐岩和砂泥岩整合产出 的玄武岩不能作为蛇绿岩的喷出岩系列, 而有可能是震旦纪的大陆溢流玄武岩, 代表新元古代全球Rodinia大陆裂解的岩浆产物。     

Two granitic plutons in Central Western Kunlun Belt: Their ages and possible sources

Geochronological and isotope studies have been carried out for two important plutons in the Central Western Kunlun Belt. U-Pb single grain zircon dating results show that the North Kudi Pluton (404 Ma) was produced near the end of Caledonian; whereas the previously labeled Hercynian Arkarz Mountain Pluton (215 Ma) is either an Indosinian pluton or a product of multiple-phase magmatism. Sm/Nd isotopic data suggest that their sources are quite heterogeneous, and continental crust played an important role during the generation of these two granitic plutons.     

U-Pb zircon age of the foliated garnet-bearing granites in western Dabie Mountains, Central China

U-Pb zircon dating on two foliated garnet-bearing granite samples in the western Dabie ultra-high-pressure (UHP) metamorphic unit yields concordant ages of (234±4) Ma and (227±5) Ma, respectively. These ages, following the UHP peak metamorphism, represent the magma emplacement ages for the foliated garnet-bearing granites. This, for the first time, shows that there are the Triassic granites in the Dabie Mountains. The foliated garnet-bearing granites resemble A-type granite in geochemical characteristics, indicating that they were formed in extensional geodynamic setting. The magma formation reflects a reheating event in the Dabie orogenic belt and it enhances the transfer of tectonic regime from collision into extension and promotes the rapid exhumation into lower crust for the UHP metamorphic rocks.     

Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication

The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclastic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spectrometry （LA-ICPMS）. The results reveal that the Wudangshan volcanic sequence was formed at （755±3） Ma （a weighted mean from the 5 samples, MSWD=0.47）, whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at （685±5） （2 samples, MSWD=0.36） and （679±3） Ma （MSWD=1.6）, respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are Identical to those of the bottom Liantuo and slightly older than those of the Nantuo Formations, respectively, lower strata of the Nanhua （middle to late Neoproterozoic） stratotype section in eastern Three Gorges, Yangtze creton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830-780 Ma igneous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze creton before the Qinling Orogeny.     

辽东青城子矿田煌斑岩锆石U-Pb年龄及其地质意义

为了深入了解辽东青城子矿集区煌斑岩岩石成因、形成的大地构造环境和地质意义,通过单颗粒锆石LA-ICP-MS U-Pb定年系统和X射线荧光光谱仪,对青城子矿集区煌斑岩进行锆石U-Pb年代学和主量元素地球化学方面研究.结果表明,煌斑岩具有低硅、富镁铁的特点,煌斑岩侵位年龄为(226.0±1.0)M a~(227.7±1.3)M a,属于晚三叠世岩浆活动的产物.结合区域构造背景和前人研究,推测煌斑岩是扬子克拉通-华北克拉通深俯冲过程的板片断离的产物,扬子克拉通的深俯冲和陆-陆碰撞可能是华北克拉通东部在中生代破坏的主要原因.     

江西乐平塔前钼(钨)矿床成岩成矿时代及意义

探讨江西省乐平市塔前钼(钨)矿床成矿岩体的形成时代。通过对塔前钼(钨)矿床进行野外地质调查和SIMS锆石U-Pb测龄,结果表明其成矿母岩为花岗闪长斑岩,其加权平均年龄为160.9±2.5 Ma(MSWD=0.69),代表矿区花岗闪长斑岩的结晶时间。这与矿区矽卡岩矿石中辉钼矿Re-Os同位素年龄(162±2 Ma)在误差范围内一致,说明此矿床形成于中侏罗世晚期。将其与钦杭成矿带东段塔前-赋春成矿带与乐华—德兴成矿带中同类矿床进行对比发现,前者成矿年龄集中于161 Ma±,控岩控矿构造皆以北东向为主;而后者成矿年龄集中于170 Ma±,控岩控矿构造以北西向为主,预示钦杭成矿带东段2个成矿阶段(170~161 Ma B.P.)区域构造应力方向可能发生了重大转变。     

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.     

Discovery of Paleoproterozoic rapakivi granite on the northern margin of the Yangtze block and its geological significance

The Huashanguan rapakivi pluton in Zhongxiang,Hubei Province,China,is the first discovered Proterozoic rapakivi pluton in the Yangtze block.Based on field and petrographical observations,a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton.Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts.Alkali feldspars and quartz had two or more generations.Petrochemically,the Huashanguan rapakivi granites were characterized as having high values of Si,K,Fe,Th,U,La,Ga,Ce,Sm and LREE,low values of Ca,Mg,Sr,Nb,Y and HREE,and a negative Eu anomaly.These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites,and had an affinity to A-type granites.LA-ICP-MS U-Pb zircon dating also was conducted.The dating yielded a 207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2),which represents the age of the pluton emplacement.The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton,and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation.The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block.These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent.     

Paleoproterozoic reworking of ancient crust in the Cathaysia Block, South China: Evidence from zircon trace elements, U-Pb and Lu-Hf isotopes

A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory zoning and high Th/U ratios (>0.1). The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1860±13 Ma (MSWD=0.084), representing the formation age of the granite. The magmatic zircons had negative εHf(t) values of −15.6 to −10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite in a post-orogenic extensional tectonic setting. We conclude that the Paleoproterozoic crustal reworking event in the Cathaysia Block of South China marked the transition from assembly to break-up of the Columbia supercontinent. Supported by National Natural Science Foundation of China (Grant No. 40873004), Special Funds for National Scientific Research of Commonweal Industries, the Ministry of Land and Resources of China (Grant No. 2008110015), Opening Foundation of State Key Laboratory of Continental Dynamics, Northwest University (Grant No. 06LCD12) and the Project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)     

Zircon U-Pb ages for Wulian granites in northwest Sulu and their tectonic implications

The Sulu orogen is the eastern termination of the Qinling-Dabie-Sulu orogenic belt that results from the Triassic collision between the North China and the Yang-tze plates[1—4]. It contains ultrahigh pressure (UHP) meta-morphic rocks such as eclogite, granitic gneiss and marble. The Wulian complex zone, north to the Wulian fault in the Jiaonan area, is about 10—14 km wide and consists of metaigneous and metasedimentary rocks that only ex-perienced greenschist-facies metamorphism (Fig. …