冀北太古代花岗质片麻岩的成因

冀北是华北克拉通早前寒武纪变质基底的主要出露地区之一。分布于承德-滦平和赤城-张家口地区的新太古代花岗质片麻岩主要由英云闪长岩、奥长花岗岩、花岗闪长岩和二长花岗岩(TTGM)组成,构成了低钾、中钾和高钾钙碱性三个岩石化学系列。二长花岗质片麻岩的LA-ICP-MS锆石U-Pb和Lu-Hf同位素特征揭示其岩浆结晶年龄为2509±10Ma。全岩岩石化学、Sm-Nd同位素和锆石Lu-Hf同位素研究表明:(1)低钾钙碱性系列的岩石形成于拉班玄武质岩石的低度部分熔融;(2)中钾钙碱性系列岩石主要形成于玄武质岩石和杂砂岩的部分熔融,局部存在英云闪长质片麻岩的部分熔融;(3)高钾钙碱性系列的岩石形成于以高钾中酸性火山岩为主要成分的杂砂岩的部分熔融。结合近年来冀北早前寒武纪地质研究成果,这些太古代花岗质片麻岩全岩Sm-Nd同位素和锆石Lu-Hf同位素特征揭示~2.7Ga是本区太古代地壳的主要生长期。在新太古代发生了大规模的火山喷发,火山物质形成后不久发生部分熔融形成花岗质岩浆,接着发生变质、变形作用。这些花岗质片麻岩的形成与南美洲西海岸的构造-岩浆活动特征有类似之处,可能反映了太古代末期冀北地区从活动大陆边缘地壳增生、加厚到弧后伸展转化的动力学背景。     

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

Mineral chemistry, major and trace elements, ⁴⁰Ar/³⁹Ar age and Sr–Nd–Pb isotopic data are presented for the Late Cretaceous Hamsilos volcanic rocks in the Central Pontides, Turkey. The Hamsilos volcanic rocks mainly consist of basalt, andesite and associated pyroclastics (volcanic breccia, vitric tuff and crystal tuff). They display shoshonitic and high-K calc-alkaline affinities. The shoshonitic rocks contain plagioclase, clinopyroxene, alkali feldspar, phlogopite, analcime, sanidine, olivine, apatite and titanomagnetite, whereas the high-K calc-alkaline rocks contain plagioclase, clinopyroxene, orthopyroxene, magnetite / titanomagnetite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic matrix. Mineral chemistry data reveal that the pressure condition of the clinopyroxene crystallisation for the shoshonitic rocks are between 1.4 and 6.3 kbar corresponds to 6–18-km depth and the high-K calc-alkaline rocks are between 5 and 12 km. ⁴⁰Ar/³⁹Ar age data changing between 72 ± .5 Ma and 79.0 ± .3 Ma (Campanian) were determined for the Late Cretaceous Hamsilos volcanic rocks, contemporaneous with the subduction of the Neo-Tethyan Ocean beneath the Pontides. The studied volcanic rocks were enriched in the large-ion lithophile and light rare earth element contents, with pronounced depletion in the contents of high-field-strength elements. Chondrite-normalised rare earth element patterns (La_N/Lu_N = 6–17) show low to medium enrichment, indicating similar sources of the rock suite. Initial ⁸⁷Sr/⁸⁶Sr values vary between .70615 and .70796, whereas initial ¹⁴³Nd/¹⁴⁴Nd values change between .51228 and .51249. Initial ²⁰⁶Pb/²⁰⁴Pb values vary between 18.001 and 18.349, ²⁰⁷Pb/²⁰⁴Pb values between 15.611 and 15.629 and ²⁰⁸Pb/²⁰⁴Pb values between 37.839 and 38.427. The main solidification processes involved in the evolution of the volcanic rocks consist of fractional crystallisation, with minor amounts of crustal contamination ± magma mixing. According to geochemical evidence, the shoshonitic melts in the Hamsilos volcanic rocks were possibly derived from the low degree of partial melting of a subcontinental lithospheric mantle (SCLM), while the high-K calc-alkaline melts were derived from relatively high degree of partial melting of SCLM that was enriched by fluids and/or sediments from a subduction of oceanic crust.     

华北克拉通东北部新太古代晚期地壳生长:来自板石沟表壳岩年代学和Hf同位素的证据

对板石沟表壳岩中的斜长角闪岩和角闪片岩进行了锆石U-Pb年代学、地球化学以及Hf同位素分析,以探讨华北克拉通东北部新太古代晚期的构造环境和地壳演化。板石沟表壳岩主要岩石类型包括斜长角闪岩、斜长片麻岩、角闪片岩和磁铁石英岩,LA-ICP-MS锆石U-Pb测年显示斜长角闪岩(BA-1)岩浆锆石形成于2548±11Ma,绿帘角闪片岩(BA-6)岩浆锆石形成于2548±23Ma,代表了表壳岩的形成时代,在绿帘角闪片岩中识别出3颗年龄为2754±80Ma~2710±92Ma的捕获锆石,表明板石沟地区可能存在新太古代早期岩浆事件。斜长角闪岩和角闪片岩的原岩为玄武质火山岩,微量元素特征指示其形成于岛弧环境。Hf同位素分析结果显示斜长角闪岩εHf(t)为正值(0.29~8.89),单阶段模式年龄(tDM1)分布在2877~2469Ma之间,绿帘角闪片岩多具正的εHf(t)值(-0.78~8.03),tDM1介于2871~2544Ma,表明岩浆主要来源于亏损地幔,伴随少量古老地壳物质的再造,部分tDM1与207Pb/206Pb年龄相近,并同时具有高εHf(t)值的锆石反映板石沟地区新太古代晚期(2550Ma)发生过地壳增生事件。结合其他地区表壳岩研究成果,认为华北克拉通可能存在新太古代吉-辽-冀弧陆碰撞造山带,板石沟地区属于该造山带的一部分。     

Geochemistry of A-type granites in the Huangshaping polymetallic deposit (South Hunan,China): Implications for granite evolution and associated mineralization

The Huangshaping granites in Hunan Province, South China were investigated for their geochemical characteristics. Three types of granites have been petrographically identified: quartz porphyry, granophyre, and granite porphyry. Whole rock geochemistry suggests that the Huangshaping granites, especially the granite porphyry, exhibit typical A-type granite characteristics with their enrichment in Si, Rb, U, Th, and Nb and significant depletion in Ba, Sr, Ti, Eu, and P. Based on the Al, Y and Zr contents as well as the REE patterns of the rocks investigated, the quartz porphyry and the granophyre are classified as A₁ type alkaline granites whereas the granite porphyry is considered as A₂ type aluminous granite. Whole rock and quartz/feldspar O isotope data yields a wide range of δ¹⁸O_SMOW values (11.09–26.32‰). The granites are characterized by high radiogenic Pb isotopic composition. The present-day whole rock Pb isotopic ratios are ²⁰⁶Pb/²⁰⁴Pb = 18.706–19.155, ²⁰⁷Pb/²⁰⁴Pb = 15.616–15.711 and ²⁰⁸Pb/²⁰⁴Pb = 38.734–39.296. Combining the O–Pb isotope compositions with major, trace and REE geochemistry and regional geology characteristics, the Huangshaping granites were determined to resemble within-plate granites that were mainly derived from a felsic infracrustal source related to continental extension. The magma source of the quartz porphyry and the granophyre may have been generated from deeper depths, and then ascended rapidly with limited water content and low oxygen fugacity, which contributed to Cu, Pb and Zn mineralization. On the other hand, the magma that generated the granite porphyry may have ascended relatively slower and experienced pronounced crystal fractionation, upper-crustal basement rock contamination (assimilation) and wall–rock interaction, producing the Sn- and W-rich granite porphyry. This study reveals the crustal extension process and associated magmatic–metallogenic activities during 180–150 Ma in South Hunan.     

湖南省道县虎子岩片麻岩包体的岩石学特征和年代学研究

通过对道县虎子岩碱性玄武岩中片麻岩包体的岩石化学、Ｎｄ同位素模式年龄ＴＤＭ和颗粒锆石Ｕ－Ｐｂ法测年结果，确定了本区片麻岩包体的变质反应、变质相和原岩类型，恢复了本区前寒武纪地壳的形成和演化历史     

Calpionellid zones of the Tithonian–Berriasian exotic limestone clasts from the Outer Carpathians,Poland

Calpionellids and chitinoidellids were identified from exotic limestone clasts occurring in flysch deposits of the Early Cretaceous to Oligocene age from the Silesian and Subsilesian nappes of the Polish Outer Carpathians. They represent the remnants of carbonate sedimentation along the northern and southern margin of the Severin-Moldavidic Basin, areas which are no longer preserved on the surface. Chitinoidellid and calpionellid assemblages characterize the Chitinoidella, Crassicollaria and Calpionella zones (latest early Tithonian–early Berriasian). The calpionellid zonation for the Western Carpathians was used for the present study, but some difficulties were encountered resulting from the application of this zonation. Cathodoluminescence imaging (CL) was useful for the identification of these microfossils in samples containing sparse and poorly preserved specimens, especially in the studied shallow-water limestone (the so-called Štramberk-type limestones).     

Genesis of the Ore-related Granite Porphyry and Molybdenite Re-Os Age of Laomiaogou Porphyry-skarn Mo Deposit,Western Henan Province: Implications for Regional MineralizationEI北大核心CSCD

The newly discovered Laomiaogou porphyry-skarn Mo deposit is located south of the Machaoying fault in western Henan province. The ore-body is hosted in the contact between the Laomiaogou granite porphyry dyke and the Duguan Formation. LA-ICP-MS U-Pb analyses for zircons from the granite porphyry yield a weighted mean 206Pb/238U age of 152.1±0.6 Ma, and seven molybdenite separates yield a weighted mean age of 151.9±0.9 Ma and isochron age of 151.6±5.1 Ma. Thus, the granite porphyry dyke and Mo mineralization are contemporaneous. The ore-related granite porphyry dyke is a peraluminous I-type granite with high contents of SiO2 and K2O. The rocks are strongly depleted in P, Nb, Ta and Ti, indicative of intensive fractionation of apatite and Fe-Ti oxides, and characterized by low whole-rock εNd(t) (-20.6 to -17.6) and zircon εHf(t) values (-26.9 to -22.6). The old tDM2(Nd) ages (2.37 to 2.61 Ga) and zircon tDM2(Hf) ages (2.62 to 2.88 Ga) suggest that the granite porphyry was likely derived from an ancient crustal source. Considering the tectonic evolution and geochemical characteristics of the granite as well as other Mesozoic granites in the southern margin of the North China Craton, we suggest that the Laomiaogou granite porphyry dyke and Mo were most likely derived from partial melting of the Taihua Group metamorphic rocks under extensional tectonic regime related to the subduction of the paleo-pacific plate. © 2018, Science Press. All right reserved.     

西昆仑赞坎铁矿地质和地球化学特征及矿床类型探讨

赞坎铁矿位于西昆仑造山带塔什库尔干地块西段, 是近年新发现的一个大型沉积变质型磁铁矿床.铁矿体的顶—底板围岩分别为古元古代布伦阔勒群斜长角闪片岩和黑云母石英片岩; 矿区南部出露早古生代花岗岩岩体; 矿石类型以条带状及浸染状磁铁矿石为主, 兼具少量块状磁铁矿石.在详细矿区地质观察的基础上, 本文报道了矿石的地球化学特征与锆石U-Pb年代学分析结果.元素地球化学分析表明, 条带状铁矿石具有较高的稀土总量, 明显富集轻稀土, 未呈现明显Ce和Y元素的异常(Ce/Ce* =0.93～1.12、Y/Y* =0.74～1.30); 部分矿石显示Eu正异常(Eu/Eu* =1.66～4.46), 稀土配分形式与沉积变质型铁矿相似.矿体围岩变粒岩锆石U-Pb年龄为2 416±54 Ma, 大致反映沉积铁矿的形成时代, 而807±51 Ma的年龄反映变质作用时代.矿区一有铁矿捕虏体的花岗岩锆石U-Pb年龄为504±26 Ma.该期花岗岩的侵入对铁矿有明显的改造和叠加作用.     

方山口铀钒型非常规铀资源地球化学特征

文章以方山口U-V型非常规铀资源为研究对象,对该区矿化层和赋矿围岩进行了元素地球化学分析,结果表明:U、V呈明显正相关;在铀多金属矿化层中,与超基性岩浆有关的Cr、Co、Ni元素超常富集;稀土元素配分模式中呈现弱Ce负异常,Eu正异常;矿化层与围岩分析数据在ω(La)/ω(Yb)-∑REE图中投影点落在玄武岩区内。研究认为,方山口铀钒型非常规铀资源形成于早寒武世裂谷环境,在同沉积海相黑色岩系形成的同时,伴随着海底喷流作用,U、V多金属矿化层的形成可能与受超基性岩浆作用影响的热水作用相关联。     

华北克拉通北缘侏罗纪造山过程及关键时限的沉积证据

宁武-静乐盆地与浑源盆地位于华北克拉通中北部,侏罗纪地层序列完整,物源指向于阴山-燕山造山带中段,通过对盆地内侏罗纪沉积特征的研究,可以演绎华北克拉通北缘侏罗纪的造山过程。在盆地沉积分析的基础上,通过宁武-静乐盆地中侏罗统云岗组顶部的凝灰质泥晶碳酸盐岩及浑源盆地上侏罗统髫髻山组玄武-安山岩锆石U-Pb同位素测年,结合国际地层年代表推荐年龄及中侏罗统的沉积速率,对整个侏罗纪沉积序列转换的关键时限进行了限定。研究认为：中侏罗统云岗组底部砾岩沉积时期,侏罗纪沉积演化序列经历了早期湖进至晚期湖退的转换过程,暗示着区域应力场由早期的拉张向晚期的挤压转换,孕育着侏罗纪造山运动的开始,具体时限大约为168 Ma;中侏罗统云岗组顶部凝灰质泥晶碳酸盐岩沉积时期,沉积地层的颜色由其下的灰绿色突变为其上的紫红色,孕育着湖盆地形的突然抬升,区域氧化性增强,气候环境的突变,侏罗纪造山运动进入了快速发展阶段,具体时限为161.0～159.0 Ma;中/晚侏罗世沉积序列具有继承性的发育特征,随着湖盆地形的进一步抬升,侏罗纪沉积范围迅速退至造山带前缘,以砾岩沉积为主,为同期造山运动的产物,侏罗纪造山运动进入了高峰期,具体时限为159.0～153.0 Ma;晚侏罗世晚期,区域上以玄武-安山岩及凝灰质角砾岩沉积为主,侏罗纪造山运动进入了造山期后的调整阶段。