广西北香铅锌锡矿区成矿地质及地球化学找矿前景评价

文章从区域成矿背景、地层、构造等几方面探讨了矿床的成矿地质条件,指出NW向同沉积断裂对矿床的空间分布、产状等起主要控制作用,其次一级NW向断裂则是矿床的主要赋存构造,矿床的形成受地层岩性和构造双重控制。通过化探次生晕异常评价,圈定出北香一下大莫和莫四一南华两个呈NW-SE走向的综合矿化异常带。认为北香一下大莫异常带的走向延伸部位以及莫四一南华异常带的深部应具有一定的找矿潜力。     

内蒙古苏莫查干地区燕山期过铝质花岗岩研究

内蒙古苏莫查干地区的燕山期花岗岩体夹持于二连浩特-贺根山和索伦山-西拉木伦河深大断裂之间,其代表性岩石样品以富K、Al、Rb、Th和轻稀土元素,亏损Sr、Ti、P和Eu为特点,属高钾钙碱性过铝质花岗岩.钕同位素研究表明,岩石全岩样品的εNd(t)变化范围为0.77～-4.65,t2DM变化范围为869～1 310 Ma(多集中于1 072 ～1 310 Ma),与兴蒙造山带中的微陆块花岗岩相似.铅同位素的206Pb/204Pb=18.114～19.150,平均18.658;207Pb/204Pb=15.517～15.598,平均15.556;208Pb/204Pb=38.384～39.054,平均38.614;μ=9.2～9.5,平均9.37.所有数据点均投绘在造山带与地幔Pb演化线之间.主元素、微量元素、钕和铅同位素数据表明,本区燕山期花岗岩可能是在华北板块和西伯利亚板块碰撞造山后的伸展构造环境中,壳幔源物质通过物理混合后,再次发生重熔、成浆和结晶分异作用的产物,并且与该区的萤石和贱金属成矿作用具有密切的时空和成因联系.     

Geochronological problems related to polymetamorphism in the Limpopo Complex, South Africa

The integration of new and published geochronologic data with structural, magmatic/anatectic and pressure–temperature (P–T) process information allow the recognition of high-grade polymetamorphic granulites and associated high-grade shear zones in the Central Zone (CZ) of the Limpopo high-grade terrain in South Africa. Together, these two important features reflect a major high-grade D₃/M₃ event at ~ 2.02 Ga that overprinted the > 2.63 Ga high-grade Neoarchaean D₂/M₂ event, characterized by SW-plunging sheath folds. These major D₂/M₂ folds developed before ~ 2.63 Ga based on U–Pb zircon age data for precursors to leucocratic anatectic gneisses that cut the high-grade gneissic fabric. The D₃/M₃ shear event is accurately dated by U–Pb monazite (2017.1 ± 2.8 Ma) and PbSL garnet (2023 ± 11 Ma) age data obtained from syntectonic anatectic material, and from sheared metapelitic gneisses that were completely reworked during the high-grade shear event. The shear event was preceded by isobaric heating (P = ~ 6 kbar and T = ~ 670–780 °C), which resulted in the widespread formation of polymetamorphic granulites. Many efforts to date high-grade gneisses from the CZ using PbSL garnet dating resulted in a large spread of ages (~ 2.0–2.6 Ga) that reflect the polymetamorphic nature of these complexly deformed high-grade rocks.     

Lead Isotope Homogeneity of NIST SRM 610 and 612 Glass Reference Materials: Constraints from Laser Ablation Multicollector ICP-MS (LA-MC-ICP-MS) Analysis

This contribution presents data for laser ablation multicollector ICP‐MS (LA‐MC‐ICP‐MS) analyses of NIST SRM 610 and 612 glasses with the express purpose of examining the Pb isotope homogeneity of these glasses at the ～ 100 μm spatial scale, relevant to in situ analysis. Investigation of homogeneity at these scales is important as these glasses are widely used as calibrators for in situ measurements of Pb isotope composition. Results showed that at the levels of analytical uncertainty obtained, there was no discernable heterogeneity in Pb isotope composition of NIST SRM 610 and also most probably for NIST SRM 612. Traverses across the ～ 1.5 mm glass wafers supplied by NIST, consisting of between 75 and 133 individual measurements, showed no compositional outliers at the two standard deviation level beyond those expected from population statistics. Overall, the measured Pb isotope ratios from individual traverses across NIST SRM 610 and 612 wafers closely approximate single normally‐distributed populations, with standard deviations similar to the average internal uncertainty for individual measurement blocks. Further, Pb isotope ratios do not correlate with Tl/Pb ratios measured during the analysis, suggesting that regions of volatile element depletion (marked by low Tl/Pb) in these glasses are not associated with changes in Pb isotope composition. For NIST SRM 610 there also appeared to be no variation in Pb isotope composition related to incomplete mixing of glass base and trace element spike during manufacture. For NIST SRM 612 there was some dispersion of measured ratios, including some in a direction parallel to the expected mixing line for base‐spike mixing. However, there was no significant correlation parallel to the mixing line. At this time this cannot be unequivocally demonstrated to result from glass heterogeneity, but it is suggested that NIST SRM 610 be preferred for standardising in situ Pb isotope measurements. Data from this study also showed significantly better accuracy and somewhat better precision for ratios corrected for mass bias by external normalisation to Pb isotope ratios measured in bracketing calibrators compared to mass bias corrected via internal normalisation to measured ²⁰⁵Tl/²⁰³Tl, although the Tl isotopic composition of both glasses appears to be homogeneous.     

210Pb and 137Cs measurements in the Circum Bohai Sea coastal region: sedimentation rates and implications

The representative ²¹⁰Pb and ¹³⁷Cs age-depth profiles were selected from more than 100 sites in the Circum Bohai Sea (CBS) coastal region to examine the sedimentation rates and associated environmental changes. There are three unique ²¹⁰Pb_exc distribution patterns: 1) ideal-decaying type, representing relatively constant sediment supply and quieter environmental setting; 2) wiggling type, but with approximately equivalent amplitude, representing coarser sediments and associated stronger flow current environment; and 3) episodic-eventinfluencing type, each representing typhoon storm-influenced depositional environment. Our results also show that there is a lower sedimentation rate (ca. 0.1 cm/a) in the coastal lowlands, a higher sedimentation rate (ca. 0.5–3 cm/a) in the intertidal flat and an intermediate rate of ca. 0.58 cm/a in the subtidal zone near the Huanghua Harbor. The interbedded silt layer occurring in the core sediment reveals lower ²¹⁰Pb activities, indicating a discontinuous sedimentation mostly due to typhoon events which dwarfs against ²¹⁰Pb and ¹³⁷Cs applicability. Overall, the ²¹⁰Pb and ¹³⁷Cs measurements of the present study provide physical insight into the evaluation of the coastal-marine ecological environment and associated management.     

山东玲珑花岗岩内脉岩年代学特征及地质意义

在胶东地区广泛分布的中生代侵入岩中发育有玲珑-招风顶、巨山-龙门口和崂山-大珠山三大脉岩带,脉岩成分十分复杂,几乎包括了所有的岩浆岩类型,从超基性基性到中酸性以及碱性脉岩皆有出露,主要有煌斑岩、闪斜云斑岩、辉绿玢岩、辉长岩脉、石英闪长玢岩、闪长玢岩、花岗闪长斑岩、石英二长斑岩、花岗斑岩、二长斑岩、正长斑岩、石英脉和碳酸盐岩脉等,它们应是不同构造期和不同时代的综合产物。该文通过对招远石门郭家-谢家庄一带产于玲珑花岗岩中的三组石英闪长玢岩进行同位素年代学研究,获得LA-ICP-MS锆石U-Pb年龄为119.5±0.9 Ma、118±2.2Ma和116±1.4Ma,代表了石英闪长玢岩的成岩年龄,而在D181199 XT2样品中所获得的176±7.0Ma、156±5.9Ma和118±2.2Ma年龄,后者代表了石英闪长玢岩的成岩年龄,前二个年龄可能是脉岩岩浆在上侵过程中,捕获了先前存在的岩体或玲珑花岗岩的地质信息,是一组继承性或捕获性年龄。同时根据区域内在玲珑花岗岩中获得的中性脉岩年龄数据及其综合分析,认为玲珑花岗岩成岩后至少有二期脉岩侵位,一期发生在142Ma左右,另一期发生在118Ma期间,可能代表了二期地壳浅层次的伸展作用。胶东地区中基性酸性脉岩形成的构造环境、成岩时限与金矿有着内在的成因联系,中基性脉岩中有一期与金矿形成关系密切。     

放射性核素210Pb、137Cs测定巴丹吉林沙漠湖泊岩芯的年代及沉积速率

巴丹吉林沙漠发育了世界上独一无二的丘间湖泊群,100多个永久性的丘间湖泊分布于沙漠的东南部。沙漠湖泊岩芯是干旱地区重要的气候、环境档案,然而受沙漠湖泊发育极端环境的影响,岩芯测年面临很大挑战。本文选择巴丹吉林的沙漠南缘的阿尔吉林和敦德吉林进行钻探,获取无扰动岩芯,利用核素（210Pb、137Cs）进行测年,并计算其沉积速率。结果表明：（1）核素（210Pb和137Cs）测年能够获取巴丹吉林沙漠丘间现代湖泊岩芯的可靠年代。（2）岩芯Ar-1的CRS测年结果为102±8a,沉积速率分布范围为0.13 ~ 0.33cma-1,岩芯Dd-1的CRS测年结果为123±2a,沉积速率分布范围为0.18 ~ 0.70cma-1。（3）沙漠岩心沉积速率空间分布具有自沙漠腹地向边缘递增的趋势,210Pbuns-CRS平均沉积速率分布范围为 0.16 ~ 0.57cma-1 ,137Cs沉积速率分布范围为0.05 ~ 0.6 cm a-1。未来对于沉积速率空间变化的可能影响因素,如高大沙山的围限阻挡效应、137Cs的分子扩散效应以及古地震等,应进行更深入研究。     

巴基斯坦雷克迪克斑岩型Cu Au矿集区典型矿床闪长岩Pb、Sr、Nd同位素组成特征及其示踪意义

雷克迪克斑岩型Cu-Au矿集区是巴基斯坦最重要的斑岩型Cu-Au矿产地之一,发育20个斑岩型Cu-Au矿床(点),其中包括世界级的H14、H15矿床。本文在前人研究基础上重新分析探讨了Pb、Sr、Nd同位素的组成特征,计算了铅同位素的H-H单阶段演化模式年龄,以及Pb、Sr、Nd同位素的μ、ω、Th/U、△α、△β、εSr、εNd等重要参数。研究结果表明,雷克迪克矿集区成矿物质主要来源于受岩浆作用控制的壳幔混合物质,是新特提斯洋岩石圈俯冲及再循环或幔源岩浆注入地壳的结果。该矿集区的含矿斑岩可能是在岛弧碰撞造山带演化过程中伴随着特提斯构造域的演化而形成的,属于洋壳俯冲消减和大陆碰撞过程中导致地壳增生加厚的结果,它们与扬子地块具有亲缘关系,属于特提斯构造区,构成了特提斯构造域多岛洋体系的组成部分之一。该矿集区的铅主要为混入了放射性成因Pb的混合铅,具有典型DUPAL异常的特征。其中,异常铅(放射性铅)来源于富含U、Th的上地壳物质,而DUPAL异常可能直接产生于欧亚大陆南缘EMII与DM的混合源区,并以异常铅的形式表现出来。     

敦煌地块三危山地区花岗岩体地球化学、锆石U Pb定年及Hf同位素特征

敦煌地块主要由前寒武纪TTG片麻岩和变质表壳岩组成,并且出露有大量古生代花岗岩,对这些花岗岩的研究工作可以更深入地了解敦煌地块的构造演化及地球动力学意义。本文对三危山地区的党河水库花岗岩体和沙枣园花岗岩体进行了岩相学、地球化学、锆石U-Pb年代学和Hf同位素的研究。研究结果表明:1党河水库岩体侵位时代为461.7~438.1Ma,沙枣园岩体的岩石组合为中粒二长花岗岩-细粒二长花岗岩,形成时代为457~433.9Ma,均属早古生代时期产物。2党河水库岩体为I型花岗岩,ε_(Hf)(t)为-5.5到+2,t_(DM2)为1.3~1.7Ga。结合地球化学特征,判断其源岩为中元古代古老地壳为主,同时含部分新生地壳成分的(变)基性岩。沙枣园岩体为S型花岗岩,ε_(Hf)(t)为-8.6到-0.9,t_(DM2)为1.5~1.9Ga,其源岩为富长石贫黏土的(变)杂砂岩,源岩时代为古元古代晚期至中元古代早期。3两个花岗岩体的残留相同样为石榴石、角闪石和斜长石为主的麻粒岩,并且部分源岩可能与Columbia超大陆的聚合和裂解有关。4党河水库岩体和沙枣园岩体均属造山带花岗岩,因此敦煌地块内的早古生代造山活动可提前至461.7Ma,并且结束时间晚于中央造山带。而敦煌地块造山活动时限和花岗岩的时空分布与北侧的天山-北山造山带具有较强的对应关系。推测敦煌地块在早古生代期间卷入了中亚造山带的造山活动中,未受或只是早期受到南侧的中央造山带影响。     

大兴安岭北段扎兰屯地区晚古生代海相火山岩年代学和地球化学特征及其构造意义

大兴安岭地区是中亚造山带构造演化的重要区域,其中关于古亚洲洋的闭合时限以及额尔古纳-兴安地块和松嫩地块的拼贴时空关系一直存在争议。本文对大兴安岭北段扎兰屯地区晚古生代海相火山岩进行了年代学和地球化学的研究,显示扎兰屯大民山组安山岩U-Pb锆石年龄为362.2±3.3Ma,结合古生物资料,大民山组火山岩喷发时代应为晚泥盆世法门期。大民山组基性火山岩具有高Al_2O_3、TiO_2和Mg~#的特点,稀土、微量元素特征与板内洋岛玄武岩(OIB)特征一致;中酸性岩石具有高Al_2O_3,低TiO_2和Mg~#的特点,稀土、微量元素特征反映出具有弧火山岩性质。综合年代学和地球化学特征,确定了扎兰屯地区发育有洋岛玄武岩,并同时存在中酸性弧火山岩的特点,说明晚泥盆世古亚洲洋在扎兰屯地区正处于闭合阶段,早期存在陆间洋盆,后期洋-陆碰撞作用持续发生而形成活动大陆边缘,也为贺根山-扎兰屯-嫩江缝合带北延及古亚洲洋构造域演化提供了新的基础地质资料。