甘肃省龙首山成矿带中段钠长岩脉地质特征及其与铀矿化关系研究

钠长岩脉是甘肃省龙首山成矿带中段常见的晚期脉体,与钠交代型铀矿化的关系十分密切。文章在野外调研、钻孔查证、放射性物探测量的基础上,深入研究钠长岩脉的岩石学、地球化学、同位素年代学和稳定同位素特征研究,并探讨其与钠交代型铀矿化之间的关系。钠长岩脉侵位于加里东中期,其LA-ICP-MS锆石U-Pb年龄为442.9±5.7Ma;具有中硅(61.48%~67.14%)、富铝(14.98%~17.59%)、高钠(9.76~%~10.59%)、贫钾(0.08%~0.30%)、低钛(0.11%~0.44%)、低磷(0.02%~0.16%)的特征;N-MORB标准化微量元素蛛网图显示钠长岩脉相对富集大离子亲石元素(LILE)Rb和Ba,不相容元素Th和U显著富集,高场强元素(HFSE)Nb和Ta相对亏损、Sr和Ti显著亏损;球粒陨石标准化稀土元素配分曲线图呈碱性花岗岩类的"海鸥"型。综合研究表明,钠长质岩浆是钠质含铀热液的孪生有效载体,钠长岩脉本身即是钠交代型铀矿有利的赋矿岩石,二者具有同源、等时、共体的特征,作为龙首山成矿带中段钠交代型铀矿的找矿标志,进而指导深部找矿和矿床外围盲矿体预测。     

Mosaic desert pavement influences water infiltration and vegetation distribution on fluvial fan surfaces

Desert pavements (DPs) are critical for maintaining ecological stability and promoting near-surface hydrological cycling in arid regions. However, few studies have focused on eco-hydrological processes of DPs in the ecological systems of fluvial fans. Although DP surfaces appear to be barren and flat, we found that the surfaces are characterized by surface mosaic patterns of desert pavement (mosaic DP) and bare ground (mosaic BG). We investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites in fluvial fans (one on a hillside and five within the sectors of fans) along a southwest belt transect in northern Linze County, in the central Hexi Corridor (China). We found significant differences in mosaic DP between the hillside and sector sites in terms of pavement thickness and vesicular horizon thickness (Av thickness), particle composition, and bulk density, although significant differences were absent for mass soil water content, gravel coverage, and surface gravel size. The mosaic DP inhibited water infiltration by the pavement layer, where the sorptivity (S), initial infiltration rate (i_int), steady-state infiltration rate (i_sat) and infiltration time (T) averaged 1.19 cm/min^-0.5, 0.64 cm/min, 0.13 cm/min and 12.76 min, respectively. Where the pavement layer was scalped, the S, i_int, and i_sat increased by 0.27 cm/min^-0.5, 0.52 cm/min, and 0.40 cm/min, respectively, and the T reduced by 7.42 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (−), surface gravel coverage (−), fine earth (+) and fine gravel (−) in the pavement layer. The DP surfaces only had a sparse covering of shrubs, but an abundance of herbs. Few shrubs were present on the mosaic DP, but a greater number of shrubs and herbs grew on the mosaic BG. It can be concluded that DPs can maintain vegetation stability for different surface mosaic patterns. This study deepens our understanding of the eco-hydrological cycle of DP landscapes in arid regions.     

扬子克拉通东南缘新元古代陆缘弧型TTG的厘定及其构造意义

在扬子克拉通东南缘的江山-绍兴结合带沿线多处出露新元古代深成杂岩,以往被认为是沿扬子克拉通和华夏地块碰撞缝合带侵入的板内型深成岩类。本文选择其中的浙江金华罗店中酸性深成杂岩进行了系统的岩石学、年代学和地球化学研究,提出它们属TTG岩石组合,包括英云闪长岩-奥长花岗岩-花岗闪长岩组合(T1T2G1)和二长花岗岩-花岗岩组合(G2QM)两类,普遍以明显富集Rb、Ba、K、Pb等大离子亲石元素而强烈亏损Nb、Ta、Ti、P等高场强元素为特征,δCe为弱负异常或无异常,属典型的弧岩浆岩类。T1T2G1组合富钠贫钾,εNd(t)值=+2.6~+9.4,Mg#值为41.5~63.1,推断由玄武质俯冲板片脱水部分熔融而成,并受到地幔楔橄榄岩熔体的混染。G2QM组合与T1T2G1组合地球化学特征类似,但又明显富K2O(2.75%~5.08%)、LILE和LREE,低Mg#值(27.2~52.31)和εNd(t)值(+1.7~+2.0),应是T1T2G1源区继续部分熔融的产物,可能未受到明显的地幔楔橄榄岩混染。测得花岗闪长岩(G1)锆石SHRIMP U-Pb年龄为841±10Ma,奥长花岗岩(T2)锆石LA-ICPMS U-Pb年龄为793±13Ma,前人报道之花岗岩(G2)年龄为832±44Ma,结合上述地球化学特征,说明T1T2G1和G2QM组合是由新元古代古华南洋向扬子东南缘持续俯冲形成的。综合区域地质资料及前人研究结果,提出金华罗店与诸暨璜山、绍兴平水等地的深成杂岩共同构成了扬子克拉通东南缘一条长达200km的青白口纪(930~793Ma)陆缘弧型深成杂岩带,反映迟至793Ma前仍存在强烈的洋壳俯冲,扬子克拉通尚未与华夏地块发生碰撞拼合,且T1T2G1-G2QM组合的出现指示洋壳俯冲正处于早-中期阶段。     

碲成矿机制研究新进展

简要总结了碲的丰度、矿物学及其分布,重点论述了“碱质类”金矿床中碲的赋存状态、载金作用、迁移形式及其来源等研究的现状、存在问题和大水沟独立碲矿床对研究元素超常富集的启示,并对超大型矿床成矿机制的研究方向进行了展望。     

快速法固结试验经验修正系数的探讨

实践证明,常规固定试验（压缩试验）可以采用快速法替代现行规范的慢速法。本文在大量统计对比和相应理论分析基础上提出上海地区经验修正系数K值,以利快速法的推行。     

广西贵县某地红粘土成因的探讨

<正> 红粘土一词在我国已沿用很久,但对其成因争议很大,就广西红粘土的成因而言,主要有两种认识,一种认为是冲积或冲—洪积;另一种则认为是残积或残—坡积。 贵县某地红粘土具有一定的胀缩性,建于其上的房屋普遍受到不同程度的损坏。不少从事膨胀土研究的同志常来此地研究,对该处红粘土的成因提出了种种看法。笔者先后在这里做了一些工作,现谈谈一孔之见,不妥之处请指正。      

贝叶斯统计方法在海浪方向谱研究中的应用

较详细介绍了贝叶斯统计方法在海浪方向谱估计中的应用,指出先验分布的不同对估计结果没有影响,由于均匀分布与最大熵原则相对应,使其具有某种特殊性.数值模拟表明贝叶斯方法对双峰方向分布估计的有效性,将其应用于黑海实测资料,证明双峰方向分布的出现依赖于估计方法分辨力的大小,而用最大似然法得到的双峰方向分布值得怀疑.最后给出出现双峰方向分布的一种可能物理解释.     

北秦岭丹凤地区产铀花岗岩稀土元素地球化学特征

针对北秦岭丹凤地区产铀花岗岩的区域地层、赋矿围岩、蚀变岩和铀矿石进行稀土元素地球化学研究,结果表明:各类样品具有大体类似的LREE富集及Eu负异常的稀土配分模式,表明它们之间稀土元素特征具有继承性;赋矿黑云母二长花岗岩与区域地层(丹凤岩群变质基性火山岩)稀土元素特征指示,二者均形成于岛弧环境;蚀变花岗岩和铀矿石主要继承了赋矿花岗岩的特征。各类样品Y/Ho值变化范围狭窄,为25.09~33.46,显示它们具有共同的源区。铀矿石具有最高的w_B(∑HREE),且与铀矿石的品位存在正相关关系,暗示HREE与铀的迁移具有同步性。     

北秦岭榴辉岩Sm-Nd同位素年龄

采自陕豫交界秦岭群中的榴辉岩主要由石榴子石和绿辉石组成，同时还含有少量的角闪石和金红石。本工作由四个单矿物和全岩五个样，测得Sm－Nd等时年龄为400±16Ma，（r＝0．997575），εNd＝十3．6，说明在加里东期北秦岭造山带发生过高压变质事件。     

Improvement on the second-order solution of artificial satellite orbits

Three methods are proposed in this paper to lessen the complexity in the derivation and the resulting expressions of second-order analytical solutions of artificial satellite orbits while retaining the advantages of analytical solutions. Of the three, the one combining the theories of elliptical perturbation and of intermediate orbits is noteworthy for its simplicity. It can also be used with advantage in first-order and third- or higher order solutions.