Tracing the 850-Ma continental flood basalts from a piece of subducted continental crust in the North Qaidam UHPM belt,NW China

A Paleozoic ultrahigh-pressure metamorphic (UHPM) belt extends along the northern margin of the Qaidam Basin, North Tibetan Plateau. Eclogites in the Yuka eclogite terrane, northwest part of this UHPM belt, occur as blocks or layers of varying size intercalated with granitic and pelitic gneisses. These eclogites have protoliths geochemically similar to enriched-type mid-ocean ridge basalts (E-MORB) and oceanic island basalts (OIB). On the basis of Ti/Y ratios, they can be divided into low-Ti and high-Ti groups. The low-Ti group (LTG) eclogites exhibit relatively low TiO₂ (most <2.5 wt%) and Ti/Y (<500) but comparatively high Mg# (48–55), whereas the high-Ti group (HTG) eclogites have high TiO₂ (most >2.5 wt%) and Ti/Y (>500) but lower Mg# (46–52). Zircons from two eclogite samples gave a magmatic crystallization (protolith) age of ∼850 Ma and a UHPM age of ∼433 Ma. The occurrence, geochemical features and age data of the Yuka eclogites suggest that their protoliths are segments of continental flood basalts (CFBs) with a mantle plume origin, similar to most typical CFBs. Our observation, together with the tectonic history and regional geologic context, lend support for the large scale onset of mantle plume within the Rodinia supercontinent at ∼850 Ma. The Qaidam block is probably one of the fragments of the Rodinia supercontinent with a volcanic-rifted passive margin. The latter may have been dragged to mantle depths by its subducting leading edge of the oceanic lithosphere in the Early Paleozoic.     

新疆卡拉麦里地区早泥盆世洋内弧：来自火山岩地球化学及锆石U-Pb 年龄的证据

新疆东准噶尔卡拉麦里地区早泥盆世火山岩由玄武岩和玄武安山岩组成,采用LA-ICP-MS锆石U-Pb定年方法,获得玄武安山岩锆石的U-Pb年龄为404.5±1.9 Ma,表明喷发时代为早泥盆世。岩石地球化学显示早泥盆世火山岩属岛弧拉斑系列,具相对较高的Mg^# 值(41.25～55.32)及较低的Nb(1.11×10^{- 6}～2.42×10^{- 6})、Zr(73.9×10^{- 6}～95×10^{- 6})和ΣREE(81.50×10^{- 6}～121.80×10^-6)含量。富集大离子亲石元素(LILE：K、Rb、Ba)和轻稀土元素(LREE),而亏损Ta、Nb和Ti高场强元素（HFSE：Ta、Nb、Ti）,并显示Eu弱的亏损,这些特征与岛弧火山岩类似,其原始岩浆可能起源于俯冲流体交代的亏损地幔楔的部分熔融。结合区域地质背景,认为早泥盆世火山形成于洋内弧的构造环境,为卡拉麦里古洋盆向北俯冲消减的产物。这是在卡拉麦里地区首次报道的洋内弧火山岩,这一新的发现和认识对研究东准噶尔古生代洋盆演化及区域构造格局均具有重要的意义。     

郯庐断裂带中-南段中生代岩浆活动的构造背景与深部过程

郯庐断裂带内岩浆岩及糜棱岩的年龄及野外研究表明以中-酸性为主的岩浆活动主要发生在早白垩世走滑运动的晚期,岩石化学以富钾、富碱为特征;稀土元素以轻稀土富集、重稀土亏损为特征;微量元素表现出富集大离子亲石元素,尤其是强不相容元素;同位素组成显示岩浆来源于壳幔过渡带.带内岩浆活动明显受断裂带控制,走滑晚期的岩浆活动起源于地幔底侵、壳幔相互作用下的壳幔过渡带,在伊泽奈崎板块斜向俯冲、中国东部遭受区域性剪切-挤压的背景下出现.在此背景下中国东部发生了岩石圈减薄,同时出现了一系列北东-北北东向已深切至壳幔边界的左行平移断裂系,从而诱发了大规模的岩浆活动.     

2005年3月一次寒潮天气过程的诊断分析

利用NECP1°×1°的6小时分析资料和常规观测等资料,对2005年3月10~13日一次全国性寒潮天气过程的环流背景、影响天气系统及成因进行了分析。结果表明:这次寒潮及寒潮天气主要成因是(1)西欧上空500hPa强暖平流致使在西伯利亚地区形成阻塞高压,建立横槽,横槽北侧的东北气流引导超极地冷空气和西路冷空气合并加强;形成了异常强的冷高压、锋区、冷温度中心和冷温度平流。(2)两个短波槽东移侵入阻塞高压,使得横槽两次建立和转为竖槽,导致强冷空气大举南侵。(3)寒潮带来大范围强降温、700hPa西南急流与冷空气交汇、1000hPa以上层气温在0℃以下的垂直分布,为南方大到暴雪提供了动力、水汽和凝结的温度条件。     

鄂西电线积冰微物理观测研究

对2009年2月25日—3月4日湖北恩施雷达站的一次电线积冰过程,使用自动气象站、能见度仪、雾滴谱仪、雨滴谱仪等实测资料进行深入研究,分析了多种气象要素的演变,发现积冰期比无积冰期平均气温低5.6℃。对积冰期间3种天气状况下雾滴谱和降水粒子谱的特征进行了分析,结果表明:雾天和雨天的雾滴谱为单峰型,雨夹雪天为双峰型;雨天和雨夹雪天的降水粒子谱都为单峰型;雾滴平均数密度从大到小依次是:雨天(223.5 cm-3)、雨夹雪天(181.3 cm-3)、雾天(138.7 cm-3);雨天雨滴平均数密度为335.6 cm-3;雨夹雪天降水粒子平均数密度为1 502.1 cm-3。另外,实测数据表明积冰增长率从大到小依次是:雨夹雪天、雨天、雾天。     

贺兰山地区沙尘暴若干问题的观测研究

利用贺兰山地区沙尘暴历史资料和综合观测资料 ,对大气背景、浮尘、扬沙和沙尘暴发生期间的大气气溶胶数浓度谱、质量谱、大气总悬浮颗粒 (TSP)及粒径分布、微气象、分光日射观测以及沙尘样品进行中子活化处理 ,分析了该地区浮尘、扬沙和沙尘暴形成规律 ,气候变化特征和贺兰山的影响。并综合研究了沙尘气溶胶尺度谱特征、光学厚度和化学组分等变化特征 ,提出了若干结果。     

Global Correlations of Ocean Ridge Basalt Chemistry with Axial Depth: a New Perspective

The petrological parameters Na₈ and Fe₈, which are Na₂O andFeO contents in mid-ocean ridge basalt (MORB) melts correctedfor fractionation effects to MgO = 8 wt%, have been widely usedas indicators of the extent and pressure of mantle melting beneathocean ridges. We find that these parameters are unreliable.Fe₈ is used to compute the mantle solidus depth (P_o) and temperature(T_o), and it is the values and range of Fe₈ that have led tothe notion that mantle potential temperature variation of T_P= 250 K is required to explain the global ocean ridge systematics.This interpreted T_P = 250 K range applies to ocean ridges awayfrom ‘hotspots’. We find no convincing evidencethat calculated values for P_o, T_o, and T_P using Fe₈ have anysignificance. We correct for fractionation effect to Mg^# = 0·72,which reveals mostly signals of mantle processes because meltswith Mg^# = 0·72 are in equilibrium with mantle olivineof Fo_89·6 (vs evolved olivine of Fo_{88·1–79·6}in equilibrium with melts of Fe₈). To reveal first-order MORBchemical systematics as a function of ridge axial depth, weaverage out possible effects of spreading rate variation, local-scalemantle source heterogeneity, melting region geometry variation,and dynamic topography on regional and segment scales by usingactual sample depths, regardless of geographical location, withineach of 22 ridge depth intervals of 250 m on a global scale.These depth-interval averages give Fe₇₂ = 7·5–8·5,which would give T_P = 41 K (vs 250 K based on Fe₈) beneathglobal ocean ridges. The lack of Fe₇₂–Si₇₂ and Si₇₂–ridgedepth correlations provides no evidence that MORB melts preservepressure signatures as a function of ridge axial depth. We thusfind no convincing evidence for T_P > 50 K beneath globalocean ridges. The averages have also revealed significantcorrelations of MORB chemistry (e.g. Ti₇₂, Al₇₂, Fe₇₂,Mg₇₂, Ca₇₂, Na₇₂ and Ca₇₂/Al₇₂) with ridge axial depth. Thechemistry–depth correlation points to an intrinsic linkbetween the two. That is, the 5 km global ridge axial reliefand MORB chemistry both result from a common cause: subsolidusmantle compositional variation (vs T_P), which determines themineralogy, lithology and density variations that (1) isostaticallycompensate the 5 km ocean ridge relief and (2) determine thefirst-order MORB compositional variation on a global scale.A progressively more enriched (or less depleted) fertileperidotite source (i.e. high Al₂O₃ and Na₂O, and low CaO/Al₂O₃)beneath deep ridges ensures a greater amount of modal garnet(high Al₂O₃) and higher jadeite/diopside ratios in clinopyroxene(high Na₂O and Al₂O₃, and lower CaO), making a denser mantle,and thus deeper ridges. The dense fertile mantle beneath deepridges retards the rate and restricts the amplitude of the upwelling,reduces the rate and extent of decompression melting, givesway to conductive cooling to a deep level, forces melting tostop at such a deep level, leads to a short melting column,and thus produces less melt and probably a thin magmatic crustrelative to the less dense (more refractory) fertile mantlebeneath shallow ridges. Compositions of primitive MORB meltsresult from the combination of two different, but geneticallyrelated processes: (1) mantle source inheritance and (2) meltingprocess enhancement. The subsolidus mantle compositional variationneeded to explain MORB chemistry and ridge axial depth variationrequires a deep isostatic compensation depth, probably in thetransition zone. Therefore, although ocean ridges are of shalloworigin, their working is largely controlled by deep processesas well as the effect of plate spreading rate variation at shallowlevels. KEY WORDS: mid-ocean ridges; mantle melting; magma differentiation; petrogenesis; MORB chemistry variation; ridge depth variation; global correlations; mantle compositional variation; mantle source density variation; mantle potential temperature variation; isostatic compensation     

地幔热柱的多级演化及其成矿作用——以冀北地区为例

冀北地区金、银金金属成矿作用研究表明，金、银等成矿元素除部分萃取自含矿围岩外，主要来自深源。幔枝构造是重要的热源释放体系，控制着深源含矿流 体的迁移，聚集和成矿，从而构成了以幔枝构为中心，内带为金、外带为银金金属的构造－岩浆成矿系列，并据此归纳出幔枝构造成矿模式。     

Numerical simulation on the evolution of cloud particles in 3-D convective cloud

A 3-D convective cloud model with compressible non-hydrostatic dynamics and the spectral bin microphysics of a 2-D slab-symmetric model has been used to simulate an observed supercell storm occurring on 29 June, 2000 near Bird City, Kansas, USA. The main objective of this paper is to study the evolution of particles in this convective storm with bin spectral microphysics scheme. Graupels form and grow through two mechanisms, deposition and riming, with the riming process dominant on top of the inflow and in the upper portion of main updraft. Over the outflow and during the developing and mature stages of the storm, graupel particles mainly grow through deposition with dominant unimodal spectra. Most fall out after growing up. Reducing initial relative humidity disturbance (increasing initial potential temperature disturbance) has negative impact on the formation and growth of graupels over the inflow (outflow). This study shows that large graupel and hail could be suppressed by altering the deposition and coalescence process over the inflow and main updraft. At different locations of the convective cells and with different initial humidity and potential temperature disturbance, the graupel formation and growth mechanisms are different, so as to the feasible hail suppression locations and methods. Supported by National Natural Science Foundation of China (Grant Nos. 40537034, 40805057), and Foundation of Key Laboratory of Meteorological Disaster of Ministry of Education in Nanjing University of Information Science & Technology (Grant No. KLME060202)     

新型随机地震动模型

在研究结构的随机地震反应时，要用大量的符合场地条件的地震记录作为输入数据。但强震历史记录却不是每个地区都有的，因此根据符合场地条件的现有地震记录建立随机地震动模型具有重要意义。本文利用中国抗震规范2001版修正选取的样本波作为目标波，考虑了幅值和频率的双重非平稳性，建立了新型随机地震动模型——改进的时变ARMA模型随机地震动模型。通过使用残差的卡方检验法，对多种非平稳ARMA模型生成的模拟波进行检验；同时又比较丁模拟波与目标波的功率谱密度图和反应谱图。结果证明：此法能够更精确地反映不同场地条件地震动的频谱和幅值的真实内容，从而建立符合目标场地条件的更为有效的模拟地震动，为相关研究与工程设计架起一座桥梁。