Modulations in incommensurate (Ca1–xSrx)2MgSi2O7 single crystals

Single crystals of (Ca_1–xSr_x)₂MgSi₂O₇ slightly doped with 1000 ppm Mn²⁺ and with x ranging from 0.04 to 0.32 were grown from the melt in a mirror furnace applying the Czochalski technique. Transmission electron microscopy (TEM) revealed incommensurately modulated structures at room-temperature for all compositions in accordance with earlier studies by electron paramagnetic resonance (EPR). Electron diffraction patterns clearly show satellite reflections typical for two-dimensional modulation, and their successive destabilization with increasing Sr content. The modulation is of tartan-like appearance. Beyond a Sr/(Sr+Ca) ratio of about 0.32 the synthesis of stable solid solution åkermanite type crystals was proved not to be feasible, indicating the existence of a miscibility gap in the Sr åkermanite system. As presumed from the diffuse scattering around the satellite reflections, and suggested more conclusively by crystallographic processing of high resolution EM images the Sr ions incorporated into the incommensurate crystal phase are distributed in an ordered fashion and are partly adapted to the displacive modulation of the pure åkermanite. This means, occupational modulation even makes a contribution to the overall modulation characteristics in (Ca_1–xSr_x)₂ MgSi₂O₇.     

Rare earth element (REE) geochemistry and genetic implications of the Morta? bauxite deposit (Seydi?ehir/Konya - Southern Turkey)

The Mediterranean-type karst-bauxite deposit of Morta?, south Turkey, placed unconformably between Cenomanian and Senonian shallow marine limestones is built of massive (MB), oolithic (OB), breccia-bearing (BB) and earthy (EB) bauxite horizons, from top to bottom. The MB layer is enriched in Al and REE (except Ce) due to loss of Si, Na, K, Mg and P. REE are accumulated in the BB but depleted in the EB layers. The ferruginous OB lost LREE and gained in HREE probable due to scavenging by authigenic heavy minerals like rutile, anatase and titanite. Total REE contents in the bauxite profile display an increasing trend from bottom to top, while negative and maximum positive Ce anomalies characterize the upper and the lower parts of the profile, respectively. This unusual REE behavior is explicable by assuming mobilization of Ce(IV) either under reducing condition or chemical complexation under alkaline conditions in the top layer and scavenging of Ce by Al-Mg hydrosilicates and Ti-oxides and/or precipitation with authigenic REE minerals, especially of the bastnäsite group near the bedrock limestones. Similarity in chondrite normalized-REE patterns of the Seydi?ehir phyllites, bauxite and terra rossa samples and the presence of tridymite (?) in bauxites makes a felsic source rock most likely and reveal a close genetic relationship between the Seydi?ehir phyllites and the recent terra rossa occurrences. The REE patterns of the bauxites resemble those of the Katrangedi?i limestone despite variations in ΣREE. Field observations and geochemical data together with mass-balance calculations suggest that the Morta? deposit was derived from the Seydi?ehir phyllites and argillic phase within the Katrangedi?i limestone which in turn have Precambrian (?) felsic, probably granitic precursors.     

三峡工程二期围堰运行期变形特性研究

基于土石坝分析的DuncanE-μ本构模型，研究了土石坝分析的3参量流变模型，并编制了围堰流变分析程序。根据三峡工程二期围堰运行前期的部分实测变形数据，反演分析了流变分析所需的计算参数。流变分析表明，三峡工程二期围堰结构的水平和垂直流变变形存在时间上的不同步性，垂直流变位移的稳定时间在堰体结构施工完成后的6个月左右，而水平流变位移的稳定时间只需要3个月。围堰结构的后期流变位移平均值是流变初期时位移的2～3倍。     

牙膏用六水氯化锶的制备

以不同纯度的自制氢氧化锶为原料与盐酸充分反应,经提纯、结晶,制备六水氯化锶（SrCl2·6H2O）。通过X射线衍射（XRD）和场发射扫描电子显微镜（FESEM）对SrCl2·6H2O的结构、形貌进行表征,通过能谱仪（EDS）和差热-热重分析仪（TG）对SrCl2·6H2O进行元素含量和热失重分析,并将制备的样品与中华人民共和国化工行业牙膏用氯化锶标准进行对比。结果表明,高纯氢氧化锶与分析纯盐酸制备的SrCl2·6H2O可以达到牙膏用标准。     

基于Matlab和灰色模型GM（1,1）预测海岸线变化*

使用灰色模型的“少数据”建模寻求现实规律的良好特性用于海岸线变迁预测,结合 MATLAB 强大的计算能力,解决了灰色预测模型在矩阵计算方面复杂的问题.利用1975-2005年珠江口内伶仃洋海区6个时期的海图提取局部时序海岸线,设置原点和28条侧线,使用侧线与海岸线的交点,建立灰色模型 GM (1,1)模型原始数列,使用 MATLAB 编制程序计算出海岸线变化的预测点,并使用2005年实际海岸线对预测结果进行验证,结果表明灰色模型 GM (1,1)进行海岸线预测是合理可靠的.     

海洋自由生活线虫群落和环境的关系研究

以2007年春季在渤海湾近岸海域进行的调查为基础,分析了海洋自由生活线虫的群落组成和环境之间的关系.以等级聚类(Cluster)、非度量多维标度(MDS)和生物-环境分析(BIO-ENV)等多元统计方法为主,采用 PRIMER 5.2软件进行数据处理和分析.在测定的约30个环境因素中,有10个因素对底栖线虫群落产生了重要影响,包括水体的 pH、硝酸盐、悬浮物、活性硅酸盐、温度、盐度、溶解氧和沉积物的脱镁色素、叶绿素 a、平均粒径等因素.一些沉积物因素和水环境因素组合后较好地解释了底栖线虫群落结构情况,这反映了水环境和沉积环境的关联性,今后的底栖生物研究中应注意水体和沉积物环境的耦合.     

Late Quaternary climatic changes in southern Chile, as recorded in a diatom sequence of Lago Puyehue (40°40′ S)

A late Quaternary diatom stratigraphy of Lago Puyehue (40°40′ S, 72°28′ W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The diatom assemblages were well preserved in a 1,122 cm long, ¹⁴C-dated sediment core spanning the last 17,900 years, and were in support of an early deglaciation of Lago Puyehue. The presence of a short cold spell in South Chile, equivalent to the Younger Dryas event in the Northern Hemisphere, the Antarctic Cold Reversal in Antarctica, or the Huelmo-Mascardi event in southern South America, was not clearly evidenced in the diatom data, although some climate instability may have occurred between 13,400 and 11,700 cal. yr. BP, and a relatively long period (between 16,850 and 12,810 cal. yr. BP) with low absolute abundances and biovolumes could be tentatively interpreted as a period of low rainfall and/or temperatures. An increase in the moisture supply to the lake was tentatively inferred at 12,810 cal. yr. BP. After 9,550 cal. yr. BP, inferred stronger and longer persisting summer stratification, may have been the result of the higher temperatures associated with an early-Holocene thermal optimum. The mid-Holocene appeared to be characterized by a decrease in precipitation, culminating around 5,000 cal. yr. BP, and rising again after 3,000 cal. yr. BP, likely associated with a previously documented lowered frequency and amplitude of El Niño events. An increase in precipitation during the late Holocene (3,000 cal. yr. BP–present) might have marked subsequent increased frequency of El Niño occurrences, leading to drier summers and slightly moister winters in the area.     

Palaeoecology of Holocene peat deposits from Nordvestø, north-west Greenland

Two extensive peat deposits on Nordvestø, between Greenland and Canada, were examined for macroscopic remains of plants and animals. One of the peat deposits accumulated during the period from c. 7,100 to 5,100 cal. years BP. This peat is guanogenic and completely dominated by the coprophilous bryophyte Aplodon wormskioldii, and also contains frequent remains of feathers. The peat formed close to a large former sea bird colony, probably a puffin (Fratercula arctica) colony. Puffins are now rare in the region, but the population may have been larger during the mid Holocene, when the sea was ice-free for a longer period than at present. The other peat deposit is dated to c. 9,300–7,400 cal. years BP, it is minerogenic and the macrofossils reflect deposition in a shallow, richly vegetated pond. This peat formed during warmer summers than at present.     

On the geodynamics of the Alpine collisional granitoids from Central Anatolia: petrology,age and isotopic characteristics of the granitoids of the Ekecikdağ Igneous Association (Aksaray/Turkey)

Granitoids of the Ekecikda? Igneous Association (Central Anatolia/Turkey) are products of collisional–post-collisional magmatism in the Ekecikda? area. These granitoids are granodiorite, microgranite and leucogranite. Field relations of granodiorites with microgranites is obscured, but leucogranites intrude both rock types. Mean zircon laser ablation (LA)-ICP-MS ²⁰⁶Pb-²³⁸U ages of granodiorites and microgranites are 84.52 ± 0.93 Ma and 80.7 ± 1.6 Ma, respectively, and age of leucogranites is suggested as 80 Ma, based on field relations combined with ²⁰⁶Pb/²³⁸U and Rb-Sr ages. Crystallisation temperatures of granodiorites, microgranites and leucogranites are 728°C-848°C, 797°C-880°C, 704°C-809°C, respectively.

Geochemical characteristics including Sr-Nd isotopic evidences infer a non-cogenetic character, as there is a high crustal contribution in I-type granodiorite sources, a crustal source with insignificant and significant mantle inputs in S-type microgranites and leucogranites, respectively. LA-ICP-MS Lu-Hf isotope data from zircons reveal their crustal nature (εHf_(t): ?1.3 ± 0.5 to ?8.8 ± 0.5). Crustal melting linked to the Alpine thickening during the Late Cretaceous led to formation of heterogeneous sourced granitoids with crustal dominated sources in the Ekecikda? area. Understanding of the nature and evolution of collisional Ekecikda? granitoids is not only important to put contribution in the geodynamic evolution of Central Anatolia and surrounding Alpine area, but also to better understand systematics of collisional magmatic systems.