The post-glacial landscape evolution of the North German Basin: morphology, neotectonics and crustal deformation

The recent evolution of the north German Basin (NGB), which is presently a low-seismic area, was partly affected by glacial loading and unloading of the ice masses. Major stresses acting within the NGB are induced by the North-Atlantic ridge push, the ongoing Alpine collision, and the post-glacial rebound of Fennoscandia. Present-day horizontal stresses within the NGB are directed generally NW–SE, but fan and bend north of 52°N towards NNE. Major basement faults are directed NW–SE, minor faults NE–SW and NNE–SSW, and are clearly detectable in geomorphological and satellite lineaments. Furthermore, the drainage pattern and the distribution of lakes in northern Germany follow exactly block boundaries and, hence, mark zones of present-day subsidence. The understanding of the post-glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the NGB. The re-adjustment of the individual fault blocks during post-glacial relaxation of the lithosphere leads to differential, crust-dependent uplift and, probably, to the formation of Urstrom valleys. The Urstrom valleys and terminal moraines in northern Germany appear to parallel the major tectonic lineaments and lithospheric “block” boundaries. The lithospheric memory is expressed in the post-glacial landscape evolution of the NGB.     

Geochemical and isotopic composition of organic matter in the Kupferschiefer of the Polish Zechstein basin: relation to maturity and base metal mineralization

max vs the present depth of the Kupferschiefer, soluble organic matter (SOM) yields, and relative proportions of saturated and aromatic hydrocarbons of the SOM provide evidence for an oxidative alteration of organic matter in highly mineralized Kupferschiefer samples near the Rote F?ule zones. This is confirmed by differences in the composition of the saturated and aromatic hydrocarbon fractions of the soluble organic matter: Saturated hydrocarbons from Rote F?ule samples are dominated by short-chain n-alkanes and higher abundances of pristane and phytane relative to heptadecane (n-C17) and octadecane (n-C18), respectively, compared with samples more distant to the Rote F?ule zone. Compositional changes of the aromatic hydrocarbon fractions with decreasing distance to that zone are characterized by the occurrence of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene to methylphenanthrenes that are attributed to demethylation reactions and resulted in a decrease of the methylphenanthrene index (MPI 1). Kupferschiefer samples from the barren zone of the Polish Basin do not show these alteration patterns. The observed variations in organic matter composition with burial depth are consistent with changes due to increasing thermal maturation. Maturity assessment is achieved from MPI 1 and the methyldibenzothiophene ratio (MDR). From the relationship between the maturity of organic matter in terms of vitrinite reflectance values and depth of the Kupferschiefer strata, a continuous increase in reflectance of vitrinite is obtained within the Polish Basin. The alteration pattern of organic matter related to base metal mineralization of the Kupferschiefer corresponds to changes in the isotopic composition of organic carbon and calcite. Kerogen within, or close to, Rote F?ule zone is enriched in ¹³C caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter. The opposite tendency towards lower δ ¹³C and δ ¹⁸O values of calcite provides evidence for isotopic exchange between carbonate and the oxidizing, ore-bearing solutions and for organic matter remineralization. In contrast, organic matter and calcite from the Kupferschiefer do not show regular trends in δ ¹³C with increasing thermal maturation. Received: 25 June 1999 / Accepted: 1 December 1999     

11 Å tobermorite from cement bypass dust and waste container glass: A feasibility study

A novel one-step hydrothermal synthesis of 11 Å tobermorite, a cation exchanger, from a unique combination of waste materials is reported. 11 Å tobermorite was prepared from stoicheiometric quantities of cement bypass dust and waste container glass at 100 °C in water. The product also comprised 10 wt.% calcite and trace quartz as residual parent phases from the cement bypass dust. In a batch sorption study at 20 °C the uptakes of Cd²⁺ and Pb²⁺ by the waste-derived tobermorite product were found to be 171 mg g^− 1 and 467 mg g^− 1, respectively, and in both cases the removal process could be described using a simple pseudo-second-order rate model (k₂ = 2.30 × 10^− 5 g mg^− 1 min^− 1 and 5.09 × 10^− 5 g mg^− 1 min^− 1, respectively). The sorption characteristics of the 11 Å tobermorite are compared with those of other waste-derived sorbents and potential applications are discussed.     

The Anna's Rust Sheet and related gabbroic intrusions in the Vredefort Dome-Kibaran magmatic event on the Kaapvaal Craton and beyond?

The Anna's Rust Sheet (ARS) and a suite of mineralogically and chemically related intrusions in the core and collar of the Vredefort Dome (in particular, the Vredefort Mafic Complex: VMC) represent a newly recognised type of high Ti gabbro in this central part of the Kaapvaal Craton. This lithology, referred to as the Vredefort Type IV mafic intrusion, is distinguished from chemically similar Type V intrusions (the Karoo dolerites) by the presence of glomeroporphyritic plagioclase and higher Th content and from Type III intrusions (≈ 1600 Ma gabbro) by the lack of cross-cutting pseudotachylitic breccia veinlets. Petrographic features and both major and trace element compositions of all Type IV intrusions are very similar. Based on its Rb-Sr isotope age and character, a gabbroic intrusion from Majuba Colliery (Mpumalanga Province) is also thought to belong to the ARS (Type IV) suite of tholeiitic intrusions. Rb-Sr isotopic analysis resulted in a preferred age of 1052±11 Ma (2ω) for biotite and plagioclase data for ARS, VMC and Majuba samples. The Rb-Sr age for the ARS is further supported by ⁴⁰Ar-³⁹Ar stepheating ages for plagioclase and pyroxene separates from two ARS and VMC samples, which favour formation of this gabbroic intrusion at ca 1000 Ma ago. These results suggest that an ≈ 120 m thick sheet intrusion may be present throughout a major part of the Vredefort Dome. While Kibaran-age (ca 1–1.2 Ga) alkaline, both mafic and felsic, magmatism, as well as tectonic and hydrothermal activity at that time, have been known in the central Kaapvaal Craton, a widespread tholeiitic magmatic component has now been added to this record. There is a strong likelihood that this magmatic event occurred throughout the southern African subcontinent and perhaps into Antarctica.     

Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ??600?m in a SW?CNE direction with chimneys occurring over a ??145-m depth interval, between ??1,690 and 1,545?m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2?C3?m in height, with some reaching 6?C7?m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35?years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2?C3?m thick. Two main types of chimney predominate: Cu-rich (up to 28.5?wt.% Cu) and, more commonly, Zn-rich (up to 43.8?wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91?ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (??0.5?m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (??300°C), acidic (pH????2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (??122°C), more acidic (pH?1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO₄ and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3?years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO₂ (e.g., 206?mM/kg at the Cone site); high CO₂/³He; negative ??D and ??¹⁸O_H2O for vent fluids; negative ??³⁴S for sulfides (to ?4.6??), sulfur (to ?10.2??), and ??¹⁵N₂ (to ?3.5??); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu?+?Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in ³He/⁴He values for both Cone and NW Caldera sites, and overprinting of ??magmatic?? mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (??2.5?km long), narrow (??300-m diameter) ??pipes,?? consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.     

Experiments on silicate melt immiscibility in the system Fe2SiO4–KAlSi3O8–SiO2–CaO–MgO–TiO2–P2O5 and implications for natural magmas

The effect of CaO and MgO, with or without TiO₂ and P₂O₅, on the two-melt field in the simplified system Fe₂SiO₄–KAlSi₃O₈–SiO₂ has been experimentally determined at 1,050°–1,240°C, 400 MPa. Despite the suppressing effect of MgO, CaO, and pressure on silicate melt immiscibility, our experiments show that this process is still viable at mid-crustal pressures when small amounts (0.6–2.0 wt%) of P₂O₅ and TiO₂ are present. Our data stress that the major element partition coefficients between the two melts are highly correlated with the degree of polymerisation (nbo/t) of the SiO₂-rich melt, whatever temperature, pressure, or exact composition. Experimental immiscible melt compositions in natural systems at 0.1 MPa from the literature (lunar and tholeiitic basalts) plot on similar but distinct curves compared to the simplified system. These relations between melt polymerisation and partition coefficients, which hold for a large range of compositions and fO₂, are extended to various volcanic and plutonic rocks. This analysis strengthens the proposal that silicate melt immiscibility can be important in volcanic rocks of various compositions (from tholeiitic basalts to lamprophyres). However, the majority of proposed immiscible compositions in plutonic rocks are at least not coexisting melts, but may have suffered accumulation of early crystallized minerals.     

同位素指示的巴丹吉林沙漠南缘地下水补给来源

通过恢复巴丹吉林沙漠及其周边地区大气降水氚值，并结合区域稳定同位素组合特征，揭示了区域地下水氚年龄的多解性与地下水稳定同位素的温度效应。恢复的1963年核试验期氚高峰值达到2 100 TU，进入90年代平均为60 TU。1960年以来降水补给的地下水氚值都应大于15 TU，而1963年的高峰氚衰变至今应在200 TU左右。地下水实测氚值较低，表明由现代少量降水补给的地下水与大量的古水进行了混合。影响降水中δ18O和δ2H分布的主要影响因子是月平均空气温度，对δ18O与δ2H的影响权重分别占到59.9%和57.0%。巴丹吉林沙漠及其周边地区地下水较低的稳定同位素组成表明，其补给主要是晚更新世较冷环境下形成的，来源于东南部的雅布赖山区，部分浅层地下水接受现代降水与河流的补给。      

土壤剖面的磁学特征及其对交通污染的指示意义——以北京首都机场高速公路为例

对北京首都机场高速公路旁采集的土壤柱状T01剖面的磁学参数和金属元素分析,探讨了研究区内现代交通导致的土壤磁学性质的变化及其对环境污染的响应.结果表明,磁参数(χ,ARM和SIRM)与重金属含量呈同步垂向变化趋势.来源于交通运输排放的污染物是土壤剖面上部(0～8 cm)磁性和金属含量增强的主要原因,8cm以下,土壤基本未受到污染,磁性矿物和重金属含量较低,磁性颗粒变化稳定,基本代表了该地区土壤的自然背景.尽管土壤岩石磁学分析表明剖面上下部受污染和未受污染样品的磁载体均是粒度较粗的多畴磁铁矿,但是结合磁参数比值曲线,说明底部样品的磁颗粒的粒度较顶部偏细.磁性矿物的含量变化没有影响磁颗粒的粒度特征.指标聚类等相关分析表明,土壤磁参数(χ,ARM和SIRM)与重金属元素(Pb,Zn和Cu)含量显著相关;结合模糊聚类分析,磁参数可用于追踪、识别交通污染物质在土壤剖面中的富集、迁移状态,揭示不同深度土壤的污染程度.