钢管高强混凝土柱抗震性能的试验研究

本文对钢管高强混凝土柱进行低周反复水平荷载作用的试验,得到了不同轴压比情况下的滞回曲线及骨架曲线,讨论了钢管高强混凝土柱压弯承载力计算公式的适用性。结果表明,钢管高强混凝土柱具有很高的承载力及良好的抗震性能。     

A depositional model for deep‐lacustrine,partially confined,turbidite fans: Early Cretaceous,North Falkland Basin

This paper presents a model of facies distribution within a set of early Cretaceous, deep‐lacustrine, partially confined turbidite fans (Sea Lion Fan, Sea Lion North Fan and Otter Fan) in the North Falkland Basin, South Atlantic. As a whole, ancient deep‐lacustrine turbidite systems are under‐represented in the literature when compared with those documented in marine basins. Lacustrine turbidite systems can form extensive, good quality hydrocarbon reservoirs, making the understanding of such systems crucial to exploration within lacustrine basins. An integrated analysis of seismic cross‐sections, seismic amplitude extraction maps and 455 m of core has enabled the identification of a series of turbidite fans. The deposits of these fans have been separated into lobe axis, lobe fringe and lobe distal fringe settings. Seismic architectures, observed in the seismic amplitude extraction maps, are interpreted to represent geologically associated heterogeneities, including: feeder systems, terminal mouth lobes, flow deflection, sinuous lobe axis deposits, flow constriction and stranded lobe fringe areas. When found in combination, these architectures suggest ‘partial confinement’ of a system, something that appears to be a key feature in the lacustrine turbidite setting of the North Falkland Basin. Partial confinement of a system occurs when depositionally generated topography controls the flow‐pathway and deposition of subsequent turbidite fan deposits. The term ‘partial confinement’ provides an expression for categorising a system whose depositional boundaries are unconfined by the margins of the basin, yet exhibit evidence of internal confinement, primarily controlled by depositional topography. Understanding the controls that dictate partial confinement; and the resultant distribution of sand‐prone facies within deep‐lacustrine turbidite fans, is important, particularly considering their recent rise as hydrocarbon reservoirs in rift and failed‐rift settings.     

Dolomitization by hypersaline reflux into dense groundwaters as revealed by vertical trends in strontium and oxygen isotopes: Upper Muschelkalk,Switzerland

The Trigonodus Dolomit is the dolomitized portion of the homoclinal ramp sediments of the Middle Triassic Upper Muschelkalk in the south‐east Central European Basin. Various dolomitizing mechanisms, followed by recrystallization, have been previously invoked to explain the low δ¹⁸O, high ⁸⁷Sr/⁸⁶Sr, extensive spatial distribution and early nature of the replacive matrix dolomites. This study re‐evaluates the origin, timing and characteristics of the dolomitizing fluids by examining petrographic and isotopic trends in the Trigonodus Dolomit at 11 boreholes in northern Switzerland. In each borehole the ca 30 m thick unit displays the same vertical trends with increasing depth: crystal size increase, change from anhedral to euhedral textures, ultraviolet‐fluorescence decrease, δ¹⁸O_VPDB decrease from ?1·0‰ at the top to ?6·7‰ at the base and an ⁸⁷Sr/⁸⁶Sr increase from 0·7080 at the top to 0·7117 at the base. Thus, dolomites at the top of the unit record isotopic values similar to Middle Triassic seawater (δ¹⁸O_VSMOW = 0‰; ⁸⁷Sr/⁸⁶Sr = 0·70775) while dolomites at the base record values similar to meteoric groundwaters from the nearby Vindelician High (δ¹⁸O_VSMOW = ?4·0‰; ⁸⁷Sr/⁸⁶Sr = >0·712). According to water–rock interaction modelling, a single dolomitizing or recrystallizing fluid cannot have produced the observed isotopic trends. Instead, the combined isotopic, geochemical and petrographic data can be explained by dolomitization via seepage‐reflux of hypersaline brines into dense, horizontally‐advecting groundwaters that already had negative δ¹⁸O and high ⁸⁷Sr/⁸⁶Sr values. Evidence for the early groundwaters is found in meteoric calcite cements that preceded dolomitization and in fully recrystallized dolomites with isotopic characteristics identical to the groundwaters following matrix dolomitization. This study demonstrates that early groundwaters can play a decisive role in the formation and recrystallization of massive dolomites and that the isotopic and textural signatures of pre‐existing groundwaters can be preserved during seepage‐reflux dolomitization in low‐angle carbonate ramps.     

Response of unconfined turbidity current to deep‐water fold and thrust belt topography: Orthogonal incidence on solitary and segmented folds

Sea‐floor topography of deep‐water folds is widely considered to have a major impact on turbidity currents and their depositional systems, but understanding the flow response to such features was limited mainly to conceptual notions inspired by small‐scale laboratory experiments. High‐resolution three‐dimensional numerical experiments can compensate for the lack of natural‐scale flow observations. The present study combines numerical modelling of thrusts with fault‐propagation folds by Trishear3D software with computational fluid dynamics simulations of a natural‐scale unconfined turbidity current by MassFlow‐3D? software. The study reveals the hydraulic and depositional responses of a turbidity current (ca 50 m thick) to typical topographic features that it might encounter in an orthogonal incidence on a sea‐floor deep‐water fold and thrust belt. The supercritical current (ca 10 m sec^?1) decelerated and thickened due to the hydraulic jump on the fold backlimb counter‐slope, where a reverse overflow formed through current self‐reflection and a reverse underflow was issued by backward squeezing of a dense near‐bed sediment load. The reverse flows were re‐feeding sediment to the parental current, reducing its waning rate and extending its runout. The low‐efficiency current, carrying sand and silt, outran a downslope distance of >17 km with only modest deposition (<0·2 m) beyond the fold. Most of the flow volume diverted sideways along the backlimb to surround the fold and spread further downslope, with some overspill across the fold and another hydraulic jump at the forelimb toe. In the case of a segmented fold, a large part of the flow went downslope through the segment boundary. Preferential deposition (0·2 to 1·8 m) occurred on the fold backlimb and directly upslope, and on the forelimb slope in the case of a smaller fold. The spatial patterns of sand entrapment revealed by the study may serve as guidelines for assessing the influence of substrate folds on turbiditic sedimentation in a basin.     

富稀土磷酸盐及其在深海成矿作用中的贡献

中国最近几年对中北太平洋海域开展了系统调查,在中太平洋海盆新发现了稀土含量高达2000×10~(-6)的富稀土泥。深海泥样品稀土与各主要氧化物相关图解中,∑REY与P_2O_5含量始终保持良好的相关性。在太平洋各沉积物柱状样中,∑REY随着P2O5变化非常敏感。如果将P_2O_5含量高于0.25%的样品剔除,深海泥的∑REY不高于400×10~(-6),指示了磷对稀土元素的控制。海洋磷酸盐能够继承海水的负Ce异常及高Y/Ho比值特征,深海泥样品具有相似特征,且表现为稀土含量越高,其稀土配分模式越接近磷酸盐。酸淋滤实验显示,滤液中萃取出大部分的P及∑REY,且∑REY与P含量具有良好的正相关关系。无论∑REY高低,滤液稀土配分均呈现出显著的负Ce异常;而难溶残留物的∑REY普遍较低,且无负Ce异常特征。根据12组滤液中PO_4~(3-)与∑REY,估算出深海泥中的磷酸盐具有的∑REY含量范围为9495×10~(-6)~28287×10~(-6),这与深海泥中生物磷灰石的稀土含量和稀土模式均吻合。综上所述,我们认为深海泥中的磷酸盐主要以富稀土磷酸盐的形式存在,其稀土含量远高于深海泥中的铁锰氧化物和铝硅酸,因此磷含量的变化对于深海泥的稀土含量和模式影响至关重要。相较于碳酸盐沉积环境下容易形成贫稀土的磷块岩,深海环境下的化学沉积以及有机P的成岩作用容易形成富稀土磷酸盐。     

湖南宝山花岗闪长质岩石混合成因证据探讨

通过对湖南宝山花岗闪长质岩石岩相学特征研究,发现存在较多矿物不平衡结构,如富Ca的斜长石熔蚀核,黑云母、石英嵌晶结构,暗色镶边的眼球状石英,针状磷灰石、辉石、黑云母共存等现象,表明宝山花岗闪长质岩石为基性岩浆与酸性岩浆的混合成因;主微量元素分析结果进一步证实了岩体属于混合成因的观点。该结论为壳幔相互作用提供了岩石学依据。     

The importance of missing strain in Deep Water Fold and Thrust Belts

Deep water fold and thrust belts (DWFTBs) are sedimentary wedges that accommodate plate-scale deformation on both active and passive continental margins. Internally, these wedges consist of individual structures that strongly influence sediment dispersal, bathymetry and fluid migration. Most DWFTB studies investigate basin- and intra-wedge- scale processes using seismic reflection profiles, yet are inherently limited by seismic resolution. Of critical importance is strain distribution and its accommodation on discrete faults compared to distributed deformation. Recent studies have considered strain distribution by investigating regional reflection DWFTBs profiles within coupled systems, which contain down-dip compression and up-dip extension. There is broad agreement of a mis-balance in compression versus extension, with ∼5% excess in the latter associated with horizontal compaction, yet this remains unproven.Using two exceptionally well exposed outcrops in the Spanish Pyrenees we consider deformation of DWFTB at a scale comparable to, and beyond, seismic resolution for the first time. By coupling outcrop observations (decametre to hectometre scale) with a re-evaluation of seismic profiles from the Orange Basin, South Africa, which contains one of the best imaged DWFTBs globally, we provide a unique insight into the deformation from metre to margin scale. Our observations reveal hitherto unrecognised second order structures that account for the majority of the previously recognised missing strain. This re-evaluation implies that ∼5% missing strain should be accounted for in all DWFTBs, therefore existing studies using restorations of the sediment wedge will have underestimated crustal shortening in active margins, or sedimentary shortening in gravity driven systems by this amount. In contrast to previous studies, our observations imply that the majority of this strain is accommodated on discrete fault surfaces and this can explain the occurrence and location of a range of intra-wedge processes that are intimately linked to structures including sediment dispersal, fluid migration pathways and reservoir compartmentalisation.     

Conserving the common heritage of humankind – Options for the deep-seabed mining regime

The seabed in areas beyond national jurisdiction is the common heritage of mankind (CHM), as declared in the 1982 United Nations Convention on the Law of the Sea. The CHM principle requires not only the sharing of benefits (the subject of a parallel article by the authors) but also the conservation and preservation of natural and biological resources for both present and future generations. The International Seabed Authority, tasked with operationalising the CHM principle in the context of deep-seabed mining, has not yet defined which measures it will take to give effect to environmental aspects of the CHM principle. This article seeks to contribute to the discussion about the operationalization of the CHM principle by specifically examining the environmental dimension of the CHM principle. To this end, the article interprets the CHM principle in the context of sustainable development and discusses a number of potential options the Authority could consider to support the application of the CHM principle. These include: funding scientific research to increase knowledge about the deep ocean for humankind; ensuring public participation in the decision-making process; debating the need for and alternatives to deep-seabed mining; determining conservation targets and levels of harm deemed acceptable; limiting environmental impacts; preserving mineable sites for future generations; compensating humankind for environmental harm; and ensuring enforcement.     

Should deep seabed mining be allowed?

Commercial interest in deep sea minerals in the area beyond the limits of national jurisdiction has rapidly increased in recent years. The International Seabed Authority has already given out 26 exploration contracts and it is currently in the process of developing the Mining Code for eventual exploitation of the mineral resources. Priority issues have so far been feasibility and profitability of this emerging industry, while relatively little consideration has been given as to how, and to an even lesser extent, whether deep seabed mining should proceed. This article makes a case that the global community should question and scrutinize the underlying assumption that deep seabed mining is going benefit humankind as a whole before commercializing the common heritage of humankind.     

西天山晚石炭世岩浆混合花岗岩的确定及其地质意义——来自玉奇布拉克和乌图精河岩体的LA-ICP-MS锆石U-Pb年龄和岩石地球化学证据

西天山博罗科努地区的玉奇布拉克和乌图精河岩体中发育大量暗色闪长质包体,包体发育矿物相互包裹的嵌晶及岩浆冷凝矿物不平衡结构,同时出现淬冷形成的针状磷灰石,指示岩体形成过程经历了二元岩浆的混合作用。包体较寄主花岗岩有明显低的SiO_2、K_2O,高CaO、FeO~T和MgO,但二者的微量元素高度一致,相对富集Rb、Th、U、K等LILE,贫HFSE,亏损Sr、Nb、Ta、P和Ti等元素,为二元岩浆混合作用所致。经LA-ICP-MS锆石U-Pb定年,两个岩体寄主花岗岩和包体分别获得301 Ma、308 Ma和303 Ma、298 Ma的形成年龄,指示同期不同源岩浆活动并存。寄主花岗岩的ε_(Hf)(t)值分别为+4.20~+8.33和+4.97~+7.0;Hf陆壳模式年龄T C_(DM)为782~1045 Ma和863~998 Ma,揭示它们主要源自新元古代早期陆壳物质。包体的εHf(t)值分别为+2.75~+6.41和+4.63~+7.92,与区域上同期基性岩脉正的εHf(t)和εNd(t)值相当。结合区域上同期花岗岩类高ε_(Hf)(t)和ε_(Nd)(t)、中等n(~(87)Sr)/n(~(86)Sr)推断,该期花岗岩是新元古代早期陆壳物质部分熔融的岩浆与被消减带组分改造的略亏损岩石圈地幔岩浆混合作用的结果,并构成由晚石炭世高钾钙碱性花岗岩向早二叠世富钾花岗岩/或A型花岗岩转换的岩浆演化系列,表明晚石炭世—早二叠世期间西天山造山带转入后碰撞晚期向伸展转化的构造环境。陆壳伸展导致幔源基性岩浆上侵,诱发陆壳部分熔融产生壳源岩浆,二者混合形成晚古生代以来西天山最为广泛的花岗岩浆活动,成为区内一次重要的地壳垂向增生事件。