大别造山带白鸭山A型花岗岩中镁铁质微粒包体成因及其地质意义

大别造山带早白垩世白鸭山A型花岗岩体中广泛分布着暗色微粒包体。对该包体及其寄主岩进行岩相学、矿物学和地球化学研究发现:镁铁质微粒包体(MME)与其寄主岩具有相同的矿物组合,相似的主量元素、微量元素和稀土元素特征,指示MME与寄主岩具有明显的亲缘关系;包体中岩浆成因褐帘石的发现,否定了富云包体的残余体成因,包体中含有碱性长石捕虏晶及大量针状磷灰石,指示岩浆混合作用的影响。结合共分母和不共分母图解判别,揭示MME与寄主岩明显具有岩浆混合作用特征,FeO*-MgO判别图解也指示包体为岩浆混合成因。Nd,Sr同位素组成指示MME的主体成分来源于富集岩石圈地幔,寄主岩体的物质来源为北大别杂岩。综合研究表明,大别地区在早白垩世存在一次壳幔混合作用,可能与岩石圈的伸展减薄有关,岩石圈的伸展导致富集地幔上涌,底侵并诱发古老下地壳熔融,同时发生岩浆混合作用。     

西拉木伦多金属成矿带鸡冠山斑岩钼矿富氟高盐度高氧逸度流体包裹体研究

鸡冠山斑岩钼矿床位于西拉木伦多金属成矿带南侧、内蒙古赤峰市北东约35km处,大地构造位置属于华北板块北缘造山带中段。辉钼矿化主要呈浸染状、细脉浸染状分布在花岗斑岩中,部分成细脉浸染状分布在流纹质角砾凝灰岩中,同时,在矿区出露的辉绿岩和流纹岩中也有少量的细网脉状钼矿化。矿石矿物主要有辉钼矿、黄铁矿和少量黄铜矿、闪锌矿、磁铁矿,脉石矿物主要有石英、长石、绢云母和少量方解石、萤石。矿脉穿插关系和矿物组合显示了早、中、晚3个阶段的矿化:(1)石英-辉钼矿阶段;(2)萤石-(石英)-辉钼矿多金属硫化物阶段;(3)贫矿萤石阶段。各阶段广泛发育流体包裹体,包裹体类型众多,包括气液两相水溶液包裹体(W型),H2O-CO2包裹体(C型)及含子矿物多相包裹体(S型),其中以大量发育含子矿物多相包裹体为特征。子矿物种类有石盐、钾盐、赤铁矿、石膏、辉钼矿、方解石等及其他未鉴别透明、不透明子矿物,有时一个包裹体含有多达4～5个子矿物。包裹体大量的赤铁矿、石膏和金属子矿物的出现,说明含矿流体具有高的氧逸度和很强的金属携带能力。包裹体岩相学、激光拉曼和显微测温结果表明,成矿流体主要为来自高温、高盐度、高氧逸度的岩浆流体和部分天水与岩浆热液混合所形成的中低温、低盐度流体两个端员组份。高温、高盐度流体以含子矿物多相包裹体为代表,其形成温度大于440℃,盐度变化范围为:28%～76%NaCleqv,部分高于76%NaCleqv。中低温、低盐度流体主要源自矿化后期天水与岩浆热液的混合,温度在322℃以下,盐度变化范围为:0.9%～20.3%NaCleqv。实验结果表明鸡冠山矿区含矿硫化物主要沉淀温度区间在310～400℃之间,其次为210～320℃,钼矿化主要形成于高温、高盐度、高氧逸度及富氟元素的H2O-NaCl流体体系,温度降低、流体沸腾作用及流体混合是该钼矿床的主要成矿机制。     

水泥搅拌桩挡土墙墙顶位移的修正算法

对水泥搅拌桩挡土墙的水平位移计算进行了探讨。以刚性桩法为基础理论和计算模型、弹性抗力法的计算结果为挠曲修正,首次提出一种既便于手算,又能考虑墙身挠曲变形的墙顶位移修正算法。     

Koolau shield basalt as xenoliths entrained during rejuvenated-stage eruptions: perspectives on magma mixing

Rejuvenated-stage tuff cones (Honolulu Volcanics) on Koolau volcano, Oahu, Hawaii, contain xenoliths of Koolau shield basalt. Because Koolau subaerial shield lavas represent a Hawaiian geochemical 'end member', and submarine shield lavas have compositions with some affinities to Mauna Loa and Kilauea, we analyzed 28 xenolithic basalts from Salt Lake and Koko Head cones to determine how these seemingly random samplings of the Koolau profile compare to established Koolau geochemistry. Analyses reveal that 24 are shield tholeiitic basalt—the focus of this study—and 4 are rejuvenated-stage basaltic rocks. The tholeiitic xenoliths represent largely upper Koolau shield lavas, as these samples (8.3 to 5.8 wt% MgO) have, with one exception, overall major- and trace-element compositions that overlap those of Koolau subaerial shield lavas. Secondary processes, however, created some distinctions—namely, enrichments/depletions in K, Ba, Sr, SiO₂, and FeO, and, due to zeolitization (chabazite with attending okenite and apophyllite), elevated CaO. One xenolithic basalt with 8.2 wt% MgO has higher Ti, Zr, Nb, and Sc, and lower Zr/Nb than subaerial lavas, and appears to represent relatively early, deeper shield—thereby reinforcing that the Koolau shield source varied temporally. Olivine, orthopyroxene, and plagioclase are the phenocrysts (clinopyroxene is rare), and their core compositions range widely across the suite—Fo_87.8–72, orthopyroxene Mg#s 85–72, and An_74–60. Several xenolithic basalts have both normally and reversely zoned orthopyroxene and plagioclase with a variety of core compositions (e.g., orthopyroxene-core Mg#s 82, 77, and 72, all in one sample). These compositions and zonations record evidence for wide compositional ranges of replenishment (MgO ~13–8 wt%) and reservoir (MgO ~7 to <5 wt%) magmas mixing in varying proportions; however, extreme MgO lavas (~13 and <5 wt%) are not observed as either subaerial or xenolithic basalt, but are indicated by phenocryst cores of Fo_87.8 and orthopyroxene-Mg# 72. The Koolau magma-mixing history resembles that of Kilauea, and is unlike the 'steady-state' mixing known for Mauna Loa. Finally, these basalt samples show that any xenolithic occurrence of Koolau lava is subject to the zeolitization prevalent in the tuff-cone hosts.Editorial handling: M. Carroll     

Role of magma mixing in the petrogenesis of tephra erupted during the 1990–98 explosive activity of Nevado Sabancaya,southern Peru

The Nevado Sabancaya in southern Peru has exhibited a persistent eruptive activity over eight years following a violent eruption in May–June 1990. The explosive activity consisted of alternated vulcanian and phreatomagmatic events, followed by declining phreatic activity since late 1997. The mean production rate of magma has remained low (10⁶–10⁷ m³ per year).The 1990–1998 eruptive episode produced andesitic and dacitic magmas. The juvenile tephra span a narrow range of compositions (60–64 wt% SiO₂). While SiO₂ contents do vary slightly, they do not show any systematic variation with time. Phenocryst assemblages in the juvenile rocks consist of mainly plagioclase, associated with high-Ca pyroxene, hornblende, biotite, and iron-titanium oxides. Rare fine-grained magmatic enclaves, with angular to subrounded shapes, are contained within some of the juvenile lava blocks, which were expelled since 1992. They have a homogeneous andesitic composition (57 wt% SiO₂) and show randomly oriented interlocking columnar or acicular crystals (plagioclase and amphibole), with interstitial glass and a few voids, which define a quench-textured groundmass.Textural, mineralogical and chemical evidence suggests that the 1990–1998 eruptions have mainly erupted hybrid andesites, except for the 1990 dacite. The hybrid andesites contain a mixed population of plagioclase phenocrysts: Ca-rich clear plagioclase (An_40–60), Na-rich clear plagioclase (An_25–35), and inversely zoned dusty-rimmed plagioclase with a sodic core (An_25–40) surrounded by a Ca-rich mantle (An_45–65). Melt-inclusions, wavy dissolution surfaces and stepped zoning within the dusty-rimmed plagioclases are compatible with resorption induced by magma recharge events. Chemical and isotopic lines of evidence also show that andesites are hybrids resulting from magma mixing processes. Repeated magma recharge, incomplete homogenisation and different degrees of crustal assimilation may explain the extended range of isotopic signatures.Our study leads to propose an evolution model for the magmatic system at Nevado Sabancaya. The main magma body consisted of dacitic magmas differentiating through extensive open-system crystallization (AFC). Repeated recharge of more mafic magmas induced magma mixing, leading to the formation of hybrid andesites. A partially crystalline boundary layer formed at the interface between the andesites and the recharge magma. The magmatic enclaves were produced by the disruption and dispersion of this andesitic layer as a result of new magma injection and/or sustained tectonic activity.Periodic magma recharge and interactions with groundwater are two processes that have enabled the explosive regime to remain persistent over an 8-year-long period. What precise mechanism triggers the eruptive activity remains speculative, but it may be related either to new magma injection, or to the sustained tectonic activity that occurred at that time in the vicinity of the volcano, or a combination of both.     

Petrogenesis of the Mesozoic intrusive rocks in the Tongling area,Anhui Province,China and their constraint on geodynamic process

TheTonglingarea,whichiscalledtheChineseCopperCapital,isoneofthemostimportantnon-ferrousmetalproducersinChina(e.g.Cu,AuandAg,especiallyCu).ManyresearchershavenotedthatthemetaldepositsarecloselyrelatedtotheMesozoicintrusiverocksinthisarea.Therefore,theTongl…     

Quantifying turbulent mixing and oxygen fluxes in a Mediterranean-type,microtidal estuary

Experiments were carried out on an intermittent estuary during its closed (summer) and open (winter) states to identify the physical processes responsible for vertical mixing across the halocline, and to quantify vertical fluxes of oxygen and salt between water layers. During the blocked phase a two-layer structure was observed, with a brackish surface layer overlying old seawater. Within a deep basin the wind-driven turbulent mixing was consistent with the measured surface-layer turbulent dissipation, but the dissipation in the bottom layer appeared to be driven by internal seiching. In the shallow regions of the estuary vertical fluxes of dissolved oxygen were indicative of oxygen demand by respiration and remineralization of organic material in bottom water and sediments. During the estuary's open phase a three-layer structure was observed, having a fresh, river-derived surface layer, a middle layer of new seawater, and a bottom layer of old seawater. In the shallower regions surface-layer turbulent diffusion was consistent with the strong, gusty winds experienced at the time. The dissolved oxygen of the incoming seawater decreased to very low values by the time it reached the upstream deep basin as a result of the low cross-pycnocline oxygen flux being unable to compensate for the oxygen utilization. At least 50 % of the cross-pycnocline salt fluxes in the shallow reaches of the open estuary are suggested to be driven by Holmboe instabilities. Responsible Editor: Hans Burchard     

泵送钢纤维混凝土在地下工程施工中的应用

钢纤维混凝土作为一种新型复合材料，已成为混凝土科学发展的一个方向，并以其良好的抗裂性、弯曲韧性、抗拉与抗弯强度等性能，正广泛应用于各类工程建设领域。阐述了特定的现场拌制条件下，泵送钢纤维混凝土在地下工程施工中的应用。     

Time-scales of hybridisation of magmatic enclaves in regular and chaotic flow fields: petrologic and volcanologic implications

This paper describes numerical models of advection/diffusion between enclaves and host magmas, applied with the aim of estimating time-scales during which enclaves can be homogenised. In particular, advection was simulated using a numerical system consisting of regular and chaotic regions. Results indicate that the homogenisation time of enclaves in chaotic regions is several orders of magnitude faster than in regular regions. For instance, an enclave with a diameter of 100 cm may be homogenised in the chaotic region in ∼ 380 years, assuming an advection velocity of 10 cm/year, whereas in the regular region it would require 6.5×10⁵ years for complete homogenisation. This implies that, in the same magmatic system, large differences in the degree of homogenisation may co-exist, generating magmatic masses with large spatial and temporal inhomogeneities. The results of this study may have significant petrological and volcanological implications. From a petrological point of view, mafic enclaves dispersed in felsic host rocks are regarded as portions of mafic magma which, trapped inside regular regions, survived the hybridisation process. Instead, host rocks are regarded as regions where efficient mixing dynamics generated hybrid magmas. The fact that a single magmatic mass may display large compositional differences at the same time undermines the assumption of most geochemical models, which assume the temporal and spatial homogeneity of the magma body. From the volcanological perspective, the presence of magmatic enclaves in volcanic rocks allows us to estimate the mixing times of magmas by analysing chemical diffusion patterns between host rocks and enclaves. Editorial responsibility: D. Dingwell     

软土型水泥土掺砂试验研究

考虑到土性对水泥土强度的影响，提出了在软土中掺砂以改进水泥土抗压强度性能的方法。选取深港西部通道填海区含有机质的淤泥，采用均匀设计法来考察水泥掺入比、砂的掺入比、龄期和水泥土抗压强度的关系；建立了其回归模型，研究了3个因素对强度的影响情况，给出了优化配比的方法；最后提出了改进机具以实现水泥土掺砂的设想。