Development of a Continental Volcanic Field: Petrogenesis of Pre-caldera Intermediate and Silicic Rocks and Origin of the Bandelier Magmas, Jemez Mountains (New Mexico, USA)

The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO₂)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements     

Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua

 Persistent activity at Masaya Volcano, Nicaragua, is characterised by cycles of intense degassing, lava lake development and pit crater formation. It provides a useful site to study the processes which govern such activity, because of its easy accessibility and relatively short cycles (years to decades). An understanding of the present activity is important because Masaya is visited by large numbers of tourists, is located close to major cities and has produced voluminous lavas, plinian eruptions and ignimbrites in the recent past. We provide structural and geophysical data that characterise the "normal" present state of activity. These indicate that the ongoing degassing phase (1993 to present) was not caused by fresh magma intrusion. It was associated with shallow density changes within the active Santiago pit crater. The activity appears to be associated predominantly with shallow changes in the pit crater structure. More hazardous activity will occur only if there are significant departures from the present gravity, deformation and seismic signatures. Received: 16 May 1997 / Accepted: 29 October 1997     

复杂地质条件下气层的多参数识别

在复杂地质条件下,应用单一或两种孔隙测井资料直接识别气层,灵敏度不高,为了准确地识别复杂地质条件下的气层,需从不同角度,应用多参数进行综合识别,本文介绍了声波法,中子－密度法,双孔隙度法,中子－伽玛法,等效弹性模量法等,并应用它们对哈盆地两口井进行了重点分析,效果良好。     

C—O—H体系高温高压流体相组成的热力学研究

本文在C－O－H体系流体相平衡基础上,利用现有的热力学数据和新的p－V－T资料,在pT=∑pi假定下,计算了高温、高压条件下流体相组成。结果表明,该体系主要存在五种流体相,在不同温压条件下各流体相所占比例不同。在相对较低的温、压条件下,CH4是体系中占主要的流体相（约占70％）,且随温、压和氧逸度的升高,它所占比例却明显降低,所获结果为探讨无机成因天然气形成的可能性、存在的量比和稳定存在的物理化学条件提供了充分的理论依据。     

地震前兆复杂性成因机理研究的讨论（一）：地震前兆复杂性的表现形式

通过国内外成功与失败的震例分析,介绍了地震前兆共性的一面,如在台网具有一定监测能力的地区,如果发生６级以上地震,震前总能或多或少地观测到异常现象。地震越大震前异常越多,分布越广,持续时间越长,异常幅度也较大,同时章着重对前兆复杂性的表现形式进行了较系统的归纳,整理,主要从以下几方面进行了分析,异常与地震关系的不确定性,主要表现在除了“有异常有地震”和“无异常无地震”的理论情况外,还存在“有异常无     

Isometamorphic variations in the reflectance and fluorescence of vitrinite—a key to depositional environment

Petrographic investigations of serial ply samples from five high- to medium-volatile bituminous coal seams from Australia (4) and Canada (1) reveal substantial in-seam variations in the reflectance and monochromatic microfluorescence intensities of the maceral subgroup telovitrinite. The variations consist of one case of reflectance enhancement and fluorescence suppression, and four cases of reflectance suppression and fluorescence enhancement. The single case of reflectance enhancement and fluorescence suppression is due to the oxidation of the vitrinite nuclei at the sequence boundary between the Bayswater and Upper Wynn seams in New South Wales. The four cases of reflectance suppression and fluorescence enhancement result from the syn- and epigenetic absorption by the vitrinite nuclei of hydrogen donated by, presumably, anaerobic bacteria-generated lipids. Two of the coals are marine-influenced: the Liskeard Seam from the Bowen Basin by combined syngenetic and epigenetic effects, and the Greta Seam from the Sydney Basin mainly by epigenetic contact with sea water. For both coals, the results are strong vitrinite reflectance suppression and fluorescence enhancement. The remaining two coals, the Bulli Seam from the Sydney Basin and a coal seam from the Gates Formation in British Columbia, show moderate epigenetic effects on the optical properties of telovitrinite by fresh-water. In the Bulli Seam which was studied in two adjacent localities, the reflectance suppression and fluorescence enhancement of telovitrinite are stronger under sandstone roof than under shale roof. In some cases, the epigenetic effects are superimposed on syngenetic telovitrinite reflectance and fluorescence variations resulting from the cogeneration and mixing of different telovitrinite precursors, for example, autochthonous roots and hypautochthonous or allochthonous shoots. A measure of the degree of dispersal and mixing is the coefficient of variation of telovitrinite reflectance and/or fluorescence. This coefficient correlates well with detrital minerals and dispersed macerals, e.g., inertodetrinite and, to a lesser extent, sporinite. Some comments are made on slitted so-called pseudovitrinite which is regarded as a telovitrinite that was subjected to very weak post-coalification desiccation and possibly oxidation without losing much of its thermoplastic properties.     

The regional dynamical model of the atmospheric ozonosphere

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FPGA在时间测量中的应用

利用现场可编程门阵列(FPGA)的内部资源，在FPGA中实现了高精度时间间隔测量系统的设计。     

A laboratory study on capillary sealing efficiency of Iranian shale and anhydrite caprocks

Caprock has the most important role in the long term safety of formation gas storage. The caprocks trap fluid accumulated beneath, contribute to lateral migration of this fluid and impede its upward migration. The rapid upward passage of invasive plumes due to buoyancy pressure is prevented by capillary pressure within these seal rocks. In the present study, two main seal rocks, from the Zagros basin in the southwest of Iran, a shale core sample of Asmari formation and an anhydrite core sample of Gachsaran formation, were provided. Absolute permeabilities of shale and anhydrite cores, considering the Klinkenberg effect, were measured as 6.09 × 10⁻¹⁸ and 0.89 × 10⁻¹⁸ m², respectively. Capillary sealing efficiency of the cores was investigated using gas breakthrough experiments. To do so, two distinct techniques including step by step and residual capillary pressure approaches were performed, using carbon dioxide, nitrogen and methane gases at temperatures of 70 and 90 °C, under confining pressures in the range 24.13–37.92 MPa. In the first technique, it was found that capillary breakthrough pressure of the cores varies in the range from 2.76 to 34.34 MPa. Moreover, the measurements indicated that after capillary breakthrough, gas effective permeabilities lie in range 1.85 × 10⁻²¹ – 1.66 × 10⁻¹⁹ m². In the second technique, the minimum capillary displacement pressure of shale varied from 0.66 to 1.45 MPa with the maximum effective permeability around 7.76 × 10⁻²¹ – 6.69 × 10⁻²⁰ m². The results indicate that anhydrite caprock of the Gachsaran formation provides proper capillary sealing efficacy, suitable for long term storage of the injected CO₂ plumes, due to its higher capillary breakthrough pressure and lower gas effective permeability.     

Optimized running conditions and sensitivity for direction sensitive detectors of WIMP dark matter

Optimum fill pressures for direction-sensitive dark matter detectors based on tracking in gases are considered. Given the minimum resolvable track length and the gas fill, the Lindhard–Scharf stopping model leads to the existence of an optimum pressure which maximizes the specific event rate R (event rate per unit detector volume). In addition, maximizing the detectibility of the recoil nucleus diurnal asymmetry is considered. Optimum fill pressures are calculated for Ar, CF₄, CS₂ and Xe gas fills, as a function of the WIMP mass and the minimum resolvable track length. The associated minimum target volumes required to achieve currently competitive WIMP-nucleon cross-section sensitivity are also calculated. The standard isothermal sphere model of the galactic WIMP halo is used throughout, but the method could be extended to use any desired WIMP distribution function.