云南省龙脖河铜矿区火山岩地质及岩石化学特征研究

龙脖河铜矿床的成矿与该区火山岩关系密切，加强对其进行岩石化学的研究，对在本区和区域上同类矿床的勘查找矿和成因研究具有重要的指导意义。在大量野外调查和室内综合分析基础上，研究了龙脖河铜矿区典型火山岩及其组构特征、副矿物特征、蚀变特点和岩石化学特征，认为龙脖河铜矿区火山岩是一套富钠质的碱性玄武岩系列岩石，与大红山群变钠质火山岩岩石组合十分相似。     

Integrated satellite observations of the 2001 eruption of Mt. Cleveland, Alaska

Satellite data were the primary source of information for the eruption of Mt. Cleveland, Alaska on 19 February, and 11 and 19 March 2001. Multiple data sets were used pre-, syn- and post-eruption to mitigate the hazard and determine an eruption chronology. The 19 February eruption was the largest of the three, resulting in a volcanic cloud that formed an arc over 1000 km long, moved to the NE across Alaska and was tracked using satellite data over more than a 50-h period. The volcanic cloud was “concurrently” detected on the GOES, AVHRR and MODIS data at various times and their respective signals compared. All three sensors detected a cloud that had a very similar shape and position but there were differences in their areal extent and internal structural detail. GOES data showed the largest volcanic cloud in terms of area, probably due to its oblique geometry. MODIS bands 31 and 32, which are comparable to GOES and AVHRR thermal infrared wavelengths, were the least effective single channels at detecting the volcanic cloud of those investigated (MODIS bands 28, 29, 31 and 32). MODIS bands 28 and 29 detected the largest volcanic clouds that could easily be distinguished from weather clouds. Of the split-window data, MODIS bands 29 minus band 32 detected the largest cloud, but the band 31 minus band 32 data showed the volcanic cloud with the most internal structural detail. The Puff tracking model accurately tracked the movement, and predicted the extent and shape of this complex cloud even into areas beyond satellite detection. Numerous thermal anomalies were also observed during the eruption on the twice-daily AVHRR data and the high spatial-resolution Landsat data. The high-resolution Radarsat data showed that the AVHRR thermal anomalies were due to lava and debris flow features and a newly formed fan along the west coast of the island. Field observations and images from a hand-held Forward Looking Infrared Radiometer (FLIR) showed that the flow features were ′a′a lava, debris flows and a warm debris fan along the west coast. Real-time satellite data were the primary tool used to monitor the eruption, track changes and to mitigate hazards. High-resolution data, even though coverage is infrequent, were critical in helping to identify volcanic processes and to compile an eruption chronology.     

Plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes

This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002-January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1-6.8 and 0.9-5.6, respectively. Plume S/Cl ratios increased by a factor of ∼10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late November) to passive degassing and minor effusion (early January), and then decreased to the low values (S/Cl=0.1) typical of the final stages of the eruption. Parallel variations in chlorine to fluorine ratios were also observed. A theoretical model is proposed for quantitative interpretation of these changes in plume composition. The model calculates the composition of a volatile phase exsolving from an ascending Etna magma, based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens [T.M. Gerlach, EOS 72 (1991), 249, 254-255]. According to this model, degassing of Etnean basaltic melt at high pressures and depths (>100 MPa, 3 km) is likely to release a CO₂+H₂O-rich vapor phase with S/Cl molar ratios ∼1. Extensive sulfur and chlorine degassing from the melt would take place at shallower depth (P<20 MPa, 0.6 km), with S/Cl ratios in the vapor phase increasing as pressure drops to 0.1 MPa. Comparisons between model compositions and volcanic plume data demonstrate that the chemical trends observed during the eruption may be explained by increased degassing due to depressurization of a basaltic magma batch ascending toward the surface.     

北山地区与火山活动有关铜多金属成矿条件及找矿前景浅析

北山地区与火山活动有关的铜多金属矿床主要有次火山斑岩型、火山喷溢型、火山沉积-变质型、沉积再造型和热液型,其中次火山斑岩型和火山沉积再造型是主要类型.通过对主要类型控矿条件的分析,得出与火山活动有关的斑岩型和海相沉积(改造)型多金属矿具有良好的找矿前景,并指出了具体的远景地区,认为本区不利于寻找海相火山岩块状硫化物型矿床.     

雅满苏铁矿床地质特征及成因浅析

雅满苏铁矿矿体的空间分布受成矿期断裂构造的控制,呈透镜状、舒缓波状延伸,分3个层位产出.铁矿的形成与火山热液活动关系密切,矿体中既有热液活动的特征又有矿质流体贯入的特征,早期热液活动形成交代充填型矿石,后期富铁流体贯入充填后形成品位较高的磁铁矿体.     

Petrogenesis of Pre-caldera Mafic Lavas, Jemez Mountains Volcanic Field (New Mexico, USA)

The Miocene–Quaternary Jemez Mountains volcanic field(JMVF), the site of the Valles caldera, lies at the intersectionof the Jemez lineament, a Proterozoic suture, and the CenozoicRio Grande rift. Parental magmas are of two types: K-depletedsilica-undersaturated, derived from the partial melting of lithosphericmantle with residual amphibole, and tholeiitic, derived fromeither asthenospheric or lithospheric mantle. Variability insilica-undersaturated basalts reflects contributions of meltsderived from lherzolitic and pyroxenitic mantle, representingheterogeneous lithosphere associated with the suture. The Kdepletion is inherited by fractionated, crustally contaminatedderivatives (hawaiites and mugearites), leading to distinctiveincompatible trace element signatures, with Th/(Nb,Ta) and La/(Nb,Ta)greater than, but K/(Nb,Ta) similar to, Bulk Silicate Earth.These compositions dominate the mafic and intermediate lavas,and the JMVF is therefore derived largely, and perhaps entirely,from melting of fertile continental Jemez lineament lithosphereduring rift-related extension. Significant variations in Pband Nd isotope ratios (²⁰⁶Pb/²⁰⁴Pb = 17·20–18·93;¹⁴³Nd/¹⁴⁴Nd = 0·51244–0·51272) result fromcrustal contamination, whereas ⁸⁷Sr/⁸⁶Sr is low and relativelyuniform (0·7040–0·7048). We compare theeffects of contamination by low-⁸⁷Sr/⁸⁶Sr crust with assimilationof high-⁸⁷Sr/⁸⁶Sr granitoid by partial melting, with Sr retainedin a feldspathic residue. Both models satisfactorily reproducethe isotopic features of the rocks, but the lack of a measurableEu anomaly in most JMVF mafic lavas is difficult to reconcilewith a major role for residual plagioclase during petrogenesis. KEY WORDS: Jemez Mountains volcanic field; Rio Grande rift; lithospheric mantle; crustal contamination; trace elements; radiogenic isotopes     

Helium and Argon Isotopes of the Tertiary Volcanic Rocks, Shandong Peninsula：Significance for Crust-Mantle Circulation

Noble gases have successfully been used to con strain the mantle structure (Allegre et al., 1983),discuss mantle heterogeneity (Ma and Tao, 2002),determine different mantle source components and soon, because of their chemical inertia and isotopicfractionation during the evolution of the earth. Het erogeneities of the subcontinental mantle beneatheastern China have been confirmed by abundant stud ies of mantle magmas and xenoliths, in mineralogy,petrology and isotop…     

Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface

By performing buoyancy-driven fracture experiments in brittle gelatin we observe that the ascent velocity of a fracture containing a finite volume of fluid increases when approaching the free surface. We theoretically describe this free-surface effect and quantify it by introducing an effective depth-dependent fracture toughness and developing an ascent model on the basis of linear fracture mechanics. We develop a successful inversion approach and resolve the actual and critical fracture length and the ascent velocity far away from the free surface from the observation of the fracture tip migration alone. Other parameters, as the fluid volume included in the fracture and the in situ fracture toughness, can be derived. Applying the model and inversion to the 1998 eruption at Piton de la Fournaise, Reunion Island, reveals estimates of the length and critical length of the feeding magma batch, the magma batch volume and the in situ fracture toughness. It further indicates that the ascent velocity of the magma batch was probably much smaller at greater depths and that the batch might have been initiated several months or years before the eruption.     

新疆察布查尔山早石炭世火山岩构造环境判别

察布查尔山位于伊犁-伊赛克湖微板块的南部,出露最老地层为下石炭统大哈拉军山组一套浅海相-陆相基性-酸性火山岩建造.通过岩石学,岩石地球化学分析,该火山岩整体碱度较高,碱性和亚碱性系列共存,正常类型和钾质类型共存,SiO2过饱和或低度不饱和.K2O平均含量3.4%,K2O/Na2O值多大于0.6,中基性岩Al2O3含量多大于16%.玄武岩RbN/YbN值4.5~19.9,属强不相容元素富集型.酸性岩CeN/YbN在5.2~7.2之间,显示地壳熔融特点.结合图解判别,确定早石炭世火山岩形成环境为活动大陆边缘.     

赣南三百山盆地岩石地层划分的新认识及其意义

分析了赣南三百山盆地地层层序和岩石地层划分的研究现状及存在分歧的原因,提出前人建立的地层层序与野外新发现的地质事实不相吻合,三百山盆地不存在所谓的双峰式火山岩组合和推覆构造。依据地层层序律,将三百山盆地自下而上可划分为砂岩层、长英质火山岩层、镁铁质火山岩层和砂砾岩层四套;通过地层对比,将第一套砂岩层划归上侏罗统武夷群双峰岭组、第二套长英质火山岩层划归上侏罗统武夷群鹅湖岭组、第三套铁镁质火山岩层和第四套砂砾岩层划归下白垩统罗塘群白埠组。