云南会泽铅锌矿喷流沉积成因研究

会泽铅锌矿床的成因认识各异,曾认为是沉积—改造层控型矿床。研究前人资料、结合亲历找矿实践,讨论该矿床另一种不同的成矿方式。研究矿床地质、地球化学、同位素组成、包裹体、方铅矿年龄测定和成矿温度测试等表明:会泽铅锌矿属海底热卤水喷流沉积—改造层控型矿床,与芒特—艾萨型热卤水喷流沉积层控矿床类似。     

Dissolution/crystallization kinetics recorded in the 2002–2003 lavas of Stromboli (Italy)

On 28 December 2002, new vents opened on the flanks of Stromboli, just below the summit craters, interrupting the persistent activity of the volcano with a 7-month-long effusive eruption. We here report on the plagioclase size distribution (PlgSD) in lava samples collected following the chronology of the 2002–2003 eruption. Data reveal a linear PlgSD similar to that found in samples of normal Stromboli activity, indicating that the switch from Strombolian explosive to effusive activity is not associated with changes in texture. Nevertheless, the crystal size distribution slopes and intercepts exhibit slight sinusoidal temporal variations that are here ascribed to a magma supply mechanism able to induce “resonance” in the crystal size distribution, with an amplitude that depends on the supply rate.     

大同第四纪火山群的活动特点

一、引言大同第四纪火山群位于山西省大同县和阳高县境内(图1),包括近5年来在大峪口,秋林地区首次发现的6个小火山。该火山群大、小火山共计31个。大同火山群南以六棱山北麓断裂为界,分布于大同盆地东部的第四纪沉积区范围。火山群南侧的六棱山和北部的小北山是由前寒武花岗片麻岩组成的山地。     

滇东南大型超大型矿床成矿规律及找矿远景

华南成矿省滇东南成矿带是国内大型超大型矿床较多地区,以往认为其成因与滇东南三大花岗岩体的侵入有关,但从上世纪80年代以后,不少科研单位及学者在3个超大型矿床的块状硫化物矿石中发现了喷流沉积的重要证据。白牛厂V1矿体的直接顶、底板地层,在多个穿矿钻孔中发现三叶虫化石以及在白羊矿段矿石中发现了沉积锡石等也难与阿尾隐伏花岗岩体的成矿作用相联系。     

马关八梅喷流沉积铅锌锡铜金多金属矿床

矿床产于中寒武田蓬组地层中,受地层、沉积岩相、变质岩相控制。围岩蚀变为黄铁矿化、锰矿化、碳酸盐化、硅化。矿床成因为海底含矿热卤水喷流沉积型。     

Thermodynamics and fluid dynamics of effusive subglacial eruptions

We consider the thermodynamic and fluid dynamic processes that occur during subglacial effusive eruptions. Subglacial eruptions typically generate catastrophic floods (jökulhlaups) due to melting of ice by lava and generation of a large water cavity. We consider the heat transfer from basaltic and rhyolitic lava eruptions to the ice for typical ranges of magma discharge and geometry of subglacial lavas in Iceland. Our analysis shows that the heat flux out of cooling lava is large enough to sustain vigorous natural convection in the surrounding meltwater. In subglacial eruptions the temperature difference driving convection is in the range 10–100??°C. Average temperature of the meltwater must exceed 4??°C and is usually substantially greater. We calculate melting rates of the walls of the ice cavity in the range 1–40?m/day, indicating that large subglacial lakes can form rapidly as observed in the 1918 eruption of Katla and the 1996 eruption of Gjálp fissure in Vatnajökull. The volume changes associated with subglacial eruptions can cause large pressure changes in the developing ice cavity. These pressure changes can be much larger than those associated with variation of bedrock and glacier surface topography. Previous models of water-cavity stability based on hydrostatic and equilibrium conditions may not be applicable to water cavities produced rapidly in volcanic eruptions. Energy released by cooling of basaltic lava at the temperature of 1200??°C results in a volume deficiency due to volume difference between ice and water, provided that heat exchange efficiency is greater than approximately 80%. A negative pressure change inhibits escape of water, allowing large cavities to build up. Rhyolitic eruptions and basaltic eruptions, with less than approximately 80% heat exchange efficiency, cause positive pressure changes promoting continual escape of meltwater. The pressure changes in the water cavity can cause surface deformation of the ice. Laboratory experiments were carried out to investigate the development of a water cavity by melting ice from a finite source area at its base. The results confirm that the water cavity develops by convective heat transfer.     

Partially melted lithic megablocks in the Yardea Dacite, Gawler Range Volcanics, Australia: implications for eruption and emplacement mechanisms

 Lithic megablocks ranging from <1 to 50 m in diameter occur in the Yardea Dacite, a widespread (12,000 km²), thick (>200 m) felsic volcanic unit in the Mesoproterozoic Gawler Range Volcanic Province (GRV) of South Australia. Throughout its vast extent, the Yardea Dacite shows typical lava-like features, in that it is massive, columnar jointed and evenly porphyritic with 30–40% crystals in a spherulitic and granophyric groundmass. In addition, flow banding is present at many locations. The megablocks are abundant at two sites 50 km apart, but isolated megablocks and smaller (<6 cm) lithic clasts are also scattered throughout the unit. At both sites the megablocks are matrix supported, non-graded, randomly oriented and show no evidence of being confined to a particular stratigraphic level in the dacite. The most abundant and largest megablocks are granitoids derived from older basement and from early-crystallised plutons of the Hiltaba Suite, which is broadly coeval and comagmatic with the GRV. The granitoid megablocks have been partially melted, most likely prior to eruption when resident in the thermal aureole of the Yardea Dacite magma chamber. The lithic megablock occurrences are unlike coarse pyroclastic breccias but are similar in distribution and abundance to xenoliths in lavas, consistent with the lava-like character of the host dacite. Using reasonable estimates of megablock density, magma density and magma viscosity, we show that the rise rate of the dacitic magma exceeded the settling velocity of the megablocks, implying that they could have been entrained and erupted effusively. All but the largest and least-melted megablocks would have remained suspended or else settled very slowly in the dacitic lava during outflow. The rapid rate of magma withdrawal required to produce such an extensive felsic sheet could have also triggered disintegration of the thermally stressed wallrock surrounding the magma chamber, dislodging megablocks that were later entrained and effusively erupted. Received: 11 November 1998 / Accepted: 18 April 1999     

辽河滩海燕南潜山带中生界火成岩储层预测及勘探潜力初探

利用地震多属性分析等技术,对辽河坳陷滩海燕南潜山带中生界火成岩储层的分布、储层物性特征以及可能的含油气特征进行了初步预测。该火成岩以安山岩为主,钻时曲线普遍偏高,表明地层坚硬致密,一经构造运动等因素改造后,可以形成良好的裂缝性储层。本区溢流相火成岩含油气前景较好,应结合地震波形分类结果精细地圈定其分布范围,以作为今后勘探的有利地区。     

麻栗坡杨万火山喷流沉积-热液改造型铜矿

杨万铜矿床位于八布裂陷槽中。矿床位于中三叠统杨万明下段（T2y^a），受层位、岩性、构造及火山活动控制。围岩蚀变发育，绿泥石化、绿帘石化、硅化、碳酸盐化、类石墨化等与矿化关系密切。矿床成困应为海相火山喷流（溢）沉积－热液改造铜矿型。