Hazards from pyroclastic density currents at Mt. Etna (Italy)

Despite the recent recognition of Mount Etna as a periodically violently explosive volcano, the hazards from various types of pyroclastic density currents (PDCs) have until now received virtually no attention at this volcano. Large-scale pyroclastic flows last occurred during the caldera-forming Ellittico eruptions, 15–16 ka ago, and the risk of them occurring in the near future is negligible. However, minor PDCs can affect much of the summit area and portions of the upper flanks of the volcano. During the past ~ 20 years, small pyroclastic flows or base-surge-like vapor and ash clouds have occurred in at least 8 cases during summit eruptions of Etna. Four different mechanisms of PDC generation have been identified during these events: (1) collapse of pyroclastic fountains (as in 2000 and possibly in 1986); (2) phreatomagmatic explosions resulting from mixing of lava with wet rock (2006); (3) phreatomagmatic explosions resulting from mixing of lava with thick snow (2007); (4) disintegration of the unstable flanks of a lava dome-like structure growing over the rim of one of the summit craters (1999). All of these recent PDCs were of a rather minor extent (maximum runout lengths were about 1.5 km in November 2006 and March 2007) and thus they represented no threat for populated areas and human property around the volcano. Yet, events of this type pose a significant threat to the lives of people visiting the summit area of Etna, and areas in a radius of 2 km from the summit craters should be off-limits anytime an event capable of producing similar PDCs occurs. The most likely source of further PDCs in the near future is the Southeast Crater, the youngest, most active and most unstable of the four summit craters of Etna, where 6 of the 8 documented recent PDCs originated. It is likely that similar hazards exist in a number of volcanic settings elsewhere, especially at snow- or glacier-covered volcanoes and on volcano slopes strongly affected by hydrothermal alteration.     

Exploration and discovery in Yellowstone Lake: results from high-resolution sonar imaging, seismic reflection profiling, and submersible studies

‘No portion of the American continent is perhaps so rich in wonders as the Yellow Stone’ (F.V. Hayden, September 2, 1874)Discoveries from multi-beam sonar mapping and seismic reflection surveys of the northern, central, and West Thumb basins of Yellowstone Lake provide new insight into the extent of post-collapse volcanism and active hydrothermal processes occurring in a large lake environment above a large magma chamber. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic, and sedimentary processes. Detailed bathymetric, seismic reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and exert fundamental control on lake bathymetry and localization of hydrothermal activity. Many previously unknown features have been identified and include over 250 hydrothermal vents, several very large (>500 m diameter) hydrothermal explosion craters, many small hydrothermal vent craters (1–200 m diameter), domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting post-glacial sediments, siliceous hydrothermal spire structures, sublacustrine landslide deposits, submerged former shorelines, and a recently active graben. Sampling and observations with a submersible remotely operated vehicle confirm and extend our understanding of the identified features. Faults, fissures, hydrothermally inflated domal structures, hydrothermal explosion craters, and sublacustrine landslides constitute potentially significant geologic hazards. Toxic elements derived from hydrothermal processes also may significantly affect the Yellowstone ecosystem.     

广西南部钦州地区早—中三叠世火山事件——台马碎斑熔岩

通过对前人划分的十万大山岩带的主要岩体——台马岩体的野外地质特征、岩石学特征的研究,认为原台马岩体主要由碎斑熔岩组成,是火山侵出相的产物而不是侵入相的花岗斑岩。结合台马碎斑熔岩与周边火山岩、侵入岩、地层的关系,认为它是早—中三叠世中心裂隙式火山构造中央部位侵出的穹状岩脊。因此,十万大山岩带是火山-侵入杂岩带,台马碎斑熔岩是该火山-侵入杂岩带的一个相。     

大兴安岭中段柴河地区碎斑熔岩的发现及其意义

近年,在大兴安岭柴河地区开展1：5万区调时发现了碎斑熔岩体.区内发育晚侏罗世满克头鄂博组（J3m）、玛尼吐组（J3mn）及白音高老组（J3b）火山岩,广泛分布在二十四道沟、敖尼尔-四道沟及柴河-固里河3个火山喷发盆地中.所发现的固里河、敖尼尔两个碎斑熔岩体,即是白音高老期火山活动晚期侵出的重要组成部分.固里河碎斑熔岩体呈一北东向延伸的椭圆形穹状岩体,可划分出内部相（似斑状）、过渡相（霏细质）和边缘相（玻质）3个相带,主要由流纹质碎斑熔岩构成;敖尼尔碎斑熔岩主体呈近东西向,平面上呈似蘑菇状,可划分出2~3个相带,其岩石类型基本同固里河碎斑熔岩体.它们的发现,对研究大兴安岭地区火山岩的形成、演化及指导找矿等具有重要意义.     

老挝万象省爬立山（PHaLek）铁矿床地质特征及成矿作用分析

爬立山铁矿床位于长山褶皱带北西端,是长山成矿带内与岩浆作用有关的一个大型铁矿床。根据野外地质观察及室内对含矿岩体、赋矿围岩和矿石开展的岩相学和地球化学研究发现：与成矿作用有关的花岗质岩石属钙碱系列准铝质的I型花岗岩,成岩的构造环境为火山弧。矿区内发育致密块状磁铁矿、孔洞状赤铁矿、砂砾土状铁矿等3种铁矿石。结合岩（矿）石微量元素分析,认为爬立山铁矿具有复合成矿作用特征,主要可分为3个成矿阶段：早期以与华力西期岩浆侵入作用有关的接触交代成矿作用为主,形成矽卡岩型磁铁矿;其后,在褶皱造山后形成的断陷盆地中,由于火山喷发（溢）作用形成孔洞状熔岩型赤铁矿;最后随着新生代地壳抬升,发生表生物理化学风化成矿作用,形成如今的砂砾土状型铁矿。     

长白山区二道白河流域早更新世玄武质熔岩的成因

采用岩石化学和同位素分析方法,研究了二道白河流域早更新世玄武质熔岩的成因。玄武质熔岩由钠质拉斑玄武岩和钾质粗面玄武岩、玄武质粗面安山岩组成。它们的REE分配形式比较相近,表明它们来自共同的源区。Sr、Nd、Pb同位素示踪表明,二道白河流域早更新世玄武质熔岩岩浆源区接近于似原始地幔。它们的Mg#=100Mg O/(Mg O+Fe O)低于中国东部新生代玄武岩原始岩浆的Mg#(60~68),Ni(27.76×10-6~200.6×10-6)低于原始地幔,Rb/Sr(0.05~0.09)、Ba/Rb(15.64~264)高于原始地幔,说明这些岩石不是源自原始地幔。玄武质熔岩的DI变化于42~67,具有高Ca、高Sr、Eu正异常,微量元素图解显示玄武岩保留部分熔融趋势,粗面玄武岩、玄武质粗安岩具有结晶分异趋势,岩浆上升过程中发生了不同程度的地壳混染作用。玄武质熔岩的Nb/Ta之比为14.8~15.8,与勘察加半岛深俯冲带火山类似。Nb/Ta-(Na2O-K2O)关系图解显示研究区玄武质岩浆的形成与俯冲板片的部分熔融有关。     

白银厂的火山碎悄岩岩石学与古海相火山作用

应用古火山地质学和岩石地球化学对白银厂中酸性火山穹隆内的凝灰岩、昌屑凝灰岩、中酸性枕状、绳状熔岩和具有特殊构造的补丁岩等火山碎屑碉进行了较快速度沉降并堆积成岩,产于火山喷口附近。海底成矿热液蚀变作用使其ＳｉＯ２、ＦｅＯ、ＭｇＯ、ＣＯ２等化学成分发生变化。凝灰质千枚岩则是细火山灰在海吕中经缓慢的沉降后形成于远离火山口的火山斜坡上的火山－沉积变质岩。根据“０补丁”的成分可将补丁岩分为两种类型：绿泥石质     

A Miocene coarse volcaniclastic mass-flow deposit in the Shimane Peninsula,SW Japan: product of a deep submarine eruption?

 A subaqueous volcaniclastic mass-flow deposit in the Miocene Josoji Formation, Shimane Peninsula, is 15–16 m thick, and comprises mainly blocks and lapilli of rhyolite and andesite pumices and non- to poorly vesiculated rhyolite. It can be divided into four layers in ascending order. Layer 1 is an inversely to normally graded and poorly sorted lithic breccia 0.3–6 m thick. Layer 2 is an inversely to normally graded tuff breccia to lapilli tuff 6–11 m thick. This layer bifurcates laterally into minor depositional units individually composed of a massive, lithic-rich lower part and a diffusely stratified, pumice-rich upper part with inverse to normal grading of both lithic and pumice clasts. Layer 3 is 2.5–3 m thick, and consists of interbedded fines-depleted pumice-rich and pumice-poor layers a few centimeters thick. Layer 4 is a well-stratified and well-sorted coarse ash bed 1.5–2 m thick. The volcaniclastic deposit shows internal features of high-density turbidites and contains no evidence for emplacement at a high temperature. The mass-flow deposit is extremely coarse-grained, dominated by traction structures, and is interpreted as the product of a deep submarine, explosive eruption of vesicular magma or explosive collapse of lava. Received: 10 January 1996 / Accepted: 23 February 1996     

Episode 49 of the Pu'u 'O'o-Kupaianaha eruption of Kilauea volcano-breakdown of a steady-state eruptive era

The Pu'u 'O'o-Kupaianaha eruption (1983-present) is the longest lived rift eruption of either Kilauea or neighboring Mauna Loa in recorded history. The initial fissure opening in January 1983 was followed by three years of episodic fire fountaining at the Pu'u 'O'o vent on Kilauea's east rift zone 19km from the summit (episodes 4–47). These spectacular events gave way in July 1986 to five and a half years of nearcontinuous, low-level effusion from the Kupaianaha vent, 3km to the cast (episode 48). A 49th episode began in November 1991 with the opening of a new fissure between Pu'u 'O'o and Kupaianaha. this three week long outburst heralded an era of more erratic eruptive behavior characterized by the shut down of Kupaianaha in February 1992 and subsequent intermittent eruption from vents on the west flank of Pu'u 'O'o (episodes 50 and 51). The events occurring over this period are due to progressive shrinkage of the rift-zone reservoir beneath the eruption site, and had limited impact on eruption temperatures and lava composition.     

欧北-大湾地区火山岩储层成因机制的研究

从分布、成分组成、形成机制等几个方面探讨了辽河油田东部凹陷中段最主要的火山岩储层－－粗面岩的成因机制，并对其成为该区良好储层的原因进行了探讨，通过对比说明了另一类火山岩－－玄武岩不含油的原因，并建立了成因模式，最后得出结论：粗面岩呈喷发状态产出，由于其硅质含量高，流动性小，容易在构造高部位形成巨厚的火山岩锥或火山岩钏，从而造成其大部分在水上，结晶较好且储层物性极佳，同时因其裂缝发育，这些因素结合起来使其成为良好的会层。从供油方式来看，其成藏方式属于侧生式，而从生储盖组合方式来看，其属于自生、自储、自盖式成藏组合。同时给出了其成藏模式。