黄土地层中奇异微颗粒的发现与初步研究

通过蓝田段家坡黄土和红粘土剖面与第四纪3次巨大撞击事件年代相应的地层内奇异微颗粒的研究,将其划分为5种不同的形态类型,并主要据化学成分,将5类奇异微颗粒归纳为撞击、火山和生物等3种成因类型。文中还提出综合成因模式来解释不同奇异微颗粒赋存于同一撞击事件时段的地层及它们所显示的因果联系。     

Comparison of volcanic rifts on La Palma and El Hierro, Canary Islands and the Island of Hawaii

The meso-scale (km) morphology of the well-studied volcanic rift zones on the Island of Hawaii is compared to the morphology of the lesser known rift zones of La Palma and El Hierro, Canary Islands. We find that there are both differences and similarities in their morphologic characteristics. In general, the rift zones on La Palma and El Hierro are shorter (a few tens of km in length) than those on Hawaii (ranging up to >100 km in length), perhaps reflecting both magma supply and composition. Many of the rift zones on Hawaii have well defined axial zones, both on-and offshore. In contrast, the rift zones on La Palma and El Hierro display various geometries ranging from linear ridges having smooth to irregular crests to structures with a broad fan-like morphology in plan view. The pronounced fanning may be a reflection of: 1) the stress field within the rift being insufficient to trap dikes within a narrow region, 2) dike injection and volcanism shifting laterally through time, 3) volcanoes building nearly one atop of another in the Canary Islands, superimposing the stress field of one structure on the other and thus yielding a more complex distribution of gravitational stresses, and 4) low rate of magma supply producing low magma pressures and thus randomly oriented dike injections. Irregularities and curvature along the axes of the rifts on La Palma and El Hierro may be a reflection of differences in the rate of magma production. Unlike the volcanoes on the Island of Hawaii there may be insufficient volumes of lavas erupted on La Palma and El Hierro to smooth out irregularities. The superposition of rifts from different volcanoes may also add to topographic irregularities in the Canary Islands, especially if eruption rates are low.     

The ocean/continent transition along a profile through the Lofoten basin,Northern Norway

The Cenozoic margins of the Norwegian-Greenland Sea offer ideal conditions for passive margin studies. A series of structural elements, first observed on these margins, led to the concept of volcanic passive margins. Questions still remain about the development of such features and the location of the boundary between oceanic and continental crust. Despite the thin sediment cover of the margins, seismic reflection data are not able to image the deeper structures due to the occurrence of igneous rocks at shallow depth.This paper presents a 320-km long profile perpendicular to the strike of the main structural units of the Lofoten Margin in Northern Norway. A geological model is proposed, based on observations made with ocean bottom seismographs, which recorded seismic refraction data and wide angle reflections, along with a seismic reflection profile covering the same area. Ray-tracing was used to calculate a geophysical model from the shelf area into the Lofoten basin. The structures typical of a volcanic passive margin were found, showing that the Lofoten Margin was influenced by increased volcanic activity during its evolution. The ocean/continent transition is located in a 30-km wide zone landwards of the Vøring Plateau escarpment.The whole margin is underlain by a possibly underplated, high velocity layer. Evidence for a pre-rift sediment basin landwards of the escarpment, overlain by basalt flows, was seen. These structural features, related to extensive volcanism on the Lofoten Margin, are not as distinct as further south along the Norwegian Margin. Viewed in the light of the hot-spot theory of White and McKenzie (1989) the Lofoten Margin can be interpreted as a transitional type between volcanic and non-volcanic passive margin.     

一门新兴的边缘科学——火山岩储层地质学

石油工业持续稳定的发展要求不断有效地寻找勘探新领域、新地区和新类型。随着国内外火山岩油气藏的发现，火山岩储层作为一种特殊的油气储层类型越来越受人们的重视。20世纪90年代末期，石油地质学中出现了一门生命力很强的边缘学科——火山岩储层地质学，其任务是深入研究火山岩油气储层的宏观展布、内部结构、储层参数分布、孔隙结构等特征以及在火山岩油气田开发过程中储层参数的动态变化特征，为油气田勘探和开发服务。其研究内容包括储层地质特征、储层物理性质及储层非均质性、储层孔隙类型与空隙结构、孔隙演化模式及其控制因素、储层地质模型、储层敏感性、储层预测与储层综合评价7个方面。     

MINERALOGY OF COASTAL DEPOSITS OF NORTH-WESTERN SEA OF JAPAN

Distribution of heavy, light and clay minerals in Late Pleistocene—Holocene deposits from different coastal environments (beaches, lagoons, dunes, relict lakes, ria bays and inlets, open inlets) was analysed. It was established that mineralogical composition of coastal deposits was a result of provenance and its hypergenous changes, transformation of material within transit zone, and accumulative conditions of inshore zone. Contents of stable minerals increase in deposits of the inlets confined to mouths of the small streams and in horizons of the sections, formed during regressive phases. Unstable minerals amount is higher in deposits of inlets, confined to mouths of the large river. The clay mineral fraction of shelf sediments consists mostly of illite. Authigenous pyrites dominate in deposits of ria bays, lagoons and relict lakes, formed during transgressive phases. Volcanic glass, found in deposits, is product of Holocene eruptions of Baegdusan (Baitushen) Volcano.     

Silica‐rich layering at Blanche Point,South Australia

The chemistry and mineralogy of much of the Late Eocene Blanche Point Formation of South Australia show that biogenic and volcanogenic products were the only significant contributor to the sedimentary record. Intermittent volcanic activity followed by dissolution of the resultant silicic ash and small scale migration of silicon with reprecipitation as the oxide, provides the simplest and most likely explanation for the repetitive nature of the silicification. Seemingly, this was controlled by local silica concentrations which in turn were apparently controlled by the biota. Changes in circulation patterns and/or water depth may have initiated the environmental variations recorded in the formation.     

Evolution of the Cañadas edifice and its implications for the origin of the Cañadas Caldera (Tenerife, Canary Islands)

The volcano-stratigraphic and geochronologic data presented in this work show that the Tenerife central zone has been occupied during the last 3 Ma by shield or central composite volcanoes which reached more than 3000 m in height. The last volcanic system, the presently active Teide-Pico Viejo Complex began to form approximately 150 ka ago. The first Cañadas Edifice (CE) volcanic activity took place between about 3.5 Ma and 2.7 Ma. The CE-I is formed mainly by basalts, trachybasalts and trachytes. The remains of this phase outcrop in the Cañadas Wall (CW) sectors of La Angostura (3.5–3.0 Ma and 3.0–2.7 Ma), Boca de Tauce (3.0 Ma), and in the bottom of some external radial ravines (3.5 Ma). The position of its main emission center was located in the central part of the CC. The volcano could have reached 3000 m in height. This edifice underwent a partial destruction by failure and flank collapse, forming debris-avalanches during the 2.6–2.3 Ma period. The debris-avalanche deposits can be seen in the most distal zones in the N flank of the CE-I (Tigaiga Breccia). A new volcanic phase, whose deposits overlie the remains of CE-I and the former debris-avalanche deposits, constituted a new volcanic edifice, the CE-II. The dyke directions analysis and the morphological reconstruction suggest that the CE-II center was situated somewhat westward of the CE-I, reaching some 3200 m in height. The CE-II formations are well exposed on the CW, especially at the El Cedro (2.3–2.00 Ma) sector. They are also frequent in the S flank of the edifice (2.25–1.89 Ma) in Tejina (2.5–1.87 Ma) as well as in the Tigaiga massif to the N (2.23 Ma). During the last periods of activity of CE-II, important explosive eruptions took place forming ignimbrites, pyroclastic flows, and fall deposits of trachytic composition. Their ages vary between 1.5 and 1.6 Ma (Adeje ignimbrites, to the W). In the CW, the Upper Ucanca phonolitic Unit (1.4 Ma) could be the last main episode of the CE-II. Afterwards, the Cañadas III phase began. It is well represented in the CW sectors of Tigaiga (1.1 Ma–0.27 Ma), Las Pilas (1.03 Ma–0.78 Ma), Diego Hernández (0.54 Ma–0.17 Ma) and Guajara (1.1 Ma–0.7 Ma). The materials of this edifice are also found in the SE flank. These materials are trachybasaltic lava-flows and abundant phonolitic lava and pyroclastic flows (0.6 Ma–0.5 Ma) associated with abundant plinian falls. The CE-III was essentially built between 0.9 and 0.2 Ma, a period when the volcanic activity was also intense in the ‘Dorsal Edifice' situated in the easterly wing of Tenerife. The so called ‘valleys' of La Orotava and Güimar, transversals to the ridge axis, also formed during this period. In the central part of Tenerife, the CE-III completed its evolution with an explosive deposit resting on the top of the CE, for which ages from 0.173 to 0.13 Ma have been obtained. The CC age must be younger due to the fact that the present caldera scarp cuts these deposits. On the controversial origin of the CC (central vertical collapse vs. repeated flank failure and lateral collapse of mature volcanic edifices), the data discussed in this paper favor the second hypothesis. Clearly several debris-avalanche type events exist in the history of the volcano but most of the deposits are now under the sea. The caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent Teide-Pico Viejo volcanoes.     

火山学述评

火山学研究有了长足的进步。本文总结近些年全球火山学研究各个方面的成果,包括对火山基本概念的新的认识、火山机构、火山的各种分类、火山岩石学和地球化学、火山岩相学、评估火山爆发大小的火山爆发指数、岩石和地球化学分类、各种常量和微量元素区分图、活火山分布与板块构造理论的关系、活火山给人类带来的灾害与利益和活火山的监测、曾经的火山活动与生物毁灭、单成因火山研究等。火山—构造是未来火山学研究的一个方向,通过火山与构造关系的研究以揭示火山的分布和地球的演化。火山喷出的岩浆是其通过地下以岩墙或管道形式为通道运移到地表的结果。中朝边境上的长白山的位置是个特例,应当值得深入的研究。中国分布有许多新生代火山,它们是否为单成因火山、这些火山在成分上是否有演化规律、它们的分布与大地构造的关系等都有待深入和系统的研究。     

Carbonate tufas as archives of climate and sedimentary dynamic in volcanic settings,examples from Gran Canaria (Spain)

Three Holocene tufas from Gran Canaria volcanic island were studied with the aim of deciphering their sedimentary evolution through space and time. Las Temisas tufa (south-eastern arid part of the island) is dominantly composed of oncoids, intraclasts, phytoclasts, coated stems, minor thin stromatolites, and a high amount of siliciclastics. It was deposited in a fluvial system with variable flow velocities and palustrine conditions areas, which alternated with high energy events. Azuaje tufa (northern humid part of the island) is composed of coated stems, stromatolites, oncoids and phytoclasts, with relatively low amounts of siliciclastics, suggesting slow-flowing and palustrine conditions and a relatively low incidence of (high energy) floodings. Los Berrazales tufa (north-west of Gran Ganaria, the most humid one), is mainly composed of coated stems and crystalline crusts, formed in a laminar flow regime. Dominant clastic sedimentation in Las Temisas and high calcite growth rates in Los Berrazales led to a poor development of stromatolites in comparison with Azuaje. Las Temisas and Azuaje deposits have similar upward evolution with decreasing trend in siliciclastics and increasing trend in carbonates. However, Las Temisas has higher siliciclastic and lower phytoclastic contents suggesting a less vegetated area and more arid climate than in the other deposits. Additionally, tufas record local events common in volcanic terrains. Azuaje presents three units bounded by erosive discontinuities, which reveal significant erosion by enhanced runoff that could be caused by loss of vegetation due to wildfires related to volcanic eruptions at headwaters. Las Temisas record a possible interruption in sedimentation represented by aligned boulders due to rockfalls from the hillsides. These deposits formed from waters with similar chemistry providing to the carbonates their similar signals in δ¹³C–δ¹⁸O stable isotopes and ⁸⁷Sr/⁸⁶Sr ratios like that of the volcanic rocks. This work shows how, in volcanic areas, tufas are unique archives of the climate, vegetation and volcanic-related processes, because all imprint the sedimentary regime of tufa deposition.