鞍山东山风景区3．8—2．5Ga古老岩带的同位素地质年代学和地球化学

鞍山东山风景区古老岩带呈巨型包体存在于立山奥长花岗岩（3．1Ga）中，其主体为条带状片麻岩（3．8Ga）。此外还有金云母透闪石岩、（含）黑云斜长角闪岩、闪长质片麻岩、变石英闪长质岩石、细粒奥长花岗岩、二长花岗岩、伟晶岩脉等。测定了部分岩石的锆石年龄，其中变石英闪长质岩石（A9604）为3．65Ga（Wan et al.,1999），闪长质片麻岩（A9317）为3．5Ga、二长花岗岩（类型I，A9605）为3．1Ga，黑云斜长角闪岩（A0019）为3．3Ga、细粒奥长花岗岩（A0017）为3．2Ga、二长花岗岩（类型Ⅱ，A0020），为2．6Ga，有关岩石的地球化学组成特征在文中地进行了简要介绍，在此基础上，提出了该古老岩带的地质同位素年代演化序列，认为鞍山地区不同时代、不同成因地质体空间上共存是该芡长期地质演化的结果，而不是后期构造作用把它们拼合到一起的，鞍山地区很可能存在＞3．8Ga的古老地壳岩石。     

Ice Sheet And Satellite Altimetry

Since 1991, the altimeters of the ERS European Satellites allow the observation of 80% of the Antarctica ice sheet and the whole Greenland ice sheet: They thus offer for the first time a unique vision of polar ice caps. Indeed, surface topography is an essential data thanks to its capacity to highlight the physical processes which control the surface shape, or to test models. Moreover, the altimeter is also a radar which makes it possible to estimate the snow surface or subsurface characteristics, such as surface roughness induced by the strong katabatic wind or ice grain size. The polar ice caps may not be in a stationary state, they continue to respond to the climatic warming of the beginning of the Holocene, that is 18000 years ago, and possibly start to react to present climatic warming: the altimeter offers the unique means of estimating the variations of volume and thus the contribution of polar ice caps to present sea level change.     

La rétromorphose du talc dans les dolomies métallifères de Boukdema (Algérie); discussion du rôle des fluides

Résumé Les échantillons étudiés proviennent du gîte stratiforme de Boukdema (Algérie), où l'on observe notamment l'association dolomite-quartz-talcsphalérite. L'étude des inclusions fluides primaires des quartz contemporains, selon toute vraisemblance, de la dissolution partielle du talc, montre que ceux-ci se sont développés dans des solutions de salinités très variables (entre 4 et 28% en équivalent pondéral NaCl). L'hypothèse d'une ébullition des solutions (par suite d'une chute brutale de pression) rend compte de ce fait inhabituel. Dans le cadre d'un tel modèle, les corrections dues à la pression sont nulles et l'on peut en déduire à partir des mesures de températures d'homogénéïsation que la croissance du quartz s'est amorcée vers 250 °C. Compte tenu de cette indication thermométrique, on discute enfin du rôle relatif des facteurs physiques et chimiques (T, f_{CO 2}, a_Mg/a_Ca) sur la stabilité du talc dans le contexte minéralogique du gîte de Boukdema.

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The samples studied were collected in the Boukdema stratabound deposit (Algeria), where the association dolomite-quartz-talc-sphalerite occurs. Cryoscopic investigations of fluid inclusions in quartz indicate a wide salinity range in mineral forming fluids (4 to 28 weight % NaCl eq). Boiling of hydrothermal fluids possibly explains this unusual characteristic. In this hypothesis thermometric data need no pressure corrections and one may conclude that quartz growth (and simultaneously talc dissolution) occurred in the 250°–200 °C range. On the basis of this last indication, the relative role of T, f_{CO 2}, a_Mg/a_Ca, on talc stability is discussed in the mineralogical environment of Boukdema.

     

Geothermal effects in the formation of electrically conducting zones and temperature distribution in the earth

Pollack and Chapman have shown that the surface heat flow in continental regions is dependent not only on the earth's crust below the observation site, but also on the upper mantle there. Therefore heat flow can be used to investigate the role of the thermal conditions in the creation of the electrically conductive zones in both the crust and mantle.Empirical exponential formulas describe the depth to the conductivity increase in the crust corresponding to granitization, the depth to the conductive zone at the top of the asthenosphere (SLVZ), as a function of heat flow. Comparing the latter with temperature estimations in the asthenosphere it is concluded that partial melting of the upper mantle occurs only where $\text{q ? 42}\text{m W m}{}^{\mathrm{?2}}\text{? 1}\text{HFU}$.The depth to the conductivity increase corresponding to the mineralogic phase transition in the upper mantle is increased with high temperatures. Such a conductive zone shows that the maximum temperature difference between stable platform areas and active zones is about 1000°C.     

Long-range Earthquake Forecasting with Every Earthquake a Precursor According to Scale

Scaling relations previously derived from examples of the precursory scale increase before major earthquakes show that the precursor is a long-term predictor of the time, magnitude, and location of the major earthquake. These relations are here taken as the basis of a stochastic forecasting model in which every earthquake is regarded as a precursor. The problem of identifying those earthquakes that are actually precursory is thus set aside, at the cost of limiting the strength of the resulting forecast. The contribution of an individual earthquake to the future distribution of hazard in time, magnitude and location is on a scale determined, through the scaling relations, by its magnitude. Provision is made for a contribution to be affected by other earthquakes close in time and location, e.g., an aftershock may be given low weight. Using the New Zealand catalogue, the model has been fitted to the forecasting of shallow earthquakes exceeding magnitude 5.75 over the period 1965–2000. It fits the data much better than a baseline Poisson model with a location distribution based on proximity to the epicenters of past earthquakes. Further, the model has been applied, with unchanged parameters, to the California region over the period 1975–2001. There also, it performs much better than the baseline model fitted to the same region over the period 1951–1974; the likelihood ratio is 10¹⁵ in favor of the present model. These results lend credence to the precursory scale increase phenomenon, and show that the scaling relations are pervasive in earthquake catalogues. The forecasting model provides a new baseline model against which future refinements, and other proposed models, can be tested. It may also prove to be useful in practice. Its applicability to other regions has still to be established.     

Establishment and data processing of high-precision city subsidence monitoring network by GPS surveying instead of leveling

The feasibility of monitoring the change of city settlement using GPS surveying instead of leveling is studied. A fiducial network and a monitoring network are established in Ningbo city. Two periods of GPS observation are completed. Some measures are taken during the observation in order to ensure to obtain the high-precise height component. The Saastamoinen model is adopted in the data processing of the dry component part of the tropospheric delay. The wet component change of the tropospheric delay is estimated by stochastic processes model. When Bernese software is used to process the data, the millimeter level precision of height measuring is achieved.     

Rapid texture mapping from image sequences for building geometry model

An effective approach,mapping the texture for building model based on the digital photogrammetric theory, is proposed. The easily-ac-quired image sequences from digital video camera on helicopter are used as texture resource, and the correspon-dence between the space edge in build-ing geometry model and its line feature in image sequences is determined semi-automatically. The experimental re-sults in production of three-dimension-al data for car navigation show us an attractive future both in efficiency and effect.     

Rift zone reorganization through flank instability in ocean island volcanoes: an example from Tenerife, Canary Islands

The relationship between rift zones and flank instability in ocean island volcanoes is often inferred but rarely documented. Our field data, aerial image analysis, and ⁴⁰Ar/³⁹Ar chronology from Anaga basaltic shield volcano on Tenerife, Canary Islands, support a rift zone—flank instability relationship. A single rift zone dominated the early stage of the Anaga edifice (~6–4.5 Ma). Destabilization of the northern sector led to partial seaward collapse at about ~4.5 Ma, resulting in a giant landslide. The remnant highly fractured northern flank is part of the destabilized sector. A curved rift zone developed within and around this unstable sector between 4.5 and 3.5 Ma. Induced by the dilatation of the curved rift, a further rift-arm developed to the south, generating a three-armed rift system. This evolutionary sequence is supported by elastic dislocation models that illustrate how a curved rift zone accelerates flank instability on one side of a rift, and facilitates dike intrusions on the opposite side. Our study demonstrates a feedback relationship between flank instability and intrusive development, a scenario probably common in ocean island volcanoes. We therefore propose that ocean island rift zones represent geologically unsteady structures that migrate and reorganize in response to volcano flank instability.Editorial responsibility: T. DruittThis revised version was published online in February 2005 with typographical corrections and a changed wording.     

西部地震资料主要处理技术研究

西部地区地表情况多样,资料品质较差,多属低信噪比资料。这对类资料,静校正叠前去噪及速度分析等技术是非常重要的基础工作。针对西部地区不同的资料采用相应的静校正方式,在叠前去噪方面,就FK域倾角滤波方法的应用上进行了改进,克服了该方法一些“蚯蚓化”、“假构造”等弊端,总结出一套切实可行的尤其是用于西部资料的去噪方法。并针对多次波的特点,采用时间域,频率域及τp域等多种方式进行多次压制,在西部资料的处理中取得了较好的效果。