原始地核:离子探针为西格陵兰和恩德比地(南极洲)太古宙地区大约4000Ma地壳物质提供的证据

对古老岩区的典型花岗片麻岩中提取单—锆石颗粒内一些直径为15μm的点,用离子探针测量了~(207)pb/~(206)pb的比值表明,这些地方保存一个~(207)pb/~(206)pb比值范围。在含有较高铀含量的锆石内一般可测得~(207)pb/~(206)pb的最低比值,计算的~(207)pb/~(206)pb年龄,一般与反映它们形成后各岩层经受的比较主要地质事件可以对比。似乎可能的是,在年轻事件期间,由于遭受锆石粒高铀区放射性的破坏,使这些地带的放射性铅损失了。在含     

西澳大利亚较老的前寒武纪地质年代学

在西澳大利亚,太古宙这个名词一般应用在早于2400Ma的岩层,这与最近由前寒武地层分会提出的2500Ma界线是有一定偏差的(James,《前寒武纪研究》,7,193—204页:1978)。无论应用那个标准,西澳大利亚地盾的二个最老部分—皮尔巴拉(Pilbara)和伊尔冈地块—在太古宙期间就已清楚确立。上述两个地块均以典型的绿岩—花岗岩类为主所组成,其中许多花岗岩类深成岩由含高比例火山岩同时形成的绿岩带所包     

RECENT RESULTS FORM EARTHBASED OBSERVATIONS OF MARS

Even in an age of increasing spacecraft exploration, telescopic observations of Mars continue to provide new data and new insights into the nature of the Martian surface, atmosphere, and climate. Three major technological advances in the last decade, combinde, have allowed telescopic observations to increase our knowledge of the planet: (1) Advances in infrared, near-infrared, and radio wavelength array detector and telescope technology, allowing high spatial and/ or high spectral resolution imaging in new and diagnostic wavelength regions; (2) The advent of routine space-based telescopic observations of Mars using the Hubble Space Telescope , providing the ability to study the planet at high spatial resolution over a much longer part of its orbit than from groundbased telescopes, and offsetting some of the inherent loss in resolution associated with the recent series of aphelic oppositions of the planet; and (3) The widespread use and availability of CCD cameras and powerful telescopes in the 10 - inch     

NEAR'S CLOSE FLYBY OF C-TYPE ASTEROID 253 MATHILDE

On June 27, 1997, the Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 1200km of the main belt asteroid 253 Mathilde. Previous observations of Mathilde had revealed it to be a C-type asteroid with an astonishingly-long rotation period of 17.4 days, an albedo of 3.8%, and a mean diameter of 60 km. Observations by NEAR reveal that Mathilde has a roughly triaxial shape of 66 × 48 × 46 km diameter and a mass of 1. 02 × 10 g, implying a mean density of only 1. 3g/cm3 . The surface of Mathilde was observed to be saturated with large impact craters, showing a range of visible topography in excess of 5 km. Multispectral observations did not reveal any substantial color differences across the surface, and coverage at multiple phase angles was used to derive a preliminary albedo of 3. 5 % to 5% .The low observed density, lack of color variations, and low albedo all suggest that Mathilde may be a primitive, carbon - rich object with an interior that contains substantial pore space.     

地貌对生态系统模式和作用的影响

地球表面的地貌特征能调节有机体的分布和活动过程只了解景观类型、变化过程、与历史的关系作为推测几个时期和地区生态系统的规模是困难的。地貌,像泛滥平原和扇形冲积地;造貌运动,像河流的侵蚀和堆积,都对该地生态系统的发展以及物质和能量流动有着重要作用。在较长时间中,造貌运动形成了地貌;而在较短时间中,地貌可作为调节造貌运动范围和速度的因子。生态系统与地貌、造貌运动密切相关。造貌运动的历史可直接从植被的组成和结构中反映出来,因为这些地方是造貌运动与植被共同作用的结果。在植被建成以前就开始了造貌运运,或是与植被同时巧妙的作用。造貌运动能通过调节一个景观(或一个地形系列)中的土壤特征而对植被分布产生很大影响。     

A hybrid artificial neural network-numerical model for ground water problems

Numerical models constitute the most advanced physical-based methods for modeling complex ground water systems. Spatial and/or temporal variability of aquifer parameters, boundary conditions, and initial conditions (for transient simulations) can be assigned across the numerical model domain. While this constitutes a powerful modeling advantage, it also presents the formidable challenge of overcoming parameter uncertainty, which, to date, has not been satisfactorily resolved, inevitably producing model prediction errors. In previous research, artificial neural networks (ANNs), developed with more accessible field data, have achieved excellent predictive accuracy over discrete stress periods at site-specific field locations in complex ground water systems. In an effort to combine the relative advantages of numerical models and ANNs, a new modeling paradigm is presented. The ANN models generate accurate predictions for a limited number of field locations. Appending them to a numerical model produces an overdetermined system of equations, which can be solved using a variety of mathematical techniques, potentially yielding more accurate numerical predictions. Mathematical theory and a simple two-dimensional example are presented to overview relevant mathematical and modeling issues. Two of the three methods for solving the overdetermined system achieved an overall improvement in numerical model accuracy for various levels of synthetic ANN errors using relatively few constrained head values (i.e., cells), which, while demonstrating promise, requires further research. This hybrid approach is not limited to ANN technology; it can be used with other approaches for improving numerical model predictions, such as regression or support vector machines (SVMs).     

Mineralogical and Petrological Characteristics of the Neoproterozoic Orthoamphibolite and Orthogneisses in the Mutki Area, the Bitlis Massif, Southeast Turkey

<正>The rocks form as amphibolite±garnet±epidote and orthogneisses in the Pan-African basement of the Bitlis Massif.The petrochemical data of the studied metamorphic rocks suggest different igneous protoliths ranging from calcalkaline basalt to andesite in composition. Petrochemically,the rocks can be classified as group 1(low Zr and La) and group 2(high Zr and La), all showing various enrichments in large ion lithophiles and light rare earth elements,and a depletion in high-field strength elements,suggestive of a destructive plate margin setting.The protoliths of the all samples might have formed mostly by the partial melting of an enriched source,possibly coupled with the fractional crystallization of plagioclase,apatite,and titaniferous magnetite±olivine±clinopyroxene±amphibole in relation with subduction-related magmatism neighboring the Andeantype active margins of Gondwana.The group 2 samples could,however,be generated by a relatively lower degree of the partial melting of an inhomogeneous source with a preponderance of a high-level, fractional crystallization process in comparison to group 1.The protoliths of the samples were metamorphosed up to amphibolite facies conditions,which destroys original igneous texture and mineral assemblages.Geothermobarometric calculations show that the metamorphic rocks are finally equilibrated between 540 and 610℃and～5 kbars,following a clockwise P-T-t path.     

钻孔应变仪的固体潮标定——消除小尺度不均匀性的影响

通过对Pion Flat观测点的Gladwin钻孔张量应变仪(BTSM)进行固体潮标定得到的应变数据,我们对地应变进行了估算并分析。小尺度地质上的不均匀性是通过远场面应变/剪应变的交互耦合方法考察面应变/剪应变时所要考虑的因素之一。一种将交互耦合引入应变仪标定的方法由此而生。以同一位置激光应变仪(LSM)观测的固体潮应变为参考,我们发现用交互耦合方法对BTSM标定消除了钻孔固体潮观测值应变中近30%的系统误差。这种标定将钻孔应变和激光应变的测量精度(大约1km)准确地联系在一起了。这种标定技术为短基线应变测量中面临的主要问题(构造应变不能表征小尺度的非均匀性)提供了解决方法。这种方法在断层滑移的残余应变测量中可能减少50%甚至更高的误差,并允许增加滑移机制的约束条件。我们发现就目前仪器而得出的固体潮应变的理论估计值来进行交互耦合标定还不够精确。将理论固体潮与激光应变仪(LSM)观测的固体潮进行比照发现,至少有一半的误差产生于对海洋负荷潮的估计。