Similar V/Sc Systematics in MORB and Arc Basalts: Implications for the Oxygen Fugacities of their Mantle Source Regions

V/Sc systematics in peridotites, mid-ocean ridge basalts andarc basalts are investigated to constrain the variation of fO₂in the asthenospheric mantle. V/Sc ratios are used here to ‘seethrough’ those processes that can modify barometric fO₂determinations in mantle rocks and/or magmas: early fractionalcrystallization, degassing, crustal assimilation and mantlemetasomatism. Melting models are combined here with a literaturedatabase on peridotites, arc lavas and mid-ocean ridge basalts,along with new, more precise data on peridotites and selectedarc lavas. V/Sc ratios in primitive arc lavas from the Cascadesmagmatic arc are correlated with fluid-mobile elements (e.g.Ba and K), indicating that fluids may subtly influence fO₂ duringmelting. However, for the most part, the average V/Sc-inferredfO₂s of arc basalts, MORB and peridotites are remarkably similar(–1·25 to +0·5 log units from the FMQ buffer)and disagree with the observation that the barometric fO₂s ofarc lavas are several orders of magnitude higher. These observationssuggest that the upper part of the Earth's mantle may be stronglybuffered in terms of fO₂. The higher barometric fO₂s of arclavas and some arc-related xenoliths may be due respectivelyto magmatic differentiation processes and to exposure to large,time-integrated fluid fluxes incurred during the long-term stabilityof the lithospheric mantle. KEY WORDS: vanadium; scandium; oxygen fugacity; mantle; arcs     

“数字台湾”与中央山脉保育轴之划设、经营和管理

本研究系应用数字地球系统理论于中央山脉保育轴经营管理机制建置 ,并依 IUCN之保育区划设标准 ,作为未来研订中央山脉保育计划之分区准则与数字台湾系统建立之发展模式。数字台湾之观念乃源于数字地球突破传统信息空间、政策经营之多向度信息整合 ,同时考虑克服科技应用与时间效益以及决策兼蓄解决传统资源管理在空间地理与生态艺术上之综合性问题。     

PROBABLE MAXIMUM FLOOD FOR DAM SAFETY ASSESSMENT

ＰＲＯＢＡＢＬＥＭＡＸＩＭＵＭＦＬＯＯＤＦＯＲＤＡＭＳＡＦＥＴＹＡＳＳＥＳＳＭＥＮＴＣ．Ｆ．ＬＥＥ（Ｆｏｒｍｅｒｌｙ，ＭａｎａｇｅｒｏｆＧｅｏｔｅｃｈｎｉｃａｌａｎｄＨｙｄｒａｕｌｉｃＥｎｇｉｎｅｅｒｉｎｇＤｅｐａｒｔｍｅｎｔ；ＭａｎａｇｅｒｏｆＣｉ...     

DETERMINISTIC ESTIMATION OF A WAVELET USING IMPEDANCE TYPE TECHNIQUE*

A new deterministic technique for estimating a wavelet suggested by Loewenthal and Jakubowicz requires measurement of both pressure and vertical particle velocity. Through construction of the impedance function a deterministic estimation of the wavelet and the reflectivity can be obtained. This idea is tested for a one-dimensional model. The test is carried out by forming a synthetic seismogram of both pressure and particle velocity and checking the formulas for obtaining the estimated wavelet under noisy conditions.     

Surging of the southwestern part of the Laurentide Ice Sheet

The southwestern part of the Laurentidc Ice Sheet, in central North America, repeatedly surged during the last part of the Wisconsin Glaciation. Evidence includes the extreme lobation of the ice margin, the gentle slopes of lateral moraines and other marginal features, a radiocarbon chronology indicating extremely rapid marginal advance and retreat, and the abundance of supraglacial flow till. Rapid ice movement was caused by subglacial water and was probably limited to areas of slowly permeable substrate, which slowed the escape of the water.     

南海东北部海陆联测与海底地震仪探测

利用三分量海底地震仪、陆上便携式地震仪和海上气枪震源在南海东北部首次进行了海陆联合的深地震探测,测线呈北北西-南南东方向,垂直于区域构造走向,总长达500km,所获得的数据质量好,深部信息丰富,可分辨出Pg、Pn、PmP等地震相,为南海东北部深部地壳结构及油气盆地形成演化的研究提供了重要的基础数据。     

Metamorphic and Tectonic Evolution of the Hwacheon Granulite Complex, Central Korea: Composite P-T Path Resulting from Two Distinct Crustal-Thickening Events

The Hwacheon granulite complex (HGC), occupying the northeasternmargin of the Gyeonggi massif, consists mainly of garnetiferousleucocratic gneiss and leucogranite together with minor kyanite–garnetgneiss, aluminous gneiss, mafic granulite and garnet amphibolite.Mineral assemblages and reaction textures in various rock typesof the HGC document five distinct metamorphic stages: pre- (M₁)and peak (M₂) granulite-facies metamorphism; lower temperature,high (M₃) and low (M₄) pressure upper amphibolite-facies metamorphism;and local retrogression (M₅) producing andalusite-bearing assemblages.Each metamorphic stage can be integrated to give a compositeP–T path consisting of two distinct trajectories, characterizedby clockwise P–T loops at relatively high and low temperatures,respectively. The first P–T trajectory (M₁–M₃) correspondsto a Palaeoproterozoic tectonometamorphic event responsiblefor the formation of the granulite complex at     

Testing the case for a Middle Pleistocene Scandinavian glaciation in Eastern England: evidence for a Scottish ice source for tills within the Corton Formation of East Anglia, UK

The provenance of the Happisburgh Till and Corton Till of the Corton Formation is investigated using erratic clast lithologies and allochthonous palynomorphs to test whether the long held assumption that they were deposited by ice that originated in Scandinavia is valid. The results show a wide range of lithologies including Carboniferous Limestone and Coal Measures, and Permian Magnesian Limestone that are not found in Scandinavia, and an absence of distinctive Scandinavian material such as rhomb porphyry and larvikite. Lithologies found indicate deposition by an ice sheet which flowed southwards into north-east East Anglia from central and southern Scotland eroding and transporting materials derived from outcrops in these areas and from eastern England and the western margins of the southern North Sea Basin. It is concluded that the long held assumption that the Happisburgh Till and Corton Till of the Corton Formation were deposited by a Scandinavian ice sheet is erroneous and that they were instead deposited by Scottish ice.     

Conodonts from the Upper Cambrian Sesong and Hwajeol Formations in the Sabuk Area, South Korea

This paper presents a conodont biostratigraphic study on the Upper Cambrian Sesong and Hwajeol Formations in the Sabuk area, Korea. Two samples near the base of the Sesong Slate at the Pukil section contain lower Upper Cambrian conodonts, comprising Furnishina furnishi, F. kranzae, F. pernical, F. triangulate, Hertzina elongata, Laiwugnathus doidyxus?, Phakelodus elongatus, Muellerodus? obliquus, Westergaardodina matsushitai and W. moessebergensis. This is the first conodont record of the Upper Cambrian formations recovered yet in the northern limb of the Paekunsan syncline. The faunal assemblage is correctable with the lower Upper Cambrian W. matsushitai Zone of North China. Four local biozones are recognized in the Hwajeol Formation, i.e. the Proconodontus, Eoconodontus notchpeakensis, Cambrooistodus minutus and Cordylodus proavus Zones in ascending order. This zonal scheme is essentially equivalent to that of the southern limb of the Paekunsan syncline and they are correlatable with zones in other pa     

SEISMIC MONITORING OF A BRIDGE: ASSESSING DYNAMIC CHARACTERISTICS FROM BOTH WEAK AND STRONG GROUND EXCITATIONS

An array of 24 strong-motion accelerometers produced records for the New-Lian River Bridge, a five-span continuous bridge, during 25 February 1995 earthquake (weak motion) and 25 June 1995 earthquake (strong motion). This paper describes the application of linear discrete-time system identification methodology to the array of strong-motion measurements, in order to assess seismic response characteristics of the bridge. The structural system identification will concentrate not only on the global identification but also on the local structural system identification. Results of this application show that: (1) weak and strong ground excitation will induce significant differences on the dynamic response of the bridge; (2) linear models provide an excellent fit to the measured motions of the bridge from the records of these two seismic events; (3) the rigid-body rocking of the bridge pier during strong shaking is significant and cannot be ignored during identification; (4) the transverse motion at mid-span of the bridge is controlled by the quasi-static response from the boundary system and this phenomenon is quite significant during strong ground excitation. Also, systematic estimates of modal damping ratio and equivalent assessments of pier stiffness developed in the bridge during earthquake are discussed. © 1997 by John Wiley & Sons, Ltd.