Mineralogic and Oxygen Isotopic Studies of Open System Magmatie Processes in the South Kawishiwi Intrusion, Spruce Road Area, Duluth Complex, Minnesota     

LEE  INSUNG; RIPLEY  EDWARD M. 《Journal of Petrology》1996,37(6):1437-1461

The South Kawishiwi intrusion, located along the western marginof the Duluth Complex, Minnesota, is one of several compositeintrusions that are found in the Complex. The Duluth Complexis the principal exposed plutonic portion of the 1.1 Ga MidcontineniRift system. In the Spruce Road area the South Kawishiwi intrusionis divided into seven distinct units that are part of the broaderSouth Kawishiwi Troctolite Series defined by Severson (Tech.Rep. NRRI/TR-91/13a, Natural Resources Research Institute, Universityof Minnesota, Duluth, 1994). Units may be characterized as follows:Unit I—basal accumulation of heterogeneous gabbro, troctolite,and norite; Unit II—norite with abundant inverted pigeonite;Unit III—troctolite and olivine gabbro with local oxide-richlayers; Unit IV—mlatroctolite, troctolite, olivine gabbro;Unit VI—increased plagioclase abundance in troctolitesand leucocratic troctolites; Unit VI—strongly alteredtroctolite; Unit VII—similar to Unit V, troctolite andleucocratic troctolite. Country rocks in the Spruce Road areaare granodiorite to quartz monzonite of the Archean Giants RangeBatholith. Sutfide mineralization, consisting of 1–5 vol.% of disseminated pyrrhotitt, cubanite, chalcopyrite and pentlandite,occurs in Units I, II, III, and VI. Oxygen isotopic analysesindicate that Unit II has experienced extensive crustal contamination.¹⁸O values of Unit II range from 6.9 to 7.1% and are ¹⁸O enrichedcompared with values of 5.1–6.8% found in other units.Silica contamination is indicated based not only on ¹⁸O values,but also by the predominance of orthopyroxene in the unit. Possiblehigh-¹⁸O contaminant rocks include the Giants Range Batholithand pelitic rocks of the Lower Proterozoic Virginia Formationor Biwabik Iron Formation. Mass balance computations suggestthat units in the Spruce Road area may be related through varyingdegrees of fractionation of a high-Al, olivine tholeiite magma.Modeling of trace element concentrations and variations in mineralchemistry suggest that discontinuities within the major unitsdeveloped by in situ boundary-layer equilibrium crystallizationof solidification zones 20–50 m in thickness, followedby recharge of fresh magma. Upward enrichment of incompatibleelements, olivine Fa content, and plagioclase Ab content maybe effectively explained by this process. ¹⁸O values of uncontaminatedrock types are strongly correlative with modal mineralogy, andcan also be modeled by boundary-layer fractionation, A parentalmagma ¹⁸ O value of 6.3% is calculated for Unit VII based onolivine and plagioclase values, and is similar to that of severalother large, layered mafic intrusives. KEY WORDS: Duluth Complex; South Kawishiwi Intrusion; high-Al olivine tholeiite; open system crystallization; oxygen isotopes ^* Present address: Korea Basic Science Center, Isotope Research Group, Yeocun Dong 224–1, Yusung Ku, Yusung P.O. Box 41, Taejean 305–333, Korea  相似文献   

ESTIMATION OF SOIL EROSION IN A RESERVOIR WATERSHED USING ^137CS FALLOUT RADIONUCLIDE     

Y. J. CHIU A. M. BORGHUIS H. Y. LEE K. T. CHANG J. H. CHAO 《国际泥沙研究》2007,22(4):304-317

Sedimentation from soil erosion is a critical reservoir watershed management issue. Due to the difficulty of field investigations, empirical formulas are commonly used to estimate the soil erosion rate. However, these estimations are often far from accurate. An effective alternative to estimating soil erosion is to analyze the spatial variation of 137Cs inventory in the soil. 137Cs can be adsorbed by the soil and is widely assumed to change its distribution only when disturbed by rainfall and human activities. Thus, 137Cs distributed in soils can be a useful environmental tracer to estimate soil erosion. In this study, the net soil loss estimate is 108,346 t/yr and the gross erosion and net erosion rates are 10.1 and 9 t/ha yr respectively. The sediment delivery ratio is therefore estimated to be 0.9 based on the two erosion rates. Because of the steep hillsides in the watershed, only 10% of the sediment yield stayed in the deposition sites and 90% was transported to the river as the sediment output. Soil erosion estimates from spatial variations of the 137Cs activity in the Baishi river watershed showed satisfactory accuracy when compared to sediment yield data. Using soil 137Cs concentrations is therefore a feasible method for estimating soil loss or deposition in Taiwan. Data sampling, analysis and result of this approach are given in this paper.  相似文献   

OCEAN BOTTOM SEISMOMETER AND ONSHOREOFFSHORE SEISMIC EXPERIMENT IN NORTHEASTERN SOUTH CHINA SEA   总被引：7，自引：0，他引：7  

QIU Xuelin~ 《大地构造与成矿学(英文版)》2004,28(1):28-35

Three-component Ocean Bottom Seismometers, portable land stations and marine air gun seismic sources were used to carry out an onshore-offshore deep seismic profile in northeastern South China Sea. This profile, orientated in NNW-SSE, was as long as 500 km and perpendicular to the strike of regional tectonics. The offshore data were processed in Taiwan Ocean University using a number of available software and the onshore data were analyzed in South China Sea Institute of Oceanology by new-written programs and public software. Preliminary results show that the seismic data are in good quality and contain rich information of deep structure. Seismic phases, e.g. Pg, PmP and Pn, are identified in the offset range 5～220 km, which will provide an important dataset for the deep crustal structure and oil-gas basin evolution studies of this region.  相似文献   

Feldspar albitization in Cretaceous non-marine mudrocks, Gyeongsang Basin, Korea   总被引：1，自引：0，他引：1  

JAE IL LEE  & YONG IL LEE 《Sedimentology》1998,45(4):745-754

Plagioclases and K-feldspars in the sandstones and mudrocks of the Cretaceous non-marine Gyeongsang Basin, Korea, were partially to completely albitized. The preservation of fresh plagioclase grains in early micrite-cemented sandstones suggests the diagenetic origin of albite. Albitization textures in mudrocks were examined using backscattered electron images. In contrast to completely albitized plagioclase grains in sandstones, those in mudrocks are mostly partially albitized. It suggests that mudrocks can be more useful for a provenance study than sandstones by preserving detrital minerals better. K-feldspar is unaltered to partially albitized in both sandstones and mudrocks. In mudrocks albitization starts preferentially along microfractures, cleavages and grain margins. Albitization along grain margins seems to be a characteristic feature in mudrocks where development of microfractures in silt-sized feldspar grains by physical compaction is limited by clayey matrix as well as by overpressure. The extent of albitization in mudrocks is mainly controlled by composition of the detrital plagioclase. Mudrocks containing calcic plagioclase grains tend to be more extensively albitized than those containing sodic varieties.  相似文献   

LANDSLIDE POTENTIALITY OF THE TSENGWEN RESERVOIR WATERSHED,TAIWAN,CHINA     

Chin-yu LEE 《国际泥沙研究》2004,19(2)

To recognize the geographical characteristics of the landslide areas will be helpful for the watershed management in the reservoir watershed.According to the quantitative analysis,we'll take different scores and weighting for the potential parameters of the landslide areas in the Tsengwen reservoir watershed,and in the meanwhile,we'll extract the different factors,including the slope,aspect,altitude,soil and geological textures etc.,and the results shown as maximum one-day rainfall,ratio of forests and average relief is the most affecting parameters on the potential risk map of landslide areas.  相似文献   

滇西新生代超钾质煌斑岩的元素和Sr-Nd同位素特征及其对岩石圈地幔组成的制约   总被引：34，自引：2，他引：34  

李献华  周汉文  韦刚健  刘颖  钟孙霖  罗清华  李寄嵎 《地球化学》2002,31(1):26-34

系统分析了滇西早第三纪晚期煌斑岩的主元素、微量元素和Sr-Nd同位素组成。绝大多数煌斑岩属超钾质系列岩石（K2O/Na2O=2.1-5.2)，少数为钾玄质系列（K2O/Na2O=1.6-1.7)。这些超钾质煌斑岩富集大离子亲石元素、轻稀土元素和Pb，亏损高场强元素，具有高的初始^87Sr/^86Sr比值（O.70624-0.70924)和负的εNd(t)值（-1.7～-4.6），类似于与俯冲环境有关的高K/Ti-低Ti钾质系列岩石。这些超钾质煌斑岩母岩浆来源于含金云母的交代地幔，经历了不同程度的结晶分异和地壳物质的同化混染。与藏北钾玄质系列岩石相比，滇西超钾质煌斑岩的Th/U比较低、Rb/Sr比较高，而且Nd模式年龄系统偏低0.1-0.4Ga，表明青藏高原北部和东南部岩石圈地幔组成存在区域性的差异。  相似文献   

Geochemistry of peridotite xenoliths in alkali basalts from Jeju Island, Korea   总被引：1，自引：0，他引：1  

SEONG HEE  CHOI  JONG IK  LEE  CHUNG-HWA  PARK  JACQUES  MOUTTE 《Island Arc》2002,11(4):221-235

Abstract   Ultramafic xenoliths in alkali basalts from Jeju Island, Korea, are mostly spinel lherzolites with subordinate amounts of spinel harzburgites and pyroxenites. The compositions of major oxides and compatible to moderately incompatible elements of the Jeju peridotite xenoliths suggest that they are residues after various extents of melting. The estimated degrees of partial melting from compositionally homogeneous and unfractionated mantle to form the residual xenoliths reach 30%. However, their complex patterns of chondrite-normalized rare earth element, from light rare earth element (LREE)-depleted through spoon-shaped to LREE-enriched, reflect an additional process. Metasomatism by a small amount of melt/fluid enriched in LREE followed the former melt removal, which resulted in the enrichment of the incompatible trace elements. Sr and Nd isotopic ratios of the Jeju xenoliths display a wide scatter from depleted mid-oceanic ridge basalt (MORB)-like to near bulk-earth estimates along the MORB–oceanic island basalt (OIB) mantle array. The varieties in modal proportions of minerals, (La/Yb)_N ratio and Sr-Nd isotopes for the xenoliths demonstrate that the lithospheric mantle beneath Jeju Island is heterogeneous. The heterogeneity is a probable result of its long-term growth and enrichment history.  相似文献   

A DISCUSSION ON SEISMIC BINARY GAIN SWITCHING AMPLIFIERS *     

LEE SIEMS  FRED W. HEFER 《Geophysical Prospecting》1967,15(1):23-34

Geophysical field equipment has undergone rapid changes in the past decade; from simple AGC amplifiers and galvo cameras to binary gain switching amplifiers and digital recorders, all in an attempt to keep pace with the new geophysical interpretive methods developed, and the growing acceptance of the terminology, methods, and philosophy of communication theory. The additional tools of the digital recorder and digital computer make it possible to utilize these new techniques in geophysical processing. Accomplishing these new techniques demands severe requirements on the digital field recording process in handling the decreasing energy return from the seismometer, and to fully realize the capabilities of digital techniques in reducing data. Simple automatic gain control may be used. However, in the more sophisticated interpretive methods, such as autoregression and deconvolution, it is necessary to reconstruct the actual energy levels in the computer. Recording the control signal used in master AGC or programmed gain control may prove satisfactory; however the accuracy of control versus gain is limited to I% for such analog instrumentation. To utilize the computer to its fullest extent, and to accurately perform these new techniques, requires an accuracy of I% or better. This accuracy is obtainable by using a step gain control where the gain is increased by fixed steps in which each step represents a gain in amplification by a constant factor. The accuracy in this case can be made dependent only on the tolerance of resistors used as attenuators or feedback elements. Preferably the constant factor of gain steps should be a number easily handled by the computer. By using 6 db steps it becomes a simple matter to shift binary numbers, such as multiplying or dividing by 10 in the decimal system. The requirements or parameters for such an amplifier system, and the elements of the amplifier necessary to achieve these requirements are presented.  相似文献   

A SURVEY OF HIGH RESOLUTION GEOMAGNETICS *     

LEE LANGAN 《Geophysical Prospecting》1966,14(4):488-503

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MULTICOMPONENT COMMON-RECEIVER GATHER MIGRATION OF SINGLE-LEVEL WALK-AWAY SEISMIC PROFILES1     

G. M. JACKSON  I. M. MASON  DELMAN LEE 《Geophysical Prospecting》1991,39(8):1015-1029

Seismic data are usually separated into P-waves and S-waves before being put through a scalar (acoustic) migration. The relationship between polarization and moveout is exploited to design filters that extract the desired wavetype. While these filters can always be applied to shot records, they can only be applied to a triaxial common-receiver gather in special cases since the moveout of scattered energy on the receiver gather relates to path differences between the surface shots and the scatterer while the polarization is determined by the path from scatterer to downhole geophone. Without the ability to separate wavefields before migration, a ‘vector scalar’ or an elastic migration becomes a necessity. Here the propagation of the elastic wavefield for a given mode (e.g. P-S) is approximated by two scalar (acoustic) propagation steps in a ‘vector scalar’ migration. ‘Vector’ in that multicomponent data is migrated and 'scalar’ in that each propagation step is based on a scalar wave equation for the appropriate mode. It is assumed that interaction between the wavefields occurs only once in the far-field of both the source and receiver. Extraction of the P, SV and SH wavefields can be achieved within the depth migration (if one assumes isotropy in the neighbourhood of the downhole receiver) by a projection onto the polarization for the desired mode. Since the polarization of scattered energy is only a function of scatterer position and receiver position (and not source position), the projection may be taken outside the migration integral in the special case of the depth migration of a common-receiver gather. The extraction of the desired mode is then performed for each depth migration bin after the separate scalar migration of each receiver gather component. This multicomponent migration of triaxial receiver gathers is conveniently implemented with a hybrid split-step Fourier-excitation-time imaging condition depth migration. The raytracing to get the excitation-time imaging condition also provides the expected polarization for the post-migration projection. The same downward extrapolated wavefield can be used for both the P-P and P-S migrations, providing a flexible and efficient route to the migration of multicomponent data. The technique is illustrated on a synthetic example and a single-level Walk-away Seismic Profile (WSP) from the southern North Sea. The field data produced images showing a P-P reflector below the geophone and localized P-P and P-S scatterers at the level of the geo-phone. These scatterers, which lie outside the zone of specular illumination, are interpreted as faults in the base Zechstein/top Rotliegendes interface.  相似文献