Author: Jonathan E. Snow Publisher: ISBN: Category : Basalt Languages : en Pages : 654
Book Description
This dissertation studies several aspects of the formation of the Earth's oceanic mantle and crust, using a variety of geologic techniques, principally major elements, radiogenic isotopes and trace elements, but including petrography, mineral chemistry, x-ray diffraction, seafloor geomorphology, and analysis of the tectonics of fracture zones. The first chapter is an introduction to the problems to be addressed in this work. The second chapter examines the composition of basalts erupted near the Atlantis II Fracture Zone on the Southwest Indian Ridge. Trends in major element compositions of those basalts can be related directly to the nearby presence of the fracture zone. The effects of mantle composition and crustal level lateral transport of magma in the rift system can be ruled out by the analysis of isotopes and the geomorphology of the fracture zone floor. This is the best demonstration to date of a transform fault effect on basalt compositions. In trying to quantify putative transform fault effects documented at other fracture zones, no systematic correlation of transform offset age with mantle temperature change can be found, suggesting that mantle composition and lateral transport phenomena play a larger than expected role in the evolution of those areas. The third chapter relates to oceanic mantle rocks as they are altered at or near the Earth's surface. The major elements which make up abyssal peridotites are extensively redistributed by the alteration they have undergone. Mg is shown to be extracted from the peridotites, and a variety of trace elements added. This elemental redistribution is taken as evidence for extensive Mg transport by circulating waters. Since the solubility of Mg-bearing minerals in hydrothermal solutions is quite limited, much lower temperatures and much higher water /rock ratios are required to explain the major element compositions of the peridotites than had previously been assumed. The behavior of the Nd, Sr and Os isotopic systems during seafloor alteration was also studied. The isotope systematics of these rocks strongly support the hypothesis of high water /rock ratios in the formation of serpentinized abyssal peridotites. Nonetheless, Nd and Sr reside in a phase which is resistant to alteration (clinopyroxene) and the concentration of Os is high relative to that of seawater, so that it too appears resistant to alteration. Primary mantle isotopic signatures may be obtained from abyssal peridotites by careful analysis, even of extremely weathered rocks. Radiogenic strontium in excess of what could be introduced by seawater contamination or in situ radiogenic growth in a reasonable period of time was also found. These observations confirm earlier work which had been discredited for many years. The only plausible mechanism for the formation of this "orphan" S7Sr is that it is introduced as part of a sedimentary component which infiltrates the rock during metamorphism and/ or weathering. The 87Sr may be contained by or sorbed onto extremely fine clay particulates, or colloidal suspensions, as opposed to the dissolved ionic Sr which is normally thought of as characterizing the Sr isotopic composition of seawater. The high water/rock ratios required by the bulk isotopic analysis, as well as the pervasive elemental redistribution arguing for extensive near-surface weathering at high water /rock ra.tios strongly support this hypothesis. Given pervasive percolation of water throughout the samples, sufficient radiogenic, sediment-derived strontium may be drawn deep into the crust in the course of its weathering to cause such high B7SrfB6Sr ratios. The fourth chapter deals exclusively with primary mantle isotopic information from abyssal peridotites. This is the first study which has attempted to relate the Os isotopic system in the oceanic mantle to other isotopic systems and to trace elements. It is possible, with some extreme assumptions, to model the range of Os isotopes in the oceanic mantle alone in a standard model of formation of the depleted mantle by extraction of the crust. The additional constraints provided by the study of Nd isotopes in depleted mantle rocks from the oceans show that partial melt extraction and the formation of a depleted reservoir alone are not sufficient to account for the range of both N d and Os isotopes in the Earth's mantle. Possible mechanisms for the decoupling of the Os and Nd isotopic systems include elemental fractionation via the porous flow of basalt through the mantle, mantle metasomatism, recycling of a subducted component in the mantle and core formation. The core extraction model is pursued in some detail. Such core extraction models can account for the distributions and isotopic compositions of compatible and incompatible trace elements in the Earth's mantle, but they are highly non-unique, and thus difficult to test
Author: Kwok-Lin Lee Publisher: ISBN: Category : Languages : en Pages : 120
Book Description
This thesis investigates the petrology and geochemistry of an abyssal peridotite dredged from the Atlantis II Fracture Zone in the southwestern Indian Ocean Ridge. Texturally, this sample is a serpentinized peridotite with a crosscutting coarse-grained clinopyroxenite vein. One of the alteration veinlets contains rutile and ilmenite in association with plagioclase and amphibole. This veinlet is not related to the pyroxenite vein. In tenns of mineralogy, the composition of the major silicate minerals indicates that this plagioclase llierzolite represents the depleted residue after mantle melting, similar to other abyssal peridotites from this region. In addition to the presence of the unique pyroxenite vein, this sample was earlier shown to be a carrier of 'orphan Sr-87'. Unfortunately, I was unable to find such high Sr isotopic ratios in the magnetic separations of different fractions of the sample. The sulfide mineralogy, together with the whole rock chemistry, suggests that sea water alteration occurs mainly as a result of serpentinization at temperatures higher than 200°C. Since the sample is less than l Ma old, and the low temperature weathering occurred only after the sample was exposed at the sea floor, it is possible that the weathering process was restricted to major alteration veins. This suggests that the alteration process is highly fracture controlled and time dependent Trace element data from clinopyroxene grains in the peridotite shows large variations from grain to grain. The (Ce/Yb)n ranges from 0.17 to 0.54 in the pyroxenite vein, and from 0.75 to 2.35 away from the vein. The tendency for LREE enrichment with the increase of distance from the vein suggests the presence of highly reacted melts. An assimilation-fractional crystallization (AFC) model was derived which supports the idea that the source of the clinopyroxenite vein reacts with the depleted peridotite to form a central reaction zone. Some of the highly reacted melt, after melt-rock reaction, migrates out of the reaction zone, and precipitates some late magmatic phases while being trapped in the country rocks. Since the sulfide is a major Os reservoir in the abyssal peridotites, as shown in leaching experiments, and the melt is saturated in sulfur as a consequence of the reaction process, it is possible to model the heterogeneous distribution of the Os isotopic data by mixing the residual peridotite with 0.2 to 0.5 wt% of sulfides precipitated from the melt. This mixing process can explain most of the heterogeneity from 1.034 to 1.148 for 187Os/186Os. The impact on the peridotite from the melt-rock reaction and impregnation of the late melt is obvious. As evident in Hess Deep gabbroic rocks, conductive heat loss in the transform fault fulfils the physical requirement to create and to preserve such geochemical signature.
Author: William M. White Publisher: John Wiley & Sons ISBN: 1118902114 Category : Science Languages : en Pages : 496
Book Description
This book provides a comprehensive introduction to radiogenic andstable isotope geochemistry. Beginning with a brief overview ofnuclear physics and nuclear origins, it then reviews radioactivedecay schemes and their use in geochronology. A following chaptercovers the closely related techniques such as fission-track andcarbon-14 dating. Subsequent chapters cover nucleosyntheticanomalies in meteorites and early solar system chronology and theuse of radiogenic isotopes in understanding the evolution of theEarth’s mantle, crust, and oceans. Attention then turns tostable isotopes and after reviewing the basic principles involved,the book explores their use in topics as diverse as mantleevolution, archeology and paleontology, ore formation, and,particularly, paleoclimatology. A following chapter explores recentdevelopments including unconventional stable isotopes,mass-independent fractionation, and isotopic‘clumping’. The final chapter reviews the isotopicvariation in the noble gases, which result from both radioactivedecay and chemical fractionations.
Author: Donald J. DePaolo Publisher: Springer Science & Business Media ISBN: 3642489168 Category : Science Languages : en Pages : 287
Book Description
This monograph was begun with two objectives in mind. The first was to provide a review of research involving the application of neodymium isotopic measurements to pro blems in earth science. In the process of organizing to do this, I realized that the research in this field had produced a need for an updated review of the underlying paradigms. This need had arisen because of the special properties of the samarium-neodymium isotopic system, and because the research had transgressed the traditional boundaries be tween the subfields of earth science. Without such a review, the significance of the results seemed likely to remain un necessarily obscure to interested scientists from related disciplines. Consequently, the second objective became the provision of a theoretical framework for the application of neodymium isotopic studies. Much of what this contains is not new, but it is drawn together here for the first time. At the time the writing was initiated, the literature of the field was still relatively limited. Over the past 5 years it has grown enormously. Considering the rate at which the writing progressed, it became clear that this could not be a fully up-to-date review and still reach completion. The selection of material for the review sections is biased toward earlier studies. Part I presents most of the background information.
Author: Jochen Hoefs Publisher: Springer ISBN: 3319197169 Category : Science Languages : en Pages : 402
Book Description
Stable Isotope Geochemistry is an introduction to the use of stable isotopes in the geosciences. For students and scientists alike the book will be a primary source of information with regard to how and where stable isotopes can be used to solve geological problems. It is subdivided into three parts: i) theoretical and experimental principles, ii) fractionation processes of light and heavy elements, iii) the natural variations of geologically important reservoirs. In the last decade, major advances in multicollector-ICP-mass-spectrometry enable the precise determination of a wide range of transition and heavy elements. Progress in analysing the rare isotopes of certain elements allows the distinction between mass-dependent and mass-independent fractionations. These major advances in analytical techniques make an extended new edition necessary. Special emphasis has been given to the growing field of “non-traditional” isotope systems. Many new references have been added, which will enable quick access to recent literature.
Author: Publisher: Newnes ISBN: 0080983006 Category : Science Languages : en Pages : 14787
Book Description
This extensively updated new edition of the widely acclaimed Treatise on Geochemistry has increased its coverage beyond the wide range of geochemical subject areas in the first edition, with five new volumes which include: the history of the atmosphere, geochemistry of mineral deposits, archaeology and anthropology, organic geochemistry and analytical geochemistry. In addition, the original Volume 1 on "Meteorites, Comets, and Planets" was expanded into two separate volumes dealing with meteorites and planets, respectively. These additions increased the number of volumes in the Treatise from 9 to 15 with the index/appendices volume remaining as the last volume (Volume 16). Each of the original volumes was scrutinized by the appropriate volume editors, with respect to necessary revisions as well as additions and deletions. As a result, 27% were republished without major changes, 66% were revised and 126 new chapters were added. In a many-faceted field such as Geochemistry, explaining and understanding how one sub-field relates to another is key. Instructors will find the complete overviews with extensive cross-referencing useful additions to their course packs and students will benefit from the contextual organization of the subject matter Six new volumes added and 66% updated from 1st edition. The Editors of this work have taken every measure to include the many suggestions received from readers and ensure comprehensiveness of coverage and added value in this 2nd edition The esteemed Board of Volume Editors and Editors-in-Chief worked cohesively to ensure a uniform and consistent approach to the content, which is an amazing accomplishment for a 15-volume work (16 volumes including index volume)!
Author: E. Jäger Publisher: Springer Science & Business Media ISBN: 3642671616 Category : Science Languages : en Pages : 507
Book Description
Our colleagues from the French-speaking parts of Switzerland - the Suisses romands - and above all the committee of the 3rd Cycle, e Earth Sciences (3 Cycle, Sciences de la Terre) honored us by asking us to give a course on Isotope Geology for the year 1977. The course, entitled Evaluation et Interpretation des Donnees Isotopiques (eval uation and Interpretation of Isotopic Data), was intended to inform earth scientists, graduate and postgraduate, from the western Swiss Universities on the subject of Isotope Geology. Such courses usually consist of two parts: lectures and excursions. Thus, in March 1977, we gave such a two-week course at the Miner alogical Institute of the University of Berne. The first week was devoted essentially to the methods of dating, the second week to the behavior of stable isotopes. In July 1977, on the occasion of an excursion to the Central and Western Alps, we were able to demonstrate our results. Guest professors were invited to make contributions to the course.
Author: John W. Valley Publisher: Walter de Gruyter GmbH & Co KG ISBN: 1501508741 Category : Science Languages : en Pages : 676
Book Description
Volume 43 of Reviews in Mineralogy and Geochemistry follows the 1986 Reviews in Mineralogy (Vol. 16) in approach but reflects significant changes in the field of Stable Isotope Geochemistry. In terms of new technology, new sub-disciplines, and numbers of researchers, the field has changed more in the past decade than in any other since that of its birth. Unlike the 1986 volume, which was restricted to high temperature fields, this book covers a wider range of disciplines. However, it would not be possible to fit a comprehensive review into a single volume. Our goal is to provide state-of-the-art reviews in chosen subjects that have emerged or advanced greatly since 1986. This volume was prepared for Short Course on Stable Isotope Geochemistry presented November 2-4, 2001 in conjunction with the annual meetings of the Geological Society of America in Boston, Massachusetts.
Author: Jonathan E. Snow
Author: Kwok-Lin Lee
Author: William M. White
Author: J. Hoefs
Author: Donald J. DePaolo
Author: Jochen Hoefs
Author: 
Author: 
Author: E. Jäger
Author: John W. Valley