Showing papers in "Treatise on Geochemistry in 2003"
2,635 citations
TL;DR: Hofmann et al. as discussed by the authors reviewed the recent advances in the field of mantle geology, geophysics, and geochemistry using seismic mantle tomography, and concluded that the established views of the mantle being engaged in simple two-or single-layer convection are becoming obsolete.
Abstract: This chapter is in part an update of a previous, more abbreviated review ( Hofmann, 1997 ) It covers the subject in greater depth, and it reflects some significant changes in the author's views since the writing of the earlier paper In particular, the spatial range of equilibrium attained during partial melting may be much smaller than previously thought, because of new experimental diffusion data and new results from natural settings Also, the question of ‘layered’ versus ‘whole-mantle’ convection, including the depth of subduction and of the origin of plumes, has to be reassessed in light of the recent breakthroughs achieved by seismic mantle tomography As the spatial resolution of seismic tomography and the pressure range, accuracy, and precision of experimental data on melting relations, phase transformations, and kinetics continue to improve, the interaction between these disciplines and geochemistry sensu stricto will continue to improve our understanding of what is actually going on in the mantle The established views of the mantle being engaged in simple two- or single-layer convection are becoming obsolete In many ways, we are just at the beginning of this new phase of mantle geology, geophysics, and geochemistry
701 citations
TL;DR: The boundary between the silicate mantle and the core is remarkable in that it is a zone of greatest contrast in Earth properties as discussed by the authors, and the density increase across this boundary represents a greater contrast than across the crust-ocean surface.
Abstract: The remote setting of the Earth's core tests our ability to assess its physical and chemical characteristics. Extending out to half an Earth radius the metallic core constitutes a sixth of the planet's volume and a third of its mass. The boundary between the silicate mantle and the core is remarkable in that it is a zone of greatest contrast in Earth properties. The density increase across this boundary represents a greater contrast than across the crust–ocean surface. Our understanding of the core is based on very few pieces of direct evidence and many fragments of indirect observations. Direct evidence comes from seismology, geodesy, geo- and paleomagnetism, and, relatively recently, isotope geochemistry. Indirect evidence comes from geochemistry, cosmochemistry, and meteoritics; further constraints on the core system are gained from studies in experimental petrology, mineral physics, ab initio calculations, and evaluations of the Earth's energy budget. Feedback loops between all of these disciplines refine other's understanding of the Earth's core.
556 citations
TL;DR: A review of anaerobic metabolism emphasizes aerobic oxidation, because the two processes cannot be separated in a complete treatment of the topic as mentioned in this paper, which is process oriented and highlights the fascinating microorganisms that mediate biogeochemistry.
Abstract: This review of anaerobic metabolism emphasizes aerobic oxidation, because the two processes cannot be separated in a complete treatment of the topic. It is process oriented and highlights the fascinating microorganisms that mediate anaerobic biogeochemistry. We begin this review with a brief discussion of CO 2 assimilation by autotrophs, the source of most of the reducing power on Earth, and then consider the biological processes that harness this potential energy. Energy liberation begins with the decomposition of organic macromolecules to relatively simple compounds, which are simplified further by fermentation. Methanogenesis is considered next because CH 4 is a product of acetate fermentation, and thus completes the catabolism of organic matter, particularly in the absence of inorganic electron acceptors. Finally, the organisms that use nitrogen, manganese, iron, and sulfur for terminal electron acceptors are considered in order of decreasing free-energy yield of the reactions.
546 citations
TL;DR: A review of the geochemistry of mantle xenoliths can be found in this article, where the authors review the geochemical properties of mantle nodules and find that they are dominantly alkaline in nature.
Abstract: Fragments of the Earth’s mantle are frequently transported to the surface via volcanic rocks that are dominantly alkaline in nature. These fragments range up to sizes in excess of 1 m across. The term “mantle xenoliths” or “mantle nodules” is applied to all rock and mineral inclusions of presumed mantle derivation that are found within host rocks of volcanic origin. The purpose of this contribution is to review the geochemistry of mantle xenoliths.
536 citations
TL;DR: Among all the c he mic al e le men ts, ox ygen has a co mbin ation of pro pe rtie s tha t ma kes it u nique ly im por ta nt in cosmoc hem is tr y as discussed by the authors.
Abstract: Among all the c he mic al e le men ts, ox ygen has a co mbin ation of pro pe rtie s tha t ma kes it u nique ly im por ta nt in cosmoc hem is tr y. I t is a n abu nda nt e leme nt , a nd is t he pr inc ipa l co nst it ue nt o f most m inera ls a nd roc ks. It is a lig ht e leme nt, so tha t its three s tab le iso to pes are s ubjec t to large mass de pe nde nt frac tio na tio n e ffec ts in bo th equ ilibr ium a nd kine tica lly-co n tro lle d processes . Its iso to pes are forme d in differe nt nuc leosynthe tic pro cesses, so t ha t s te lla r n ucleo syn the si s can pro duce i so to pi c he te rogenei ty. It ca n un de rgo c hem ica l reac tio ns in w hic h no n-mass -de pe nde nt iso to pe frac tio na tio ns occ ur . I ts cosm ic abu nda nce , re la tive to tha t o f carbo n, o n the o ne ha nd, a nd me ta llic e leme nts o n the o ther , causes it to occur simu lta neous ly i n two cosmochemica l reser voirs: a gas (most ly CO a nd H 20) a nd a so lid (o xides a nd s ilica tes o f the me ta llic e leme nts ). This las t pro per ty is es pec ia lly im por ta nt, as i t a llows ox ygen to avoi d i so to pic ho mogeni zation in the in te rste llar me di um a nd in the e arly so lar syste m, a nd t hus to ser ve as a nat ura l tracer for interact io ns o f differe nt reser voirs . The ab unda nt iso to pe, 160 ( 99. 76% ), is pro duce d in s te llar nuc leo s ynthes is b y he lium b ur ning, a nd is re tur ne d to the inters te llar me dium in s uper nova e xplos io ns . T he rare iso to pes, 170 (0.04%) a nd 180 (0.20%), are pro duced b y hot CNO c yc les i n zo nes ric h i n H a nd He , res pecti ve ly, in bo th no vae an d supe rno vae (Audo uze & Va uc la ir 19 80). For all three iso to pes , rap id coo ling o f s te llar ejec ta ca n lea d to the format io n o f mo l ec ules a nd/or re frac tor y so lids , w hic h bear the s igna ture o f the par tic ular nuc leos ynt hetic processes (Lat timer et a l 197 8). It mig ht , there fore , be
444 citations
TL;DR: The continental crust is the principal record of how conditions on the Earth have changed, and how processes of crust generation have evolved through geological time as mentioned in this paper, and it preserves evidence of secular variation in crustal compositions, and thus the way in which the crust has formed throughout Earth's history.
Abstract: Every geologist is acquainted with the principle of “uniformitarianism,” which holds that present-day processes are the key to those that operated in the past. But the extent this applies to the processes driving the growth and differentiation of the Earth's continental crust remains a matter of debate. Unlike its dense oceanic counterpart, which is recycled back into the mantle by subduction within 200 Ma, the continental crust comprises buoyant quartzofeldspathic materials and is difficult to destroy by subduction. The continental crust is, therefore, the principal record of how conditions on the Earth have changed, and how processes of crust generation have evolved through geological time. It preserves evidence of secular variation in crustal compositions, and thus the way in which the crust has formed throughout Earth's history. Exploring the nature and origin of these variations is the focus of this chapter.
324 citations
TL;DR: A brief overview of the various components of the global phosphorus cycle is given in this paper, including a discussion of the most pressing research questions currently being posed and research efforts presently underway to address these questions.
Abstract: Phosphorus is an essential nutrient for all life-forms It is a key player in fundamental biochemical reactions involving genetic material (DNA and RNA) and energy transfer (ATP) and in structural support of organisms provided by membranes (phospholipids) and bone (the biomineral hydroxyapatite) Photosynthetic organisms utilize dissolved phosphorus, carbon, and other essential nutrients to build their tissues using energy from the sun Biological productivity is contingent upon the availability of phosphorus to these simple organisms that constitute the base of the food web in both terrestrial and aquatic systems It begins with a brief overview of the various components of the global phosphorus cycle Estimates of the mass of important phosphorus reservoirs, transport rates (fluxes) between reservoirs Following the overview, various aspects of the global phosphorus cycle are examined in more depth, including a discussion of the most pressing research questions currently being posed and research efforts presently underway to address these questions
311 citations
TL;DR: The application of strontium, neodymium, and lead isotopes for tracing the sources of continental detritus brought to the oceans by icebergs and implications for the history of the North Atlantic ice sheets is discussed in this article.
Abstract: This chapter focuses on the basis for using authigenic neodymium, lead, and hafnium isotopes in oceanography and paleoceanography. In particular, it reviews in detail the currently available data on neodymium isotopes in the oceans in order to evaluate its strengths and weaknesses as an oceanographic tracer and a proxy to investigate paleocirculation. Neodymium isotope ratios are highlighted because lead isotopes in the present day oceans are contaminated by anthropogenic input, and dissolved hafnium thus far has not been measured. This chapter only gives a cursory summary of the results of studies on Fe–Mn crusts. This chapter also summarizes the application of strontium, neodymium, and lead isotopes for tracing the sources of continental detritus brought to the oceans by icebergs and implications for the history of the North Atlantic ice sheets.
307 citations
279 citations
TL;DR: In this article, the authors propose a method to solve the NOMENCLATURE 2 5.16.16 problem, i.e., the problem of homonymity.
Abstract: NOMENCLATURE 2 5.16.
TL;DR: This chapter introduces some of the general principles of molecular biomarkers, provides examples of their use for discerning the identities and physiologies of microbes in contemporary environments and summarizes biomarker research aimed at elucidating aspects of biological and environmental evolution in the Precambrian.
Abstract: Molecular biological markers, or biomarkers, are natural products that can be assigned to a particular biosynthetic origin. For environmental and geological studies, the most useful molecular biomarkers are organic compounds with high taxonomic specificity and potential for preservation. This chapter introduces some of the general principles, provides examples of their use for discerning the identities and physiologies of microbes in contemporary environments and summarizes biomarker research aimed at elucidating aspects of biological and environmental evolution in the Precambrian.
TL;DR: The role of trace elements in marine bioinorganic chemistry has been discussed in this article, where the authors examine the evidence, emanating from both laboratory cultures and field measurements, relevant to the mechanisms and the extent of control by trace metals of marine biogeochemical cycles.
Abstract: The bulk of living biomass is chiefly made up of only a dozen ‘major’ elements whose proportions vary within a relatively narrow range in most organisms. A number of trace elements, particularly first row transition metals are also ‘essential’ for the growth of organisms. We begin this chapter by discussing what we know of the concentrations of trace elements in marine microorganisms and of the relevant mechanisms and kinetics of trace-metal uptake. We then review the biochemical role of trace elements in the marine cycles of carbon, nitrogen, phosphorus, and silicon. Using this information, we examine the evidence, emanating from both laboratory cultures and field measurements, relevant to the mechanisms and the extent of control by trace metals of marine biogeochemical cycles. Before concluding with a wistful glimpse of the future of marine bioinorganic chemistry we discuss briefly some paleoceanographic aspects of this new field: how the chemistry of the planet ‘Earth’ – particularly the concentrations of trace elements in the oceans – has evolved since its origin, chiefly as a result of biological processes and how the evolution of life has, in turn, been affected by the availability of essential trace elements.
TL;DR: In the early 1970s, marine chemists gained a first-order understanding of the concentrations, distributions, and chemical behaviors of trace metals in seawater as mentioned in this paper, along with the development and adoption of clean techniques.
Abstract: Since the early 1970s, marine chemists have gained a first-order understanding of the concentrations, distributions, and chemical behaviors of trace metals in seawater. Important factors initiating this quantum leap in knowledge were major advances in modern analytical chemistry and instrumentation, along with the development and adoption of clean techniques. An instrumental development in the mid-1970s that spurred the early research on trace metals was the availability of the sensitive graphite furnace as the sample introduction system to an atomic absorption spectrometer. More recently, the appearance of inductively coupled plasma (ICP) mass spectrometers has provided an even more sensitive and powerful instrumental capability to the arsenal of marine chemists. In addition to these instruments back in shore-based laboratories, there has been the development of sensitive shipboard methods such as stripping voltammetry and flow injection analysis (FIA) systems with either chemiluminescence or catalytically enhanced spectrophotometric detection. Along with the development of these highly sensitive analytical techniques came a recognition and appreciation of the importance of handling contamination issues by using clean techniques during all phases of sampling and analysis. This is
TL;DR: In this paper, the authors discuss the general techniques for measurement of dissolution and precipitation rates of rock-forming silicates and carbonates, and then, seven of these nine factors are discussed sequentially.
Abstract: This article firstly discusses the general techniques for measurement of dissolution and precipitation rates of rock-forming silicates and carbonates, and then, seven of these nine factors are discussed sequentially. Full discussions of the last two phenomena, transport and biologic processes, are not included. Throughout the article, it also discusses how surface complexation models can now be used to understand the reactive sites on mineral surfaces. Nonetheless, the intent here is mostly to emphasize simpler rate equations that emphasize solution chemistry instead of surface chemistry because these are often used in reactive transport codes. Techniques to predict the rates of mineral dissolution for mineral compositions where data are unavailable are summarized.
TL;DR: In this paper, the authors present a survey of geochromatic variations in lava compositions, including the shape of the melting regime, the generation of diverse melt compositions, and the transformation of pyroxenite melting.
Abstract: 3.13.4 WORLDWIDE GEOCHEMICAL VARIATIONS AMONG OCEAN RIDGE BASALTS 437 3.13.4.1 Crystallization 438 3.13.4.1.1 Major elements 438 3.13.4.1.2 Trace elements 438 3.13.4.1.3 Correcting for crystallization 443 3.13.4.2 Melting 444 3.13.4.2.1 Major elements 444 3.13.4.2.2 Trace elements 446 3.13.4.2.3 The shape of the melting regime and the generation of diverse melt compositions 447 3.13.4.3 Mantle Heterogeneity 447 3.13.4.3.1 Pyroxenite melting 448 3.13.4.3.2 Assimilation of altered crust 449 3.13.4.3.3 Local trends in basalt composition 450 3.13.4.4 Spatial Variations in Lava Compositions 451 3.13.4.4.1 Along-axis chemical variations 451 3.13.4.4.2 Temporal variations on lava composition 454
TL;DR: Halogens are very reactive chemical compounds that are known to play an important role in anthropogenic stratospheric ozonedepletion chemistry, first recognized by Molina and Rowland (1974) as discussed by the authors.
Abstract: Halogens are very reactive chemical compounds that are known to play an important role in anthropogenic stratospheric ozone-depletion chemistry, first recognized by Molina and Rowland (1974) Halogens, however, also affect the chemistry of the troposphere They are of special interest because they are involved in many reaction cycles that can influence the oxidation power of the atmosphere indirectly by influencing the main oxidants O 3 and its photolysis product OH, and NO x (=NO + NO 2 ) and directly, for example, by reactions of the Cl radical with hydrocarbons (eg, CH 4 )
TL;DR: In this article, the Moho heat flux of a large volume of rocks over the entire crustal column is calculated to provide complementary information on the concentration of heat-producing elements in the crust, including the lower crust.
Abstract: The continental crust is rich in the radioactive elements uranium, thorium, and potassium that produce energy. Because their concentration varies on many different scales, determining the crustal heat production by sampling the rocks exposed at the surface is prone to large errors. Heat-flow measurements, which integrate the heat production of a large volume of rocks over the entire crustal column, provide complementary information on the concentration of heat-producing elements in the crust, including the lower crust, which is not accessible for direct sampling. This information is more robust than averaging rock samples if the Moho heat flux can be determined.
TL;DR: In this paper, the first major chemical divides occur for gypsum, magnesite, and sulfates of magnesium and sodium, as shown in the revised brine evolution flowchart.
Abstract: Saline lakes are important environmental features in continental basins worldwide. They are critical for water and mineral resources, economic activity, and paleoenvironmental studies. Water and solute sources for saline lake brines are direct precipitation, surface flow, local or regional meteoric groundwaters, interstitial water of sediments, or deep basinal fluids. Solute concentrations are controlled by the weathering of source rocks, evaporation, and solute losses to minerals and biota. Aquifer residence times, rock dissolution rates, leakage ratios, and dissolution–precipitation fractionation are also important factors. With evaporation, inflow waters generally reach supersaturation first with respect to alkaline-earth carbonates, the first of several major ‘chemical divides.’ Subsequent chemical divides occur for gypsum, magnesite, and sulfates of magnesium and sodium, as shown in the revised brine evolution flowchart. Brine evolution along different flow paths is therefore controlled by the molar ratio of solutes, eventually producing diagnostic mineral assemblages. Idealized brine evolution paths and the associated evaporite mineral assemblages are complicated by local variation in hydrology, biotic activity, mineral kinetics, and diagenesis.
TL;DR: Henderson et al. as discussed by the authors proposed a U-Pb systematics of monazite and xenotime: case studies from the Paleoproterozoic of the Grand Canyon, Arizona.
Abstract: s (eds. A. M. Macfarlane, R. B. Sorkhabi, and J. Quade), pp. 58–59. Harrison T. M., Ryerson F. J., Le Fort P., Yin A., Lovera O., and Catlos E. J. (1997) A Late Miocene–Pliocene origin for the central Himalayan inverted metamorphism. Earth Planet. Sci. Lett. 146, E1–E7. Hart S. R. (1964) The petrology and isotopic-mineral age relations of a contract zone in the front range, Colorado. J. Geol. 72, 493–525. Hartz E. H., Andresen A., Martin M. W., and Hodges K. V. (2000) U–Pb and Ar/Ar constraints on the Fjord region detachment zone: a long-lived extensional fault in the East Greenland Caledonides. J.Geol. Soc. London 157, 795–809. Hawkins D. P. and Bowring S. A. (1997) U–Pb systematics of monazite and xenotime: case studies from the Paleoproterozoic of the Grand Canyon, Arizona. Contrib. Mineral. Petrol. 127, 87–103. Hawkins D. P. and Bowring S. A. (1999) U–Pb monazite, xenotime, and titanite geochronological constraints on the prograde to post-peak metamorphic thermal history of Paleoproterozoic migmatites from the Grand Canyon, Arizona. Contrib. Mineral. Petrol. 134, 150–169. Hess J. C., Lippolt H. J., Gurbanov A. G., and Michalski I. (1993) The cooling history of the Late Pliocene Eldzhurtinskiy granite (Caucasus, Russia) and the thermochronological potential of grain-size/age relationships. Earth Planet. Sci. Lett. 117, 393–406. Hodges K., Bowring S., Davidek K., Hawkins D., and Krol M. (1998) Evidence for rapid displacement on Himalayan normal faults and the importance of tectonic denudation in the evolution of mountain ranges. Geology 26, 483–486. Hodges K. V. (1991) Pressure–Temperature– time paths. Ann. Rev. Earth Planet. Sci. 19, 207–236. Geochronology and Thermochronology in Orogenic Systems 288
TL;DR: In this article, the authors propose a new algorithm called 5.11.5.0-11.1-5.5-0-0.0/0.00
Abstract: 5.11.