Deep drilling into a Hawaiian volcano

Hawaiian volcanoes are the most comprehensively studied on Earth. Nevertheless, most of the eruptive history of each one is inaccessible because it is buried by younger lava flows or is exposed only below sea level. For those parts of Hawaiian volcanoes above sea level, erosion typically exposes only a few hundred meters of buried lavas (out of a total thickness of up to 10 km or more).Available samples of submarine lavas extend the time intervals of individual volcanoes that can be studied. However, the histories of individual Hawaiian volcanoes during most of their ~1-million-year passages across the zone of melt production are largely unknown

Introduction to special section: Hawaii Scientific Drilling Project

Intraplate or "hot spot" volcanic island chains, exemplified by Hawaii, play an important role in plate tectonic theory as reference points for absolute plate motions, but the origin of these volcanoes is not explained by the plate tectonic paradigm [Engebretson et al., 1985; Molnar and Stock, 1987; Morgan, 1971, 1981, 1983; Wilson, 1963]. The most widely held view is that these chains of volcanoes form from magma generated by decompression melting of localized, buoyant upwellings in the mantle [Ribe and Christensen, 1994; Richards et al., 1988; Sleep, 1990; Watson and McKenzie, 1991] . These upwellings, or "plumes," are believed to originate at boundary layers in the mantle (e.g., at the core-mantle boundary or near the boundary at-670 km between the upper and lower mantle), and the cause of the buoyancy may be both compositional and thermal [Campbell and Griffiths, 1990; Griffiths, 1986; Richards et al., 1988; Watson and McKenzie, 1991]. Mantle plumes are responsible for about 10% of the Earth's heat loss and constitute an important mechanism for cycling mass from the deep mantle to the Earth's surface. Studies of the chemical and isotopic compositions of lavas from intraplate volcanoes, especially ocean island volcanoes, have contributed significantly to our knowledge of magma genesis in the mantle [Carmichael et al., 1974; Macdonald et al., 1983] and the compositional heterogeneity of the mantle [Allègre et al., 1983; Hart, 1988; Hart et al., 1986; Kurz et al., 1983]. Of particular importance is the identification of distinct compositional end members in the mantle, the origin and distribution of which provide insight into the long-term differentiation of the mantle-crust system, the recycling of oceanic crust and continental sediment into the mantle, and the history of the lithosphere [Allègre et al., 1995; Farley et al., 1992; Hart, 1988; Hofmann and White, 1982; McKenzie and O'Nions, 1983; Weaver, 1991; Zindler and Hart, 1986]

Isotopic Tracers for Waste Fluid Tracking and Fluid-Soil Interactions: Hanford, Washington

The objective of this research is to develop and advance isotopic methods for characterizing fluid flow and chemical transport through the vadose zone to groundwater. Previous research has been concentrated on developing and comparing different isotopic systems (e.g., hydrogen, oxygen and strontium isotopes) for determining fluid infiltration rates and pathways in the vadose zone (e.g., Maher et al., 2003; DePaolo et al., 2004; Singleton et al., in press). The focus of our current efforts is on using the isotopic compositions of different chemical phases (e.g., uranium, nitrate) to track their movement through the vadose zone. Preliminary results indicate that this will be a powerful tool for assessing environmental risks associated with vadose zone contamination

Formation of Box Canyon, Idaho, by megaflood: implications for seepage erosion on Earth and Mars

Amphitheater- headed canyons have been used as diagnostic indicators of erosion by groundwater seepage, which has important implications for landscape evolution on Earth and astrobiology on Mars. Of perhaps any canyon studied, Box Canyon, Idaho, most strongly meets the proposed morphologic criteria for groundwater sapping because it is incised into a basaltic plain with no drainage network upstream, and approximately 10 cubic meters per second of seepage emanates from its vertical headwall. However, sediment transport constraints, ^4He and ^14C dates, plunge pools, and scoured rock indicate that a megaflood (greater than 220 cubic meters per second) carved the canyon about 45,000 years ago. These results add to a growing recognition of Quaternary catastrophic flooding in the American northwest, and may imply that similar features on Mars also formed by floods rather than seepage erosion

Precise overgrowth composition during biomineral culture and inorganic precipitation

We introduce a method to analyze element ratios and isotope ratios in mineral overgrowths. This general technique can quantify environmental controls on proxy behavior for a range of cultured biominerals and can also measure compositional effects during seeded mineral growth. Using a media enriched in multiple stable isotopes, the method requires neither the mass nor the composition of the initial seed or skeleton to be known and involves only bulk isotope measurements. By harnessing the stability and sensitivity of bulk analysis the new approach promises high precision measurements for a range of elements and isotopes. This list includes trace species and select non-traditional stable isotopes, systems where sensitivity and external reproducibility currently limit alternative approaches like secondary ion mass spectrometry (SIMS) and laser ablation mass spectrometry. Since the method separates isotopically labeled growth from unlabeled material, well-choreographed spikes can resolve the compositional effects of different events through time. Among other applications, this feature could be used to separate the impact of day and night on biomineral composition in organisms with photosymbionts

Physics and Chemistry of Mantle Plumes

Hot spot volcanic chains are a fundamental feature of the Earth's crust, but their origins are still poorly understood [Okal and Batiza, 1987]. The Hawaiian-Emperor volcanic chain, which dominates the topography of the central Pacific ocean floor, is the best developed and most intensely studied of the known hot spot tracks. It continues to be one of the world's most important field laboratories for the study of igneous processes, plate movements, mantle convection, structure, geochemical evolution, and the properties of the lithosphere. Despite continued effort, fundamental questions regarding the composition, structure, and evolution of Hawaiian volcanos and their magma sources remain unanswered. This is largely due to the fact that only lavas representing the late stages in the evolution of the volcanos can be sampled at the surface. Most of the internal structure of the volcanos and evidence of their growth history and geochemical evolution are hidden from view. The most deeply eroded volcanos are exposed only to depths of a kilometer or so, whereas the volcanos rise some 5–15 km above the old ocean floor [Moore, 1987]

Basic Research Needs for Geosciences: Facilitating 21st Century Energy Systems

Executive Summary Serious challenges must be faced in this century as the world seeks to meet global energy needs and at the same time reduce emissions of greenhouse gases to the atmosphere. Even with a growing energy supply from alternative sources, fossil carbon resources will remain in heavy use and will generate large volumes of carbon dioxide (CO2). To reduce the atmospheric impact of this fossil energy use, it is necessary to capture and sequester a substantial fraction of the produced CO2. Subsurface geologic formations offer a potential location for long-term storage of the requisite large volumes of CO2. Nuclear energy resources could also reduce use of carbon-based fuels and CO2 generation, especially if nuclear energy capacity is greatly increased. Nuclear power generation results in spent nuclear fuel and other radioactive materials that also must be sequestered underground. Hence, regardless of technology choices, there will be major increases in the demand to store materials underground in large quantities, for long times, and with increasing efficiency and safety margins. Rock formations are composed of complex natural materials and were not designed by nature as storage vaults. If new energy technologies are to be developed in a timely fashion while ensuring public safety, fundamental improvements are needed in our understanding of how these rock formations will perform as storage systems. This report describes the scientific challenges associated with geologic sequestration of large volumes of carbon dioxide for hundreds of years, and also addresses the geoscientific aspects of safely storing nuclear waste materials for thousands to hundreds of thousands of years. The fundamental crosscutting challenge is to understand the properties and processes associated with complex and heterogeneous subsurface mineral assemblages comprising porous rock formations, and the equally complex fluids that may reside within and flow through those formations. The relevant physical and chemical interactions occur on spatial scales that range from those of atoms, molecules, and mineral surfaces, up to tens of kilometers, and time scales that range from picoseconds to millennia and longer. To predict with confidence the transport and fate of either CO2 or the various components of stored nuclear materials, we need to learn to better describe fundamental atomic, molecular, and biological processes, and to translate those microscale descriptions into macroscopic properties of materials and fluids. We also need fundamental advances in the ability to simulate multiscale systems as they are perturbed during sequestration activities and for very long times afterward, and to monitor those systems in real time with increasing spatial and temporal resolution. The ultimate objective is to predict accurately the performance of the subsurface fluid-rock storage systems, and to verify enough of the predicted performance with direct observations to build confidence that the systems will meet their design targets as well as environmental protection goals. The report summarizes the results and conclusions of a Workshop on Basic Research Needs for Geosciences held in February 2007. Five panels met, resulting in four Panel Reports, three Grand Challenges, six Priority Research Directions, and three Crosscutting Research Issues. The Grand Challenges differ from the Priority Research Directions in that the former describe broader, long-term objectives while the latter are more focused

Isotopic Constraints on the Chemical Evolution of Geothermal Fluids, Long Valley, CA

Abstract A spatial survey of the chemical and isotopic composition of fluids from the Long Valley hydrothermal system was conducted. Starting at the presumed hydrothermal upwelling zone in the west moat of the caldera, samples were collected from the Casa Diablo geothermal field and a series of monitoring wells defining a nearly linear, ~14 km long, west-to-east trend along the proposed fluid flow path Introduction The efficiency of heat extraction from geothermal reservoir rocks is limited by chemical processes and the physical characteristics of the reservoir. Specifically, mineral dissolution and precipitation and the geometry of heat and mass exchange between fluids and the reservoir lithologies of fractured dominated systems define the long term efficiency of heat extraction but are difficult to quantify and therefore predict. Increased knowledge about the water-rock exchange in geothermal systems and the size and spacing of the major fluid transporting fractures would be valuable information that impact decisions guiding the management of natural and enhanced geothermal systems

Geochemistry, detrital zircon geochronology and Hf isotope of the clastic rocks in southern Tibet: implications for the Jurassic-Cretaceous tectonic evolution of the Lhasa terrane

In order to reconstruct tectonic evolution history of the southern margin of Asia (i.e., Lhasa terrane) before the India-Asia collision, here we present a comprehensive study on the clastic rocks in the southern Lhasa terrane with new perspectives from sedimentary geochemistry, detrital zircon geochronology and Hf isotope. Clasts from the Jurassic-Early Cretaceous sedimentary sequences (i.e., Yeba and Chumulong Formations) display high compositional maturity and experienced moderate to high degree of chemical weathering, whereas those from the late Early-Late Cretaceous sequences (Ngamring and Shexing Formations) are characterized by low compositional maturity with insignificant chemical weathering. Our results lead to a coherent scenario for the evolution history of the Lhasa terrane. During the Early-Middle Jurassic (∼192-168Ma), the Lhasa terrane was speculated to be an isolated geological block. The Yeba Formation is best understood as being deposited in a back-arc basin induced by northward subduction of the Neo-Tethys ocean with sediments coming from the interiors of the Lhasa terrane. The Middle Jurassic-Early Cretaceous Lhasa-Qiangtang collision resulted in the formation of a composite foreland basin with southward-flowing rivers carrying clastic materials from the uplifted northern Lhasa and/or Qiangtang terranes. During the late Early-Late Cretaceous (∼104-72Ma), the Gangdese magmatic arc was uplifted rapidly above the sea level, forming turbidites (Ngamring Formation) in the Xigaze forearc basin and fluvial red beds (Shexing Formation) on the retro-arc side. At the end of Late Cretaceous, the Lhasa terrane was likely to have been uplifted to high elevation forming an Andean-type margin resembling the modern South America before the India-Asia collision