December 2010 Geology and GSA Today highlights
Geology presents evidence that today's C4 plants grew 14 million years earlier than previously thought; a 3-D view of ocean floor "rivers"; swarm seismicity and a Yellowstone tree-ring core; mysterious rock layers containing the petrified remains of bizarre early life-forms, complete with eyes, guts, and muscles; cohabiting bacteria in a 3.4 billion-year-old beach-like environment; and deep-cave stromatolites in Spain. GSA Today calls for and details the use of geoinformatics to transform science data to knowledge.
Representatives of the media may obtain complementary copies of Geology articles by contacting Christa Stratton at the address above. Abstracts for the complete issue of Geology are available at http://geology.gsapubs.org/.
GSA Today articles are open access. Access the GSA Today science article by clicking on the issue cover icon at http://www.geosociety.org/pubs/.
Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to Geology or GSA Today in articles published. Contact Christa Stratton for additional information or assistance.
Non-media requests for articles may be directed to GSA Sales and Service, email@example.com.
KEY WORDS: Chemical kinetic modeling, submarine channels, granite genesis, retrograde metamorphism, tree ring, seismicity, CO2, Yellowstone, rainforest, reptiles, dinosaurs, tetrapod, diamonds, biosignatures, C4 grasses, C3 plants, T-J boundary, Vishnu Schist, Soom Shale, South Africa, anoxic conditions, Cretaceous, organic-rich sediments, sulfur, bacteria, sandstone, pyrite, El Soplao Cave, Spain, vorticity, kinematics, platinum, Nile, Space Shuttle Radar Topography, Kilauea, pseudotachylyte, geoinformatics
Testing competing hypotheses for soil magnetic susceptibility using a new chemical kinetic model
John F. Boyle et al., Univ. of Liverpool, Geography, Chatham Street, Liverpool, Merseyside L69 7ZT, UK. Pages 1059-1062.
Soil magnetic properties are widely studied by earth and environmental scientists. For example, magnetic susceptibility measurements have been used to generate Quaternary climate records from loess-paleosol sequences; to fingerprint fluvial sediment sources; to quantify atmospheric pollution; to assess atmospheric conditions on Mars; and to assist in the detection of land mines. Yet, despite these many applications, the mechanisms that govern soil magnetic properties are disputed, with no agreement about which chemical pathways are important. To address these questions, John F. Boyle of the University of Liverpool and colleagues have developed a quantitative process model that integrates different conceptual models with existing laboratory and field studies, allowing them to assess competing processes more critically. The model suggests soil magnetism is largely controlled by secondary iron oxide reactions controlled by weathering and climate that do not necessarily involve bacteria. These findings are borne out by observations that show highest values of magnetic susceptibility associated with relatively old soils lying over iron-rich parent materials.
Gravity-driven flow in a submarine channel bend: Direct field evidence of helical flow reversal
Daniel Parsons et al., School of Earth and Environment, Univ. of Leeds, West Yorkshire LS2 9JT, UK. Pages 1063-1066.
The biggest channels on Earth are not the Amazon and the Mississippi -- they are the "rivers" that run along the ocean floor. Though they can extend to tens of kilometers wide and hundreds of meters deep, little is known about the flows within these submarine channels and how they change over time. These channels are the main transport pathway taking sediments to the deep sea, where the largest sedimentary deposits on our planet are formed. These deposits ultimately not only hold untapped reserves of gas and oil; they also house important secrets, from clues to past climate change to the ways in which mountains were formed. Daniel Parsons of the University of Leeds and colleagues report the first 3-D measurements of flow a submarine channel in the Black Sea. The results demonstrate that the flow around submarine channel bends can spiral in the opposite sense to that typically found in river channels on land. This reversal in helical flow direction will have major implications for how these channels develop over time, and our interpretations of the sedimentary record that they leave behind.
Granite genesis and mafic-felsic magma interaction in the lower crust
George Christopher Koteas et al., Dept. of Geosciences, Univ. of Massachusetts, Amherst, Massachusetts 01003, USA. Pages 1067-1070.
The composition and appearance of Earth's continental crust is fundamentally linked to the origin and evolution of felsic magmas that produce granites. The Athabasca granulite terrane in northern Saskatchewan, Canada, preserves a large slice of the lower part of the ancient crust of North America. Studies of rocks in this region provide information about the thermal and mechanical processes that are currently at work at the crust-mantle interface, but cannot be observed at the surface of the Earth. This region reveals a snapshot of the deep crust, showing it to be dynamic and a compositionally heterogeneous region of Earth's interior. The research by George C. Koteas of the University of Massachusetts and colleagues suggests that mantle-derived mafic magmas impart heat that partially melts the crust and produces granitic magma. This process of partial melting also weakens the lower crust, making it ductile. Research in this region is essential to better understand sources of magma in the deep crust, the overall strength and conditions present at these depths in the Earth, and the mechanisms by which the North American continent evolved over time.
Growth conditions of symplectic muscovite + quartz: Implications for quantifying retrograde metamorphism in exhumed magmatic arcs
Emily Peterman and Marty Grove, Dept. of Geological & Environmental Sciences, Green Earth Sciences Building, 367 Panama Street, Stanford Univ., Stanford, California 94305-2115, USA. Pages 1071-1074.
The style and extent to which the Earth's crust deforms is largely controlled by temperature. At sustained elevated temperatures, crust is generally ductile; as it cools, it becomes more brittle. Emily Peterman and Marty Grove, both of Stanford University, seek to understand the mechanical and thermal evolution of arc crust post-intrusion by measuring the temperatures of peak-grade and retrograde metamorphism in adjacent wallrocks. To investigate the temperature range of metamorphism, Peterman and Grove focus on textures that record retrograde metamorphism -- symplectites. Symplectites form when the rate of grain boundary migration outpaces diffusion, which is generally in response to rapidly falling temperature. The authors measured titanium concentrations in symplectic quartz to calculate the temperature of retrograde mineral growth. These measurements reveal that symplectic quartz grew at 575-375 degrees C, which reflects temperatures up to 250 degrees C lower than peak-grade metamorphism. This result indicates that arc crust cools rapidly post-intrusion, and implies that it can attain significant strength shortly after batholith emplacement.
Tree-ring 14C links seismic swarm to CO2 spike at Yellowstone
William C. Evans et al., U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA. Pages 1075-1078.
William C. Evans of the U.S. Geological Survey and colleagues present a unique long-term record of magmatic carbon dioxide emissions within the Yellowstone caldera (USA), with particular focus on a period of swarm seismicity in 1978. The record is derived from the radiocarbon concentrations in annual growth rings of an 80-yr-old lodgepole pine, growing near the locus of seismicity. The sharp drop in radiocarbon in 1978-1980 is compelling evidence that an intra-caldera earthquake swarm was associated with, and likely caused by, rapid escape of magmatic carbon dioxide through the overlying brittle crust. The tree-core record provides the first geochemical confirmation of a linkage between seismicity and fluid flow at Yellowstone, long proposed on geophysical, geothermal, and seismic grounds. Pressure changes associated with episodic fluid flow from ductile to brittle zones thus remain a viable hypothesis for caldera deformation that is not linked directly to magmatic intrusion.
Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica
Sarda Sahney et al., Dept. of Earth Sciences, Royal Holloway, Univ. of London, Surrey TW20 0EX, UK. Pages 1079-1082.
Global warming devastated tropical rainforests 300 million years ago. Now Sarda Sahney of the University of London and colleagues report the unexpected discovery that this event triggered an evolutionary burst amongst reptiles -- and inadvertently paved the way for the rise of dinosaurs one hundred million years later. This event happened during the Carboniferous Period, the time when the coal deposits of Europe and North America formed. The deposits formed from the compacted remains of rainforest trees. But when climates became drier rainforests collapsed, thus triggering reptile evolution. Dr. Howard Falcon-Lang, part of the research team at Royal Holloway, Univ. of London, UK, explains, "Climate change caused rainforests to fragment into a small 'islands' of forest. This isolated populations of reptiles, and each community evolved in separate directions, increasing diversity." Professor Mike Benton of the Univ. of Bristol, UK, adds, "This is a classic ecological response to habitat fragmentation. You see the same process happening today whenever a group of animals becomes isolated from its parent population. It's been studied on traffic islands between major road systems or, as Charles Darwin famously observed in the Galapagos, on oceanic islands." Sarda Sahney, also of the Univ. of Bristol, UK, said, "Even in the face of devastating ecosystem collapse, animals may continue to diversify through the creation of endemic populations." To reach their conclusions, the scientists studied the fossil record of reptiles before and after rainforest collapse. They showed that reptiles diversified and even changed their diet as they struggled to adapt to rapidly changing climate and environment.
Coupled evolution of Archaean continental crust and subcontinental lithospheric mantle
Hugh Rollinson, School of Science, Univ. of Derby, Derby DE22 1GB, UK. Pages 1083-1086.
For many years, it has been known that there is an association between areas of very ancient crust and unusually thick underlying subcontinental mantle -- not least because this is where we find diamonds. Southern Africa is a good example of where very ancient rocks (more than 2.5 billion years old) crop out at the surface and where the underlying mantle is twice the thickness of mantle normally associated with the continental crust. Geoscientists have proposed a variety of models to explain this relationship, sometimes invoking processes that are not very familiar on modern Earth. Here, Hugh Rollinson of the University of Derby proposes an elegant and simple model in which modern plate tectonic processes are slightly modified to accommodate a slightly hotter early Earth, and the familiar relationship between old crust and old mantle emerges as a consequence. It seems as though, with slight modifications, plate tectonics has been around for a long time.
Carbon isotope fractionation by circumneutral iron-oxidizing bacteria
Chris Kennedy et al., SRK Consulting, 25 Adelaide Street E., Toronto, Ontario M5C 3A1, Canada. Pages 1087-1090.
The ability to identify microbiological processes in the environment using isotopic ratios as "biosignatures" is important to a wide range of investigations, ranging from contaminant fate in aqueous systems to the study of ancient life on Earth and the possibility of life beyond our planet. Chris Kennedy of SRK Consulting and colleagues believe this is the first study of its kind to focus on the ability of bacteria to create a carbon biosignature in iron oxide minerals. Kennedy and colleagues investigated a range of sites, including submarine hydrothermal vents, a nuclear waste repository 500 m below the surface, groundwater seeps, and laboratory cultures of Gallionella ferruginea. Their results show that samples containing evidence of bacteria also possessed the most fractionated carbon, and one sample without bacteria contained the least fractionated carbon. The consistency of carbon isotope values in relation to the presence of bacteria from natural and laboratory samples is interpreted as the ability of these microorganisms to fractionate carbon, and this isotopic ratio holds promise as a viable biosignature in contemporary and paleo-environments.
Isotopic evidence of C4 grasses in southwestern Europe during the Early Oligocene-Middle Miocene
Michael A. Urban et al., Univ. of Maryland Center for Environmental Science, Appalachian Laboratory, 301 Braddock Road, Frostburg, Maryland 21532, USA. Pages 1091-1094.
C4 plants account for approximately 25% of terrestrial primary production on earth, dominate warm-climate grasslands, and include important crops such as maize. Thus, the evolution of the C4 photosynthetic pathway, which occurred first in the grass family, was a significant event in plant evolutionary history, according to Michael A. Urban of the University of Maryland and colleagues. Unlike the ancestral C3 pathway, the C4 pathway has a carbon-concentrating mechanism that provides C4 plants with a competitive advantage over C3 plants when atmospheric carbon dioxide concentrations are low. It has long been thought that declining atmospheric carbon dioxide concentrations in Earth's history should have caused, or been a precondition for, the origin of C4 grasses. But testing this idea using geological records has been challenging. Urban et al. employed a novel technique for analysis of carbon isotopes in individual grains of grass pollen extracted from Oligocene-Miocene sediments in southwestern Europe. They found that C4 grasses occurred on the landscape during the early Oligocene, about 14 million years earlier than previous isotopic evidence of first C4 plants, and before carbon dioxide concentrations fell during the Oligocene. So, rather than carbon dioxide concentrations, factors such as warm temperatures and/or aridity may have been important controls of the origin of C4 photosynthesis.
Marine osmium isotope record across the Triassic-Jurassic boundary from a Pacific pelagic site
Junichiro Kuroda et al., Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan. Pages 1095-1098.
The Triassic-Jurassic (T-J) boundary (about 200 million years ago) represents one of the major mass extinction events in Earth's history. In this study, Junichiro Kuroda of the Japan Agency for Marine-Earth Science and Technology and colleagues present an isotopic record of osmium of siliceous pelagic sediments deposited in an ancient Pacific deep basin. The osmium isotopic data suggest that a gradual increase in supply rate of osmium from the mantle has began a few million years before the T-J boundary, possibly because of the enhanced volcanic activity associated with the formation of the Central Atlantic Magmatic Province, which has been thought to be one of the world's largest basaltic provinces. Subsequently, the osmium isotopic record shows an abrupt shift immediately before the T-J boundary, suggesting a rapid increase in the rate of continental weathering. This interval marks abrupt perturbation of the global carbon cycle, the onset of radiolarian faunal turnover, and conodont extinctions. Although the massive eruptive episode has previously been considered the cause of mass extinction, Kuroda et al.'s data suggest that the rapid increase in continental weathering rate was more closely linked to the environmental and biotic crises across the T-J boundary.
Archean detrital zircons in the Proterozoic Vishnu Schist of the Grand Canyon, Arizona: Implications for crustal architecture and Nuna supercontinent reconstructions
Owen Shufeldt et al., Dept. of Earth and Planetary Sciences, Univ. of New Mexico, Albuquerque, New Mexico 87131, USA. Pages 1099-1102.
Researchers Owen Shufeldt and Karl Karlstrom of the University of New Mexico, George Gehrels of the University of Arizona, and Katherine Howard of the University of Adelaide present results from a detailed geochronologic investigation of one of the oldest rock units of the Grand Canyon, the Vishnu Schist. Their data reveal a large population of minerals that range from 1 to 2 billion years older than the rock itself. The ages of these minerals suggest an exotic source for the sedimentary material that became the Vishnu Schist. Possible provenances include Australia, North China, Antarctica, or older blocks within southwestern North America that are not presently exposed. The new data provide evidence for a more complex tectonic history of the southwest United States than presently accepted, including input from nearby cratons and the possibility of undiscovered ancient blocks mixed in with the Proterozoic terranes of southwestern Laurentia.
Eolian input into the Late Ordovician postglacial Soom Shale, South Africa
Sarah Gabbott et al., Dept. of Geology, Univ. of Leicester, Leicester, Leicestershire LE1 7RH, UK. Pages 1103-1106.
Near Table Mountain in South Africa lies one of the world's most mysterious rock layers. Just a few meters thick and almost half a billion years old, the rock layer contains the petrified remains of bizarre early life-forms, complete with eyes, guts, and muscles. Yet why are these animals so marvelously preserved when most fossils are just fragments of bone and shell? The answer seems to lie in a bitter wind, blowing off a landscape left devastated by a massive ice-cap. Microscopic analysis of the shale layers by Sarah Gabbott, Jan Zalasiewicz, and Richard Abbott of the University of Leicester, UK, along with Johannes Theron of the University of Stellenbosch, South Africa, reveal remarkable and so-far unique structures -- myriads of silt grains, neatly wrapped in the remains of marine algae. The silt grains are sedimentary aliens; much bigger than the marine mud flakes in which they are embedded. They could only have been blown by fierce glacial winds onto the sea surface from that distant landscape. Arriving thick and fast, they carried nutrients into the surface waters, fuelling its prolific life. The deep waters, though, were overwhelmed by rotting, sinking vegetation, becoming stagnant and lifeless -- ideal conditions to preserve the animal remains, down to their finest details. A cold wind, here, was key to both life and death.
Iodine to calcium ratios in marine carbonate as a paleo-redox proxy during oceanic anoxic events
Zunli Lu et al., Dept. of Earth Sciences, Univ. of Oxford, Parks Road, Oxford OX1 3PR, UK. Pages 1107-1110.
Iodine is a redox-sensitive halogen commonly found in seawater. Its dominant chemical form is iodide in anoxic conditions and iodate in oxic conditions. Zunli Lu, Hugh Jenkyns, and Rosalind E.M. Rickaby of the University of Oxford use calcite synthesis experiments to demonstrate that only iodate can be incorporated into carbonate minerals. A strong decrease in I/Ca ratios in marine limestone deposited during the early Toarcian, 183 million years ago, suggests that strong deoxygenation occurred in shallow waters of the European basin. Their finding supports the notion of Toarcian Oceanic Anoxic Events.
Nutrient trap for Late Cretaceous organic-rich black shales in the tropical North Atlantic
Alvaro Jimenez Berrocoso et al., Univ. of Manchester, Manchester, Lancashire M13 9PL, UK. Pages 1111-1114.
Neodymium isotopic ratios of Cretaceous fish debris indicate circulation patterns may have trapped nutrients in the tropical western Atlantic Ocean and, thus, stimulated productivity. The Cretaceous includes a well-known greenhouse interval characterized by global warmth, high sea level, and, in certain times and places, both oxygen depletion of bottom waters and accumulation of organic-rich sediments. Cretaceous rocks are often studied to illuminate greenhouse climate dynamics, but lack of constraints on ocean circulation has limited the understanding of circulation's role in the greenhouse climate system. In this study by Alvaro Jimenez Berrocoso of the University of Manchester and colleagues, neodymium isotopes of fossil fish debris from the Demerara Rise, a submarine plateau located in the tropical western Atlantic, were used to track ocean circulation. Results indicate the existence of a nutrient trap in intermediate waters (about 1000 m depth) of the tropical western Atlantic Ocean, controlled by circulation and without topographic barriers. The dynamic trapping model proposed by Jimenez Berrocoso et al. could explain why there was continuous deposition of organic-rich sediments on the Demerara Rise for up to 15 million years. Further, if true, it suggests a physical oceanographic mechanism that might contribute to high productivity on a basin-wide scale as suggested by the widespread, synchronous deposition of organic-rich sediments during oceanic anoxic events.
Two coexisting sulfur metabolisms in a ca. 3400 Ma sandstone
David Wacey et al., Centre for Microscopy, Characterisation and Analysis, Univ. of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia. Pages 1115-1118.
One of the most profound questions that science seeks to address is: what were the earliest types of life on Earth? This article by David Wacey of the University of Western Australia and colleagues provides two specific examples that appear to have been cohabiting in a 3.4 billion-year-old beach-like environment; namely, sulfate-reducing bacteria and sulfur disproportionating bacteria. Their evidence comes from multiple sulfur isotope analyses of tiny pyrite grains, measured using high-resolution mass spectrometry. These findings enhance the understanding of Earth's early biological evolution and help to calibrate the tree of life. This study also shows that one hitherto unexplored habitat holds exciting potential for preserving the first cells and their activities -- the earliest beach sands. This is particularly timely given the current investment and interest surrounding the search for signs of life on other planets. In showing that pyrite-rich sandstones can host primitive life, Wacey et al.'s findings may be able to refocus this search onto more suitable host rocks.
Manganese stromatolites in caves: El Soplao (Cantabria, Spain)
Carlos Rossi et al., Depto. de Petrologia Geoquimica, Facultad de Ciencias Geologicas, Universidad Complutense, 28040 Madrid, Spain. Pages 1119-1122.
Carlos Rossi of Madrid's Universidad Complutense and colleagues describe for the first time manganese-oxide stromatolites formed in the deep interior of a cave. Stromatolites are laminated sedimentary deposits induced by microbes, typically photosynthetic cyanobacteria (blue-green algae), and represent the earliest known record of life. Most stromatolites form, or are inferred to have formed, in marine and fluvio-lacustrine settings. However, in the dark regions of caves, stromatolites are virtually unknown. This is not surprising since the perpetual darkness of caves precludes photosynthesis, and the scarcity of organic matter and nutrients hinders the development of microbial communities. Nevertheless, in the El Soplao Cave (Cantabria, Spain), Rossi et al. have recently discovered stromatolites of decimetric thickness and kilometric extent. The El Soplao stromatolites are also remarkable because their biogenic origin is evidenced by the exceptional abundance and preservation of fossil microbes, which are not observed in most stromatolites. The El Soplao stromatolites are mainly formed by manganese oxides, and Rossi et al.'s data indicate that they were mainly induced by chemolithotrophic microbes. These microbes obtain their energy by catalyzing the oxidation of dissolved manganese ions, which allows them to synthesize organic compounds in the absence of light, creating an underground ecosystem essentially independent of sunlight that is beautifully fossilized in these stromatolites.
Lawsonite vorticity and subduction kinematics
Christian Teyssier et al., Univ. of Minnesota, Geology and Geophysics, Pillsbury Drive, Minneapolis, Minnesota 55455, USA. Pages 1123-1126.
The distribution and orientation of crystals of lawsonite, a mineral that crystallized at great depth (50-70 km) within a Cretaceous high-pressure belt in central Turkey (blueschist and very rare lawsonite eclogite), record a transition from shearing to flattening during the early stages of ascent of this subduction complex. Therefore, Christian Teyssier and colleagues from the University of Minnesota argue that flattening may participate in "squeezing" high-pressure rocks out of their site of formation and allowing them to reach Earth's surface sufficiently and rapidly, such that lawsonite eclogite is preserved. Based on strain modeling, this squeezing component may contribute significantly to the exhumation of high-pressure rocks.
Platinum ore in three dimensions: Insights from high-resolution X-ray computed tomography
Belinda Godel et al., CSIRO (Commonwealth Scientific and Industrial Research Organization) Earth Science and Resource Engineering, Australian Resources Research Centre, Kensington, Western Australia 6151, Australia. Pages 1127-1130.
Platinum and palladium are strategic metals that are used in various domains such as medicine (e.g., cancer treatments, pacemakers, and dentistry); jewelry; the automobile industry (catalytic converters); and other high-technology sectors. Most of the world's platinum and palladium is currently mined from a large body of igneous rock, where the metals in most cases appear as micrometer-scale minerals referred to as platinum-group minerals (PGM). CSIRO's Belinda Godel and colleagues present the first detailed 3-D in-situ analysis of the PGM at the sample scale using high-resolution X-ray computed tomography coupled with conventional microscopic and mineralogical study. Their results provide new insight on the genesis of platinum and palladium deposits.
Origin of Cl-bearing silica-rich melt inclusions in diamonds: Experimental evidence for an eclogite connection
Konstantin D. Litasov et al., Dept. of Earth and Planetary Material Science, Faculty of Science, Tohoku Univ., Sendai 980-8578, Japan. Pages 1131-1134.
Melting of a chloride- and carbonate-bearing eclogite at 7.0-10.5 GPa provides silicon dioxide-rich melt (up to 53 wt%) at relatively low degrees of melting. These compositions are comparable with those of silicic end member inclusions in fibrous diamonds worldwide, implying that they may be produced via chemical reactions of alkalic chloride-carbonate liquids with mantle eclogites. Experiments by Konstantin Litasov of Tohoku University and colleagues reproduce the trends of the compositional variations of the fluid or melt inclusions within eclogitic diamonds and thus suggest a reliable model for their origin. The role of water in this process should be examined in further experiments.
Evidence for Pleistocene lakes in the Tushka region, south Egypt
Ted Maxwell et al., Center for Earth and Planetary Studies, National Air and Space Museum, Box 37012, Smithsonian Institution, Washington, D.C. 20013, USA. Pages 1135-1138.
Throughout history, Egypt has been known as the "gift of the Nile" because of the annual floods of the Nile River. Now, based on Space Shuttle Radar Topographic Mission data, it appears that those floods started at a much earlier time -- a quarter million years ago -- and were much more extensive than has previously been thought. According to Ted Maxwell of the National Air and Space Museum and colleagues, newly processed topographic data show drainage channels in the desert more than 100 miles west of the Nile that end abruptly in the desert, where an ancient lake would have had its shoreline. This lake and subsequent lakes would have been larger than Lake Michigan, extending halfway across the Western Desert of Egypt. These "mega-lakes" explain the presence of fossil fish found 250 miles west of the Nile in the desert, the same species as those in the Nile. During the middle Pleistocene, rainfall in northeast Africa was in the range of 20 inches per year, enough to form scattered channels, but not enough to sustain lakes of this size. Instead, overflow of the Nile during peak seasons spilled over into the desert, providing the source for these standing bodies of water. The Western Desert today is hyperarid, where a few drops of rain may fall every decade, but not enough to sustain either plant or animal life, a stark contrast to its appearance 300,000 years ago.
Shallow magma accumulation at Kilauea Volcano, Hawai'i, revealed by microgravity surveys
Daniel J. Johnson et al., Hawaiian Volcano Observatory, U.S. Geological Survey, Hawai'i Volcanoes National Park, Hawaii 96718, USA. Pages 1139-1142.
Microgravity measurements on volcanoes can reveal changes in the distribution of subsurface mass over time. Specifically, increases in gravity can be tied to magma accumulation in the subsurface, while gravity decreases may indicate subsurface withdrawal of magma. At Kilauea Volcano, Hawai'i, microgravity surveys of a large network of stations in the summit area were conducted in 1975, 1981, 1998, 2003, and 2008. Analyses of these data indicate a long-term gravity increase near the center of the caldera, suggesting shallow (about 1 km depth) magma accumulation. Surprisingly, surface uplift, which would be expected to accompany magmatic intrusion, was not measured in the same area. The presence of a gravity increase in the absence of uplift implies that magma was filling void spaces in the subsurface -- a result that would not have been recognized from either data set individually. Kilauea's current summit eruption, which began in 2008, appears to tap this zone of magma storage. These gravity results from Kilauea, presented here by Daniel Johnson of the Hawaiian Volcano Observatory and colleagues, reaffirm the importance of this technique as a monitoring tool on active volcanoes.
Experimental evidence for the simultaneous formation of pseudotachylyte and mylonite in the brittle regime
Jong-Wook Kim et al., Dept. of Earth and Environmental Sciences, Korea University, Seoul 136-701, South Korea. Pages 1143-1146.
Jong-Wook Kim of Korea University and colleagues report the first high-velocity friction experiments that simultaneously generated two incompatible fault rocks: mylonite and pseudotachylyte. Pseudotachylyte is a cooled frictional melt formed by seismic fault motion in the brittle regime, whereas mylonite is an aseismic fault rock produced in the plastic or semiplastic regime. Their coexistence in natural fault zones has been an enigma, and Kim et al.'s experiments indicate that mylonite can be generated with enhanced plastic deformation aided by heat conducted from the molten layer (pseudotachylyte) of the principal slip zone.
GSA Today Science Article
Geoinformatics: Transforming data to knowledge for geosciences
A. Krishna Sinha et al., Dept. of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA. Pages 4-10.
In this short but timely contribution, A. Krishna Sinha of Virginia Tech and colleagues propose an informatics system that would allow the seamless melding and interpretation of data from disparate fields in the sciences. For them, it is all about integration -- the establishment of an infrastructure system to facilitate communication, to transform, as they say, "data into knowledge." The authors argue persuasively that the solutions to the most significant problems currently facing us are fundamentally multidisciplinary and that these different disciplines commonly use different languages. An example, that of Quito, Ecuador, shows the criticality of communication by geoscientists -- who might be concerned with natural disasters such as volcanism or flooding -- with other disciplines, such as epidemiology, so that medical attention can be prompt and effective. Recent events in Haiti, for example, underscore the importance of the authors' approach. For the authors, the problem is one of semantics -- that is, the development of an integrated machine and Web language that pertains to all sciences and scientists, so that data can be not only displayed, but understood. The vision of the authors "is to create a fully integrated geosciences information network with free access to Earth-science related data, tools, and services."
Provided by Geological Society of America