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Mapping the Moho With GOCE

This map shows the global Mohorovičić discontinuity – known as Moho – based on data from the GOCE satellite. Moho is the boundary between the crust and the mantle, ranging from about 70 km in depth in mountainous areas, like the Himalayas, to 10 km beneath the ocean floor. (Credit: GEMMA project)
The first global high-resolution map of the boundary between Earth’s crust and mantle — the Moho — has been produced based on data from ESA’s GOCE gravity satellite. Understanding the Moho will offer new clues into the dynamics of Earth’s interior.
Earth’s crust is the outermost solid shell of our planet. Even though it makes up less than 1% of the volume of the planet, the crust is exceptionally important not just because we live on it, but because is the place where all our geological resources like natural gas, oil and minerals come from.
The crust and upper mantle is also the place where most geological processes of great importance occur, such as earthquakes, volcanism and orogeny.
Until just a century ago, we didn’t know Earth has a crust. In 1909, Croatian seismologist Andrija Mohorovičić found that at about 50 km underground there is a sudden change in seismic speed.
Ever since, that boundary between Earth’s crust and underlying mantle has been known as the Mohorovičić discontinuity, or Moho.
Even today, almost all we know about Earth’s deep layers comes from two methods: seismic and gravimetric.
Seismic methods are based on observing changes in the propagation velocity of seismic waves between the crust and mantle.
Gravimetry looks at the gravitational effect due to the density difference caused by the changing composition of crust and mantle.
But the Moho models based on seismic or gravity data are usually limited by poor data coverage or data being only available along single profiles.
The GOCE Exploitation for Moho Modelling and Applications project — or GEMMA — has now generated the first global high-resolution map of the boundary between Earth’s crust and mantle based on data from the GOCE satellite.
GOCE measures the gravity field and models the geoid with unprecedented accuracy to advance our knowledge of ocean circulation, which plays a crucial role in energy exchanges around the globe, sea-level change and Earth interior processes.
GEMMA’s Moho map is based on the inversion of homogenous well-distributed gravimetric data.
For the first time, it is possible to estimate the Moho depth worldwide with unprecedented resolution, as well as in areas where ground data are not available. This will offer new clues for understanding the dynamics of Earth’s interior, unmasking the gravitational signal produced by unknown and irregular subsurface density distribution.
GEMMA is being carried out by Italian scientist Daniele Sampietro, and is funded by the Politecnico di Milano and ESA’s Support To Science Element under the Changing Earth Science Network initiative.
This initiative supports young scientists at post-doctoral level in ESA Member States to advance our knowledge in Earth system science by exploiting the observational capacity of ESA missions.
Note : The above story is reprinted from materials provided by European Space Agency (ESA), via AlphaGalileo. 

Internal Structure of the Moon

An artist’s rendering of the lunar core as identified in new findings by a NASA-led research team. (NASA/MSFC/Renee Weber)

Apollo Data Revealed Moon’s Internal Structure:

NASA deployed the frist seismographs on the moon as part of the Apollo Mission in 1969. These seismographs collected data and enabled researchers to determine that the moon’s structure consisted of a thin crust of about 65 kilometers, a mantle about 100 kilometers thick and a core with a radius of about 500 kilometers. At that time seismic data processing was not advanced enough to determine the characteristics of the core.

NASA researchers have recently applied state-of-the-art seismological techniques applied to the Apollo-era data and discovered that the moon probably has a core that is very similar to Earth’s.

Moon’s Formation and Magnetic Field :

Uncovering details about the lunar core is critical for developing accurate models of the moon’s formation. The data sheds light on the evolution of a lunar dynamo — a natural process by which our moon may have generated and maintained its own strong magnetic field.

The team’s findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles. The research indicates the core contains a small percentage of light elements such as sulfur, echoing new seismology research on Earth that suggests the presence of light elements — such as sulfur and oxygen — in a layer around our own core.

Data from Apollo-Era Seismometers :

The researchers used extensive data gathered during the Apollo-era moon missions. The Apollo Passive Seismic Experiment consisted of four seismometers deployed between 1969 and 1972, which recorded continuous lunar seismic activity until late-1977.
“We applied tried and true methodologies from terrestrial seismology to this legacy data set to present the first-ever direct detection of the moon’s core,” said Renee Weber, lead researcher and space scientist at NASA’s Marshall Space Flight Center in Huntsville, Ala.
The team also analyzed Apollo lunar seismograms using array processing, techniques that identify and distinguish signal sources of moonquakes and other seismic activity. The researchers identified how and where seismic waves passed through or were reflected by elements of the moon’s interior, signifying the composition and state of layer interfaces at varying depths.

Comparison with Apollo-Era Results :

Although sophisticated satellite imaging missions to the moon made significant contributions to the study of its history and topography, the deep interior of Earth’s sole natural satellite remained a subject of speculation and conjecture since the Apollo era. Researchers previously had inferred the existence of a core, based on indirect estimates of the moon’s interior properties, but many disagreed about its radius, state and composition.
A primary limitation to past lunar seismic studies was the wash of “noise” caused by overlapping signals bouncing repeatedly off structures in the moon’s fractionated crust. To mitigate this challenge, Weber and the team employed an approach called seismogram stacking, or the digital partitioning of signals. Stacking improved the signal-to-noise ratio and enabled the researchers to more clearly track the path and behavior of each unique signal as it passed through the lunar interior.
“We hope to continue working with the Apollo seismic data to further refine our estimates of core properties and characterize lunar signals as clearly as possible to aid in the interpretation of data returned from future missions,” Weber said.

New Data From the GRAIL Mission : Future NASA missions will help gather more detailed data. The Gravity Recovery and Interior Laboratory, or GRAIL, is a NASA Discovery-class mission set to launch this year. The mission consists of twin spacecraft that will enter tandem orbits around the moon for several months to measure the gravity field in unprecedented detail. The mission also will answer longstanding questions about Earth’s moon and provide scientists a better understanding of the satellite from crust to core, revealing subsurface structures and, indirectly, its thermal history.

The Research Team : 

In addition to Weber, the team consisted of scientists from Marshall; Arizona State University; the University of California at Santa Cruz; and the Institut de Physique du Globe de Paris in France. Their findings are published in the online edition of the journal Science.

NASA and other space agencies have been studying concepts to establish an International Lunar Network — a robotic set of geophysical monitoring stations on the moon — as part of efforts to coordinate international missions during the coming decade

Note : Republished from a January, 2011 press release by NASA.

New Research Supports Theory of Extraterrestrial Impact

The ‘tectonic’ effects of the collision of one spherule with another during the cosmic impact. (Credit: Image courtesy of University of California – Santa Barbara)
A 16-member international team of researchers that includes James Kennett, professor of earth science at UC Santa Barbara, has identified a nearly 13,000-year-old layer of thin, dark sediment buried in the floor of Lake Cuitzeo in central Mexico. The sediment layer contains an exotic assemblage of materials, including nanodiamonds, impact spherules, and more, which, according to the researchers, are the result of a cosmic body impacting Earth.
These new data are the latest to strongly support of a controversial hypothesis proposing that a major cosmic impact with Earth occurred 12,900 years ago at the onset of an unusual cold climatic period called the Younger Dryas. The researchers’ findings appear  in the Proceedings of the National Academy of Sciences.
Conducting a wide range of exhaustive tests, the researchers conclusively identified a family of nanodiamonds, including the impact form of nanodiamonds called lonsdaleite, which is unique to cosmic impact. The researchers also found spherules that had collided at high velocities with other spherules during the chaos of impact. Such features, Kennett noted, could not have formed through anthropogenic, volcanic, or other natural terrestrial processes. “These materials form only through cosmic impact,” he said.
The data suggest that a comet or asteroid — likely a large, previously fragmented body, greater than several hundred meters in diameter — entered the atmosphere at a relatively shallow angle. The heat at impact burned biomass, melted surface rocks, and caused major environmental disruption. “These results are consistent with earlier reported discoveries throughout North America of abrupt ecosystem change, megafaunal extinction, and human cultural change and population reduction,” Kennett explained.
The sediment layer identified by the researchers is of the same age as that previously reported at numerous locations throughout North America, Greenland, and Western Europe. The current discovery extends the known range of the nanodiamond-rich layer into Mexico and the tropics. In addition, it is the first reported for true lake deposits.
In the entire geologic record, there are only two known continent-wide layers with abundance peaks in nanodiamonds, impact spherules, and aciniform soot. These are in the 65-million-year-old Cretaceous-Paleogene boundary layer that coincided with major extinctions, including the dinosaurs and ammonites; and the Younger Dryas boundary event at 12,900 years ago, closely associated with the extinctions of many large North American animals, including mammoths, mastodons, saber-tooth cats, and dire wolves.
“The timing of the impact event coincided with the most extraordinary biotic and environmental changes over Mexico and Central America during the last approximately 20,000 years, as recorded by others in several regional lake deposits,” said Kennett. “These changes were large, abrupt, and unprecedented, and had been recorded and identified by earlier investigators as a ‘time of crisis.’ “
Other scientists contributing to the research include Isabel Israde-Alcántara and Gabriela Dominguez-Vásquez of the Universidad Michoacana de San Nicólas de Hidalgo; James L. Bischoff of the U.S. Geological Survey; Hong-Chun Li of National Taiwan University; Paul S. DeCarli of SRI International; Ted E. Bunch and James H. Wittke of Northern Arizona University; James C. Weaver of Harvard University; Richard B.
Firestone of Lawrence Berkeley National Laboratory; Allen West of GeoScience Consulting; Chris Mercer of the National Institute for Materials Science; Sujing Zie and Eric K. Richman of the University of Oregon, Eugene; and Charles R. Kinzie and Wendy S. Wolbach of DePaul University.
Note : The above story is reprinted from materials provided by University of California – Santa Barbara.  

Contamination of La Selva geothermal system in Girona, Spain

The system works by refilling meteoric waters that penetrate the earth in high areas, move underground and reach an unknown thermal hot spot, where they heat up and acquire CO2, and probably metals as well. Afterwards the water leaches out (dissolve) the host rocks and flows out from the upwellings. – SINC/A. Navarro et al.
Monitoring the construction of wells, avoid over-exploiting cold groundwater close to hot groundwater, and controlling mineral water extraction. These are the recommendations from the Polytechnic University of Catalonia and the University of Barcelona, after analyzing the contamination of La Selva geothermal system, above all by arsenic pollution. In this region, which is known for its spa resorts and bottling plants, as well as in other Catalan coastal mountain ranges, uranium levels higher than what is recommended by the WHO have been detected.

The groundwater in La Selva (Girona, Spain) area show high levels of arsenic, antimony and other polluting elements. The area’s geothermal system, where hot and cold groundwater flow naturally, are the cause of this situation, according to a study that researchers from the Polytechnic University of Catalonia (UPC) and the University of Barcelona (UB) have published in the journal Geothermics.

“The system works by refilling meteoric waters that penetrate the earth in high areas, move underground and reach an unknown thermal hot spot, where they heat up and acquire CO2, and probably metals as well “Andrés Navarro, a lecturer at UPC and co-author of the project explained to SINC. “Afterwards the water leaches out (dissolve) the host rocks and flows out from the upwellings”.
In this process the waters naturally pick up pollutants. Consequently, the researchers have found high volumes of arsenic, silver, lead, antimony, zinc and other metals in the hydrothermal deposits, especially in the area of Caldes de Malavella (Girona), an area famous for its spa resorts and mineral water bottling companies.
The results show that groundwater in some areas has arsenic levels of up to 0.069 mg/l, when the legal limit in Spain and the rest of the European Union was 0.01 mg/l in water for human consumption.
“Fortunately, a few years ago a legislation for this was created, and since then bottled mineral has been controlled, although before then this did not occur” the researcher says. Furthermore, a plant to remove arsenic from public water supplies has been built in Caldes de Malavella.
In any case, the study recommends controlling the extraction of water for bottling plants, as well as over-exploiting cold groundwater close to hot water springs. This way the mixing of waters is avoided and so are the pollutants.
For the same reason it is not advisable to build wells close to geothermal upwellings, especially illegal ones for private supplies or irrigation. Studying geothermal liquid outlets in areas of diffused discharge, such as some humid areas, is also proposed.
“Making a model for managing the whole aquifer to rationalize water extraction and consumption would be the solution” Navarro says. He also highlights the need to take action regarding the natural water pollutants: uranium.
The analysis in La Selva shows “relatively high” levels (37.7 microg/l) of this element, especially in samples from sources and wells not directly linked to thermal activity.
The mobility of uranium is linked to granite rocks and is frequently found in Catalan coastal mountain ranges, where researchers have carried out specific studies on the topic. The samples have been taken from wells and drilling at a depth of up to 100 metres.
The results published in the journal Tecnología del agua and they show “significant concentrations” of uranium in groundwater used for public supply and bottling. Specifically, in some parts of the Montseny-Guilleries mountain range, these levels are more than 140 microg/l.
There are no legal limits for uranium concentrations in water in the European Union, but the analysis carried out in Catalan coastal mountain ranges shows that these levels far exceed the recommendations of the World Health Organisation (WHO), or for example, the standard established by the Environmental Protection Agency (EPA) in the USA.
Both the EPA and the WHO establish a maximum uranium level of 30 microg/l. The European Food Safety Authority (EFSA) is considering establishing a guideline level for this element, but at the moment the legal loophole remains.
The toxicity of uranium is linked to the solubility of the compound: the more soluble it is, the more toxic it is. The experiments carried out on animals and people show the most affected organ is the kidney, and alterations in reproduction and development are seen when this element exists in high concentrations.
Note: This story has been adapted from a news release issued by the FECYT – Spanish Foundation for Science and Technology

Thickest Parts of Arctic Ice Cap Melting Faster

How perennial sea ice has declined from 1980 to 2012. The bright white central mass shows the perennial sea ice while the larger light blue area shows the full extent of the winter sea ice including the average annual sea ice during the months of November, December and January. (Credit: NASA/Goddard Scientific Visualization Studio)
A new NASA study revealed that the oldest and thickest Arctic sea ice is disappearing at a faster rate than the younger and thinner ice at the edges of the Arctic Ocean’s floating ice cap.
The thicker ice, known as multi-year ice, survives through the cyclical summer melt season, when young ice that has formed over winter just as quickly melts again. The rapid disappearance of older ice makes Arctic sea ice even more vulnerable to further decline in the summer, said Joey Comiso, senior scientist at NASA Goddard Space Flight Center, Greenbelt, Md., and author of the study, which was recently published in Journal of Climate.
The new research takes a closer look at how multi-year ice, ice that has made it through at least two summers, has diminished with each passing winter over the last three decades. Multi-year ice “extent” — which includes all areas of the Arctic Ocean where multi-year ice covers at least 15 percent of the ocean surface — is diminishing at a rate of -15.1 percent per decade, the study found.
There’s another measurement that allows researchers to analyze how the ice cap evolves: multi-year ice “area,” which discards areas of open water among ice floes and focuses exclusively on the regions of the Arctic Ocean that are completely covered by multi-year ice. Sea ice area is always smaller than sea ice extent, and it gives scientists the information needed to estimate the total volume of ice in the Arctic Ocean. Comiso found that multi-year ice area is shrinking even faster than multi-year ice extent, by -17.2 percent per decade.
“The average thickness of the Arctic sea ice cover is declining because it is rapidly losing its thick component, the multi-year ice. At the same time, the surface temperature in the Arctic is going up, which results in a shorter ice-forming season,” Comiso said. “It would take a persistent cold spell for most multi-year sea ice and other ice types to grow thick enough in the winter to survive the summer melt season and reverse the trend.”
Scientists differentiate multi-year ice from both seasonal ice, which comes and goes each year, and “perennial” ice, defined as all ice that has survived at least one summer. In other words: all multi-year ice is perennial ice, but not all perennial ice is multi-year ice (it can also be second-year ice).
Comiso found that perennial ice extent is shrinking at a rate of -12.2 percent per decade, while its area is declining at a rate of -13.5 percent per decade. These numbers indicate that the thickest ice, multiyear-ice, is declining faster than the other perennial ice that surrounds it.
As perennial ice retreated in the last three decades, it opened up new areas of the Arctic Ocean that could then be covered by seasonal ice in the winter. A larger volume of younger ice meant that a larger portion of it made it through the summer and was available to form second-year ice. This is likely the reason why the perennial ice cover, which includes second year ice, is not declining as rapidly as the multiyear ice cover, Comiso said.
Multi-year sea ice hit its record minimum extent in the winter of 2008. That is when it was reduced to about 55 percent of its average extent since the late 1970s, when satellite measurements of the ice cap began. Multi-year sea ice then recovered slightly in the three following years, ultimately reaching an extent 34 percent larger than in 2008, but it dipped again in winter of 2012, to its second lowest extent ever.
For this study, Comiso created a time series of multi-year ice using 32 years of passive microwave data from NASA’s Nimbus-7 satellite and the U.S. Department of Defense’s Defense Meteorological Satellite Program, taken during the winter months from 1978 to 2011. This is the most robust and longest satellite dataset of Arctic sea ice extent data to date, Comiso said.
Younger ice, made from recently frozen ocean waters, is saltier than multi-year ice, which has had more time to drain its salts. The salt content in first- and second-year ice gives them different electrical properties than multi-year ice: In winter, when the surface of the sea ice is cold and dry, the microwave emissivity of multiyear ice is distinctly different from that of first- and second-year ice. Microwave radiometers on satellites pick up these differences in emissivity, which are observed as variations in brightness temperature for the different types of ice. The “brightness” data are used in an algorithm to discriminate multiyear ice from other types of ice.
Comiso compared the evolution of the extent and area of multi-year ice over time, and confirmed that its decline has accelerated during the last decade, in part because of the dramatic decreases of 2008 and 2012. He also detected a periodic nine-year cycle, where sea ice extent would first grow for a few years, and then shrink until the cycle started again. This cycle is reminiscent of one occurring on the opposite pole, known as the Antarctic Circumpolar Wave, which has been related to the El Niño-Southern Oscillation atmospheric pattern. If the nine-year Arctic cycle were to be confirmed, it might explain the slight recovery of the sea ice cover in the three years after it hit its historical minimum in 2008, Comiso said.
Note : The above story is reprinted from materials provided by NASA/Goddard Space Flight Center.  

Albite

Albite , Plagioclase Location: Taquaral, Minas Gerais, Brazil. Scale: 7.4 x 5 cm. Copyright: © John Veevaert

Chemical Formula: NaAlSi3O8
Locality: Finnbo, Falun, Dalarna, Sweden. Bourg d’Oisans and Isere, France.
Name Origin: From the Latin, albus, in allusion to the common color.

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence its name from Latin albus. It is a common constituent in felsic rocks.

Albite crystallizes with triclinic pinacoidal forms. Its specific gravity is about 2.62 and it has a Mohs hardness of 6 – 6.5. Albite almost always exhibits crystal twinning often as minute parallel striations on the crystal face. Albite often occurs as fine parallel segregations alternating with pink microcline in perthite as a result of exolution on cooling.

It occurs in granitic and pegmatite masses, in some hydrothermal vein deposits and forms part of the typical greenschist metamorphic facies for rocks of originally basaltic composition.

It was first reported in 1815 for an occurrence in Finnbo, Falun, Dalarna, Sweden.

Physical Properties

Cleavage: {001} Perfect, {010} Good
Color:     White, Gray, Greenish gray, Bluish green, Gray.
Density: 2.61 – 2.63, Average = 2.62
Diaphaneity: Transparent to translucent to subtranslucent
Fracture: Uneven – Flat surfaces (not cleavage) fractured in an uneven pattern.
Hardness: 7 – Quartz
Luminescence: Fluorescent, Short UV=herry-red blue, Long UV=white.
Luster: Vitreous (Glassy)
Streak: white

Photos:

Serandite with Aegirine and Albite Specimen size: 5.4 × 2.7 × 2.6 cm © Fabre Minerals
Serandite, Albite, Aegerine 2.5×1.6×1.9 cm Mont Saint-Hilaire Quebec, Canada Copyright © David K. Joyce Minerals
Albite (var. Pericline), Fiesch, Goms, Wallis, Switzerland Specimen weight:94 gr. Crystal size:28 mm Overall size: 84mm x 68 mm x 50 mm minservice
Serandite, Albite, Aegerine 2.5×1.6×1.9 cm Mont Saint-Hilaire Quebec, Canada Copyright © David K. Joyce Minerals

Salty Soil Can Suck Water out of Atmosphere: Could It Happen On Mars?

McMurdo Dry Valleys. These wet patches in Antarctica’s McMurdo Dry Valleys are created by the salty soils sucking water out of the atmosphere. (Credit: Joseph Levy, Oregon State University)
The frigid McMurdo Dry Valleys in Antarctica are a cold, polar desert, yet the sandy soils there are frequently dotted with moist patches in the spring despite a lack of snowmelt and no possibility of rain.
A new study, led by an Oregon State University geologist, has found that that the salty soils in the region actually suck moisture out of the atmosphere, raising the possibility that such a process could take place on Mars or on other planets.
The study, which was supported by the National Science Foundation, has been published online this week in the journal Geophysical Research Letters, and will appear in a forthcoming printed edition.
Joseph Levy, a post-doctoral researcher in OSU’s College of Earth, Ocean, and Atmospheric Sciences, said it takes a combination of the right kinds of salts and sufficient humidity to make the process work. But those ingredients are present on Mars and, in fact, in many desert areas on Earth, he pointed out.
“The soils in the area have a fair amount of salt from sea spray and from ancient fjords that flooded the region,” said Levy, who earned his doctorate at Brown University. “Salts from snowflakes also settle into the valleys and can form areas of very salty soil. With the right kinds of salts, and enough humidity, those salty soils suck the water right out of the air.
“If you have sodium chloride, or table salt, you may need a day with 75 percent humidity to make it work,” he added. “But if you have calcium chloride, even on a frigid day, you only need a humidity level above 35 percent to trigger the response.”
Once a brine forms by sucking water vapor out of the air, Levy said, the brine will keep collecting water vapor until it equalizes with the atmosphere.
“It’s kind of like a siphon made from salt.”
Levy and his colleagues, from Portland State University and Ohio State University, found that the wet soils created by this phenomenon were 3-5 times more water-rich than surrounding soils — and they were also full of organic matter, including microbes, enhancing the potential for life on Mars. The elevated salt content also depresses the freezing temperature of the groundwater, which continues to draw moisture out of the air when other wet areas in the valleys begin to freeze in the winter.
Though Mars, in general, has lower humidity than most places on Earth, studies have shown that it is sufficient to reach the thresholds that Levy and his colleagues have documented. The salty soils also are present on the Red Planet, which makes the upcoming landing of the Mars Science Laboratory this summer even more tantalizing.
Levy said the science team discovered the process as part of “walking around geology” — a result of observing the mysterious patches of wet soil in Antarctica, and then exploring their causes. Through soil excavations and other studies, they eliminated the possibility of groundwater, snow melt, and glacial runoff. Then they began investigating the salty properties of the soil, and discovered that the McMurdo Dry Valleys weather stations had reported several days of high humidity earlier in the spring, leading them to their discovery of the vapor transfer.
“It seems kind of odd, but it really works,” Levy said. “Before one of our trips, I put a bowl of the dried, salty soil and a jar of water into a sealed Tupperware container and left it on my shelf. When I came back, the water had transferred from the jar to the salt and created brine.
“I knew it would work,” he added with a laugh, “but somehow it still surprised me that it did.”
Evidence of the salty nature of the McMurdo Dry Valleys is everywhere, Levy said. Salts are found in the soils, along seasonal streams, and even under glaciers. Don Juan Pond, the saltiest body of water on Earth, is found in Wright Valley, the valley adjacent to the wet patch study area.
“The conditions for creating this new water source into the permafrost are perfect,” Levy said, “but this isn’t the only place where this could or does happen. It takes an arid region to create the salty soils, and enough humidity to make the transference work, but the rest of it is just physics and chemistry.”
Other authors on the study include Andrew Fountain, Portland State University, and Kathy Welch and W. Berry Lyons, Ohio State University.
Note : The above story is reprinted from materials provided by Oregon State University. 

When Continents Collide: New Twist to 50-Million-Year-Old Tale

The eastern Himalaya Mountains. These mountains formed soon after India collided with Asia 50 million years ago. (Credit: Marin Clark)
Fifty million years ago, India slammed into Eurasia, a collision that gave rise to the tallest landforms on the planet, the Himalaya Mountains and the Tibetan Plateau.
India and Eurasia continue to converge today, though at an ever-slowing pace. University of Michigan geomorphologist and geophysicist Marin Clark wanted to know when this motion will end and why. She conducted a study that led to surprising findings that could add a new wrinkle to the well-established theory of plate tectonics — the dominant, unifying theory of geology.
“The exciting thing here is that it’s not easy to make progress in a field (plate tectonics) that’s 50 years old and is the major tenet that we operate under,” said Clark, an assistant professor in the Department of Earth and Environmental Sciences in the College of Literature, Science, and the Arts.
“The Himalaya and Tibet are the highest mountains today on Earth, and we think they’re probably the highest mountains in the last 500 million years,” she said. “And my paper is about how this is going to end and what’s slowing down the Indian plate.”
Clark’s paper is scheduled for online publication Feb. 29 in the journal Nature.
In it, she suggests that the strength of the underlying mantle, not the height of the mountains, is the critical factor that will determine when the Himalayan-Tibetan mountain-building episode ends. Earth’s mantle is the thick shell of rock that separates the crust above from the core below.
According to the theory of plate tectonics, the outer part of Earth is broken into several large plates, like pieces of cracked shell on a boiled egg. The continents ride on the plates, which move relative to one another and occasionally collide. The tectonic plates move about as fast as your fingernails grow, and intense geological activity — volcanoes, earthquakes and mountain-building, for example — occurs at the plate boundaries.
The rate at which the Indian sub-continent creeps toward Eurasia is slowing exponentially, according to Clark, who reviewed published positions of northern India over the last 67 million years to evaluate convergence rates. The convergence will halt — putting an end to one of the longest periods of mountain-building in recent geological history — in about 20 million years, she estimates.

And what will cause it to stop?

Until now, conventional wisdom among geologists has been that the slowing of convergence at mountainous plate boundaries was related to changes in the height of the mountains. As the mountains grew taller, they exerted an increasing amount of force on the plate boundary, which slowed the convergence.
But in her Nature paper, Clark posits that a different model, one based on the strength of the uppermost mantle directly beneath the mountains, best explains the observed post-collisional motions of the Indian plate.
By “strength” Clark means the uppermost mantle’s ability to withstand deformation, a property called viscous resistance. Clark suggests that the relatively strong mantle directly beneath Tibet and the Himalayas acts as a brake that slows — and will eventually halt — the convergence of the two continents.
“My paper is arguing that it’s not the height of the mountains, it’s the strength of the mantle that’s controlling this slowing,” Clark said. “This is something that hasn’t been considered before and basically grew out of field observations in northern Tibet.”
But viscous resistance doesn’t tell the whole story. Other factors may also contribute to the slowing of the Indian plate, Clark said.
“For me, critical field observations showed that the northern edge of the Tibetan Plateau hasn’t moved since the collision 50 million years ago,” she said. “Therefore, the Tibetan Plateau is getting smaller in width. It’s like squeezing a box and making it narrower while squeezing it up.”
The rate at which the box is being squeezed is the average rate of mountain-building, and it provides important clues about the factors controlling plate motion. Clark analyzed how the convergence is slowing as compared to the shrinking of the plateau.
“If the height of the mountains were important in slowing India’s convergence, then the rate of mountain-building should also slow down as the Himalaya and Tibet grew to high elevation,” Clark said. “But when I analyzed how the mountain-building rate changed over the past 50 million years, I was surprised to find that it didn’t change at all.
“From this I conclude that the strength of the uppermost mantle is keeping this mountain- building constant. But as the box is shrinking, the plate motion must slow down to keep the shrinking rate the same,” she said.
Support for the research was provided by the National Science Foundation’s Continental Dynamics Program.
Note : The above story is reprinted from materials provided by University of Michigan, via Newswise. The original article was written by Jim Erickson. 

Volcanoes Deliver Two Flavors of Water

Volcanic eruption. (Credit: © bierchen / Fotolia)
Seawater circulation pumps hydrogen and boron into the oceanic plates that make up the seafloor, and some of this seawater remains trapped as the plates descend into the mantle at areas called subduction zones. By analyzing samples of submarine volcanic glass near one of these areas, scientists found unexpected changes in isotopes of hydrogen and boron from the deep mantle. They expected to see the isotope “fingerprint” of seawater.
But in volcanoes from the Manus Basin they also discovered evidence of seawater distilled long ago from a more ancient plate descent event, preserved for as long as 1 billion years. The data indicate that these ancient oceanic “slabs” can return to the upper mantle in some areas, and that rates of hydrogen exchange in the deep Earth may not conform to experiments.
The research is published in the February 26, 2012, advanced on line publication of Nature Geoscience.
As Carnegie coauthor Erik Hauri explained, “Hydrogen and boron have both light and heavy isotopes. Isotopes are atoms of the same element with different numbers of neutrons. The volcanoes in the Manus Basin are delivering a mixture of heavy and light isotopes that have been observed nowhere else. The mantle under the Manus Basin appears to contain a highly distilled ancient water that is mixing with modern seawater.”
When seawater-soaked oceanic plates descend into the mantle, heavy isotopes of hydrogen and boron are preferentially distilled away from the slab, leaving behind the light isotopes, but also leaving it dry and depleted of these elements, making the “isotope fingerprint” of the distillation process difficult to identify. But this process appears to have been preserved in at least one area: submarine volcanoes in the Manus Basin of Papua New Guinea, which erupted under more than a mile of seawater (2,000 meters). Those pressures trap water from the deep mantle within the volcanic glass.
Lead author Alison Shaw and coauthor Mark Behn, both former Carnegie postdoctoral researchers, recognized another unique feature of the data. Lab experiments have shown very high diffusion rates for hydrogen isotopes, which move through the mantle as tiny protons. This diffusion should have long-ago erased the hydrogen isotope differences observed in the Manus Basin volcanoes.
“That is what we typically see at mid-ocean ridges,” remarked Hauri. “But that is not what we found at Manus Basin. Instead we found a huge range in isotope abundances that indicates hydrogen diffusion in the deep Earth may not be analogous to what is observed in the lab.”
The team’s * finding means is that surface water can be carried into the deep Earth by oceanic plates and be preserved for as long as 1 billion years.
They also indicate that the hydrogen diffusion rates in the deep Earth appear to be much slower than experiments show. It further suggests that these ancient slabs may not only return to the upper mantle in areas like the Manus Basin, they may also come back up in hotspot volcanoes like Hawaii that are produced by mantle plumes.
The results are important to understanding how water is transferred and preserved in the mantle and how it and other chemicals are recycled to the surface.
*Other researchers on the team include lead author A.M. Shaw and M.D. Behn from Woods Hole Oceanographic Institution, D.R. Hilton Scripps Institution of Oceanography and UC San Diego, C.G. Macpherson Durham University, and J.M. Sinton University of Hawaii.
Note : The above story is reprinted from materials provided by Carnegie Institution. 

Erosional Origin of Linear Dunes On Earth and Saturn’s Moon Titan

Artificially excavated cross sections showing internal structures of linear dunes (Fig. 2 of Zhou et al.). (Credit: Image courtesy of Geological Society of America)
Linear dunes, widespread on Earth and Saturn’s moon, Titan, are generally considered to have been formed by deposits of windblown sand. It has been speculated for some time that some linear dunes may have formed by “wind-rift” erosion, but this model has commonly been rejected due to lack of sufficient evidence. Now, new research supported by China’s NSF and published this week in GSA BULLETIN indicates that erosional origin models should not be ruled out.
The linear dunes in China’s Qaidam Basin have been proposed to have formed as self-extending lee dunes under a unidirectional wind regime owing to a high level of total silt, clay, and salt content or cohesiveness of sediments, and they have undergone southward lateral migration at rates of up to 3 m/yr.
New GSA BULLETIN research examines the sediments, internal structures, and optically stimulated luminescence ages of the linear dunes in the central Qaidam Basin approximately 80 km north of the city Golmud. The study’s findings suggest that the linear dunes are most likely of erosional origin similar to yardangs with orientations controlled by strikes of joints.
According to the study’s lead author, Jianxun Zhou of the China University of Petroleum’s State Key Laboratory of Petroleum Resource & Prospecting, “If the control of tectonic structures on the orientation of wind-eroded ridges is taken into account, morphodynamic interpretations for the wind-rift model may become much simpler.
No one has considered the possibility of erosional origin for the linear dunes on Titan. Nearly all researchers consider the linear dunes on Titan to be of depositional origin, but their morphodynamic interpretations are complicated and their relationships to wind directions are in dispute.
If an erosional origin is considered, the morphodynamic interpretations of the linear dunes on Titan can also be greatly simplified.”
Note:The above story is reprinted from materials provided by Geological Society of America. 

Building Blocks of Early Earth Survived Collision That Created Moon

Unexpected new findings by a University of Maryland team of geochemists show that some portions of Earth’s mantle (the rocky layer between Earth’s metallic core and crust) formed when the planet was much smaller than it is now, and that some of this early-formed mantle survived Earth’s turbulent formation, including a collision with another planet-sized body that many scientists believe led to the creation of the Moon.

“It is believed that Earth grew to its current size by collisions of bodies of increasing size, over what may have been as much as tens of millions of years, yet our results suggest that some portions of the Earth formed within 10 to 20 million years of the creation of the Solar System and that parts of the planet created during this early stage of construction remained distinct within the mantle until at least 2.8 billion years ago.” says UMD Professor of Geology Richard Walker, who led the research team.
Prior to this finding, scientific consensus held that the internal heat of the early Earth, in part generated by a massive impact between the proto-Earth and a planetoid approximately half its size (i.e., the size of Mars), would have led to vigorous mixing and perhaps even complete melting of Earth. This, in turn, would have homogenized the early mantle, making it unlikely that any vestiges of the earliest-period of Earth history could be preserved and identified in volcanic rocks that erupted onto the surface more than one and a half billion years after Earth formed.
fig(1)
However, the Maryland team examined volcanic rocks that flourished in the first half of Earth’s history, called komatiites, and found that these have a different type of composition than what they, or anyone, would have, expected. Their findings were just published in the journal Science.

An Isotopic Signature

“We have discovered 2.8 billion year old volcanic rocks from Russia that have a combination of isotopes of the chemical element tungsten that is different from the combination seen in most rocks — different even from the tungsten filaments in incandescent light bulbs,” says the first author, Touboul, a research associate in the University of Maryland’s Department of Geology. “We believe we have detected the isotopic signature of one of the earliest-formed portions of the Earth, a building block that may have been created when the Earth was half of its current mass.”
As with many other chemical elements, tungsten consists of different isotopes. All isotopes of an element are characterized by having the same number of electrons and protons but different numbers of neutrons. Therefore, isotopes of an element are characterized by identical chemical properties, but different mass and nuclear properties. Through radioactive decay, some unstable (radioactive) isotopes spontaneously transform from one element into another at a specific, but constant, rate. As a result, scientists can use certain radioactive isotopes to determine the age of certain processes that happen within Earth, as well as for dating rocks.
For the Maryland team the tungsten isotope182-tungsten (one of the five isotopes of tungsten) is of special interest because it can be produced by the radioactive decay of an unstable isotope of the element hafnium, 182-hafnium.
According to the UMD team, the radioactive isotope 182-hafnium was present at the time our Solar System formed, but is no longer present on Earth today. Indeed, decay of 182-hafnium into 182-tungsten is so rapid (~9 million year half-life) that variations in the abundance of 182-tungsten relative to other isotopes of tungsten can only be due to processes that occurred very early in the history of our Solar System, they say.
fig(2)
The Maryland geochemists found that the 2.8 billion year old Russian komatiites from Kostomuksha have more of the tungsten isotope 182-W than normal. “This difference in isotopic composition requires that the early Earth formed and separated into its current metallic core, silicate mantle, and perhaps crust, well within the first 60 million years after the beginning of our 4.57-billion-year-old Solar System,” says Touboul.
“In itself this is not new,” he says, “but what is new and surprising is that a portion of the growing Earth developed the unusual chemical characteristics that could lead to the enrichment in 182-tungsten; that this portion survived the cataclysmic impact that created our moon; and that it remained distinct from the rest of the mantle until internal heat melted the mantle and transported some of this material to the surface 2.8 billion years ago, allowing us to sample it today.”

Higher Precision Yields New Findings, Insights

The UMD team explained that they were able to conduct this research because they have developed new techniques that allow the isotopic composition of tungsten to be measured with unprecedented precision. “We do this by chemically separating and purifying the tungsten from the rocks we study. We then use an instrument termed a mass spectrometer to measure the isotopic composition of the tungsten”
According to the researchers their new findings have far reaching implications for understanding how Earth formed; how it differentiated into a metallic core, rocky mantle and crust; and the dynamics of change within the mantle.

“These findings indicate that the Earth’s mantle has never been completely melted and homogenized, and that convective mixing of the mantle, even while Earth was growing, was evidently very sluggish,” says Walker. “Many questions remain. The rocks we studied are 2.8 billion years old. We don’t know whether the portion of the Earth with this unusual isotopic composition or signature can be found in much younger rocks. We plan to analyze some modern volcanic rocks in the near future to assess this.”

fig(3)
Fig(1): Photograph of a complete section of a komatiite lava flow that solidified on an ocean floor 2.82 billion years ago. Komatiites can provide extremely valuable evidence of the distant geological past of our planet. Photo Credit – Igor Puchtel, UMD
Fig(2):Photomicrograph of a small, thin section of komatiite lava. The “spinifex texture” is a hallmark and considered unequivocal evidence of their ancient origin as molten rock extruded from deep in the Earth. (Credit: Igor Puchtel, UMD)
Fig(3):Komatiite drill core obtained via drilling a hole through a sequence of komatiite lava flows. The technology allows us to obtain and document fresh rock material from horizons located as deep as several miles below the Earth’s surface, which otherwise would be inaccessible for scientists.
Photo Credit – Igor Puchtel, UMD
 Note: The above story is reprinted from materials provided by University of Maryland.  

300-Million-Year-Old Forest Discovered Preserved in Volcanic Ash

A reconstruction of the 300-million-year-old peat-forming forest at a site near Wuda, China. (Credit: Image courtesy of University of Pennsylvania)
Pompeii-like, a 300-million-year-old tropical forest was preserved in ash when a volcano erupted in what is today northern China. A new study by University of Pennsylvania paleobotanist Hermann Pfefferkorn and colleagues presents a reconstruction of this fossilized forest, lending insight into the ecology and climate of its time.
Pfefferkorn, a professor in Penn’s Department of Earth and Environmental Science, collaborated on the work with three Chinese colleagues: Jun Wang of the Chinese Academy of Sciences, Yi Zhang of Shenyang Normal University and Zhuo Feng of Yunnan University.
Their paper was published this week in the Early Edition of the Proceedings of the National Academy of Sciences.
The study site, located near Wuda, China, is unique as it gives a snapshot of a moment in time. Because volcanic ash covered a large expanse of forest in the course of only a few days, the plants were preserved as they fell, in many cases in the exact locations where they grew.
“It’s marvelously preserved,” Pfefferkorn said. “We can stand there and find a branch with the leaves attached, and then we find the next branch and the next branch and the next branch. And then we find the stump from the same tree. That’s really exciting.”
The researchers also found some smaller trees with leaves, branches, trunk and cones intact, preserved in their entirety.
Due to nearby coal-mining activities unearthing large tracts of rock, the size of the researchers’ study plots is also unusual. They were able to examine a total of 1,000 m2 of the ash layer in three different sites located near one another, an area considered large enough to meaningfully characterize the local paleoecology.
The fact that the coal beds exist is a legacy of the ancient forests, which were peat-depositing tropical forests. The peat beds, pressurized over time, transformed into the coal deposits.
The scientists were able to date the ash layer to approximately 298 million years ago. That falls at the beginning of a geologic period called the Permian, during which Earth’s continental plates were still moving toward each other to form the supercontinent Pangea. North America and Europe were fused together, and China existed as two smaller continents. All overlapped the equator and thus had tropical climates.
At that time, Earth’s climate was comparable to what it is today, making it of interest to researchers like Pfefferkorn who look at ancient climate patterns to help understand contemporary climate variations.
In each of the three study sites, Pfefferkorn and collaborators counted and mapped the fossilized plants they encountered.In all, they identified six groups of trees. Tree ferns formed a lower canopy while much taller trees — Sigillaria and Cordaites — soared to 80 feet above the ground. The researchers also found nearly complete specimens of a group of trees called Noeggerathiales. These extinct spore-bearing trees, relatives of ferns, had been identified from sites in North America and Europe but appeared to be much more common in these Asian sites.
They also observed that the three sites were somewhat different from one another in plant composition. In one site, for example, Noeggerathiales were fairly uncommon, while they made up the dominant plant type in another site. The researchers worked with painter Ren Yugao to depict accurate reconstructions of all three sites.
“This is now the baseline,” Pfefferkorn said. “Any other finds, which are normally much less complete, have to be evaluated based on what we determined here.”
 The findings are indeed “firsts” on many counts.
“This is the first such forest reconstruction in Asia for any time interval, it’s the first of a peat forest for this time interval and it’s the first with Noeggerathiales as a dominant group,” Pfefferkorn said.
Because the site captures just one moment in Earth’s history, Pfefferkorn noted that it alone cannot explain how climate changes affected life on Earth. But it helps provide valuable context.
“It’s like Pompeii: Pompeii gives us deep insight into Roman culture, but it doesn’t say anything about Roman history in and of itself,” Pfefferkorn said. “But on the other hand, it elucidates the time before and the time after. This finding is similar. It’s a time capsule and therefore it allows us now to interpret what happened before or after much better.”
The study was supported by the Chinese Academy of Science, the National Basic Research Program of China, the National Natural Science Foundation of China and the University of Pennsylvania.
Note : The above story is reprinted from materials provided by University of Pennsylvania.

Acanthite

Acanthite, Silver Locality: Imiter Mine, Boumalne-Dadès, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco (Locality at mindat.org) Size: miniature, 4.3 x 4.1 x 2.1 cm Photo Copyright © Rob Lavinsky / iRocks “iRocks.com”

Chemical Formula: Ag2S
Locality: Freiberg, Schneeberg, Annaberg, Germany.
Name Origin: From the Greek, akanta, meaning “arrow.” After the Latin, argentum, meaning “silver”. Argentite is stable above 179 C. Acanthite is stable below 179 deg. C.

Acanthite, Ag2S, crystallizes in the monoclinic system and is the stable form of silver sulfide below 173 °C. Argentite is the stable form above that temperature. As argentite cools below that temperature its cubic form is distorted to the monoclinic form of acanthite. Below 173 °C acanthite forms directly. Acanthite is the only stable form in normal air temperature.

Occurrence

Acanthite is a common silver mineral in moderately low-temperature hydrothermal veins and in zones of supergene enrichment. It occurs in association with native silver, pyrargyrite, proustite, polybasite, stephanite, aguilarite, galena, chalcopyrite, sphalerite, calcite and quartz.

Acanthite was first described in 1855 for an occurrence in the Jáchymov (St Joachimsthal) District, Krušné Hory Mts (Erzgebirge), Karlovy Vary Region, Bohemia, Czech Republic. The name is from the Greek “akantha” meaning thorn or arrow, in reference to its crystal shape.

Physical Properties

Cleavage: {001} Poor, {110} Poor
Color:     Lead gray, Gray, Iron black.
Density: 7.2 – 7.4, Average = 7.3
Diaphaneity: Opaque
Fracture: Sectile – Curved shavings or scrapings produced by a knife blade, (e.g. graphite).
Hardness: 2-2.5 – Gypsum-Finger Nail
Luminescence: Non-fluorescent.
Luster: Metallic
Magnetism: Nonmagnetic
Streak: shining black

Photos:

Acanthite, chalcopyirte, pyrargyrite?, Guanajuato, Mexico Specimen weight:35 gr. Crystal size:2 mm Overall size: 36mm x 25 mm x 34 mm Photo Copyright © minservice
Acanthite Locality: Imiter Mine, Boumalne-Dadès, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco (Locality at mindat.org) Size: miniature, 4.3 x 3.2 x 3 cm Photo Copyright © Rob Lavinsky / iRocks”iRocks.com”
Acanthite Locality: San Juan de Rayas Mine (Rayas Mine; Reyes Mine), Guanajuato, Mun. de Guanajuato, Guanajuato, Mexico Dimensions: 2.4 cm x 1.1 cm x 1.1 cm Photo Copyright © Rob Lavinsky & irocks
Acanthite Locality: Chispas Mine (Pedrazzini mine), Arizpe, Mun. de Arizpe, Sonora, Mexico Photo Copyright © Rock Currier
Acanthite – Mina Rayas, Municipio de Guanajuato, Mexico Specimen size: 1.9 × 1.6 × 0.7 cm Photo Copyright © Fabre Minerals

Lava Formations in Western U.S. Linked to Rip in Giant Slab of Earth

A new model by Scripps researchers details a rupture inside the Farallon slab that caused a magma flow now known as Columbia River flood basalt in the Western U.S. (Credit: Image courtesy of University of California, San Diego)
Like a stream of air shooting out of an airplane’s broken window to relieve cabin pressure, scientists at Scripps Institution of Oceanography at UC San Diego say lava formations in eastern Oregon are the result of an outpouring of magma forced out of a breach in a massive slab of Earth. Their new mechanism explaining how such a large volume of magma was generated is published in the Feb. 16 issue of the journal Nature.
For years scientists who study the processes underlying the planet’s shifting tectonic plates and how they shape the planet have debated the origins of sudden, massive eruptions of lava at the planet’s surface. In several locations around the world, such “flood basalts” are marked by immense formations of volcanic rock. A famous example is India’s Deccan flood basalt, a formation widely viewed as related to the demise of the dinosaurs 65 million years ago.
Such eruptions are thought to typically occur when the head of a mantle plume, a mushroom-shaped upwelling of hot rock rising from deep within Earth’s interior, reaches the surface. Now Scripps postdoctoral researcher Lijun Liu and geophysics professor Dave Stegman have proposed an alternative origin for the volcanic activity of Oregon’s Columbia River flood basalt.
Liu and Stegman argue that around 17 million years ago the tectonic plate that was subducting underneath the western United States began ripping apart, leading to massive outpourings of magma. Their proposed model describes a dynamic rupture lasting two million years — a quick eruption in geological terms — across the so-called Farallon slab, where the rupture spread across 900 kilometers (559 miles) along eastern Oregon and northern Nevada.
“Only with a break of this scale inside the down-going slab can we reach the present day geometry of mantle we see in the area,” said Liu, “and geochemical evidence from the Columbia River lavas can also be explained by our model.”

“When the slab is first opened there’s a little tear, but because of the high pressure underneath, the material is able to force its way through the hole. It’s like in the movies when a window breaks in an airplane that is at high altitude — since the cabin is at higher pressure, everything gets sucked out the window,” said Stegman, an assistant professor with Scripps’ Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics.

Liu and Stegman came upon their new mechanism by attempting to describe how the complicated structure of Earth’s mantle under the western U.S. developed during the past 40 million years. The final state of their model’s time-evolution matches the present day structure as imaged by the USArray, the National Science Foundation’s transportable seismic network of 400 sensor stations leapfrogging across the United States.

The John Miles Fellowship, the Cecil and Ida Green Foundation and the G. Unger Vetlesen Foundation funded the study.

Note : The above story is reprinted from materials provided by University of California, San Diego, via Newswise.

Fukushima at Increased Earthquake Risk, Scientists Report

This is a map of Japan’s islands indicating the area of study (black box). The purple star marks the epicentre of the March 11 earthquake and the red star the Iwaki epicentre. Fukushima Daiichi is highlighted by a red square. Black triangles indicate active volcanoes. Numbers on the side of the image represent latitude and longitude. (Credit: Ping Tong, Dapeng Zhao and Dinghui Yang)
Seismic risk at the Fukushima nuclear plant increased after the magnitude 9 earthquake that hit Japan last March, scientists report. The new study, which uses data from over 6,000 earthquakes, shows the 11 March tremor caused a seismic fault close to the nuclear plant to reactivate.
The results are now published in Solid Earth, an open-access journal of the European Geosciences Union (EGU).
The research suggests authorities should strengthen the security of the Fukushima Daiichi nuclear power plant to withstand large earthquakes that are likely to directly disturb the region. The power plant witnessed one of the worst nuclear disasters in history after it was damaged by the 11 March 2011 magnitude 9 earthquake and tsunami. But this tremor occurred about 160 km from the site, and a much closer one could occur in the future at Fukushima.
“There are a few active faults in the nuclear power plant area, and our results show the existence of similar structural anomalies under both the Iwaki and the Fukushima Daiichi areas. Given that a large earthquake occurred in Iwaki not long ago, we think it is possible for a similarly strong earthquake to happen in Fukushima,” says team-leader Dapeng Zhao, geophysics professor at Japan’s Tohoku University.
The 11 April 2011 magnitude 7 Iwaki earthquake was the strongest aftershock of the 11 March earthquake with an inland epicentre. It occurred 60 km southwest of the Fukushima nuclear power plant, or 200 km from the 11 March epicentre.
The research now published in EGU’s Solid Earth shows that the Iwaki earthquake was triggered by fluids moving upwards from the subducting Pacific plate to the crust. The Pacific plate is moving beneath northeast Japan, which increases the temperature and pressure of the minerals in it. This leads to the removal of water from minerals, generating fluids that are less dense than the surrounding rock. These fluids move up to the upper crust and may alter seismic faults.
“Ascending fluids can reduce the friction of part of an active fault and so trigger it to cause a large earthquake. This, together with the stress variations caused by the 11 March event, is what set off the Iwaki tremor,” says Ping Tong, lead author of the paper.
The number of earthquakes in Iwaki increased greatly after the March earthquake. The movements in Earth’s crust induced by the event caused variations in the seismic pressure or stress of nearby faults. Around Iwaki, Japan’s seismic network recorded over 24,000 tremors from 11 March 2011 to 27 October 2011, up from under 1,300 detected quakes in the nine years before, the scientists report.
The 6,000 of these earthquakes selected for the study were recorded by 132 seismographic stations in Japan from June 2002 to October 2011. The researchers analysed these data to take pictures of Earth’s interior, using a technique called seismic tomography.
“The method is a powerful tool to map out structural anomalies, such as ascending fluids, in the Earth’s crust and upper mantle using seismic waves. It can be compared to a CT or CAT scan, which relies on X-rays to detect tumours or fractures inside the human body,” explains Zhao.
While the scientists can’t predict when an earthquake in Fukushima Daiichi will occur, they state that the ascending fluids observed in the area indicate that such an event is likely to occur in the near future. They warn that more attention should be paid to the site’s ability to withstand strong earthquakes, and reduce the risk of another nuclear disaster.
The scientists also note that the results may be useful for reviewing seismic safety in other nuclear facilities in Japan, such as nearby Fukushima Daini, Onagawa to the north of Fukushima, and Tōkai to the south.
Note : The above story is reprinted from materials provided by European Geosciences Union, via AlphaGalileo. 

3-D Laser Map Shows Earthquake Before and After

An image of the 3-D visualization of an earthquake zone. (Credit: Image courtesy of University of California – Davis)
Geologists have a new tool to study how earthquakes change the landscape down to a few inches, and it’s giving them insight into how earthquake faults behave. In the Feb. 10 issue of the journal Science, a team of scientists from the U.S., Mexico and China reports the most comprehensive before-and-after picture yet of an earthquake zone, using data from the magnitude 7.2 event that struck near Mexicali, northern Mexico in April, 2010.
“We can learn so much about how earthquakes work by studying fresh fault ruptures,” said Michael Oskin, geology professor at the University of California, Davis, and lead author on the paper.

The team, working with the National Center for Airborne Laser Mapping (NCALM), flew over the area with LiDAR (light detection and ranging), which bounces a stream of laser pulses off the ground. New airborne LiDAR equipment can measure surface features to within a few inches. The researchers were able to make a detailed scan over about 140 square miles in less than three days, Oskin said.

Oskin said that they knew the area had been mapped with LiDAR in 2006 by the Mexican government. When the earthquake occurred, Oskin and Ramon Arrowsmith at Arizona State University applied for and got funding from the National Science Foundation to carry out an immediate aerial survey to compare the results.
Co-authors John Fletcher and graduate student Orlando Teran from the Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE) carried out a traditional ground survey of the fault rupture, which helped guide planning of the aerial LiDAR survey and the interpretation of the results.
From the ground, features like the five-foot escarpment created when part of a hillside abruptly moved up and sideways are readily visible. But the LiDAR survey further reveals warping of the ground surface adjacent to faults that previously could not easily be detected, Oskin said. For example, it revealed the folding above the Indiviso fault running beneath agricultural fields in the floodplain of the Colorado River.
“This would be very hard to see in the field,” Oskin said.
Team members used the “virtual reality” facility at UC Davis’ W.M. Keck Center for Active Visualization in Earth Sciences to handle and view the data from the survey. By comparing pre- and post-earthquake surveys, they could see exactly where the ground moved and by how much.
The survey revealed deformation around the system of small faults that caused the earthquake, and allowed measurements that provide clues to understanding how these multifault earthquakes occur.
 The 2010 Mexicali earthquake did not occur on a major fault, like the San Andreas, but ran through a series of smaller faults in Earth’s crust. These minor faults are common around major faults but are “underappreciated,” Oskin said.
“This sort of earthquake happens out of the blue,” he said.

The new LiDAR survey shows how seven of these small faults came together to cause a major earthquake, Oskin said.

Ken Hudnut, a geophysicist with the U.S. Geological Survey and co-author on the paper, made the first use of airborne LiDAR about 10 years ago to document surface faulting from the Hector Mine earthquake. But “pre-earthquake” data were lacking. Since then, NCALM has carried out LiDAR scans of the San Andreas system (the “B4 Project”) and other active faults in the western U.S. (a component of the EarthScope Project), thereby setting a trap for future earthquakes, he said.

“In this case, fortunately, our CICESE colleagues had set such a trap, and this earthquake fell right into it and became the first ever to be imaged by ‘before’ and ‘after’ LiDAR. It is a thrill for me to be on the team that reached this important milestone,” Hudnut said.

The post-event dataset collected by the team is publicly available through http://opentopography.org/.

Other authors on the paper are, at UC Davis: graduate student Austin Elliott and researcher Peter Gold; J. Ramon Arrowsmith, Arizona State University; Alejandro Hinojosa Corona and J. Javier Gonzalez Garcia, CICESE, Mexico; Eric Fielding, NASA Jet Propulsion Laboratory, Pasadena; and Jing Liu-Zeng, Chinese Academy of Sciences, Beijing. The work was supported by the National Science Foundation, the U.S. Geological Survey, Consejo Nacional de Ciencia y Tecnología (Mexico) and NASA.
Note : The above story is reprinted from materials provided by University of California – Davis. 

Global Extinction: Gradual Doom Is Just as Bad as Abrupt

The barren arctic landscape of Ellesmere Island was the site of the scientists’ research. (Credit: C.M. Henderson)
A painstakingly detailed investigation shows that mass extinctions need not be sudden events. The deadliest mass extinction of all took a long time to kill 90 percent of Earth’s marine life, and it killed in stages, according to a newly published report.
Thomas J. Algeo, professor of geology at the University of Cincinnati, worked with 13 co-authors to produce a high-resolution look at the geology of a Permian-Triassic boundary section on Ellesmere Island in the Canadian Arctic.
Their analysis, published Feb. 3 in the Geological Society of America Bulletin, provides strong evidence that Earth’s biggest mass extinction phased in over hundreds of thousands of years.

About 252 million years ago, at the end of the Permian period, Earth almost became a lifeless planet.

Around 90 percent of all living species disappeared then, in what scientists have called “The Great Dying.” Algeo and colleagues have spent much of the past decade investigating the chemical evidence buried in rocks formed during this major extinction.

The world revealed by their research is horrific and alien: a devastated landscape, barren of vegetation and scarred by erosion from showers of acid rain, huge “dead zones” in the oceans, and runaway greenhouse warming leading to sizzling temperatures.
The evidence that Algeo and his colleagues are looking at points to massive volcanism in Siberia. A large portion of western Siberia reveals volcanic deposits up to five kilometers (three miles) thick, covering an area equivalent to the continental United States. And the lava flowed where it could most endanger life, through a large coal deposit.
“The eruption released lots of methane when it burned through the coal,” he said. “Methane is 30 times more effective as a greenhouse gas than carbon dioxide. We’re not sure how long the greenhouse effect lasted, but it seems to have been tens or hundreds of thousands of years.”
A lot of the evidence ended up being washed into the ocean, and it is among fossilized marine deposits that Algeo and his colleagues look for it. Previous investigations have focused on deposits created by a now vanished ocean known as Tethys, a kind of precursor to the Indian Ocean. Those deposits, in South China particularly, record a sudden extinction at the end of the Permian.
“In shallow marine deposits, the latest Permian mass extinction was generally abrupt,” Algeo said. “Based on such observations, it has been widely inferred that the extinction was a globally synchronous event.”
Recent studies are starting to challenge that view.

Algeo and his co-authors focused on rock layers at West Blind Fiord on Ellesmere Island in the Canadian Arctic. That location, at the end of the Permian, would have been a lot closer to the Siberian volcanoes than sites in South China.

The Canadian sedimentary rock layers are 24 meters (almost 80 feet) thick and cross the Permian-Triassic boundary, including the latest Permian mass extinction horizon. The investigators looked at how the type of rock changed from the bottom to the top of the section. They looked at the chemistry of the rocks. They looked at the fossils contained in the rocks.
They discovered a total die-off of siliceous sponges about 100,000 years earlier than the marinemass extinction event recorded at Tethyan sites. Chemical clues, Algeo said, confirm that life on land was in crisis. Dying plants and eroding soil were being flushed into the ocean where the over-abundant nutrients led to a microbial feeding frenzy and the removal of oxygen — and life — from the late Permian ocean.
What appears to have happened, according to Algeo and his colleagues, is that the effects of early Siberian volcanic activity, such as toxic gases and ash, were confined to the northern latitudes. Only after the eruptions were in full swing did the effects reach the tropical latitudes of the Tethys Ocean.
The research was supported by the National Science Foundation, Canadian Natural Sciences and Engineering Research Council and the National Aeronautics and Space Administration Exobiology Program.
 
Note : The above story is reprinted from materials provided by University of Cincinnati. The original article was written by Greg Hand.

New Way to Study Ground Fractures

Boise State University geophysics researchers have created a new way to study fractures by producing elastic waves, or vibrations, through using high-intensity light focused directly on the fracture itself. (Credit: Image courtesy of Boise State University)
Boise State University geophysics researchers have created a new way to study fractures by producing elastic waves, or vibrations, through using high-intensity light focused directly on the fracture itself. The new technique developed in the Physical Acoustics Lab at Boise State may help determine if there is a fluid, such as magma or water, or natural gas inside fractures in the Earth.
Typically, scientists create sound waves at the surface to listen for echoes from fractures in the ground, but this new technique could provide more accurate information about the cracks because sound does not have to travel to the fracture and back again.
The new technique aims to enhance scientists’ abilities to image faults in the Earth, including those human-made through the process of hydraulic fracturing, or fracking.
The new method is explained in a paper that appears online in the journal Physical Review Letters.

“These concepts are of great importance in earthquake dynamics, but also in exploration of hydrocarbons,” said study coauthor Thomas Blum, a Boise State doctoral student. “If we can understand, for example, the microscopic structure of fracture points using this technique, we might be able to learn how, exactly, earthquakes happen. Scientists do not yet fully understand the structure of the faults, so if we could remotely sense the structure of faults, we might be able to learn more.”

Blum and Kasper van Wijk, associate professor of geosciences at Boise State, came up with the new technique by focusing laser light directly onto a fracture inside a transparent sample to create elastic waves. The researchers proved that laser-based ultrasonic techniques can “excite,” or cause vibrations, in the fracture. The result — jointly obtained with scientists at Colorado School of Mines and ConocoPhillips — opens up the possibility of measuring variations in the fracture and diagnosing the mechanical properties of fractures by directly exciting them.
Note : The above story is reprinted from materials provided by Boise State University, via Newswise. 

Life Beyond Earth? Underwater Caves in Bahamas Could Give Clues

Typical Bahamian Blue Hole entrance pool. (Credit: Photo by Tamara Thomsen)
Discoveries made in some underwater caves by Texas &M University at Galveston researchers in the Bahamas could provide clues about how ocean life formed on Earth millions of years ago, and perhaps give hints of what types of marine life could be found on distant planets and moons.
Tom Iliffe, professor of marine biology at the Texas A&M-Galveston campus, and graduate student Brett Gonzalez of Trabuco Canyon, Calif., examined three “blue holes” in the Bahamas and found that layers of bacterial microbes exists in all three, but each cave had specialized forms of such life and at different depths, suggesting that microbial life in such caves is continually adapting to changes in available light, water chemistry and food sources. Their work, also done in conjunction with researchers from Penn State University, has been published in Hydrobiologia.

“Blue holes” are so named because from an aerial view, they appear circular in shape with different shades of blue in and around their entrances. There are estimated to be more than 1,000 such caves in the Bahamas, the largest concentration of blue holes in the world.

‘We examined two caves on Abaco Island and one on Andros Island,” Iliffe explains. “One on Abaco, at a depth of about 100 feet, had sheets of bacteria that were attached to the walls of the caves, almost one inch thick. Another cave on the same island had bacteria living within poisonous clouds of hydrogen sulfide at the boundary between fresh and salt water. These caves had different forms of bacteria, with the types and density changing as the light source from above grew dimmer and dimmer.
“In the cave on Andros, we expected to find something similar, but the hydrogen sulfide layer there contained different types of bacteria,” he adds. “It shows that the caves tend to have life forms that adapt to that particular habitat, and we found that some types of the bacteria could live in environments where no other forms of life could survive. This research shows how these bacteria have evolved over millions of years and have found a way to live under these extreme conditions.”

Iliffe says the microbes change where the salt water meets fresh water within the caves and use chemical energy to produce their food. They can survive in environments with very low amounts of oxygen and light.

There are tens of thousands of underwater caves scattered around the world, but less than 5 percent of these have ever been explored and scientifically investigated, Iliffe notes.
“These bacterial forms of life may be similar to microbes that existed on early Earth and thus provide a glimpse of how life evolved on this planet,” he adds. “These caves are natural laboratories where we can study life existing under conditions analogous to what was present many millions of years ago.
“We know more about the far side of the moon than we do about these caves right here on Earth,” he adds. “There is no telling what remains to be discovered in the many thousands of caves that no one has ever entered. If life exists elsewhere in our solar system, it most likely would be found in water-filled subterranean environments, perhaps equivalent to those we are studying in the Bahamas.”
Over the past 30 years, Iliffe has discovered several hundred species of marine life, and has probably explored more underwater caves — at least 1,500 — than anyone in the world, examining such caves in Australia, the Caribbean, Mediterranean and North Atlantic regions of the world.
Note : The above story is reprinted from materials provided by Texas A&M University, via Newswise.

Underwater River of Mud and Sand Tells Tale of Climate Change and Ocean Gateways

Ending a successful expedition, the JOIDES Resolution arrives in Lisbon, Portugal. (Credit: Fernando Barriga, ECORD Portugal)
Mediterranean bottom currents and the sediment deposits they leave behind offer new insights into global climate change, the opening and closing of ocean circulation gateways and locations where hydrocarbon deposits may lie buried under the sea.

A team of 35 scientists from 14 countries recently returned from an expedition off the southwest coast of Iberia and the nearby Gulf of Cadiz. There the geologists collected core samples of sediments that contain a detailed record of the Mediterranean’s history. The scientists retrieved the samples by drilling into the ocean floor during an eight-week scientific expedition onboard the ship JOIDES Resolution.

The group — researchers participating in Integrated Ocean Drilling Program (IODP) Expedition 339: Mediterranean Outflow — is the first to retrieve sediment samples from deep below the seafloor in this region.
Much of the sediment in the cores is known as “contourite” because the currents that deposit it closely follow the contours of the ocean basin.
“The recovery of nearly four kilometers of contourite sediments deposited from deep underwater currents presents a superb opportunity to understand water flow from the Mediterranean Sea to the Atlantic Ocean,” says Jamie Allan, program director at the National Science Foundation (NSF), which co-funds IODP.
“Knowledge of this water flow is important for understanding Earth’s climate history in the last five million years.”
“We now have a much greater insight into the distinctive character of contourites, and have validated beyond doubt the existing paradigm for this type of sedimentation,” says Dorrik Stow of Heriot-Watt University in the United Kingdom and co-chief scientist for Expedition 339.
The world’s oceans are far from static. Large currents flow at various depths beneath the surface. These currents form a global conveyor belt that transfers heat energy and helps buffer Earth’s climate.
Critical gateways in the oceans affect circulation of these major currents.
The Strait of Gibraltar is one such gateway. It re-opened less than six million years ago.
Today, deep below the surface, there is a powerful cascade of Mediterranean water spilling out through the strait into the Atlantic Ocean.
Because this water is saltier than the Atlantic–and therefore heavier–it plunges more than 1,000 meters downslope, scouring the rocky seafloor, carving deep-sea canyons and building up mountains of mud on a little-known submarine landscape.
The sediments hold a record of climate change and tectonic activity that spans much of the past 5.3 million years.
The team found evidence for a “tectonic pulse” at the junction between the African and European tectonic plates, which is responsible for the rising and falling of key structures in and around the gateway.
This event also led to strong earthquakes and tsunamis that dumped large flows of debris and sand into the deep sea.
At four of the seven drill sites, there was also a major chunk of the geologic record missing from the sediment cores–evidence of a strong current that scoured the seafloor.
“We set out to understand how the Strait of Gibraltar acted first as a barrier and then a gateway over the past six million years,” says Javier Hernandez-Molina of the University of Vigo in Spain and co-chief scientist for Expedition 339. “We now have that understanding and a record of a deep, powerful Mediterranean outflow through the Gibraltar gateway.”
The first drill site, located on the west Portuguese margin, provided the most complete marine sediment record of climate change over the past 1.5 million years of Earth history.
The sediment cores cover at least four major ice ages and contain a new marine archive to compare against ice core records from Greenland and Antarctica, among other land-based records.
The team was surprised to find exactly the same climate signal in the mountains of contourite mud they drilled in the Gulf of Cádiz.
Because these muds were deposited much faster than the sediments at the Portuguese margin site, the record from these cores could prove to yield even richer, more detailed climate information.
“Cracking the climate code will be more difficult for contourites because they receive a mixed assortment of sediment from varying sources,” Hernandez-Molina says.
“But the potential story that unfolds may be even more significant. The oceans and climate are inextricably linked. It seems there is an irrepressible signal of this nexus in contourite sediments.”
The team also found more sand among the contourite sediments than expected.
The scientists found this sand filling the contourite channels, deposited as thick layers within mountains of mud, and in a single, vast sand sheet that spreads out nearly 100 kilometers from the Gibraltar gateway.
All testify to the strength, velocity and duration of the Mediterranean bottom currents. The finding could affect future oil and gas exploration, the researchers believe.
“The thickness, extent and properties of these sands make them an ideal target in places where they are buried deeply enough to allow for the trapping of hydrocarbons,” Stow explains.
The sands are deposited in a different manner in channels and terraces cut by bottom currents; in contrast, typical reservoirs form in sediments deposited by downslope “turbidity” currents.
“The sand is especially clean and well-sorted, and therefore very porous and permeable,” says Stow. “Our findings could herald a significant shift in future exploration targets.”
IODP is an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring, and monitoring the subseafloor.
IODP is supported by two lead agencies: the U.S. National Science Foundation and Japan’s Ministry of Education, Culture, Sports, Science, and Technology. Additional program support comes from the European Consortium for Ocean Research Drilling, the Australia-New Zealand IODP Consortium, India’s Ministry of Earth Sciences, the People’s Republic of China (Ministry of Science and Technology), and the Korea Institute of Geoscience and Mineral Resources.
The JOIDES Resolution is a scientific research vessel managed by the U.S. Implementing Organization of IODP (USIO). Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University, and the Consortium for Ocean Leadership comprise the USIO.
For more information visit IODP’s Expedition 339: Mediterranean Outflow web page (http://iodp.tamu.edu/scienceops/expeditions/mediterranean_outflow.html).
Note : The above story is reprinted from materials provided by National Science Foundation. 
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