Magma mix-up

Basalts from the Snake River Plain (pictured above) in Yellowstone National Park in the northern United States look like they originate from deep in Earth’s mantle. But they have the characteristic isotopic signature of rocks from shallower reaches — from the continental lithosphere. This curiosity has been explained by Barry Hanan of San Diego State University, California, and his colleagues. Using mass spectrometry on samples of volcanic rock, the authors showed that deep-mantle magma can inherit the lithosphere’s isotopic signature when it rises and picks up contamination. The findings warn geologists about assuming too much from isotopic signatures.

Source: Nature, Vol 45618/25 December 2008

Reference: Geology 36, 51–54 (2008)

WEBINAR - Kathleen R. Johnson

Reconstructing Asian Monsoon History from Chinese Speleothems

Kathleen R. Johnson
Department of Earth System Science
University of California, Irvine



While we know that modern anthropogenic climate change is superimposed upon significant natural climate variability, the instrumental record of climate is too short to capture the full range of this variability. In order to fully understand and predict future changes, therefore, high-resolution, welldated paleoclimate records are needed to extend the record. This paleoclimate data allows us to quantify natural variability and learn how the climate system responded to past changes in boundary conditions and forcings and provides a vital test for state-of-the-art coupled climate models. Cave calcite deposits (speleothems) are widely studied paleoclimate archives that have led to significantly improved records of past climate variability over a wide range of timescales (seasonal to glacialinterglacial), most notably in low-latitude and monsoon regions. Speleothems are well-suited for terrestrial climate reconstruction because: they tend to be very pure and well-preserved; they usually contain clear visible growth banding which, like tree rings, is often annual in nature; they can be very precisely dated using uranium-series radiometric dating methods; and they contain numerous types of physical and geochemical proxy data. In this lecture, I will present an introduction to speleothem based paleoclimate proxies and describe ongoing modern calibration studies we are conducting at Heshang Cave, China to test and develop new seasonal resolution proxies of Asian monsoon rainfall. In addition, I will present multiple records of Asian monsoon rainfall obtained from stable isotope and trace element variations in Chinese speleothems and discuss the important role of the Asian monsoon in the global climate system.

WEBINAR - Jared Kluesner

Geologic and Hydrologic Role of Sill Intrusion and Delineation of the Oceanic Crustal Boundary in the Central Gulf of California

Jared Kluesner
Marine Physical Laboratory
Scripps Institution of Oceanography




Geologic and Hydrologic Role of Sill Intrusion and Delineation of the Oceanic Crustal Boundary in the Central Gulf of California High-resolution multichannel profiles recently shot in the central Gulf of California display concordant and discordant (concave-upwards) sills intruded shallowly within (I) young sediments in the axial troughs of Guaymas, Carmen and Farallon Basins, (II) off-axis in the basin floors, and (III) within the sediment cover of subsided and extended continental crust. We interpret some imaged sills as 3D saucer-shaped intrusions based on their concave-upward profiles, the overlying circular and elliptical plans of domal uplifts of the present multibeam-mapped seafloor, and their striking resemblance to field-mapped and 3-D seismically imaged saucer-like sills. Vertical zones of high-amplitude, disturbed reflectors leading up from sills are probably "blow-out pipes" acting as conduits for hydrothermal fluids and gases migrating up and away from the heated sill-sediment contact aureole, forming pockmarks on the present seafloor. Bright spots, dim spots, phase reversals, and acoustic turbidity in the sediments above sill intrusions suggest the presence of hydrocarbons and fluid flow throughout the study area. Seismic evidence of sill intrusions into the shallow crust throughout the central gulf suggests melt is being delivered not just to spreading centers, but to a much broader area of oceanic and continental crust. We have improved the delineation of the oceanic/continental crustal boundary in the central and southern gulf by sampling igneous basement (tholeiitic basalt and gabbro = oceanic; granitic = continental), by identifying the extent of magnetic stripes diagnostic of seafloor spreading, by interpreting multichannel reflection profiles, and by geomorphology. Although the "boundary" is somewhat smeared by the intrusion of shallow sills (some known to be tholeiitic, most inferred to be) into the cover of both granitic and oceanic basement, we find no evidence of "transitional zones" of hybrid crust; at those sheared and rifted margins where basement is accessible, granite commonly abuts tholeiitic flows and sills. Seafloor spreading magnetic anomalies, with low amplitudes and broad transition widths, can be read out to C2Ar in Alarcon Basin, and C2An.1 in Guaymas Basin (but only on profiles that avoid major off-axis seamounts and intrusions); in both cases they indicate significantly slower accretion during the first 1 m.y. of spreading, presumably because of concurrent continued extension of the rifted margin. Widespread sill intrusion over continental basement does hamper identifying the ocean/continental boundary on seismic reflection profiles, and because the already thin Cordilleran crust was clearly highly extended during prolonged rifting we do not think that crustal thickness is a reliable criterion for the extent of oceanic crust.

Tsunami safety stressed

Children's video puts focus on preparedness

Source San Diego Union Tribune
By Robert Krier
Union-Tribune Staff Writer

Students at Del Mar Heights Elementary School watched an animated DVD about tsunami preparedness yesterday. (Eduardo Contreras / Union-Tribune) - Online: For Robert Krier's Weather Watch blog, go to weatherwatch. uniontrib.com. To view the video “Tsunamis: Know What to Do!” go to readysandiego.org.
DEL MAR — Colorful crabs gave snappy, rhyming pointers for responding to a potential tsunami to second-and third-graders at Del Mar Heights Elementary School yesterday.
In a six-minute video, the animated characters sang, “If the count goes to 20 when an earthquake starts to shake, then we won't hesitate but instead evacuate.”
So sang the children – who also danced along with the crustaceans – during the premiere of the video, which the San Diego County Office of Emergency Services created with a $30,000 federal grant.
The trick for emergency-preparedness officials is getting the tsunami message out to everyone who needs to hear it. They know that most residents along San Diego's coast laugh at the idea of a tsunami smashing into their area.
But the county isn't free of tsunami risks. The waves are “very likely, but not very frequent,” said geologist Pat Abbott, a professor emeritus at San Diego State University.
The last time a tsunami caused damage in the region was in 1964, after a quake in Alaska sent waves that banged boats and piers on San Diego Bay.
More destructive tsunamis are possible, Abbott said.
“It may happen only once every several thousand years, but you never know when that last day is up,” he said.
The new video is part of a multiagency effort to spread the word: If you're at the beach or in a low-lying coastal area and you feel a prolonged earthquake, head at least one mile inland or to higher ground as soon as possible.
“We know from past experience that schoolchildren are very good conduits for information about hazards,” said Jim Goltz, manager of the California Emergency Management Agency's Earthquake and Tsunami Program.
Three children of county emergency-services workers – Claire Amabile, a student at Twin Peaks Middle School in Poway, and Del Mar Heights students Joseph and Esther Olsen – supplied some of the crabs' voices.
Jack O'Connell, the state's superintendent of public instruction, yesterday urged students throughout California to watch the video. Goltz hopes the footage of singing crabs also will be shown at state coastal parks and, eventually, in beach towns around the nation.
San Diego County's beach communities have been slow at becoming what the National Weather Service considers “tsunami ready.” The agency is responsible for preparing coastal cities for a tsunami.
Only Imperial Beach has earned the designation in this region, said Ed Clark, warning-coordination meteorologist for the weather service. In contrast, all of Orange County's seaside cities are tsunami-ready.
To qualify for the designation, cities must set up warning systems and communication links with the weather service, promote public readiness through education programs and develop a tsunami plan that includes emergency drills.
“There hasn't been the push here that there has been in Orange (County),” partly because of greater attention paid to major wildfires in San Diego County since 2003 and extra terrorism concerns related to the military's presence, Clark said.
San Diego County's shoreline is unlikely to suffer major damage from a tsunami generated by a distant quake, Abbott said. But underwater faults nearby are capable of unleashing a 7.0-magnitude quake that might cause undersea landslides, which could then send large waves toward the region's beaches.
“It's entirely reasonable to visualize a tsunami of 20 feet or higher” washing ashore at Mission Beach or other low-lying spots, Abbott said.

WEBINAR - Stephen T. Hasiotis

Ichnology for the 21st Century: Understanding the differences between continental and marine trace fossils, with implications to the diversity, distribution, and evolution of soil biota

Stephen T. Hasiotis
Department of Geology
University of Kansas
Coeditor PALAIOS




The study of ichnology has come a long way since its inception and it continues to evolve. In particular, progress is being made in understanding the implications of trace fossils in the continental realm and how they can be used in conjunction with subdisciplines in geology to reconstruct the past. Organisms in all domains of life display behaviors that greatly expanded our definition of ichnology. Ichnology is the study of all organism behavior-not just animals. Accordingly, a trace fossil is the product of an organism interacting with a medium in an environment, which generates a three-dimensional physical structure-the resultant trace fossil can be micrometers to kilometers in scale. Though behaviors and resultant trace fossils may be similar morphologically in continental and marine settings, the organisms and behaviors that produced them and the physicochemical factors that controlled their distribution, depth, diversity, and abundance can be strikingly different. Ongoing research with modern terrestrial and aquatic organisms in the field and laboratory reveal the behaviors behind the production of burrow morphologies whose genesis and significance would otherwise be misinterpreted. The study of these modern traces, organisms, and their distribution allows us to recognize how their burrow morphologies and sedimentary associations record the environmental, ecologic, hydrologic, and climatic settings in which they are formed. Comparison of these modern structures and their tracemakers to trace fossils in continental deposits in the geologic record provide stronger clues about the implications of trace fossils for interpreting and reconstructing the sequence of events and conditions that produced those deposits. They also provide information on the evolution and radiation of organisms and ecosystems where the body fossil record is poor. As a result of these new research endeavors, trace fossils are being used to (1) extend the fossil record and understand the radiation of organisms, (2) interpret more accurately environments of deposition and the extent of pedogenesis that have modified those deposits, (3) contribute to understanding better the effects of climate change on biota, environments, and hydrologic systems, and (4) correlate significant surfaces in continental strata and identify subtle but significant shifts in physicochemical conditions and environments.

New Publication - Dr. Barry Hanan

Geochemical stages at Jasper Seamount and the origin of intraplate volcanoes

Geochemical stages at Jasper Seamount and the origin of intraplate volcanoes
J. G. Konter
Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0225, USA

H. Staudigel
Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0225, USA

J. Blichert-Toft
Laboratoire des Sciences de la Terre, Ecole Normale Supérieure de Lyon, F-69364 Lyon CEDEX 7, France

B. B. Hanan
Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA

M. Polvé
Observatoire Midi-Pyrénées, Université Paul Sabatier, F-31400 Toulouse, France

G. R. Davies
Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, Netherlands

N. Shimizu
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543-1541, USA

P. Schiffman
Department of Geology, University of California, Davis, California 95616, USA

Ocean intraplate volcanoes (OIVs) are formed in a sequence of stages, from large to small, that involve a systematic progression in mantle melting in terms of volumes and melt fractions with concomitant distinct mantle source signatures. The Hawaiian volcanoes are the best-known example of this type of evolution, even though they are extraordinarily large. We explore the Pb-Sr-Nd-Hf isotopic evolution of much smaller OIVs in the Fieberling-Guadalupe Seamount Trail (FGST) and small, near-ridge generated seamounts in the same region. In particular, we investigate whether we can extend the Hawaiian models to Jasper Seamount in the FGST, which displays three distinct volcanic stages. Each stage has characteristic variations in Pb-Sr-Nd-Hf isotopic composition and trace element enrichment that are remarkably similar to the systematics observed in Hawaii: (1) The most voluminous, basal “shield building” stage, the Flank Transitional Series (FTS), displays slightly isotopically enriched compositions compared to the common component C and the least enriched trace elements (143Nd/144Nd: 0.512866–0.512909, 206Pb/204Pb: 18.904–19.054; La/Sm: 3.71–4.82). (2) The younger and substantially less voluminous Flank Alkalic Series (FAS) is comparatively depleted in Sr, Nd, and Hf isotope compositions plotting on the side of C, near the least extreme values for the Austral Islands and St. Helena. Trace elements are highly enriched (143Nd/144Nd: 0.512912–0.512948, 206Pb/204Pb: 19.959–20.185; La/Sm: 9.24). (3) The Summit Alkalic Series (SAS) displays the most depleted Sr, Nd, and Hf isotope ratios and is very close in isotopic composition to the nearby near-ridge seamounts but with highly enriched trace elements (143Nd/144Nd: 0.512999–0.513050, 206Pb/204Pb: 19.080–19.237; La/Sm: 5.73–8.61). These data fit well with proposed multicomponent melting models for Hawaii, where source lithology controls melt productivity. We examine the effect of melting a source with dry peridotite, wet peridotite, and pyroxenite, calculating melt productivity functions with depth to evaluate the effect of potential temperature and lithospheric thickness. This type of melting model appears to explain the isotopic variation in a range of small to large OIVs, in particular for OIVs occurring far from the complicating effects of plate boundaries and continental crust, constraining their geodynamic origin.

Received 10 September 2008; accepted 26 November 2008; published 3 February 2009.

Citation: Konter, J. G., H. Staudigel, J. Blichert-Toft, B. B. Hanan, M. Polvé, G. R. Davies, N. Shimizu, and P. Schiffman (2009), Geochemical stages at Jasper Seamount and the origin of intraplate volcanoes, Geochem. Geophys. Geosyst., 10, Q02001, doi:10.1029/2008GC002236.