Research challenges theory on New Zealand prehistory


A combination of geological and biological findings are lending weight to the possibility that the Chatham Islands were under water until three million years ago, and that New Zealand’s flora and fauna may have evolved in another large island near New Zealand.



Traditional thinking is that the islands of New Zealand split from the ancient super-continent Gondwanaland about 85 million years ago, and stayed above the oceans since then. This is challenged by the findings of the multidisciplinary project that has been researching the Chathams, named the Chatham Islands Emergent Ark Survey. The team of biologists and geologists includes Dr Steve Trewick, Senior Lecturer at the Allan Wilson Centre for Molecular Ecology and Evolution. Dr Trewick was part of a team who visited the islands in 2004.



Findings include identification of remnants of deepwater limestone from about three million years ago, overlaid by beach deposits of sand, indicating that the Chathams may be much younger than previously thought. A further significant discovery was the previously unmapped formation in the southwest corner of the Chathams, volcanic rocks of a type that erupted and accumulated on the seashore. By using fossils from within the rocks and radiometric ageing, researchers found the formation was deposited between 2.5 million and 4.5 million years ago. The rocks were originally on the seabed, but now form the highest point on the Chathams, indicating that the entire land area was under the sea until uplift about two million years ago raised it to above the water level.


Biological findings now coming to hand are compatible with the geological findings, indicating that Chatham Islands birds and plants have been separated from their New Zealand relatives for up to three million years.



The final report on the Marsden-funded project is due next year. Participants include staff from Otago, Lincoln and Massey universities and GNS Science.

Tectonic Plates Like Variable Thermostat





View of the San Andreas Fault on the Carrizo Plain in central California
View of the San Andreas Fault on the Carrizo Plain in central California

Like a quilt that loses heat between squares, the earth’s system of tectonic plates lets warmth out at every stitch.



But a new study in PNAS Early Edition finds the current blanket much improved over the leaky patchwork of 60 million years ago.



The study, appearing online the week of Aug. 13-17, shows that heat flowed out of Earth’s mantle at a high rate 60 million years ago, when small tectonic plates made up the Pacific basin.



The reason, the authors said, is that much of the heat from the mantle escapes near the ridges between newly formed plates. Those areas are thinner and allow more heat to pass.



The smaller the plates, the greater the heat loss from the mantle on which they float, said geophysicists from the University of Southern California, Johns Hopkins University and the University of Michigan at Ann Arbor.



Several small plates have more area close to the ridge — and allow more heat to pass — than one large plate, explained lead author Thorsten Becker, assistant professor of earth sciences at USC.



“When you go back 60 million years there were a bunch more smaller plates in the Pacific basin,” Becker said.



Using seafloor age reconstructions published last year, Becker and his co-authors found that heat flow out of the mantle in the last 60 million years was greater than previously estimated.


They also found that heat flow is relatively low now that the Pacific basin consists mainly of one large plate.



Becker added that variations in heat flow would not necessarily affect surface temperature, which depends on many factors, including solar activity and greenhouse gases in the atmosphere.



However, Becker said, a leaky tectonic quilt on average would lead to greater volcanic activity, earthquakes and plate movement. This would affect almost every aspect of Earth’s geography, from sea level to erosion to climate.



“There’s sort of a chain of things that follows from a good mechanical understanding of how plate tectonics works,” he said.



Like previous estimates of heat flow, the new study raises a nagging question. If heat loss for the past few billion years was comparable to Becker’s estimate, the mantle would have had to be impossibly hot at the beginning of Earth’s history.



Becker’s study, which implies an even greater rate of heat loss, shows that previous models designed to avert a “thermal catastrophe” do not work.



“A different solution to the thermal catastrophe needs to be found,” he said.



Becker’s co-authors were Frank Corsetti, USC associate professor of earth sciences, USC graduate student Sean Lloyd, Clint Conrad of Johns Hopkins University and Carolina Lithgow-Bertelloni of the University of Michigan at Ann Arbor.

2006 Plate Motion Reversal Unlikely To Have Eased Seismic Strain, Earthquake Anticipation Near Acapulco





A reversal of tectonic plate motion near Acapulco, Mexico, in 2006 (colored arrows) as measured by GPS satellites did little to ease seismic strain in the region and the potential for a large earthquake that could impact Mexico City 175 miles away, according to a new study led by CU-Boulder.
A reversal of tectonic plate motion near Acapulco, Mexico, in 2006 (colored arrows) as measured by GPS satellites did little to ease seismic strain in the region and the potential for a large earthquake that could impact Mexico City 175 miles away, according to a new study led by CU-Boulder.

A reversal of tectonic plate motion between Acapulco and Mexico City in the last half of 2006 probably didn’t ease seismic strain in the region or the specter of a major earthquake anticipated there in the coming decades, says a University of Colorado at Boulder professor.



Instead of creeping toward Mexico City at about one inch per year – the expected speed from plate tectonic theory – the region near Acapulco moved in the opposite direction for six months and sped up by four times, said CU-Boulder aerospace engineering Professor Kristine Larson. The changes in motion were detected by analyzing data from GPS satellite receivers set up in Guerrero, Mexico, that were installed by the National Autonomous University of Mexico (UNAM) under the direction of UNAM geophysicist Vladimir Kostoglodov and augmented by CU-Boulder.



“The million-dollar question is whether the event makes a major earthquake in the region less likely or more likely,” said Larson, whose research is funded in part by the National Science Foundation. “So far, it does not appear to be reducing the earthquake hazard.”



A paper on the subject by Larson, the University of Tokyo’s Shin’ichi Miyazaki and UNAM’s Kostoglodov and José Antonio Santiago was published Aug. 1 in Geophysical Research Letters.



Scientists use GPS satellite receivers to record laser pulses from spacecraft to measure tiny movements in Earth’s crust.



The question of earthquake hazard is particularly important for Guerrero, since it is located 175 miles southwest of Mexico City, Larson said. “A very large earthquake in Guerrero would produce seismic waves that would travel quickly to the Mexican capital, and since Mexico City is built on water-saturated lakebed deposits that amplify seismic energy, the results would be catastrophic,” she said.


In 1985, a magnitude 8.1 earthquake triggered by the Cocos Plate dipping under the North American Plate off the west coast of southern Mexico struck along the coast north of Guerrero and killed 10,000 people in Mexico City, injured about 50,000 and caused an estimated $5 billion in property damage.



Since the last major earthquake in northwest Guerrero was a 7.6 magnitude event in 1911, many scientists think the area is ripe for a much larger earthquake, likely in the range of 8.1 to 8.4, Larson said. Geophysicists refer to the impending earthquake as the “Guerrero Gap,” she said.



“Before GPS we thought the ground moved at a constant speed between earthquakes,” Larson said. “The recognition of these transient events where the plate reverses direction is arguably the most important geophysical discovery that has stemmed from the introduction of GPS measurements.”



The Guerrero slip events recorded by Larson and Kostoglodov’s research team in 2006 are the largest ever reported in the world.



Studies of the Guerrero Gap are helping scientists better understand other subduction zones around the world, including the Cascadia region off the coast of Washington and Oregon, Larson said. Smaller but much faster backwards slip events have occurred there, as have very large earthquakes in previous centuries.

Alaskan Earthquake In 2002 Set Off Tremors On Vancouver Island





Alaskan Coast Line - Photo Credit: Web Doodle, LLC
Alaskan Coast Line – Photo Credit: Web Doodle, LLC

Perhaps it was just a matter of sympathy, but tremors rippled the landscape of Vancouver Island, the westernmost part of British Columbia, in 2002 during a major Alaskan earthquake. Geoscientists at the University of Washington have found clear evidence that the two events were related.



Tremor episodes have long been observed near volcanoes and more recently around subduction zones, regions where the Earth’s tectonic plates are shifting so that one slides beneath another. Tremors in subduction zones are associated with slow-slip events in which energy equivalent to a moderate-sized earthquake is released in days or weeks, rather than seconds.



Now researchers studying seismograph records have pinpointed five tremor bursts on Vancouver Island on Nov. 3, 2002, the result of a magnitude 7.8 earthquake on the Denali fault in the heart of Alaska.



As surface waves, called Love waves, shook Vancouver Island they triggered tremors underneath the island in the subduction zone where the Explorer tectonic plate slides beneath the North American plate. The tremors were measured by seismometers along roughly the northern two-thirds of the island.



“What we found is that when the waves pushed the North American plate to the southwest, the tremor episode turned on and when the motion reversed it turned off,” said Justin Rubinstein, a UW postdoctoral researcher in Earth and space sciences and lead author of a paper describing the work published in the Aug. 2 edition of Nature.



Though the Denali quake was mostly felt in Alaska, its effects were apparent thousands of miles away. It sloshed lakes from Seattle to Louisiana, muddied wells as far east as Pennsylvania and triggered small earthquakes in seismic zones across the Western United States.



Still, finding evidence of tremors on Vancouver Island was unusual.



“A few people have seen tremor episodes triggered by earthquakes, but not as clearly as we have. This is by far the clearest and easiest to interpret,” said co-author John Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismic Network.



“This shows us it’s just like a regular fault — you add stress and it slips,” Vidale said. “It’s like regular faulting but on a different time scale.”



Other authors are Joan Gomberg of the U.S. Geological Survey in Seattle and UW researchers Paul Bodin, Kenneth Creager and Stephen Malone.



An earthquake typically will appear suddenly on a seismograph, while the much more subtle ground motion from a tremor burst gradually emerges from the background noise and then fades again, Rubinstein said.



By comparison, tremors typically produce the strongest seismic signals in a slow-slip event, in which seismic energy is released very gradually during periods as long as three weeks.


In this case, the authors suggest that the force of the Love waves induced slow slip on the interface between the North American and Explorer tectonic plates near Vancouver Island and triggered the tremor bursts, each lasting about 15 seconds.



“That made it easier for us to observe because there were these five distinct bursts,” Rubinstein said. “Normally you are not going to feel these tremors. The shaking in the tremors we observed was 1,000 times smaller than the surface waves from the earthquake.”



Being able to spot the tremors was largely a matter of distance and timing, Vidale said.



“We were able to separate the tremor signal from that of the distant earthquake because the surface waves had traveled more than 1,200 miles, losing the high-frequency vibrations that would have masked the high-frequency tremor vibrations,” Vidale said.



While the tremors were recorded a great distance from the rupture that triggered the Denali earthquake, the scientists suggest the same process could occur closer to the fault and might actually be important in the rupture process.



Seismograph data for the research came from the Canadian National Seismograph Network and was distributed by the Geological Survey of Canada.

Groundbreaking Research Changing Geological Map Of Canada


Researchers exploring a remote terrain in Arctic Canada have made discoveries that may rock the world of Canadian geology.



Geologists from the University of Alberta have found that portions of Canada collided a minimum of 500 million years earlier than previously thought. Their research, published in the American journal Geology, is offering new insight into how the different continental fragments of North America assembled billions of years ago.



Lead researcher Michael Schultz, a graduate student at the U of A, took advantage of a rare opportunity to explore the Queen Maud block of Arctic Canada, a large bedrock terrain that is said to occupy a keystone tectonic position in northern Canada.



Because of its remote location, the Queen Maud block has remained understudied – until now. “In terms of trying to figure out how Canada formed, this block held a lot of secrets,” said Schultz.



The U of A team reached the rugged Northern Canadian location in helicopters and discovered – through field work and lab analysis – that the sedimentary basins within the terrain, and the age and timing of high-temperature metamorphism of the rocks found there, challenged previous models.


“Every time we did an analysis, it gave us a new piece of information that was nothing we were expecting, based on what was known in the geological community,” said Schultz.



Schultz credits cutting-edge technology only recently developed in the department of Earth and Atmospheric Sciences at the U of A with the ability to acquire large amounts of data from rocks of the Queen Maud block in record time. The technique, known as in-situ laser ablation, substantially reduces the preparation time for geochronology, the process of dating rocks and minerals.



As the Canadian Arctic starts to gain attention nationally and globally, Schultz believes the time is right to push for more geological exploration in the region.



“All this newly discovered geological information means that large portions of Northern Canada are still very poorly understood, and in fact may contain rocks that nobody knows about. This has many implications, both academically and for mineral resources,” said Schultz. “Given the remote nature of these areas, investigation has to be initiated and funded by federal, provincial or territorial governments, in cooperation with universities for facilities and additional expertise.”