olelog

Few people know where Franz Josef Land is, or have ever heard of it. Except for a few Russian army border guards, Franz Josef Land is totally uninhabited. It has no native inhabitants. This is not because the area is small - Its 191 islands have a total area of 16,134 km². It is however situated far up north in the Arctic - and was furthermore completely closed to visitors for roughly 60 years until 1991. It is the most northerly group of islands associated with Eurasia and the Eurasian continental plate. Gakkel Ridge further north is normally seen as on the border zone between The Eurasian and the North American plate.

The situation may change now that the sea ice in the Arctic is melting and icebreakers in a few years perhaps no longer may be needed to reach the islands (Most of the Russian icebreakers in the area are - as far as I know - nuclear icebreakers). Since 2005 cruises are organised from Murmansk.

The archipelago is dominated by Jurassic to Tertiary basalts, but there are also late Triassic and Jurassic sediments lying in near horizontal strata. Fossil tree trunks show that the climate here was warmer in the Mesozoic. The basalt layer above the Jurassic sediments is up to 500 m thick and part of a Large Igneous Province (LIP) formed in the Cretaceous, and called the High Arctic Large Igneous Province (HALIP). This is a major Late Cretaceous large igneous province located in the Arctic. It includes the Ellesmere Island Volcanics, Strand Fiord Formation, Alpha Ridge, Franz Josef Land and Svalbard. These areas were closer to each other in the Cretaceous - since then the spreading ridge (Gakkel Ridge) has brought them further apart. A multitude of tectonic fault lines has broken the archipelago into many relatively small islands.

The age of the HALIP volcanic rocks is rather uncertain, but a long period of magmatism between ca. 136 and 80 million years ago has been suggested for the whole LIP.

From 15 June 2009 the archipelago became part of the newly established Russkaya Arktika National Park.

• http://maps.unomaha.edu/maher/svalbard/wwwHALIP/
  
• http://www.largeigneousprovinces.org/06apr.html
  
• Google Books - Bradt's Spitsbergen Guide
  

The USArray network of seismometers is revealing an impressive subsurface collection of slabs, drips, and plumes across the U.S. USArray is part of the EarthScope experiment, a 15-year program to place a dense network of permanent and portable seismographs across the continental United States. By analyzing the records of earthquakes obtained from this dense grid of seismometers, scientists can learn about Earth structure and dynamics and the physical processes controlling earthquakes and volcanoes. You can follow the work through the EarthScope quarterly newsletter (onSite) all free downloadable in pdf-format from here.

The work is most recently featured in an article by Richard A. Kerr in the 25 September 2009 issue of the journal Science.

Mantle plume:
Transportable Array data add to evidence of a seismically slow zone beneath Yellowstone extending to a depth of at least 1000 kilometres (that means down into the lower mantle). Some scientists see this as evidence that a mantle plume exists to lower mantle depth. Is there a single tall plume or a random series of unconnected blobs beneath Yellowstone?

Lithospheric drip (also called “Mantle Drip”):

Combined data from the Flexible Array and the Transportable Array as the latter was passing over the Isabella Anomaly (a blob of rock lying 70 km to 250 km beneath the western edge of the Sierra Nevada mountains of central California). A density was calculated for the anomaly’s rock, which shows that it is so dense that it must contain just the kind of rock hypothesized to have dripped away from the base of the Sierra Nevada. It was concluded that the drip could have triggered the Sierra Nevada’s uplift. (See my post on Litospheric Drip).

And there are more strange features still to be further explored. Indeed relating geological traces at the surface to underlying seismic anomalies could help explain why there’s such a weird assortment of still-active deep processes shaping the surface of the American West.

The Fall 09 issue of the EarthScope onSite newsletter features the Heterogeneous Lowermost Mantle Beneath the Pacific Ocean and Tectonic Block Motions in Southeast Alaska and Adjacent Canada.

• http://www.sciencemag.org/cgi/content/summary/325/5948/1620-a
  
• http://www.earthscope.org/
  
• http://www.iris.edu/USArray/
  

A 6.8-magnitude quake occurred in the Banda Sea, Indonesia, on Friday 28 August at 09:51 local time. It caused no severe damage, and although it was under sea it triggered no tsunami.

If you wonder why? the answer is simple, it was far too deep. And by deep I mean really deep - at a depth of 633.2 km. It is about as deep as earthquakes go. The deepest earthquake ever recorded is 705 km deep, under the Fiji Islands in the Southwest Pacific, on 6 May 2007.

Such deep earthquakes only occur in subduction zones - and only in some old subduction zones.



Looking at a map of historic seismicity from USGS we can see that the quake occurred in a band of former deep earthquakes (marked in red) at a certain distance from the surface frontier of the subduction zone marked as a purple line. In this area it is in fact relatively easy (even though the plate tectonics in the area are rather complex) to follow the inclination of the Benioff zone from shallow earthquakes, 0 – 36 km deep, to the deepest earthquakes 500 – 800 km deep. The earthquake foci normally plot along a dipping plane at an angle of 33 to 60 degrees and such a plane is called a Benioff zone. Earthquakes along Benioff zones define a lithospheric plate that descends into the mantle beneath another, overlying plate. The zone is named after Hugo Benioff, a US seismologist who first described this feature.

• http://www.etaiwannews.com/etn/news_content.php?id=1043099&lang=eng_news
  
• http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009kwae.php#details
  
• http://my.opera.com/nielsol/blog/2007/05/09/deep-fiji-eartquake
  

In Danish:

• http://www.dr.dk/Nyheder/Udland/2009/08/28/061109.htm?rss=true
  

Jade is a cultural term for two rare metamorphic rocks known as jadeitite and nephrite that are both extremely tough and have been used as tools and talismans throughout the world. Jadeitite is rare, with less than 10 identified deposits worldwide. The jadeitite (or jadeite jade) is a sort of scar tissue from some collisions between Earth's plates. As ocean crust is pushed under another block, or subducted, pressure increases with only modest rise in temperature, squeezing and drying the rocks without melting them. Jade precipitates from fluids flowing up the subduction channel and into the chilled, overlying mantle that becomes serpentinite. The serpentinite assemblage, which includes jade and has a relatively low density, can be uplifted during subsequent continental collisions and extruded along the band of the collision boundary, such as those found in the Alps, California, Iran, Russia, and other parts of the world.

Jadeite rocks (jadeitites) were discovered of in Guatemala in 1954, and the discovery led to the recognition of the Motagua River Valley as a Maya jade source. Guatemala is second only to Myanmar (Burma) as a modern jadeite jade source and is the most important archaeological source.

A new analysis of jade found along the Motagua fault, where the North American Plate and the Carribean Plate slide past each other underline the fact that this region has a more complex geologic history than previously thought. Because jade and other associated metamorphic rocks are found on both sides of the fault, and because the jade to the north is younger by about 60 million years, a team of geologists argue in a new research paper, published in Earth and Planetary Science Letters, that the North American and Caribbean plates have done more than simply slide past each other: they have also collided - not only once, but twice.

This is not the first paper on Guatemalean jade combined with Guatemalean tectonics. In an earlier paper, the authors found evidence of two different collisions by dating mica found in collisional rocks (including jade) from the North American side of the fault to about 70 million years ago and from the southern side (or the Caribbean plate) to between 120 and 130 million years ago. But mica dates can be "reset" by subsequent heating (See my post on fission track dating). Now, the authors have turned to eclogite, a metamorphic rock that forms from ocean floor basalt in the subduction channel. Eclogite dates are rarely reset, and the authors found that eclogite from both sides of the Motagua dates to roughly 130 million years old.

A possible scenario is that a collision 130 million years ago created a serpentinite belt that was subsequently sliced into segments. Then, after plate movement changed direction about 100 million years ago, a second collision between one of these slices and the North American plate reset the mica clocks in jadeitite found on the northern side of the fault to 70 million years. Finally, plate motion in the last 70 million years juxtaposed the southern serpentinites with the northern serpentinites, which explains why there are collisional remnants on both sides of the Motagua.

• http://www.eurekalert.org/pub_releases/2009-07/amon-jsl072709.php
  
• http://www.physorg.com/news167936004.html
  
• http://www.scienceblog.com/cms/jade-sheds-light-guatemalas-geologic-history-23427.html
  
• http://www.amnh.org/science/papers/jade_guatemala.php
  
• http://my.opera.com/nielsol/blog/2009/04/24/north-and-south-islands-new-names
  
• http://research.amnh.org/eps/staff/georgeharlow/jade
  
  

I think most of you will agree with me that NASA’s Earth Observatory brings some beautiful (and interesting) satellite images. Here is one of Novaya Zemlya:

Larger solution is available at EO.
Novaya Zemlya is an Arctic archipelago off the north coast of the Russian Federation. Besides several smaller isles, Novaya Zemlya consists of two major islands, Severny in the north and Yuzhny in the south, separated by a narrow strait, Matochkin Shar. An extension of the Ural Mountains, this mountainous archipelago has an average altitude of roughly 1,000 m above sea level, and glaciers cover much of the northern island.

The Uralian orogenic belt is usually thought of as the boundary between Europe and Asia. It extends from the Aral Sea to Novaya Zemlya, and it includes the Ural Mountains, the Pay-Khoy Ridge, and the Mughalzhar Hills of northwest Kazakhstan. Its total length is about 3,500 km, of which the Ural Mountains are about 2,500 km.

The physical manifestations of orogenesis (the process of orogeny/mountain buidling) are orogenic belts or orogens. The name of such orogenic belts often end in -ides, like the Caledonides from the Caledonian orogeny, the Ketilides from the Ketilidian orogen, and indeed the Uralides from the Uralian orogen.

The Uralide/Uralian orogen of central Russia, the geographic and geologic divide between Europe and Asia, marks the Paleozoic collision zone of the East European craton with the Asian collage of terranes. Together with the Appalachian, Caledonian, and Variscan orogens, the Urals were one of the major zones of continental convergence that contributed to the assembly of the late Paleozoic Pangea supercontinent. Tectonic evolution of the Urals began with rifting and the development of a passive continental margin on the East European platform in latest Cambrian to early Ordovician time, followed by Middle Paleozoic rifting of microcontinental fragments, the formation of island arcs and back-arc basins, and assembly of these terranes within the Uralian paleo-ocean. The final collision of Eastern Europe with this complex collage and the Siberian craton took place in Late Carboniferous and Permian time. In contrast to the classic Alpine or Himalayan style of orogeny, involving collision between large continental masses, the Altaids developed through the assembly of a collage of island-arc and microcontinental fragments that subsequently impacted the East European margin in the Late Paleozoic. The Urals are among the world's oldest extant mountain ranges. For its age of 250 to 300 million years, the elevation of the mountains is unusually high (see also my post on Why are the (Norwegian) Mountains so High).

Although Novaya Zemlya can be seen as the most northern part of the Urals, some geologist do not consider it a part of the Uralides, as the Novaya Zemlya fold belt is much younger than the Ural. The Ural is of Hercynian age (late Carboniferous to early Permian) with orogenic activity diminishing until the Triassic, while the Novaya Zemlya fold belt had it's most important orogeny in the Triassic.

Before the turn of the twentieth century, Arctic sea ice used to linger along the coast of Novaya Zemlya’s larger island each July. After the turn of the century, however, increased summertime melt made open ocean more common. On the image we see how a narrow band of sea ice hugs the southeastern coast, and smaller pieces of sea ice float off the northern island’s northeastern tip.

In my youth Novaya Zemlya was particularly known for the Russian nuclear testing, that started in October 1954 (I was 13-14 years old at the time!). All that went wrong at the time - especially bad weather, but apart from that practically everything - was said to be caused by the nuclear testing on Novaja Zemlya, just like global warming gets the blame for everything today. The world needs a scapegoat. This does of course by no means imply that we should not condemn todays nuclear testing by whomever, or do nothing to hinder global warming.

• http://earthobservatory.nasa.gov/IOTD/view.php?id=39591&src=eorss-iotd
  
• http://www.redorbit.com/images/images-of-the-day/img/23769/novaya_zemlya/index.html?source=r_earthiod