Category Archives: Geology

Antediluvian Continents and Modern Sovereignty Over Continental Seabeds

Ignatius Donnelly was the author of the book, Atlantis: The Antediluvian World, which was published in 1882. I remember reading this book in 1969, and being fascinated by the concept of a lost continent hidden somewhere beneath today’s oceans. While Atlantis is yet to be found, researchers have reported finding extensive continental landmasses beneath the waters of the South Pacific and Indian Oceans. Let’s take a look at these two mostly submerged continents and how improved knowledge of their subsea geography and geology can affect the definition of sovereign maritime zones.

Zealandia

In a 2016 paper entitled, “Zealandia: Earth’s Hidden Continent,” the authors, N. Mortimer, et al., reported on finding a submerged, coherent (i.e., not a collection of continental fragments) continental landmass about the size of India, located in the South Pacific Ocean off the eastern coast of Australia and generally centered on New Zealand. The extent of Zealandia is shown in the following map.

Source: N. Mortimer, et al., “Zealandia: Earth’s Hidden Continent,” GSA Today

The authors explain:

“A 4.9 Mkm2 region of the southwest Pacific Ocean is made up of continental crust. The region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure. Its isolation from Australia and large area support its definition as a continent—Zealandia. Zealandia was formerly part of (the ancient supercontinent) Gondwana. Today it is 94% submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup and consequent isostatic balance. The identification of Zealandia as a geological continent, rather than a collection of continental islands, fragments, and slices, more correctly represents the geology of this part of Earth. Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup.”

The authors claim that Zealandia is the seventh largest continental landmass, the youngest, and thinnest. While they also claim it is the “most submerged,” that claim may have been eclipsed by the discovery of another continental landmass in the Indian Ocean.

You can read the complete paper on Zealandia on the Geological Society of America (GSA) website at the following link:

http://www.geosociety.org/gsatoday/archive/27/3/pdf/GSATG321A.1.pdf

Mauritia

In the February 2013 paper, “A Precambrian microcontinent in the Indian Ocean,” authors T. Torsvik, et al., noted that an arc of volcanic islands in the western Indian Ocean, stretching from the west coast of India to the east coast of Madagascar, had been thought to be formed by the Réunion mantle plume (a hotspot in the Earth’s crust) and then distributed by tectonic plate movement over the past 65 million years. Their analysis of ancient rock zircons 660 million to 2 billion years old, found in beach sand, led them to a different conclusion. The presence of the ancient zircons was inconsistent with the geology of the more recently formed volcanic islands, and was evidence of “ancient fragments of continental lithosphere beneath Mauritius (that) were brought to the surface by plume-related lavas.”

The ages of the zircon samples were determined using U-Pb (uranium-lead) dating. This dating technique is particularly effective with zircons, which originally contain uranium and thorium, but no lead. The lead content of a present-day zircon is attributed to uranium and thorium radioactive decay that has occurred since the zircon was formed. The authors also used gravity data inversion (a technique to extract 3-D structural details from gravity survey data) to map crustal thicknesses in their areas of interest in the Indian Ocean.

The key results from this study were:

“…..Mauritius forms part of a contiguous block of anomalously thick crust that extends in an arc northwards to the Seychelles. Using plate tectonic reconstructions, we show that Mauritius and the adjacent Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia.”

This paper is available for purchase on the Nature Geoscience website at the following link:

http://www.nature.com/ngeo/journal/v6/n3/full/ngeo1736.html

This ancient continent of Mauritia is better defined in the 2016 article, “Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius,” by L. Ashwai, et al.. The authors provide further evidence of this submerged continental landmass, the approximate extent of which is shown in the following map.Source: L. Ashwai, et al., Nature Communications

The authors report:

“A fragment of continental crust has been postulated to underlie the young plume-related lavas of the Indian Ocean island of Mauritius based on the recovery of Proterozoic zircons from basaltic beach sands. Here we document the first U–Pb zircon ages recovered directly from 5.7 Ma (million year old) Mauritian trachytic rocks (a type of igneous volcanic rock). We identified concordant Archaean xenocrystic zircons ranging in age between 2.5 and 3.0 Ga (billion years old) within a trachyte plug that crosscuts Older Series plume-related basalts of Mauritius. Our results demonstrate the existence of ancient continental crust beneath Mauritius; based on the entire spectrum of U–Pb ages for old Mauritian zircons, we demonstrate that this ancient crust is of central-east Madagascar affinity, which is presently located ∼700 km west of Mauritius. This makes possible a detailed reconstruction of Mauritius and other Mauritian continental fragments, which once formed part of the ancient nucleus of Madagascar and southern India.”

Starting about 85 million years ago, the authors suggest that the former contiguous continental landmass of Mauritia was “fragmented into a ribbon-like configuration because of a series of mid-ocean ridge jumps,” associated with various tectonic and volcanic events.

You can read the complete article on the Nature Communications website at the following link:

http://www.nature.com/articles/ncomms14086

Implications to the definition of maritime zones

The UN Convention on the Law of the Sea (UNCLOS) provides the basic framework whereby nations define their territorial sea, contiguous zone, and exclusive economic zone (EEZ). These maritime zones are depicted below.

Source: http://continentalshelf.gov/media/ECSposterDec2010.pdf

UNCLOS Article 76 defines the basis whereby a nation can claim an extended territorial sea by demonstrating an “extended continental shelf,” using one of two methods: formula lines or constraint lines. These options are defined below.

Source: http://continentalshelf.gov/media/ECSposterDec2010.pdf

You’ll find more details (than you ever wanted to know) in the paper, “A Practical Overview of Article 76 of the United Nations Convention on the Law of the Sea,” at the following link:

http://www.un.org/depts/los/nippon/unnff_programme_home/fellows_pages/fellows_papers/persand_0506_mauritius.pdf

New Zealand’s Article 76 application

New Zealand ratified UNCLOS in 1996 and undertook the Continental Shelf Project with the firm GNS Science “to identify submarine areas that are the prolongation of the New Zealand landmass”. New Zealand submitted an Article 76 application on 19 April 2006. Recommendations by the UN Commission on the Limits of the Continental Shelf (CLCS) were adopted on 22 August 2008. A UN summary of New Zealand’s application is available here:

http://www.un.org/depts/los/clcs_new/submissions_files/submission_nzl.htm

The detailed CLCS recommendations are available here:

http://www.un.org/depts/los/clcs_new/submissions_files/nzl06/nzl_summary_of_recommendations.pdf

Additional information in support of New Zealand’s application is available on the GNS Science website here:

https://www.gns.cri.nz/static/unclos/

Seychelles and Mauritius joint Article 76 application

The Republic of Seychelles ratified UNCLOS on 16 November 1994 and the Republic of Mauritius followed suit on 4 December 1994. On 1 December 2008, these countries jointly made an Article 76 application claiming continental shelf extensions in the region of the Mascarene Plateau. A UN summary of this joint application is available here:

http://www.un.org/depts/los/clcs_new/submissions_files/submission_musc.htm

The CLCS recommendations were adopted on 30 March 2011, and are available here:

http://www.un.org/depts/los/clcs_new/submissions_files/musc08/sms08_summary_recommendations.pdf

Implications for the future

The recent definitions of the mostly submerged continents of Zealandia and Mauritia greatly improve our understanding of how our planet evolved from a supercontinent in a global sea to the distributed landmasses in multiple oceans we know today.

Beyond the obvious scientific interest, improved knowledge of subsea geography and geology can give a nation the technical basis for claiming a continental shelf extension that expands their EEZ. The new data on Zealandia and Mauritia postdate the UNCLOS Article 76 applications by New Zealand, Seychelles and Mauritius, which already have been resolved. It will be interesting to see if these nations use the new research findings on Zealandia and Mauritia to file new Article 76 applications with broader claims.

Strange Things are Happening Underground

In the last month, there have been reports of some very unexpected things happening under the surface of the earth. I’m talking about subduction plates that maintain their structure as they dive toward the Earth’s core and “jet streams” in the Earth’s core itself. Let’s take a look at these interesting phenomena.

What happens to subduction plates?

Oceanic tectonic plates are formed as magma wells up along mid-ocean ridges, forming new lithospheric rock that spread away from both sides of the ridge, building two different tectonic plates. This is known as a divergent plate boundary.

As tectonic plates move slowly across the Earth’s surface, each one moves differently than the adjacent plates. In simple terms, this relative motion at the plate interfaces is either a slipping, side-by-side (transform) motion, or a head-to-head (convergent) motion.

A map of the Earth showing the tectonic plates and the nature of the relative motion at the plate interfaces is shown below (click on the image to enlarge).

ESRT Page5

Source: http://www.regentsearth.com/

When two tectonic plate converge, one will sink under (subduct) the other. In the case of an oceanic plate converging with a continental plate, the heavier oceanic plate always sinks under the continental plate and may cause mountain building along the edge of the continental plate. When two oceanic plates converge, one will subduct the other, creating a deep mid-ocean trench (i.e., Mariana trench) and possibly forming an arc of islands on the overriding plate (i.e., Aleutian Islands and south Pacific island chains). In the diagram above, you can see that some subduction zones are quite long.

subd_zoneSource: http://www.columbia.edu/~vjd1/subd_zone_basic.htm

The above diagram shows the subducting material from an oceanic plate descending deep into the Earth beneath the overriding continental plate.  New research indicates that the subducting plates maintain their structure to a considerable depth below the surface of the Earth.

On 22 November 2016, an article by Paul Voosen, “’Atlas of the Underworld’ reveals oceans and mountains lost to Earth’s history,” was posted on the sciencemag.org website. The author reports:

“A team of Dutch scientists will announce a catalog of 100 subducted plates, with information about their age, size, and related surface rock records, based on their own tomographic model and cross-checks with other published studies.”

“…geoscientists have begun ….peering into the mantel itself, using earthquake waves that pass through Earth’s interior to generate images resembling computerized tomography (CT) scans. In the past few years, improvements in these tomographic techniques have revealed many of these cold, thick slabs as they free fall in slow motion to their ultimate graveyard—heaps of rock sitting just above Earth’s molten core, 2900 kilometers below.”

The following concept drawing illustrates how a CT scan of the whole Earth might look, with curtains of subducting material surrounding the molten core.

Atlas_1121_1280x720Source: Science / Fabio Crameri

The author notes that research teams around the world are using more than 20 different models to interpret similar tomographic data. As you might expect, results differ. However, a few points are consistent:

  • The subducting slabs in the upper mantle appear to be stiff, straight curtains of lithospheric rock
  • These slabs may flex but they don’t crumble.
  • These two features make it possible to “unwind” the geologic history of individual tectonic slabs and develop a better understanding of the route each slab took to its present location.
  • The geologic history in subducting slabs only stretches back about 250 million years, which is the time it takes for subducting material to fall from the surface to the bottom of the mantle and be fully recycled.

You can read the fill article by Paul Voosen at the following link:

http://www.sciencemag.org/news/2016/11/atlas-underworld-reveals-oceans-and-mountains-lost-earths-history

Hopefully, the “Atlas of the Underworld” will help focus the dialogue among international research teams toward collaborative efforts to improve and standardize the processes and models for building an integrated CT model of our Earth.

A “jet stream” in the Earth’s core

The European Space Agency (ESA) developed the Swarm satellites to make highly accurate and frequent measurements of Earth’s continuously changing magnetic field, with the goal of developing new insights into our planet’s formation, dynamics and environment. The three-satellite Swarm mission was launched on 22 November 2013.

3 satellite SWARMSwarm satellites separating from Russian booster. Source: ESA

ESA’s website for the Swarm mission is at the following link:

http://www.esa.int/Our_Activities/Observing_the_Earth/Swarm/From_core_to_crust

Here ESA explains the value of the measurements made by the Swarm satellites.

“One of the very few ways of probing Earth’s liquid core is to measure the magnetic field it creates and how it changes over time. Since variations in the field directly reflect the flow of fluid in the outermost core, new information from Swarm will further our understanding of the physics and dynamics of Earth’s stormy heart.

The continuous changes in the core field that result in motion of the magnetic poles and reversals are important for the study of Earth’s lithosphere, also known as the ‘crustal’ field, which has induced and remnant magnetized parts. The latter depend on the magnetic properties of the sub-surface rock and the history of Earth’s core field.

We can therefore learn more about the history of the magnetic field and geological activity by studying magnetism in Earth’s crust. As new oceanic crust is created through volcanic activity, iron-rich minerals in the upwelling magma are oriented to magnetic north at the time.

These magnetic stripes are evidence of pole reversals so analyzing the magnetic imprints of the ocean floor allows past core field changes to be reconstructed and also helps to investigate tectonic plate motion.”

Data from the Swarm satellites indicates that the liquid iron part of the Earth’s core has an internal, 420 km (261 miles) wide “jet stream” circling the core at high latitude at a current speed of about 40 km/year (25 miles/year) and accelerating. In geologic terms, this “jet stream” is significantly faster than typical large scale flows in the core. The basic geometry of this “jet stream” is shown in the following diagram.

jet-stream-earth-core-ESA-e1482190909115Source: ESA

These results were published on 19 December 2016 in the article, An accelerating high-latitude jet in Earth’s core,” on the Nature Geoscience website at the following link:

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2859.html

A subscription is required for access to the full paper.

The Swarm mission is ongoing. Watch the ESA’s mission website for more news.

What Satellite Data Tell Us About the Earthquake in Nepal

A 7.8 magnitude earthquake occurred in the Gorkha region of Nepal on 29 April 2015. A ground displacement map based on data gathered from the Sentinel-1A satellite is shown below. In this image, yellow areas represent uplift and the blue areas represent subsidence.

image Source: ESA

Surface ruptures are places in the ground where the quake has cracked the rock all the way up to the surface. Preliminary satellite data indicate that the Nepal earthquake did not cause any new surface ruptures.

Interferometric analysis of before and after satellite data can be used to measure more subtle changes in the vertical height of the ground along the fault line. Preliminary results from an interferometric analysis by the European Space Agency (ESA), generated from satellite scans of Nepal from April 17 and 29, 2015, is shown in the following image.

image  Source: ESA

Each fringe of color represents 2.8 cm of ground deformation. Areas immediately south of the fault line, like Kathmandu, sank more than a meter into the ground as a result of the quake. Directly north of the fault slip, further into the Himalayas, the ground was lifted up by about a half meter, indicated by the yellow in the first image, above.

Imagine the difficulty of gathering such data from direct physical examination of the affected area.

Read the full article on the Nepal earthquake preliminary satellite data analysis at the following link:

http://www.wired.com/2015/05/satellite-data-tells-us-nepals-brutal-quake/

Read a general article on the use of satellite data to map earthquakes at the following link:

http://www.wired.com/2015/04/turns-satellites-work-great-mapping-earthquakes/

 

2014 U.S. National Seismic Hazard Model and Induced Seismicity

The U.S. Geologic Society (USGS) National Seismic Hazard Model for the conterminous United States was updated in 2014 to account for new methods, input models, and data necessary for assessing the seismic ground shaking hazard from natural (tectonic) earthquakes. The National Seismic Hazard Maps are derived from seismic hazard curves calculated on a grid of sites across the U.S. that describe the annual frequency of exceeding a set of ground motions. Data and maps from the 2014 U.S. Geological Survey National Seismic Hazard Mapping Project are available for download at the following link:

http://earthquake.usgs.gov/hazards/products/conterminous/

The 2014 maps show higher seismicity in the Eastern U.S. than predicted in previous models. This reflects the significance of the 23 August 2011 magnitude 5.8 earthquake that occurred in Mineral, VA, about 11 miles from the North Anna nuclear power plant. That earthquake was felt as far north as Rhode Island, New York City and Martha’s Vineyard, Mass. The North Anna plant responded well and safely shutdown following the earthquake, which exceeded the plant’s seismic design basis.

The seismic hazard from “potentially induced” earthquakes (I.e., earthquakes that can be associated with man-made activities) was intentionally not considered because there was not a consensus on how to properly treat these earthquakes in a seismic hazard analysis.

The USGS issued a new report on 23 April 2015 examining the sensitivity of the seismic hazard from induced seismicity to five parts of the hazard model: (1) the earthquake catalog, (2) earthquake rates, (3) earthquake locations, (4) earthquake Mmax (maximum magnitude), and (5) earthquake ground motions. In the report, the USGS describes alternative input models for each of the five parts that represent differences in scientific opinions on induced seismicity characteristics.

You can download this interim report for free at the following link:

http://pubs.usgs.gov/of/2015/1070/

The USGS plans to issue a final model after further consideration of the reliability and scientific acceptability of each alternative input model. This matter could have important implications for industries, such as hydraulic fracking and geologic carbon dioxide sequestration, that may contribute to induced seismicity.