Images of the Earth's Crust & Upper Mantle

Updated: Dec 09, 2024

10th International Symposium on Deep Structure of the Continents and their Margins
Taupo, New Zealand, January 2003

(Extract from the IGCP Project 474 Annual Report, 2003)

In January 2003 deep seismic profiling seismologists from around the world attended their biannual meeting in Taupo, New Zealand. In anticipation of a successful outcome of the IGCP proposal, the project was discussed and a possible program of work for 2003 considered. This included the establishment of an Executive Committee for the project and decisions on what data sets should be worked on in the first year of the project. This enabled seismologists to focus on the project scientific commitments at opportune times throughout the year. It was also decided to hold a symposium and business meeting at the time of the AGU Fall Meeting in San Francisco in December to review the work in progress and the establishment of the project web site. The meeting in New Zealand also set out the criteria for selecting transects for compilation, and a first pass list of desired transects to compile.

It is possible to categorize the tectonic setting of terranes into the following:

1. Continent-continent collision zones and orogenic belts
2. Convergent continental margins
3. Passive continental margins
4. Spreading zones (continental and oceanic)
5. Transcurrent fault zones (dextral, sinistral, transform)
6. Other structures and tectonic features

At the January 2003 informal project meeting in New Zealand, 30 transects were considered that may possibly be included on the IGCP 474 web site. The list was not regarded as being complete but it did give an idea of terranes suitable for inclusion at that stage of the project. The 30 transects are divided into their tectonic setting below.

Continent-continent collision zones and orogenic belts

1. Iapetus Suture Transect: a BIRPS Transect across the suture in the North Sea; significance of the Iapetus Suture in understanding Wilson Cycles.
2. Baltic Sea Transect: BABEL deep seismic profiling including the interpretation of an eclogitic lower crust that looks identical to mantle - not a new idea but the first probable candidate imaged in a believable way in seismic data.
3. Western Canada Transect: Lithoprobe SNORCLE transect (now on IGCP474 web site), Archean Shield to the coast across the Cordillera - across much of geological time, with mantle structures clearly imaged.
4. Pyrenees Transect (now on IGCP474 web site): ECORS seismic line across an orogen presently in exhumation.
5. Central Australian Basins Transect: Across major gravity anomalies and a Precambrian orogen showing major Moho offsets
6. Eastern European Alps: present day collision orogeny.
7. Urals Transect: deep seismic profile URSEIS95 across a major continental collision zone.
8. Tibet Transect: Multinational transect INDEPTH across the Earth's thickest crust and highest plateau.
9. Central German Transect: DEKOPR II seismic profiles introducing the 'crocodile' seismic signature of orogens.

Convergent continental margins

1. Timor - Australia Transect: incorporating BIRPS seismic line; one of the few continuous profiles across a continental boundary
2. Appalachian Transect: illustrating thin skinned thrust tectonics, geological evolution of eastern North American continent.
3. Wind River Basin Transect: early deep seismic transect illustrating thrust structures; historically important.
4. Abitibi Transect, Canadian Shield: Lithoprobe; first images with evidence to support Archaean subduction
5. Grenville Front Transect, eastern Canada: important because of the significance of tectonics of equivalent age world-wide.
6. North American West Coast Margin Transect: perhaps LARS 1 with its bright spot against the San Andreas fault. There may be scope for more than one line, eg., Vancouver Island.
7. Andes-Pacific Margin Transect: combined ANCORP96 and CINCA95 seismic profiling across Chile and Bolivia.
8. Hokkaido Ocean-Island Arc Transect: Profiling across a deep trench from the Pacific to an island arc.
9. Trans-Alaska Crustal Transect (TACT).

Passive continental margins

1. Northern UK Margins Transect: DRUM Transect from BIRPS Group demonstrating extensional terrane and fault structures extending into the upper mantle.
2. North Sea Transect: an early seismic transect across the North Sea showing major impact on understanding extensional tectonics, intra-cratonic basins and passive margins.
3. Galicia Bank Transect: Atlantic margin transect off Spain and Portugal; the S reflector and its significance.
4. FIRST Transect: Falkland Islands Regional Seismic Traverse
5. Australia - Antarctic Conjugate Margins Transect: Seismic profiles from the conjugate margins of Australia and Antarctica.
6. North America - Europe Conjugate Margins Transect: Compilation of seismic profiles across the conjugate margin between North America and Europe.

Spreading zones (continental and oceanic)

1. Basin and Range Transect, USA: COCORP profiles illustrating intracratonic extension.
2. Witswaterand Basin, South Africa: industry deep profiling across the Proterozoic basins of southern Africa.

Transcurrent fault zones (dextral, sinistral, transform)

1. Geophysical Profile 973 across the northeast margin of the Tibet Plateau

Other structures and tectonic features

1. Socorro Bright Spot Transect: seismic line in New Mexico showing an intra-crustal bright spot interpreted to be a possible magma reservoir.
2. KTB Deep Crustal Borehole Transect, Germany: 3D imaging at the site of one of the most comprehensively studied deep continental crustal boreholes.
3. Chicxulub Transect: Deep seismic profile across the major 200-300 km wide Chicxulub impact structure on the Yucatan Platform, Mexico.