ProjectB4

From !khure

(Difference between revisions)
(New page: <center><h2>Project B4: Anatomy of an old giant impact crater using magnetic imaging (from the city of Paris to the town of Parys)</h2> <h3>French pi: A. Galdeano (with S. Gilder)<br> Sout...)
Line 9: Line 9:
* '''France''': Armand Galdeano, Maxime Legoff
* '''France''': Armand Galdeano, Maxime Legoff
* '''Other''': Stuart Gilder (Munich), Laurent Carpozen
* '''Other''': Stuart Gilder (Munich), Laurent Carpozen
 +
 +
<h3>Aims and objectives</h3>
 +
# To apply magnetic imaging to map out the structure of the Vredefort impact crater in high resolution.
 +
# To heighten the profile of the Vredefort impact crater in the light of its world heritage status, by producing useful images of important faults and subtle structural features that have an important bearing on land use (e.g. bridges, water resources).
 +
# To apply our knowledge of the effects of meteorite impacts, to further our understanding on the relative strength of the magnetic field of Earth and other planets in our solar system.
 +
# To provide MSc training for at least one black South African student. A student for this project has already been identified.
 +
 +
<h3>Introduction.</h3>
 +
<p>The Vredefort dome is the largest impact crater on Earth, and any new information on Vredefort sets a precedent for understanding meteorite impacts both on Earth and on the other planets in our solar system. However, our understanding of the Vredefort structure is still far from complete, and in particular we have very little knowledge of the structure of the crater core, largely because the central area is covered by younger rocks. The central core is key, as it preserves a history of crustal strength, impact, flexure and relaxation from the time when the impact formed. By combining gravity, magnetics, seismics (both Vibroseis and teleseismic), and MT data we can build up an unprecedented 3D model of the structure at depth.</p>
 +
 +
<h3>Aeromagnetic Surveys</h3>
 +
[[image:Fig1_B4.jpg|right|350px|thumb|Fig. 1. Aeromagnetic map over the Vredefort crater flown in 1981 by the South African Geological Survey. The inserts show the proposed survey regions.]]
 +
<p>Low resolution aeromagnetic images with 1km line spacing over the structure show strong, well-defined concentric patterns (Fig. 1). In the rim, the patterns reflect the different sedimentary strata of the Witwatersrand basin. A prominent negative magnetic anomaly that extends in a broad semicircular belt ~2 to 4 km wide around most of the basement core (inner 30x 30km insert; Fig.1.) is roughly centered above the amphibolite-granulite facies transition which is recognized as a fundamental boundary within the crust and is commonly considered to designate the transition from middle to lower crustal levels [1]. The Vredefort crater contains the only exposure of the amphibolite-granulite facies transition in Southern Africa.</p>

Revision as of 13:36, 6 July 2009

Project B4: Anatomy of an old giant impact crater using magnetic imaging (from the city of Paris to the town of Parys)

French pi: A. Galdeano (with S. Gilder)
South African pi: R. Hart

Contents

Project Participants

  • South Africa: Rodger Hart, Susan Webb
  • France: Armand Galdeano, Maxime Legoff
  • Other: Stuart Gilder (Munich), Laurent Carpozen

Aims and objectives

  1. To apply magnetic imaging to map out the structure of the Vredefort impact crater in high resolution.
  2. To heighten the profile of the Vredefort impact crater in the light of its world heritage status, by producing useful images of important faults and subtle structural features that have an important bearing on land use (e.g. bridges, water resources).
  3. To apply our knowledge of the effects of meteorite impacts, to further our understanding on the relative strength of the magnetic field of Earth and other planets in our solar system.
  4. To provide MSc training for at least one black South African student. A student for this project has already been identified.

Introduction.

The Vredefort dome is the largest impact crater on Earth, and any new information on Vredefort sets a precedent for understanding meteorite impacts both on Earth and on the other planets in our solar system. However, our understanding of the Vredefort structure is still far from complete, and in particular we have very little knowledge of the structure of the crater core, largely because the central area is covered by younger rocks. The central core is key, as it preserves a history of crustal strength, impact, flexure and relaxation from the time when the impact formed. By combining gravity, magnetics, seismics (both Vibroseis and teleseismic), and MT data we can build up an unprecedented 3D model of the structure at depth.

Aeromagnetic Surveys

Fig. 1. Aeromagnetic map over the Vredefort crater flown in 1981 by the South African Geological Survey. The inserts show the proposed survey regions.

Low resolution aeromagnetic images with 1km line spacing over the structure show strong, well-defined concentric patterns (Fig. 1). In the rim, the patterns reflect the different sedimentary strata of the Witwatersrand basin. A prominent negative magnetic anomaly that extends in a broad semicircular belt ~2 to 4 km wide around most of the basement core (inner 30x 30km insert; Fig.1.) is roughly centered above the amphibolite-granulite facies transition which is recognized as a fundamental boundary within the crust and is commonly considered to designate the transition from middle to lower crustal levels [1]. The Vredefort crater contains the only exposure of the amphibolite-granulite facies transition in Southern Africa.