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We have a magnetic field that it is very similar to the one of a dipole. Well in reality this is true close to the surface if we go far away enough it looks more complex. Magnetopause 10Re Moon 60Re. Magnetic Field is a vector. It has an intensity (can be measured looking

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We have a magnetic field that it is very similar to the one of a dipole

We have a magnetic field that it is very similar to the one of a dipole.

Well in reality this is true close to the surface if we go far away enough it looks more complex

Magnetopause 10Re Moon 60Re


Magnetic field is a vector

Magnetic Field is a vector

It has an intensity (can be measured looking

At the oscillation of a compass)

And a direction

The direction change with the position

Magnetic Pole:

The place where the compass is

pointing down

Magnetic Equator:

The place where the compass

is horizontal


We have a magnetic field that it is very similar to the one of a dipole

The Earth’s Magnetic Field

B = (X, Y, Z)

Or B = (F, I, D ) OrB = (D, H, Z)

F: intensity

I: inclination

D: declination

H: Horizontal component

The seven elements of the (local) magnetic fieldin the geographic coordinate system

I. Geomagnetic field – Local Geomagnetic Field Vector


We have a magnetic field that it is very similar to the one of a dipole

The Earth’s Magnetic Field

From this:

Magnetic pole is the point where

H=0 I= +- 90

Magnetic Equator the point where

I=0

F: intensity

I: inclination

D: declination

H: Horizontal component

Where 3000nT<H<6000nT erratic zone (compass work badly)

Where H<3000nT unusable zone (compass does not work)

I. Geomagnetic field – Local Geomagnetic Field Vector


We have a magnetic field that it is very similar to the one of a dipole

From Press, 1992.

90% of spatial field distribution can be explained by a simple dipolar field


We have a magnetic field that it is very similar to the one of a dipole

Geomagnetic inclination (IGRF)

I. Geomagnetic field – Worldwide Variation of I


We have a magnetic field that it is very similar to the one of a dipole

Hierbei ist θ die sogenannte magnetische Co-Latitude.


We have a magnetic field that it is very similar to the one of a dipole

Beispiel-Rechnung:

Basalt-Probe aus einem gegenwärtigen Ort an 47 S, 20 E.

Die remanente Magnetisierung ergibt eine Paleo-Inklination

von 30 Grad.

Bestimmen wir die Paläolatitude


We have a magnetic field that it is very similar to the one of a dipole

Position: 47S 20E

StereoNet


We have a magnetic field that it is very similar to the one of a dipole

Position: 47S 20E

Declination: N30E


We have a magnetic field that it is very similar to the one of a dipole

Position: 47S 20E

Declination: N30E

Inclination: 30 grad

Paleolat:16 grad

Distance Pole:74 grad


We have a magnetic field that it is very similar to the one of a dipole

Position: 47S 20E

Declination: N30E

Inclination: 30 grad

Paleolat:16 grad

Distance Pole:74 grad


We have a magnetic field that it is very similar to the one of a dipole

APW

Apparent Polar Wander


We have a magnetic field that it is very similar to the one of a dipole

Since the mechanism of generation of the magnetic field is influenced by the rotation the dipole is mainly oriented along the rotation axis and people use the magnetic pole as past proxy for the rotation axis


Paleomagnetic field magnetization of rocks

PaleoMagnetic Field:Magnetization of Rocks

DRM

Detrital

Remanent

Magnetization

TRM

Thermal

Remanent

Magnetization


We have a magnetic field that it is very similar to the one of a dipole

Gesteinsmagnetisierung:

Curie Temperatur: etwa 580 Grad C für Magnetit

680 Grad C für Hämatit

Blocking Temperatur:

Typische Schmelztemperaturen liegen allerdings bei

1100 – 800 Grad C, also wesentlich höher.

Das heißt, Gesteine können eine Magnetisierung im

Umfeld annehmen, und diese bei Abkühlung unter die

Blocking-Temperatur auf geologische Zeiträume hinweg

behalten.


We have a magnetic field that it is very similar to the one of a dipole

Wir unterscheiden:

Thermoremanente Magnetisierung: TRM

Depositionale Magnetisierung (in Sedimenten): DRM

Chemoremanente Magnetisierung: CRM

DRM entsteht durch die geordnete Ablagerung magnetischer

Minerale in Sedimentgesteinen zur Zeit der Deposition.

CRM entsteht durch das langsame Mineralwachstum nach der

Ablagerung oder Erstarrung.


A tape recorder an essay of geopoetry

A tape recorder “An essay of GeoPoetry”

Submarine Lava flow at ridge

From

www.ridge2000.org/science/tcs/epr06activity.php


A tape recorder an essay of geopoetry1

A tape recorder “An essay of GeoPoetry”


Dating the magnetic reversal

Dating the Magnetic Reversal


We have a magnetic field that it is very similar to the one of a dipole

Chron


A tape recorder an essay of geopoetry2

A tape recorder “An essay of GeoPoetry”

Isochron (or chron)


We have a magnetic field that it is very similar to the one of a dipole

Chron 13

~ 34 Ma


We have a magnetic field that it is very similar to the one of a dipole

Realität:

Die Magnetisierung wird nicht in einem infinitesimalen Bereich um den Rücken

angenommen.

Die Magmenkammern und die Zone vulkanischer Aktivität an einem Rücken, an

denen die Magnetisierung stattfindet haben eine Ausdehnungen von mehreren

Kilometern (bekannt z.B. durch seismische Messungen). (~5-15 km)

(Im Bild: Mit zunehmender Entfernung vom Rücken werden die Krustengesteine

Älter. )


We have a magnetic field that it is very similar to the one of a dipole

Modell mit zeitlicher und räumlicher Zufallsverteilung der Magmenentstehung in

Aktivitätszonen unterschiedlicher (10km, 2km, 0km) Weite. Spreizungsrate: 1cm/yr (Atlantik).

(i)/(ii)/(iii) 10 Km Aktivitätszone

2 Km “

0 Km (sog. ideales Blockmodell)

Beachte: (i)/(ii)/(iii) ergeben komplexere mag. Anomalien.

Jeweils berechnete mag. Anomalien


We have a magnetic field that it is very similar to the one of a dipole

Berechnung mariner geomagnetischer Anomalien (I):

Die theoretische Modellierung magnetischer Anomalien auf dem Ozeanboden ermöglicht es

uns, geologische (vergangene) Spreizungsraten aus den heute beobachten Anomalien zu

berechnen.

Daneben lässt sich aber mit Hilfe der quantitativen Modellierung auch feststellen, ob die

Platten ihre Latitude im Laufe der Zeit verändert haben. Dieses Frage ist natürlich der von

uns schon behandelten Frage analog, wie man die Paläo-Latitude z.B. von Laven auf den

Kontinenten aus Messung remanenter Magnetisierung (z.B. Inklination) bestimmt.

Beispiel:

Mittelozeanischer Rücken, am Äquator, symmetrische (Ost-West gerichtete) Spreizungsrate;

Am Äquator ist die Vertikalkomponente (Z) des Erdmagnetfeldes identisch Null. In diesem

Fall ist die permanente Magnetisierung eines idealisierten Blocks am Rücken M=0, My, 0


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