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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.

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 of a dipole.

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


The Earth’s Magnetic Field of a dipole.

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


The Earth’s Magnetic Field of a dipole.

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


From Press, 1992. of a dipole.

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


Geomagnetic inclination (IGRF) of a dipole.

I. Geomagnetic field – Worldwide Variation of I



Beispiel-Rechnung: of a dipole.

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


Position: 47S 20E of a dipole.

StereoNet


Position: 47S 20E of a dipole.

Declination: N30E


Position: 47S 20E of a dipole.

Declination: N30E

Inclination: 30 grad

Paleolat:16 grad

Distance Pole:74 grad


Position: 47S 20E of a dipole.

Declination: N30E

Inclination: 30 grad

Paleolat:16 grad

Distance Pole:74 grad


APW of a dipole.

Apparent Polar Wander


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: 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 axisMagnetization of Rocks

DRM

Detrital

Remanent

Magnetization

TRM

Thermal

Remanent

Magnetization


Gesteinsmagnetisierung: 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

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.


Wir unterscheiden: 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

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 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“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 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“An essay of GeoPoetry”


Dating the magnetic reversal
Dating the Magnetic Reversal 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


Chron 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


A tape recorder an essay of geopoetry2
A tape recorder 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“An essay of GeoPoetry”

Isochron (or chron)


Chron 13 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

~ 34 Ma


Realität: 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

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. )


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


Berechnung mariner geomagnetischer Anomalien (I): Magmenentstehung in

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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