Introduction to Earth System Solid Earth part Rocco Malservisi Phone:

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 The Magnetic Poles are close to the geographical Poles but do not coincide (~11 off) Magnetic Pole: The place where the compass is pointing Down Magnetic Equator: The place where the compass is horizontal

The seven elements of the (local) magnetic field in the geographic coordinate system B = (X, Y, Z) Or B = (F, I, D ) Or B = (D, H, Z) The Earths Magnetic Field I. Geomagnetic field – Local Geomagnetic Field Vector F: intensity I: inclination D: declination H: Horizontal component

The place where the axis of the dipole intersect the surface Of the earth are called geomagnetic poles

From Butler, Palaeomagnetism, Slide I. Geomagnetic field – Temporal Variations other secular variation: reversal

PaleoMagnetic Field: Magnetization of Rocks DRM Detrital Remanent Magnetization TRM Thermal Remanent Magnetization

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.

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 Submarine Lava flow at ridge From

Dating the Magnetic Reversal

PaleoPole position If we measure I we can compute The original Latitude, from this If we know the position of the Sample we compute the Position of the paleopole. Note if the plate move we have an Apparent Polar Wander

I. Geomagnetic field – Worldwide Variation of I Geomagnetic inclination (IGRF)

Hierbei ist θ die sogenannte magnetische Co-Latitude.

Beispiel-Rechnung: Basalt-Probe aus einem gegenwärtigen Ort an 47 S, 20 E. Die remanente Magnetisierung ergibt eine Paleo-Inklination von 30 Grad. Paleo-Deklination N30E. Bestimmen wir die Paläolatitude

Position: 47S 20EStereoNet

Position: 47S 20E Declination: N30E

Position: 47S 20E Declination: N30E Inclination: 30 grad Paleolat:16 grad Distance Pole:74 grad

Position: 47S 20E Declination: N30E Inclination: 30 grad Paleolat:16 grad Distance Pole:74 grad

APW 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

APW Apparent Polar Wander

Ocean Spreading Looking for subs the British and Americans developed a map of Magnetic anomalies of the sea floor, in 1961 Harry Hess explained It using seafloor spreading theory.

A tape recorder An essay of GeoPoetry

Dating the Magnetic Reversal

Chron

A tape recorder An essay of GeoPoetry Isochron (or chron)

Continental Drift In 1912 Wegener suggested that the current position of the continents has evolved and that the continents were once fit together in a supercontinent called PANGAEA.

Evidences for Continental Drift The shape of the continent seems to fit together.

Evidences for Continental Drift The shape of the continent seems to fit together. Matching Geological Units

Evidences for Continental Drift The shape of the continent seems to fit together. Matching Geological Units Distribution of Fossils

Evidences for Continental Drift The shape of the continent seems to fit together. Matching Geological Units Distribution of Fossils Distribution of Climatic Belts

Evidences for Continental Drift The shape of the continent seems to fit together. Matching Geological Units Distribution of Fossils Distribution of Climatic Belts Location of past glacial regions.

Evidences for Continental Drift The shape of the continent seems to fit together. Matching Geological Units Distribution of Fossils Distribution of Climatic Belts Location of past glacial regions. BIG PROBLEM!!!! HOW CAN THE WEAK CONTINENTS MOVE TROUGH THE STRONG OCEANS?? WHERE THE FORCES TO MOVE THE CONTINENTS COME FROM???

APW 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

A tape recorder An essay of GeoPoetry

Magnetic Reversal on Sea Floor

PLATE TECTONICS Plate Tectonic is a theory that unify different previous geological theories (CONTINENTAL DRIFT and OCEAN SPREADING) and that can explain the majority of the solid earth system observations. Basic concept: The outermost layer (LITHOSPHERE) is divided in a small number of rigid plates in relative motion one respect to the other and that are moving on a weak ASTHENOSPHERE

PLATE TECTONICS Basic concept: The outermost layer (LITHOSPHERE) is divided in a small number of rigid plates in relative motion one respect to the other and that are moving on a weak ASTHENOSPHERE Basic Assumptions: The astenosphere viscosity is low enough to allow on long time scale for viscous flow; The generation of new plate material occurs by sea floor spreading; The new oceanic lithosphere form part of a rigid plate that may or may not include continental material; Earths surface area remains constant; this means that seafloor spreading must be balanced by consumption of plate elsewhere; Lithospheric plate are capable of transmitting stress over great horizontal scale. In other words plates are rigid and the deformation is concentrated along the boundaries.

Brittle Ductile behavior brittle ductile The behavior is dependent on the temperature, the material But also by the RATE!!!!