University:
Amherst College
Course:
GEOL 105 | Introduction to Oceanography
Academic year:

2021
Views:

223

Pages:

24
Author:

umfikie3qn

Global topography & bathymetry ocean floor bathymetry: ridges and transforms Sea-floor magnetic anomalies preserve a VERY PRECISE record of the creation of oceanic lithosphere with: MAGNETIC REVERSAL TIME SCALE Homework question: Age of anomaly 34: It is the very long one! Spreading rate: spacing of magnetic anomalies 0 5 Ma 5 Ma 1 5 4 3a 3 2a 2 2 2a 3 3a 4 ridge axis Spreading rate = 225 km/ 5 Ma = 45 km/Ma = 4.5 cm/yr 5 both ridges and magnetic anomalies are offset by transforms offset remains constant for long periods of time ridge-ridge transforms are only active between ridge offsets fracture zones are extinct transforms ridge offset across a ridge-ridge transform remains constant over time locked locked Different age lithosphere is juxtaposed across a fracture zone fracture zones traverse entire ocean basin Transforms are parallel to the direction of plate motion On a spherical earth, transforms are curved. They are “small” circles- similar to latitude lines transforms ARE curved pole of rotation (location) determined from transform curvature The San Andreas fault is a transform fault between the North American and Pacific plates The Mendocino fault is a transform fault between the Juan de Fuca and Pacific plates How does the Pacific plate “turn the corner” at the Mendocino triple junction? Three plates: •Pacific •North American •Juan de Fuca come together at the Mendocino triple junction Juan de Fuca plate North American plate Pacific plate Triple junction: How does that work? 3 plates means 3 plate boundaries: JdF-NA; NA-Pac; Pac-JdF JdF-NA: subduction NA-Pac: San Andreas ridge in Gulf of CA Pac-JdP: JdF ridge Mendocino FZ Direction of motion JdF-NA: ???? NA-Pac: San Andreas Pac-JdF: Mendocino FZ Rate of motion JdF-NA: ???? NA-Pac: Gulf of CA spreading Pac-JdF: JdF spreading Vector circuit around a triple junction: Start in NA. Draw a vector to show NA-Pac (NW @ 5.6 cm/yr) From Pac. Draw a vector to show Pac-JdF (ESE@ 5.8 cm/yr) From JdF. Draw a vector to connect to NA. That is the vector for JdF-NA (SSW @ 5.0 cm/yr) NNE-SSW 5.0 cm/yr oblique subduction Dead Sea transform: Saudi Arabia moving northward into Iran Dead Sea transform: Dead Sea where fault steps to left

Global Topography & Bathymetry Ocean Floor Bathymetry Ridges and Transforms

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