Publication Date:
2020-03-13
Description:
The permanent rotation of the N.E.Pacific Rift is divided into three first-order rotations covering the whole rift between 20° and 60° N. during the last 80 mio years. The general movement of a clockwise rotation (35-40° altogether) was interrupted during the time between 40 and 20 m.y.b.p. by a weak counterclockwise one (8° altogether). These superordinate rotations can be subdivided in smaller ones with an average duration of 10 m.y. only. It is to suppose that all these rotations are a readjustment of the rift to a changed position of the spreading pole. Compared to it, short-time, oscillatory rotations represent compensating movements of the rift and stabilizing efforts of the plate. For the S.E.Pacific Rift it is supposed that the. Counterclockwise rotation taking place there for the last 7 m.y. is continuing, as may be concluded from the distribution of earthquake epicentres. Furthermore, the problems of pendulum movements and hinge zones at the S.E. and N.E.Pacific Rifts are discussed, which represent the magmatic activity of the rift. Hinge zones are lines of weakness of rifts, which can become fault zones. Up to now they were not mentioned in literature. The internal deformations of the Pacific Plate and Juan de Fuca Plate off California indicated by kinks of the rift, fault-folding and strike slip faults became intense about 1-2 m.y.b.p.
Description:
1. Introduction 2. Superordinate rotations of the East Pacific Rift between 20° and 60° N. 2.1. The clockwise rotation of the N.E. Pacific Rift 80 m.y.b.p. (1st period) 2.2. The counterclockwise rotation of the N.E. Pacific Rift :from 71 to 63 m.y.b.p. (2nd period) 2.3. Rotations of the rift during a transitional stage about 65 to 60 m.y.b.p. (3rd period) 2.4. The great clockwise rotation of the N.E. Pacific Rift 63 to 50 m.y.b.p. (4th period) 2.5. Rotations with a stabilizing function in a transitional stage from 50 to 40 m.y.b.p. (5th period) 2.6. The great counterclockwise rotation of the N.E. Pacific Rift 43 to 20 m.y.b.p. (6th period) 3. Total rotation of the East Pacific Rift between Clarion and Aja Fracture Zones 3.1. Sum of rotations of the rift 3.2. Special position of the plate section between 33° and 37° N. 3.3. The significance of the Mendocino-Pioneer double structure 4. Rotations of the Pacific-Antarctic Rift between 30° and 65° s. 4.1. Complex movements of the rift 4.2. Recent tendencies 5. Magmatic activity of the rift 5.1. Characteristics of rift activity 5.2. Hinge zones of the rift rotations 6. Plate deformation 6.1. Rift rotation at a collision of plates 6.2. Rift shortening due to compression 7. Conclusions References
Language:
English
Type:
info:eu-repo/semantics/book
Format:
application/pdf
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