Gorda plate
The Gorda Plate is a tectonic plate that lies beneath the eastern Pacific Ocean off the coast of northern California and southern Oregon . It emerged from the disintegration of the northern Farallon Plate and now forms a 45,000 square kilometer microplate .
definition
The east side of the Gorda Plate, which consists of oceanic lithosphere, is a convergent plate boundary, at which it is subducted under the North American Plate in a northeast direction at a rate of 18 millimeters / year (relative to the fixed African plate ). Its southern boundary follows the east-west reaching Mendocino Fault , a transform fault that separates it from the Pacific Plate to the south. In the west, between 40 and 43 ° north latitude in the east Pacific, the Gorda Ridge rises , a divergent plate boundary on which the Gorda plate is formed. On its north side is the northwest-trending Blanco fracture zone , which is also a transform fault and separates the Gorda Plate from the Juan de Fuca Plate in the north. However, some authors recognize that the Gordaplatte is independent and only see the southern extension of the Juan de Fuca plate in it. Occasionally the Gordaplatte is further subdivided into a South Gordaplatte and a North Gordaplatte , the borderline of which runs approximately at the level of the Oregon / California state border.
Emergence
Like the Nazca plate , the Cocos plate , the Rivera plate , the Juan de Fuca plate and the Explorer plate , the Gorda plate also emerged from the disintegration of the Farallon plate, which was caused by the subduction of the Farallon plate under the North American and South American continents in the Jura began. From 18 million years BP (lower Miocene - Burdigalium ) the Gorda plate then separated from the Juan de Fuca plate.
The spread on the north-east-trending Gorda Ridge was neither temporally nor spatially uniform. In addition, a reorganization in spreading mode occurred 2 million years ago and the speeds (reported as half-spreading rates) decreased considerably. Two million years ago, the half-spread rate on the northern ridge of the Gorda was 30 to 40 millimeters / year, after that it was only 27.5 millimeters / year. Similar to the southern section, which 2 million years ago was still spreading at 20 to 32.5 millimeters / year and now only at 14 millimeters / year.
On the basis of the magnetic anomalies ("stripe pattern") the history of the Gorda plate can be traced back to 7 million years BP (beginning of the Messinian ), but the plate is undoubtedly much older.
deformation
Compared to other tectonic plates, which are characterized by their rigidity, the Gorda plate shows strong internal deformations . In the Gorda Basin of the interior of the plate, south of 41.6 ° N, numerous faults were mapped in both the sediments and the basement. Voltages that are transmitted from both the North American plate and extending from the Pacific plate and the Gorda plate, loosen inside her frequent earthquakes such as the earthquake in from Humboldt County in 1980 that a magnitude reached 7.2 and 1 , Caused $ 75 million in damage.
Subduction and volcanism
The subduction of the Gorda Plate in the Cascadia Subduction Zone is directly related to the appearance of volcanoes in Northern California, most notably Mount Shasta and Lassen Peak , which last erupted in 1914-1917.
See also
Individual evidence
- ^ Wilson, DS: Deformation of the so-called Gorda plate . In: Journal of Geophysical Research . v. 94, 1989, pp. 3065-3075 .
- ^ Wilson, DS: Confidence intervals for motion and deformation of the Juan de Fuca plate . In: Journal of Geophysical Research . v. 98, 1993, pp. 16.053-16.071 .
- ↑ Gulick, S., Meltzer, A. and S. Clarke: Seismic structure of the southern Cascadia subduction zone and accretionary prism north of the Mendocino triple junction . In: Journal of Geophysical Research-Solid Earth . 103 (B11), 1998.