Arabian Plate

In the Persian Gulf, two tectonic plates are colliding; the Arabian plate (lower left) is running up on the Eurasian plate (upper right). At lower left in the MODIS image is the younger Arabian plate, and it is moving northward to collide with the Eurasian plate. The Persian Gulf (top) and the Gulf of Oman (bottom) were once the site of a rift, a place where two plates pull apart from each other, and the Indian Ocean filled in the widening gap between the two plates; however, the process then reversed, and about 20 million years ago, the gulf began to close up. The collision of the two continental plates gives Iran its mountainous terrain. (http://visibleearth.nasa.gov/view_rec.php?id=2363)

Dead Sea a Pull-apart Basin

Posted in Olelog on Thursday, 29 January 2009.

The shores of the Dead Sea are the lowest point on the surface of the Earth on dry land. It is about 420 metres below sea level and getting lower and lower because the lake is slowly shrinking due to overuse of water from the Jordan river. The dead Sea is also one of the world's saltiest lakes.

The tectonic evolution of the Jordan valley is closely connected with that of the Red Sea. The Red Sea is the classic example of an incipient ocean. It represents the classic transition from a continental to an ocean rift to a narrow ocean. The formation of this new ocean has only gone on within the latest 40 million years (or a bit less). A quick glance at a map discloses a geometrical problem with the plate movements. The transform fault (system) up through the Jordan Valley does not run parallel with the extension of the Red Sea. About 105-110 km of left-lateral displacement between the African and Arabian tectonic plates took place along this fault system during the last 15 million years. The average rate of motion during the last 5 million years is 5 millimeters per year.

Because of the geometrical irregularities the fault has evolved in an en echelon pattern as can be seen on the more detailed map of the system produced by the U. S. Geological Survey. The fault-parallel extensions have lead to a series of so called pull-apart basins - the Dead Sea located in one of them. The two sides of the basin are bounded by faults with primarily horizontal displacement, and the other two sides are bounded by faults with vertical components of slip. They are called pull-apart basins because the crust is literally pulled apart in the section between the two strike-slip faults . Or in other words pull-apart basins are depressions that form as the result of crustal extension along strike-slip systems where the sense of fault stepping or bending coincides with that of fault slip. See the diagram further below.

In the course of its existence the basin has been filled with a layer of sediments that is up to ten kilometers thick.

In a paper published in Physics of the Earth and Planetary Interiors (Volume 171, Issues 1-4, December 2008, Pages 387-399) Petrunin and Sobolev demonstrate which parameters control the subsidence rate, by the use of three-dimensional numerical models.

Part of this post is reworked material from the U.S. Geological Survey site on Tectonics and Geology of the Dead Sea.

Apart from wishing all people in the area shalom, salaam and peace I shall refrain from political, religious and cultural comments. This is about geology. I have by the way had the privilege to see the Dead Sea from both the Israeli and the Jordanian side, and to swim in the Dead Sea, which is a weird experience.

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