Great Rift Valley

Great Rift Valley

The Great Rift Valley is a long Rift Valley bounded by a series of faults. In addition, there is the TV drama "the Great Rift Valley" with the same name.

Basic introduction

A long fault depression Valley bounded by a series of faults. The Great Rift Valley is mostly 30-75 km wide and hundreds to thousands of km long. The East African Rift Valley is the longest rift system in the world. The East Branch starts from the estuary of the sire River in the south, passes through the East African plateau and the central part of the Ethiopian plateau in the north through Lake Malawi, extends northward along the Red Sea to the Jordan Valley in Western Asia, with a total length of more than 6400 km; the West Branch starts from the northwest end of Lake Malawi, and reaches the Nile valley through Lake Tanganyika, Lake Kivu, Lake Amin and lake moboto, with a total length of about 1700 km

Km. Lake Baikal in the Soviet Union is the deepest lake in the Great Rift Valley, with a maximum depth of more than 1600 meters. The Shanxi Graben System in China may be the early stage of the development of the Great Rift Valley.

Geomorphological features

① The length of rift exceeds the width, and many rift basins are distributed in regular echelon pattern with asymmetric cross sections.

② There are volcanoes in the rift valley.

③ Planation surface remains are often found in the mountains on both sides of the rift valley.

④ The thickness of sediments in the rift valley is large, with an average of 1.5-2.5 km, and the thickest of 7-8 km (South Baikal Basin). The grain size of the sediments gradually coarsens from bottom to top; horizontally, it changes from the Piedmont clastic sedimentary facies at the edge of the rift to the middle of the rift into fine-grained lacustrine or swamp facies; the sediments are often mixed with volcanic rocks.

⑤ The modern crustal movement in the rift is very active, and the maximum subsidence velocity can reach 60-100 mm / year (Lake Galilee area); the horizontal movement is also obvious, and the tension of the Ethiopian Rift is 3-8 mm / year; the heat flow value of the rift is generally 2.0 microcar / (s · cm 2), which is higher than the global average heat flow value of 1.5 microcar / (s · cm 2); the crustal thickness of the rift is 20-30 km, It is thinner than the average thickness of the continental crust (40 km); most of the gravity anomalies are negative; there are many earthquakes, which are distributed along a certain direction, and the focal depth is mostly within 30 km.

Cause of formation

Due to the ascending action of the hot mantle, the dome shape is formed at the place where the mantle convection rises, resulting in regional tension, where the rock (layer) is continuously thinning, resulting in the collapse of the dome axis and the formation of rift. For example, the Baikal rift belt first formed in the South Baikal Basin, and then extended to the northeast and southwest until the middle Quaternary. According to the grain size of the sediments in the rift valley, rifting can be divided into two stages: ① in the initial formation stage of the basin, the ancient weathering crust, which had been flattened for a long time and had little undulation, was eroded and deposited in the basin, and they were all fine-grained sediments; ② in the stage of the basin's great decline, the terrain elevation difference increased, the mountain erosion on both sides of the basin strengthened, and the coarse-grained sediments accumulated in the rift valley.

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