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The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 ± 4 mm/yr between the Pacific and Nazca plates. [20] The Mid-Atlantic Ridge is a slow-spreading center, while the East Pacific Rise is an example of fast spreading.
Within the trough is a slowly spreading north–south ridge which may be the result of an offset or gap of approximately 420 kilometres (260 mi) along the main fault trace. The Cayman spreading ridge shows a long-term opening rate of 11–12 mm/yr. [4] The eastern section of the trough has been named the Gonâve Microplate.
Harry Hess proposed the seafloor spreading hypothesis in 1960 (published in 1962 [1]); the term "spreading of the seafloor" was introduced by geophysicist Robert S. Dietz in 1961. [2] According to Hess, seafloor was created at mid-oceanic ridges by the convection of the Earth's mantle, pushing and spreading the older crust away from the ridge. [3]
DSDP provided crucial data to support the seafloor spreading hypothesis and helped to prove the theory of plate tectonics. DSDP was the first of three international scientific ocean drilling programs that have operated over more than 40 years.
Correlation of the anomalies to the history of Earth's magnetic field reversals allowed the age of the seafloor to be estimated. [22] This connection was interpreted as the spreading of the seafloor from the ridge crests. [23] [22] Linking spreading centers and transform faults to a common cause helped to develop the concept of plate tectonics ...
Evidence of seafloor spreading has been seen in cores of the basin floor. The thickness of sediment that collected in the basin decreased toward the center of the basin, indicating a younger surface. The idea that thickness and age of sediment on the sea floor is related to the age of the oceanic crust was proposed by Harry Hess. [5]
A propagating rift is a seafloor feature associated with spreading centers at mid-ocean ridges and back-arc basins. [1] They are more commonly observed on faster rate spreading centers (50 mm/year or more). [2] These features are formed by the lengthening of one spreading segment at the expense of an offset neighboring spreading segment. [3]
The seafloor spreading center jumps three times, at 25.5 Ma, at 24.7 Ma and at 20.5 Ma. [7] These jumps are regarded as the boundaries of the three sea floor spreading episodes that moved the extension to the south out of its original position in the Xisha Trough. Figure 4 shows the trajectory of the seafloor spreading center. 37 Ma to 25.5 Ma.