GFZ German research centre for geo sciences

Monsoon affects tectonics

15.06.2015|Monsoon affects tectonics- A new climate-tectonic coupling mechanism: Climate change after 23 million years ago intensified the East Asian Summer Monsoon. This strongly increased the sediment flux into the South China Sea basin and lead to anomalous subsidence of the Earth’s surface. The deep basins on the northern margin of the South China Sea result from this coupling mechanism of climatic and tectonic processes.

A new climate-tectonic coupling mechanism

15.06.2015: Climate change after 23 million years ago intensified the East Asian Summer Monsoon. This strongly increased the sediment flux into the South China Sea basin and lead to anomalous subsidence of the Earth’s surface. The deep basins on the northern margin of the South China Sea result from this coupling mechanism of climatic and tectonic processes.

When continents break apart, new sedimentary basins are formed at the rifted margins, such as offshore West Africa. When continental rupture is complete, these basins cool continuously sinking steadily and slowly to great ocean depths.

Basins of the South China Sea near the island of Hainan, especially the Baiyun Basin, defy this rule. Instead of slowing down, subsidence even accelerated, postdating break-up by several million years. A team of scientists from the US, Germany, and Australia found a mechanism to explain this observation.

The enormous sediment thickness is key in understanding these basins,” explains Co-author Sascha Brune of the GFZ German Research Centre for Geosciences. “We combined geophysical observations and well data with numerical forward modelling to show that the exceptionally weak continental crust of the South China Sea margins began to flow under the sedimentary load.

Where did the immense volume of sediments come from? A change of South Asia’s climate starting about 23 million years ago lead to intensification of the monsoon and causing higher precipitation and enhanced erosion in the high Asian mountain chains. The eroded material was distributed into the surrounding seas and oceans by large rivers like the Ganges, Indus, and Pearl River. In contrast to the Indus and Bengal fan, continental crust of the South China Sea is extremely weak. Here, the sedimentary load deformed the ductile crustal material to 15,000 metres depth, squeezing out the ductile material from under the heavy load and enabling the observed unusual thinning of the crust. Peter Clift from the Louisiana State University: “This mechanism constitutes a newly recognized component of climate-tectonic coupling.” When the monsoon intensified after about 23 million years ago, accelerated subsidence commenced within the deep South China Sea basins.

"Peter D. Clift, Sascha Brune, Javier Quinteros: Climate changes control offshore crustal structure at South China Sea continental margin”, Earth and Planetary Science Letters EPSL, Advance Online Publication, 15.06.2015, Doi: 10.1016/j.epsl.2015.03.032

 

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