Abstract
The formation of mud volcanoes/mud diapirs is directly related to oil and gas accumulation and gas-hydrate mineralization. Their eruptive activities easily cause engineering accidents and may increase the greenhouse effect by the eruption of methane gas. Many scholars have performed much research on the developmental characteristics, geochemistry, and carbon emissions of mud diapirs/mud volcanoes, but the formation mechanism of mud diapirs/mud volcanoes is still controversial. Mud diapirs and mud volcanoes are especially developed in the northern South China Sea and are accompanied by abundant oil, gas, and gas-hydrate resources. Based on the mud volcanoes/mud diapirs in the northern South China Sea, the physical simulation experiments of mud diapir/mud volcano formation and evolution under different fluid pressures and tectonic environments have been performed by loading a fluid-input system in traditional sandbox simulation equipment. The genetic mechanism of mud diapirs/mud volcanoes is revealed, and a fluid-leakage model of mud diapirs/mud volcanoes under different geological conditions is established. We believe that in an overpressured environment, the greater the thickness of the overlying strata is, the greater the pressure or power required for the upward migration of muddy fluid to penetrate the overlying strata. Tectonic activity promotes the development of mud volcanos/mud diapirs. To a certain extent, the more intense the tectonic activity is, the more significant the effect of promoting the development of mud volcanoes/mud diapirs and the larger the mud diapirs/mud volcanoes become.
Highlights
Mud diapirs and mud volcanoes are two kinds of geological phenomena caused by the upward migration of deep fluid under overpressure that penetrates the overlying strata
In the overpressure group experiment, we changed the formation pressure by changing the thickness of the overlying strata and simulated the pressure required for fluid upwelling to form mud diapirs/mud volcanoes
When the depth of the fluid source is deeper or the sedimentary cap on the mud-source layer is thicker, the pressure/power is greater that is required for the upward migration of the fluid to penetrate the overlying strata and to reach the seabed to accumulate and form mud volcanoes
Summary
Mud diapirs and mud volcanoes are two kinds of geological phenomena caused by the upward migration of deep fluid under overpressure that penetrates the overlying strata. The submarine mud diapirs and mud volcanoes have the same genetic mechanism and similar evolutionary characteristics and can even be considered as the late evolution product of the mud-diapir structure [1,2,3,4,5,6]. The mud diapirs/mud volcanoes in the northern continental margin basins of the South China Sea are mainly distributed in the central mud diapir belt of the Yinggehai Basin in the shallow water area of the continental shelf, the central and southern depression belts of the Qiongdongnan Basin in the deepwater area of the continental slope, the Baiyun Sag of the Zhu II Depression in the Pearl River Mouth Basin, the southeastern Dongsha Sag, and the deepwater area of the southern sag of the Southwest Taiwan Basin, as well as some adjacent onshore areas.
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