博士 / 國立中央大學 / 地球科學學系 / 101 / In order to identify the mud diapirs and mud volcanoes off SW Taiwan, we have examined ~1,530 km long MCS profiles, multibeam bathymetric data, and deep-towed sidescan sonar images and sub-bottom profilers. Our results show ten quasi-linear mud diapirs, oriented NNE-SSW to N-S directions. Most of the diapiric structures are covered by a layer of young sediments, but some have pierced through thick sediments and exposed to the seafloor, such as the Shell-Tomb Ridge, the south pinnacle of MD5, the Fangliao Ridge (MD8) and Xiaoliuchiu islet (MD2). The disturbance of sedimentary strata on both sides and top of the diapiric structures suggests that the diapirism is active. However, MD10 is probably no more active because modern sedimentary strata deposited above the diapir are undisturbed.
Thirteen mud volcanoes are identified from the multibeam bathymetric data off SW Taiwan. These mud volcanoes generally occur on tops of the diapiric structures. The mud volcanoes are typically cone-shaped, except MV6 which is more elongated. The heights of the cone-shaped mud volcanoes range from 65 m to 345 m, and the diameters at base from 680 m to 4,100 m. These mud volcanoes have very steep slopes (from 5.3° to 13.6°). We suggest that the mud volcanoes are fed by high-viscosity flows. The 10 mud volcanoes (except MV8, MV11 and MV12) with steep cone-shaped craters could be produced by higher viscous flows. In contrast, 3 mud volcanoes (MV8, MV11 and MV12) could be fed by relatively low viscosity flows, resulting in the flat volcanic edifice on the crest.
For the first time, a ROV observation was conducted to observe the mud volcanoes off SW Taiwan in 2011. The results of ROV observations reveal three mud volcanoes (MV1, MV5 and MV12) with active eruptions. The eruption cycles of MV1 and MV5 are about 3~5 minutes and 5~8 minutes, respectively. However, the MV12 is characterized by continuous outpouring of mud together with gas plume (the cycle is about 3~10 seconds). Two modes of eruption (explosive and effusive eruptions) can be identified. The MV1 and MV5 are characterized by explosive eruption, indicating that they could be formed by relative lower-permeability feeder, which can generate excessive pore fluid pressure beneath the mud volcano. The MV12 shows an effusive eruption type is related to high permeability conduit facilitates fluid flow and leads to more effusive eruption. In terms of size, the MV9~MV13 (diameters of 2,800 m to 4,100 m) located at deeper water depths are rather large than the other MV1~MV8 (diameters of 680 m to 2,200 m) located at shallower water depths. In addition, the effusive eruption of MV12 (diameter ~4,100 m) is rather larger than the explosive eruptions of MV1 (diameter of ~1,250 m) and MV5 (diameter of ~2,200 m). The larger cone-shaped mud volcanoes located at deeper water depths could be related to a longer eruption history. However, the large mud volcano is also common associated with effusive eruption. The mud flows on the flank of six mud volcanoes (MV1, MV3, MV5, MV6, MV9 and MV10), imaged by the high backscatter intensity bands from the sidescan sonar images. In general, the mud volcanoes in the continental slope off SW Taiwan are very active. The MV10 is the most active one because its edifice shows the steepest slope (~13.6°) and highest (345 m), and the only high methane concentration (200 nL/L) was detected in water column near sea surface above the mud volcano. The formation of mud diapirs and volcanoes in the study area are ascribed to the over-pressured fluid in sedimentary layers and compressional tectonic forces. Especially, the gas-bearing fluid plays an important role in enhancing the intrusion after the diapirism.
In our study area, the gas source is characterized by a mixture of thermogenic and biogenic gases. As shown in the Fangliao Ridge (MD8), in the north end of MD5 areas, MV4 and MV11, the mud diapir is an efficient pathway for the vertical migration of thermogenic gas fluid from the deeper part of the sedimentary layers. Seafloor photos were taken by ROV observations and TowCam system, which shows the chemosynthetic communities (shells and bacteria mats) and authigenic carbonates are widely distributed on the seafloor. The gas seeps, pockmark, gas plumes and active mud volcanoes eruptions are observed in the study area. In addition, the anomalous high methane concentrations of seawater are detected in the water column above the mud volcanoes. Accordingly, we suggest the high methane fluxes in the study area.
The morphology of the upper Kaoping Slope is mainly controlled by mud diapiric intrusions. The mud diapiric intrusions have resulted in a series of structural highs and three slope basins are formed between the structural highs. Due to the uplifting diapirs the canyon courses have developed along the flanks of structural high or between structural highs. We suggest that the courses and morphologies of the Kaoping Canyon and Fangliao Canyon are strongly dominated by mud diapiric intrusions.
| Identifer | oai:union.ndltd.org:TW/101NCU05134007 |
| Date | January 2013 |
| Creators | Song-chuen Chen, 陳松春 |
| Contributors | Shu-kun Hsu, 許樹坤 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 132 |
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