Mud volcanoes at the front of the Makran accretionary complex,Pakistan |
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| Institution: | 1. CAS Key Laboratory of Crust-Mantle Materials and Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China;2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, The Chinese Academy of Sciences, Xi''an, Shaanxi 710075, China;3. University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Centre, Suzhou, Jiangsu, 215123, China |
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| Abstract: | Conical mounds, 1–1.5 km in diameter, and up to 65 m high were mapped at the foot of the active Makran continental margin. The mounds developed seaward of the accretionary front in a relatively planar zone where the beginning of build-up of tectonic pressure initiates deformation. Based on shallow high-resolution 4 kHz sediment echosounding, the sedimentary sequence in this area is generally well stratified, as indicated by closely spaced horizontal reflections. However, in the vicinity of the mounds the sediment is characterised by many acoustically transparent zones, which are 100–300 m in diameter and cut near-vertically through the horizontal reflectors.Two sediment cores from the top of the largest cone and a neighbouring acoustically transparent zone reveal small-scale post-depositional deformation in a stratified sequence and methane concentrations up to 40,000 ng/g. This deformation and disruption of potential reflectors provides a clue to explain the acoustic transparency: we interpret it as caused by the rise of charged fluids and mud, leading initially to the (slight) disturbance of the generally good acoustic reflectors and eventually to the formation of conical mud mounds (mud volcanoes). MCS data, showing a buried mound in an analogous structural position, support the idea of tectonically induced mud/fluid expulsion seaward of the accretionary front. |
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