Abstract
Seafloor mounds are enigmatic features along many continental margins and are often interpreted as gas hydrate pingoes, seep deposits, mud volcanoes, or hydrothermal mounds. When such mounds occur in basins with past volcanic activities, they have the potential to host seafloor metalliferous deposits, which is generally overlooked. Using geophysical datasets, we document the fluid plumbing systems that promoted the formation of seafloor mounds in the Great South Basin (GSB), offshore New Zealand. We also investigate these mounds as potential seafloor metalliferous deposits. Our results reveal 9 seafloor mounds (~ 137 m high) above gigantic (~ 5.4 km high) fluid escape pipes that are associated with deeper crystalline rocks. The structural make-up of the mounds, their geospatial relationships with the pipes and intrusive rocks, and geophysical properties suggest a primary volcanic or hydrothermal origin for the culpable fluids and mounds respectively. Fluids derived from deeper coal beds and shallow foraminiferal oozes in the basin constitute secondary fluid sources focused along polygonal faults and lateral flow cells. A main sub-vertical and minor lateral fluid plumbing patterns are proposed. The relationship between the mounds, pipes, underlying intrusive rocks, and upward routing of mineral-rich fluids could have implications for the formation of ore-grade mineral deposits on the seafloor in the GSB.
Highlights
Enigma of interpreting seafloor anomalies from seismic reflection data Numerous modern seafloors are characterized by sites of focused fluid discharge
This structural boundary is defined by linear gravity and magnetic anomalies otherwise known as the Campbell Magnetic Anomaly System (CMAS)[18]
The chaotic and discontinuous low amplitude reflections at the base of the Eocene sequence are correlated to the Laing Formation Coastal sand facies (Fig. 2)
Summary
Enigma of interpreting seafloor anomalies from seismic reflection data Numerous modern seafloors are characterized by sites of focused fluid discharge. Many seafloor mounds have been observed to be linked to underlying high amplitude features (e.g. magmatic sills or dykes, etc.) and vertical zones of disturbed seismic reflections (conduits/fluid escape pipes), allowing a volcanic or hydrothermal origin to be inferred for the m ounds[9,11] Such seafloor mounds provide an avenue to study the interaction between the oceans and the subsurface sedimentary units, the geology associated with their formation and their potential for forming economic ore-grade metalliferous deposits is not well understood[12]. This work investigates the origin of nine seafloor mounds and the fluid plumbing systems associated with their formation It assesses their potential for forming deep-sea metalliferous deposits, using 2D seismic, gravity, magnetic and well log datasets from the Great South Basin (GSB), offshore New Zealand. This group is composed of syn-rift deposits, such as non-marine conglomerates, sandstone, mudstone, and in Scientific Reports | (2021) 11:9185 |
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