Fluid Geochemistry and Migration Processes at the Lusi Mud Eruption, Indonesia

Abstract

Lusi is a large hydrothermal vent system, constantly erupting since 14 years in the East Java sedimentary basin. Its activity is fuelled by a subsurface magmatic intrusion and associated hydrothermal fluid migration taking place at ~4.5 km depth. This thesis investigates the geochemical processes that triggered the eruption of massive amounts of gas, water, oil, mud, and rock clasts. A set of combined geological-geochemical-geophysical methods revealed the pathways for the continuous regional migration of mantle-derived volatiles from the volcanic complex towards the sedimentary basin. Results indicated ongoing hydrocarbon generation at depth, ultimately leading to the continuous eruption of large amounts of oil and gas at the crater site. Extensive flow rate monitoring and mud sampling allowed to estimate that more than 0.3 km3 of mud and 0.3 million tonnes of oil have been erupted during the first 13 years of Lusi activity. These large volumes of discharged fluids represent a potential environmental hazard for the neighbouring aquatic system where they are being released. Further, this study provides insights to understand the similarly operating palaeo hydrothermal vent complexes that have been suggested to contribute to rapid climate change and mass extinctions since 260 Ma.