Geochemistry of volcanics and fluid-rock interactions in hydrothermal systems in the Manus Basin

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The eastern Manus Basin (EMB) is one of world’s most plate-tectonically active and geochemically diverse regions. Many volcanic centers in the Manus Basin host hydrothermal systems that are affected by magma degassing to variable extent. The geochemical diversity of these systems provides an unparalleled opportunity to examine magma degassing and its consequences for mass transport in hydrothermal systems. During a recent RV Melville cruise volcanic rocks as well as hydrothermal fluids and sulfides were collected in different areas of the EMB. The rocks cover a range from pillow basalt to highly vesicular felsic lava, some of which are highly porphyritic. Rock alteration in the immediate vicinity of the fluid discharge area is also strongly variable, ranging from argillaceous to acid-sulfate alteration. These samples will allow the assessment of magmatic differentiation in relation to input of magmatic components into the hydrothermal system and consequences for fluid-rock interactions and metal transport. Geochemical data of fresh and altered rocks from hydrothermally active areas will be combined with chemical analyses of vent fluids in model calculations aimed at explaining (1) the phase assemblages observed and (2) the vent fluid chemistry. We will use reaction path models to simulate fluid-rock interactions with variable input of magmatic components. The results will be combined with data from NSF-funded companion projects in order to obtain a comprehensive understanding of mass transfers in the Manus Basin magmatic-hydrothermal systems.