MOLYALOC

Behavior of molybdenum and its isotopes during alteration of the oceanic crust

 Partecipanti

Mappa

 Word cloud

Esplora la "nuvola delle parole (Word Cloud) per avere un'idea di massima del progetto.

 Obiettivo del progetto (Objective)

'Alteration of ocean crust is a fundamental on-going geological process. High-temperature alteration of the ocean crust occurs at the ridge, while diffusive, low temperature alteration is present off-ridge. Both alteration processes produce secondary minerals and change the primary chemical and isotopic signal of the oceanic crust. These signals can be brought into the mantle as altered oceanic crust enters a subduction zone and produces mantle inhomogeneities. As molybdenum is low in abundance in the mantle, but high in abundance in seawater with a distinct isotopic signal from each other, it is a promising element to study these processes. Prior to study deep cycling of molybdenum via ocean island basalts, detailed understanding of the behavior of molybdenum during alteration is needed. In this framework, we propose a study to identify the major molybdenum-bearing phase as well as the processes influencing the molybdenum isotope signal of the altered oceanic crust. Two cross-sections through the oceanic crust will be studied for this purpose, ODP Site 1256 and Macquarie Island (14 Ma and 7 Ma old, respectively). In-situ molybdenum concentrations and whole rock molybdenum isotope measurements are planned to understand on- and off-ridge alteration in the oceanic plate. This research will be groundbreaking, using molybdenum as a novel tracer to better constrain the behavior of on-/off-ridge alterations and to quantify the Mo-isotopic composition of the oceanic crust potentially entering the subduction zone.'

Introduzione (Teaser)

EU-funded scientists studied molybdenum (Mo) to determine its suitability as a tracer for use in investigating geological changes taking place on the ocean floor.

Descrizione progetto (Article)

Alteration of the ocean crust, the outermost rocky layer of the Earth found under the oceans, is a fundamental ongoing geological process. High-temperature changes to the ocean crust occur at the oceanic ridges, the underwater mountain systems formed by plate tectonics.

Diffusive low-temperature changes occur further away from the ridges (off-ridge). However, both processes produce secondary minerals and alter the chemistry of the oceanic crust. These changes can be introduced into the mantle layer within the Earth. This takes place in subduction zones, where one tectonic plate moves over another causing it to sink into the mantle.

The 'Behavior of molybdenum and its isotopes during alteration of the oceanic crust' (MOLYALOC) project used Mo to study changes on- and off-ridge. The initiative also measured the Mo isotopic composition of the oceanic crust potentially entering the subduction zone.

Mo is found in low levels in the mantle, but is extremely abundant in seawater where it occurs as a different isotope. These factors make Mo highly suitable for studying these geological processes.

Samples of oceanic crust were taken from a drilling site situated at an oceanic ridge in the Pacific, off the coast of Central America. A profile of Mo isotopes through the altered oceanic crusts was constructed and the potential role of serpentine in carrying Mo into the mantle was examined.

Research was also conducted into the effect of the subduction process in separating different Mo isotopes using eclogites, a type of metamorphic rock. The data were combined and used to gain an understanding of the composition of Mo isotopes entering the deep mantle and thus the composition of recycled components.

MOLYALOC therefore showed that Mo could be used to study on- and off-ridge alterations to the oceanic plate.