『Abstract
Much of the author's research career has been spent working both
on modern oceanic volcanic systems and at the same time looking
at their Archean counterparts. Many authors have attempted to
make inferences on early Earth models based on modern processes
which can be increasingly well constrained. In this short review
it will be shown how we are beginning to understand and quantify
inputs to modern subduction systems and some questions are posed
as to how these processes may have affected Earth's evolution
in its distant past.
Geochemical models have convincingly demonstrated that sediment
and altered oceanic crust must be recycled into the mantle through
subduction zones. These ‘subduction factories’ use these components,
along with molten mantle, to create arc magmas. The ‘residue’
from this process is recycled into the mantle and has a modified
chemical and mineralogical composition. The altered oceanic crust
input function in the current plate tectonic cycle seems to be
relatively constant in composition, but the chemical compositions
of the sediment fluxes into subduction zones vary widely and control
many of the end-member compositions of arc magmas. They must also
control the compositions of fluids and gases derived from these
magmas and ultimately ore-deposition and atmospheric fluxes associated
with arc volcanoes.
There is relatively strong evidence for subduction processes
for at least the past 3.5 Ma and some would argue that exogenic
components have been recycled into the mantle since at least 〜4.3
Ma. How might the subduction fluxes have changed through time,
and how might they have influenced crust, ocean and atmospheric
compositions? Can different ore regimes in temporal and spatial
distribution on Earth be related to the change in inputs and residues
from the subduction factory through time?』
1. Introduction
1.1. Fluxes at subduction zones
1.2. The U/Pb ratio of altered recycled basaltic oceanic crust
1.3. Sediment input into the subduction system
2. Subduction zones in the early Earth
3. How the geochemical recycling process may have changed through
time
Acknowledgements
References