This clearly works a little better as it can explain concentration of
trace elements in a given magma chamber. And what does the non
melted walls of the magma chamber consist off? Perhaps it is that
portion best able to transmit heat. Just what happens to the
elemental carbon also?
This remains a complex problem and we are never prepared to simply
accept a model as complete. everything we have came from the top
hundred miles or so of rock. After that we are with the cosmos.
Anyway this is an addition to our theory.
Oceanic crust
breakthrough: Solving a magma mystery
by Staff Writers
Washington DC (SPX) Dec 04, 2012
Oceanic crust
covers two-thirds of the Earth's solid surface, but scientists still
don't entirely understand the process by which it is made. Analysis
of more than 600 samples of oceanic crust by a team including
Carnegie's Frances Jenner reveals a systemic pattern that alters
long-held beliefs about how this process works, explaining a crucial
step in understanding Earth's geological deep processes. Their
work is published in Nature.
Magmas generated by
melting of the Earth's mantle rise up below the oceanic crust and
erupt on the Earth's surface at mid-ocean ridge systems, the longest
mountain ranges in the world. When the magma cools it forms basalt,
the planet's most-common rock and the basis for oceanic crust.
It has long been
assumed that the composition of magmas erupting out of mid-ocean
ridges is altered when minerals that form during cooling sink out of
the remaining liquid, a process called fractional crystallization.
In theory, trace
elements that are not included in the crystallizing minerals should
be little affected by this process, and their ratios should be the
same in the erupting magma as they were in the original magma before
cooling.
If this is true, trace
element ratios in magmas erupting at mid-ocean ridges should
represent those of the original parental magma that formed deep in
the Earth's mantle.
However, this process
doesn't account for the high abundance of trace elements found in
samples of basalt from mid-ocean ridges around the world, so the
reality of the situation is obviously more complicated than previous
theories indicated.
Using the extensive
array of samples and advanced modeling, Jenner and her research
partner Hugh O'Neill of the Australian National University
demonstrated that the concentration of trace elements is due to the
process by which the magma is cycled through the oceanic crust prior
to being erupted on the sea floor at the mid-ocean ridges.
Magma collects under
the Earth's surface in a pool of liquid rock called a magma chamber.
Each chamber is frequently flushed with new magma, which mixes
with the old magma that was already there, and then this blended
magma erupts out onto the ocean floor.
Following the influx
of new magma and eruption, the remaining magma undergoes fractional
crystallization. This means that minerals are separated out from the
magma as it cools.
However, these
minerals contain only minor amounts of the trace elements. As a
result, trace elements build up in the magma over time, as the
magma chamber is continually replenished by new magma coming in to
the system.
"It's a simple
idea, but it fits remarkably well," Jenner said. "These new
findings will permit us to explore the conditions of mantle melting
and production of the Earth's most-common rock."
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