A
Giant
Impact
Origin
for
the
First
Subduction
on
Earth
Qian
Yuan
1,2
,
Michael
Gurnis
2
,
Paul
D.
Asimow
1
,
and
Yida
Li
2
1
Division
of
Geological
and
Planetary
Sciences,
California
Institute
of
Technology,
Pasadena,
CA,
USA,
2
Seismological
Laboratory,
California
Institute
of
Technology,
Pasadena,
CA,
USA
Abstract
Hadean
zircons
provide
a
potential
record
of
Earth's
earliest
subduction
4.3
billion
years
ago.
It
remains
enigmatic
how
subduction
could
be
initiated
so
soon
after
the
presumably
Moon‐forming
giant
impact
(MGI).
Earlier
studies
found
an
increase
in
Earth's
core‐mantle
boundary
(CMB)
temperature
due
to
the
accumulation
of
the
impactor's
core,
and
our
recent
work
shows
Earth's
lower
mantle
remains
largely
solid,
with
some
of
the
impactor's
mantle
potentially
surviving
as
the
large
low‐shear
velocity
provinces
(LLSVPs).
Here,
we
show
that
a
hot
post‐impact
CMB
drives
the
initiation
of
strong
mantle
plumes
that
can
induce
subduction
initiation
∼
200
Myr
after
the
MGI.
2D
and
3D
thermomechanical
computations
show
that
a
high
CMB
temperature
is
the
primary
factor
triggering
early
subduction,
with
enrichment
of
heat‐producing
elements
in
LLSVPs
as
another
potential
factor.
The
models
link
the
earliest
subduction
to
the
MGI
with
implications
for
understanding
the
diverse
tectonic
regimes
of
rocky
planets.
Plain
Language
Summary
Plate
tectonics
remains
unique
to
Earth,
but
when
and
how
it
started
is
debated.
Earth's
oldest
minerals
indicate
a
clement
surface
by
4.3
Ga,
resembling
the
modern
Earth
with
its
granitic
crust
and
oceans.
Granite
is
most
easily
explained
as
originating
from
subduction.
However,
the
mechanisms
for
subduction
initiation,
especially
so
soon
after
the
Moon‐forming
giant
impact,
remain
elusive.
Earlier
studies
indicate
that
the
core‐mantle
boundary
(CMB)
temperature
is
increased
due
to
accumulation
of
the
impactor's
core
during
the
impact.
Our
recent
work
further
shows
that
the
lower
half
of
Earth's
mantle
remains
mostly
solid
after
this
impact
and
that
parts
of
the
impactor's
mantle
might
have
survived
as
the
two
seismically‐observed
large
low‐shear
velocity
provinces
(LLSVPs).
In
this
study,
we
perform
whole‐mantle
convection
models
to
illustrate
that
strong
mantle
plumes
can
arise,
weaken
the
lithosphere,
and
eventually
initiate
subduction
∼
200
Myr
after
the
giant
impact.
Our
systematic
computations
reveal
that
the
hot
CMB
temperature
after
the
impact
is
the
primary
factor
determining
whether
there
is
early
subduction
initiation,
with
enrichment
of
heat‐producing
elements
in
LLSVPs
as
another
potential
contributor.
Our
model
ties
the
Moon's
formation
to
incipient
subduction,
providing
insights
for
understanding
the
diverse
tectonic
regimes
of
rocky
planets.
1.
Introduction
As
planetary
exploration
continues,
Earth
remains
unique
as
the
only
planet
that
is
known
to
operate
in
the
plate
tectonic
regime.
In
plate
tectonics,
subduction
is
the
major
process
affecting
the
geodynamic
and
geochemical
evolution
of
our
planet,
but
when
and
how
the
first
subduction
occurred
remains
contentious.
Although
their
interpretation
is
debated
(Kemp
et
al.,
2010
),
analyses
of
Hadean
detrital
zircons
show
geochemical
signals
consistent
with
subduction
as
early
as
4.3
Ga
(Valley
et
al.,
2002
;
Watson
&
Harrison,
2005
).
Thus,
the
earliest
subduction
may
have
followed
less
than
∼
200
million
years
after
the
Moon‐forming
giant
impact
(MGI)
(Canup
&
Asphaug,
2001
).
The
collision
of
a
protoplanet
called
Theia
with
the
proto‐Earth
at
∼
4.51
Ga
is
expected
to
largely
reset
the
initial
conditions
of
Earth's
evolution,
creating
a
need
for
systematic
and
quantitative
exploration
of
the
planetary
state
established
by
MGI
and
its
lasting
influence
on
Earth's
tectonic
evolution.
Here
we
propose
that
the
thermal
and
chemical
structure
established
by
a
canonical
MGI
creates
favorable
conditions
for
the
initiation
of
subduction
in
Earth's
earliest
period,
exemplifying
the
pivotal
influence
of
initial
conditions
set
by
giant
impact
processes
for
the
tectonic
evolution
of
terrestrial
planets.
A
number
of
mechanisms
have
been
proposed
to
initiate
early
subduction
(Stern
&
Gerya,
2018
),
but
all
except
three
of
these
models
require
a
pre‐existing
weakness
in
the
lithosphere.
The
exceptions
are
grainsize
evolution
(Foley
et
al.,
2014
),
impact‐driven
(Borgeat
&
Tackley,
2022
;
O’Neill
et
al.,
2017
)
and
plume‐induced
(Gerya
et
al.,
2015
;
Ueda
et
al.,
2008
)
subduction
initiation.
However,
large
(
>
700
km)
and
energetic
impacting
bolides
capable
of
initiating
subduction
are
rare
and
only
occurred
very
early
in
Earth's
history
(Marchi
et
al.,
2014
;
RESEARCH
LETTER
10.1029/2023GL106723
Key
Points:
•
The
mantle
thermochemical
structure
left
by
the
Moon‐forming
impact
trig-
gers
strong
plumes
that
may
have
initiated
the
first
subduction
•
The
strong
mantle
plumes
may
rise
from
a
heated
core
or
from
large
low‐
shear
velocity
provinces
enriched
in
heat‐producing
elements
•
Early
giant
impact
events
may
have
a
profound
influence
on
the
diverse
tectonic
regimes
of
rocky
planets
Supporting
Information:
Supporting
Information
may
be
found
in
the
online
version
of
this
article.
Correspondence
to:
Q.
Yuan,
qyuan@caltech.edu
Citation:
Yuan,
Q.,
Gurnis,
M.,
Asimow,
P.
D.,
&
Li,
Y.
(2024).
A
giant
impact
origin
for
the
first
subduction
on
Earth.
Geophysical
Research
Letters
,
51
,
e2023GL106723.
https://doi.org/10.1029/2023GL106723
Received
10
OCT
2023
Accepted
14
APR
2024
Author
Contributions:
Conceptualization:
Qian
Yuan
Formal
analysis:
Qian
Yuan
Funding
acquisition:
Qian
Yuan,
Michael
Gurnis
Investigation:
Qian
Yuan,
Yida
Li
Methodology:
Qian
Yuan
Software:
Qian
Yuan
Supervision:
Michael
Gurnis,
Paul
D.
Asimow
Validation:
Qian
Yuan,
Michael
Gurnis,
Paul
D.
Asimow
Visualization:
Qian
Yuan
Writing
–
original
draft:
Qian
Yuan
Writing
–
review
&
editing:
Qian
Yuan,
Michael
Gurnis,
Paul
D.
Asimow,
Yida
Li
©
2024.
The
Authors.
This
is
an
open
access
article
under
the
terms
of
the
Creative
Commons
Attribution
License,
which
permits
use,
distribution
and
reproduction
in
any
medium,
provided
the
original
work
is
properly
cited.
YUAN
ET
AL.
1
of
10
O’Neill
et
al.,
2017
),
which
may
coincide
with
the
period
of
magma
ocean
solidification.
Recently,
plume‐
induced
subduction
has
been
increasingly
proposed
as
a
viable
mechanism
for
subduction
initiation
in
the
early
Earth
(Baes
et
al.,
2021
).
Nevertheless,
it
is
unclear
how
to
generate
strong
mantle
plumes
in
a
vigorous
convecting
Hadean
mantle
(Korenaga,
2008
).
The
MGI
is
typically
thought
violent
enough
to
melt
a
substantial
portion
or
even
the
entire
mantle,
especially
in
scenarios
involving
high
energy
and
high
angular
momentum
(Lock
&
Stewart,
2017
;
Nakajima
&
Steven-
son,
2015
).
Using
two
different
giant
impact
computational
methods
with
improved
equations
of
state
(Stewart
et
al.,
2020
)
and
at
high
(Deng
et
al.,
2019
)
and
ultra‐high
(Kegerreis
et
al.,
2022
)
resolution,
our
recent
work
(Yuan
et
al.,
2023
)
demonstrates
that
the
lower
half
of
Earth's
mantle
would
have
remained
mostly
solid
after
a
canonical
MGI.
It
also
suggests
that
large
intact
domains
of
Theia's
likely
Fe‐rich
mantle
are
candidates
of
the
two
seismically‐observed
large
low‐shear
velocity
provinces
(LLSVPs).
Furthermore,
the
concomitant
core
formation
process
during
the
MGI
may
substantially
heat
the
core
to
raise
the
temperatures
at
the
core‐mantle
boundary
(CMB)
(Canup,
2004
;
Deng
et
al.,
2019
).
This
unique
thermochemical
structure,
featuring
a
solid
lower
mantle
and
a
hotter
CMB
resulting
from
the
MGI,
provides
ideal
conditions
for
the
formation
of
strong
mantle
plumes,
a
scenario
less
likely
when
the
mantle
and
core
are
in
equilibrium.
Accretion
scenarios
built
from
only
smaller‐scale
impacts
dissipate
more
of
their
gravitational
potential
energy
in
the
mantle
and
yield
a
more
stable
initial
thermal
structure.
Here,
we
test
the
hypothesis
that
such
strong
mantle
plumes
can
be
developed
in
the
early
Hadean,
weakening
the
lithosphere
and
eventually
causing
subduction
initiation
(Figure
1
).
We
model
this
scenario
using
2‐D
and
3‐D
whole‐mantle
thermo‐chemical‐mechanical
models
with
a
visco‐elasto‐plastic
rock
rheology.
2.
Geodynamic
Models
We
compute
whole‐mantle
convection
models
in
2D
and
3D
Cartesian
geometries
using
Underworld2
,
an
open‐
source,
particle‐in‐cell,
finite
element
code
(Mansour
et
al.,
2020
;
Moresi
et
al.,
2007
).
2.1.
Governing
Equations
and
Material
Description
The
computations
solve
the
conservation
equations
of
mass,
momentum,
and
energy:
∇
·
u
=
0
(
1
)
∇
·
σ
′