Download Primary Initiation of Submarine Canyons J. Marvin Herndon

Primary Initiation of Submarine Canyons
J. Marvin Herndon
Transdyne Corporation
San Diego, CA 92131 USA
[email protected]
Key Words: submarine canyon, whole-Earth decompression dynamics, coastal canyons,
erosion processes
Abstract: The discovery of close-to-star gas-giant exo-planets lends support to the idea of
Earth’s origin as a Jupiter-like gas-giant and to the consequences of its compression, including
whole-Earth decompression dynamics that gives rise, without requiring mantle convection, to the
myriad measurements and observations whose descriptions are attributed to plate tectonics. I
propose here another, unanticipated consequence of whole-Earth decompression dynamics:
namely, a specific, dominant, non-erosion, underlying initiation-mechanism precursor for
submarine canyons that follows as a direct consequence of Earth’s early origin as a Jupiter-like
gas-giant.
The origin of submarine canyons, ubiquitous, prominent features of continental margins
that sometimes in scale rival the Grand Canyon, has been the subject of much debate. Virtually
all submarine canyons are subject to erosion, so the origin-debate generally focuses on the nature
and circumstances of their formation by erosion-processes [1-3]. While there may be more than
one submarine-canyon initiation-process, the commonality of their occurrence in diverse
environments suggests the potential dominance of one underlying mechanism. The purpose of
this brief communication is to propose that specific, dominant, underlying initiation-mechanism:
an unanticipated, non-erosion precursor that follows as a direct consequence of Earth’s early
origin as a Jupiter-like gas-giant.
The presently popular idea of Solar System formation began with publication in 1963 of
an assumption-based model by Cameron [4]. The idea, later called the “standard model of solar
system formation”, was that dust would condense from a diffuse, hot gas of solar composition at
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a pressure of about 10-5 bar. The dust would then collect into balls, then into rocks, then into
boulder-size accumulations, and finally into planetesimals; these would eventually gather to form
a planet like Earth. Subsequently, I showed from thermodynamic considerations why the model
was wrong: Essentially all of the condensable elements of a gas of solar composition at such a
low pressure would condense as oxides leaving no iron metal for a massive-core planet like
Earth [5].
In 1944, Eucken [6] described from thermodynamic considerations Earth’s formation by
condensation at high pressures, ≥ 100 bar, in the interior of a hot gaseous protoplanet of solar
composition. In such an environment, molten iron (and the elements dissolved therein), being the
most refractory condensate, rain-out to form Earth’s core before condensation forms the mantle.
I have verified Eucken’s calculations and extended his concept to include complete condensation
of volatile elements [5, 7, 8]. Fully condensed with about 300 Earth-masses of hydrogen,
helium, and other volatiles, Earth’s gas-giant, pre-Hadean mass was virtually identical to that of
Jupiter [5]. My idea of Earth having an early origin as a Jupiter-like gas giant is not at all strange
as close-to-star gas-giant exo-planets are observed in other planetary systems [9].
The dynamics of planet Earth, a direct consequence its early gas-giant origin, is described
by my new geodynamic theory, called whole-Earth decompression dynamics [10-12], which
gives rise to the myriad measurements and observations whose descriptions are attributed to
plate tectonics, but without requiring mantle convection. It provides a basis for Earth’s
previously having had reduced radius and a mechanism and powerful energy source for its
decompression. Whole-Earth decompression dynamics obviates the primary pitfall of plate
tectonics theory, the necessity of mantle convection, and overcomes the problems of endemic to
Earth expansion theory, the absence of basis, energy source, and appropriate mechanism.
Envision pre-Hadean Earth, compressed to about 64% of present radius by about 300
Earth-masses of primordial gases and ices. At some point, after being stripped of its massive
volatile envelope, presumably by the Sun’s super-intense T-Tauri solar winds, internal pressures
would build, eventually cracking the rigid crust. Powered by the stored energy of protoplanetary
compression, Earth’s progressive decompression is manifest at the surface by the formation of
cracks: primary decompression cracks with underlying heat sources capable of extruding basalt,
and secondary decompression cracks without heat sources that serve as ultimate repositories for
basalt extruded from primary decompression cracks. Mid-ocean ridges and submarine trenches,
respectively, are examples of these. Secondary decompression cracks serve to increase surface
area in response to decompression-driven volume expansion. Basalt extruded at mid-ocean
ridges becomes seafloor, spreading and eventually subducting, i.e., falling into secondary
decompression cracks, seismically imaged as “down-plunging slabs”, but without engaging in
the process of mantle convection.
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Whole-Earth decompression dynamics not only gives rise to the multitude of
observations attributed to plate tectonics (and without mantle convection), but it affords
understanding that transcends, being responsible for Earth’s well-documented features: (1)
Orogeny occurs not only by “plate collision”, but by the vertical uplift intrinsic to
decompression; (2) Partially in-filled secondary decompression cracks uniquely explain oceanic
troughs, which are generally inexplicable by plate tectonics; and, (3) Compression heating at the
base of the rigid crust is a direct consequence of mantle decompression, but has no parallel in
plate tectonics. Here I present another extension by proposing dominant submarine-canyoninitiation as a consequence of whole-Earth decompression dynamics.
As illustrated in Figure 1, consider a hypothetical 4000 km “ancient” continent crosssection (arc ABC) at a radius of 64% of Earth’s present radius, OB, and the same “present”
continent cross-section (arc DEF) at present Earth radius, OE. Consider the line OR as a fixed
reference, indicating that no “continental drift” has occurred, as the reference line OR bisects
both the ancient and present continent. Observe that the ancient continent subtends an angle,
<AOC, that is considerable greater than the angle the present continent subtends, <DOF: 56.3
degrees versus 36.0 degrees. Note that, although the length of the both the ancient and present
surface continent cross-section are the same, 4,000 km, the chord lengths, indicated by dotted
lines, differ: 3841.3 km versus 3934.5 km, respectively. Whole-Earth decompression causes
changes in surface curvature that, I submit, are responsible for the primary initiation of
submarine canyons.
Suppose that the coastline of the hypothetical continent, shown in Figure 1, is circular.
Then the perimeter of its circular coast line is simply π times its chord length. Whole-Earth
decompression, in the example above, necessitates an increase in peri-continental circumference
of about 2.4%. The percent circumference-increase for other hypothetical continental arc lengths
is shown in Figure 2.
Whereas rocks can undergo considerable compression, their brittle nature and low tensile
strength precludes adjusting to the requisite increase in circumference caused by whole-Earth
decompression without tension fractures occurring. Such decompression-generated, pericontinental tension-fractures, I posit, initiate the formation of submarine canyons; erosionprocesses do the rest.
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Figure 1. Hypothetical 4000 km “ancient” continent cross-section at a radius of 64% of Earth’s
present radius and the same 4000 km “present” continent cross-section at present-day Earth
radius, taken as 6366 km.
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Figure 2. Percent increase in peri-continental circumference due to decompression for the
hypothetical circular continent shown, if Figure 1, as a function of cross-section arc length.
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