AQUEOUS DIFFERENTIATION OF KUIPER BELT OBJECTS (KBOs)

Ptygmatic Folds in gneiss migmatite from Helsinki Finland –used with permission of Sameli Kujala, http://www.flickr.com/photos/sameli/2040126969/

Ptygmatic Folds in gneiss migmatite from Helsinki Finland
–used with permission of Sameli Kujala,
http://www.flickr.com/photos/sameli/2040126969/

Abstract:

This section suggests an alternative extraterrestrial origin for metamorphic gneiss, along with its associated mantling rock of quartzite, carbonate rock and schist. Authigenic gneissic sediments are suggested to have been precipitated in the cores of Kuiper belt objects (KBOs) undergoing ‘aqueous differentiation’, with aqueous differentiation caused by orbital perturbation.

Our suggested former binary brown-dwarf Companion to the Sun perturbed binary KBOs to spiral in and merge during the Archean Eon, catastrophically forming authigenic sedimentary cores with a typically tonalite–trondhjemite–granodiorite (TTG) composition, characteristic of Archean cratons.

The tidal inflection point (associated with the former Sun-Companion solar system barycenter) is suggested to have initiated orbital perturbation of KBOs. The tidal inflection point spiraled out from the Sun at an exponential rate, passing through the cubewanos of the Kuiper belt from 4.1 to 3.9 Ga, causing the late heavy bombardment of the inner solar system. The growing Sun-Companion eccentricity around the solar system barycenter, which caused the tidal inflection point to spiral out from the Sun, was driven by the spiral in of the binary brown-dwarf components of binary-Companion.

Solitary KBOs, which did not undergo catastrophic binary spiral-in merger, may have experienced smaller, repeated instances of aqueous differentiation, forming multiple gneiss domes in KBO cores, compared to catastrophic binary spiral-in merger which formed TTG cores.

Finally, perturbation by binary-Companion came to an end when the binary brown-dwarf components ultimately merged at 542 Ma in an asymmetrical merger explosion that gave the Companion escape velocity from the Sun.

Neptune became the nemesis of the Kuiper belt in the new Phanerozoic Eon, with the loss of the perturbing and stabilizing influence of the Companion at 542 Ma, with Neptune causing orbital perturbation of KBOs in newly-unstable orbits. Neptune also caused smaller instances of aqueous differentiation, such as forming the Eocene gneiss domes which are scattered through the Middle East from Greece to Nepal. Neptune is responsible for injecting KBOs into the inner solar system in the Phanerozoic Eon, likely by the intermediate pathway of the minor-planet centaurs.

Sedimentary KBO cores lithify into TTG cores and gneiss domes, with subsequent metamorphism occurring as saltwater oceans freeze solid. The expansion of water ice in solidifying KBO oceans builds the tremendous pressure which causes high-pressure metamorphism in extraterrestrial metamorphic rock.

Perturbation of KBOs into the inner solar system by Neptune cause extinction event impacts on Earth, with highly-compressible KBO ices generally clamping the Earth-impact shock-wave pressure below the melting point of silicates, masking the impact origin of the continental tectonic plates.
………………..

Introduction:

In conventional geology, the supposed segregation of metamorphic migmatite into felsic leucosome and mafic melanosome layers by metamorphism of protolith rock is explained by the partial melting (anatexis) of lower-melting-point (primarily felsic) minerals and the extrusion of this melt down a “potential force gradient.” “The consensus today is that both in situ melt and externally derived melt are present in most migmatites (Kriegsman, 2001).” (Urtson, 2005) This means that adjacent layers alone can not explain the local enrichments and depletions of felsic and mafic layering, and so non-local externally-derived melt is needed for mass balance. Finally, “commingling and mixing of mafic and felsic magmas” is also also suggested as an explanation for alternating felsic/mafic layers. (Sandeman et al., 2000) In the alternative aqueous differentiation context, adjacent felsic and mafic leucosomes and melanosomes have the entire Kuiper belt object (KBO) ocean, as a reservoir to draw upon.

Conventionally, gneiss domes are divided into two classes: fault related and fault unrelated. Larger gneiss-dome systems are divided into evenly spaced and unevenly spaced. Evenly spaced dome systems are considered to be instabilities caused by vertical-density or -viscosity contrast and horizontal loads, leading to buckling. Unevenly spaced dome systems are associated with fault development or “superposition of multiple deformational phases.” “In nature, gneiss domes are often produced by superposition of several dome-forming mechanisms. This has made determination of the dynamic cause of individual domes and dome systems exceedingly challenging.” (Yin, 2004)

Rayleigh–Taylor (RT) instability is a favored explanation for the formation of evenly-spaced gneiss domes which is sometimes called a fingering instability where a finger is theorized to spread into a mushroom cap to explain concentric layering in ellipsoid gneiss domes. RT instabilities, however, fail to explain the typical sedimentary basements: “In some, the lowest horizon of the mantle consists of basal conglomerate with boulders of the same gneiss that forms the dome; in others, the basement stratum is a layer of quartzite, above which follow dolomite and mica schist; and in still others, dolomite forms the basement.” (Eskola, 1948)

“The mantled domes apparently represent earlier granite intrusions related to a orogenic period. The plutonic mass was later eroded and levelled, and thereafter followed a period of sedimentation. During a subsequent orogenic cycle the pluton was mobilized anew and new granite magma was injected into the plutonic rock at the same time as it was deformed into gneiss, causing its migmatization and granitization, or palingenesis.”
(Eskola, 1948)
………………..

Alternative solar system formation ideology:

The problem of planetesimal formation is a major unsolved problem in astronomy, since meter-sized “boulders are expected to stick together poorly, and to spiral into the protostar in a few hundred orbits owing to a ‘head wind’ from the slower rotating gas” (Johansen et al., 2007).

This alternative ideology rejects pebble accretion in favor of gravitational instability (GI) for the formation of planetesimals. In protoplanetary disks or subsequent debris disks GI is suggested to occur in the pressure dam at the inner edge of accretion disks and against heliocentric resonances of giant planets. Around young solitary stars, the inner edge of the accretion disk is sculpted by the magnetic corotation radius, where sufficient numbers of planetesimals may condense to form super-Earths by ‘hybrid accretion’, where hybrid accretion describes gravitational core accretion of planetesimals formed by GI, hence hybrid. (See section, CASCADE FORMATION OF SUPER-EARTHS BY HYBRID CORE ACCRETION OF PLANETESIMALS ‘CONDENSED’ BY GRAVITATIONAL INSTABILITY AT THE INNER EDGE OF ACCRETION DISKS) Heliocentric resonances of giant planets also create pressure dams, which may promote gravitational instability in primary accretion disks and/or in secondary debris disks, such as chondrites condensed against Jupiter’s strongest inner resonances and KBOs against Neptune’s outer resonances.

The Jeans instability which formed our solar system is suggested to have undergone ‘flip-flop fragmentation’ ‘with bifurcation’ due to excess angular momentum, forming a quadruple star–brown-dwarf system, composed of binary-Sun and binary-Companion in a wide-binary separation orbiting the solar system barycenter (SSB). Secular perturbation caused binary-Sun to spiral in and merge at 4,567 Ma, creating a ‘primary debris disk’, which condensed asteroids against the Sun’s magnetic corotation radius near the orbit of Mercury, and condensed chondrites in situ against Jupiter’s inner resonances and condensed Kuiper belt objects (KBOs) in situ against Neptune’s strongest outer resonances, principally the 2:3 resonance. Continued secular perturbation caused the binary brown-dwarf components of binary-Companion to spiral in over the next 4 billion years, causing the wide-binary (Sun-Companion) system to become increasingly eccentric over time until the binary brown-dwarf components merged at 542 Ma in an asymmetrical merger explosion that gave the newly-merged Companion escape velocity from the Sun. Cold classical KBOs condensed from this ‘secondary debris disk’, likely including the geologically-young Pluto system.

(See section, STARS, PLANETS, MOONS, MINOR PLANETS AND COMETS)
………………..

Perturbation of KBOs by former binary-Companion:

Binary-Companion is suggested to have progressively perturbed KBOs by means of the ‘tidal inflection point’, associated with the solar system barycenter (SSB).

Earth’s lunar tides can be used as an analogy for understanding flip-flop perturbation of KBO orbits by the solar system barycenter. Earth has two lunar tides, one high tide facing the Moon, gravitationally attracted into a high tide by the lunar gravity, and a symmetrical high tide on the back side of the Earth, centrifugally slung away from the Moon as Earth rotates around the Earth-Moon barycenter. As Earth rotates on its axis, once a day, ocean water crosses the tidal inflection point between the high tide facing the Moon and the high tide on the back side of the Earth. This is a direct analogy of the tidal inflection point between the Sun and former binary-Companion, where KBO aphelia were gravitationally attracted to the Companion on the Companion side of the tidal inflection point, and the 8 planets and KBO aphelia were centrifugally slung 180° away from the Companion on the Sun side of the tidal inflection point. The tidal inflection point was associated with the SSB between Sun and former binary-Companion, but not coincident with it, just as the tidal inflection point on Earth today is associated with the Earth-Moon barycenter, but not coincident with it.

The Sun-Companion orbit around the SSB became progressively more eccentric for 4 billion years (between 4,567-542 Ma), fueled by the orbital energy of the binary brown-dwarf components spiraling in. As the Sun-Companion apoapsis spiraled out from the SSB at an exponential rate over time, the tidal inflection point crossed the semimajor axes of progressively more distant KBOs over time, initiating orbital perturbation designated, ‘flip-flop perturbation’, caused by aphelia precession of KBO aphelia. When the tidal inflection point caught up with the semimajor axis of a KBO for the first time, its aphelion began to precess from pointing 180° away from the Companion to being gravitationally attracted toward it. But once initiated, aphelia precession was reset toward Sun-Companion periapsis. So once initiated for the first time, KBOs underwent two episodes of flip-flop perturbation (aphelia precession toward the Companion and aphelia precession away from it) with each Sun-Companion orbit around the SSB.

The tidal inflection point passed through the Plutinos (in a 2:3 resonance with Neptune at 39.4 AU), at about 4,220 Ma, creating the first pulse in a bimodal late heavy bombardment (LHB) of the inner solar system. The longer, broader, more sustained main pulse of the LHB occurred from 4.1 to 3.9 Ga, as the tidal inflection point passed through the cubewanos, between the 2:3 and 1:2 resonances with Neptune. So flip-flop perturbation not only caused binary KBOs to spiral in and merge, but it also perturbed KBOs into the inner solar system, predominantly during the early LHB portion of the Archean Eon. (See subsection: Exponential rate of increase in the wide-binary (Sun-Companion) period, within the section, STARS, PLANETS, MOONS, MINOR PLANETS AND COMETS)
………………..

Archean tonalite–trondhjemite–granodiorite (TTG) KBO cores:

Binary KBOs resisted aphelia precession with the angular momentum of their binary orbits, but resistance extracted orbital energy and angular momentum from their binary orbits, causing their binary components to spiral in until they merged, forming ‘contact binary’ KBOs.

Binary spiral-in merger is suggested to have initiated catastrophic aqueous differentiation, perhaps forming authigenic sedimentary cores composed of tonalite–trondhjemite–granodiorite (TTG) sediments, which were largely devoid of K-feldspar. Aqueous potassium-salt solubility is more temperature dependent than sodium salt solubility, so perhaps the high temperatures incurred in binary spiral-in mergers precipitated relative little authigenic K-feldspar, where most of the potassium remained in aqueous solution, explaining the typically potassium-poor TTG composition of Archean cratons.

If greenstone belts are the extraterrestrial mantling rock surrounding TTG cores, then the typical dome-and-keel structure relationship between the TTG core and its greenstone belt mantling rock may be explained by dehydration of the sedimentary core during lithification, like the shriveling of a plum dehydrating to form a prune, where the dome-and-keel structure represents the wrinkles in the dehydrated core. And if so, the typical pillow lava form of greenstone belts points to a greenstone belt formation temperature exceeding the melting point of silicates.
………………..

Gneiss dome formation in KBOs:

If TTG cores were formed by catastrophic binary spiral-in merger, gneiss domes are suggested to have formed by smaller catastrophic subsidence events, which presumably occurred during ‘KBO quakes’.

Following binary spiral-in merger, or alternatively in solitary KBOs that never underwent binary spiral-in merger, flip-flop perturbation may have promoted the intermittent catastrophic release of potential energy in the form of massive KBO-quake subsidence events which initiated local rather than global aqueous differentiation to precipitate gneissic sediments which lithified to form gneiss domes.

Thus multiple gneiss domes may form in solitary KBOs without an Archean TTG core, where the temperature of gneiss dome formation is typically insufficient to prevent authigenic precipitation of K-feldspar.

Small gneiss domes may have formed (and may still be forming) during the Phanerozoic Eon, due to orbital perturbation by Neptune, such as the Eocene Epoch gneiss domes found from Greece to Nepal. And if the centaur minor planets, with semimajor axes between those of the outer planets, were originally KBOs, then perhaps aqueous differentiation can be sustained by orbital perturbation by the other giant planets as well, as centaurs are either induced to continue to spiral inward or are ejected from the inner solar system altogether.

So while the SSB was the KBO perturbator of the Precambrian Era, binary-Companion may have also acted as a stabilizing influence, resulting in Neptune being the nemesis of the Phanerozoic Eon. Apollo spherule counts suggest that the Moon (and by extension the Earth) has received significantly-more impacts in the Phanerozoic Eon than in the proceeding Eons since the LHB, suggesting that binary-Companion protected the inner solar system from KBOs, while still perturbing KBOs to induce aqueous differentiation. “Culler et al. [2000] studied 179 spherules from 1 g of soil collected by the Apollo 14 astronauts, and found evidence for a decline in the meteoroid flux to the Moon from 3000 million years ago (Ma) to 500 Ma, followed by a fourfold increase in the cratering rate over the last 400 Ma.” (Levine et al., 2005)
………………..

S-type granite:

Intrusive S-type granite is suggested to be caused by authigenic precipitation of granitic sediments between layers of older rock, most likely forced to delaminate by intrusive hydrothermal fluids. While I-type granite may indeed be terrestrial, intrusive plutonic rock, S-type granite is typically older than I-type plutons and contains detrital zircons, pointing to an aqueous origin.

(See section: THE ORIGIN OF S-TYPE GRANITE PLUTONS IN KUIPER BELT OBJECTS (KBOs))
………………..

Aqueous differentiation of KBOs:

When binary planetesimals are induced to spiral in and merge, potential and kinetic energy is converted to heat, melting saltwater oceans in their cores. Dissolved nebular dust precipitates authigenic mineral grains that grow through crystallization until falling out of suspension at a characteristic mineral-grain size for the microgravity, forming authigenic sedimentary cores. Additionally, microbes may catalyze chemical reactions, greatly increasing the variety and complexity of precipitated minerals.

The gravitational acceleration, and thus buoyancy in KBO saltwater oceans is also dependent on location within the planetesimal, ranging from zero at the gravitational center to a peak value some 2/3 of the way to the surface, so the largest authigenic mineral-grain size should be in the center, with progressively decreasing authigenic mineral grain size with distance from the gravitational center.
………………..

Leucosome/melanosome layering in migmatite/gneiss/schist:

The partial pressure of CO2 in trapped gas pockets between a saltwater ocean and the overlying icy crust will force carbon dioxide into solution where it reacts with water to form carbonic acid, lowering the pH in KBO oceans.

As aqueous differentiation densifies a KBO, subsidence events (‘KBO quakes’) may vent trapped gas to outer space, reducing the partial pressure of CO2 in solution, which may cause carbonic acid to bubble out of solution in the form of CO2. Additionally, seismic vibrations of KBO quakes alone would tend to nucleate CO2 bubbles, like shaking a carbonated beverage.

The solubility of aluminum salts is particularly pH sensitive, so the concentration of carbonic acid in solution may control the reservoir of dissolved aluminous species. Aluminous species solubility is U-shaped with respect to pH, with an inflection point at about 6-1/2 pH (Driscoll and Schecher, 1990). A rise in pH from 3.5 to 6.5 would decrease the aluminous species solubility by a factor of more than 100,000, effectively dumping the entire reservoir of dissolved aluminous species, presumably in the form of precipitated feldspar mineral grains.

And CO2 bubbling out of solution will tend to nucleate on precipitating feldspar mineral grains, tending to float feldspar mineral grains to the icy ceiling.

The aqueous solubility of aluminous mineral species is particularly pH sensitive

Aqueous silica solubility, by comparison, is particularly temperature sensitive, with silica reaching minimum solubility at the cold ice ceiling, where silica solubility is lowest and quartz precipitation and crystallization is most likely. So with quartz precipitation at the icy ceiling and with catastrophically precipitated feldspar mineral grains floated to the ceiling by nucleating CO2 bubbles, the flotsam at the icy ceiling would tend to have felsic (leucosome) composition. And mineral grains trapped in the flotsam would grow in size by crystallization.

When the felsic flotsam becomes waterlogged it sinks onto the more mafic precipitates of the sedimentary core, creating the alternating felsic-mafic layering typical of gneiss, migmatite and schist in the form of felsic leucosomes and mafic melanosomes.

If the felsic flotsam material forms into a mechanically competent mat, perhaps with cohesive organic material such as slime bacteria, its mechanical competency may cause the felsic mineral grains to hold together as a cohesive membrane that holds together as it becomes waterlogged and sags and finally sinks onto the core sediments below. The felsic mat is forced to crumple as it maps from the larger surface area of the icy ceiling onto the smaller area of the sedimentary core, forming characteristic hairpin turns, as it folds back on itself like ribbon candy. Ribbon candy like folds in the resulting lithified migmatite are described as ‘convolute folds’ or ‘ptygmatic folds’.

Ptygmatic folds in two contrasting matrix materials

Image credit, Mountain Beltway, Callan Bentley structural geology blog

http://blogs.agu.org/mountainbeltway/2010/10/15/friday-fold-wavelength-contrast/

In the above image from the following source,
Mountain Beltway (click on link)
the white lithosome is crumpled into ptygmatic folds in the dark-colored slate (above), whereas it’s undistorted in the lighter-colored sandstone (below), presumably due to the relative compressibility of the two types of matrix sediments. If the silty slate sediments are comparatively compressible during lithification compared to the larger sand grains that form sandstone, then the competent lithosome mat was forced to crumple and fold like the bellows of an accordion in the highly-compressible silty sediments of the slate.

Relative mineral grain size may play as much of a role in the degree of compressibility during lithification as the mineral type, with smaller mineral grains tending to deform by dissolution at mineral grain contacts, compared to interstitial infilling between larger mineral grains during lithification. Additionally, quartz grains in quartz sandstone is relatively hard and highly inert, reducing its tendency to deform at mineral grain contacts, compared to softer and less inert minerals.

Convolute folding wavelengths vs. membrane thickness/stiffness
Image credit, Structural Geology, RWTH Aachen University
https://www.youtube.com/watch?v=qOtdn8nt1RA&feature=share&ab_channel=StrucGeology

The above still image taken from the following video,
“Folding of two silicone layers of different thickness (Structural Geology, analogue modelling)”
The video demonstrates two separate principles of folding;
1) Convolute folding of a less compressible (leucosome) membrane within a more compressible (melanosome) matrix, and
2) Folding wavelength is related to the relative thickness and stiffness by the Ramberg-Biot equation, where a thicker ‘dike’ folds with a longer wavelength.

The video description makes no reference to or acknowledgement of the relative compressibility of the foam matrix, compared to the silicon membrane, pretending that both materials of comprised of virtually incompressible rock, with differing competencies (stiffnesses).
………………..

Authigenic Mineral-grain size:

A major difference between authigenic terrestrial sediments and authigenic extraterrestrial sediments is mineral grain size. On the surface of our high-gravity planet, precipitated authigenic mineral grains fall out of aqueous suspension at clay size and are sequestered in sediments, which may go on to lithify into mudstone, but in the microgravity deep inside KBO oceans, aqueous dispersion commonly reaches sand grain size before falling out of aqueous suspension.

The felsic flotsam at the icy ceiling enables gneissic leucosome mineral grains to continue to grow by ‘crystallization’, prior to waterlogged and sinking into the mafic sediments of the core to become sequestered from further crystal growth. This ‘larval’ stage at the icy ceiling explains why felsic mineral grains in leucosomes are often much larger than the mafic mineral grains in melanosomes in gneiss, migmatite and schist.

Additionally, gravitational acceleration increases from zero at the gravitational center of an object to a maximum value about 2/3 of the way to the surface, so mineral grain sizes would tend to decrease from the inside out in sedimentary KBO cores, with mineral grain size tending to decrease over time with the growing size of the sedimentary core.

The trend of decreasing mineral grain size per radial distance must be understood in the context where the local agitation of the saltwater ocean may have as great an effect on mineral grain size as the radial distance form the core, so mineral grain size would tend to increase dramatically at KBO quakes, and decrease exponentially thereafter until the next seismic event which stirs the pot.
………………..

‘Slump folding’ in metamorphic rock:

Lithification of sediments into sedimentary rock occurs partially by destruction of porosity, which reduces the volume of the sediments. In sedimentary KBO cores, volume reduction during lithification is occurs in the expulsion of interstitial saltwater through hydrothermal vents into the overlying ocean.

The volume reduction of a sedimentary KBO core is accompanied by a significant circumference reduction of the core during lithification, enforcing ‘circumferential folding’ at various scales, like a smooth grape dehydrating to become a wrinkled raisin, where circumferential folding is a form of enforced ‘slump folding’, enforced because the circumference of sedimentation is reduced in the lithified core.

While slump folding can occur in terrestrial sedimentary rock, it’s relatively rare, as is evident from the flat layers of Phanerozoic rock that make up the Grand Canyon. By comparison, KBO metamorphic rock, like gneiss and schist, frequently exhibit slump folding on various scales, so enforced circumferential folding may represent the majority of the total slump folding in KBO metamorphic rock.

Conventional geology suggests that metamorphism is the result of elevated pressure and temperature at great depth below Earth’s surface, with folding caused by shear forces. Tectonic folding, which creates the synclines and anticlines of valleys and mountains in orogeny can not occur 10s of kilometers below the surface, where there’s no void of the atmosphere to fold into. In conventional geology, sharp isoclinal folds are often misrepresented as sheath folds, fortuitously cut through the nose of a sheath fold, since the origin of point forces necessary to explain centimeter-scale isoclinal folds in virtually-incompressible protolith can not be explained without significant hand waving. By comparison, sharp isoclinal folds in the context of a sedimentary KBO origin are nothing more than circumferential slump folding, which is as easy to describe as grapes shriveling to form raisins. So while the synclines and anticlines of orogeny on the surface of the Earth has the void of the atmosphere to fold into, sediments at depth also have the collective space of many collective interstitial voids to fold into, when the saltwater is forced out through hydrothermal vents.

A sedimentary KBO origin for gneiss domes recognizes prograde and retrograde metamorphism at various temperature and pressure regimes, which may transform one suite of minerals into another and may recrystallize mineral grains, typically increasing the mineral grain size. The typically large mineral grains in granulite are assumed to have recrystallize from their sedimentary protolith. And gneiss which is uniformly flecked on a millimeter scale with dark mafic minerals which have reformed is also very likely the result of prograde metamorphism, with the flecks running perpendicular to the applied pressure. And sedimentary leucosome-melanosome layering and metamorphic folding is often muted by subsequent recrystallization metamorphism, blurring the originally distinctive sedimentary boarders, and increasing the difficulty of interpretation.

The pressure causing metamorphism in KBO cores is likely the result of the saltwater ocean freezing solid around a lithifying sedimentary core, with the expansion of water ice building the tremendous pressure that causes high-pressure metamorphism.

Authigenic gneiss with sharp isoclinal folds

Authigenic gneiss with sharp isoclinal folds

Millimeter-scale crenellations are common in phyllite, known as ‘overprinting’, with a definite orientation indicating the direction of the shear force. Crenellations in phyllite represent true metamorphic folding, occurring in nearly-incompressible lithified or metamorphic rock. While the effect may be widespread, the regrowth in (mica) minerals which result in the crenellations are typically at the recrystallized mineral grain scale and thus relatively small. Isoclinal folds, by comparison are not directional and therefore not the result of applied shear forces.
………………..

Gneiss-dome mantling rock; quartzite, marble and schist:

Gneiss domes are typically covered in mantling rock in a specific sequence of layers, with carbonate rock sandwiched between quartzite and schist, where the quartzite is in contact with basement gneiss. Thus the typical order of mantling rock is gneiss, quartzite, carbonate rock and schist.

Typical gneiss-dome mantle sequence: gneiss--quartzite--limestone/dolostone/marble--schistReference: Fourteen Geologic Cross Sections through the Gneiss Domes near Baltimore Maryland Geological Survey, 1937; Volume 13, Plate 32

Typical gneiss-dome mantle sequence: gneiss–quartzite–limestone/dolostone/marble–schist

Reference: Fourteen Geologic Cross Sections through the Gneiss Domes near Baltimore Maryland Geological Survey, 1937; Volume 13, Plate 32

Quartzite and carbonate rock/marble:
If the pH rises above about 9, as the ocean cools down and the precipitation of gneissic sediments tails off, silica will begin to precipitate out of solution, depositing authigenic sand over gneissic sediments, which may metamorphose into quartzite. And if the pH continues to rise after the bulk of silica has precipitated in the form of sand, then bicarbonate ions in solution increasingly convert to carbonate ions, lowering the solubility of calcium carbonate in solution, which ultimately precipitates calcium carbonate, which may metamorphose into marble.

Graph showing silica precipitation above pH 9 and calcite precipiation above pH 10

From Muskingum University petrology course

http://www.muskingum.edu/~ericlaw/courses/petrology/images/silica-pH.jpg

Schist:
Schist is typically the third and final authigenic mantling layer of gneiss domes, which is suggested to precipitate as the KBO ocean freezes solid. Freezing water tends to exclude solutes from the solid phase, raising the dissolved solute load to the point of (super)saturation, ultimately precipitating even incomparable elements, perhaps explaining the high degree of variability of rock and mineral types in authigenic schist, compared to other authigenic rock types, where schist is the sludge of the rock world.

Clastic conglomerate frosting over authigenic gneiss-dome:
While schist is the final authigenic mantling layer, gneiss dome mantles often have a clastic frosting in the form of conglomerate or greywacke, which may result from grinding of the rocky core against the icy ceiling, as the ocean freezes solid and the icy ceiling closes in on the rocky core. Often the pebbles, cobbles and boulders in the conglomerate frosting are highly polished, with a higher polish than pebbles, cobbles and boulders achieve when tumbling in terrestrial streams and rivers. The pebbles, cobbles and boulders in the conglomerate frosting often exhibit an indurated case-hardened-like surface, which might be expected as the solutes are forced out of solution, promoting the ‘plating out’ (crystallizing) of silicates on the exposed surfaces of boulders, cobbles and pebbles, creating the observed indurated effect.

Broken quartzite cobble from the Susquehanna River with an indurated dark brown outer shell. A few Skolithos pock marks are visible in cross section to the right.

Broken quartzite cobble from the Susquehanna River with an indurated dark brown outer shell. A few Skolithos pock marks are visible in cross section to the right.

Euhedral garnets in schist:
Euhedral almandine garnets often exhibit a round dodecahedron shape and are often orders of magnitude larger than the next-largest mineral grains. Their distinctly rounded shapes suggest authigenic crystallization while trapped by the Bernoulli effect of hydrothermal vent plumes emanating from the sedimentary core.

Euhedral garnets in schist“Almandin” by Didier Descouens – Own work. Licensed under CC BY-SA 4.0 via Commons – https://commons.wikimedia.org/wiki/File:Almandin.jpg#/media/File:Almandin.jpg

Euhedral garnets in schist
“Almandin” by Didier Descouens – Own work. Licensed under CC BY-SA 4.0 via Commons – https://commons.wikimedia.org/wiki/File:Almandin.jpg#/media/File:Almandin.jpg

………………..

Shock-wave pressure clamping in icy object impacts:

Work = force times change in distance, and similarly, Work = pressure times change in volume (W = PdV). If volatile ices are significantly more compressible than silicates, then the ice in icy impacts will act like a shock absorber to absorb the vast majority of impact energy. And if compressible ices clamp the impact shock-wave pressure below the melting point of silicates and below pressures required to form shatter cones, shocked quartz and high-pressure polymorphs like coesite, then icy-body KBO impacts may be masked from detection as such.

The relative compressibility of ices is suggested to lower the specific impact power of icy-body impacts by extending the shock-wave duration through an extended rebound period of the compressed ices.

If rocky-iron asteroid impacts resemble the sharp blow of a ball peen hammer, forming bowl-shaped craters with melt rock and overturned target rock, icy-body impacts may resemble the compressive thud of a dead blow hammer, where the prolonged rebound duration of c ompressed ice rebound promotes distortion of Earth’s crust into a perfectly-circular basin, with the sustained compression of the rebounding ice largely preventing the excavation of a crater, such as the perfectly-round Nastapoka arc of Lower Hudson Bay. And in the case of a circa 12,900 ya Nastapoka arc impact, the multi-kilometer-thick Laurentide ice sheet would have provided an additional endothermic shock-absorbing cushion.

So while rocky-iron impacts form impact craters with melt rock, shatter cones, shocked quartz and high-pressure polymorphs, icy-body impacts are suggested to merely form perfectly-round impact basins. But if impacting KBO cores extend down into Earth’s mantle where they melt to form sinking plumes, the sinking plumes will entrain and subduct the adjacent ocean plates, which in turn draw in the adjacent continental tectonic plates, tending to erase the impact basin signature. So if large KBO impacts draw in adjacent continental tectonic plates to form supercontinents, then large KBO impacts actively erase their own impact signatures.
………………..

References:

Eskola, Pentti Eelis, (1948), The problem of mantled gneiss, Feb. 1948 Quarterly Journal of the Geological Society, 104, 461-457

Levine, Johanthan; Becker, Timothy A.; Muller, Richard A.; Renne, Paul R., 2005, 40Ar/39Ar dating of Apollo 12 impact spherules, Geophysical Research Letters, Volume 32, Issue 15, CiteID L15201

Sandeman, Clark, Scott and Malpas, (2000), The Kennack Gneiss of the Lizard Peninsula, Cornwall, SW England: commingling and mixing of mafic and felsic magmas accompanying Givetian continental incorporation of the Lizard ophiolite, Journal of the Geological Society; November 2000; v. 157; no. 6; p. 1227-1242

Yin, An, (2004), Gneiss domes and gneiss dome systems, Geological Society of America Special Paper 380
………………..

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s