This section suggests an alternative extraterrestrial origin for gneiss domes, along with their associated mantling rock of quartzite, carbonate rock and schist. Authigenic gneissic sediments are suggested to precipitate in the cores of Kuiper belt objects (KBOs) undergoing ‘aqueous differentiation’, with aqueous differentiation caused by orbital perturbation by a former binary-Companion to the Sun in the Precambrian era, and/or by Neptune in the Phanerozoic Eon.
Authigenic KBO sediments are suggested to be gneissic in composition and in mineral grain size, with alternating felsic leucosomes and mafic melanosomes likely caused by sawtooth pH variations in the internal KBO oceans.
Most folding in metamorphic rock is slump folding, caused by dehydration of the sedimentary KBO core during lithification, like a grape drying to form a raisin, with attendant wrinkling.
Aqueous dikes drain water from the dehydrating core during lithification, with the dikes feeding hydrothermal vents into the internal KBO saltwater ocean. Felsic mineral grains precipitate in the aqueous dikes and grow by crystallization, with the felsic mineral grains acting as a French drain, providing a conduit for the buoyant aqueous fluids. And the growth of felsic mineral grains in aqueous dikes by crystallization causes buckling, resulting in ptygmatic folding of the felsic dikes prior to their lithification.
Gneiss-dome mantling rock, consisting of quartzite, marble and schist is presumably caused by elevated pH toward the end of an aqueous differentiation phase. Rising pH precipitates silica, which falls out of aqueous suspension at sand grain size, and metamorphoses into quartzite. Continued increase in pH causes high-solubility bicarbonate ions to convert to lower-solubility carbonate ions, precipitating carbonates which metamorphose into marble. Ultimately schist sediments precipitate as the ocean ultimately freezes solid, with water ice concentrating solutes of all types in solution which precipitate as schistose sediments that metamorphose into schist. And finally, the volume increase of the saltwater ocean freezing solid provides the pressure to induce metamorphism in the core, converting gneissic sediments to gneiss, sandstone to quartzite, limestone and dolostone to marble, and schistose sediments to schist.
Some aqueously-differentiated KBOs were and are perturbed into centaur orbits, where they fall under the influence of Jupiter and Saturn. Former KBOs in unstable centaur orbits will either be kicked out of the inner solar system or will continue to spiral down into the terrestrial planet region where they may impact Earth. The gneiss dome cores in KBO impacts are protected by a thick icy mantle where the relative compressibility of ices absorb the lion’s share of the impact energy, clamping the impact shock-wave pressure below the melting point of silicates.
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. “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, alternating precipitation of felsic and mafic layers occurs from the overlying KBO saltwater ocean, with the ocean providing the mineral species reservoir.
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 leveled, 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.”
In the alternative aqueous differentiation context, gneiss-dome multiplicity represents localized and perhaps repeated aqueous differentiation within the KBO interior, with each localized aqueous differentiation episode concluding with more-or-less quartzite, marble and schist mantling rock.
Aqueous differentiation of KBOs:
Our solar system is suggested to have had a former binary brown-dwarf Companion, which sculpted the inner edge of the inner Oort cloud (see section, GALAXIES, STARS, PLANETS, MOONS, MINOR PLANETS AND COMETS). Our former binary-Companion tidally perturbed KBOs to undergo aqueous differentiation, causing authigenic precipitating, creating sedimentary cores with a gneissic composition.
Perturbation of KBOs by our former binary-Companion caused aqueous differentiation of KBOs, with aqueous differentiation defined as the melting of water ice to form internal saltwater oceans. The nebular dust liberated during aqueous differentiation partially dissolved into solution and partially nucleated crystallization, where and when the solution was (super)saturated with dissolved mineral species. These authigenic mineral crystals grow by crystallization until precipitating (falling out of suspension) at a mineral grain size dependent on the microgravitational acceleration and the local circulation rate of the internal saltwater ocean.
On Earth, authigenic mineral grains precipitate out of solution at clay particle scale, which may lithify to form authigenic mudrock. By comparison, aqueous differentiation of KBOs is suggested to precipitate gneissic mineral-grain-sized sediments, forming gneiss.
Tonalite-trondhjemite-granodiorite (TTG) series, typical of Archean cratons may derive from particularly-large KBOs, the vast majority of which rained down on the inner solar system during the late heavy bombardment, circa 4.13.8 Ga. Aqueous potassium solubility is particularly temperature sensitive, so elevated temperatures in larger early KBOs may have resulted in K-feldspar deficient TTG sediments, compared to younger gneiss domes in smaller KBOs.
The binary brown-dwarf components of our former binary-Companion spiraled in to merge at 542 Ma in an asymmetrical merger explosion which gave the newly-merged companion escape velocity from the Sun.
With the loss of former binary-Companion, KBOs have fallen under the influence of Neptune in the Phanerozoic Eon, with KBOs settling into post binary-Companion orbits. While most KBOs have presumably settled into more quiescent orbits, with the loss of binary-Companion, some KBOs have apparently undergone more-intense Phanerozoic perturbation, presumably due to the alteration of resonances. With the change in resonance intensities and locations, a subset of KBOs are apparently undergoing a new era of perturbation, with attendant orbital alterations and aqueous differentiation. Resonant perturbation of KBOs Neptune has apparently resulted in orbital perturbation of KBOs into the inner solar system, presumably by the intermediate pathway of centaur orbits, making Neptune the Nemesis of the Phanerozoic Eon, in terms of showering the inner solar system with KBOs.
Gneissic leucosome/melanosome layering in (extraterrestrial) metamorphic rock:
Conventionally, migmatites form by the secondary mechanism of partial melting (anatexis) of a lithified protolith under elevated temperature and pressure metamorphism at 10s of kilometers below the surface, resulting in the partial melting of lower-melting-temperature felsic minerals of the protolith mesosome and the physical segregation of the partial melt into felsic-enriched leucosomes and felsic-depleted melanosomes. This simplistic treatment is problematic, however, since leucosomes are often too voluminous to have been derived from their adjacent melanosomes alone, requiring a remote injection of molten felsic material. “The consensus today is that both in situ melt and externally derived melt are present in most migmatites (Kriegsman, 2001).” (Urtson, 2005)
Alternatively, the alternating felsic-mafic layering in gneiss is not secondary mechanism, but instead a primary mechanism caused caused by alternating authigenic deposition of felsic and mafic sediments. This alternating deposition may be attributable to sawtooth changes in the pH of the overlying ocean. The potential of hydrogen in solution, pH, strongly affects the solubility of aluminous species, presumably resulting in the alternating deposition of aluminous feldspar mineral grains.
The partial pressure of carbon dioxide gas trapped in pockets between a internal saltwater ocean and its overlying icy crust would force carbon dioxide into solution where it reacts with water to form carbonic acid, lowering the pH in internal KBO oceans.
As aqueous differentiation densifies a KBO, subsidence events (‘KBO quakes’) may vent trapped gas to outer space, reducing the partial pressure of carbon dioxide, causing carbonic acid to bubble out of solution in the form of gaseous carbon dioxide bubbles. 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.
FFF: The aqueous solubility of aluminous mineral species is particularly pH sensitive
And CO2 bubbling out of solution will nucleate on precipitating feldspar mineral grains, floating them to the icy ceiling.
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 quartz would tend to crystallize on feldspar mineral grains floated to the surface on CO2 bubbles, forming felsic quartz-feldspar conglomerate particles, which would tend to be larger than the more-mafic mineral grains precipitated during the intervening quiescent periods.
Gneiss-dome mantling rock, quartzite, carbonate rock and schist:
Gneiss domes are typically covered in mantling rock in a specific sequence of layers, with carbonate rock sandwiched between quartzite and schist, with quartzite in contact with basement gneiss. Thus the typical order of mantling rock is gneiss, quartzite, carbonate rock and schist.
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.
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 exhibit an indurated case-hardened-like surface, which might be expected as the solutes are forced out of solution, promoting the crystallization of silicates on the exposed surfaces of boulders, cobbles and pebbles, creating the observed indurated effect. Finally, pebbles, cobbles and boulders in the conglomerate frosting often exhibit greater degree of polish than pebbles, cobbles and boulders achieve when tumbling smooth in terrestrial streams and rivers.
Porphyroblast garnets in schist:
Euhedral almandine garnets in schist 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 in hydrothermal vent plumes emanating from the sedimentary core undergoing lithification. This IMAGE shows the dropstone effect of garnet porphyroblasts in layered schist, revealing its sedimentary origin.
While the partial melting metamorphism of migmatites is dismissed here as having a layered sedimentary origin instead, the conversion of sandstone to quartzite, limestone to marble and various types of protolith to eclogite or granulite is very real indeed. A high degree of subsequent metamorphism, however, may largely erase the original authigenic mineral grains through recrystallization, as in granulite or eclogite, where the recrystallized mineral grains are typically larger than the authigenic mineral grains that fell out of aqueous suspension.
Much of the pressure required for high-pressure metamorphism in extraterrestrial gneiss-dome rock may partly be attributable to the volume increase of an internal, KBO saltwater ocean freezing solid, with the expansion of water ice creating elevated pressures necessary for metamorphism for converting gneissic sediments to gneiss, sandstone to quartzite, limestone and dolostone to marble, and schistose sediments to schist. Much of the high-temperature metamorphism found in metamorphic rock, however, may be terrestrial following Earth impact.
While slump folding and ptygmatic folding in gneiss, migmatites and schist are suggested to occur prior to lithification, S-C fabric typical in phyllite is definitely (post-lithification) metamorphic in origin.
While some types of minerals may require high pressure conditions to crystallize from an igneous melt, some of those supposed high pressure minerals may form at much lower temperatures by authigenic crystallization from an aqueous solution; however, the petrology that could justify that suggestion is beyond the limited scope of this conceptual approach.
(Slump) folding in (extraterrestrial) metamorphic rock:
Conventional geology suggests that metamorphic folding occurs at great depth below Earth’s surface under elevated pressures and temperatures under the influence of shear and compressional forces, and often with the assistance of partial melting, as in migmatites.
Tectonic orogeny, which creates the synclines and anticlines of valleys and mountains, can not occur 10s of kilometers below the surface where there’s no void of the atmosphere to fold rock layers into. In conventional geology, sharp isoclinal folds are often misrepresented as sheath folds caused by shear forces, since the origin of point forces necessary to explain centimeter-scale isoclinal folds on multiple scales in virtually-incompressible protolith is inexplicable.
Alternatively, extraterrestrial metamorphic rock begins as authigenic sedimentary precipitation in KBO cores. The sedimentary core undergoes slump folding during destruction of voids (dehydration) phase of lithification during which the aqueous fluids are buoyantly forced out of the core. And the core shrivels (slump folds) during lithification, like a grape dehydrating to form a raisin, with sediments folding into voids created by expelled fluids.
In an authigenic sedimentary KBO core undergoing lithification, a pithy sedimentary core shrinks in circumference and volume, while increasing in density during lithification. The reduction in circumference and volume forces ‘circumferential slump folding’, as a given volume and circumference of sediments is shrunk into a smaller volume and circumference of lithified rock. In sediments undergoing lithification on Earth, the circumference change of lithifiying sediments is imperceptible compared to their volume reduction, resulting in no circumferential slump folding on Earth. Something similar to circumferential slump folding can occur on Earth under unusual circumstances, such as the lithification of sediments in a sharp V-shaped valley or crevice, where pithy sedimentary layers are forced to fold as they densify toward the pointy end of the V during lithification.
While the majority of folding in ‘metamorphic rocks’ is attributable to circumferential slump folding, ptygmatic folding has a different origin.
Fluids are presumably drained from the lithifying core into the overlying KBO ocean through hydrothermal vents, with vents fed by ‘aqueous dikes’. Aqueous dikes are suggested to form as tears in gradually lithifying sediments, either formed by positive hydraulic pressure of buoyant fluids escaping to the surface, and/or as extensional pull-apart rifts of a contracting core.
Fluids draining to the surface through aqueous dikes are rich in dissolved mineral species, which may authigenically nucleate and precipitate in the dikes. These felsic mineral grains prevent the aqueous dikes from closing up, and moreover act as French drains, with the felsic mineral grains in the aqueous dikes presumably having a lower resistance to aqueous fluid flow than the surrounding matrix.
The fluid flow, channeled through these aqueous dikes, promotes the growth of the felsic mineral grains in the dike by crystallization, causing the mineral grains in felsic dikes to typically exceed the mineral grain size of the more-mafic surrounding matrix.
Growth of felsic mineral grains by crystallization in aqueous dikes increases the grain-to-grain pressure compared to the surrounding matrix. Thus the over-pressurized felsic mineral grains of the aqueous dike expand laterally and longitudinally into the surrounding matrix. Lateral expansion, perpendicular to the dike plane, increases the dike width, while longitudinal expansion, in the dike plane, causes dike buckling in the form of ptygmatic folding. This ideology presumes that the felsic mineral grains of aqueous dikes are more or less composed of discrete mineral grains, during their ptygmatic folding phase, that have not substantially begun to fuse together to form solid rock.
The internal force of expansion within veins due to crystallization has been recognized for its contribution in the formation of ptygmas.
“There are two internal forces of expansion
within the vein: that of increase in volume
due to crystallization from solution and
that of force of crystallization of the vein
mineral.” (Shelley 1968)
The intrinsic expansion of aqueous dikes, in which the center point of every mineral grain is expanding from the centerpoint of every other mineral grain, readily explains the maintenance of dike width typical of ptygmatic folding. Slump folding, however, may be superimposed over ptygmatic folding, thinning or breaking dikes, and variable plasticity of the surrounding matrix may result in aneurysms in aqueous dikes, forming boudinage.
While the mineral grain pressure in aqueous dikes is positive, compared to the surrounding matrix, the aqueous fluid pressure is presumably negative, to the extent that aqueous dikes act as fluid drains for the surrounding matrix. Perhaps these counteracting pressures help to maintain the sharp dike/matrix boundaries during the intrusive buckling of ptygmatic folding.
When and where the matrix surrounding matrix of an aqueous dike is too stiff or too lithified to permit ptygmatic folding, all the mineral grain pressure may be displaced laterally, forming local aneurysms, where the surrounding matrix is somewhat more plastic, which lithify into boudinage.
Increasing back pressure from the matrix ultimately converts from mineral grain growth, between impinging mineral grains, to pressure dissolution, which shrinks the center-to-center distance between impinging felsic mineral grains, and the discrete felsic mineral grains lithify into a solid dike.
The following image shows a pair of white quartz or calcite veins cutting through two very different rock matrix types, namely tan sandstone in the bottom half of the image, and black shale above. The two veins, presumably representing former aqueous dikes, exhibit a dramatically different response to the two different enveloping matrix types. Felsic mineral grain growth in the former aqueous dikes is partly expressed longitudinally as buckling (ptygmatic folding) in the presumably softer shale sediments, whereas the mineral grain growth is entirely expressed laterally as increased dike width in the presumably stiffer sandy sediments, with no longitudinal buckling.
Tangled clumps of ptygmatic folding may occur where the surrounding matrix sediments are particularly soft, which may represent areas where fluid pooling occurs, promoting bucking in both the X and Y planes. And if the soft regions are soft due a soggy super concentration of aqueous fluids, then the resulting elevated local fluid flow through the aqueous dike drains will accelerate the local precipitation and crystallization of felsic mineral grains, and may grow branching dikelet feeders to better drain the soggy area.
In gneissic sediments with alternating felsic-mafic leucosome-melanosome layering, some felsic, depositional leucosome layers may function as built-in aqueous dike drains. These fortuitously placed layers will experience felsic mineral grain growth with attendant ptygmatic folding, whereas nearby nearby depositional leucosome layers which do not act as aqueous drains will remain unfolded, except for overarching slump folding. Depositional leucosomes, which act as aqueous dike drains, run parallel to the sedimentary layering, whereas aqueous tear dikes will often cut through layering plane diagonally or perpendicularly, and tear dikes will more often exhibit radiating dikelets, as in streams feeding creeks which feed still-larger rivers leading to hydrothermal vents.
Mineral grain growth may reach pegmatite scale within aqueous dikes when conditions are favorable, perhaps in the absence of suitable nuclei for nucleating and precipitating new mineral grains.
And finally, aqueous dikes may reach the massive proportions of S-type granite plutons and batholiths in internal anticline folds which trap buoyant aqueous fluids. (See section, THE ORIGIN OF S-TYPE GRANITE PLUTONS IN KUIPER BELT OBJECTS (KBOs)).
Ptygmatic accordion folding:
If ptygmatic folding is caused by a differential increase in the length of aqueous dikes over that of the background matrix, then ‘ptygmatic accordion folding’ is suggested to result in differential shrinkage during lithification between leucosomes/aqueous dikes and mafic melanosomes/matrix rock, where overall ptygmatic folding may be a combination of the two.
Fine mafic sediments may typically undergo a greater degree of shrinkage during lithification than the larger mineral grains in felsic leucosomes and aqueous dikes, with the greater degree of mafic shrinkage presumably due to a greater degree of pressure dissolution of smaller mineral grains at impinging mineral-grain boundaries, so presumably ptygmatic accordion folding typically causes more accordion folding.
Shock-wave pressure clamping in icy object impacts:
Work equals 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 the impact energy. And if relatively-compressible ices clamp the impact shock-wave pressure below the melting point of silicates. The relative compressibility of ices compared to silicates 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.
The absence of meltrock in icy body impacts would not necessarily preclude the formation of lower-pressure shock wave effects, such as shatter cones, shocked quartz and high-pressure polymorphs like coesite, but the slow-motion deceleration of an object on the order of 100 km diameter with Earth may blunt the effect of the elevated impact pressure.
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 compressed ice promotes distortion of Earth’s crust into a perfectly-circular basin, with the sustained rebound of the compressed ice largely preventing the explosive excavation of a crater, such as the perfectly-round Nastapoka arc basin of Lower Hudson Bay. And in the case of a circa 12,900 ya Nastapoka arc impact, the Laurentide ice sheet would have provided an additional endothermic shock-absorbing cushion.
So while rocky-iron impacts form impact craters with overturned rock layers, melt rock, shatter cones, shocked quartz and high-pressure polymorphs, icy-body impacts are suggested to form perfectly-round impact basins.
And if rocky KBO cores following impact extend down into Earth’s mantle, the KBO core rock may melt, forming sinking plumes. And sinking plumes from melting KBO cores would tend to subduct the adjacent ocean plates, drawing in the adjacent continental tectonic plates to form supercontinents.
Eskola, Pentti Eelis, (1948), The problem of mantled gneiss, Feb. 1948 Quarterly Journal of the Geological Society, 104, 461-457
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
Shelley, David, 1968, PTYGMA-LIKE VEINS IN GRAYWACKE, MUDSTONE, AND LOW-GRADE SCHIST FROM NEW ZEALAND, The Journal of Geology, Vol. 76, No. 6 (Nov., 1968), pp. 692-701
Yin, An, (2004), Gneiss domes and gneiss dome systems, Geological Society of America Special Paper 380