Migmatite gneiss with associated mantling rock, of typically quartzite, marble and schist, is suggested to possibly have an extraterrestrial origin in the form of authigenic sedimentary Kuiper belt object (KBO) core rock, particularly when metamorphosed massifs present with a mantled gneiss dome structure. This is not to suggest that all or even most metamorphic gneiss, schist, quartzite, marble and gneiss domes are extraterrestrial in origin, since rock types are defined by composition rather than genesis, and gneiss domes are defined by their domal structure, independent of their origins.
Authigenic gneissic sediments are suggested to precipitate in the cores of Kuiper belt objects (KBOs) undergoing ‘aqueous differentiation’, where aqueous differentiation is defined as the melting of water ice. Aqueous differentiation is presumably caused by orbital perturbation. Orbital perturbation may directly cause melting of water ice by tidal heating, or indirectly by causing a binary spiral-in merger of a binary KBO which merges to form a contact binary, initiating catastrophic aqueous differentiation. Pre-Ediacaran orbital perturbation is suggested to have been principally caused by a former binary-Companion to the Sun, and post-Cryogenian orbital perturbation is suggested to be caused by the continuing adjustment of the outer solar system to Neptune following the loss of former binary-Companion, presumably at the Cryogenian-Ediacaran boundary.
Authigenic KBO sediments are suggested to be gneissic in composition and in mineral grain size, with alternating felsic leucosomes and mafic melanosomes caused by sawtooth pH variations in the internal KBO oceans.
The majority of folding in KBO metamorphic rock is suggested to be slump folding during lithification, as the sediments densify by destruction of voids, like a grape drying to form a raisin, with attendant wrinkling.
Aqueous dikes are presumed to drain water from the dehydrating core during lithification, with the dikes feeding hydrothermal vents into the overlying, internal, KBO saltwater ocean. These aqueous dikes are the leucosomes of migmatite, with the porosity of felsic dikes acting as low-resistance French drains to the surface.
As the mineral-laden water drains out through the felsic dikes, some of minerals precipitate or crystallize on existing mineral grains, swelling the felsic dikes until they may buckle into the surrounding more-mafic matrix as ptygmatic folds.
Gneiss-dome mantling rock, typically consisting of quartzite, marble and schist, forms toward the end of the authigenic precipitation, as the internal ocean is cooling off and beginning to refreeze.
Finally, as the saltwater ocean freezes solid from the outside in, the volume increase of freezing water builds tremendous pressure on the core which accelerates lithification and causes high-pressure metamorphism converting authigenic sediments into metamorphic rock.
Some aqueously-differentiated KBOs were and are occasionally perturbed into centaur orbits where they fall under the influence of Jupiter and Saturn and may be induced to spiral down into the inner solar system where they may impact Earth.
The lithified cores of KBO impacts are protected by their thick icy mantle, where the relative compressibility of ice compared to the relative incompressibility of KBO core silicates and terrestrial target rock silicates causes compressible ices to absorb the lion’s share of impact energy, which may clamp the impact shock-wave pressure below the shock-melting point of silicates, allowing extraterrestrial KBO core rock to survive impact intact.
In conventional geology, the theorized 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 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 suspended mineral grains and dissolved solutes providing the reservoir of mineral species, with pH dictating the dominant precipitation species.
Conventional geology particularly struggles to explain gneiss dome mantling rock.
“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.”
Alternatively, basal conglomerate could form as the freezing saltwater ocean converges on the metamorphosing silicate core, causing grinding of the ice ceiling on the silicate floor, forming conglomerate.
“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.”
Alternatively, authigenic felsic precipitation, forming sedimentary felsic leucosomes could represent ‘earlier granite intrusions’, and ‘new granite magma’ is suggested to form during lithification, as felsic mineral grains precipitate and grow by crystallization within porous aqueous dikes, with aqueous dikes serving to discharge buoyant aqueous fluids from the core during lithification.
Aqueous differentiation of KBOs:
Our solar system is suggested to have had a former binary-Companion to the Sun with super-Jupiter-mass components that tidally perturbed many Plutino and cubewano binary KBO orbits to spiral in and merge, and deflected many KBOs into the inner solar system during the late heavy bombardment, 4.1-3.8 Ga.(see section, STARS, PLANETS, MOONS, MINOR PLANETS AND COMETS). The super-Jupiter binary components are suggested to have spiraled in to merge at 635 Ma, giving the newly-merged Companion escape velocity from the Sun.
The binary spiral-in merger of a pre-Ediacaran binary KBO is suggested to have caused catastrophic aqueous differentiation, melting saltwater oceans in the merged contact-binary cores. The subliming and melting ices liberated nebular dust into solution and suspension, with gneissic mineral grains precipitating and (falling out of aqueous suspension) at a mineral grain size dependent on the local microgravity of the ocean and its circulation rate. On Earth, authigenic mineral grains precipitate out of solution at the clay particle scale, which may lithify to form authigenic mudrock, while in the microgravity of KBO saltwater oceans, mineral grains are suggested to typically fall out of aqueous suspension at sand grain size, such that much of the sand on Earth may be extraterrestrial authigenic quartz.
In addition to causing binary spiral-in merger of KBOs, orbital perturbation by former binary-Companion caused smaller degrees of aqueous differentiation by tidal torquing. Following the suggested loss of former binary-Companion at 635 Ma, the Kuiper belt fell under the influence of Neptune alone, initiating a new era of orbital perturbation by Neptune, as the KBO population continues to settle into its post-Cryogenian configuration, sans Companion.
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, 4.1-3.8 Ga. Aqueous potassium solubility is particularly temperature sensitive, so elevated temperatures in large early KBOs may have resulted in K-feldspar deficient TTG sediments, compared to younger gneiss domes from smaller 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 at depth beneath the Earth’s surface, causing physical segregation of the protolith mesosome into felsic-enriched leucosomes and felsic-depleted melanosomes
Alternatively, the felsic-mafic layering in migmatites is formed by primary sedimentation, with alternating authigenic felsic-mafic deposition, generally followed by a variable degree of secondary slump folding during lithification. This alternating felsic mafic deposition is suggested to be attributable to sawtooth changes in pH in the overlying saltwater 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 between an 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.
As aqueous differentiation densifies a KBO, subsidence events (‘KBO quakes’) may vent trapped gas to outer space, reducing the partial pressure of carbon dioxide on the ocean, causing carbonic acid to bubble out of solution in the form of gaseous carbon dioxide bubbles. And even in the absence of CO2 venting, seismic vibrations from KBO quakes would 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 precipitating feldspar mineral grains.
And the increased ocean circulation caused by a seismic event would tend to increase precipitation of quartz at the cold icy ceiling where silica solubility is lowest, since silica solubility is particularly temperature sensitive.
Catastrophic precipitation of quartz and feldspar are suggested to create felsic leucosome layers in migmatite, with enlarged mineral grain size in the leucosome layers due to enhanced saltwater ocean circulation during and following seismic events.
The catastrophic deposition of coarse felsic mineral grains is suggested to form felsic leucosome layers, while fine mafic mineral grains are suggested to precipitate during the intervening periods, forming mafic melanosome layers, as the pH creeps back up to quiescent levels.
Gneiss-dome mantling rock, quartzite, carbonate rock and schist:
Gneiss domes are often capped with mantling rock composed of quartzite, carbonate rock (often marble), and schist.
Mantling rock apparently forms toward the end of authigenic precipitation due to changing conditions, presumably precipitating as the saltwater ocean freezes solid. As saltwater freezes, dissolved solutes are excluded from the ice crystal structure. On Earth, the exclusion of salt creates convection beneath the sea ice. This convection may cause precipitation of dissolved silica in the form of quartz crystals at the cold ice-water ceiling, where silica solubility is lowest.
As the sea ice temperature decreases,
brine becomes further concentrated and carbonate minerals,
such as ikaite (CaCO3.6H2O), can precipitate from the
solution [Dieckmann et al., 2008; Marion, 2001] decreasing
(Loose et al., 2009)
Finally everything that doesn’t freeze in the solidifying ocean may precipitate as schist.
Gneiss dome mantles often also contain a clastic conglomerate layer, which suggests grinding of the icy ceiling against the rocky core. Gneiss-dome conglomerate boulders, cobbles and pebbles are apparently tumbled smoother in the microgravity KBO ocean than can occur in terrestrial streams, with large boulders often attaining a similar polish as small pebbles. Additionally, boulders, cobbles and pebbles typically exhibit a thin, indurated case-hardened-like surface, which might be expected in the presence of (super)saturated solutions, resulting in crystallization on exposed surfaces.
The Grenville Supergroup overlying the Brandywine massifs and Baltimore gneiss may be a good example of KBO mantling rocks in the Mid-Atlantic region, which presumably impacted sometime during the Ediacaran Period. Paleozoic formations assigned to the supergroup are likely terrestrial, however, such as the Cambrian(?) volcanic Chopawamsic Formation and the fossiliferous Ordovician Quantico Formation. Formations containing volcanic rock with basaltic flows, tuffaceous rock and/or pillow lava is presumably terrestrial, along with any formations containing recognizable lifeform fossils. Setters Formation, Cockeysville Formation and the Wissahickon group are presumed to be extraterrestrial Precambrian mantling rock over coincidentally Grenville age gneiss of the Brandywine massifs and Baltimore gneiss.
Circumferential slump folding in authigenic metamorphic rock:
Conventional geology suggests that metamorphic folding occurs at elevated temperature and pressure to already lithified rock, deep below Earth’s surface. Indeed tectonic orogeny creates the synclines and anticlines of mountain ranges by large-scale folding of rock up into the void of the atmosphere, but alternatively, sharp isoclinal small-scale folding in metamorphic rock on a centimeter to 10s of meter scale, or so, is suggested to be caused by slump folding of sediments.
If metamorphic folding looks like slump folding, maybe it actually is slump folding.
Conventional geology can not explain the origin of the point forces necessary to fold virtually-incompressible lithified rock into sharp isoclinal folds on a centimeter scale at depth and temperature beneath the Earth’s surface. Because small-scale isoclinal folds can’t be explained in a conventional lithified setting, randomly-oriented isoclinal folds in metamorphic rock are often dismissed as two-dimensional sheath folds, fortuitously cut through the nose of the fold, since sheath folds might be explained as smearing across shear zones.
In a sedimentary setting, the water between authigenic mineral grains provides the void to fold sediments into during the destruction of voids (dehydration) phase of lithification, as the buoyant water creates voids by rising upward.
In an authigenic sedimentary KBO core undergoing lithification, the sedimentary core shrinks in circumference and volume, while increasing in density during lithification at it progressively expels the low-density water.
As the water is forced out of a sedimentary KBO core, the core densifies and its volume and circumference shrink. Since the entire core shrinks by a large percentage, like a grape shriveling to form a raisin, each and every sedimentary layer is forced into a smaller circumference, causing dramatic ‘circumferential slump folding’. The circumference change of lithifiying sediments on Earth is imperceptible because of the imperceptible circumferential change of the circumference of the Earth between the unlithified sediments and the lithified rock. 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 a crevice or valley during lithification.
While the majority of folding in ‘metamorphic rocks’ is suggested to be attributable to circumferential slump folding, ptygmatic folding is suggested to have a different origin.
Fluids are presumably drained from a lithifying KBO core into the overlying saltwater ocean through hydrothermal vents, with vents fed by ‘aqueous dikes’ composed of porous sediments.
Layered, authigenic migmatite gneiss may have built-in porous aqueous dikes in the form of the felsic leucosome layers, where felsic mineral grains in leucosome layers tend to have a larger mineral grain size than the the mafic mineral grains in the melanosome layers. Thus the felsic leucosomes may act as French drains in transporting the buoyant water out of the core. Felsic leucosome layers, however, are laid down concentrically (horizontally), and also require vertical dikes to reach the surface.
Pressure forces water to flow buoyantly to the surface thorough porous aqueous dikes, and as the fluid pressure and temperature decrease enroute to the surface, dissolved mineral species with solubility proportional to temperature and pressure that reach aqueous saturation will tend to crystallize on existing mineral grains and precipitate new authigenic mineral grains. And this increase in mineral grain number and size within aqueous dikes will cause aqueous dikes to expand in 3 dimensions, with longitudinal expansion tending to cause buckling of aqueous dikes into the adjacent more-mafic sediments in the form of ptygmatic folds in aqueous dikes. The cause of the apparent propensity to favor the precipitation and crystallization of felsic minerals in aqueous dikes compared to mafic mineral grains is at present beyond the scope of this conceptual ideology.
Dramatic ptygmatic folding resembling ribbon candy, which folds back on itself, is particularly difficult to explain in conventional geology within lithified rock at depth, even with the assistance of partial melting, whereas the bucking process is as self evident in the manufacturing of sausage, as circumferential slump folding is in the drying of grapes to form raisins.
The internal force of expansion within veins due to crystallization has been recognized for its contribution to the formation of ptygmas by Shelley in a 1968 paper.
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
The ptygmatic veins, having a relatively small surface area for internal volume, were formed as a result of expansion of the vein material during growth and simultaneous accommodation of the host. Possible mechanisms are that the initial cracking of the rock is the result of high water pressures developed during metamorphism and that the vein expansion results from internal forces created during crystallization of the vein mineral from highly supersaturated solutions.
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 veins were presumably former aqueous dikes which exhibit a dramatically different response to the differing matrix types. The former sediments of the black shale in the top half of the image were apparently much more compliant than the former sandy sediments of the tan/gray sandstone in the bottom half of the image. The aqueous dike was evidently able to buckle ptygmatically into soft shale sediments, while only increasing its dike width within the presumably much-stiffer sandy sediments, assuming both matrices were unconsolidated sediments at the time of dike formation.
The the growth of felsic mineral grains by crystallization in aqueous dikes increases the grain-to-grain pressure, which causes ptygmatic buckling into lower pressure surrounding mafic sediments until the back pressure of the lithifying mafic sediments is as likely to cause dissolution as crystallization where mineral grains impinge. After this solution-dissolution quiescent point is reached, crystallization can only occur into unstressed voids between mineral grains, progressively decreasing the porosity of the aqueous dike.
The 3-dimensional expansion of aqueous dikes explains the tendency to maintain constant dike width in ptygmatic folds; however, superimposed slump folding may locally thin or break dikes, and variable plasticity of the confining mafic matrix may variably constrain dike growth, causing creating aneurysms in aqueous dikes, which lithify into boudinage.
If a substantial aqueous dike is blocked the backup of fluids may precipitate a pluton of S-type granite. (See section, THE ORIGIN OF S-TYPE GRANITE PLUTONS IN KUIPER BELT OBJECTS (KBOs))
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 crosscutting dikes 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 partly in the absence of suitable nuclei for precipitating new mineral grains.
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 ices will compress significantly more than silicates in a terrestrial impact of an icy KBO and absorb the lion’s share of the impact energy. The compressibility of KBO ices and terrestrial ices/ocean water is suggested to clamp the impact shock wave pressure below the melting point of silicates, including KBO core rock silicates, as well as terrestrial target rock silicates.
And the relative compressibility of ices compared to silicates will lower the specific impact power of icy-body impacts (without affecting the total impact energy) by blunting the shock wave pressure and extending its duration through an extended rebound of the compressed ices. This extended shock wave duration may allow Earth’s crust to deform into a basin, spreading the energy over a greater volume of silicates, as well as venting the majority of the energy to the atmosphere in the form of superheated vaporized ices. Vaporized ices will also tend to vaporize airborne silicates, eliminating tektites found around smaller impacts. The sustained decompression of impact-compressed ices may also help prevent the excavation of ejecta from impact craters,
If rocky-iron asteroid impacts resemble the sharp blow of a ball peen hammer, forming bowl-shaped craters with melt rock, breccia and overturned target rock, icy-body impacts may more closely resemble the compressive thud of a dead blow hammer, where the prolonged rebound duration of compressed ices promotes distortion of Earth’s crust into a perfectly-circular basin, and with the sustained rebound largely preventing the excavation of target rock. The almost perfectly-round
Nastapoka arc basin of Lower Hudson Bay comes to mind, and in the case of a circa 12,900 ya Nastapoka arc impact, the 2 kilometer thick Laurentide ice sheet would have provided a substantial additional endothermic shock-absorbing cushion.
Additionally, the impact of very-large (circa 100 km) objects would appear to impact in slow motion compared to much-smaller objects moving at similar speeds, providing more time to couple the energy to Earth’s crust, and perhaps reflecting less impact energy back towards the KBO core rock.
Shatter cones apexes point toward ground zero, but if the extended duration of a very-large impact greatly also blunts the directionality of the shock wave pressure, shatter cones and planar deformation features (PDFs) in quartz may fail to form; however, distributed pressure of extended duration would not seem to prevent the formation of high-pressure polymorphs like coesite, stishovite and seifertite. Elevated temperatures accompanying super-high pressures, however, may tend to cause retrograde metamorphism, perhaps resetting high-density polymorphs to lower-density polymorphs, particularly if the cooling occurs over many years in very-large impacts.
So while rocky-iron impacts form impact craters with overturned rock layers, melt rock, breccia, shatter cones, shocked quartz and high-pressure polymorphs, icy-body impacts are suggested to form monster multi-ring impact basins with few other impact indicators, and ocean plates have a lifespan of no more than 250 million years, so impacts at sea are quickly erased. If the doming in gneiss domes, however, represent elevated ring chunks of multi-ring impact craters, then gneiss domes may be telegraphing their impact origin.
The silicate cores of very large impacts may rival or exceed the thickness of Earth’s crust, and may greatly exceed the thickness of the much-thinner oceanic crust, causing a very-large impacting KBO core to spread out to many times its original footprint, and perhaps forming a particularly asymmetrical final shape.
Eskola, Pentti Eelis, (1948), The problem of mantled gneiss, Feb. 1948 Quarterly Journal of the Geological Society, 104, 461-457
Loose, B.; McGillis, W. R.; Schlosser, P.; Perovich, D.; Takahashi, T., (2009), Effects of freezing, growth, and ice cover on gas transport processes in laboratory seawater experiments, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L05603
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