¶ Gneissic continental basement rock is suggested here to be extraterrestrial in origin, from aqueously-differentiated Kuiper belt objects (KBOs), with terrestrial emplacement during the late heavy bombardment (LHB), circa 4.1-3.8 Ga.
¶ An extraterrestrial origin for gneiss requires an alternative solar system origin, with hot classical KBOs ‘condensing’ by streaming instability against Neptune’s outer 2:3 resonance from a siderophile-depleted debris disk reservoir prior to 4,567 Ma that lay on the 3-oxygen-isotope terrestrial fractionation line. The siderophile-depleted composition of the debris disk and its oxygen isotopic signature is a requirement of an alternative planet formation mechanism that predicts and explains the three sets of twin-binary planets of the solar system, namely, Jupiter-Saturn, Uranus-Neptune and Venus-Earth.
¶ ‘Condensation’ of KBOs by streaming instability converted the potential energy of the dust and ice into heat during freefall collapse, with ‘large’ KBOs exceeding the melting point of water ice, initiating ‘aqueous differentiation’.
¶ Aqueous differentiation was accompanied by authigenic crystallization of silicates within a saltwater core, precipitating mineral grains with a gneissic composition that fell out of aqueous suspension at a mineral grain size determined by the microgravitational acceleration and by the local circulation rate. This formed authigenic sedimentary cores with a gneissic composition.
¶ Much of the authigenic sedimentation was modulated into banded migmatite sediments, presumably due to sawtooth pH variations resulting from subsidence shocks that caused dissolved carbon dioxide to catastrophically bubble out of solution, raising the pH. Aluminous mineral-species solubility is particularly pH sensitive, such that when subsidence shocks catastrophically raised the pH, aluminous minerals rapidly precipitated, predominantly as felsic feldspars. Thus felsic-leucosome mineral grains are suggested to have precipitated rapidly following subsidence events, while more-mafic melanosome mineral grains precipitated in the relative quiescence between repeated subsidence shocks.
¶ Slump folding occurred during lithification, accounting for a majority of supposed metamorphic folding in continental basement rock.
¶ Geochronology of KBO rock dates to its apparent age at its closure temperature. As gneissic KBO core rock exhumes from deep within its LHB-era impact basins of the lithosphere, the rock undergoes retrograde metamorphism during cooling and depressurization. When KBO rock cools to the ‘closure temperature’, its mineral grains begin to retain the daughter products of radioactive decay, initiating the geochronological clock that had been reset by the high temperatures inherent in terrestrial metamorphism at its impact-implanted depth.
¶ In conventional geology, migmatite differentiation occurs at sufficient depth and temperature to initiate partial melting of a protolith, accompanied by physical segregation of the partial melt into enriched felsic leucosomes and depleted mafic melanosomes, with residual mesosomes, where lower-melting-point minerals are extruded 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 of migmatite can not explain the local enrichments and depletions of felsic and mafic layering, and so externally-derived melt is needed for mass balance. “Commingling and mixing of mafic and felsic magmas” is also suggested as an explanation for alternating felsic/mafic layers. (Sandeman et al., 2000)
¶ Aqueous differentiation presumably occurs at formation by streaming instability, where the potential energy released during gravitational collapse melts water ice and liberates nebular dust, that dissolves and crystallizes into authigenic mineral grains that fall out of aqueous suspension at a mineral grain size dependent on the microgravitational acceleration and on the local circulation rate.
¶ Felsic-mafic modulation is suggested to be caused by pH modulation controlled by the concentration of carbonic acid in solution. Carbonic acid solubility is shock sensitive, such that subsidence events during KBO cooling are suggested to control the alternating felsic-mafic deposition. Since precipitation is governed by solute loads and pH excursions of the overlying saltwater ocean, the mass balance problem of conventional geology is moot.
¶ Metamorphic overprinting is nearly an exact science in conventional geology, often revealing timing, degree and direction of multiple tectonic episodes. Compared to overprinting, however, the origin of primary folding is often much more problematic. Primary isoclinal folding is often dismissed as sheath folds, fortuitously sectioned through their nose, since randomly-oriented isoclinal folds on various scales can not be explained by conventional geology.
¶ Alternatively, primary folding in migmatites is suggested to be simple slump folding in KBO sediments during the destruction of voids phase of lithification, long before Earth impact.
¶ Ptygmatic folds in migmatites are the most challenging types of folds for conventional geology, particularly in the most dramatic specimens where ptygma fold back on themselves like ribbon candy. Two unconventional explanations for terrestrial folding are presented that attempt to circumvent the most glaring shortcomings of partial-melt theory alone.
Stel (1999) theory of ptygma:
¶ One suggested solution to ptygma enigma is a progressive replacement front which migrates away from the vein boundary, in which “volume loss takes place in the vein mantles, while the limbs of the folds increase in volume” (Stel, 1999). Harry Stel agrees with Brown (Brown et al.,1995) that “ptygmatic structures are not ‘diagnostic’ for the presence of partial melt phases in migmatites”, and “[t]he most direct evidence for the relation of fluid activity and mica breakdown is the presence of offshoot veinlets”, with some veinlets exhibiting relict foliation of the host rock, indicating that veinlets are not melt-injection structures, where ‘fluid’ is understood to be an aqueous brine.
¶ The typically narrow melanosome ‘shadows’ surrounding much-fatter ptygmatic leucosome veins would require additional distant felsic input for mass balance. Additionally, no motive force is offered as an explanation to drive the replacement front, and no explanation is provided for why here and not there.
Shelley (1968) theory of ptygma:
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.
¶ Shelley states that the force of crystallization within veins creates expansion of veins into the accommodating surrounding host. Shelley does not waffle between melts and (aqueous) ‘solutions’ as Stel appears to do with his “not ‘diagnostic'” remark, and Shelley is does not confine himself to (superficial) replacement fronts, but states that the driving force is caused crystallization on bulk mineral grains in the vein.
¶ Shelley’s mechanism is essentially the very mechanism suggested to operate in an authogenic sedimentary KBO setting, but Shelley is constrained to operate within dense lithified rock undergoing metamorphism at depth and temperature on Earth. By comparison, crystallization during lithification of KBO sediments operates on unconsolidated/partly-consolidated sediments, where the ptygma are able to fold into the voids vacated by escaping hydrothermal fluids during lithification.
¶ “Most gneiss domes are elongate parallel to the strike of the orogen” (Whitney et al., 2004)
¶ “Domes with long dimension ≤90 km have a ratio of long to short axes of ~2:1–3:1.” “Despite
the wide range of dimensions, most gneiss domes have map-view axial ratios between 1:1 and 3.5:1, independent of the size of the dome (Fig. 5B), indicating that the elliptical shape is independent
of dome size.” (Whitney et al., 2004)
¶ In linear belts of gneiss domes, there may be a characteristic spacing between domes (Fletcher, 1972; Yin, 1991); e.g., 40–50 km in the northern Cordillera (e.g., the Frenchman Cap, Thor-Odin, Pinnacles, Passmore-Valhalla domes of the Shuswap metamorphic complex; Whitney et al. ), 25 ± 5 km in the northern Appalachians (Fletcher, 1972), and 8–22 km along ridges in the Karelides gneiss domes of eastern Finland (Brun, 1980)” (Whitney et al., 2004)
¶ Gneiss dome formation is far from settled science in conventional geology, with numerous proposed mechanisms representing differing theories and differing contexts.
¶ Alternatively, gneiss domes are suggested here to be anticline wrinkles on the former KBO sedimentary core, as the core densifies by expelling aqueous solution during lithification, like the skin of a grape wrinkling as it shrivels to form a raisin.
Alternative solar system dynamics:
¶ An extraterrestrial origin for continental basement rock places stringent constraints on the composition of hot-classical KBOs, namely a siderophile-depleted composition that lies on the three-oxygen-isotope terrestrial fractionation line (TFL), with sufficient buoyancy to float above the terrestrial ocean plates and stand proud above sea level. The inner solar system asteroids and chondrites possess none of these properties, requiring that the high-angular-momentum hot classical KBOs formed from a different reservoir than the low-angular-momentum reservoir that formed the inner solar system asteroids and chondrites.
‘Symmetrical FFF’ and ‘trifurcation’:
¶ A former binary-Companion and three sets of twin-binary planets in our solar system-Jupiter-Saturn, Uranus-Neptune, and Venus-Earth-are suggested here to have formed in 4 generations, like Russian nesting dolls from a former ‘Brown Dwarf’, the original stellar core of our solar system.
¶ Brown Dwarf formed at the center of a massive accretion disk, where the accretion disk was much-more massive than the diminutive brown-dwarf-mass protostellar core. The accretion disk underwent a bilateral disk instability (symmetrical flip-flop fragmentation (FFF)), condensing a twin-binary pair of disk-instability objects, which were much more massive than the Brown Dwarf core. During a brief period of orbital interplay, the protostellar disk instability objects progressively ‘evaporated’ Brown Dwarf into a circumbinary orbit, with the disk instability objects collapsing to form ‘binary-Sun’. And the orbital dynamics that evaporated Brown Dwarf into a hierarchical circumbinary orbit around former binary-Sun also caused Brown Dwarf to ‘spin up’ and undergo centrifugal fragmentation, by way of ‘trifurcation’.
¶ In orbital close encounters between objects with differing masses, the principle of ‘equipartition’ of kinetic energy dictates that the less massive object typically leaves the close encounter with a kinetic-energy kick at the expense of the more-massive object, tending to evaporate Brown Dwarf into a circumbinary orbit at the expense of the much-more-massive stellar components, which sank inward into a close-binary pair. But not only did Brown Dwarf gain orbital energy and angular momentum kicks, but it also received rotational spin up to the point of centrifugal fragmentation. Brown Dwarf was evaporated into a circumbinary orbit around binary-Sun at a distance of about 15 AU, but not before centrifugal fragmentation (trifurcation).
¶ Spin up causes a gravitationally bound object to deform into an oblate sphere. Continued spin up deforms the oblate sphere into an ellipsoid and finally into a bilaterally-symmetrical bar-mode instability that fails (fragments) when the bar gravitationally fragments by way of trifurcation, forming a twin-binary pair in orbit around the much-less-massive residual core (gravitationally fragmenting into 3 components, hence ‘trifurcation’).
¶ Thus, Brown Dwarf orbited by the much-more-massive twin-binary disk instability objects induced trifurcation, fragmenting Brown Dwarf into a twin-binary pair of super-Jupiter-mass objects orbiting a much-less-massive residual core. And first-generation trifurcation promotes second-generation trifurcation, and etc,, like Russian nesting dolls, forming;
– 1st gen, binary-Companion + SUPER-Jupiter residual core,
– 2nd gen. Jupiter-Saturn + SUPER-Neptune residual core,
– 3rd gen. Uranus-Neptune +SUPER-Earth residual core, and
– 4th gen. Venus-Earth + Mercury(?) residual core.
¶ Binary-binary resonances caused eccentricity pumping of the twin-binary trifurcation pairs, causing the trifurcation pairs to escape from binary-Companion and be captured by binary-Sun. Jupiter-Saturn, with Venus-Earth in tow, were captured via binary-Companion’s inner L1 Lagrangian point, while Uranus-Saturn were captured via binary-Companion’s outer L2 Lagrangian point. Then Venus-Earth-Mercury escaped from Jupiter-Saturn via Jupiter-Saturn’s inner L1 Lagrangian point, resulting in the following configuration, listed in increasing radial distance from the solar system barycenter;
– Trifurcation debris disk.
Additional eccentricity pumping by binary-Sun caused all trifurcation pairs to separate except binary-Companion.
¶ Because Brown Dwarf had internally differentiated into a siderophile-enriched iron core, the resulting trifurcation debris was necessarily siderophile depleted. All trifurcation products presumably lie on the 3-oxygen-isotope Brown Dwarf fractionation line, which we know as the ‘terrestrial fractionation line’, including the hot classical KBOs that condensed from the siderophile-depleted ‘trifurcation debris disk’.
¶ Shortly after the trifurcation era, the stellar components of former binary-Sun spiraled in to merge at 4,567 Ma in a luminous red nova that scrubbed the solar system of the earlier trifurcation debris disk, leaving behind its own low-angular-momentum ‘solar-merger debris disk’
that condensed asteroids with live stellar-merger radionuclides, and later, chondrites, largely after the short-lived radionuclides had decayed away.
Late heavy bombardment:
¶ Perturbation of binary-Companion by the newly-merged Sun caused the super-Jupiter-mass binary components to spiral in, transferring their close-binary potential energy to progressively-increasing the heliocentric eccentricity of binary-Companion over time, which also progressively increased binary-Companion’s heliocentric period. The progressively-increasing heliocentric period of binary-Companion caused its 1:4 mean-motion resonance to migrate through the Kuiper belt, perturbing KBOs into the inner solar system, causing the late heavy bombardment that embedded gneissic KBO cores into Earth’s lithosphere, ~4.2-3.8 Ga.
¶ Binary-Companion overran Uranus’ orbit, resulting in Uranus’ severe axial tilt. As spiral-in progressed, the super-Jupiter components progressively accreted their own moons, fogging the solar system, which caused the Sturtian glaciation of Snowball Earth. Ultimately the super-Jupiter components merged at 650 Ma in an asymmetrical merger explosion that gave newly-merged Companion escape velocity from the Sun, with the merger debris causing the ‘Companion-merger debris disk’, which condensed the young, cold classical KBOs against Neptune’s outer 2:3 resonance by streaming instability and caused the Marinoan glaciation of the Cryogenian Period.
See section, STARS, PLANETS, MOONS, MINOR PLANETS AND COMETS
Aqueous differentiation of KBOs:
¶ Aqueous differentiation is defined here as the melting of water ice in the core of a minor planet or smaller planetesimal. ‘Spontaneous aqueous differentiation’ is presumed to have occurred in large KBOs at the time of formation by gravitational collapse, presumably by streaming instability, converting the kinetic and potential energy of the component dust and ice to heat.
¶ Another form of aqueous differentiation may have occurred in the spiral-in merger of binary KBOs, forming contact binaries. This would be particularly significant in binary KBOs too small to have undergone spontaneous aqueous differentiation at the time of formation. Perturbation by the Sun-Companion tidal inflection point presumably caused many former binary KBOs to spiral in to merge, whether or not they were subsequently perturbed out of the Kuiper belt.
¶ Aqueous differentiation was followed by an exponential rate of radiative heat loss, which began freezing the core saltwater ocean from the outside in. The temperature at the icy ceiling was clamped to the freezing point of saltwater, with a temperature gradient with depth driving thermal circulation.
¶ Nebular dust released into aqueous suspension at the time of differentiation would have both dissolved into solution and also nucleated new crystallization. This suggests that trifurcation debris disk condensates should be represented in crystalline gneiss; however, these condensates may differ significantly from the condensates of the solar-merger debris disk that condensed asteroids and chondrites in the inner solar system. But there should be a minor component of presolar mineral grains in crystalline gneiss, similar to those in inner solar system chondrites.
¶ Solute solubility is variously dependent on temperature, but the solubility of most mineral species is proportional to temperature, tending to cause crystallization near the icy ceiling cold junction during thermally-driven circulation. Additionally, freezing saltwater tends to exclude solutes from water-ice crystals, increasing the dissolved solute load to and above the saturation point, so as KBOs gradually cooled and froze solid, ‘freeze out’ caused mineral grains in aqueous suspension to grow by crystallization until falling out of suspension by sedimentation, adding to a growing authigenic sedimentary core. And exponential cooling of differentiated KBOs reduced thermally-driven circulation rates, tending to progressively decrease the mineral grain size in aqueous suspension over time; however, violent subsidence shocks would have repeatedly interrupted quiescent thermal circulation, creating bright lines with larger mineral grain sizes.
¶ A majority of the sand on Earth is suggested to be authigenic, KBO mineral grains that fell out of aqueous suspension at a characteristic sand-grain scale in the microgravity of KBO oceans. Authigenic mineral grains also precipitate on Earth, but on our high-gravity planet, they fall out of aqueous suspension on the scale of clay particles, sometimes forming authigenic mudstone on Earth.
Felsic-mafic layering in migmatite:
¶ Conventionally, migmatites form by the secondary mechanism of partial melting (anatexis) of a protolith under elevated temperature and pressure at great depth beneath the Earth’s surface, resulting physical segregation of a partial-melt into felsic-enriched leucosomes and felsic-depleted melanosomes.
¶ Alternatively, the felsic-mafic layering in authigenic sedimentary migmatites is formed by modulated felsic-mafic deposition, with a variable degree of secondary slump folding superimposed during lithification. This felsic-mafic layering is suggested to be caused by sawtooth modulation in pH of the overlying saltwater ocean.
¶ The solubility of aluminous species is particularly pH sensitive, so the concentration of carbonic acid would effectively control the reservoir of dissolved aluminous species in solution. Aluminous species solubility is U-shaped with respect to pH, with an inflection point at about 6-1/2 pH (Driscoll and Schecher, 1990). An abrupt rise in pH from 3.5 to 6.5 would decrease the aluminous species solubility by a factor of more than 100,000, effectively precipitating the entire reservoir of dissolved aluminous species, presumably predominantly in the form of feldspars, the simplest aluminous silicates.
¶ Carbon dioxide solubility can be catastrophically reduced by physical shock, as can be demonstrated by shaking a carbonated beverage. And when dissolved CO2 bubbles out of solution, carbonic acid breaks down into gaseous carbon dioxide to restore the carbonic acid-CO2 equilibrium, raising the pH. Thus, subsidence shocks (KBO-quakes) of aqueously-differentiated KBOs could cause rapid super saturation of aluminous species, causing a frenzy of aluminous mineral grain nucleation and crystallization on aqueously-suspended mineral grains, presumably resulting in sedimentation of feldspar mineral grains.
¶ So KBO aftershocks are suggested to nucleate feldspar mineral grains that grow by crystallization until falling out of aqueous suspension at a mineral grain size characteristic for the increased agitation rate following subsidence shocks. And the increased circulation following an subsidence shock may also induce crystallization of other minerals whose solubility is proportional to temperature, such as quartz/silica, caused by the increased circulation of saltwater past the cold icy ceiling.
¶ (Super) saturation of aluminous species may favor crystallization on existing mineral grains in aqueous suspension for simple minerals, like the feldspar group, whereas the same conditions may favor nucleation of new mineral grains for more complex minerals, like biotite. Crystallization and nucleation requires the proximity of the constituent ions and cations (species); however, the more complex the silicates, the smaller the chance that the necessary species converge on suspended mineral grains, forcing nucleation where the mineral species happen to converge. So simple feldspars may tend to crystallize on existing mineral grains, forming large feldspar mineral grains, whereas more complex minerals, like biotite, may tend to nucleate new mineral grains, forming more numerous but much-smaller mineral grains. Thus, the simplest minerals, such as felsic quartz and feldspar, may rain down on the sedimentary core immediately following subsidence shocks, creating felsic leucosome layers, with mineral grain size decreasing over time until the smaller more numerous mafic mineral grains come to predominate sedimentation during intervening the quiescent intervals between subsidence shocks, creating mafic melanosome layers. Thus, authigenic sedimentation should be upward fining following subsidence events, with large felsic mineral grains in light-colored leucosomes gradually grading to fine mafic mineral grains in dark-colored melanosomes.
¶ Therefore, in the crystallization urgency of super saturated aluminous species, feldspar mineral grains may quickly grow to sufficient size to fall out of aqueous suspension in the agitated circulation rate following an subsidence shock, whereas smaller, more complex aluminous species may remain in aqueous suspension until the agitation rate approaches quiescence.
¶ Additionally, KBO subsidence shocks may dislodge oversized euhedral mineral grains trapped in the slush of ice crystals floating at the ice ceiling.
¶ Progressive heat loss by differentiated KBOs presumably causes ice crystal nucleation, which float to the ice ceiling to form a slush of ice crystals. And since most mineral species solubility is reduced at colder temperatures, mineral grains may grow by crystallization to outsize proportions when supported by icy slush at the ice ceiling until possibly becoming dislodged by the vibration of subsidence events.
¶ The vibration and agitation of subsidence shocks may free enlarged euhedral mineral grains from their slushy prison, which fall through the water column to nominally become incorporated into the margins of felsic leucosomes. Thus, outsized euhedral mineral grains in metamorphic rock that are not pegmatites to possibly have a dropstone origin.
Gneiss-dome mantling rock, typically consisting of quartzite, marble/dolomite, and schist:
¶ Gneiss domes are often mantled with metasedimentary rock, typically comprised of quartzite, marble/dolomite, and schist. The compositional differences between the gneiss core and its surmounting mantle represents differing depositional conditions of the various regimes.
¶ Gneiss dome mantling rock is suggested here to be the authigenic frosting on the gneissic cake, with gneiss dome mantling rock representing the final authigenic deposition of the KBO sedimentary core prior to the ocean freezing solid, ending authigenic deposition.
¶ In his seminal 1948 paper, The problem of mantled gneiss domes, Eskola notes the composition of Finland’s gneiss domes, “the basement stratum is a layer of quartzite, above which follow dolomite and micaschist; and in still others, dolomite forms the basement”. “In some, the lowest horizon of the mantle consists of basal conglomerate with boulders of the same gneiss that forms the dome.”
¶ Baltimore gneiss domes also appear to have the same gneiss-quartzite-marble-schist sequence noticed by Eskola in Finland’s gneiss domes, as illustrated in the following sketches.
¶ Authigenic gneiss is suggested to be primary precipitation from the overlying ocean, whereas authigenic schist is suggested to be secondary precipitation from hydrothermal fluids emanating from hydrothermal vents in the sedimentary core. Lithification of the core entails the expulsion of hot aqueous fluids from the lithifying sediments with leached minerals through hydrothermal vents into the overlying ocean, and when the hot hydrothermal fluids enter the cold overlying ocean, the leached mineral species become (super) saturated and precipitate schistic sediments.
¶ Schist is often named for its primary mineral constituent, with its wide-ranging variability presumably attributable to variable hydrothermal chemistry related to its leached mineral content. The frequent proximity of chemically different schists in the geologic record points to highly localized deposition, suggesting chemical modulation of hydrothermal fluids, perhaps after the overlying ocean is mostly frozen solid.
¶ Euhedral-crystal dropstones, such as garnets and staurolite, are particularly prevalent in schist, which may be liberated from the icy ceiling when hydrothermal vents increase their flow rate, melting portions of the overlying ceiling which liberate oversized euhedral-crystal dropstones.
¶ The origin of the schistosity of schist is unclear, with the flat sheet-like grains (mica, talc, and etc.) likely forming by secondary metamorphism from clay-like precursors.
¶ Schist can also contain prominent ptygmatic leucosomes like migmatite gneiss, and presumably from the same cause, forming as aqueous drains where the constituent mineral grains grow by crystallization, sometimes buckling outward into the surrounding matrix as ptygmatic folds.
¶ Quartzite is typically the first mantling layer overlying basement gneiss in gneiss domes. Quartz being the simplest silicate may be the most likely silicate to crystallize on suspended mineral grains, while more complex silicates tend to nucleate more-numerous but smaller mineral grains. Thus quartz sand may be the first mineral to fall out of aqueous suspension in new hydrothermal vents or reactivated hydrothermal vents, tending to form a layer of quartz sand over gneissic sediments that may go on to lithify and metamorphose into quartzite.
¶ Notably, calcium carbonate solubility has a negative temperature dependence, such that hot hydrothermal fluids that locally warm the overlying ocean saturated in carbonates or locally melt the ice ceiling will tend to calcium and magnesium carbonates that may lithify into dolostone or limestone and may metamorphose into marble.
Domal structure of gneiss domes:
¶ The domal structure of gneiss domes as the anticline wrinkles of a former KBO sedimentary core is suggested to be the expected outcome of densification of a sedimentary core during lithification.
¶ Lithification involves the destruction of voids, expelling the aqueous fluid that filled the interstitial voids through hydrothermal vents into the overlying saltwater ocean. This shrinks the diameter, circumference and volume of the sedimentary core, causing the sedimentary surface to map onto a smaller area, forcing it to crumple into synclines and gneiss-dome anticlines, like the wrinkling of a grape dehydrating to form a raisin.
¶ Presumably the scale of gneiss domes is proportional to the scale of the originating KBO and its gneissic core, with larger gneiss dome systems corresponding to larger former KBOs. Gneiss domes exceeding 100 km in length presumably belonged to former KBOs exceeding 1000 km Dia.
¶ “Most gneiss domes are elongate parallel to the strike of the orogen” (Whitney et al., 2004) While wrinkling of all types is invariably elongate, gneiss-dome alignment with the strike of exhumed orogens is surprising, with orogeny driven by tectonic collision; however, the underlying basement geometry may dictate the strike of the local orogen. I.e., orogen exhumation apparently typically follows the long axis of underlying gneiss domes.
¶ Anticline domes on a lithifying sedimentary core may cause the dome to grate against the ice ceiling that may be the origin of gneissic conglomerate that
Eskola states sometimes comprises the lowest horizon of a gneiss-dome mantling regime. This suggests that gneiss-dome conglomerate forms prior to the deposition of overlying mantling rock.
Slump folding in authigenic metamorphic rock:
¶ Conventional geology suggests that metamorphic folding occurs at elevated temperature and pressure in lithified rock, deep below Earth’s surface, with the fold type illuminating the cause of the folds. 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 this form of tectonic folding is many orders of magnitude larger than the centimeter-scale folding typical in migmatites, and solid rock at depth-partial melting or no partial melting-has no voids to fold into. Conventionally, migmatite folding is generally dismissed as being self evident, and when addressed in particular, sharp (isoclinal) folding is identified as 2-dimensional sheath folding, fortuitously sectioned through the nose of the fold, since sheath folding can be credibly explained by shear forces, although the origin of shear forces within blocks of rock 10s of km on a side is best left to the imagination.
¶ Alternatively, migmatite folding can be simple slump folding, if the protolith of metamorphic gneiss is sedimentary rock. On a macro scale, slump folding generally entails briefly fluidizing unconsolidated sediments driven by density inversions, where denser sediments exchange places with less-dense sediments, and where sediment density is largely a factor of buoyant water concentration. On a micro scale, densification during lithification is driven by the destruction of voids between authigenic mineral grains, driven by metasomatism, pressure dissolution at pressure points between mineral grains, and crystallization, and etc. And micro-scale heterogeneity in lithification creates the macro-scale density inversions that drives slump folding.
¶ Additionally, the densification of a spherical sedimentary KBO core has geometry driving slump folding. During lithification of a spherical sedimentary core, not only does the thickness of each sedimentary layer decrease during lithification, but the circumference of every layer also decreases as the spherical core densifies, forcing ‘circumferential slump folding’. On Earth, the vast circumference of the planet means that the circumference change of lithifying sediments is imperceptibly small, whereas in a sedimentary KBO core undergoing lithification, not only does the radial thickness shorten during lithification, as it does on Earth, but the lateral (circumferential) dimensions shorten as well. Bulk KBO sediments are forced to undergo circumferential slump folding for the same reason that spherical grapes are forced to wrinkle when dehydrating into raisins, whereas paint drying on a flat surface is not forced to wrinkle. Something similar to circumferential slump folding can occur on Earth under unusual conditions, such as the lithification of sediments in a V-shaped trench or crevice, where pithy sedimentary layers are forced to fold as they densify toward the pointy end of a trench or crevice during lithification.
¶ Migmatite may be particularly susceptible to slump folding due to the dramatic variation in mineral grain size and composition between juxtaposed felsic leucosomes with large mineral grains, and mafic melanosomes with small mineral grains, resulting in differential rates of lithification, resulting in frequent density inversions.
¶ The most exaggerated examples of a physical phenomenon will cause a genuine theory to shine, while forcing flawed theories to differentiate an unexplainable phenomenon into potentially explainable sub phenomena. Thus the genuine theory will tend toward simplicity and unification, whereas flawed theories will tend toward complexity and differentiation.
¶ The most extreme examples of ptygmatic folds, that repeatedly double back on themselves like ribbon candy, are clearly most dramatic of all metamorphic folds, so it’s not encouraging for academic petrology that these folds are typically played down in significance.
¶ The conventional anatectic explanation for ptygmatic folding appears to engender a contradiction. Felsic leucosomes are presumed to form by felsic-melt segregation, where felsic minerals tend to melt at lower temperatures than mafic minerals following Bowen’s reaction series; however, ptygmatically folded veins rely on the felsic vein having greater competence than the host rock, which presumes that more-mafic surrounding matrix (mesosome) is dramatically more plastic than the ptygmatically-folded leucosome vein which supposedly formed by partial melting. The circa 6:1 matrix shortening required to fold the leucosome back onto itself, resembling ribbon candy, invariably fails to balloon out adjacent felsic-mafic layering, requiring matrix shortening to fortuitously extrude the supposedly less competent host rock perpendicular to (into and out of) the section plane.
¶ While the majority of folding in KBO migmatite is suggested to be slump folding, ptygmatic folding requires a different explanation.
¶ In lithifying KBO cores, the destructed voids between sedimentary particles were once filled with brine that buoyantly escaped into the overlying ocean through hydrothermal vents. Brine naturally followed path of least resistance though the variably-porous lithifying sediments, preferentially flowing through the coarse mineral grains of felsic leucosomes, which acted as French drains. When acting as aqueous drains, these felsic leucosomes are designated ‘veins’. Felsic leucosome layers were laid down the bedding plane, but to vent aqueous brine to the surface required additional cross bedding veins as well.
¶ Hot brine tends to leach minerals from leucosome veins, but as the brine cools on its buoyant ascent, leaching transitions to crystallization, enlarging the mineral grains in the veins. And the growth of felsic mineral grains within veins creates outward pressure, both lateral and longitudinal. “The grain size of quartz and feldspar in the veins is between 10 and 25 times larger than in the host rock (0.2 mm in the latter” (Stel, 1999).
¶ Growth of mineral grains by crystallization caused 3-dimensional expansion of the veins, fattening veins in the two lateral dimensions and buckling veins in the longitudinal dimension, creating ptygmatic folds. Again, this is the mechanism suggested by Shelley, “[t]here 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). Shelley, however, envisioned ptygmatic folding under the stringent conditions of lithified rock undergoing metamorphism, requiring high water pressure to crack the rock, whereas the buckling of unconsolidated sediments in an extraterrestrial setting is much more intuitive.
¶ The following image shows a pair of white (quartz or calcite?) veins cutting through two very different matrix types, apparently tan sandstone at the bottom and black shale above. The veins were presumably former aqueous veins, which developed very differently in the contrasting mediums. The black shale sediments were apparently much more compliant than the former tan sandy sediments, such that the vein was evidently able to buckle ptygmatically into the soft shale sediments, while the stiffer sandy sediments effectively prevented longitudinal buckling, forcing the volume increase of the vein growth to manifest itself exclusively in the lateral direction by way of fattening the vein. In this case, the ptygmatic folding may be terrestrial, albeit by the mechanism suggested for extraterrestrial ptygmatic folding in migmatites.
¶ Three-dimensional expansion of veins due to internal crystallization explains the tendency to maintain constant vein width in ptygmatic folds; however, superimposed slump folding may locally thin or break veins, and variable plasticity of the confining mafic matrix may variably constrain longitudinal buckling into ptygmatic folds. When progressive lithification stiffens the surrounding matrix to the point of preventing longitudinal ptygmatic buckling, veins may still be able to fatten in the lateral direction. And as lateral fattening is resisted by still-greater lithification, the force of crystallization may balloon into aneurysms at points of relative weakness in the surrounding matrix, forming boudinage.
¶ Finally, resistance from the lithifying matrix prevents any further lateral or longitudinal growth of the veins when impinging mineral grains within the veins become more susceptible to pressure dissolution at points of contact than growth by crystallization, with subsequent crystallization confined to filling in the remaining voids.
Neptunism vs. Plutonism: Authigenic S-type vs. Plutonic I-type Granites:
¶ S-type granites are suggested here to be intrusive, authigenic felsic sediments that may be terrestrial or extraterrestrial, and I-type granites are exclusively-terrestrial, intrusive igneous granites. Both authigenic S-type and igneous I-type granites are presumed to be emplaced by intrusive hydraulic pressure.
¶ Within mixed S-type and I-type batholiths, S-types (with whitish microcline) tend to be older, more chemically reduced, formed at lower temperature, surrounded by metasomatic skarns and pegmatites, with muscovite rather than hornblende mafic minerals, and often containing inherited zircons and supracrustal enclaves. I-types (with pinkish orthoclase), by comparison, tend to be younger, higher temperature, surrounded by contact-metamorphic hornfels and aureoles, and sometimes associated economic mineralization, with hornblende common. (Chappell and White 2001)
¶ “S-type granites crystallizes from the viscous, relatively water-saturated magma at great depths. They can form autochthonous bodies and may be surrounded by gneisses and crystalline schists, very similar in composition. I-type granites are formed from the drier and more mobile magma melted deeper, but crystallize at higher levels. Their contacts are well defined, and high grade metamorphic rocks are usually not observed in the frame. ” (Anna Soboleva, 2016)
¶ Blockage of a hydrothermal vent in a lithifying KBO core may have created hydraulic pressure that delaminated the country rock, creating aqueous pockets that cooled in situ and precipitated authigenic sediments with a typically granitic composition. Freezing solid of the overlying ocean may have been a common cause of hydrothermal blockage, forcing buoyant fluids to intrude the surrounding country rock. And the low density of intruding hydrothermal fluids would not support partially-lithified ceiling sediments from ceiling collapse, resulting in the observed gneissic or supracrustal xenoliths and enclaves, common in S-type granite.
¶ In Black Hills National Forest, the Calamity Peak Granite of the Yavapai Mazatzal craton is texturally stratified into alternating textures of fine-grained granite, with < 2 mm grains, and coarse-grained pegmatite, with perthite crystals up to 1 meter long. Additionally, the granite layers are themselves laminated on a millimeter scale, with laminae, 2-20 mm thick. This laminated fine-grained granite is known as ‘line rock’, composed of alternating bands of light and dark minerals, with tourmaline constituting the bulk of the dark mineral.
¶ The textural granite-pegmatite lamination, with superimposed millimeter-scale laminae suggests a state of orbital perturbation while still in the Kuiper belt. The millimeter-scale laminae suggests the circa 300 year orbital period of the former KBO itself, while the wider textural granite-pegmatite layering suggests the much-longer period of the former Sun-Companion orbits around the solar system barycenter. In this orbital barycentric setting, perhaps granite formed near apoapsis (greatest Sun-Companion separation), when the tidal inflection point created active aphelia precession (orbital perturbation), actively squeezing water from the core. Then perhaps pegmatite layers may formed during the quiescent remainder of the Sun-Companion orbit, with low flow rates promoting metasomatism, forming massive pegmatites under nearly quiescent conditions.
¶ The above scenario suggests a LHB age for the granite, with a > 4,567 age for the surrounding gneissic/schistose country rock. Late granite formation from latent aqueous fluids also suggests that core lithification was not complete at the time of the LHB, and perhaps tidal torquing by the Sun-Companion tidal inflection point was even significant in lithification. I.e., perhaps tidal torquing by the Sun-Companion tidal inflection point was significant in pumping water from the sedimentary core.
¶ This conceptual approach offers several alternative primary mechanisms for structure in metamorphic rock that is academically attributed to secondary metamorphic mechanisms; however this alternative approach does not dismiss the attribution of secondary metamorphic grades based on index minerals, secondary metamorphic foliation. Some index minerals may have an alternative primary authigenic origin with a mechanical element, such as the suggested crystallization of large euhedral almandine crystals in slush at the ice ceiling that are mechanically liberated when hot hydrothermal fluids melt ceiling ice, but this type of mechanical origin creates a concentrating effect that differs from the in situ conversion of low-pressure minerals into higher-pressure minerals.
¶ Metamorphic petrology at a mineral grain scale is beyond the scope of this conceptual approach, although it’s suspected that so-called metamorphic index minerals may not have the same relationship to pressure if formed authigenically, rather than igneously or metamorphically as generally supposed.
¶ Metamorphism of continental basement rock may be partially extraterrestrial and partially terrestrial. Extraterrestrial metamorphism might be caused by tidal torquing during orbital perturbation of KBOs by the former Sun-Companion tidal inflection point. Additionally, the freezing solid of the overlying ocean would develop pressure on the core, since water expands when it freezes. Shock metamorphism may have occurred at impact, followed by annealing of shock effects at depth and temperature within LHB-era impact craters/basins. Then a degree of retrograde metamorphism may occur during exhumation to the surface. Foliation, such as mica schistosity, seems more likely in the presence of aqueous fluids (metasomatic), suggesting a extraterrestrial metamorphism, although this could also occur on Earth at depth.
¶ Pegmatites in continental basement rock are presumably metasomatic, and as such more likely to have been formed during extraterrestrial lithification than subsequently during terrestrial metamorphism. Largely-felsic pegmatites presumably formed as part of vein systems that once served as the conduits of buoyant aqueous fluids during the lithification of KBO cores, with more voluminous instances forming S-type granitoids by hydrothermal intrusions.
¶ The foliation of mica schistosity in schist reveals the importance of vertical pressure in forming oriented mica flecks in bulk schist. Additionally, large centimeter-scale mica books appear in pegmatites, but foliation typically disappears in pegmatites, with randomly-oriented mica books appearing to grow from large quartz crystals. If oriented mica schistosity is indicative of vertical pressure, then pegmatite book mica may also be indicative of pressure, but perhaps in the form of unoriented hydraulic pressure with little mineral grain impingement, where euhedral minerals are free to grow in random directions. These conditions would tend to be most prevalent in hydrothermal intrusions into authigenic sediments.
¶ Foliation can also be caused by elongation of mineral grains that may be partly due to mineral-grain dissolution in the vertical direction, between impinging mineral grains, and possibly crystallization in the horizontal direction into voids between mineral grains. Again pressure solution/dissolution requires aqueous fluids that would be more prevalent prior to Earth impact.
¶ The ‘bulk modulus’ (inverse of compressibility) of granite is more than 20 times that of water, such that water ice would absorb more than 20 times as much compressive work energy of an impact shock wave of an icy-body impact, compared to an equal volume of silicates. Thus a thick mantle of relatively-compressible water ice surrounding a gneissic KBO core would absorb the lion’s share of the kinetic energy of a KBO impact as compressive work energy. Thus the icy mantle of a KBO is suggested to have acted as a sacrificial envelope that clamped the impact shock wave pressure below the melting point of silicates.
¶ The shock absorbing potential of relatively-compressible ices, however, would not have been sufficiently protective to prevent the formation of high-pressure polymorphs in silicates, such as coesite, so their absence is presumably due to prolonged dwell time at metamorphosing temperatures and pressures on Earth within their impact craters, deep below the surface.
¶ Terrestrial metamorphism deep within LHB-era impact basins presumably erased high-pressure polymorphs and reset the radiometric age of authigenic mineral grains, with geochronology recording the ‘closure temperature’ during exhumation at which mineral grains, such as zircon, began to retain the daughter products of radioactive decay.
¶ The continental tectonic plates are suggested to be a mash-up of KBO cores that impacted during the LHB following numerous supercontinent mergers and breakups. Tectonic collisions appear to promote exhumation of gneiss domes oriented along the strike of tectonic orogens.
¶ Hot classical KBOs are suggested to have ‘condensed’ by streaming instability (gravitational collapse) against Neptune’s strongest outer resonances from a siderophile-depleted reservoir that lay on the 3-oxygen isotope terrestrial fractionation line.
¶ Large KBOs underwent spontaneous aqueous differentiation at formation, melting saltwater oceans in their cores. Aqueous differentiation was accompanied by authigenic precipitation, with felsic-mafic modulation mediated by sawtooth pH fluctuations, forming sedimentary cores with a gneissic composition.
¶ KBO core rock slump folded during lithification, as the densifying core expelled brine through a network of felsic veins that acted as French drains, channeling the buoyant brine out of the core. Lithification was accompanied by slump folding, which is most prominent in migmatites. Additionally, ptygmatic folding occurred in felsic veins that channeled brine from the core, due to the outward pressure of crystallization, forcing some felsic veins to buckle into ptygmatic folds.
¶ A former binary-Companion to the Sun is suggested to have caused orbital perturbation of hot classical KBOs, causing the LHB of the inner solar system, circa, 4.1–3.8 Ga.
¶ S-type granite is suggested to be the intrusive precipitation of authigenic sediments with a granitic composition, much of which may have intruded during the LHB, caused by tidal torquing by the Sun-Companion tidal inflection point.
¶ The vast majority of gneissic continental KBO rock was presumably delivered to Earth by way of very-large >> 100 km KBO impacts of the LHB era, with subsequent impactors being substantially smaller and unlikely to have undergone aqueously differentiation. An extraterrestrial origin for continental basement rock also depends on its surviving Earth impact without melting or vaporizing. Presumably the relatively-high compressibility of thick icy mantles surrounding the gneissic sedimentary cores absorbed the lion’s share of the impact energy, protecting the silicate cores from melting on Earth impact.
¶ Then, a variable degree of metamorphism of KBO core rock occurred on Earth, 10s of kilometers beneath the surface within their KBO impact craters. Geochronology of KBO core rock, however, dates to closure temperatures as it cools during ascent and exhumation at the surface in orogenies.
Bosbyshell, Howell, (2012), Presentation at Northeastern Section – 47th Annual Meeting
Chappell, B. W. and White, A. J. R., (2001), Two contrasting granite types: 25 years later, Australian Journal of Earth Sciences, Volume 48, Issue 4, pages 489–499, August 2001.
Duke, Edward F.; Papike, James J.; Laul, Jagdish C., (1992), GEOCHEMISTRY OF A BORON.RICH PERALUMINOUS GRANITE PLUTON: THE CALAMITV PEAK LAYERED GRANITE_PEGMATITE COMPLEX, BLACK HILLS, SOUTH DAKOTA, Canadian Mineralogist, Vol. 30, pp. 811-833 (1992)
Eskola, Pentti Eelis, (1948), The problem of mantled gneiss domes, 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
Soboleva, Anna, (2016), in response to the ResearchGate question, “I-type granite and S-type granite, how can we distinguish in these granite.”, ResearchGate
Stel, Harry Stel, (1999), Evolution of ptygmatic folds in migmatites from the type area (S. Finland), Journal of Structural Geology, Volume 21, Issue 2, February 1999, Pages 179-189
Whitney, Donna L.; Teyssier, Christian; Vanderhaeghe, Olivier, (2004), Gneiss domes and crustal flow, Special Paper of the Geological Society of America, Volume 380
Yin, An, (2004), Gneiss domes and gneiss dome systems, Geological Society of America Special Paper 380