Ptygmatic Folds in gneiss migmatite from Helsinki Finland –used with permission of Sameli Kujala,

Ptygmatic Folds in gneiss, Helsinki Finland
–used with permission of Sameli Kujala,


    Continental basement rock, with its typical gneissic composition, is suggested to have an extraterrestrial origin from Kuiper belt objects (KBOs) of the Kuiper belt.

    A former binary-Companion to the Sun is suggested to have perturbed KBOs into the inner solar system. Then the twin-binary super-Jupiter-mass components of binary-Companion presumably spiraled in to merge at about 650 Ma in an asymmetrical merger explosion which gave the newly-merged Companion escape velocity from the Sun, making all KBO core rock Neoproterozoic or older.

    KBOs are suggested to have formed by streaming instability against Neptune’s outer 2:3 resonance, with a majority forming in binary pairs, and the orbital perturbation of these binary comets by former binary-Companion is suggested to have caused the components to have spiraled in and merged to form contact-binary KBOs. The potential and kinetic energy converted to heat in newly-merged contact binaries melted water ice, initiating ‘aqueous differentiation’. And internal aqueous differentiation precipitated authigenic mineral grains which precipitated to form a sedimentary core with a gneissic composition.

    The felsic-mafic layering in migmatite gneiss was presumably caused by alternating felsic-mafic sedimentation. Aluminous mineral species solubility is particularly sensitive to pH, such that merger aftershocks (KBOquakes)–which caused CO2 to bubble out of solution and raise the pH–catastrophically precipitated felsic (aluminous) feldspar. Thus the felsic leucosomes were precipitated rapidly following catastrophic aftershocks, while the more-mafic mesosomes were precipitated in the relative quiescence between aftershocks. This alternative ideology elevates a formerly ad hoc secondary mechanism (of felsic-mafic segregation during partial melting) to a primary sedimentation mechanism.

    Then sedimentary cores underwent slump folding during lithification, followed by metamorphism. This again elevates a formerly ad hoc secondary mechanism (of enigmatic folding during partial melting) to the primary mechanism of straight-forward slump folding during lithification.

    Finally, the lithified cores of KBO impacts were presumably protected from melting in Earth impacts by their thick icy mantles. The relative compressibility of ice compared to silicates is suggested to have clamped the impact shock wave pressure below the melting point of silicates, protecting the KBO cores from melting on Earth impact.


  In conventional geology, migmatite metamorphism occurs at sufficient depth and pressure to cause partial melting of a protolith, accompanied by segregation of the partial melt into enriched felsic leucosomes, depleted mafic melanosomes, and residual mesosomes; however, the segregation mechanism is somewhere between enigmatic and problematic, 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 also suggested as an explanation for alternating felsic/mafic layers. (Sandeman et al., 2000)

    Alternatively, primary authigenic sedimentation with felsic-mafic modulation eliminates an ad hoc secondary segregation mechanism. with its inherent mass balance problem, albeit in an extraterrestrial Kuiper belt object (KBO) setting.
    Orbital perturbation by a former binary-Companion to the Sun is posited as the prime mover to initiate binary–spiral-in–merger ‘aqueous differentiation’ of former binary KBOs. Then the aftershocks of the binary spiral-in merger indirectly provide the felsic-mafic modulation, by way of controlling the carbonic acid concentration. The solubility of aluminous mineral species is particularly pH sensitive, such that aftershocks which cause the carbonic acid to bubble out of solution as gaseous CO2 causes rapid sedimentation of aluminum-bearing mineral grains, predominantly in the form of felsic feldspar. Then the more mafic mesosomes form during the quiescent phase between aftershocks, as the saltwater reservoir is recharged with aluminum from melting of virgin overburden, releasing nebular dust into aqueous suspension.

    Primary folding in migmatites is generally limited to classification by type and degree, compared to secondary tectonic overprinting, which has been elevated to something approaching an exact science. Conventionally ‘primary folds’ are often assumed to be sheath folds, fortuitously sectioned through their nose, since sheath folding can be readily explained by shear forces, where primary sheath folding et al. are facilitated by the secondary mechanism of partial melting.

    Alternatively, primary folding in migmatites is suggested to be slump folding, which is a primary mechanism occurring during lithification, requiring no secondary mechanism such as partial melting. Slump folds and sheath folds are more about origins than physical characteristics, so a close examination of a specimen would not contribute to resolving the controversy.

    Ptygmatic folds in migmatites present difficulties for all conventual folding mechanisms, particularly where felsic leucosome ptygma are dramatically folded back on themselves like ribbon candy. Two more unconventional explanations for a terrestrial setting are presented, whose unconventional ideology attempts to circumvent the most glaring shortcomings of more orthodox theories.

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.

Stel critique:
    The typically narrow melanosome ‘shadows’ surrounding much-fatter ptygmatic leucosome veins would require additional distant felsic input for mass balance, particularly where the ptygma doubles back itself and completely pinches out the mesosome and melanosome altogether. Additionally, while not a critique of the proposed mechanism as such, no motive force is offered 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 1968)

Shelley critique:
    Shelley does not waffle between melts and (aqueous) solution as Stel appears to do with his “not ‘diagnostic'” remark, and Shelley is does not confine himself to (superficial) replacement fronts, but acknowledges that outward growth and pressure is developed by crystallization on bulk mineral grains in the vein. Shelley’s mechanism is nearly the same as the mechanism suggested to operate in a KBO setting, with the primary difference being the state of the surrounding matrix; however, Shelley is constrained by operating in the setting of lithified rock, which requires cracking the surrounding matrix with developed water pressure to accommodate the expanding ptygma. Shelley presumably also relies on partial melting to develop the felsic-mafic layering in migmatite.

Aqueous differentiation of KBOs:

    Our solar system is suggested to have had a former binary-Companion to the Sun, with super-Jupiter-mass close-binary components. Secular perturbation of former binary-Companion caused the twin-binary components to spiral inward, transferring the close-binary potential energy into the wide-binary Sun-Companion system, progressively increasing the Sun-Companion eccentricity over time. This energy transfer dynamism caused tidal dynamism in the Kuiper belt, with the focal point of tidal disruption spiraling outward from the Sun over time. The Sun-Companion tidal disruption focal point plowed through the classical Kuiper belt (cubewanos), causing orbital perturbation of KBOs. This orbital perturbation caused binary KBOs to spiral in until they merged, converting the potential and kinetic energy to heat, which melted water ice in a process designated, ‘aqueous differentiation’.
    Orbital perturbation by binary-Companion also injected many KBOs into the inner solar system, predominantly from 4.1-3.8 Ga when the tidal disruption focal point passed through the highest concentration of cubewano KBOs, around 43 AU, causing the late heavy bombardment (LHB) of the inner solar system. KBO perturbation continued beyond the classical Kuiper belt into the scattered disc until the super-Jupiter components of binary-Companion ultimately merged around 650 Ma, in an asymmetrical merger explosion that gave the newly-merged Companion escape velocity from the Sun. (see section, STARS, PLANETS, MOONS, MINOR PLANETS AND COMETS).

    The kinetic and potential energy released in a binary spiral-in merger of a large 100+ km binary KBO elevated the core temperature above the melting point of water ice, initiating aqueous differentiation in newly-merged contact binaries. Subliming and melting ices liberated nebular dust, which dissolved in the churning brine in its microgravity setting. As the temperature of the internal saltwater ocean declined exponentially, authigenic mineral grains precipitated out of solution and grew by crystallization until falling out of aqueous suspension at a mineral grain size characteristic of the microgravity setting and the local circulation rate. This authigenic silicate precipitation
created a growing sedimentary core at the center of gravity, with a gneissic composition.

    A majority of the sand on Earth is suggested to be composed of authigenic, KBO mineral grains which fell out of aqueous suspension at a characteristic sand-grain scale. Authigenic mineral grains precipitate on Earth, but on our high-gravity planet, authigenic mineral grains fall out of aqueous suspension on the scale of clay particles.

Felsic-mafic layering in migmatite:

    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, resulting physical segregation of partially-melted protolith 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 caused by sawtooth changes in pH in the overlying saltwater ocean.

    The solubility of aluminous species is particularly pH sensitive, so the concentration of carbonic acid in solution may effectively control the reservoir of dissolved aluminum. 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 feldspar, the simplest aluminous silicate

Aluminous mineral species solubility vs. pH

    If aluminous species solubility is particularly sensitive to pH, CO2 solubility is particularly sensitive to physical shock, as is readily observed when shaking a carbonated beverage. And when dissolved CO2 bubbles out of solution, carbonic acid breaks down to restore the carbonic acid-CO2 equilibrium, raising the pH. Additionally, if the aftershock vents gaseous CO2 into outer space through newly opened faults in the icy overburden, the local rise in pH may be larger and more sustained. So KBO aftershocks are suggested to precipitate feldspar mineral grains, which grow by crystallization until falling out of aqueous suspension at a mineral grain size characteristic for the increased agitation rate following the aftershock. And the increased agitation rate following an aftershock may also induce quartz crystallization as well, with greater circulation of warm saltwater to the cold icy ceiling, where quartz and silica solubility are at their lowest.

    Thus KBO aftershocks are suggested to rapidly precipitate and crystallize feldspar and likely quartz, which fall out of aqueous suspension at a larger than average mineral grain size in the agitated aftermath of an aftershock. More complex aluminous mineral species, like biotite and muscovite, may also precipitate and crystallize rapidly following aftershocks, but more complex minerals may preferentially nucleate new biotite grains rather than crystallizing on suspended mineral grains. The greater complexity of biotite compared to feldspar may lower the likelihood that the necessary mineral species are available for crystallization on suspended mineral grains, whereas nucleation of new biotite grains can occur anywhere the components happen to be in proximity.
    So large feldspar mineral grains may rain down rapidly following a KBO aftershock, forming a coarse felsic (leucosome) layer, while the smaller grains of biotite et al. may only fall out of suspension when the circulation rate approaches its quiescent level, forming a finer, more-mafic mesosome layer. And likewise, quartz grains grains will also be coarser in the leucosome layers and finer in the mesosome layers.

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. ‘Metasedimentary’ mantling rock often shrouds gneiss domes, with mantling rock as the terminal authigenic sedimentation on gneissic cores. The compositional differences between gneissic core rock, quartzite, marble/dolomite and schist mantling rock bespeaks the differing depositional conditions of the various regimes.
    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.”
    A basal conglomerate, with boulders of the underlying gneiss, suggests a hiatus between core sedimentation and mantle sedimentation, allowing lithification and metamorphosing of the gneissic sediments prior to brecciation, and tumbling smooth into conglomerate, followed by authigenic deposition of mantling sediments.

    Grenville gneisses, with their Glenarm Supergroup mantling rock of the Delaware piedmont adjacent Pennsylvania, is suggested to have arrived with a bang, between 1.4 and 1.3 Ga, and accreted onto Laurentia in the Grenville orogeny.
    The Glenarm Supergroup may be a mixture of KBO and terrestrial formations, but the Wissahickon Group and its underlying formations, including Cockeysville Marble, are assumed to be of extraterrestrial origin, with heavy terrestrial overprinting.
    In Pennsylvania, the ‘Glenarm Wissahickon’, the ‘Mt. Cuba Wissahickon’, and the ‘type-Wissahickon’ all contain Mesoproterozoic (1600–1000 Ma) zircons, with variable counts of younger zircons (Bosbyshell, 2012).

Quartzite-marble/dolomite-schist mantling sequence:
    Conglomerate composed of the basal gneiss suggests core lithification and metamorphism, followed by reactivation of authigenic mantling deposition, with altered environmental conditions. Reactivation of authigenic mantling deposition suggests renewed melting, requiring renewed heat input. The aqueously-differentiated KBO metamorphic rock we sample on Earth are suggested to be KBOs that have undergone binary spiral-in merger, followed by perturbation into the inner solar system, so perhaps the subsequent authigenic mantling deposition is caused by intermittent gravitational tidal strain on KBOs during close orbital encounters with the giant planets.
    Repeated close orbital encounters may accord with the diversity of named schist formations in the Grenville orogeny, suggesting localized reactivation of authigenic precipitation by localized remelting of saltwater pockets, creating a diversity of schist formations.
    Remelting itself is an altered environmental condition, not encountered in the exponential cooling following binary spiral-in merger, punctuated by aftershocks. The temperature rise associated with remelting offers a potential mechanism for calcium carbonate precipitation, in that calcium carbonate solubility is inversely proportionate to temperature. This implies that marble/dolomite is the first mantling layer deposited during reactivation, suggesting that basal quartzite, in contact with core gneiss, is the terminal composition of the binary spiral-in merger deposition. Lithification of the sedimentary core involves expulsion of hot, void-filling aqueous brine into the cold overlying ocean, which would be in the process of freezing solid. Thus the temperature drop alone of hot hydrothermal fluids gushing into the cold overlying ocean would promote precipitation of authigenic quartz sand over the lithifying core forming a cap quartzite mantling layer. Subsequent lithification of schist deposits would similarly explain quartz layers associated with schist formations.
    Finally, brecciation forming basal conglomerate (or otherwise) in mantling rock might be explained as grinding between a lithified core and its overlying icy ceiling during the gravitational tidal strain experienced by a KBO in an orbital close encounter with a giant planet during its downward spiral into the inner solar system.

Domal structure of gneiss domes:
    Large (complex) impact craters develop a central uplift when the floor of the crater rebounds in the center. Still-larger impact craters form topographic rings, called multi-ringed basins, such as Orientale on the Moon. In aqueously-differentiated, 100+ km KBO impacts on Earth, fragmented sections of impact ring synclines, composed of KBO core rock, presumably accrete onto the preexisting margins of continental tectonic plates during orogenesis, incorporating gneiss domes in orogenic settings.
    Even if the syncline geometry of gneiss domes are molded at Earth impact, the age of gneiss domes is typically calculated by argon-argon geochronology, which measures the closure temperature of exhumed gneiss domes, which could be a billion years after Earth impact.

Slump folding in authigenic metamorphic rock:

Slump Folding in Migmatite

    Conventional geology suggests that metamorphic folding occurs at elevated temperature and pressure in 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 the scale of syncline-anticline folding is several orders of magnitude larger than the centimeter-scale folding typical in migmatites, and migmatites at depth lack void to fold into.
    Folding in migmatites resembles acknowledged slump folding in sedimentary rock, and by reimagining migmatite in a sedimentary setting allows apparent slump folding to be actual slump folding.
    Since conventional geology can not explain the origin of point forces necessary to randomly fold virtually-incompressible lithified rock into isoclinal folds on a centimeter scale at depth (as in slump folding), these 3-dimensional isoclinal folds are often dismissed as 2-dimensional sheath folds, fortuitously cut through the nose of the fold, since sheath folds are more readily explained by smearing across shear zones.

    In a sedimentary setting, the voids necessary for slump folding are inherent in the imperfect fit between impinging sedimentary mineral grains, and the very definition of lithification is the destruction of voids (with the accompanying expulsion of the void-filling, aqueous brine solution).

    Sedimentary slump folding in KBO cores has the additional mechanism of geometry, driving slump folding. On Earth, the vast circumference of the planet means that the vertical reduction of lithifying sediments generally results in lithification without slump folding. By comparison, in a lithifying sedimentary core undergoing a substantial volume reduction, the circumference of the lithifying layer would be substantial, forcing ‘circumferential slump folding’ on the sediments. This folding mechanism can be demonstrated by the relative absence of slump folds in drying paint, versus the dramatic folding of a grape drying to form a raisin, and like the drying grape, the KBO sedimentary core similarly dehydrates during lithification, by way of hydrothermal vents. Something similar to circumferential slump folding can occur on Earth under unusual conditions, such as the lithification of sediments in a sharp 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.

    And strongly felsic-mafic segregated migmatite sedimentation is particularly slump folded, due to the dramatic variation in mineral grain size and mineral grain composition between juxtaposed authigenic felsic and mafic mineral grain layers, where late lithifying sediments fold toward early lithifying sediments, undergoing destruction-of-voids densification.

IMAGE: Ptygmatic folding with radiating dikelets
Copyright 2004-2016 by Roberto Weinberg

Ptygmatic folding:

    The most exaggerated examples of a physical phenomenon will cause the genuine theory to shine, while pushing a flawed model to rely on ad hoc hypotheses to prevent falsification or to rely on fine tuning.
    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.

    While the majority of folding in authigenic KBO migmatites is suggested to form by slump folding, ptygmatic folding requires a different explanation.

    In lithifying KBO cores, the voids destructed were filled with brine, which buoyantly flowed through hydrothermal vents into the overlying ocean. Brine followed paths of lowest resistance though porous lithifying rock, which were predominantly through felsic leucosome layers that acted like French drains because of their larger mineral grain size, hereafter designated ‘veins’. Felsic leucosome layers were laid down the bedding plane, but to get to the surface, brine also required cross bedding veins as well, which often cut through the nose of slump folds.

    Additionally, as the brine cooled on its buoyant rise, mineral species crystallized on existing felsic mineral grains in the veins, further increasing the size of predominantly quartz and feldspar mineral grains in the veins. “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, fattening the veins in the lateral dimension and buckling them in the 2 longitudinal dimensions, 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).

    Ptygmatically folded veins are often fed by smaller ptygmatically folded ‘veinlets’, like tributaries flowing into rivers. In conventional geology, partial melts with a granitic composition presumably flow upstream and uphill, from fatter veins into narrower veinlets, whereas in an aqueous KBO setting, brine flowed downstream but buoyantly uphill, from the narrow veinlets into the fatter veins, finally discharging through hydrothermal vents. The physical implications of these contradictory philosophies may help to resolve the conflict.

    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 dikes which developed very differently, presumably due to the difference in the confining matrix types. The former 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 all the volume increase of the vein growth to manifest itself in the lateral direction.

Ptygmatic folds:
Image credit, Mountain Beltway, Callan Bentley structral geology blog

    The 3-dimensional expansion of aqueous dikes due to internal crystallization 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 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 balloon into aneurysms at relative weaknesses in the surrounding matrix, lithifying into boudinage.
    Finally, resistance from the lithifying matrix causes pressure dissolution at impinging mineral grain boundaries in veins to exceed the pressure of crystallization, and vein growth comes to an end, with crystallization confined to the voids.

KBO impacts:

    The bulk modulus of granite is more than 20 times that of water, such that water would absorb more than 20 times as much work energy due to compression in an impact shock wave (where the bulk modulus is the inverse of compressibility). Thus a thick mantle of water ice, and other relatively-compressible ices, would absorb the lion’s share of the incoming kinetic energy as compressive work energy, which is suggested to clamp the impact shock wave pressure below the melting point of silicates. Presumably water trapped in permeable KBO rock and in aqueous inclusions within silicate crystals would also be heated to near white-hot temperatures by the impact shock wave, which should have easily-detectable consequences, such as perhaps melting permeable rock into granite plutons at the moment of impact.

    The shock absorbing potential of relatively-compressible ices, however, would presumably not be sufficiently protective to prevent the formation of high-pressure polymorphs in silicates, such as coesite, so their conspicuous absence in suggested KBO metamorphic rock can not be explained.


Bosbyshell, Howell, (2012), Presentation at Northeastern Section – 47th Annual Meeting

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

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

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


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