Anisotropy of magnetic susceptibility (AMS) has become a widely accepted method of fabric analysis in rocks, especially those which have been deformed tectonically.  The use of anisotropy of complex magnetic susceptibility (ACMS) is a new potential method of fabric analysis in which the imaginary, or out of phase A.C. component of an induction coil used for the measurement of magnetic susceptibility is used to delineate rock fabric.  Complex magnetic susceptibility is a function of electrical conductivity, thus making it potentially useful in the analysis of highly conductive sulphide-rich rocks, some of which are not suitable for AMS analysis.

A supracrustal sequence of rocks near Manitouwadge, Ontario consists of metavolcanic rocks, including pillow lavas, banded iron formation, amphibolite, and a quartzofeldspathic hornblende-biotite gneiss.  This rock has been given the name bladed gneiss to reflect the blade-like appearance of its mafic components.  Results of a detailed geological investigation of the entire supracrustal sequence suggests that the apparent fragmental appearance of the gneiss, and to a lesser degree the other rock types, is not a primary feature, but rather, the product of deformation.  The rocks were initially part of a layered sequence which became variably fragmented.  The blades are in part the result of the transposition of layers and the variations in blade morphology are attributable to the response of the layers to strain during folding.  Individual layers deform by the development of cuspate-lobate folds, buckle folds, and boudinage.  The extent of fragmentation during deformation is controlled by competency contrasts between adjacent layers, absolute and relative layer thickness, and layer orientation with respect to principal finite strain directions. 

Planar and linear structural elements in the metasedimentary and metavolcanic rocks suggest a deformational history which includes two episodes of folding accompanied by medium grade metamorphism and recrystallization.  Similarities in lithology and structural elements between the rocks of the study area and those of the nearby Manitouwadge synform suggest that parent rock assemblages were closely related and that structures present in both locations developed contemporaneously in response to regional tectonic activity.  "Mobilist" tectonic models for the development of the Superior Province entail northward directed subduction and accretion, and are popular with many workers.  The recumbent nature of F₁ folds, the shallow plunging hinge lines of F₂ folds, and their coaxial relationship may be related to low angle thrust faults and nappe structures which would be likely consequences in the proposed subduction model.

Many workers have attempted to map subprovince boundaries.  In the region of the present study, the boundary between the Wawa and Quetico Subprovinces is traditionally placed a few miles north of Manitouwadge.  If this is correct, the rocks studied form part of the Wawa Subprovince.  Results of this investigation suggest that, on the basis of lithology and structure, such a placement of the boundary is inappropriate.  It appears more appropriate to suggest that the terrain discussed in this thesis, as well as the rocks of the Manitouwadge synform, is best considered to form a zone of transition between the two subprovinces.

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The comparison of three mapped successions in northern Ontario to glacial deltas reviewed in the literature results in the definition of four end-member depositional environments for glacial deltaic sedimentation.  Similar processes of sedimentation occur within two main glacial delta types, distal-fed, and ice-contact.  Distal-fed deltas divide into nonglacial and ice-influenced.  The other two end member types defined are subglacial and supraglacial ice-contact deltas.

Fine-grained laminated beds sedimented by interflows and overflows, as well as diamict and subaqueous outwash deposits underlie the glacial deltaic sequences.  The prodelta region consists of multiple reverse-graded beds, massive units, and laminated sediments deposited from interflows and overflows, and minor rippled units indicating intermittent underflows.  Within the delta front underflows deposited rippled and graded units, and occasionally planar cross-stratified units were sedimented by grainflows.  The delta plain contains trough cross-stratified sands and gravels which infill multiple distributary channels.  Dropstone deposition was restricted to the prodelta and delta front regions of ice-influenced distal-fed deltas, and ice-contact deltas.

Distributary mouth bars, large scale cyclic sedimentation, subaqueous outwash systems overlain by a glacial deltaic sequence, multiple processes of sedimentation within the delta front, and reworking of glaciogenic deposits have not previously been documented in glacial deltaic systems.   These deposits and processes, as well as the inability to define the strandline position indicated glacial deltaic systems are complex.

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The Quetico subprovince is a northeast-southwest striking linear belt of migmatites, gneisses, and metasedimentary rocks.  These Archean rocks form part of the southern Superior Province.  This study involves an examination of variations in metamorphic grade along cross-strike transects in an area north of Thunder Bay, Ontario.

The rocks of the Quetico subprovince include metasedimentary rocks with well preserved primary structures, knotted schists, gneisses, migmatites, and anatectic granitic rocks.  Metamorphic porphyroblasts include muscovite, biotite, garnet, staurolite, cordierite, andalusite, and sillimanite.  Chemical analyses of garnets, geothermobarometry, and mineral assemblage data were used to determine variations in metamorphic grade in transects across the subprovince.

Mineral assemblages characteristic of low to high grade metamorphism are exposed along an across-strike transect.  Metamorphic grade rises gradually from low grade (521°C) to high grade (714°C) northwards along Highway 527.  North of the peak conditions, the grade drops off sharply.  Garnet-biotite geothermometry confirms this pattern.  Maximum pressure reached in the study area is approximately 5 kbar.  

The model proposed to account for the distribution of metamorphic assemblages and minerals involves transpression of the Quetico accretionary prism between the Wabigoon volcanic cratonic margin to the north and the docking Wawa volcanic complex to the south.  Buckling and folding of the sedimentary rocks was accompanied by thrusting.  Erosion has exposed high grade migmatitic and anatectic rocks within the Quetico fold belt which developed as a result of thermal relaxation of depressed isotherms.  The boundaries between metavolcanic and metasedimentary terranes are structurally complex.  Boundaries may be best described as geometrically complex zones up to several kilometres in extent in which various rock types representative of the adjacent terranes have been folded, faulted, and intruded.

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The Seine Group metasedimentary rocks are situated between two converging major dextral transcurrrent faults, the Quetico Fault to the north and the Seine River Fault to the south.  To the west lies the Bad Vermilion Intrusive Complex (B.V.I.C).  The Seine Group shows one major period of deformation resulting in major F₁ folds.  Regional metamorphism of chlorite to biotite zone greenschist facies was synkinematic with the deformation.  Later minor deformation include localized crenulation cleavage and faults and shear zones.

Strain analysis of deformed conglomerates indicates 50-67% shortening in a north-south direction.  The B.V.I.C. has behaved rigidly during the deformation and produced a strain shadow in which only 18-42% shortening has occurred, deflected to a WNW-ESE direction.

The schistosity has an average trend of 252.3/85.7°NW, and the average trend of the stretching lineations is 063.4/43.4°.  However in the strain shadow of the B.V.I.C. the strikes are deflected to the NNE.

The AMS fabric in the Seine Group is controlled by paramagnetic chlorite and biotite.  The AMS foliation has an average orientation of 251.6/81.4°NW.  The AMS lineation has a peak trend of 059.7/41.7°.  The AMS ellipsoids are mostly oblate, with the least anisotropic fabric located in the strain shadow.  The AMS fabrics are deflected in the strain shadow of the B.V.I.C. in the same sense as the schistosity.

The anisotropy of isothermal remanent magnetization (ASIRM) of each sample was determined, using a saturating field of 500 mT, and then repeated at 800 mT.  The ASIRM fabric in the Seine Group is controlled by the ferromagnetic minerals magnetite and pyrrhotite.  The ASIRM lineation has a peak trend of 060.3/33.3°.  These fabrics are deflected in the same sense as the schistosity in the strain shadow of the B.V.I.C.

Although the three steep planar fabrics measured are similar in orientation, they are offset in plan view.  The angle between the schistosity and the AMS foliation is 4.4°.  The angle between the AMS and ASIRM foliation is 4.2°.  The schistosity, defined by deformed quartz and feldspar, is the oldest fabric.  The AMS fabric is younger, as the chlorite and biotite formed during metamorphism.  The magnetite and pyrrhotite which define the ASIRM formed later still, and thus represent the youngest fabric.

The successive offsets between the three fabrics is consistent with a dextral transpressional strain history operating throughout the fabric development.  The strain history had components of simple shear and non-coaxial shortening.  The initial shortening probably took place in a SE-NW direction.

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The metasedimentary rocks along the traverse reveal low to high grade metamorphism from chlorite schist near Atikokan, through biotite schist to migmatites in the west within the centre of the Quetico Belt.  Continuing toward the ESE, near Huronian Lake, the metamorphic grade decreases symmetrically but with somewhat less steep gradients to Kahabowie.  The metamorphism was syn- to late-tectonic.

Only one pervasive tectonic fabric was observed in the interior of the belt, with NE-SW striking S₁ foliations (mean direction:  256/85°NW, n=121) and extension lineations L₁ plunging shallowly to the NE (mean direction:  70-20°, n=52).  In migmatite and pegmatite zones foliation was often less steep.  It was probably deflected due to the intrusion of pegmatite or granitoid bodies.

Minerals contributing to ferromagnetic properties are mostly monoclinic ferromagnetic pyrrhotite within the belt with some magnetite in medium grade amphibolite - rich outcrops in metavolcanics of Shebandowan Belt.

Anistropy of magnetic susceptibility fabric (AMS) is mainly controlled by paramagnetic biotite or chlorite and subordinate ferromagnetic pyrrhotite in metasediments of the Quetico Belt.  In some outcrops of mafic metavolcanics near Kashabowie, the high magnetite content controls bulk susceptibility more than its anisotropy.  Variations in AMS fabric are largely due to variations in relative composition of magnetite, pyrrhotite and paramagnetic sheet silicates, not due to changes in strain along the traverse.

AMS foliations and lineations within the belt and on its south-east margin are generally coaxial with tectonic fabric, with AMS foliation less steep (dip of 70°) in the interior of the belt.  However a slight (2-5°) anticlockwise offset of the mean AMS foliation from S₁ can be postulated in the centre of the belt and at the southern margin.  When fabric data is studied separately for each sample, such offsets are not significant.  In the Atikokan area, AMS fabric is partly of sedimentary origin.  The offset of mean AMS lineations with respect to L₁ was confirmed for the Kashabowie - Huronian Lake area (also reported by Borradaile and Spark, 1990) but it is not prominent in the centre of the belt.

Anisotropy of remanence based on acquisition of anhysteretic remanence (AARM) is controlled by preferred crystallographic orientation of pyrrhotite in metasediments and partly by preferred dimensional orientation of magnetite in metavolcanics.  It is substantially higher than AMS fabric (mean P' of order 3 to 5).  AARM foliation is usually oriented closer to the tectonic fabric than AMS foliation; it is vertical at the margins and less steep in the centre of the Belt.  AARM lineations usually plunge more gently than tectonic and AMS lineations in the centre of the Belt and at the southern margin in the Kashabowie - Huronian Lake area.  At the northern margin, AARM fabric is highly oblate, so that fabric lineations are difficult to define. 

At the belt margins, a slight anticlockwise offset of AARM foliations with respect to the tectonic fabric exists, when fabrics for individual samples are examined.  However, the relative orientation of tectonic and magnetic fabric (AMS and AARM) are not a region - wide consistent kinematic indicator of dextral transpression.

Correlation studies between magnetic susceptibility and ARM intensity indicate that a monotonic correlation between ARM and MS exists only in the Calm Lake - Perch Lake area, in which pyrrhotite controls ARM.  In other areas a higher content of magnetite increases magnetic susceptibility in several samples, but not ARM.

Both magnetic fabric (AMS and ARM) are usually oblate in low grade metasedimentary rock (at the Belt margins), but in metavolcanic rocks magnetite can produce prolate ARM, but in metavolcanic rocks magnetite can produce prolate ARM, whereas ARS is oblate.  In the interior of the Belt, 50% of samples have prolate AARM, but most of them are pyrrhotite-bearing.

The AARM fabric is believed to have arisen by the growth of ferromagnetic grains (at least in case of pyrrhotite) in the later stages of transpressive penetrative deformation with a dominant dextral shear component of deformation along an ENE - SWS, vertical plane.  The preferred orientation of pyrrhotite grains was probably controlled by the older biotite - chlorite matrix fabric.  This would explain the lack of a more significant deflection of the youngest ARM fabric from the oldest tectonic fabric.  However, the accuracy of determinations of ARM axes (at least 5-10°) limits the validity of these conclusions.

Characteristics directions of magnetic remanence obtained during thermal or AF step-wise demagnetization form a weakly developed girdle along the basal plane of ARM anisotropy.  Therefore natural remanent magnetization is probably entirely of chemical origin and controlled mostly by high anisotropy of pyrrhotite and its preferred crystallographic orientation.  The orientation of NRM toward basal plane of ARM is believed to be mostly an effect of deflection from the true Earth's magnetic field direction due to anisotropy of pyrrhotite (P' of values of 3-5, Fuller, 1963), and not the effect of grain rotation.  Stress control of post - metamorphic remagnetization of  primary ChRM is also a possibility.  Therefore, it is suggested that NRM was acquired in the same late stage of deformation as AARM, when sizes of individual ferromagnetic grains were suitable to carry a stable remanence.  Any primary magnetization acquired at the time of rock formation was not preserved.

The model of different ages of development of paramagnetic and ferromagnetic fabric is consistent with the dextral transpression model of the deformation for both margins and the fabric of the Quetico Belt.  The latest ferromagnetic sub-fabric formed along the shear plane when the paramagnetic matrix was already oriented subparallel to this plane and mimetically controlled the orientation of crystallization of ferromagnetic phase.  The ferromagnetic fabric is not therefore useful as a kinematic indicator of shear component in those areas.

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The gold-bearing Metalore shear zone and Golden Highway quartz-carbonate vein in the Beardmore-Geraldton Archean Greenstone Belt occur along the Paint Lake splay faults at the contact between metavolcanic rocks and metaconglomerates intruded by pre-ore diorite.  The Metalore and Golden Highway deposits were emplaced during a late tectonic event.  They consist primarily of quartz, clinochlore, ankerite, potassium feldspars, sericite, pyrite, argentite and chalcopyrite with native gold.  The minerals have been deformed and are cut by at least three healed fractures by fluid inclusions.  Gold typically occurs in recrystallized quartz.  Microthermometric and Raman spectroscopy techniques were used to study fluid inclusions in quartz, calcite, ankerite, chlorites and potassium feldspars.

Six types of fluid inclusions were found to occur in three separate generations of hydrothermal fluid activity in the Metalore and Golden Highway.  The three generations of hydrothermal fluids represented by fluid inclusions are:  (1) pre-ore, low-salinity (<2wt.%) NaCl-CaCl₂ aqueous inclusions with small amounts of daughter mineral and H₂O-CO₂ inclusions with 10 and 40 mole percent CO₂ occurring in the Golden Highway and Metalore respectively; (2) syn-ore, MgCl₂ - H₂O-CO₂ aqueous and vapour rich inclusions with small amounts of daughter minerals with 50 and 80 mole percent in the Golden Highway and Metalore, respectively;  (3) post-ore, CO₂-H₂O liquid-vapour and CO₂ -rich liquid-vapour inclusion with variable CO₂ contents ranging from 10 to 50 mole percent CO₂.  Homogenization temperatures of pre-ore H₂O-CO₂ inclusions during are 220°-230°C and 356°C; syn-ore 266°C; and post-ore 21°C to 66°C.

The aqueous and CO₂-rich inclusions are interpreted to have been trapped as two immiscible phases in three separate generations.  Precipitation of gold may have been induced by pressure, temperature fluctuations and chemical changes from CO₂ effervescence.  Metamorphic fluids are the likely source for the onset of precious-metal deposition from reduced sulphur complexes along the Metalore splay fault and precious- and base-metal deposition from both reduced sulphur and chloride complexes along the Golden Highway splay fault.

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The Coldwell alkaline Complex is located on the north shore of Lake Superior, and consists of three Centers representing three magmatic episodes.  Center I consists of gabbro, and layered and unlayered ferroaugite syenite.  Center II consists of alkalic biotite gabbro, miaskitic nepheline syenite, amphibole nepheline syenite, perthitic nepheline syenites and recrystallized nepheline syenites.  Center III consists of magnesio-hornblende syenite, ferro-edenite syenite, contaminated ferroedenite syenite, and quartz syenite.

The textures and compositions of the feldspars and apatite from these three Centers were examined using cathodoluminescence (CL) and the scanning electron microscope (SEM).  All of the colours described in the text refer to cathodoluminescence colours.  The feldspars in Center I consist of light blue to light violet blue, optically homogeneous alkali feldspar; braid microperthite and incipient perthite; and irregular vein or patch perthite.  The irregular vein patch perthite contain light violet blue cryptoperthitic patches, light blue exsolved albite and dull blue exsolved K-feldspar.  During late-stage fluid-induced alteration, these feldspars were replaced by violet secondary albite and purple secondary K-feldspar; and were coarsened by a deuteric antiperthitic rim.  The Fe-rich antiperthitic rim consists of deep red secondary albite and brown secondary K-feldspar.  The later dominates in the upper series of the layered and unlayered syenites.  The homogeneous alkali feldspar crystallized at high temperatures ≤700°C, exsolved into microperthite at 650-550°C and formed irregular vein and patch perthite at 520-420°C.  Late-stage fluid-induced replacement and deuteric coarsening occurs at relatively low temperatures 500-300°C.

The feldspars in Center II consist of light blue or light bluish grey oligoclase; light violet blue homogeneous alkali feldspar; and irregular vein or patch perthite.  A few oligoclase crystals are mantled by a light blue alkali feldspar rim.  Most of the irregular vein and patch perthite contain light blue exsolved albite and dull blue K-feldspar host; and some of them contain light violet blue to light violet unexsolved alkali feldspar patches in the core, and violet blue to dull blue cross hatched microcline along the margin.  During late-stage fluid-induced deuteric alteration, the alkali feldspar was replaced by light violet blue to light violet secondary albite or dull blue to dark brown secondary K-feldspar along the margins; and the alkali feldspar was coarsened by a red to deep red secondary albite rim.  The oligoclase crystallized at high temperatures 800-750°C, and the homogeneous alkali feldspar crystallized at ³710-620°C.  The perthite texture and the unexsolved alkali feldspar patches may have formed at 600-450°C.  The K-feldspar host may have transformed to the cross-hatched microcline at ≈300°C.  The deuteric coarsened and replaced secondary feldspar formed at low temperatures <350°C.

In the recrystallized nepheline syenites of Center II, the feldspar crystals are usually mantled with a relict core and a light violet blue recrystallized alkali feldspar rim.  The relict cores usually are a light blue albite or light violet homogeneous alkali feldspar.

The feldspars in Center III consist of zoned plagioclase crystals with light greenish blue andesine-oligclase cores and light violet blue to light blue oligoclase-albite rims; light blue to blue homogeneous alkali feldspar, K-rich feldspar, braid microperthite and oscillatory zoned alkali feldspar; irregular vein perthite consisting of light blue to light violet exsolved albite and dull blue K-feldspar host; and regular to irregular vein antipperthite consisting of dull blue to dark blue exsolved K-feldspar and dull red to deep red albite host.  Most irregular vein antiperthite grains reveal alternating dull red, violet and deep red oscillatory zones.  During late-stage fluid-induced alteration, most light blue to blue original alkali feldspar were coarsened by a deuteric antiperthite rim which consists of red secondary albite and dark brown secondary K-feldspar.  The plagioclase crystallized at high temperatures about 900-750°C, the homogeneous alkali feldspar crystallized at ³725-520, and the K-rich feldspar crystallized at 580-450°C.  The microperthitic texture may have formed at 650-420°C, and the perthite and antiperthite textures may have formed at non-equilibrium temperatures about 520-350°C.  The deuteric coarsened antiperthitic rim formed at temperatures <350°C.

The apatite crystals in the Coldwell complex exhibit a variety of CL textures which include: (1) uniform light pink to pink grains;  (2) growth zones with a small brownish pink core and light pink to pink rims;  (3) light pink to pink alternating oscillatory zones;  (4) mantled grains with light pink to pink cores and brownish pink reaction rims.  Some of the reaction rims are overgrown by light pink and yellow secondary apatite.

The light pink and pink CL colours in the apatite crystals are dominantly caused by Eu²⁺ activation, the brownish pink CL colour is dominantly caused by Dy³⁺, Sm³⁺ and Pr³⁺, and the yellow luminescent secondary apatite is characteristic of Dy³⁺ and Tb³⁺ activation.  The brownish pink apatites have higher contents of total REE and Si than the light pink apatites.  The yellow or light pink secondary apatites have relatively low contents of total REE and Si.  The apatite crystals in the Coldwell complex are characterized by LREE-enrichment which is caused by the coupled substitution of 2Ca²⁺+P⁵⁺X(REE³⁺+REE²⁺)+Si⁴⁺.  The Si content in the apatite crystals increase from Center I through Center II to Center III.

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The McKellar Habour Sequence is located on the shore of Lake Superior approximately 40 km west of the town of Marathon, Ontario.  The Sequence was examine in detail through stratigraphic and geochemical investigations in order to determine the depositional environment and provenance of these rocks.

Four subsequences were identified in the McKellar Harbour Sequence, consistent with the facies associated with a distal submarine ramp environment.  The Sequence shows thickening and coarsening upward trends, indicative of progradation of the ramp onto the basin floor.  This indicates that the rocks of the McKellar Harbour Sequence are the distal equivalents of the proximal submarine ramp facies identified in the Beardmore-Geraldton and Quetico terranes to the north of the study area.  Sedimentary strata from other potential source regions did not exhibit the characteristic features of a submarine ramp, and were likely deposited through different processes.  Insufficient data were collected to determine the depositional environment for these units.

Geochemical analyses indicate that the rocks of the McKellar Harbour Sequence have immobile element chemistry that is very similar to that of the Beardmore-Geraldton and Quetico terranes, and that a continuum of deposition from the north to south is present.  Sediments generated in the Beardmore-Geraldton terrane were transported to small basins associated with the Schreiber-Hemlo volcanic island system by a submarine ramp. 

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The thesis area is located 120 km west of the City of Thunder Bay, Ontario, straddling the contact of the Quetico and Wawa subprovinces of the Archean Superior Province.

Metasedimentary rocks of the Quetico Subprovince with basic and granitic intrusions occupy the northwestern portion of the study area and are in contact to the southeast with metamorphosed mafic and felsic metavolcanic rocks of the Wawa Subprovince.

Tectonic compression has shortened the metasedimentary rock layers a minimum of 80%.  Bedding dips steeply to the northwest and a later cleavage, developed by transpression, is sub-parallel to bedding.  Graded beds young predominantly to the northwest.  Some graded beds young to the southeast and may represent pre-cleavage folding.  No large-scale folds are present.  Metamorphic grade increases northwest from greenschist to amphibolite facies over a distance of about 10 km.

Magnetite is the predominant magnetic component of the Moss Lake stock; hematite is present in trace amounts.  Magnetic susceptibility of the stock is high (12,000 X10^-6 SI), making the intrusion amenable to anisotropy of magnetic susceptibility (AMS) work.

AMS study of the Moss Lake Stock shows that individual directions of maximum susceptibility have been reoriented, in most cases sub-parallel to the local planar fabric strike of the Quetico Subprovince.  Magnetic fabric parameters show that the rock magnetic fabric of the intrusion is deformed.  Vestiges of original magmatic fabric are evidenced by prolate (constricted) magnetic fabric associated with the central long axis of the stock by magnetic fabric parameters confirm that the intrusion margin is more deformed than the interior.  The predominant oblate (flattened) magnetic fabric of the Moss Lake stock is the product of northwest-southeast tectonic compression.

Alternating field and thermal demagnetization of oriented rock specimens confirm that the Moss Lake stock is deformed by tectonic compression.  Separation of magnetite and hematite magnetic contributions, by blocking temperature, reveals that primary natural remanent magnetization (NRM) orientations from hematite are parallel to the local planar fabric strike of the Quetico Subprovince.  Minor preservation of primary magmatic fabric is indicated by the mean principal component analysis (PCA) orientation for magnetite which corresponds closely in trend to the mean paleomagnetic orientation for the region, obtained by previous investigators.  Original Moss Lake stock magnetic fabric is overprinted by compression and shearing.

Comparison of magnetic studies (AMS and NRM) of the Moss Lake stock to structural data of country rocks argues in favour of a common tectonic control.

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