Michael Higgins
Université du Québec à Chicoutimi, Sciences appliquées, Faculty Member
The Sept Iles Intrusive Suite (Quebec, Canada) is made up of a large layered intrusion, late gabbro intrusions and a composite sill (Pointe du Criard Sill). The layered intrusion crystallized from a ferrobasaltic magma and is subdivided... more
The Sept Iles Intrusive Suite (Quebec, Canada) is made up of a large layered intrusion, late gabbro intrusions and a composite sill (Pointe du Criard Sill). The layered intrusion crystallized from a ferrobasaltic magma and is subdivided into a Layered Series of troctolite and gabbro, an anorthositic Upper Border Series and a granitic Upper Series. The formation of the Upper Border Series resulted from plagioclase flotation from the base to the roof of the magma chamber. Fractionation of troctolites and gabbros in the Layered Series resulted in SiO2-enrichment and FeOt-depletion of the residual melt, ultimately forming the granite of the Upper Series. The solidification history of the Layered Series was interrupted by two major and a series of minor influxes of ferrobasaltic melt, significantly enlarging the size of the initial magma chamber. As a consequence, the Layered Series can be subdivided into three megacyclic units (MCU I, II and III). Mixing between resident magma and undifferentiated melt during replenishments had an important influence on both mineral compositions and the liquid lines of descent during the crystallization of the various megacyclic units. It is shown that the liquid line of descent during crystallization of MCU II reached silicate liquid immiscibility. Immiscible melts crystallized two different types of apatite-bearing gabbros, one of which is a major P–Ti–Fe deposit. Cumulate rocks in the layered intrusion show a wide range of crystallized interstitial liquid content. Expelling of this liquid from the crystal mush during solidification is explained both by compaction and compositional convection, but the relative efficiency of these two processes is shown to change significantly with differentiation.
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The Sept Iles Mafic Intrusion (SIMI)(Quebec, Canada), part of the Sept Iles Intrusive Suite (SIIS), is a 6 km-thick layered troctolite-gabbro intrusion with a funnel shape of 80 km in diameter. The SIIS has been dated at 564±4 Ma [1] and... more
The Sept Iles Mafic Intrusion (SIMI)(Quebec, Canada), part of the Sept Iles Intrusive Suite (SIIS), is a 6 km-thick layered troctolite-gabbro intrusion with a funnel shape of 80 km in diameter. The SIIS has been dated at 564±4 Ma [1] and supposedly results from the activity of a mantle plume related to the formation of the St-Laurent rift system. Flood basalts may have erupted before its emplacement [2]. A detailed petrologic study of the SIMI has been undertaken with the aim of better constraining the differentiation of ferrobasaltic liquids [3]. ...
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Anisotropy of magnetic susceptibility data validated by image analysis were acquired on the Sept Îles Layered Intrusion. Most data come from the mafic Layered Series of the intrusion, although the overlying anorthositic Upper Border... more
Anisotropy of magnetic susceptibility data validated by image analysis were acquired on the Sept Îles Layered Intrusion. Most data come from the mafic Layered Series of the intrusion, although the overlying anorthositic Upper Border Series and felsic Upper Series were also investigated. In the Layered Series, Type 1 magnetic fabric defined by gently to moderately dipping foliations and horizontal to moderately plunging lineations dominates over Type 2 fabric characterized by steeply dipping magnetic foliations and lineations of variable plunge, although steep on average. The inverse relationship holds true for the Upper Border Series and only Type 1 fabric occurs in the Upper Series. Several observations, mainly centripetal disposition of the igneous layering, and inclination of the mean Type 1 foliation and lineation towards the deepest point of the intrusion, near its centre, demonstrate post-cumulus, central sagging of the Layered Series. The Type 2 fabric recorded the effect of ...
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Imaging rocks in three-dimensions through X-ray microtomography enables routine visualization of structures in samples, which can be spatially resolved down to the sub-micron scale. Although X-ray tomography has been applied in biomedical... more
Imaging rocks in three-dimensions through X-ray microtomography enables routine visualization of structures in samples, which can be spatially resolved down to the sub-micron scale. Although X-ray tomography has been applied in biomedical research and clinical settings for decades, it has only recently been applied to studies of rocks, and few geoscientists realize its value and potential. This contribution provides an introduction to the principles and techniques of X-ray microtomography to the study of igneous rock textures ...
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It has been proposed that the degree of alteration of basic rocks, as quantified by alteration indices based on H 2 O+ contents or X-ray diffraction methods, can be used as a predictor of Ar loss. These hypotheses were tested using a... more
It has been proposed that the degree of alteration of basic rocks, as quantified by alteration indices based on H 2 O+ contents or X-ray diffraction methods, can be used as a predictor of Ar loss. These hypotheses were tested using a sample of 36 zeolite facies metavolcanic basic rocks from Skye, Scotland, UK, and found to be wanting. Hence, no independent criteria of Ar loss can be determined using these indicators.
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Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ascent to the surface. While variations in mineral compositions, sizes and number densities are routinely analysed to reconstruct... more
Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ascent to the surface. While variations in mineral compositions, sizes and number densities are routinely analysed to reconstruct pre-eruptive magmatic histories, crystal shapes are often assumed to be constant, despite experimental evidence for the sensitivity of crystal habit to magmatic conditions. Here, we develop a new program (ShapeCalc) to calculate 3D shapes from 2D crystal intersection data and apply it to study variations of crystal shape with size for plagioclase microlites (l < 100 µm) in intermediate volcanic rocks. The smallest crystals tend to exhibit prismatic 3D shapes, whereas larger crystals (l > 5–10 µm) show progressively more tabular habits. Crystal growth modelling and experimental constraints indicate that this trend reflects shape evolution during plagioclase growth, with initial growth as prismatic rods and subsequent preferential overgrowth of the interme...
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Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, and granite) of the unmetamorphosed Sept Iles complex have been evaluated to determine if these rocks can be related by simple magmatic... more
Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, and granite) of the unmetamorphosed Sept Iles complex have been evaluated to determine if these rocks can be related by simple magmatic processes or if it is necessary to invoke separately derived magmas. Major-element mass-balance and trace-element distribution calculations indicate that the diorite and quartz syenite were produced by fractional crystallization of plagioclase and augite, together with minor hypersthene and ilmenite, from a parental gabbroic magma. The Sr depletion of the granite, as compared with the quartz syenite, cannot be developed readily by partial melting and is better explained by fractional crystallization models. Major-element mass-balance solutions indicate that the granite was formed by removal of alkali feldspar, plagioclase, amphibole, and ilmenite from a quartz syenitic magma. Depletion of REE in the granite was probably the result of amphibole or REE-ric...
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The Sept Iles anorthosite complex is located in the Grenville (structural) Province of the Canadian Shield. Geochronological studies of both the basic and acidic portions of the complex show that it was intruded approximately 540 Ma ago... more
The Sept Iles anorthosite complex is located in the Grenville (structural) Province of the Canadian Shield. Geochronological studies of both the basic and acidic portions of the complex show that it was intruded approximately 540 Ma ago and thus post-dates the Grenville orogeny by at least 500 Ma. Field relationships confirm the contemporaneity of the basic (anorthosite and gabbro) and acidic (syenite and granite) rocks. Differentiation of the basic magma was controlled by preferential nucleation in the boundary layer. Crystal separation due to gravity and possibly liquid immiscibility caused differentiation once intermediate or acidic magma compositions were formed. There is no evidence that crustal contamination has played a role in the generation of the acidic rocks. The complex has been intruded along the St. Lawrence graben fault, known to have been active at this time from the profusion of igneous rocks elsewhere along this structure, which are contemporaneous with the Sept Il...
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U–Pb zircon dating of the southwest lobe of the Havre-Saint-Pierre anorthosite intrusion indicates that it is 1062 ± 4 Ma old. Parallelism of magmatic and solid-state foliations with the adjacent Abbé–Huard lineament suggest that... more
U–Pb zircon dating of the southwest lobe of the Havre-Saint-Pierre anorthosite intrusion indicates that it is 1062 ± 4 Ma old. Parallelism of magmatic and solid-state foliations with the adjacent Abbé–Huard lineament suggest that anorthosite parental magmas rose up this shear zone, which was active at that time. The age of igneous crystallization is much younger than that of a spatially associated mangerite intrusion, but accords with age data from other granitoid intrusions elsewhere in the Grenville Province. Evidence points to a widespread 1.09–1.05 Ga magmatic event that included massif anorthosite intrusions. This magmatic event coincided with late stage convergent tectonics in the southwestern Grenville Province.
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High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence of mantle-derived xenoliths indicate that a subvolcanic nephelinite intrusion in northwestern British Columbia represents an unmodified... more
High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence of mantle-derived xenoliths indicate that a subvolcanic nephelinite intrusion in northwestern British Columbia represents an unmodified primary magma. A separate, closely associated nephelinite intrusion shows evidence of minor olivine fractionation from a similar composition. Only three other occurrences of primary nephelinite have been described. This new occurrence suggests that these magmas may not be so rare as previously supposed. The trace-element abundances closely resemble those of primary nephelinites of similar La content from Freemans Cove, Canada. Such compositions are usually taken as evidence of intraplate rifting and doming. Therefore, these rocks are further evidence of late Tertiary or Quaternary rifting in the Stikine volcanic belt.
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The Chatham–Grenville stock is an anorogenic multiple intrusion that shows a complete gradation from early cumulate and noncumulate syenites to slightly peralkaline granites. It can be divided into four units. Unit 1, the first unit, is a... more
The Chatham–Grenville stock is an anorogenic multiple intrusion that shows a complete gradation from early cumulate and noncumulate syenites to slightly peralkaline granites. It can be divided into four units. Unit 1, the first unit, is a noncumulate syenite with modal quartz less than 5%. Unit 2 has a wide range in composition from cumulate syenites (no modal quartz) to noncumulate syenites and quartz syenites (modal quartz = 20%). Units 3 and 4 are granites with modal quartz up to 25 and 30%, respectively. The parental magma of the whole complex was syenitic. Differentiation occurred as a result of crystal fractionation by filter pressing both at depth and in situ. Ba, Sr, Rb, and Eu abundances and major-element mass-balance calculations show that alkali feldspar, mafic minerals, and apatite were fractionated. At least 79% fractionation is necessary to transform the mean composition of the first unit (1) into the mean composition of the last unit (4). The rare-earth elements, Th, ...
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The Sept Iles layered intrusion (Quebec, Canada) is an Ediacaran (564 Ma), dinner-plate shaped plutonic body with a diameter of 80 km and a maximum thickness of 7 km. It is the third largest layered intrusion in the world, after the... more
The Sept Iles layered intrusion (Quebec, Canada) is an Ediacaran (564 Ma), dinner-plate shaped plutonic body with a diameter of 80 km and a maximum thickness of 7 km. It is the third largest layered intrusion in the world, after the Bushveld complex and the Dufek intrusion. From base to top, the Sept Iles intrusion is made up of a Layered Series (at least 4800 m thick) dominated by troctolite and gabbro, an anorthositic Upper Border Series and a broadly granitic Upper Series. About 90% of the intrusion is covered by the St. Lawrence River and only its northwesternmost portion is partly visible on the mainland and on islands. We have conducted a structural study of the outcropping part of the Layered Series, using the technique of low-field anisotropy of magnetic susceptibility. The bulk magnetic susceptibility (values from 5 to 280x10 SI, excluding one strongly altered sample) is largely ferromagnetic and dominated by magnetite. The magnetic fabrics can be divided into three categor...
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Although the size and shape of crystals in thin sections have been measured in a number of studies, it has not been possible so far to calculate from these data the true, three-dimensional shape and size of the crystals. A numerical... more
Although the size and shape of crystals in thin sections have been measured in a number of studies, it has not been possible so far to calculate from these data the true, three-dimensional shape and size of the crystals. A numerical model, based on orthogonal solids, has been developed to attack this problem. This model shows that crystal habit can be calculated from width to length ratio distributions for most crystals in massive rocks and for all crystals in laminated or lineated rocks. Variations in the habit of minerals can reveal aspects of the physicochemical conditions of crystallization. The same model has also been used to develop the equations necessary to transform two-dimensional crystal size istributions into true crystal size distributions. Corrections for the cut effect and the intersection probability effect both require a knowledge of the crystal habit.
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Research Interests: Growth, Crystals, Depth, Volcanoes, Nucleation, and 12 moreVolcanic Rocks, Basalts, Crystallinity, Magma, Basalt, Texture, Csd, Magma mixing, Fractionation, Lava, Saturation, and Igneous Rocks
Undeformed and unmetamorphosed diabase dykes up to 5 m wide occur in an area of ∼100 km2 about 50 km northwest of Montreal near the village of Sainte-Sophie. The dykes are subvertical and oriented east–west. The most common phenocryst... more
Undeformed and unmetamorphosed diabase dykes up to 5 m wide occur in an area of ∼100 km2 about 50 km northwest of Montreal near the village of Sainte-Sophie. The dykes are subvertical and oriented east–west. The most common phenocryst phase is plagioclase (1–2 mm, exceptionally 10 mm), followed by olivine, and in one dyke, pyroxene. Most dykes have vesicles 0.1–10 mm in diameter and fine-grained margins. Alteration is extensive: plagioclase is partly sericitized, olivine is serpentinized, and zeolites and carbonate are developed in the vesicles and matrix. Ar–Ar dating was challenging, but the weighted mean of two plateau ages indicates intrusion and cooling at 591.6 ± 2.5 Ma. The overall characteristics of these dykes suggest that they may be a facies of the much larger Grenville dyke swarm to the west. However, there are distinct chemical differences that suggest they were fed from a different, generally more enriched mantle source. This zone may be related to the one that produce...
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Quantification of rock textures (= microstructures), in the form of crystal sizes, shapes and orientations, complements chemical and isotopic approaches to the determination of the petrogenesis of rocks in layered mafic intrusions.... more
Quantification of rock textures (= microstructures), in the form of crystal sizes, shapes and orientations, complements chemical and isotopic approaches to the determination of the petrogenesis of rocks in layered mafic intrusions. Textures develop initially by nucleation and kinetic growth, but this process is commonly obscured in layered mafic intrusions by later textural modifications. Foliation in layered mafic intrusions is common but lineation of non-equant crystals is generally weak or absent. This makes it difficult to determine if simple shear (flow) or pure shear (compaction) is dominant. However, if pure shear is important then it must be accompanied by significant pressure-solution to produce the strength of the observed foliations. Correlation of fabric strength and overall crystal shape suggest that growth and shear were concurrent. But by far the most important textural process is equilibration (coarsening), testified by crystal size distributions. Almost all rocks in layered mafic intrusions have equilibrated, but the degree of progress towards equilibrium is very variable, even within layered mafic intrusions. It appears that the process is controlled by local variations in liquid content, mineral mixture and temperature.
Research Interests: Geology and Geochemistry
ABSTRACT Lac de la Presqu&#39;ile is a sub-circular lake, about 7 km in diameter with a prominent central peninsula. The shape of this lake and the occurrence of shatter cones to the east suggest that an impact created a crater with... more
ABSTRACT Lac de la Presqu&#39;ile is a sub-circular lake, about 7 km in diameter with a prominent central peninsula. The shape of this lake and the occurrence of shatter cones to the east suggest that an impact created a crater with an original diameter of at least 12 km (Tait, 1990). Deep erosion of the structure suggests that it was formed in the distant past, at least several hundred million years ago.
Research Interests: Geology and Meteoritics
Processes involved in the development of igneous and metamorphic rocks involve some combination of crystal growth, solution, movement and deformation, which is expressed as changes in texture (microstructure). Advances in the... more
Processes involved in the development of igneous and metamorphic rocks involve some combination of crystal growth, solution, movement and deformation, which is expressed as changes in texture (microstructure). Advances in the quantification of aspects of crystalline rock textures, such as crystal size, shape, orientation and position, have opened fresh avenues of research that extend and complement the more dominant chemical and isotopic studies. This book discusses the aspects of petrological theory necessary to understand the development of crystalline rock texture. It develops the methodological basis of quantitative textural measurements and shows how much can be achieved with limited resources. Typical applications to petrological problems are discussed for each type of measurement. This book will be of great interest to all researchers and graduate students in petrology.
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Summary K-feldspar megacrysts are common in granitoids, but rare in chemically equivalent volcanic rocks, of which the Taapaca dacites are the best known. Sanidine megacrysts up to 10 cm long occur in some of the lavas, and contain... more
Summary K-feldspar megacrysts are common in granitoids, but rare in chemically equivalent volcanic rocks, of which the Taapaca dacites are the best known. Sanidine megacrysts up to 10 cm long occur in some of the lavas, and contain abundant chadocrysts of plagioclase, sanidine, amphibole and oxides, as well as glassy magmatic inclusion and voids. Chadocrysts are generally isolated from the host by a thin film of glass. The matrix contains abundant plagioclase crystals, as well as amphiboles and oxides. Both megacrysts and ...
Research Interests: Geology and Geochemistry
Research Interests: Geology and Geochemistry
Research Interests: Geology and Geochemistry
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Abstract Magma mixing is widely recognized in contemporary petrology as one of the primary igneous processes. Microgranitoid enclaves (MEs) are considered to be remnants of such mixing processes, and the term has a well-established... more
Abstract Magma mixing is widely recognized in contemporary petrology as one of the primary igneous processes. Microgranitoid enclaves (MEs) are considered to be remnants of such mixing processes, and the term has a well-established genetic implication. However, microgranitoid enclaves span a wide range of compositions, and felsic varieties are also frequently reported. Nd–Sr isotope and textural data from felsic microgranitoid enclaves (FMEs), mafic microgranitoid enclaves (MMEs) and host granites from the Salto pluton, Itu Granitic Province, show that the cm-sized MMEs are dioritic, have medium-grained igneous textures and xenocrysts of alkali feldspar and quartz. The FMEs are cm- to meter-sized, have spheric shapes, show corrugated contacts with the host granites, and have resorbed feldspars and deformed quartz crystals interpreted as xenocrysts set in a fine-grained groundmass. Compared to the host granites, both MME and FME samples have increased FeO, MgO, TiO2, P2O5 and Zr contents, but their Sr and Nd isotope signatures are identical: FME 87Sr/86Sri = 0.7088–0.7063, eNdi = − 10.0 to − 10.2; MME 87Sr/86Sri = 0.7070, eNdi = − 10.5; host granite 87Sr/86Sri 0.7056–0.7060, eNdi = − 10.2 to − 10.3. These indicate that the enclaves derive from a similar source, although the melts from which they formed were probably hotter and chemically more primitive than their host granites. Crystal size distributions (CSDs) of plagioclase in samples drilled from rinds and cores of three FMEs show that the rind samples are systematically finer-grained than the samples from the cores, which indicates that the FMEs cooled inwards and contradict interpretations that the FMEs are autoliths. Thermal modeling suggests that a slightly more primitive, hotter magma would be thermally equilibrated with an evolved resident melt within weeks after mixing/mingling. Upon thermal equilibrium, the FMEs would have an increased crystal cargo, and the resulting touching framework would impart a solid-like behavior to the FME-forming magma, which would lead to a contrast in rheology, fragmentation, dragging and preservation of felsic replenishment batches as distinct enclaves.
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ABSTRACT Marsh (Contrib Miner Petrol 166:665-690, 2013) again claims that crystal-free basalt magmas are unable to differentiate in crustal magma chambers and regards layered intrusions as primarily due to the repeated emplacement of... more
ABSTRACT Marsh (Contrib Miner Petrol 166:665-690, 2013) again claims that crystal-free basalt magmas are unable to differentiate in crustal magma chambers and regards layered intrusions as primarily due to the repeated emplacement of crystal suspensions. He ignores an earlier critique of his unconventional inferences (Latypov, J Petrol 50:1047-1069, 2009) as well as a wealth of petrographic, geochemical and experimental evidence supporting the dominant role of fractional crystallization in the solidification of layered intrusions. Most tellingly, the cryptic variations preserved in the Skaergaard and many other basaltic layered intrusions would require an exceedingly implausible sequence of phenocrystic magmas but are wholly consistent with in situ fractional crystallization. A major flaw in Marsh’s hypothesis is that it dismisses progressive fractional crystallization within any magma chamber and hence prohibits the formation of crystal slurries with phenocrysts and melts that change systematically in composition in any feeder system. This inherent attribute of the hypothesis excludes the formation of layered intrusions anywhere.
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Linear cross-polarized optical images reveal the birefringence of mineral grains and are very useful in petrography. However, if the vibration directions of the crystal are not at 45 to the polarizers, then the intensity of the... more
Linear cross-polarized optical images reveal the birefringence of mineral grains and are very useful in petrography. However, if the vibration directions of the crystal are not at 45 to the polarizers, then the intensity of the interference colors is reduced, and in some orientations, to zero (extinction). This reduction in intensity, and extinction, can be eliminated if circular polarizers are used in place of linear polarizers. The interference colors of colorless minerals then correspond exactly with those on the Michel-Lévy chart. Similarly, ...
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The geology and geochemistry of the Canton Saint-Onge wollastonite deposit indicate that it is a skarn formed by silica metasomatism of dolomite-rich rocks. Oxygen isotopic compositions of the skarn rocks and the nearby plutons show that... more
The geology and geochemistry of the Canton Saint-Onge wollastonite deposit indicate that it is a skarn formed by silica metasomatism of dolomite-rich rocks. Oxygen isotopic compositions of the skarn rocks and the nearby plutons show that the fluids responsible for the metasomatism were not meteoric, but were probably associated with the Du Bras granitic pluton. However, the granite is not in contact with the wollastonite rocks at the present level of exposure, hence the fluids must have been released at greater depths. Wollastonite- ...
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The geology and geochemistry of the Canton Saint-Onge wollastonite deposit indicate that it is a skarn formed by silica metasomatism of dolomite-rich rocks. Oxygen isotopic compositions of the skarn rocks and the nearby plutons show that... more
The geology and geochemistry of the Canton Saint-Onge wollastonite deposit indicate that it is a skarn formed by silica metasomatism of dolomite-rich rocks. Oxygen isotopic compositions of the skarn rocks and the nearby plutons show that the fluids responsible for the metasomatism were not meteoric, but were probably associated with the Du Bras granitic pluton. However, the granite is not in contact with the wollastonite rocks at the present level of exposure, hence the fluids must have been released at greater depths. Wollastonite- ...