Michael Higgins | Université du Québec à Chicoutimi (original) (raw)
Books by Michael Higgins
Papers by Michael Higgins
Igneous zircon crystallization ages are presented for five intrusions in the Chicoutimi area, Que... more Igneous zircon crystallization ages are presented for five intrusions in the Chicoutimi area, Quebec, to the southeast of the Lac-St-Jean Anorthosite Complex. The age of the Ruisseau a Jean-Guy mafic intrusion is 1393 +22/-10 Ma and a diabase dyke cutting this intrusion is dated as 1050 ± 10 Ma. Two units that border the complex, a ferrodiorite and a farsundite, have ages of 1153 ± 7 and ca. 1160 Ma, respectively, similar to that of the complex. The large Chicoutimi mangerite intrusion southeast of the complex is 1082 ± 3 Ma. A compilation of geochronological data shows that, since mid-Proterozoic gneiss formation, this portion of the Central Granulite Terrane was subjected to at least three pulses of igneous activity, around 1.40 Ga, 1.15 Ga and 1.08-105 Ga. Les auteurs presentent les âges de la cristallisation de zircons ignes pour cinq intrusions dans la region de Chicoutimi (Quebec), au sud-est du Complexe d'anorthosite du Lac-St-Jean. L'âge de !'intrusion mafique du ruisseau a Jean-Guy est de 1393 +22/-10 Ma, et un dyke de diabase recoupant cette intrusion remonte a 1050 ± 10 Ma. Deux unites en bordure du complexe, soit une ferrodiorite et une farsundite, sont datees a 1153 ± 7 Ma et a environ 1160 Ma, respectivement, ce qui est proche de l'âge du complexe. La vaste intrusion de mangerite de Chicoutimi, au sud-est du complexe, remonte a I 082 ± 3 Ma. Une compilation des donnees geochronologiques indique que, depuis la formation du gneiss au Proterozolque moyen, cette partie du terrane granulitique central a ete soumis a au moins trois impulsions d'activite ignee, soit vers 1,40 Ga, 1,15 Ga et 1,08-1,05 Ga.
![Research paper thumbnail of Corrigendum to What can crystal size distributions and olivine compositions tell us about magma solidification processes inside Kilauea Iki lava lake, Hawaii[J. Volcanol. Geotherm. Res. 208 (2011) 136-162]](https://attachments.academia-assets.com/117453739/thumbnails/1.jpg)
](Journal of Volcanology and Geothermal Research, 2012
ABSTRACT Lava lakes offer the opportunity to investigate magma solidification and can be consider... more ABSTRACT Lava lakes offer the opportunity to investigate magma solidification and can be considered as a proxy for small magma chambers or layered intrusions. Here we present data from Kilauea Iki Lava Lake, which formed during the near-summit 1959 picritic eruption of Kilauea Volcano, Hawaii. Microprobe geochemical analyses and crystal size distributions (CSDs) of olivine were determined from three eruption scoria samples, and 34 drill core samples taken from 1967 to 1988. The data provide valuable information on the dynamics and timescales of the intra-lake solidification processes, along with origin of, and temporal constraints on, the distinct olivine populations. Based on their core and rim forsterite (Fo) content, three distinct olivine populations were distinguished: (1) a high-Fo population (Fo85-88); (2) an intermediate-Fo population (Fo77-81); and (3) a low-Fo population (Fo72-76). Groups 1 and 2 both have deformed and undeformed crystals indicating that they formed partly within Kilauea plumbing system before the eruption. The second group seems to be associated with the `vertical olivine-rich bodies' (VORBs) of Helz (1980). These structures raise magma from the lower part of the lake; hence they may have a contrasting composition maintained from the initial filling of the lake. The third population may be the result of rejuvenation within the lake during its cooling. Although the shape of the olivine CSDs is fairly uniform, we note significant variations that allow the recognition and quantification of multiple solidification processes. Our data display evidence of minor accumulation occurring by settling modified by convection currents. The concave-up curvature of at least half of the CSDs is strong evidence for mixing of magmas or crystal populations. The turndown at smallest sizes of the CSD, particularly present for samples at the edge of the lake, is thought to be the result of coarsening. Our CSD and crystal chemistry data suggest that the early populations and their related magmas underwent several solidification processes at depth, such as minor growth, coarsening, aggregation and deformation, plus settling and mixing maybe, no matter the order of appearance. The CSD analysis also yields estimates of the crystal residence time for different olivine populations, which are not necessarily the same as those defined using the olivine composition. For a growth rate of 10-9 mm/s, the range of residence times is 2-30 years. The CSDs can be segmented into three main groups: (a) a minor 2-4 yr-old population of smaller, rejuvenated crystals; (b) a dominant 10-18 yr-old population of intermediate-sized crystals; and (c) a 20-30 yr-old population of larger, coarsened, and often deformed crystals. Although the focus is here on volcanic rocks, our work gives a new perspective on the solidification of basic magma that can gain valuable insights into the overall understanding of mafic layered intrusions. References: Helz (1980), Bull. Volc. 43 (4): 675-701
American Mineralogist, Aug 1, 2002
Springer Geology, 2015
The Sept Iles Intrusive Suite (Quebec, Canada) is made up of a large layered intrusion, late gabb... 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.
Geochimica et Cosmochimica Acta, 2007
The Sept Iles Mafic Intrusion (SIMI)(Quebec, Canada), part of the Sept Iles Intrusive Suite (SIIS... 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]. ...
Journal of the Geological Society, 2020
Anisotropy of magnetic susceptibility data validated by image analysis were acquired on the Sept ... 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 ...
Lithos, 2012
Imaging rocks in three-dimensions through X-ray microtomography enables routine visualization of ... 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 ...
Chemical Geology, 1984
It has been proposed that the degree of alteration of basic rocks, as quantified by alteration in... 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.
Springer Geology, 2015
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
Contributions to Mineralogy and Petrology
Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ... 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...
Geological Society, London, Memoirs, 2016
The majority of confirmed impact craters on Earth have been discovered on land. However, the incr... more The majority of confirmed impact craters on Earth have been discovered on land. However, the increased use of high-resolution, full-bottom-coverage seafloor mapping methods such as multibeam bathymetry have enabled the discovery of previously unknown subaqueous impact craters on continental margins and in large lakes. High-resolution bathymetric and sub-bottom profiler data collected south of the city of Sept-Îles in the northwestern Gulf of St Lawrence, eastern Canada (Fig. 1a), revealed a previously unreported circular structure of possible impact origin located 20 km off the mainland in water depths of 40-208 m (Fig. 1b, c) that had been overrun by the Laurentide Ice Sheet (Lajeunesse et al. 2013).
Canadian Journal of Earth Sciences, 1986
Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, ... 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...
Canadian Journal of Earth Sciences, 1981
The Sept Iles anorthosite complex is located in the Grenville (structural) Province of the Canadi... 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...
Canadian Journal of Earth Sciences, 1993
U–Pb zircon dating of the southwest lobe of the Havre-Saint-Pierre anorthosite intrusion indicate... 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.
Canadian Journal of Earth Sciences, 1985
High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence o... 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.
Canadian Journal of Earth Sciences, 1985
The Chatham–Grenville stock is an anorogenic multiple intrusion that shows a complete gradation f... 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, ...
Igneous zircon crystallization ages are presented for five intrusions in the Chicoutimi area, Que... more Igneous zircon crystallization ages are presented for five intrusions in the Chicoutimi area, Quebec, to the southeast of the Lac-St-Jean Anorthosite Complex. The age of the Ruisseau a Jean-Guy mafic intrusion is 1393 +22/-10 Ma and a diabase dyke cutting this intrusion is dated as 1050 ± 10 Ma. Two units that border the complex, a ferrodiorite and a farsundite, have ages of 1153 ± 7 and ca. 1160 Ma, respectively, similar to that of the complex. The large Chicoutimi mangerite intrusion southeast of the complex is 1082 ± 3 Ma. A compilation of geochronological data shows that, since mid-Proterozoic gneiss formation, this portion of the Central Granulite Terrane was subjected to at least three pulses of igneous activity, around 1.40 Ga, 1.15 Ga and 1.08-105 Ga. Les auteurs presentent les âges de la cristallisation de zircons ignes pour cinq intrusions dans la region de Chicoutimi (Quebec), au sud-est du Complexe d'anorthosite du Lac-St-Jean. L'âge de !'intrusion mafique du ruisseau a Jean-Guy est de 1393 +22/-10 Ma, et un dyke de diabase recoupant cette intrusion remonte a 1050 ± 10 Ma. Deux unites en bordure du complexe, soit une ferrodiorite et une farsundite, sont datees a 1153 ± 7 Ma et a environ 1160 Ma, respectivement, ce qui est proche de l'âge du complexe. La vaste intrusion de mangerite de Chicoutimi, au sud-est du complexe, remonte a I 082 ± 3 Ma. Une compilation des donnees geochronologiques indique que, depuis la formation du gneiss au Proterozolque moyen, cette partie du terrane granulitique central a ete soumis a au moins trois impulsions d'activite ignee, soit vers 1,40 Ga, 1,15 Ga et 1,08-1,05 Ga.
Journal of Volcanology and Geothermal Research, 2012
ABSTRACT Lava lakes offer the opportunity to investigate magma solidification and can be consider... more ABSTRACT Lava lakes offer the opportunity to investigate magma solidification and can be considered as a proxy for small magma chambers or layered intrusions. Here we present data from Kilauea Iki Lava Lake, which formed during the near-summit 1959 picritic eruption of Kilauea Volcano, Hawaii. Microprobe geochemical analyses and crystal size distributions (CSDs) of olivine were determined from three eruption scoria samples, and 34 drill core samples taken from 1967 to 1988. The data provide valuable information on the dynamics and timescales of the intra-lake solidification processes, along with origin of, and temporal constraints on, the distinct olivine populations. Based on their core and rim forsterite (Fo) content, three distinct olivine populations were distinguished: (1) a high-Fo population (Fo85-88); (2) an intermediate-Fo population (Fo77-81); and (3) a low-Fo population (Fo72-76). Groups 1 and 2 both have deformed and undeformed crystals indicating that they formed partly within Kilauea plumbing system before the eruption. The second group seems to be associated with the `vertical olivine-rich bodies' (VORBs) of Helz (1980). These structures raise magma from the lower part of the lake; hence they may have a contrasting composition maintained from the initial filling of the lake. The third population may be the result of rejuvenation within the lake during its cooling. Although the shape of the olivine CSDs is fairly uniform, we note significant variations that allow the recognition and quantification of multiple solidification processes. Our data display evidence of minor accumulation occurring by settling modified by convection currents. The concave-up curvature of at least half of the CSDs is strong evidence for mixing of magmas or crystal populations. The turndown at smallest sizes of the CSD, particularly present for samples at the edge of the lake, is thought to be the result of coarsening. Our CSD and crystal chemistry data suggest that the early populations and their related magmas underwent several solidification processes at depth, such as minor growth, coarsening, aggregation and deformation, plus settling and mixing maybe, no matter the order of appearance. The CSD analysis also yields estimates of the crystal residence time for different olivine populations, which are not necessarily the same as those defined using the olivine composition. For a growth rate of 10-9 mm/s, the range of residence times is 2-30 years. The CSDs can be segmented into three main groups: (a) a minor 2-4 yr-old population of smaller, rejuvenated crystals; (b) a dominant 10-18 yr-old population of intermediate-sized crystals; and (c) a 20-30 yr-old population of larger, coarsened, and often deformed crystals. Although the focus is here on volcanic rocks, our work gives a new perspective on the solidification of basic magma that can gain valuable insights into the overall understanding of mafic layered intrusions. References: Helz (1980), Bull. Volc. 43 (4): 675-701
American Mineralogist, Aug 1, 2002
Springer Geology, 2015
The Sept Iles Intrusive Suite (Quebec, Canada) is made up of a large layered intrusion, late gabb... 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.
Geochimica et Cosmochimica Acta, 2007
The Sept Iles Mafic Intrusion (SIMI)(Quebec, Canada), part of the Sept Iles Intrusive Suite (SIIS... 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]. ...
Journal of the Geological Society, 2020
Anisotropy of magnetic susceptibility data validated by image analysis were acquired on the Sept ... 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 ...
Lithos, 2012
Imaging rocks in three-dimensions through X-ray microtomography enables routine visualization of ... 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 ...
Chemical Geology, 1984
It has been proposed that the degree of alteration of basic rocks, as quantified by alteration in... 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.
Springer Geology, 2015
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
Contributions to Mineralogy and Petrology
Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ... 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...
Geological Society, London, Memoirs, 2016
The majority of confirmed impact craters on Earth have been discovered on land. However, the incr... more The majority of confirmed impact craters on Earth have been discovered on land. However, the increased use of high-resolution, full-bottom-coverage seafloor mapping methods such as multibeam bathymetry have enabled the discovery of previously unknown subaqueous impact craters on continental margins and in large lakes. High-resolution bathymetric and sub-bottom profiler data collected south of the city of Sept-Îles in the northwestern Gulf of St Lawrence, eastern Canada (Fig. 1a), revealed a previously unreported circular structure of possible impact origin located 20 km off the mainland in water depths of 40-208 m (Fig. 1b, c) that had been overrun by the Laurentide Ice Sheet (Lajeunesse et al. 2013).
Canadian Journal of Earth Sciences, 1986
Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, ... 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...
Canadian Journal of Earth Sciences, 1981
The Sept Iles anorthosite complex is located in the Grenville (structural) Province of the Canadi... 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...
Canadian Journal of Earth Sciences, 1993
U–Pb zircon dating of the southwest lobe of the Havre-Saint-Pierre anorthosite intrusion indicate... 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.
Canadian Journal of Earth Sciences, 1985
High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence o... 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.
Canadian Journal of Earth Sciences, 1985
The Chatham–Grenville stock is an anorogenic multiple intrusion that shows a complete gradation f... 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, ...
A 35 mm square slice of Buzzard Coulee meteorite was cut with a wire-saw and polished. The brecci... more A 35 mm square slice of Buzzard Coulee meteorite was cut with a wire-saw and polished. The brecciated structure of the meteorite is evident, especially in the silicate matrix. The slice was further examined using a micro-XRF. Approximately 1 million spots in five images were mosaiced to give an overall resolution of 40 micrometres per pixel. 8-bit grey scales images were produced for many major and minor elements, however, the system is not very sensitive for elements lighter than magnesium. Elemental maps were adjusted for contrast and then assembled into three-colour composite images for further interpretation. The overall composition was kamacite = 10.9%; taenite = 0.23%; troilite = 3.7% with the remainder dominated by silicates. Maps of Cr, Cu, P and Ca reveal the presence of sparse grains of chromite, chalcopyrite and Ca-phosphate (merrilite?). Mineral distribution was heterogeneous throughout the slice and conformed to some extent to the fragments identified in the scanned image. The distribution of sulphides is particularly interesting and may reveal other fragments. In one part of the slice a foliation is clearly visible, revealed both by the orientation of flattened chondrules and metal grains. Adjoining chondrules are indented suggesting pressure solution during compaction. Hence, there seems to evidence of deformation during lithification, a normal process on earth but perhaps less expected on an asteroid.
American Mineralogist, 2011
Deformation of olivine in a volcanic context is poorly constrained, although deformed olivine is ... more Deformation of olivine in a volcanic context is poorly constrained, although deformed olivine is abundant in some volcanic rocks, and its presence is important for the definition of the magmatic history of volcanic edifices such as Kilauea Volcano, Hawaii. Deformed olivines at Kilauea originate in the lower crust; therefore, the classic approaches and interpretations applied to mantle-derived olivine are not applicable. Deformed olivine crystals from Kilauea lava samples were examined using an in situ XRD technique. Our results validate and refine optical observations of olivine deformation. We also confirm the presence of deformation and quantify it for olivine crystals of any size, even for small crystals (0.15 mm). There are significant correlations between deformation intensity (strainrelated mosaicity) and olivine composition and crystal size. Although this technique does not allow the simple estimation of the P-T conditions of deformation, crystal formation, or magmatic history, some constraints are provided herein. In particular we estimate the threshold degree of mosaicity, above which we consider that a crystal underwent deformation. In situ XRD is shown to be an easyto-use, fast, low-cost, non-destructive technique and is less ambiguous than optical microscopy. For crystals optically exhibiting subgrain formation, analysis of asterism by in situ XRD has been used to reconstruct the mosaic spread of the original grain, and thus its original strain condition prior to subgrain formation.