Henry Halls (UTM)

Emeritus Professor
University of Toronto
Department of Earth Sciences
University of Toronto at Mississauga

Tel.: 416-978-1581

Biography

After obtaining B.Sc. (Geology) and M.Sc. (Geophysics) degrees at the Universities of Sheffield and Durham (UK), I obtained my Ph.D. in 1970 in the Department of Geology at the University of Toronto, under the supervision of Gordon West, Department of Physics. The topic of my dissertation was The Geology and Geophysics of the Lake Superior Basin. I have been a faculty member at the University of Toronto in Mississauga since 1970, where I have held the rank of Emeritus Professor since 2010. My general field of research is the application of geophysical methods (gravity, magnetics and paleomagnetism) to the solution of geological problems, mainly involving major tectonic units of the Canadian shield. More recently, I have concentrated on the integrated paleomagnetic, geochronological and geochemical study of Precambrian dyke swarms worldwide in an effort to understand their origins and their use as links between dispersed Precambrian terranes. I have authored or co-authored over 90 refereed papers in internationally-recognized journals.

In 1985 I organized the first International Dyke Conference which brought together more than 100 scientists from 20 countries, the results of which were published as a Geological Association of Canada Special Paper 34 “Mafic Dyke Swarms” (Halls & Fahrig 1987). Since this inaugural meeting, International Dyke Swarm Conferences have been held approximately every five years. The sixth meeting (IDC6) was held February 4-7, 2010 in Varanasi, India, and a volume of papers presented at this meeting has been published by Springer Verlag (2011). The last meeting (ICD7) was held 18-20 August, 2016 in Beijing, China. The next meeting in Marrakesh, Morocco, will be held in 2020.

In 1988 I was elected the international leader of IGCP (International Geological Correlation Program) Project 257 on Mafic Dyke Swarms from which more than 30 publications including two books were produced. In the last five years about 30 dyke swarms from about 15 Precambrian cratons worldwide have been the subject of completed or ongoing studies by research groups from many countries including Canada, China, Australia, Finland, Russia, India, and Brazil. The last 10 years has seen a burgeoning of papers on dykes and particularly on the recognition of “giant radiating dyke swarms”. This term was first used in the title of a Special Session I convened at the Geological Association of Canada Annual Meeting in Toronto in 1991. The session entitled “Giant Radiating dyke swarms and mantle plumes” drew more than 100 participants (standing room only!) and has been an important influence on subsequent thinking.

Research Accomplishments

Mid-Continent Rift

The ~2000 km-long 1.1 Ga Mid-Continent Rift System is formed of Keweenawan volcanic and clastic sedimentary rocks that only outcrop around Lake Superior, being otherwise buried to the south under a thick Phanerozoic sedimentary cover. In the course of seismic, magnetic, gravity and paleomagnetic surveys, to understand the origin of this enigmatic feature, I have visited nearly all of the shoreline and major islands of Lake Superior, and in 1992 took part in a Johnson Sea-Link submersible dive on Superior shoal, in the centre of the lake, where glacially-scoured, vertical-walled canyons occur that are more than 200 metres deep (Manson & Halls 1991). Major results of my Lake Superior Research include:

A seismic refraction survey (Halls & West 1971) showed for the first time that friable Keweenawan sandstones floored most of the lake and that their excavation during the last Ice Age was responsible for the physiographic form of the present lake depression;
The discovery of the Slate Islands meteorite impact site, an early Paleozoic complex crater ~30 km across (Halls 1975; Halls & Grieve 1976) that includes detailed studies of shock remanence (Halls 1979) and of the effect of elastic wave anisotropy on the form and orientation of shatter cones (Stesky & Halls, 1983).
The demonstration that major reverse faults bounding the Keweenawan rift in western Lake Superior may join with reverse faults, revealed by gravity surveys, along the eastern Ontario shoreline (Manson & Halls 1997).
The demonstration that the asymmetry of the Keweenawan magnetic polarity reversal is not caused by a magnetic overprint (Palmer and Halls 1981; Palmer et al. 1981) and that the lower normal polarity unit as previously reported in the Powder Mill Group is the result of remagnetization (Palmer & Halls 1986). A review of Keweenawan paleomagnetic data attempted to make one of the earliest appraisals of the relative reliability of paleomagnetic data using more than 60 previously published pole positions (Halls & Pesonen 1982).

In addition to my research on the Mid-continent rift, I have been involved in applying geophysical methods to the further understanding of three other major features of Precambrian geology:

Kapuskasing Structural Zone

The ~ 1.9 Ga Kapuskasing Zone is a 500 km long, fault-bounded crustal uplift that slices across the Archean Superior Province from James Bay to Lake Superior. It was the subject of a Lithoprobe transect between 1985 and 1992. Three major discoveries have been made:

A 50 km long segment of the structure occurs to the southwest of the Chapleau block and is sinistrally offset about 20 km (Halls & Mound 1998;Halls & Zhang 2003),
Gravity data show that the western boundary fault is of reverse nature and dips eastward indicating that uplifted crustal blocks along the Zone have the form of pop-ups, necessitating a revision of previously-held ideas that the structure is the result of east-verging thrusting (Halls & Mound 1998; Halls & Zhang 1998; 2003; Nitescu & Halls 2002).
Paleomagnetic data on Paleoproterozoic dykes swarms (see below) show that the Kapuskasing Zone has been the locus of a major disconnect between the eastern and western halves of the Superior Province, the western part having rotated about 10-20° in an anticlockwise direction, relative to the eastern half, at approximately 1.9 Ga.

Sudbury Igneous Complex

A paleomagnetic study of Sudbury breccia around the northern half of the 1850 Ma Sudbury Igneous Complex shows a variation in paleomagnetic direction which is similar to that obtained by Morris (1980) from the basal norites and interpreted by him to reflect the deformation of an originally flatter igneous sheet. Our results also support the idea that the present basin is partly the result of folding, but also show that the folding has involved the surrounding basement (Szabo & Halls 2006).
A 100 km-long paleomagnetic traverse along Highway 144 produced paleomagnetic data from 2.45 Ga Matachewan dykes and Sudbury Breccia along a line approximately normal to the Sudbury Igneous Complex (Halls 2009), in order to test the extent of deformation in the surrounding basement during and subsequent to the formation of the Complex. The results showed basement tilting to the south underlying the North Range norites, out to a distance of about 10 km. The Matachewan dykes showed amphibolite metamorphism and a steep secondary magnetization out to a distance of about 50 km from the North Range norite, whereupon over a distance of a kilometer and in a region on strike with the Flack Lake fault to the west, the dykes showed fresh primary mineralogy and a shallow primary magnetization. The metamorphism was attributed to the Penokean orogen , as a result of fluids migrating into the Archean hinterland. The boundary could be followed farther west into the area of the Quirke Lake syncline. (Halls 2009).

Proterozoic dyke swarms

A major interest (Halls 1982; Halls and Fahrig 1987) is in the global characterization of Proterozoic dyke swarms in terms of their structure, petrography, geochemistry, absolute age and paleomagnetic signature, for the purposes of Precambrian continental reconstruction and for discovering their origin and mode of emplacement. Don Davis and Mike Hamilton of the Jack Satterly Geochronological Laboratory have played central roles in this work.

Grenville dyke swarm

A paleomagnetic study of the western end of the ~585 Ma Grenville dyke swarm shows that individual dykes are characterized by high coercivity and unblocking temperature magnetizations that can differ in direction by as much as 90°. Field tests including baked contact studies and the continuity of paleomagnetic direction along dyke strike, suggest that the magnetizations are primary. Precise U-Pb baddeleyite dating on these dykes indicates that changes in magnetization direction of ~90° occur in less than 4 million years, and their close temporal association with reversals of the axial dipole field suggest that certain dykes are recording an equatorial dipole field as a transitional field between opposite polarity states. The documented instability in the Earth’s field occurs less than 10 Myr before the first recorded appearance of macroscopic multi-cellular organisms on Earth, inviting speculation that an extended period of frequent magnetic reversals may play a part in faunal evolution. A paper concerning this work will be published in the journal Precambrian Research early in 2015.

Feldspar clouding in dykes

A study of Proterozoic diabase dyke swarms worldwide, shows that many of them exhibit a brown clouding of their feldspar, even when visible alteration of the rock is absent (Halls & Palmer 1990; Halls & Zhang 1995; 2003). This clouding is the consequence of precipitation of magnetite and other minerals within the feldspar as a result of slow cooling at depth. The intensity of the clouding increases with the amount of exhumation experienced by the dyke. In this way the relative degree of uplift of the 2.45 Ga Matachewan dyke swarm where it crosses the Kapuskasing Zone can be gauged and this together with changes in paleomagnetic polarity and feldspar clouding intensity has led to the discovery of a new fault-bounded block of the Zone (see coloured figures A and B).
Inside the Kapuskasing Zone the dykes have cloudy feldspar and an opposite paleomagnetic polarity to those outside with clear feldspar. In explanation, the dykes acquired a magnetization at the time of initial cooling at shallow crustal levels, but at greater depths where ambient crustal temperatures were higher and crustal cooling slower, magnetite, exsolving from feldspars to form the clouding, became a carrier of thermochemical magnetization that was not acquired until after a reversal of Earth’s magnetic field. Subsequent uplift exposed the oppositely magnetized roots of the dykes within the Kapauskasing Zone. The change in magnetic polarity and feldspar clouding level thus occurs across major faults defining the Kapuskasing Zone, and helps to map these faults even in areas where lithological changes in Archean gneisses are subtle (Halls & Palmer 1990; Halls & Zhang 2003). This novel method has potential application to other shields where Proterozoic dykes are abundant. It was applied to Matachewan dykes north of the Sudbury basin which revealed an increase in feldspar clouding intensity northwards from the northern margin of the Sudbury Igneous Complex to the Benny fault Zone, with a sudden drop in intensity to the north of the fault zone. This result suggested that the Archean crust was tilted to the south as a result of northward thrusting along the Benny fault zone, probably during the Penokean orogeny at about 1.8 Ga (Siddorn & Halls 2002).

The Florida dyke swarm, Uruguayan shield

The only opportunity to obtain a well-dated Precambrian pole position from the Uruguayan shield (whose original position with respect to the Brazilian shield is unknown) is to carry out a U-Pb and paleomagnetic study of the petrologically fresh Florida dyke swarm which covers the southern half of the shield. Although a precise U-Pb age of 1790 Ma was obtained, the primary nature of the characteristic remanent magnetization remains in doubt. The dyke swarm has a bimodal composition, and the more iron rich (and more magnetic) diabases are used in the monument stone industry. A susceptibility study suggests that a high resolution aeromagnetic survey could locate further potentially economic dykes and that it would be possible to obtain the width and depth to their unweathered upper surface (Halls et al. 2001).

The Taihang dyke swarm, North China Craton

A paleomagnetic and U-Pb geochronological study of the 1000km-long Taihang dyke swarm from the North China craton suggests that the North American, Siberian and North China cratons have remained more or less as they are now since 1.77 Ga. Intervening Phanerozoic orogens such as the Innuitian/Ellesmerian in northern Canada and the Mongol-Okhotsk between China and Siberia appear not to have had any major or long-term effect in changing the continental configuration (Halls et al. 2000).

This paper provided the first detailed U-Pb and paleomagnetic study of a dyke swarm in China and has formed a basis for all subsequent work on dyke swarms in China.

Dykes in the Dharwar craton, India

Feldspar clouding in east-trending 2.37 Ga diabase dykes of the Bangalore dykes (Halls et al. 2007a) has been documented in India where the degree of clouding increases southwards in the Dharwar craton indicating that the crust has been tilted northwards after dyke emplacement. The paleomagnetic direction of the dykes changes abruptly in the south where the brown feldpar clouding takes on a blacker appearance coinciding with the onset of a metamorphic front. It is concluded that magnetite in feldspars with brown clouding may record a primary magnetisation, but that feldspars with sooty clouding record a secondary magnetization. This result is important in granulite terranes such as the southern Dharwar charnockite belt, where the dykes are otherwise completely fresh (Halls et al., 2007b).

It has long been speculated (Halls 1982) that the Bangalore swarm, together with the NE-trending Karimnagar swarm to the north form a single giant radiating swarm (now known as the Dharwar swarm). This has been recently confirmed through U-Pb dating by Mike Hamilton, and that the entire swarm may have formed in as little as 3 million years! The dyke convergence direction suggests a plume centre somewhere to the west, unless the entire Dharwar craton has suffered “oroclinal” bending resulting in the swarm being linear (Kumar et al. 2012). In either case the dykes represent the earliest major swarm on the Dharwar craton and are orthogonal to the trend of the Archean supercrustal sequences, a general relation first noticed by Halls(1978). This orthogonal relationship and dyke emplacement about 200 Myr after cratonization occurs in other shield areas (Matachewan dykes in the Superior craton of Canada, Widgiemooltha dykes in the Yilgarn craton of Australia and at an earlier time the ~3.0 Ga Baadplaas dykes cutting the 3.2-3.4 Ga Barberton Mountain Land volcanics).

Proterozoic dykes of the Lake Superior region

An integrated study of the paleomagnetism, U-Pb geochronology and geochemistry of 2.125 to 2.067 Ga dykes around Lake Superior suggests that they are genetically related and the product of a long-lived plume with episodic magmatic activity over a 60 My time interval. After closure of the 1.1 Ga Kewenawan rift, the dykes converge towards a focal area approximately in the vicinity of Wisconsin. This focal area is assumed to mark the position of a plume at depth and its lack of major movement during the extended period of plume activity is compatible with paleomagnetic data (Halls, H.C., Davis, D.W., Stott, G. M. and Ernst, R.E. 2008).

Dykes as indicators of broad-scale deformation of the shield

The study of Matachewan dykes has helped define a new segment of crustal uplift along the Kapuskasing Zone, but has also shown that the Superior Province has been regionally tilted towards the south (see coloured figure C) because the dykes show a general southerly increase in deuteric alteration consistent with their emplacement in shallow, fractured and relatively wet crust. Along the southern edge of the Superior Province, the dykes are overlain by the basal members of the Huronian sequence comprising lava flows that yield a U-Pb age similar to that of the Matachewan swarm.
A paleomagnetic study of dykes of two different ages (~2.45, and 2.17 Ga) that occur on both sides of the Kapuskasing fault zone, suggest that the western half of the Superior Province has rotated counter-clockwise about 10 to 20° with respect to the eastern half, across the Kapuskasing zone (Bates & Halls 1991; Halls & Davis 2004, Evans and Halls 2010). An earlier study of Matachewan dykes was carried out along the eastern side of the Lake Superior Rift, where the dykes were found to depart from their usual verticality and to dip eastwards, often at angles as low as 50°. Paleomagnetic data on the dykes showed this was the result of a westward tilting of the crust, in full agreement with Keweenawan volcanics in the same region that are observed to dip westwards at similar angles (Halls and Shaw 1988). This result shows that the Keweenawan rift is not just the result of crustal foundering along boundary faults, but involves a major component of tilting of the surrounding basement.

Dykes as barriers to subsurface groundwater flow

The recognition of dykes acting as fluid barriers has importance in relation to water supply, mineral deposition, induced seismicity and to failure planes related to major volcanic landslides. A LANDSAT and aeromagnetic study was carried out in a region of the Zimbabwean craton where linear magnetic anomalies indicated the presence of dykes and where well-defined wet and dry seasons were accompanied by changes in vegetation. LANDSAT difference maps, which quantified these changes, were compared with the known dyke locations, and asymmetric linear patterns were discovered, with smaller differences being found on the interpreted drier, lea-side of the dyke. The method may be useful in locating potential areas of water supply in semi-arid Precambrian shield areas, especially those crossed by several orientations and ages of dykes as found in India, Tanzania and Australia (Bailey & Halls 2000).

A comparison of 720 Ma dykes between Thule, Greenland and Devon and Ellesmere islands, Canada

The U-Pb geochronology of dykes that lie on either side of the Davis and Nares straits that separate Canada from Greenland give ages of about 720 Ma, thereby allowing the dykes to be correlated with the larger Franklin dyke swarm. The dykes occur as two sub-swarms that appear offset about 200 km across the channel, the possible result of a major sinistral transcurrent fault (The Wegener fault) that intervenes, the geological evidence for which is generally negative as detailed correlations of Neoproterozoic sedimentary successions across the strait by previous workers suggest no fault. However, major Proterozoic swarms, where well exposed, such as the giant 1.27 Ga Mackenzie event show no offsets of subswarms as original emplacement features, or , like the 2.4 Ga Matachewan swarm, only show offsets caused by strike slip faulting. Paleomagnetic results from the Greenland dykes, when compared to those from the same swarm on Laurentia, lead to a reconstruction that involves rifting within the Arctic islands, and indirectly supports sinistral fault displacement along the Nares Strait (Denyszyn et al. 2009a,b; Denyszyn and Halls 2014).

Contributions in the fields of rock- and paleo-magnetism.

The often complex paleomagnetic signatures of Precambrian rocks have necessitated development of methods to separate magnetization components. My contributions to this topic have been in the analysis of converging circles of remagnetization (Halls 1976, 1978; Bailey and Halls 1984) and in the integrated analysis of graphical methods. In particular my interpretation of shock remanent magnetization on the Slate Islands impact is the only in-depth study of this rare kind of remanence (Halls 1979).

In 1990 a novel method was developed to measure the anisotropy of fluid permeability in sedimentary rocks. The magnetic susceptibility of a sample was first injected under vacuum with ferro-fluid (a suspension carrying sub-micron size magnetite particles) in order to render the sample magnetic, and then the anisotropy of magnetic susceptibility was measured on the saturated sample (Pfleiderer & Halls 1993, 1994).

In 1983 a large number of paleointensity determinations verified that inclination differences between normal and reverse polarity Keweenawan volcanics and dykes were the result of latitudinal drift of the North American continent (Pesonen & Halls 1983). More recently I was involved in the measurement of paleointensity using a unique microwave facility developed by Professor John Shaw and co-workers at the University of Liverpool. I measured chilled margin samples from Proterozoic dykes of several ages, all of which carried a single primary component of magnetization. The results showed that from about 2.45 to 2.1 Ga, Earth’s magnetic field was about one third of the present field intensity. The frequency of dyke swarm emplacement throughout earth history (about one every 50 million years) means that the method has potential to examine long-term variations in the geomagnetic field (Halls et al. 2004; McArdle et al. 2004).

Acknowledgements

I would like to emphasise and to recognize the key and sometimes leading roles that my publication co-authors have played as collaborators in the research described above. At the time when the work was done they included undergraduates (Kevin Burns and Jonathon Mound); graduate students (Debbie Hutchinson, Lauri Pesonen, Richard Ernst, Erik Shaw, Sebastian Pfleiderer, Matt Manson, Baoxing Zhang, James Siddorn, Bogdan Nitescu, Erika Szabo and Steve Denyszyn); Research Associate Alan Lovette, Post Doctoral Fellows (Monika Bailey, Martin Bates, Yongjian Zhai); Professional colleagues either within my own Department (Gordon West, Richard Bailey, Robert Stesky, Don Davis, Mike Hamilton) or at other institutions (Jorge Bossi, Ken Buchan, Nestor Campal, Walter Fahrig, Martin Gratton, Richard Grieve, John Hanes, Larry Heaman, Mimi Hill, Guiting Hou, Don Hunter, Anil Kumar, Nick McArdle, Satu Mertanen, Currie Palmer, William Phinney, Xianglin Qian, John Shaw, Greg Stott, Sinu Srinivasan and Mike Wingate).

Finally I would like to acknowledge David Ball (now at Queens University) who, as an undergraduate in ~1983 wrote an excellent paleomagnetic program for the DIGICO magnetometer incorporating averaging techniques, which has been used, with only minor subsequent modifications, almost since the inception of my paleomagnetic research.

My thanks to all!

Current Research Projects

Paleomagnetism of the River Valley anorthosite (with Alan Lovette)

Twenty paleomagnetic sites have been obtained from the 2.47 Ga River Valley anorthorsite. The anorthosite lies within the Grenville Province and is metamorphosed. The remanence is very stable and not dissimilar to the shallow down to the SE component found in Grenville dykes. The remanence is best preserved in a dark anorthosite that owes its colour to cloudy feldspar.

A further 10 sites have been obtained in metamorphosed Sudbury dykes and Nipissing intrusions, and a similar direction has been obtained.

The study is important because units of different ages show the shallow down SE component, which either suggests that Laurentia did not move for over 500 million years or that everything has been pervasively overprinted by the effects of alkaline magmatism after intrusion of the Grenville dykes.

Research Facilities

The paleomagnetic laboratory is housed in a non-magnetic hut in a secluded and scenic wooded setting at the University of Toronto, Mississauga (UTM). It houses a DIGICO spinner magnetometer that has been electronically modified to include an averaging method that allows smooth demagnetization paths at higher AF demagnetization steps when the percent of remanence remaining falls below ~10% of the initial value. The laboratory has Schonstedt AF and thermal demagnetizers, a Sapphire thermomagnetic curve generator and a large inventory of oriented diabase dyke samples from Proterozoic swarms worldwide.

As of May 2019 the lab has been decommissioned with most equipment now being in the custody of Dr. Phil McCausland of Western University. He has also received unused cores of a number of dyke swarms (Matachewan, Marathon, Kapuskasing, Grenville, Florida, Taihang, Dharwar, Melville Bugt, Franklin) which are stored at Western. They can be accessed by contacting Phil at pmccausl@uwo.ca

Recent Publications

2021

Simon J. Lloyd, Andrew Biggin, Henry Halls and Mimi J. Hill. 2021. First paleointensity data from the cryogenian and their potential implications for inner core nucleation age. Geophysical J. International, 226, Issue 1, pp. 66-77.

Thallner, D, Biggin, A.C and Halls, H.C. 2021. An extended period of extremely weak geomagnetic field suggested by paleointensities from the Ediacaran Grenville dykes (SE Canada). Earth Planet. Sci. Lett. v. 568, 15th August 2021, 117025.

2019

Westgate, J.A., Woldegabriel, G., Halls, H.C., Bray, C.J., Barendregt, R.W., Pearce, N.J.G., Sarna-Wojcicki, A.M., Gorton, M.P., Kelley, R.E. and Schultz-Fellenz, E. 2019. Quaternary tephra from the Valles Caldera in the volcanic field of the Jemenez Mountains of New Mexico identified in western Canada. Quaternary Research 91, Issue 2, pp. 813-828.

2015

Halls, H.C. 2015. Paleomagnetic evidence for ~4000km of crustal shortening across the 1Ga Grenville orogen of North America. Geology, 43, 1051-1054

Halls, H.C., Lovette, A., Hamilton, M.A., Söderlund, U. 2015. A paleomagnetic and U-Pb geochronology study of the western end of the Grenville dyke swarm: rapid changes in paleomagnetic field direction at ca. 585 Ma related to polarity reversals? Precambrian Research, 257,137-166.

2014

Denyszyn, S.W. and Halls, H.C. 2014. Comment on “A new model for the Paleogene motion of Greenland relative to North America: Plate reconstructions of the Davis Strait and Nares Strait regions between Canada and Greenland” by G.N. Oakey and J.A. Chalmers. J. Geophys. Res. Solid Earth 119, doi:10.1002/2013JB010323.

Halls, H.C. 2014. Crustal shortening during the Paleoproterozoic: can it be accommodated by paleomagnetic data? Precambrian Research 244, 42-52.

Salminen, J., Halls, H.C., Mertanen, S., Pesonen, L.J., Vuollo, J., Söderlund, U. 2014. Paleomagnetic and geochronological studies on Paleoproterozoic diabase dykes of Karelia, East Finland – Key for testing the Superia supercontinent. Precambrian Research 244, 87-99

2013

Bunger, Andrew P., Menand, Thierry, Cruden, Alexander, Zhang, Li, Halls, Henry. 2013. Analytical predictions for a natural spacing within dyke swarms. Earth and Planetary Science Letters 375, 270-279.

Previous years (2012-2006 only)

Kumar, A., Hamilton, M.A. and Halls, H.C. 2012 A paleoproterozoic giant radiating dyke swarm in the Dharwar Craton, southern India. Geochem. Geophys. Geosyst. doi:1029/2011GC003926.

Halls, H.C., Hamilton, M.A. and Denyszyn, S.W. 2011. The Melville Bugt dyke swarm of Greenland: a connection to the 1.5-1.6 Ga Fennoscandian Rapakivi granite province? In Dyke Swarms: Keys for Geodynamic Interpretation. Ed. R.K. Srivastava, Pub. Springer-Verlag, Berlin, 605 p., Chapter 27, pp. 509-535. Proceedings of the 6^th International Dyke Symposium, Varanasi, India, February 4 to 7, 2010.

Evans, D.A.D. and Halls, H.C. 2010. Restoring Proterozoic deformation within the Superior Craton. Precambrian Research 183: 474-489.

Hollings, P., Smyk, M., Halls, H.C. and Heaman L.M. 2010. The geochemistry, geochronology and paleomagnetism of dikes and sills associated with the Mesoproterozoic Midcontinent Rift of Northwestern Ontario. Precambrian Research 183: 553-571.

Halls, H.C. 2010. Regional dyke swarms of the Reguibat Shield, Mauritania and Morocco: plumbing systems for Precambrian Large Igneous Provinces. February 2010 LIP of the Month in www.largeigneousprovinces.org

Halls, H. C. 2009. A 100 km-long paleomagnetic traverse radial to the Sudbury Structure,Canada and its bearing on Proterozoic deformation and metamorphism of the surrounding basement. Tectonophysics 474: 493-506.

Denyszyn S. W., Davis D. W., Halls H. C. 2009. Paleomagnetism and U-Pb geochronology of the Clarence Head dykes, Arctic Canada: Orthogonal emplacement of mafic dykes in a large igneous province. Canadian Journal of Earth Sciences 46:155-167.

Denyszyn S. W., Halls H. C., Davis D. W., Evans, D. A. D. 2009. Paleomagnetism and U-Pb geochronology of Franklin dykes in High Arctic Canada and Greenland: A revised age and paleomagnetic pole constraining block rotations in the Nares Strait region. Canadian Journal of Earth Sciences 46: 689-705.

Halls, H.C. 2008. The Importance of integrating paleomagnetic studies of Proterozoic dykes with U-Pb Geochronology and Geochemistry. In: Indian Dykes, Eds. Srivastava, R.K., Sivaji, C., and Rao, N.V.C. Narosa Publishing House Pvt. Ltd., New Delhi, India, pp. 1-22.

H.C. Halls, D.W. Davis, G.M. Stott, R.E. Ernst and M.A. Hamilton. 2008. The Paleoproterozoic Marathon Large Igneous Province: new evidence for a 2.1 Ga long-lived mantle plume event along the southern margin of the North American Superior Province. Precambrian Research 162: 327-353

H.C. Halls, A. Kumar, R. Srinivasan and M.A. Hamilton. 2007. Paleomagnetism and U–Pb geochronology of easterly trending dykes in the Dharwar craton, India: feldspar clouding, radiating dyke swarms and the position of India at 2.37 Ga, Precambrian Research 155: 47-68.

Szabo, E. and Halls, H.C. 2006. Deformation of the Sudbury Structure: Paleomagnetic evidence from the Sudbury breccia. Precambrian Research 150: 27-48.

Denyszyn, S.W., Halls, H.C. and Davis, D.W. 2006. A paleomagnetic, geochemical and U-Pb geochronological comparison of the Thule (Greenland) and Devon Island (Canada) dyke swarms and its relevance to the Nares Strait problem. Polarforschung 74: 63-75.

References cited in text

Hamilton , M., Davis , D.W., Buchan, K.L. and Halls, H.C. 2002. New U-Pb geochronological data from the Marathon dyke swarm, Ontario , and its paleomagnetic significance. Current Research 2002-F6, Geological Survey of Canada , 8 p.

Nitescu, B. and Halls, H.C. 2002. A gravity profile across southern Saganash Lake fault: implications for the origin of the Kapuskasing Structural Zone. Canadian Journal of Earth Sciences 39: 469-480.

Siddorn, J. and Halls,H.C. 2002. Variation in plagioclase clouding intensity in Matachewan dykes: evidence for the exhumation history of the northern margin of the Sudbury Igneous Complex. Canadian Journal of Earth Sciences 39: 933-942.

Bailey, R.C. and Halls, H.C. 1984. Estimate of confidence in paleomagnetic directions derived from mixed magnetization circle and direct observational data. Journal of Geophysics 54: 174-182.

Bailey, M. E. and Halls, H.C. 2000. Use of remote sensing data to locate groundwater trappedby dykes in Precambrian basement terrains. Canadian J. Remote Sensing 26: 111-120.

Bates, M.P. and Halls, H.C. 1991. Broad-scale deformation of the central Superior Province revealed by paleomagnetism of the 2.45 Ga Matachewan dyke swarm. Canadian Journal of Earth Sciences 28: 1780-1796.

Halls, H.C. 1975. Shock-induced remanent magnetization in Late Precambrian rocks from Lake Superior, Nature 225: 692-695.

Halls, H.C., 1976. A least squares method to find a remanence direction from converging remagnetization circles. Geophys. Jour. R. astr. Soc. 45: 297-304.

Halls, H.C., 1978. The use of converging remagnetization circles in paleo-magnetism. Phys. Earth Planet. Interiors 16: 1-11.

Halls, H.C., 1979, The Slate Islands meteorite impact site: a study of shock remanent magnetization. Geophys. Jour.R. astr. Soc. 59: 553-591.

Halls, H.C., 1982. The importance and potential of mafic dyke swarms in studies of geodynamic processes. Geoscience Canada 9: 145-154.

Halls, H.C. 1991. The Matachewan dyke swarm, Canada: an early Proterozoic magnetic field reversal. Earth and Planetary Science Letters 105: 279-292.

Halls, H.C. and West, G.F. 1971. A seismic refraction survey in Lake Superior. Canadian Journal of Earth Sciences 8: 610-630.

Halls, H.C., and Grieve, R.A.F. 1976. The Slate Islands: a probable complex meteorite impact structure in Lake Superior. Canadian Journal of Earth Sciences 13: 1301-1309

Halls, H.C. and Palmer,H.C. 1981. Remagnetization in Keweenawan rocks, Part II: lava flows within the Copper Harbor Conglomerate, Michigan. Canadian Journal of Earth Sciences 18:1395-1408.

Halls, H.C. and Pesonen,L.J. 1982. Paleomagnetism of Keweenawan rocks. In Geology and Tectonics of the Lake Superior Basin, Geological Society of America, Memoir 156:173-203.

Halls, H.C. and W.F. Fahrig, Eds. 1987. Mafic Dyke Swarms, Geological Association of Canada, Special Paper 34, with Introduction and Concluding Remarks by H.C. Halls. 503 p.

Halls, H.C. and Palmer,H.C. 1990. The Tectonic relationship of two early Proterozoic dyke swarms to the Kapuskasing Structural Zone: a Paleomagnetic and Petrographic study. Canadian Journal of Earth Sciences 27: 87-103.

Halls, H.C. and Zhang, B., 1995. Tectonic implications of clouded feldspar in Proterozoic mafic dykes. In Dyke Swarms of Peninsular India, edited by Devaraju, T.C., Geological Society of India, Memoir 33: 65- 80.

Halls, H.C. and Zhang, B. 1998. Uplift structure of the southern Kapuskasing zone from 2.45 Ga dike swarm displacement. Geology 26: 67-70.

Halls, H.C. and Mound, J. 1998. The McEwan Lake fault: gravity evidence for a new structural element of the Kapuskasing Zone. Canadian Journal of Earth Sciences35: 696-701.

Halls, H.C., Li, J., Davis, D., Hou, G., Zhang, B. and Qian, X. 2000. A precisely dated Proterozoic palaeomagnetic pole from the North China craton, and its relevance to palaeocontinetal reconstruction. Geophysical Journal International 143: 1-24.

Halls, H.C., Campal, N., Davis , D.W. and Bossi, J. 2001. Magnetic studies and U-Pb geochronology of the Uruguayan dyke swarm, Rio de la Plata craton, Uruguay : paleomagnetic and economic implications. South American Journal of Earth Sciences 14: 349-361.

Halls, H.C., McArdle, N.J., Gratton, M.N., Hill, M.J. and Shaw, J. 2004. Microwave Paleointensities from dyke chilled margins: a way to obtain long-term variations in geodynamo intensity for the last three billion years. Physics of the Earth and Planetary Interiors 147: 183-195.

McArdle, N.J., Halls, H.C. and Shaw, J. 2004. Rock magnetic studies and a comparison between microwave and Thellier paleointensities for Canadian Precambrian dykes. Physics of the Earth and Planetary Interiors 147: 247-254.

Halls, H.C. and Davis, D.W. 2004. Paleomagnetism and U-Pb geochronology of the 2.17 Ga Biscotasing dyke swarm, Ontario, Canada: evidence for vertical-axis crustal rotation across the Kapuskasing Zone. Canadian Journal of Earth Sciences 41: 255- 269.

Manson, M.L. and Halls, H.C. 1991. A submersible dive on Superior Shoal, central Lake Superior. Canadian Journal of Earth Sciences 28: 145-150.

Manson, M.L. and Halls, H.C. 1994. Geology and Geophysics of post-Keweenawan faults in the eastern Lake Superior region. Canadian Journal of Earth Sciences 31: 640-651.

Manson, M.L. and Halls, H.C. 1997. Proterozoic reactivation of the southern Superior Province and its role in the evolution of the Midcontinent Rift., Canadian Journal of Earth Sciences 34: 562-575.

Palmer, H.C., Halls, H.C. and Pesonen,L.J. 1981. Remagnetization in Keweenawan rocks. Part I: conglomerates. Canadian Journal of Earth Sciences 18: 599-618.

Palmer, H.C. and Halls, H.C. 1986. Paleomagnetism of the Powder Mill Group, Michigan Wisconsin: A re-assessment of the Logan Loop. Journal Geophysical Research 91: 11571- 11580.

Pesonen, L.J. and Halls, H.C. 1983. Geomagnetic field intensity and reversal asymmetry in late Precambrian Keweenawan rocks. Geophysical Journal of the Royal Astr. Society 73: 241-270.

Pfleiderer, S. and Halls, H.C. 1994. Magnetic pore fabric analysis: a rapid way to estimate permeability anisotropy. Geophysical Journal International 116: 39-45.

Pfleiderer, S. and Halls, H.C. 1993. Magnetic pore fabric analysis: Verification through image autocorrelation. Journal of Geophysical Research 98: 4311-4316.

Phinney, Wm. C. and Halls, H.C. 2001. Petrogenesis of the Early Proterozoic Matachewan dyke swarm, Canada , and implications for magma emplacement and subsequent deformation. Canadian Journal of Earth Sciences 38: 1541-1563.

Stesky, R.M. and Halls, H.C. 1983. Structural analysis of shatter cones from the Slate Islands, northern Lake Superior. Canadian Journal of Earth Sciences 20: 1-18.

Other relevant publications not cited in text

Bates, M.P. and Halls, H.C. 1991. Paleomagnetism of dykes from the Groundhog River Block, northern Ontario: implications for the uplift history of the Kapuskasing Structural Zone. Canadian Journal of Earth Sciences 28: 1424-1428.

Halls, H.C. 1998. Comment on “Global mafic magmatism at 2.5 Ga: remnants of an ancient large igneous province? by L.M. Heaman, Geology 26: 93-94.

Halls, H.C. 1997. Comment on “New Constraints on the Slate Islands impact structure” by Sharpton et al. Geology 25: 666.

Halls, H.C. and Hanes, J.A. 1999. Paleomagnetism, anisotropy of magnetic susceptibility and argon-argon geochronology of the Clearwater Anorthosite, Saskatchewan, Canada, Tectonophysics 214:1-15.

Halls, H.C.and Heaman, L.M. 2000. The Paleomagnetic significance of new U-Pb age data from the Molson dyke swarm, Cauchon Lake area, Manitoba. Canadian Journal of Earth Sciences 37: 957-966.

Halls, H.C. and Wingate, M.T.D. 2001. Paleomagnetic pole from the Yilgarn (YB) dykes of Western Australia : no longer relevant to Rodinia reconstructions. Earth and Planetary Science Letters 187: 39-53.

Halls, H.C., Palmer, H.C., Bates, M.P. and Phinney, Wm.C. 1994. Constraints on the nature of the Kapuskasing zone from the study of Proterozoic dyke swarms. Canadian Journal of Earth Sciences 31: 1182-1196.

Hunter, D.R. and Halls, H.C.. 1992. A geochemical study of a Precambrian Mafic Dyke Swarm, eastern Transvaal, South Africa. Journal of African Earth Sciences 15: 153-168.

Mertanen, S., Halls, H.C., Vuollo, J., Pesonen, L.J. and Stepanov, V.S. 1999.
Paleomagnetism of 2.44 Ga mafic dykes in Russian Karelia, eastern Fennoscandian Shield: implications for continental reconstructions. Precambrian Research 98: 197-221.

Zhai, Y., Halls, H.C. and Bates, M.P., 1994. Multiple episodes of dike emplacement along the northwestern margin of the Superior Province, Manitoba. Journal of Geophysical Research 99: 21717-21732.