Nickel Irruptive Research Articles

Clarification to “The Sudbury structure: Controversial or misunderstood?”

Journal of Geophysical Research: PlanetsVolume 98, Issue E11 p. 20903-20904 CorrectionsFree Access Clarification to “The Sudbury structure: Controversial or misunderstood?” R. A. F. Grieve, R. A. F. GrieveSearch for more papers by this authorD. Stöffler, D. StöfflerSearch for more papers by this authorA. Deutsch, A. DeutschSearch for more papers by this author R. A. F. Grieve, R. A. F. GrieveSearch for more papers by this authorD. Stöffler, D. StöfflerSearch for more papers by this authorA. Deutsch, A. DeutschSearch for more papers by this author First published: 25 November 1993 https://doi.org/10.1029/93JE02139Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References Deutsch, A., P. Brockmeyer, D. Buhl, Sudbury again: New and old isotope data, Lunar Planet Sci. Conf., XXI, 282– 283, 1990. Fairbairn, H. W., P. M. Hurley, W. H. Pinson, Rb-Sr whole rock age of the Sudbury 1opolith and basin sediments, Can. J. Earth Sci., 5, 707– 714, 1968. Gibbins, W. A., R. H. McNutt, Rubidium-Strontium mineral ages and polymetamorphism at Sudbury, Ontario: The age of the Sudbury nickel irruptive and the Murray Granite, Can. J. Earth Sci., 12, 1990– 003, 1975. Grieve, R. A. F., R. J. Floran, The Manicouagan impact melt, Quebec, 2, Chemical interrelations with basement and formational processes, J. Geophys. Res., 83, 2761– 2771, 1978. Stöckelmann, D., W. U. Reimold, The HMX mixing calculation program, Math. Geol., 21, 853– 860, 1989. Wright, T. L., P. C. Doherty, A linear programming and least squares computer method for solving petrologic mixing problems, Geol. Soc. Am. Bull., 81, 1995– 2008, 1970. Citing Literature Volume98, IssueE1125 November 1993Pages 20903-20904 ReferencesRelatedInformation

Regional cross section of the Southern Province adjacent to Lake Huron, Ontario: implications for the tectonic significance of the Murray Fault Zone

The Southern Province in the Lake Huron area of Ontario, and the Penokean Fold Belt of Minnesota, Wisconsin, and Michigan have the earmarks of a collisional orogen. The Huronian Supergroup, a southerly facing passive margin sequence, was deposited during early Aphebian (Early Proterozoic) crustal stretching (and ocean basin formation?) along the southern margin of the Superior Province Archean craton. It accumulated as four unconformity-bounded, northerly tapering, onlapping clastic wedges (megacycles). The thickness and facies variations reflect syndepositional down-to-the-basin (south) normal faulting that controlled the accumulation and preservation of the lower three Huronian megacycles. These are overlapped northward by the youngest megacycle, an extensive sheet of clastic sediments recording post-stretching regional subsidence of the cratonic margin due to cooling and thermal contraction. Soft-sediment folds in the rocks of the youngest megaycycle to the extreme south probably indicate southward slumping into an adjacent basin. Nipissing diabase instrusions, 2100 Ma old, cut Huronian strata and soft-sediment folds.An enigmatic episode of compressional deformation is dated by 2333 Ma old plutons. During the first ductile (penetrative cleavage and peak metamorphism) phase of the Penokean Orogeny (ca. 1900 Ma), the thicker part of the Huronian supracrustal wedge was overridden and depressed to mid-crustal levels, presumably because it was overridden by an allochthonous terrane, the remainder of which is postulated to lie south of the Manitoulin Island Discontinuity. The early down-to-the-basin normal faults were reactivated and became the loci of north-verging, listric reverse faults. The thick wedge of Huronian rocks south of the Murray Fault Zone, which was deformed and metamorphosed as it was carried down to mid-crustal levels, subsequently was thrust northward over a thinner sequence of Huronian rocks that apparently was never deeply buried. Concurrently, the edge of the Superior craton and its cover of Huronian deposits were compressed as thrusting propagated northward and eventually deformed the 1850 Ma old Sudbury Nickel Irruptive. Structures that formed in the thick part of the wedge during the ductile deformation were rotated during the thrusting to their present near-vertical position. Late or post-Penokean brittle deformation marked by conjugate small strike-slip faults reflects continued or renewed north–south compresssion in an isostatically rising foldbelt, and post-Penokean right-lateral strike slip along the Murray Fault Zone is probably related to northwestward compression during the Grenville (approx. 1000 Ma) Orogeny.

On comparative probabilities for normal confidence intervals by pearson's Types III and VII, and the Edgeworth series models for biotite data

Biotite crystals were counted in standard thin sections which originated from the diamond drill core of the mafic norite formation at Strathcona mine, Sudbury Nickel Irruptive. Pearson's method of moments is suitable to fit Types III and VII to the biotite data and its log10transformation values, as the number of samples (thin sections)is large (351).Based on the two models and the Edgeworth series (utilizing the log10data)probability values p,that biotite occurrences lie in the interval “mean ± Z ⋅standard deviations” is derived. Results are compared with the usual normal probability values pZcorresponding to Zand it is shown that the Edgeworth series generated the largest pvalues for intervals when pZvalues are large; for intermediate or lower pZs. Types VII and III models produced larger ps, relative to the Normal and the Edgeworth series.

Two high precision U–Pb zircon ages for the Sudbury Nickel Irruptive

Two independent U–Pb zircon ages were measured using norite samples from the North and South Ranges of the Sudbury Nickel Irruptive. Ages of [Formula: see text] and [Formula: see text] Ma were obtained with a probability of fit within experimental error of 51 and 57%, respectively.Previous determinations by the Rb–Sr whole-rock method gave ages between about 1700 and 2000 Ma, with errors of the order of ± 100 Ma. The difference in precision is inherent in the two methods: zircons from the norite are highly radiogenic and almost concordant whereas Rb–Sr whole-rock ages are determined by very small increments in radiogenic 87Sr.The two zircon ages have completely different discordia so that all simple models for lead loss by continuous diffusion can be excluded.

The Creighton pluton, Ontario: an unusual example of a forcefully emplaced intrusion: Discussion

Dutch (1979) states that pre-Sudbury breccia tectonic structures are confined to the immediate vicinity of the Creighton pluton and are not present in the country rocks in areas removed from this body. His contention that this early deformation is 1 attributable to forceful (diapiric) emplacement of the pluton is based in large part on the assumptions that: (1) the pluton was emplaced as a diapir capable of generating and transmitting the necessary stress; and (2) there was no deformation of regional significance prior to the formation of the Sudbury I breccia (and, by inference, the associated Sudbury : Nickel Irruptive and Whitewater Group). The Creighton pluton was forcefully emplaced into its host rocks, but this probably occurred in connection with a tectono-metamorphic event of regional significance. The pluton does not display many of the features characteristic of diapirs, such as outward-plunging lineations, a rim syncline, or development of contact shear and mylonite zones (Stephannson 1977). It does contain abundant, rotated country-rock inclusions. The contacts between the granite and the inclusions are generally sharp and unsheared and many inclusions display metamorphic reaction rims indicating lack of postsolidification movement (see Card 1968, photo 7, page 15). Numerous granite dykes and apophyses cut the inclusions and extend into the country rocks. Agmatitic contact zones of foliated countryrock inclusions in foliated granite are present (Card 1978a). These features, along with its porphyritic texture and restricted composition indicate that the Creighton pluton was emplaced as a magma, primarily by a block-stoping mechanism, rather than as a diapir. The structural patterns observed by Dutch (closed foliation loop in an inclusion, parallelism of foliation to contacts, etc.) are probably ascribable to the combined effects of preintrusion deformation of the country rocks, magi matic (crystal mush) Row, and later, superimposed deformation that has affected the pluton, its inclusions, and the country rocks (Card 1978~). In stating that there was no deformation of regional significance prior to the formation of the Sudbury breccia (and hence no pre-breccia tectonic structures in areas removed from the Creighton pluton), Dutch follows Brocoum and Dalziel's (1974) contention that the Sudbury Structure and the adjacent Southern and Grenville Provinces were affected by a single, post-Nickel Irruptive tectonometamorphic event. Brocoum and Dalziel's hypothesis is untenable for a number of reasons, including the following: (1) There is geological, geochronological, and paleomagnetic evidence for a regional event involving deformation, metamorphism, and plutonism prior to emplacement of the Nipissing Diabase some 2150 Ma ago (Card 1968; Church and Young 1972; Van Schmus 1976; Morris 1977). Indeed, emplacement of the Creighton pluton some 2200 Ma ago is part of this event. (2) The available geochronological data indicate that major metamorphism of the Huronian occurred about 1900 Ma ago (Fairbairn et al. 1969; Van Schmus 1976) prior to the formation of the Sudbury breccia and emplacement of the Nickel Irruptive some 1840 Ma ago (Krogh and Davis 1974). Huronian rocks, both regionally and adjacent to the Nickel Irruptive, have metamorphic mineral assemblages and structural elements that are not present in the Nickel Irruptive or the Whitewater Group. Huronian rocks adjacent to the Nickel Irruptive have mineral assemblages diagnostic of the amphibolite facies. The Nickel Irruptive and the Whitewater Group, in contrast, display low greenschist facies assemblages (Card 1978b). Regionally, the Huronian rocks display several generations of major and minor tectonic struc-

Rare earth elements in the Sudbury Nickel Irruptive; comparison with layered gabbros and implications for nickel irruptive petrogenesis

The rare earth element content of rocks from the Sudbury Nickel Irruptive has been determined by neutron activation analysis. The Irruptive rocks are characterized by high absolute rare earth element contents and chondrite-normalized rare earth element fractionation patterns which show strong enrichment of light, relative to heavy rare earth elements. Correlative rock units from the north and south ranges have very similar chondrite-normalized rare earth element fractionation patterns. Micropegmatites and norites are characterized by negative and positive Eu anomalies, respectively, whereas border norites and oxide-rich gabbros lack prominent Eu anomalies.The Irruptive border norites are considered to have crystallized as a relatively closed system and their rare earth element fractionation patterns are regarded as representative of the parental Irruptive magma. The mirror-image Eu anomaly characteristics of the micropegmatite and norite and the likelihood that they arise from a nonanomalous parental magma indicate that these rocks are comagmatic and that they are related by gravitational fractional crystallization processes. The norites represent cumulates and the oxide-rich gabbros are transitional rocks with micropegmatites crystallizing from a residual liquid.Mass balance considerations based on Eu anomaly characteristics suggest that a micropegmatite to gabbro proportion of 1:3 should apply to the Irruptive as a whole rather than the observed outcrop proportions of 1:1 or greater. A funnel-shaped geometry for the Irruptive is inferred from these considerations.Compared to other continental basic rocks the Sudbury Irruptive has much more fractionated rare earth element patterns and generally higher total rare earth element contents. These properties together with the siliceous nature of the Irruptive rocks suggest that mixing of a silicic component of high La/Yb ratio with a normal basaltic melt may be responsible for the distinctive rare earth element characteristics of the Irruptive magma. Further, the Eu anomaly properties are most readily accounted for if mixing occurred prior to intrusion of the Irruptive magma to its present site, so that initial rare earth element characteristics are represented by the border norites and rare earth element properties of the main rock units developed by fractional crystallization in a substantially closed system.

Geochronologic investigations of the Sudbury Nickel Irruptive and the Superior Province granites north of Sudbury

RbSr ( λ Rb = 1.39 × 10 −11 yr −1) and U-Pb ( λ 238 = 1.54 × 10 −10 yr −1, λ235 = 9.72 × 10 −10 yr −1 ) measurements were undertaken in the Sudbury area, Sudbury, Ontario to determine the ages of the Sudbury Nickel Irruptive, Superior Province granites north of Sudbury, Sudbury Breccia and subsequent metamorphism. The Sudbury Nickel Irruptive norite whole rock Rb-Sr data yield an age of 1883 ± 136 Myr ( I.R. = 0.7071 ± 0.0005 ; all results quoted at 2π level) while the Nickel Irruptive micropegmatite Rb-Sr system has been disturbed and does not yield an isochron. A plagioclase-whole rock pair from the norite near the norite-micropegmatite transition yields an age of 1866 Myr, which when taken in conjunction with field ( Stevenson and Colgrove, 1968) and geochemical ( Naldrett et al., 1970, 1972) data does not support the conclusion of gibbins and McNurr (1972) that the micropegmatite is a later intrusion rather than a differentiate of the magma which produced the norite. Rb-Sr studies of the Superior Province granites north of Sudbury yield an age of 2698 ± 162 Myr ( I.R. = 0.7019 ± 0.0012 ). U-Pb zircon studies of these granites and granitic clasts within the Sudbury Breccia yield an age of 2.71 ± 0.05 Byr and suggest the breccia granitic clasts were derived from the Superior Province granites. The granitic rocks ~150 km north of Sudbury have been undisturbed for ~ 2.6 Byr based on Rb-Sr mineral studies, whereas the granites and Sudbury Breccia within ~ 15 km of the Nickel Irruptive, as well as the Sudbury norite at the perimeter of the Irruptive have been disturbed by the Penokean Orogeny 1.7–1.75 Byr ago. The Penokean event appears to have overprinted isotopic evidence of the Sudbury impact event at least in the area studied.

Additional note on the origin of the Sudbury structure

It has been suggested that the Sudbury Basin could be compared with the Brent meteorite impact crater and that Sudbury may also have developed a relatively flat crater floor at a very early stage. More recent paleomagnetic interpretations appear to fit an original, subhorizontal, sill-like form for the Nickel Irruptive at Sudbury. These suggestions in turn permit formulation of a more satisfying model for the early stages of Sudbury basin evolution.

The Age of the Sudbury Nickel Irruptive and the Murray Granite

Whole-rock samples of norite from the North and South Ranges of the Sudbury Irruptive yield a rubidium strontium isochron of 1956 ± 98 Ma age and (87Sr/86Sr)o = 0.7063 (λ87Rb = 1.39 × 10−11 a−1). Five samples of ore bearing 'sub-layer' from the South Range are compatible with this age. Four new determinations of South Range and six published analyses of North Range micropegmatite define an isochron of age = 1680 ± 30 Ma with (87Sr/86Sr)o = 0.708.The norite age is believed to represent the 'Sudbury event', a local event marked by the development of shock metamorphism and intrusion of the nickel irruptive. The 1680 Ma micropegmatite age is believed to be secondary and related to greenschist-facies metamorphism in the center of the Sudbury Basin during the Penokean Orogeny. Evidence supporting a later separate intrusion of granophyre-rich micropegmatite suggests that the time of this intrusion was relatively soon after the norite rather than 1680 Ma ago.Analyses of Murray granite samples indicate a pre-norite age of 2260 Ma. Most of the Murray granite shows evidence of later metamorphic events including the Sudbury event. Late (post-norite and post-Murray granite) granitic dikes (i.e., the Murray offshoots) intrude the norite near the Murray granite. These and other smaller granitic dikes appear to have formed 1700 to 1800 Ma ago. The origin of these dikes remains problematical.

Petrology of the upper irruptive rocks, Sudbury, Ontario

The upper part of the Sudbury Nickel Irruptive, referred to locally as the micropegmatite, is recognized as consisting of two distinctive rock types. One is granophyre-rich (the granophyric micropegmatite) and the other is rich in plagioclase (referred to as the plagioclase-rich rock). Field observations suggest that the granophyric micropegmatite intrudes and engulfs the plagioclase-rich rock. Modally the latter rock is distinguished from the former by its higher plagioclase and ferromagnesian mineral content; it resembles the upper part of the oxide-rich gabbro, a unit that immediately overlies the norite of the Irruptive.Augite of the plagioclase-rich rock is MgO-rich in comparison with that of the granophyric micropegmatite and has FeO:(FeO + MgO) atomic ratios similar to those in the oxide-rich gabbros and upper norite. Its CaO content, however, is higher than that in the norite and closer to that in the oxide-rich gabbro. Whole rock chemical data indicate that the plagioclase-rich rock is similar to the upper part of the oxide-rich gabbro in the normative anorthite content of its plagioclase and in total Na 2 O, K 2 O, and CaO.It is concluded that the plagioclase-rich rock is a phase of the upper part of the oxide-rich gabbro which was split off from the remainder of this unit by a later injection of granophyric micropegmatite. This micropegmatite is thought to be an extreme differentiate of the Irruptive that collected at its top, toward the center of the structure.

Magnetite and Ilmenite in the Sudbury Nickel Irruptive

Magnetite and ilmenite occur throughout the Sudbury Nickel Irruptive. The magnetite almost invariably contains oriented lamellae of ilmenite and the ilmenite often contains lamellae of oxide magnetite and/or hematite. The upper and oxide-rich gabbros and the micropegmatite contain between 1 and 10 percent oxide minerals with magnetite far in excess of ilmenite. The felsic and south range norites contain 0.1 to 2 percent oxide minerals with ilmenite in excess of magnetite. The mafic norite, a unit developed intermittently around the perimeter of the north range of the intrusion, contains 0.5 to 1 percent oxide (largely magnetite) while the quartz-rich norite, developed continuously along the margin of the south range, contains the same amount of oxide, largely ilmenite.Electron microprobe data on magnetite, coupled with estimates of the proportion of ilmenite lamellae developed within grains, indicates that magnetite from the upper levels of the Irruptive was very much richer in titanium at the time of its crystallization than that from lower levels. Chromium shows the reverse trend. Magnetite from the upper part of the mafic norite contains 8 to 13 percent Cr 2 O 3 but this decreases rapidly to less than 2 percent across the 10-50 ft transition zone between the mafic and over-lying felsic norite and then falls more gradually to less than 0.1 percent in the micro-pegmatite. Magnetite from the upper part of the quartz-rich norite and lower south range norite is also rich in Cr 2 O 3 (3-5 wt %) and this decreases upwards to less than 1.5 percent halfway up this unit. These variations in magnetite composition support previous evidence (Naldrett et al., 1970) of cryptic variation in the Irruptive.The final partitioning of iron and titanium between magnetite and ilmenite occurred at high ( nearly equal 900 degrees C) temperatures on the north range and much lower (<600 degrees C) temperatures on the south range, indicating a very different cooling history for the two ranges. This is consistent with the hypothesis that the Irruptive is funnel shaped and that the south range is a section through a deeper, thicker portion of the funnel.

Rb–Sr Study of Shock-metamorphosed Inclusions from the Onaping Formation, Sudbury, Ontario

Sixteen inclusions from the Onaping Formation, a possible meteorite impact breccia at Sudbury, Ontario, were analyzed for Rb, Sr, and Sr isotopic composition. Inclusions ranged from weakly shocked granitic rocks to heterogeneous glassy inclusions (impact melt?). Strongly shocked and glassy inclusions yield separate isochrons of 1430 ± 65 m.y. and 1480 ± 55 m.y., respectively (λ 87Rb = 1.39 × 10−11 y−1). Twenty-eight samples, including data for Onaping Formation samples from the literature, have an isochron age of 1515 ± 65 m.y. Isochron initial 87Sr/86Sr ratios range from 0.714 to 0.717, The Onaping samples thus appear anomalously younger than the 1700 m.y. ages reported for the geologically younger Nickel Irruptive and Whitewater sediments. If the highly shocked granitic inclusions and glasses in the Onaping Formation are relatively susceptible to radiogenic Sr loss during subsequent thermal events, the data are compatible with an impact origin for the Sudbury structure. The whole-rock ages, combined with reported mineral ages, suggest a metamorphic event in the Sudbury area 1400–1500 m.y. ago.

Possible relations between meteorite impact and igneous petrogenesis, as indicated by the Sudbury structure, Ontario, Canada

Recent investigations indicate the importance of meteorite impact as a process which has operated throughout geologic time to produce numerous originally circular structures as much as 50 km in diameter. One such structure, at Sudbury, Ontario, is associated with large volumes of internally derived igneous rock. Geological and experimental studies have demonstrated that rocks subjected to intense shock waves produced by hypervelocity meteorite impacts and by nuclear or chemical explosions develop distinctive and uniqueshock-metamorphic features, including: (1) high-pressure minerals such as coesite and stishovite; (2) crystal lattice deformation features such as isotropic feldspar (maskelynite) and « planar features » (shock lamellae) in quartz; (3) ultra-high-temperature reactions not produced by normal geological processes, such as decomposition of zircon to baddeleyite and melting of quartz to lechatelierite. These petrographic features, currently regarded as unequivocal evidence for meteorite impact, can be preserved and recognized even in very old and deeply eroded structures. Such features have now been observed in more than 50 « crypto-explosion » structures ranging in size from 2 km to more than 60 km in diameter. The recent discovery of shock-metamorphic features in rocks of the Sudbury structure, Ontario, indicates that this old and complex structure was also produced by a large meteorite impact. Petrographic shock effects are widespread in inclusions of « basement » rock in the Onaping « tuff », a unit now regarded as afallback breccia deposited in the original crater immediately after impact. Similar shock effects also occur in the footwall rocks around the basin, associated with shatter cones and unusual Sudbury-type breccias. Study of Sudbury specimens has establishedgrades of progressive shock metamorphism comparable to those recognized at younger impact structures (Brent, Ontario; Ries basin, Germany). Igneous activity associated with known meteorite impact structures takes two forms: The inferred development of the Sudbury structure was a complex process involving: (1) impact of an asteroidal body, forming a large (100-km) diameter crater with a central uplift; (2) subsidence of the central uplift and simultaneous emplacement of the Nickel Irruptive; (3) metamorphism, deformation, and erosion to its present appearance. The post-impact history of the Sudbury structure thus corresponds closely to that established for many ring-dike complexes and caldera subsidences. Similar compound impact-igneous structures, in which internal igneous activity is superimposed on a large impact crater, probably exist on both the earth and the moon. Future examination of « roofed lopoliths » and « ring-dike structures » for shock-metamorphic effects, combined with serious consideration of the geophysical effects produced by large-energy meteorite impacts, will be a productive field for cooperative studies by astrogeologists and igneous petrologists.

Cryptic variation and the petrology of the Sudbury nickel irruptive

Silica-rich magma, gravitational crystal settling, funnel-shaped body, norites and gabbros, Ontario, Canada

A Study of the Strathcona Mine and Its Bearing on the Origin of the Nickel-Copper Ores of the Sudbury District, Ontario

A Study of the Strathcona Mine and Its Bearing on the Origin of the Nickel-Copper Ores of the Sudbury District, Ontario

Paleomagnetic study of the Sudbury Basin

A reconnaissance paleomagnetic study has been carried out on the Precambrian nickel irruptive of the Sudbury basin. A total of 60 oriented samples was collected along a single traverse across the northern range and along four traverses across the southern range of the basin. The remanent magnetism (RM) vectors of the 266 specimen cubes cut from the samples were subsequently measured with a ‘spinner’ magnetometer. The RM directions for the south range are closely grouped on the Schmidt equal-area plot, and this fact indicates that there has been negligible relative rotary movement along the 16 miles of the south range sampled since the irruptive last cooled through the Curie point of its magnetic constituents. It was also found that the RM directions for the N and S ranges differ by approximately 40°, and this may be explained by assuming that there has been 40° of relative tilting about an E-W axis through the middle of the basin. In three of the S range traverses the susceptibility (κ) of the collected samples was higher on the S end of the traverse than on the N end, and in general the κ's obtained for the N range were much higher than those obtained on the S range. It would appear that the magnetic anomalies observed over the norite sections of the N and S ranges are mainly due to the presence of RM and to a lesser extent to an induced magnetization. The pole position calculated from the RM directions is dependent on the amount of assumed relative tilting. However if the rotation is equally divided between the two ranges, the resultant pole position is 38.4°N, 99.4°W, which is in the central U.S.

The Age Relation and Origin of Common Sudbury Breccia

This paper includes Sudbury breccias not previously examined in detail; particular emphasis is placed on the relations between Sudbury breccias and the Onaping volcanics and nickel irruptive. Comparison is made with breccias described elsewhere and particularly with the very similar pseudotachylite which is abundant around the upthrust granite core of the Vredefort dome, South Africa. In post-Huronian time the central core of a large dome structure is believed to have been thrust upward, and explosive volcanoes developed at its apex. The volcanic center then collapsed, to form the great caldera now known as the Sudbury Basin. The stretching of the crust resulted in the formation of multitudes of tension fissures; earth movements related to the upthrust, explosive volcanism, and collapse of the structure caused crush breccias to form in the tension fractures. Fluids related to the volcanism passed through the breccia zones and may have assisted in the formation or modification of the breccias.

Life-History of the Sudbury Nickel Irruptive

Life-History of the Sudbury Nickel Irruptive