How Do Passive Margins Become Active? Paul F

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The Tooth of Time: How do passive margins become active? Paul F. Hoffman

Volume 39, Number 2, 2012

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The Tooth of Time: How do restrial rift-basin. The Paleozoic ‘geo- Carboniferous molasse, the so-called syncline’ began with an Eocambrian Catskill Delta. But what were ‘geosyn- passive margins become (Ediacaran) conglomerate-basalt rift clines’ (Kay 1951; Aubouin 1965), and active? assemblage, overstepped by a west- why did long-lived carbonate shelves ward-tapering wedge of lower Cambri- suddenly founder at the beginning of Paul F. Hoffman an clastics derived from the craton, a the orogenic stage? 1216 Montrose Ave., Victoria, BC middle Cambrian clastic-carbonate I had heard Harry Hess speak V8T 2K4 transition, and an upper Cambrian at McMaster on the impermanence of through lower Ordovician sequence of ocean basins (Hess 1962), but all I Orogenic belts should be studied from shallow-marine carbonate rocks, mem- remember of the lecture was his ability the outside inwards: that was drummed orably exposed in cattle pastures in the to smoke two cigarettes simultaneously, into me at McMaster University by Great Valley of Virginia. The eastern without tipping an ash, while pacing Vint Gwinn, a young American sedi- limit of shallow-water carbonate rocks back and forth, or writing on the mentary and structural geologist with lay just to the east of the Blue Ridge blackboard. Bob Dietz, who had con- oil industry experience. It was 1963 Anticlinorium. Pettijohn called this ceived of sea-floor spreading inde- and he was putting the finishing touch- Sauk Sequence (Sloss et al. 1949; Sloss pendently of Hess (Menard 1986) and es on a paper, still cited today, proving 1963) the ‘pre-orogenic orthoquartzite- who had postulated that North Ameri- carbonate stage’ of the geosyncline, ca was overriding the Pacific Ocean that thin-skinned thrusts underlie the noting that a lithologically similar stage floor, based on the truncation of sea- Central Appalachian Plateau and occurs in the middle Precambrian floor magnetic anomalies at the conti- northwestern Valley and Ridge, where (Paleoproterozoic) geosyncline of Min- nental margin (Dietz 1961), visited no fault breaks the surface (Gwinn nesota (Pettijohn 1957, p. 641). Com- Johns Hopkins in 1965. Appropriately, 1964). Gwinn was informal yet pas- ing from the Devonian of the Niagara he presented his actualistic interpreta- sionate, invoking sedimentary succes- Escarpment, nonbioturbated carbon- tion of geosynclines as Atlantic-type sions in orogenic forelands as the best ates for me were a revelation. continental shelves (‘miogeoclines’) and records of subsidence and sedimenta- Then something different rises (‘eugeoclines’), that undergo tion related to orogenesis, as controls occurred: shallow-water carbonate gave orogeny when the overburdened on the trajectories of faults and related way unexpectedly to black sulfidic oceanic lithosphere spontaneously rup- folds, and as horizons for tracking shale, locally associated with submarine tures and ‘slides’ (subducts) under the deformation. Gwinn’s course primed landslides (‘olistostromes’). This was continental margin (Dietz 1963). His me to appreciate graduate school in the overlain by a thick middle Ordovician talk was not well received, paleocurrent Central Appalachians. sequence of greywacke turbidites, fol- studies having shown that the two At Johns Hopkins University, lowed by upper Ordovician–lower Sil- Appalachian molassic sequences were structural geologist Ernst Cloos and urian crossbedded sandstones of east- derived from the east (Pelletier 1958; sedimentologist Francis Pettijohn led erly derivation. Adopting terminology Yaekel 1959), implausibly from the off- field trips every weekend during the from a younger orogen, the European shore in Dietz’s (1963) model. Grant- Fall and Spring semesters. The field Alps, Pettijohn (1957) referred to the ed, his model worked pretty well for trips were obligatory for incoming ‘euxinic’ (black shale), ‘flysch’ the pre-orogenic stage, with the eastern graduate students and they offered an (greywacke turbidite) and ‘molasse’ limit of shallow-water carbonate mark- Appalachian cross-section from the (crossbedded sandstone) stages of the ing the continental shelf-slope break. inner edge of the Allegheny Plateau to geosynclinal cycle, and he related them But the orogenic scenario was not in the Atlantic coastal plain, encompass- to the Taconic orogeny. The geosyncli- fact actualistic because nowhere is sub- ing the Valley and Ridge fold-and- nal cycle was then repeated with a Sil- duction being initiated at an Atlantic- thrust belt, the basement-cored Blue urian–lower Devonian pre-orogenic type margin at present, not even in the Ridge anticlinorium, the metamorphic orthoquartzite-carbonate stage overlain Bay of Bengal where subduction initia- Piedmont, and the post-orogenic by middle Devonian euxinic shale and tion is optimized by the enormous load Newark Basin—a Triassic-Jurassic ter- flysch, followed by upper Devonian– of sediment and strong in-plane com- 68 pressive stress, related to subduction at the Java Trench and the topographic head of the Tibetan Plateau. After teaching at Franklin and Marshall College in southeastern Penn- sylvania for a year, I joined GSC in May 1969 in a position vacated by Pre- Rt cambrian paleontologist Hans Hof- mann. Ending was the era of military- style reconnaissance operations north of 60°, when 12 or more 1:250,000- Er scale sheets were mapped in a single sub-Arctic summer. Topical studies logically followed. Within weeks I was standing at the edge of the Wopmay Subprovince (Stockwell 1961), the Paleoproterozoic (then Aphebian) orogenic belt I had invoked in my PhD thesis to account for the paleocurrent reversal in the East Arm of Great Slave Lake (Hoffman 1969), 600 km to the south. Actually, I was standing on Figure 1. Abrupt drowning of the Rocknest Formation (Er) marks the abortive 1.5 meters of lake ice, 20 km from the subduction of the passive-margin carbonate shelf in Wopmay orogen at 1882 Ma Arctic Ocean, looking at 70% snow (Bowring and Grotzinger 1992). Here, 30 km east of the frontal thrust and 300 km cover. If my timing was impetuous, the (palinspastic) landward of the ancient shelf-slope break, the basal foredeep deposits location was deliberate: under the melt- consist of craton-derived glauconitic siltstone (Rt), which tapers westward to a few ing snow was the best-exposed meters of granular ironstone, overlain by graphitic-pyritic slate and felspathic- autochthonous sedimentary section at greywacke flysch. Abortive subduction of the passive margin caused a subduction the edge of the orogen. To the west zone flip, forming an active margin with subduction dipping beneath the continent. was a broad belt of tightly-folded sedi- S.B. Lucas (foreground) ponders the metamorphic temperature. Tree River fold belt mentary rocks and beyond that was the at 67°26’05”N, 112°22’38”E, Nunavut, Canada. volcanic, plutonic and metamorphic core of the orogen. Our guides to this provide us with more structural relief cycle by a factor of four in its age. The place were an 8-mile-to-the-inch recon- than is exposed on any mountain on parallel tectonic development of geo- naissance map (Fraser 1960), a vision- Earth (Hoffman et al. 1988). synclines over the last two billion years ary regional stratigraphy (Fraser and A day later we returned to the was empirically evident, but not yet Tremblay 1969) and the Canadian Arc- top of the allochthonous dolomite, their interpretation in terms of plate tic Expedition (1913-1918) report on marked by a long narrow valley and a tectonics (Pettjohn 1957; Hoffman et the geology along the coast (O’Neill structurally intact sedimentary al. 1970). 1924). The next day we dropped down sequence. Bioherms of sunlight-seek- What caused the carbonate stratigraphically to the Archean base- ing columnar stromatolites distinguish shelves to founder at the beginning of ment, finding a depositional unconfor- the final meters of dolomite the orogenic stage? The answer would mity at the base of a transgressive (Grotzinger 1986b). They are abruptly eventually come from the Appalachian- marine quartzite sequence (Odjick For- overlain by a few meters of glauconitic Caledonian orogen, informed by theo- mation), gradationally overlain by 0.8 quartz-siltstone (Tree River Forma- retical geophysics and modern exam- km of cyclic peritidal dolomite, the tion), several decameters of sulfidic- ples. In 1964, Hank Williams (1964) Rocknest Formation (Grotzinger graphitic slate (Fontano Formation), recognized the Newfoundland 1986a). The 1.6-km-thick ortho- and then a kilometer or more of Appalachians as an orogenic system in quartzite-carbonate sequence dips to immature, coarse-grained, feldspathic- which two different continental shelves the west and above it we found a greywacke turbidites (Asiak Forma- (Dietz’s ‘miogeoclines’) face each other duplicate sequence, which rides on a tion). The abruptness of the transition across an early Paleozoic oceanic tract. paper-thin thrust fault detached a few and the thickness of greywacke tur- Tuzo Wilson (1966) extended this meters above the basal unconformity bidites diminish eastward (Fig. 1), interpretation throughout the North (Tirrul 1982). The snowy slog back to implying that the anomalous subsi- Atlantic region, based on a long-known camp was painless, given the prospect dence was limited to the outer 300 km faunal discordance. He inferred that of a 140-km-wide foreland thrust-fold (palinspastic) of the carbonate shelf. intra-oceanic island arcs got lodged belt to work on in the years ahead (Tir- The abrupt drowning of the Rocknest between the collided margins when the rul 1983; Hoffman and Tirrul 1994), platform, and its burial by euxinic and Paleozoic ocean closed. On the west- conveniently planed off by the Lauren- flysch-type deposits, anticipated Petti- ern margin in Newfoundland, Bob tide Ice Sheet. Plunge reversals would john’s lower Ordovician geosynclinal Stevens (1970) recognized two Cam- GEOSCIENCE CANADA Volume 39 2012 69 bro-Ordovician flysch sequences, the ancient example of subduction zone Manila Trench–Luzon arc, at the lead- older distinguished by quartzo-felds- flip: it is a speculation. John Dewey, ing edge of the Philippine Sea plate, pathic turbidites shed from Laurentia then 32, immediately recognized the against the oblique, southeast-facing, (Dietz’s ‘eugeocline’) and the younger generic significance of subduction passive continental margin of China. (Arenig-Caradocian) derived from the polarity flip as a consequence of arc- The arc-continent collision is diachro- east and distinguished by detrital continent collision, but he did not nous, progressing southwestward along chromite and other ultramafic detritus favour its application to the Taconic the continental margin, converting it (Stevens and Church 1969). Two (or Grampian) orogeny (Dewey and from a passive to an active margin. months before I first saw the drowned Horsfield 1970; Dewey and Bird 1970, Every stage in the process is simultane- carbonate shelf in Wopmay orogen, 1971). ously active at different latitudes. South John Dewey (1969; see also Bird and To the best of my knowledge, of Taiwan, the Manila Trench con- Dewey 1970) published a plate tectonic the late Bill Chapple (1973) of Brown sumes ocean crust of the South China model for the development of the University was the first to invoke sub- Sea and the China margin is unaffect- Appalachian-Caledonian orogen. He duction flip for the Appalachians in a ed. Taiwan marks the abortive subduc- ascribed the Ordovician (Taconic) talk at the 1973 GSA Annual Meeting tion of the China margin eastward orogeny on the Laurentian margin to in Dallas. It was a rare foray into under the Luzon arc: causing the South the effects of west-dipping subduction, regional tectonics for a numerical mod- China Sea slab to tear off, arc volcan- initiated spontaneously at the distal eler (Chapple 1968, 1969, 1970), who ism to shut down, and the accretionary edge of a passive continental margin. is remembered for his later insights on prism to be engorged with sediment His model for the Laurentian margin the force balance acting on lithospheric from the China margin. Mountainous was basically an elaboration of Dietz’s plates (Chapple and Tullis 1977) and a topography and heavy precipitation (1963) concept of collapsing continen- ground-breaking approach to the drive exhumation of metamorphic tal rises. It had the same defects as mechanics of thin-skinned thrust-and- rocks in central Taiwan. North of cen- Dietz’s model: it didn’t account for fold belts (Chapple 1978). Chapple tral Taiwan, the southeast-facing Ryuku abrupt drowning of the miogeocline; it (1973) proposed that the Taconic Trench and arc mark the subduction of predicted arc magmatism on the Lau- orogeny was the result of ‘abortive the Philippine Sea plate northwestward rentian margin where none existed, and subduction’ of the Laurentian passive beneath the Eurasian plate. The latest it was non-actualistic. margin beneath a west-facing island volcano of the Ryuku arc is at the A more satisfactory model arc. Assuming an average modern rate northern tip of Taiwan, and roll-back (McKenzie 1969) appeared just three of plate convergence, he estimated of the Philippine Sea slab creates a rift months after our slog in the snow in how long different stages of the arc- basin, the Okinawa Trough, behind the the Wopmay foreland. It was a generic continent collision including thermal Ryukyu arc. The entire process, from model with no particular regional relaxation would last, and compared the collapse of the passive margin to application and its author was a 27- these estimates with geological con- the establishment of an active conti- year-old geophysicist from Cambridge straints. His model explained the nental margin arc above the flipped University on a Fairchild Fellowship at abrupt but diachronous foundering of subduction zone, takes around 4 mil- Caltech. Two years earlier, Dan the continental terrace as it entered the lion years (Suppe 1984). At a given lati- McKenzie (McKenzie and Parker trench, and the associated ‘staircase’ tude, a collision-induced mountain 1967)—and independently Jason Mor- normal faults through plate flexure. It range rises and falls on the same time- gan (Morgan 1971; Le Pichon 1991)— accounted for the subsequent euxinic scale. A broadly similar process was had conducted the first quantitative (trench outer-slope) and flysch (trench shown to have occurred in New test of Tuzo Wilson’s (1965) concept axis) deposits, as well as deformation Guinea in the late Miocene (Hamilton of plate tectonics. McKenzie’s subse- during detachment and accretion onto 1979; van Ufford and Cloos 2005) and quent 1969 paper is accurately titled, the upper plate. It conformed with the to be ongoing in Timor, where the “Speculations on the consequences and causes absence of arc magmatism on the Lau- northwest margin of Australia enters of plate motions”, and it deals with rentian margin until shortly after the the Java Trench (Von der Borch 1979). dynamic coupling and feedback arc-continent collision. It was never In 1978, the Rangoon-based economic between plate motions and mantle written up as a paper. geologist Andrew Mitchell (1978) inter- convection at subduction zones. He Nothing Bill Chapple could preted the Taconic-age Grampian views continents as non-subductable have written would have supported orogeny of the Scottish Caledonides as due to compositional buoyancy: their Dan McKenzie’s (1969) speculation of a subduction flip tripped by arc-conti- arrival at a trench inevitably results in subduction flip so eloquently as the nent collision. The next year, having strong crustal deformation and “a active arc-continent collision in Taiwan completed the northern transect of change in the motion or the boundaries of the (Fig. 2), described by geologist R.W. Wopmay orogen, I followed suite plates” (McKenzie 1969). “If the trench Murphy in Kuala Lumpur and pub- (Hoffman 1979, 1980, 1982). and island arc originally had oceanic crust on lished (Murphy 1973; see also Suppe The subduction flip scenario both sides, the island arc is likely to flip, and 1981, 1984) the same year as Chapple’s makes falsifiable predictions about the instead of attempting to consume the continent GSA talk in Dallas. Convergence timing and polarity of arc magmatism, it will consume oceanic crust originally behind between the Philippine Sea and relative to shelf drowning and to sub- the arc.” McKenzie gives no active or Eurasian plates drives the west-facing duction-related deformation and meta- 70

These are stories for another time. Eurasian In Wopmay orogen (Fig. 3) there are two magmatic belts, the older h Plate g Akaitcho-Hepburn belt to the east and u the younger MacTavish-Great Bear belt ro T c to the west. The younger belt has all Active margin ar China a c the trappings of a continental magmat- aw i i n an ic arc and it must have faced to the O k lc west because no ocean existed to the N vo R y y u east when it was active (Hildebrand et u k al. 1987, 2010b; Cook 2011). The older belt is the leading edge of an arc (Hot- ch ren tah terrane) that collided with the Slave Ryukyu T passive margin, causing the Calderian orogeny and triggering the subduction

c ~7 cm/yr flip (Hildebrand et al. 2010a). The arc-

a continent collision is best dated by the

c collapse of the passive margin (Fig. 1)

Passive margin i c

n at 1882 Ma, ~132 million years after

n a e the rift-to-drift transition (Bowring and

c Philippine

r l T Grotzinger 1992; Hoffman et al. 2011). o a v Sea When Marc St-Onge and I, under the l i n tutelage of Dugald Carmichael, n o Plate mapped the prograde metamorphic South China a z u sequence related to the Hepburn intru- M L 100 km Sea Google sions, we inferred that the metamorphic isograds to the east cut distal cor- Figure 2. Taiwan island (center) marks the active collision of the Luzon arc with relatives of the passive continental the passive continental margin of southeast China. Continued convergence margin (St-Onge 1981, 1984; St-Onge between the Philippine Sea and Eurasian plates causes subduction to flip during and King 1987). This should not occur arc-continent collision, resulting in northwest-dipping subduction at the Ryukyu if the Hepburn intrusions were part of Trench. The conversion of the passive margin into an active margin progresses an arc that collided with the passive southwestward at a rate of ~95 km per million years (Suppe 1984). Teeth on margin. Accordingly, I attributed the trench-lines indicate the upper plate. Hepburn intrusions to the tearing off morphism. Arc magmatism should not tinues into the New England of the westerly-dipping slab during touch the passive margin until a few Appalachians (Karabinos et al. 1998; arc-continent collision (Hoffman million years after shelf drowning, Dorais et al. 2012) and the Irish Cale- 1980). This implied that the intrusions when it will have the opposite tectonic donides (Friedrich et al. 1999). In fact, should be derived from Archean crust polarity compared with the collided the vast majority of all active margins, of the Slave craton, which was contra- arc. The model predicts that both arcs both modern and ancient, were the dicted by isotopic tracers (Bowring and will be deformed by subsequent colli- result of subduction flip following arc- Podosek 1989; Housh et al. 1989). sions—a subduction flip never involves continent collision (Bradley 2008). In a recent synthesis of the the terminal collision in an orogen. There are good mechanical reasons for Calderian orogeny and northern Wop- Tectonism subsequent to arc-continent this: it is very difficult to initiate sub- may orogen, Robert Hildebrand collision can be protracted, as in the duction at a subsided passive margin (Hildebrand et al. 2010a; Hildebrand Appalachians, if a large ocean basin because of the strength of the plate 2011) affiliates all of the Hepburn existed behind the collided arc. Inte- (Cloetingh et al. 1989). In the high intrusions and the high-grade part of gration of structural mapping with heat-flow region behind the arc, the the metamorphic sequence with the metamorphic petrology, basalt and plate is more easily ruptured. leading edge of the accreted terrane. granitoid petrochemistry, high-resolu- Surprisingly, there are two oro- Both the integrity of the prograde tion (ID-TIMS) U-Pb geochronology, gens in which there was an active mar- metamorphic sequence and the post- and isotopic tracers has confirmed the gin whose origin remains unresolved, collisional age of peak metamorphism Taconic subduction flip scenario for mainly because the question in the title are questioned in this scenario. For my active margin inception and a complex has not been seriously asked until part, I have more confidence in the accretionary history in the Canadian recently. One is the orogen in which I integrity of Marc’s metamorphic Appalachians (van Staal 1994; van Staal live, the North and South American sequence than in my own correlation et al. 2007, 2009; van Staal and Barr, in Cordillera. The other is the orogen in of the high-grade metamorphic rocks press). The same overall scenario con- which I work, the Damara of Namibia. with the passive-margin Odjick Forma- GEOSCIENCE CANADA Volume 39 2012 71

abortive subduction of the North Hottah Great Bear Slave Slave American continental plate?: Geologi- cal Society of America, Abstracts with Programs, v. 5, p. 573. 1890 Ma 1870 Ma Chapple, W.M., 1978, Mechanics of thin- skinned thrust-and-fold belts: Geo- Slave craton logical Society of America Bulletin, v.

rgin passive margin 89, p. 1189-1198. e ma activ Chapple, W.M., and Tullis, T.E., 1977, Evaluation of the forces that drive the Hottah plates: Journal of Geophysical Slave Research, v. 82, p. 1967-1984. Cook, F.A., 2011, Multiple arc develop- 1880 Ma ment in the Paleoproterozoic Wopmay Viewed from the west orogen, northwest Canada, in Brown, D., and Ryan, P.D., eds, Arc-Continent Collision: Springer-Verlag, Berlin, p. 403-427. Dewey, J.F., 1969, Evolution of the Appalachian/Caledonian orogen: Nature, v. 222, p. 124-129. Dewey, J.F., and Bird, J.M., 1970, Mountain Figure 3. Block diagram of an oblique arc-continent collision with diachronous belts and new global tectonics: Jour- subduction flip (d). Cross-sections illustrate Wopmay orogen (looking north) at nal of Geophysical Research, v. 75, p. 65°N present latitude at ~1890 Ma (a), 1880 Ma (b) and 1870 Ma (c). Passive conti- 2625-2685. nental margin (a) is converted to an active margin (c). Dewey, J.F., and Bird, J.M., 1971, Origin and emplacement of the ophiolite suite: Appalachian ophiolites in New- tion. When the metamorphic isograds Bird, J.M., and Dewey, J.F., 1970, Litho- foundland: Journal of Geophysical sphere plate–continental margin tec- Research. v. 76, p. 3179-3206. were mapped, there wasn’t a single U- Dewey, J.F., and Horsfield, B., 1970, Plate Pb date in the entire orogen; with tonics and the evolution of the Appalachian orogen: Geological Soci- tectonics, orogeny and continental modern isotopic diagnostics, it should growth: Nature, v. 225, p. 521-525. be possible to distinguish accreted ety of America Bulletin, v. 81, p. 1031- 1060. Dietz, R.S., 1961, Continent and ocean (Hottah terrane) from indigenous Bowring, S.A., and Grotzinger, J.P., 1992, basin evolution by spreading of the (Odjick Formation) protoliths in the Implications of new chronostratigra- sea floor: Nature, v. 190, p. 845-857. metamorphic sequence, as well as the phy for tectonic evolution of Wopmay Dietz, R.S., 1963, Collapsing continental metamorphic chronology. Sedimentary orogen, northwest Canadian Shield: rises: an actualistic concept of geosyn- protoliths derived from the Archean American Journal of Science, v. 292, clines and mountain building: Journal Slave craton will be easy to distinguish p. 1-20. of Geology, v. 71, p. 314-333. from the more juvenile signature of Bowring, S.A., and Podosek, F.A., 1989, Dorais, M.J., Atkinson, M., Kim, J., West, Hottah terrane (Bowring and Podosek Nd isotopic evidence from Wopmay D.P., and Kirby, G.A., 2012, Where is the Iapetus suture in northern New 1989; Housh et al. 1989), given appro- orogen for 2.0-2.4 Ga crust in western North America: Earth and Planetary England? A study of the priate samples, but if the Odjick For- Ammonoosuc Volcanics, Bronson Hill mation was sourced from the contem- Letters, v. 94, p. 217-230. Bradley, D.C., 2008, Passive margins terrane, New Hampshire: Canadian poraneous Thelon orogen (Hoffman through earth history: Earth-Science Journal of Earth Sciences, v. 49, p. and Grotzinger 1993), isotopic finger- Reviews, v. 91, 1-26. 189-205. printing will be more of a challenge. Cloetingh, S., Wortel, R., and Vlaar, N.J., Fraser, J.A., 1960, North-central District of Two months before writing this col- 1989, On the initiation of subduction Mackenzie, Northwest Territories: umn, I got an unexpected email from zones: Pure and Applied Geophysics, Geological Survey of Canada, Map GSC in Ottawa. Did I still possess my v. 129, p. 7-25. 18-1960. old field notes and annotated air pho- Chapple, W.M., 1968, A mathematical theo- Fraser, J.A., and Tremblay, L.P., 1969, Cor- tos from Wopmay orogen? They were ry of finite-amplitude rock-folding: relation of Proterozoic strata in the needed to select samples from the Geological Society of America Bul- northwestern Canadian Shield: Cana- GSC collections. Three boxes of field letin, v. 79, p. 47-68. dian Journal of Earth Sciences, v. 6, p. Chapple, W.M., 1969, Fold shape and rhe- 1-9. notes and air photos were soon taking ology: the folding of an isolated vis- Friedrich, A.M., Bowring, S.A., Martin, the fourth transcontinental trip of cous-plastic layer: Tectonophysics, v. M.W., and Hodges, K.V., 1999, Short- their 20-year diaspora, this time by air. 7, 97-116. lived continental magmatic arc at Con- Chapple, W.M., 1970, The finite-amplitude nemara, western Irish Caledonides: REFERENCES AND NOTES instability in the folding of layered implications for the age of the Aubouin, J., 1965, Geosynclines: Develop- rocks: Canadian Journal of Earth Sci- Grampian orogeny: Geology, v. 27, p. ments in Geotectonics, v. 1, Elsevier, ences, v. 7, p. 457-466. 27-30. Amsterdam, 335 p. Chapple, W.M., 1973, Taconic orogeny: Grotzinger, J.P., 1986a, Cyclicity and pale- 72

oenvironmental dynamics, Rocknest Shield, in Strangway, D.W., ed., The Royal Astronomical Society, v. 18, p. 1- platform, northwest Canada: Geolog- Continental Crust and Its Mineral 32. ical Society of America Bulletin, v. 97, Deposits: Geological Association of McKenzie, D.P., and Parker, R.L., 1967, p. 1208-1231. Canada, Special Paper 20, p. 523-549. The North Pacific: an example of tec- Grotzinger, J.P., 1986b, Evolution of Early Hoffman, P.F., 1982, Geology, northern tonics on a sphere: Nature, v. 216, p. Proterozoic passive-margin carbonate internides of Wopmay orogen, Dis- 1276-1280. platform, Rocknest Formation, Wop- trict of Mackenzie: Geological Survey Menard, H.W., 1986, The Ocean of Truth: may orogen, Northwest Territories, of Canada, Map 1576A, scale A personal history of global tectonics: Canada: Journal of Sedimentary 1:250,000. Princeton University Press, Princeton, Petrology, v. 56, p. 831-847. Hoffman, P.F., and Grotzinger, J.P., 1993, New Jersey, 353 p. Gwinn, V.E., 1964, Thin-skinned tectonics Orographic precipitation, erosional Mitchell, A.H.G., 1978, The Grampian in the Plateau and northwestern Valley unloading, and tectonic style: Geolo- orogeny in Scotland: arc-continent and Ridge provinces of the Central gy, v. 21, p. 195-198. collision and polarity reversal: Journal Appalachians: Geological Society of Hoffman, P.F., and Tirrul, R., 1994, Geolo- of Geology, v. 86, p. 643-646. America Bulletin, v. 75, p. 863-900. gy, northern externides of Wopmay Morgan, W.J., 1971, Rises, trenches, great Hamilton, W., 1979, Tectonics of the orogen, District of Mackenzie: Geo- faults, and crustal blocks: Journal of Indonesian Region: United States logical Survey of Canada, Open File Geophysical Research, v. 73, p. 1959- Geological Survey, Professional Paper 3251, colour map scale 1:250,000. 1982. 1078, 345 p. Hoffman, P.F., Fraser, J.A., and McGlynn, Murphy, R.W., 1973, The Manila Trench— Hess, H.H., 1962, History of ocean basins, J.C., 1970, The Coronation geosyn- West Taiwan Foldbelt in a flipped sub- in Engel, A.E.J., James, H.L. and cline of Aphebian age, District of duction zone: in Tan, B.K., ed., Leonard, B.F., eds, Petrologic Studies: Mackenzie, in Baer, A.J., ed., Basins Regional Conference of the Geology A volume to honor A.F. Buddington: and Geosynclines of the Canadian of Southeast Asia: Geological Society Geological Society of America, Boul- Shield: Geological Survey of Canada, of Malaysia Bulletin, v. 6, p. 27-42. der, Colorado, p. 599-620. Paper 70-40, p. 201-212. O’Neill, J.J., 1924, The geology of the Arc- Hildebrand, R.S., 2011, Geological synthe- Hoffman, P.F., Bowring, S.A., Buchwaldt, tic Coast of Canada, west of Kent sis: northern Wopmay orogen / Cop- R., and Hildebrand, R.S., 2011, Birth- Peninsula: Report of the Canadian permine Homocline, Northwest Terri- date for the Coronation paleocean: Arctic Expedition, 1913-18, v. 11, Part tories – Nunavut: Geological Survey age of initial rifting in Wopmay oro- A, King’s Printer, Ottawa, 107 p. of Canada, Open File 6390, scale gen, Canada: Canadian Journal of Pelletier, B.R., 1958, Pocono paleocurrents 1:500,000. Earth Sciences, v. 48, p. 281-293. in Pennsylvania and Maryland: Geo- Hildebrand, R.S., Hoffman, P.F., and Hoffman, P.F., Tirrul, R., King, J.E., St- logical Society of America Bulletin, v. Bowring, S.A., 1987, Tectonomagmat- Onge, M.R. and Lucas, S.B., 1988, 69, p. 1033-1064. ic evolution of the 1.9 Ga Great Bear Axial projections and modes of Pettijohn, F.J., 1957, Sedimentary Rocks, magmatic zone, Wopmay orogen, crustal thickening, eastern Wopmay 2nd ed.: Harper & Bros., New York, northwest Territories, Canada: Journal orogen, northwest Canadian Shield, in 718 p. of Volcanology and Geothermal Clark, S.P., Jr., and Suppe, J., eds, Sloss, L.L., Krumbein, W.C., and Dapples, Research, v. 32, p. 99-118. Processes in Continental Lithospheric E.C., 1949, Integrated facies analysis, Hildebrand, R.S., Hoffman, P.F., and Deformation: Geological Society of in Longwell, C.R., ed., Sedimentary Bowring, S.A., 2010a, The Calderian America, Special Paper 218, p. 1-56. Facies in Geologic History: Geologi- orogeny in Wopmay orogen (1.9 Ga), Housh, T., Bowring, S.A., and Villeneuve, cal Society of America, Memoir 39, p. northwestern Canadian Shield: Geo- M., 1989, Lead isotopic study of early 91-123. logical Society of America Bulletin, v. Proterozoic Wopmay orogen, NW Sloss, L., 1963, Sequences of the Cratonic 122, p. 794-814. Canada: role of continental crust in Interior of North America: Geologi- Hildebrand, R.S., Hoffman, P.F., Housh, T., arc magmatism: Journal of Geology, cal Society of America Bulletin, v. 74, and Bowring, S.A., 2010b, The nature v. 97, p. 735-747. p. 93-114. of volcano-plutonic relations and the Karabinos, P., Sampson, S.D., Hepburn, Stevens, R.K., 1970, Cambro-Ordovician shapes of epizonal plutons of conti- J.C., and Stoll, H.M., 1998. Taconian flysch sedimentation and tectonics in nental arcs as revealed in the Great orogeny in the New England west Newfoundland and their possible Bear magmatic zone, northwestern Appalachians: collision between Lau- bearing on a proto-Atlantic ocean, in Canada: Geosphere, v. 6, p. 1-28. rentia and the Shelbourne Falls arc: Lajoie, J., ed., Flysch Sedimentology in Hoffman, P.F., 1969, Proterozoic paleocur- Geology, v. 26, p. 215-218. North America: Geological Associa- rents and depositional history of the Kay, M., 1951, North American Geosyn- tion of Canada, Special Paper No. 7, East Arm fold belt, Great Slave Lake, clines: Geological Society of America, p. 165-177. Northwest Territories: Canadian Jour- Memoir 48, 143 p. Stevens, R.K., and Church, W.R., 1969, Age nal of Earth Sciences, v. 6, p. 441-462. Le Pichon, X., 1991, Introduction to the of ultramafic rocks in the north-west- Hoffman, P.F., 1979, Wopmay orogen: con- publication of the extended outline of ern Appalachians: Geological Society tinent-microcontinent-continent colli- Jason Morgan’s April 17, 1967 Ameri- of America, Abstracts with Programs, sion of early Proterozoic age in the can Geophysical Union paper on v. 1, p. 215-216. Canadian Shield: Geological Associa- “Rises, Trenches, Great Faults and Stockwell, C.H., 1961, Structural provinces, tion of Canada, Program with Crustal Blocks”: Tectonophysics, v. orogenies, and time classification of Abstracts, v. 4, p. 58. 187, p. 1-22. rocks of the Canadian Precambrian Hoffman, P.F., 1980, Wopmay orogen: a McKenzie, D.P., 1969, Speculations on the Shield, in Lowden, J.A., ed., Age Deter- Wilson cycle of early Proterozoic age consequences and causes of plate minations by the Geological Survey of in the northwest of the Canadian motions: Geophysical Journal of the Canada, Report 2 isotope Ages: Geo- GEOSCIENCE CANADA Volume 39 2012 73

logical Survey of Canada, Paper 61-17, of America, Memoir 200, p. 511-552. p. 108-118. van Staal, C.R., Whalen, J.B., Valverde- St-Onge, M.R., 1981, “Normal” and Vaquero, P., Zagorevski, A., and “inverted” metamorphic isograds and Rogers, N., 2009, Pre-Carboniferous, their relation to syntectonic Protero- episodic accretion-related, orogenesis zoic batholiths in the Wopmay orogen, along the Laurentian margin of the Northwest Territories, Canada: northern Appalachians, in Murphy, Tectonophysics, v. 76, p. 295-316. J.B., Keppie, J.D., and Hynes, A.J., eds, St-Onge, M.R., 1984, The muscovite-melt Ancient Orogens and Modern Ana- bathograd and low-P isograd suites in logues: Geological Society, London, the north-central Wopmay orogen, Special Publications, v. 327, p. 271- Northwest Territories, Canada: Jour- 316. nal of Metamorphic Petrology, v. 2, p. van Ufford, A.Q., and Cloos, M., 2005, 315-326. Cenozoic tectonics of New Guinea: St-Onge, M.R., and King, J.E., 1987, Ther- AAPG Bulletin, v. 89, p. 119-140. mo-tectonic evolution of a moramor- Von der Borch, C.C., 1979, phic internal zone documented by Continent–island arc collision in the plunge projections and petrological P- Banda arc: Tectonophysics, v. 54, 169- T paths, Wopmay orogen, northwest 193. Canada: Geology, v. 15, p. 155-158. Williams, H., 1964, The Appalachians in Suppe, J., 1981, Mechanics of mountain north eastern Newfoundland—a two- building and metamorphism in Tai- sided symmetrical system: American wan: Memoir of the Geological Socie- Journal of Science, v. 262, p. 1137- ty of China, No. 4, p. 67-89. 1159. Suppe, J., 1984, Kinematics of arc-conti- Wilson, J.T., 1965, A new class of faults nent collision, flipping of subduction, and their bearing on continental drift: and back-arc spreading near Taiwan: Nature, v. 207, 343-347. Memoir of the Geological Society of Wilson, J.T., 1966, Did the Atlantic close China, No. 6, p. 21-33. and then re-open?: Nature, v. 211, p. Tirrul, R., 1982, Frontal thrust zone of 676-681. Wopmay orogen, Takijuq Lake map- Yaekel, L.S., 1959, Tuscarora, Juniata and area, District of Mackenzie, in Current Bald Eagle paleocurrents and paleo- Research, Part A: Geological Survey geography in the central Appalachians: of Canada, Paper 82-1A, p. 119-122. Unpublished PhD thesis, The Johns Tirrul, R., 1983, Structure cross-sections Hopkins University, Baltimore, Mary- across Asiak foreland thrust and fold land, 454 p. belt, Wopmay orogen, District of Mackenzie, in Current Research, Part B: Geological Survey of Canada, Paper 83-1B, p. 253-260. van Staal, C.R., 1994, The Brunswick subduction complex in the Canadian Appalachians: record of the Late Ordovician to Late Silurian collision between Laurentia and the Gander margin of Avalon: Tectonics, v. 13, p. 946-962. van Staal, C.R., and Barr, S.M., in press, Lithospheric architecture and tectonic evolution of the Canadian Appalachi- ans and associated Atlantic margin, in Percival, J.A., Cook, F.A., and Clowes, R.M., eds, Tectonic Srtyles in Canada: the LITHOPROBE Perspective: Geo- logical Association of Canada, Special Paper 49. van Staal, C.R., Whalen, J.B., McNicholl, V.J., Pehrsson, S., Lissenberg, C.J., Zagorevski, A., van Breemen, O., and Jenner, G.A., 2007, The Notre Dame arc and the Taconic orogeny in New- foundland, in Hatcher, R.D., Jr., Carl- son, M.P., McBride, J.H., and Martínez Catalán, J.R., eds, 4-D Framework of Continental Crust: Geological Society