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The Canadian Cordillera

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    In its simplest form the Canadian Cordillera has been represented as a bisymmetrical unit composed  of three tectonic zones:

Western Cordilleran Fold Belt                        |  Intermontane zone   |                Eastern Cordilleran Fold Belt

    Subdivided further into:

Insular Zone                                                                                                                    Eastern Marginal Zone

                                                                Coast Crystalline Complex                                    | Core Zone

        The Core zone, commonly also known as the Omineca Geanticline, merges at its  northern end with the Yukon-Tanana Platform, a structural unit which to the west of the Intermontane zone can be traced southwards into the Coast Crystalline complex.

       The relative plate tectonic evolution of these three tectonic elements remains one of the major 'unknowns' of Cordilleran and Canadian geology.

        In terms of the concept of 'suspect terranes', the Cordillera is now recognized as   an accretionary complex composed, from east to west, of the following native and accreted terranes:

        1) The North American craton and its cover of deformed Phanerozoic sediments (oil bearing).
        2) North American craton rocks forming uplifted core complexes within the Omineca
               - the Monashee
        3) Displaced continental margin rocks
                - the Cassiar (north) and Cariboo (south)
        4) Pericratonic terranes
                - Kootenay: Barkerville (south), Nisutlin, Yukon-Tanana (north), and Nisling? (west)

        Accreted terranes
        5) Intermontane Superterrane
           Slide Mountain Ocean (East), Quesnellia arc, Cache Creek ocean, Stikinia arc (West)
        6) Coast Belt
                  a) Southern Cordillera - Methow (East);Bridge River/Hozameen (= Cache Creek?),  Cadwallader,
                      Shuksan (West)
                  b) Northern West Coast - Taku
                  c) Gravina
        7) Insular Superterrane
                 a) Inner - Alexander (East) Wrangellia (West)
                 b) Outer - Chugach (East), Yakutat (West)

    Terrane Map of the Canadian Cordillera - cord2terr1.jpg
    Simplified terrane map of the Cordillera
    A detailed but incomprehensible grey scale map of the Canadian Cordillera - cord2mapcan.jpg
        The Pericratonic terranes contain volcanic and continental derived sedimentary  rocks laid down during early Phanerzoic rifting of the western margin of North America They have a late Proterozoic to Paleozoic history of deformation and plutonism.
       The Slide Mountain (Miss. to Permian), and Cache Creek/Bridge River (Mississipian  to Upper Triassic) terranes represent Paleozoic/Mesozoic oceans, whereas the Quesnellia  (Upper Triassic to Middle Jurassic), Stikinia (Devonian to Middle Jurassic),  Cadwallader (Upper Triassic to Mid Cretaceous), and Gravina (Jurassic to Cretaceous)  terranes are remnants of arc systems accreted to North America. The Alexander  (Precambrian to Lower Triassic) and Wrangellia (Permian to Lower Jurassic) terranes  were amalgamated during the Middle Jurassic but were not accreted to North America  until the Cretaceous. The exact timing and mechanism of accretion, and the original  location of the terranes, remains a subject of debate.
    Geological Time Chart, Phanerozoic, GSC-1999

    Geological Time Chart: Triassic-Jurassic, GSC-1999
Middle Jurrassic to Paleogene tectonic events in the Canadian Cordillera - cord2terr2.jpg

    The continental margin miogeoclinal rocks (Ketchika basin) of the Cordilleran System
      Ferri, Filippo, Rees, Chris, Nelson, JoAnne, Legun, Andrew, Orchard, M-J, Norford, B-S, Fritz, W-H,  Mortensen, J.K, Gabites, J-E, 1999. Geology and mineral deposits of the northern Kechika Trough between Gataga River and the 60th parallel. Bulletin - British Columbia Ministry of Energy and Mines, Energy and Minerals Division, Geological Survey Branch. 107,  122 p., 2 sheets.
        Abstract - The Kechika Trough represents a Lower Paleozoic basin developed between the MacDonald Platform to  the east and the Cassiar Platform to the west. This basin was well established by Late Cambrian time and ceased to be a depositional entity at the beginning of the Late Devonian. Mapping along the western part of the trough, between the Gataga River and the 60th parallel, encountered layered rocks of Proterozoic to Cenozoic age. These include: Late Proterozoic siliciclastics, carbonates and volcanics; siliciclastics and carbonates of  Cambrian age; Late Cambrian to Early Ordovician calcareous argillites and argillites of the Kechika Group; slate, siltstone and minor limestone of the Middle Ordovician to Middle Devonian Road River Group; Late Devonian to Early Mississippian argillite, chert and minor limestone of the Earn Group; chert, tentatively  assigned to the Mississippian to Permian Mount Christie Formation; conglomerate and sandstone of possible Tertiary age; and Tertiary to Quaternary mafic volcanics assigned to the Tuya Formation. Intrusive rocks represent a very minor component of the map area and consist of Early Paleozoic sills and dikes of gabbroic composition, feldspar porphyry dikes of Cretaceous or Tertiary age and small Early Cretaceous stocks, dikes and sills of broadly granitic composition. Periodic extensional tectonism during the Paleozoic, which led to the formation and subsequent modification of the Kechika Trough, was followed by intense, easterly directed, compressional tectonics and associated metamorphism of Mesozoic age, resulting in the present structural configuration. Rocks of the trough belong to the Rocky Mountain structural province and structures are
dominated by easterly verging folds and thrusts. Thrust faulting predominates in the southern part of the map area where lithologies are dominated by thick, competent Cambrian carbonate and quartzite units. Their disappearance to the north results in a structural style dominated by folding and penetrative cleavage.  Sedimentary exhalative mineralization (sedex) represents the most important mineral deposit type found within the Kechika Trough, ranking it, and the more northerly Selwyn Basin, as one of the most important  metallotects of the Canadian Cordillera. These stratiform Zn-Pb-Ag-Ba deposits are found at several stratigraphic levels: Cambrian, Middle Ordovician, Lower Silurian and Upper Devonian. Upper Devonian deposits are by far the most numerous and economically important within the map area, and throughout the Kechika and Selwyn basins. The large Cambrian and Early Silurian deposits found in the Anvil and Howards  Pass districts, respectively, highlight the potential that all these horizons have for hosting economically significant sedex deposits. Tungsten-molybdenum porphyry/skarn mineralization related to Early Cretaceous intrusions is the next most important mineral deposit type. Minor lead, zinc and copper-bearing veins are  scattered throughout the map area.

    Smith, M. Gehrels, G., 1994, Detrital zircon geochronology and the provenance of the Harmony and Valmy formations, Robert Mountains allochthon, Nevada: BGSA, 106, 7, 968-979.
    Abstract- Valmy zircons - 2 of 1050, 4 of 1830-1845, 5 of 1910-1960, 2 of 2270-2340, 8 of 2650-2750, 1 of 2900 and discordant ages 1 of 2070 1 of 3240; derivation from the North, Slave Craton and Medicine Hat province and central/northern Alberta; Valmy is Ordovician volcanic bearing equivalent of the Eurekea Quartzite of the shelf miogeocline; Harmony Fm is Upper Cambrian and immature, zircons - 9 of 695-710, 12 of 1015-1225, 2 of 1330, 1 of 1745, 1 of 1915, 1 of 2570; the c 700 and c 1100 have no western North American basement source; five foliated intrusive bodies spatially associated primarily with the Windermere Supergroup and Yukon-Tanana terrane , as well as one extrusive unit Mount Harper rhyolite in the Ogilvie Mountains 751+26-18, yield ages in the 670-750 range. Two 680 orthgneiss bodies occur in the Seward Peninsula;evidence for Grenville age basement includes clasts and xenoliths entrained in two diatremes and a monazite age from a breccia pipe; Pahrump sills of Death Valley are 1069 1087 and sills in the Apache quartzite of Arizona are 1150 Ma.

        What is the Monashee?
    James L. Crowley, 2001.  U-Pb geochronologic constraints on Paleoproterozoic tectonism in the Monashee complex, Canadian Cordillera: Elucidating an overprinted geologic history Canada.Geological Society of America Bulletin: Vol. 111, No. 4, pp. 560–577.
    Abstract: The effects of Paleoproterozoic tectonism are best preserved in deep structural levels of the complex, where overprinting related to high-grade Cordilleran (early Tertiary) metamorphism and deformation was incomplete. Determination of precise crystallization ages is hindered by the U-Pb age discordance in the zircon, monazite, and titanite; the discordance is attributed to inherited Pb in some of the grains and to Pb loss, overgrowth, and recrystallization that ccurred during one or more thermal overprints. Igneous crystallization ages are interpreted from the upper intercepts of linear arrays that are defined  by three or more analyses. Varying degrees of confidence are attributed to the ages based on the probability of inheritance. Large bodies of augen orthogneiss and granodioritic orthogneiss yield precise igneous crystallization ages of 2077 ± 2 and 1862 ± 1 Ma, respectively. Crystallization ages of about 2.27 and 2.10 Ga are interpreted with less certainty from dioritic orthogneiss and granitic orthogneiss, respectively. Deformation associated with  a migmatitic gneissosity occurred after ntrusion of the 2077 ± 2 Ma augen gneiss, the youngest dated rock that contains the fabric, and before intrusion of a 1848 ± 3 Ma granite, the oldest confidently dated rock that postdates the fabric. Postdeformational pegmatite dikes are dated as 1845 ± 3 nd  1836 ± 2 Ma. Metamorphism is interpreted as occurring during monazite growth at 2060 ± 1 Ma in pelitic schist and during titanite growth at ca. 1.85  Ga in amphibolitic gneiss. The gneisses are basement to an unconformably overlying cover sequence, the lower part of which was deposited prior to intrusion of a 1852 ± 4 Ma pegmatite.
                  What is the age, source, and nature of  Slide Mountain rocks?
Nelson, J.L., 1993. The Sylvester Allochthon: Upper Paleozoic marginal-basin and island arc terranes in northern British Columbia. CJES, 30, 631-643.
    Geological map of the northern part of the Sylvester allochthon - cord2nelson1.jpg
    Schematic cross section of the Sylvester allochthon - cord2nelson2.jpg
    Geochemical discrimination plots for rocks of the Sylvester allochthon - cord2nelson3.jpg

Roback, R.C., Sevigny, J.H., and Walker, N.W., 1994. Tectonic setting of the Slide Mountain terrane, southern British Columbia. Tectonics, 13, 5, 1242-1258.
    Abstract - SMT consists of fine grained quartzose clastic rocks, limestone and lesser amounts of conglomerate and volcanic rocks of the Carboniferous McHardy assemblage conformably overlain by the Permian Kaslo Group ultramafic, volcanic and sedimentary rocks. Kalso volcanics are MORB. McHardy conglomerates contain clasts of Silurian granitoid rocks, and detrital zircons in the McHardy are 1.7 to 3.1 Ga, similar to ages of zircons in the Kootenay and miogeoclinal sediments. The SMT is unconformably overlain by Late Triassic fined grained sedimentary rocks of the Slocan Group of the Quesnellia terrane (Monger and Berg, 1987). The Slide Mountain may therefore be in part a 'native' foreland basin assemblage, rather than an exotic section of oceanic crust.

        Henderson-Charles-M, 1998. Tectonic control and biotic change at the Permian-Triassic (P-T) and Dienerian-Smithian (D-S) sequence boundaries,  Western Canada.   Abstracts with Programs - Geological Society of America.  30, 7, p. 152.
    Abstract - Permian and Lower Triassic strata in western Canada are difficult to correlate because of major thickness and lithofacies variations and the scarcity of index fossils. However, sequence  biostratigraphic analysis using conodonts, has resulted in the  development of a complex tectono-stratigraphic history for the cratonic margin of northwestern Pangea. At least five third-order sequences are recognized for the Permian and Lower Triassic of western Canada. A thin Upper Asselian/Lower Sakmarian sequence, is sporadically distributed as a result of sub-Permian tectonic uplift and buckling on the craton margin. The remaining two Permian sequences (Artinskian-Lower Kungurian and Roadian-Wordian) are more widespread and are characterized by condensed sedimentation and decreasing biotic diversity that point to a protracted extinction interval. A low diversity Upper Permian fauna is dominated by siliceous sponges and associated with dropstones, suggesting that climatic cooling as well as the subsequent regression were important contributing factors to the P-T extinction locally. Truncation of various Upper Paleozoic units and localized distribution of latest Permian and earliest Triassic strata indicates another major tectonic uplift and buckling event that correlates with the Sonoman Orogeny, immediately before the Permian-Triassic biostratigraphic boundary. A relatively thick latest Changhsingian to Dienerian sequence includes a very low diversity fauna and few ichnotaxa. The D-S sequence boundary has a comparable tectonic signature that isolated overlying biotic accumulations, forming important reservoir units in the region.  Evidence supports emplacement of allochthonous terranes (Slide Mt.) onto pericratonic terranes (Kootenay) and imbrication of Upper Permian rocks beginning in pre-Late Triassic time. Therefore, it is probable that tectonic stress buildup and release events associated with major plate reorganizations or interaction between the craton margin and pericratonic and allochthonous terranes controlled these northwestern Pangea sequence boundaries and influenced biotic extinction and migration patterns.

        Struik, L.C. and Orchard, M.J., 1985. Late Paleozoic conodonts from ribbon chert delineate imbricate thrusts within
the Antler Formation of the Slide Mountain terrane, central British Columbia. Geology, v. 13, no. 11, pp. 794-798.

Structural relationship of the Slide Mountain, Cariboo and Quenelle terranes - cord2struik.jpg

       Is Quesnellia 'exotic' or 'native'?
    Armstrong, R.L. and Ghosh, D.K. 1990. Westward movement of the 87Sr/86Sr=0.704 line in southern B.C. from Triassic to Eocene time: monitoring the tectonic overlap of accreted terranes on North America. GAC Abst. w. Prog., Vancouver, pA4.
    Abstract - Prior to late Triassic and early Jurassic all magmatic rocks of Quesnellia had Sr/Sr below .704, therefore oceanic.By middle Jurassic  (accretion of Stikinia - Western Paleozoic and Triassic of the Klamaths) the .704 line had shifted 200 km westward of the leading edge of Quesnellia to just west of the Okanagan Valley. In the east Middle Jurassic plutons stitch the fault separating Quesnellia from North America; suturing took place in late Early to early Middle Jurassic.  By mid-Cretaceous (accretion of Wrangellia) the .704 line had moved only a further 25km westwards, but by Eocene time ( it had moved 75 km west of the Okanagan valley. During mid-Cret to Eocene seds of the fold and thrust belt in eastern B.C. moved 200 km eastwards.  At depth this movement must have been partitioned into crustal thickening to accommodate 125 km of shortening, and 75 km of additional overriding of N.America by Quesnellia.  The amount of tectonic overlap observed today must be reduced by 75 km to account for extension. Seds of the fold and thrust belt were deposited on the basement which presently underlies Quesnellia.

    Smith, A.D. and Lambert, R.S., 1995. Nd, Sr, Pb isotopic evidence for contrasting origins of late Paleozoic volcanic rocks from the Slide Mountain and Cache Creek terranes, south-central British Columbia. CJES, 32, 447-459.
    Map of sample areas in the Fennel allochton (Slide Mountain) and southern Cache Creek terranes - cord2smith1.jpg
    Comment - Slide Mountain Fennell Fm Late Pennsylvanian basalts resemble MORB but have kaersutite or augite dominated mineralogies;  EpND300 = +7.7 to +10.2. Pb isotope values favour a marginal basin rathern than a back arc. Cache Creek of the Bonaparte subterrane (middle Mississippian?) are within-plate. EpNd340 = +4.2-+5.6, and lead shows a transition towards DUPAL signatures. Baslatic andesite and andesitic tuffs, also found in the Bonaparte subterrane, are tentatively correlated with Late Triassic to Early Jurassic low-K tholeiite of the Nicola Group of Quesnellia.

    Smith, A.D., Brandon, A.D., and Lambert, StJ., 1995. Nd-Sr isotope systematics of Nicola Group volcanic rocks, Quesnel terrane. CJES, 32, 4, 437-446.
    Comment - EpsilonNd3\222 = +5.1 - +7.8 = early Mesozoic island arcs; +5 - +7.9 for picrite -shoshonite samples.

    Ferri, F., 1997. Nina Creek Group and Lay Range assemblage, north-central British Columbia: remnants of late Paleozoic oceanic and arc terranes. CJES, 34, 853-874.
    comment: volcanic rocks are MORB with no interbedded arc rock types.

    Distribution of Slide Mountain and Harper Ranch terranes along the length of the Cordillera - cord2ferri1.jpg
    Map of the Nina Creek area - cord2ferri2.jpg
    Stratigraphy of the Nina Creek Group and Lay Range assemblage - cord2ferri3.jpg
    Spidergrams for the Nina Creek Group and Lay Range assemblage - cord2ferri4.jpg
    Plate tectonic model with Slide Mountain as a back arc basin - cord2ferri5.jpg

    Erdmer, P. Thompson, R. I., and Daughtry, K. L., 1999. Pericratonic Paleozoic succession in Vernon and Ashcroft map areas, British Columbia. In: Cordillera and Pacific margin/ Interior Plains and Arctic Canada. Current Research - Geological Survey of Canada. 205-213.
        Comment:  Ductilely deformed and metamorphosed pericratonic rocks of inferred Early Paleozoic age overlie the
    Neoproterozoic-Eocambrian Silver Creek schist in the Vernon map area along an apparent stratigraphic contact. Permian (Harper Ranch Group) and Triassic (Nicola Group and Slocan Formation) strata overlie the pericratonic succession along an unconformable depositional contact. The pericratonic succession, long  recognized to include amphibolitic schist, marble, and quartzite,  includes in addition to these a distinctive metaconglomerate, and  forms a robust regional marker. The tripartite regional stratigraphy and its inferred Proterozoic or older depositional basement cross the Okanagan Valley without apparent offset, and persist for at least 100 km westward, as far as the Nicola horst.  The pericratonic succession underlies rocks presently assigned to the Quesnellia terrane at this latitude.

Eocambrian granite clasts in southern British Columbia shed light on Cordilleran hinterland crust  Philippe Erdmer, Larry Heaman, Robert A. Creaser, Robert I. Thompson, and Ken L. Daughtry  Can. J. Earth Sci./Rev. Can. Sci. Terre 38(7): 1007-1016
                The Spa Creek assemblage is a distinctive thin pericratonic succession that crosses the Okanagan Valley in the hinterland of the southern Cordilleran  Orogen in Canada. The succession was ductilely deformed and metamorphosed before deposition of overlying Triassic dark metaclastic strata. A metaconglomerate within the succession, locally  composed of more than 90% biotite granite clasts, yielded five fractions of euhedral zircon that define a   precise U–Pb upper intercept of 555.6 ± 2.5 Ma, inferred to be the age of a nearby pluton. Other clasts in the metaconglomerate are generally more abundant, consisting of quartzite, amphibole schist, chlorite schist,  sericite schist, biotite schist, and quartz–feldspar porphyry. They are likely host rocks of the pluton and, if so, are Late Proterozoic or older. The granite is interpreted as a terminal product of the Eocambrian rifting that preceded Paleozoic miogeoclinal sedimentation farther inboard. The continuity of  pericratonic rocks west of the miogeocline and the occurrence of Proterozoic cratonic rocks at the surface west of the Okanagan Valley show that the ancient continental margin extends into a region where most of the crustal lithosphere was until now thought to consist of accreted Phanerozoic arc and accretionary complexes.
        Western extent of the eastern Cordillera beneath Quesnellia - cordspacreek.jpg

Nature of the basement to Quesnel Terrane near Christina Lake, southeastern British Columbia S.L. Acton, P.S. Simony, and L.M. Heaman, Can. J. Earth Sci., 39(1), p. 65-78
             The character of the Paleozoic basement of Quesnel Terrane and the position of the terrane accretion surface that separates Quesnel and Kootenay terranes  from rocks of the ancient North American margin are  subjects of debate. To address these problems, detailed  mapping and U–Pb geochronologic studies were carried out in the Christina Lake area to define the relationship of the Mollie Creek assemblage, Josh Creek diorite, and Fife diorite to similar lithologies in the Greenwood – Grand Forks and Rossland regions, and to place limits on the ages of regional deformation and local position of the terrane accretion surface. Deformed metasedimentary rocks of the Mollie Creek assemblage may correlate with sedimentary rocks of the Pennsylvanian to Early  Triassic Mount Roberts Formation in the Rossland area. The Mollie Creek assemblage is intruded by the foliated  Late Triassic Josh Creek diorite. The Josh Creek diorite and Mollie Creek assemblage have been deformed together as a result of phase two deformation, following  the intrusion of the Josh Creek diorite in the Late Triassic and prior to the intrusion of the Fife diorite and  deposition of the overlying Rossland Group in the Early Jurassic. Based on relative age, structural position, and lithological similarities to other units within Quesnel  Terrane, the Mollie Creek assemblage, Josh Creek diorite, and Fife diorite are a part of Quesnel Terrane and lie above the terrane accretion surface in theChristina Lake area. Therefore, Quesnel Terrane does not unconformably overlie basement rocks of known North American affinity in this region.
        Relative disposition  allochthonous and pericratonic terranes according to Acton et al. - cordchris1.jpg
        Distribution of North American Precambrian crust within the Quesnel Terrane of the Southern Canadian Cordillera - cordchris2.jpg
        Geological section across the Quesnel Terrane showing the horst structure of the Grand Forks - Kettle River Complex - cordchris3.jpg

       What do the isotopic characteristics of Cordilleran terranes tell us about their origin?

            Patchett, P. J. and Gehrels, G. E, 1998. Continental influence of Canadian Cordilleran terranes from  Nd isotopic study, and significance for crustal growth processes. Journal of Geology. 106, 3, 269-280.
        Comment - Nd isotopic data are presented for rocks of the terrane assembly that lies inboard of the Stikine terrane in the Canadian  Cordillera of British Columbia and Yukon. These are, from most  inboard outward: Cassiar, Kootenay, Slide Mountain, Quesnel, and Cache Creek terranes. They are regarded as documenting a  transition from terranes whose evolution was closely tied to that  of the North American continental margin out to far-traveled  oceanic terranes. The results emphasize sedimentary rocks as  indicators of tectonic position of the crustal fragments. Sedimentary rocks of the Cassiar and Kootenay terranes show a  strong connection to miogeoclinal sediment sources. Argillites of  Pennsylvanian-Permian age from a paleontologically controlled  section in the Slide Mountain terrane are also consistent with sediment sources in the North American miogeocline. Igneous rocks of the Slide Mountain, Quesnel, and Cache Creek terranes show juvenile oceanic or arc origins based on epsilonNd values between +3 and +10, and are essentially identical with published results. Cache Creek and Quesnel terranes also contain sediments with positive epsilonNd values, suggesting a juvenile, ultimately volcanogenic, origin. Both terranes, however, also contain some Triassic and apparently Pennsylvanian-Permian sedimentary rocks with negative epsilonNd values between  -5 and -7, like those of Devonian to Jurassic sedimentary rocks of the North American miogeocline. Possible explanations include proximity to sources of North American terrigenous sediment, expected in Triassic time, or very far-traveled fine-grained sediment in the form of hemipelagic clay or eolian dust for older samples. The addition of a continental sedimentary component to wide areas of the Cordillera represents an important point of comparison to Proterozoic orogens, where this component affected the isotopic signatures, but usually cannot be separately identified due to intense reprocessing during orogenesis.

        Cui, Y. and Russell, J.K. 1995. Nd-Sr-Pb isotopic studies of the southern Coast Plutonic Complex, Southwestern British Columbia. BGSA, 107, 2, 127-138.
        Abstract - Plutonic and volcanic rocks have EpNd values of +4.2 to +8.9.  There are no significant variations in Nd or Sr isotopic composition with rock type or age. Many intrusions have isotopic compositions and TDM ages consistent with the combined effects of melting of mantle and mixing with subordinate istopically juvenile terranes, e.g. Wrangellia.

            Samson, S.D., et al. 1989. Evidence from neodymium isotopes for mantle contributions to Phanerozoic crustal genesis in the Canadian Cordillera. Nature, 337, 705-709.

EpsilonNd characteristics of rocks from the Stikinia and Alexander terranes - cord2samson1.jpg

    The age and tectonic environment of the rocks of the Stikinia terrane

    Johannson-G.G.; Smith-P.L.; Gordey-S.P., 1997. Early Jurassic evolution of the northern Stikinian Arc: evidence from the Laberge Group, northwestern British Columbia. Canadian-Journal-of-Earth-Sciences. 34, 7, 1030-1057.
      Abstract: This study resolves fundamental questions concerning the age, provenance, and depositional history of Laberge Group strata in the Whitehorse Trough. The Jurassic Inklin Formation straddles the Stikine and Cache Creek terranes along much of the length of the Whitehorse Trough. Ammonite biochronology indicates an age range of early Sinemurian to late Pliensbachian and provides the temporal framework for interpreting basin history. Strong temporal trends in both paleocurrent patterns and sandstone-conglomerate petrofacies allow definition of three discrete phases in basin-fill history. Stable tectonics characterized by relative volcanic quiescence and low sedimentation rates prevailed during the Sinemurian. Sinemurian sandstone-conglomerate petrofacies record a transitional-arc provenance derived from erosion of the Upper Triassic volcanic pile, flanking coastal sediments, and arc roots of Stikinia to the southwest. During the early Pliensbachian, arc dissection was interrupted by a major magmatic episode with widespread rejuvenated volcanism that caused a strong provenance shift to volcanigenic sources, indicating derivation from a largely undissected Stikinian arc. Southwest-derived, northerly longitudinal paleoflow during the Sinemurian changed to opposed bidirectional radial or transverse paleoflow systems in the early Pliensbachian. Cannibalism of broadly coeval basinal strata and/or reflected sediment gravity flows were the result of episodic growth of a mobile outer forearc rise, initiating southwest-directed paleoflow systems during the early Pliensbachian and the possible development of a ridged forearc phase. U-Pb dates of 186.6 -1/+-.5 and 186 +/- 1 Ma from a granite clast and tuff unit, respectively, of the Kunae Zone (early late Pliensbachian) and sandstone-conglomerate petrofacies indicate a late Pliensbachian  depositional regime dominated by tectonic controls. The influx of  granitic detritus indicates a rapid transition to a fully dissected arc  provenance, where accelerated uplift of segments of the arc massif, accompanied by intra-arc strike-slip faulting, resulted in rapid arc dissection and unroofing of comagmatic Pliensbachian plutons.

           The Cache Creek Terrane

  Ghent, E.D., Erdmer, P., Archibald, D.A., and Stout, M.Z., 1996. Pressure-temperature and tectonic evolution of Triassic lawsonite-aragonite blueschists from Pinchi lake, British Columbia. CJES, 33, 800-810.

    Hrudey-M-G; Struik-L-C; Whalen-J-B, 1999. Geology of the Taltapin Lake map area, central British Columbia. In: Cordillera and Pacific margin/ Interior Plains and Arctic Canada--Cordillere et marge du Pacifique/ Plaines interieures et  regions arctiques du Canada.
    Abstract: : The Taltapin Lake map area (93 K/6) is characterized by  Permian to Jurassic Sitlika assemblage volcanic and sedimentary
    rocks, the Late Triassic-Middle Jurassic Taltapin metamorphic complex of mainly amphibolite and strongly foliated to gneissic diorite, and Jurassic diorite to granite plutons of the Stag Lake and Francois Lake suites. Tertiary Ootsa Lake and Endako groups blanket older units, and are vesicular andesites, and basalts. Ootsa Lake Group also contains dacite, rhyolite, and rhyodacite breccia. The Permo-Triassic mafic Volcanic unit, and Triassic-Jurassic Eastern clastic unit of the Sitlika assemblage appear distinct lithologically, metamorphically, and structurally from Taltapin
    metamorphic complex units. The Sitlika assemblage separates rocks of Cache Creek and Stikine terranes, hence Taltapin metamorphic complex is interpreted as a metamorphic equivalent of Stikine Terrane, rather than metamorphosed Cache Creek Terrane. The Taltapin metamorphic complex was deformed and metamorphosed prior to the Late Triassic. It was further metamorphosed and juxtaposed with Sitlika assemblage between the Late Triassic and Middle Jurassic.

Orchard-M-J; Struik-L-C; Taylor-H; Quat-M, 1999. Carboniferous-Triassic conodont biostratigraphy, Nechako NATMAP Project area, central British Columbia.  In: Cordillera and Pacific margin/ Interior Plains and Arctic Canada--Cordillere et marge du Pacifique/ Plaines interieures et
    regions arctiques du Canada. Current Research - Geological Survey of Canada.  97-108.
    Abstract: Fifty-seven new conodont collections from the Nechako NATMAP area contribute to a conodont biostratigraphic framework for the region. Most collections are from the Pope unit of the Cache Creek complex and are early Late Carboniferous (Bashkirian-Moscovian) to Middle Permian (Wordian). The most extensive carbonate buildup is Bashkirian-Moscovian, whereas latest Carboniferous to Permian limestone is much less common and Middle Permian buildups are known only in the north. The Sowchea clastic-volcanic unit is Late Permian to Late Triassic (Norian); it includes unique records of (?)Changshingian, Griesbachian, and Smithian fauna, and the first records of Middle Triassic Tethyan Gladigondolella in Canada. At two widely separated localities, breccia containing mixed conodont faunas show that Paleozoic and Triassic strata were reworked during or after the Late Triassic. Late Triassic conodonts are also reported from the Tezzeron unit and adjacent Takla Group of the Quesnellia terrane.

        The 'exotic' nature of Stikinia and Wrangellia
    Aberhan, M. 1999.Terrane history of the Canadian Cordillera: Estimating amounts of latitudinal displacement and rotation of Wrangellia and Stikinia.Geological-Magazine. 136, 5,  481-492.
    Comment: The Canadian Cordillera is largely a mosaic of terranes that are allochthonous relative to the autochthonous North American craton. Palaeobiogeographic data on pectinoid bivalves from various cratonal areas and from two western Canadian terranes, Wrangellia and Stikinia, are used to estimate the amounts of latitudinal displacement and rotation of these terranes that took place during and after Early Jurassic times. Distributional patterns of various species of the distinctive, very common bivalve Weyla, and a comparison of the positions of biogeographic boundaries between high-palaeolatitude, mixed and low-palaeolatitude faunas on the terranes and on the craton indicate that Wrangellia was displaced northward relative to the craton by at least several  hundred and possibly more than 1000 km since Sinemurian and Pliensbachian times. For Stikinia such estimates are even higher and exceed 1000 km. Biogeographic patterns also suggest that Wrangellia experienced at best minor rotation since Sinemurian times, while rotation from a more or less east-west alignment to its present northwest-southeast position seems possible for Stikinia prior to the Pliensbachian. Palaeomagnetic interpretations, suggesting that during Sinemurian and Pliensbachian times Wrangellia and Stikinia were in much the same latitudinal position relative to the craton as they are now, are in sharp contrast to the results from faunal data. The presence of warm oceanic surface currents, oceanographic effects of elongated barriers, climatic change and differential latitudinal displacements due to rotation appear to be insufficient explanations for the discrepancy between the interpretation of palaeomagnetic and faunal evidence.

    Aberhan, M, 1998. Paleobiogeographic patterns of pectinoid bivalves and the early Jurassic tectonic evolution of western Canadian terranes. Palaios. ; 13(2): 129-148.
    Asbtract:  Utilizing new data from western Canada, the biogeography of Early Jurassic pectinoid bivalves along the eastern paleo-Pacific margin has been analyzed qualitatively and quantitatively. The studied areas range from the Andean Basin in the southern hemisphere to the Sverdrup Basin of Arctic Canada and include major allochthonous terranes of western Canada. While the Andean Basin exhibits a mixed bivalve fauna of austral, bipolar, and low latitude-East Pacific forms, pectinoid bivalves from the Canadian craton are characterized by a high percentage of boreal and bipolar taxa. The western Canadian allochthonous terranes Wrangellia and Stikinia show a mixed influence of low latitude-East Pacific and boreal/bipolar forms until Pliensbachian times. During the Toarcian/Early Aalenian, taxa typical of low latitudes disappeared. This pattern of a latitudinally differentiated Early Jurassic bivalve fauna, which apparently is climatically   controlled, seriously undermines the hypothesis of a uniform West American bivalve province. Based on diversity gradients, similarity coefficients, cluster analyses, and distributional patterns of characteristic taxa, biogeographic data have been used to constrain the latitudinal positions of Wrangellia and Stikinia through time. During the three analyzed time intervals (Hettangian/Sinemurian, Pliensbachian, and Toarcian/Early Aalenian), both terranes were in the northern hemisphere and in the eastern paleo-Pacific. During all of the Early Jurassic, Wrangellia and Stikinia were close together and were moving northward. Paleolatitudes corresponding to those of the Western Canada Sedimentary Basin in Alberta were not reached before Toarcian times. By the end of the Early Jurassic, both terranes were in much the same latitudinal position relative to the craton as they are now. Consistent with biogeographic patterns are Early Jurassic latitudinal displacements of approximately 1300 km.

        Harris-M.J.; Symons-D.T.A.; Blackburn-W.H.; Hart-C.J.R., 1997. Paleomagnetic and geobarometric study of the mid-Cretaceous Whitehorse Pluton, Yukon Territory. Canadian-Journal-of-Earth-Sciences. 34, 10, 1379-1391.
       Abstract:  This is the first of several Lithoprobe paleomagnetic studies underway to examine geotectonic motions in the northern Canadian Cordillera. Except for one controversial study,  estimates for terranes underlying the Intermontane Belt in the Yukon have been extrapolated from studies in Alaska, southern British Columbia, and the northwestern United States. The  Whitehorse Pluton is a large unmetamorphosed and undeformed tonalitic body of mid-Cretaceous age ( ~112 Ma) that was intruded into sedimentary units of the Whitehorse Trough in the Stikinia terrane. Geothermobarometric estimates for eight sites around the pluton indicate that postmagnetization tilting has been negligible since cooling through the hornblende-crystallization temperature and that the pluton is a high-level intrusion. Paleomagnetic measurements for 22 of 24 sites in the pluton yield a well-defined characteristic remanent magnetization (ChRM) direction that is steeply down and northwards. The ChRM direction gives a paleopole of 285.5 deg;E, 81.7 deg;N (dp/inf = 5.3 deg;, infm/inf = 5.7 deg;). When compared with the 112 Ma reference pole for the North American craton, this paleopole suggests that the northern Stikinia terrane has been translated northwards by 11.0 +/- 4.8 deg; (1220 +/- 530 km) and rotated clockwise by 59 +/-17 deg. Except for an estimate from the 70 Ma Carmacks Group volcanics, this translation and rotation estimate agrees well with previous estimates for units in the central and southern Intermontane Belt. They suggest that the terranes of the Intermontane Belt have behaved as a fairly coherent unit since the  Early Cretaceous, moving northward at a minimum average rate of 2.3 +/- 0.4 cm/a between 140 and 45 Ma.

Distribution of Permian fusilinacean faunas in the Canadian Cordillera - cord2fusil1.jpg


    Gabrielse-H., 1998. Geology of Cry Lake and Dease Lake map areas, north-central British Columbia. Bulletin-of-the-Geological-Survey-of-Canada. 504, 1-147.
    Abstract: Cry Lake and Dease Lake map areas include six well defined  terranes each characterized by distinctive lithological assemblages of different ages, structural styes, and contained mineral deposits. Miogeoclinal strata of Ancestral North America  range in age from Late Proterozoic to Early Mississippian. They  have been intruded by voluminous Mesozoic and Cenozoic  granitic rocks, in places associated with tungsten, lead, and zinc  occurrences. The Slide Mountain Terrane contains Devonian to  Permian rocks typical of oceanic and island are environments.  The Kootenay(?) Terrane is characterized by strongly tectonized,  mainly weakly metamorphosed, siliceous strata. Ultrabasic rocks  have potential for jade occurrences and a few vein deposits of  lead, zinc, gold, and silver have been explored. Rocks assigned to  Quesnellia are of Mesozoic island arc lithologies. In one locality,  granodiorite is host to an important copper deposit. Low grade  nickel and chromite deposits are hosted by an Alaskan-type  ultramafic body. The Cache Creek Terrane is dominantly oceanic in lithology but includes some assemblages of island arc or rift  affinity. The terrane ranges in age from Devonian through Early Jurassic. Ultrabasic rocks host jade and asbestos deposits and are spatially related to numerous placer gold deposits. The island arc or rift volcanics host a large zinc and copper volcanogenic sulphide deposit. Rocks of Stikinia represent upper Paleozoic to Lower Jurassic island arc assemblages which are overlain by upper Mesozoic to Recent sedimentary and volcanic overlap assemblages. Copper, molybdenum, gold, lead, and zinc occurrences are found in the volcanic and plutonic rocks. Coal occurs locally in overlap sedimentary rocks.

    The accretionary history of the Canadian Cordillera

    Anderson, P.G.and Hodgson, C.J., 1989. The structure and geological development of the Erickson gold mine, Cassiar District, British Columbia, with implications for the origin of mother-lod-type gold deposits. CJES, 26, 12, 2645-2660.
    Comment - Slide Mountain ocean separates Quesnel arc from continent; amalgamation at 208 = Triassic Jurassic boundary; amalgamation of Stikine arc above an east dipping subduction zone at 180 = late Early Jurassic; amalgamation of Alexander at 130 = early Early Cretaceous.

    The accretionary history of the Canadian Cordillera, Anderson and Hodgson, 1989 - cord2hodg1.jpg

    The accretion of Wrangellia at the southern end of the Cordillera

    On the following terrane map note the convergence of Wrangellia with Quesnellia at the expense of Stikinia at the southern end of the Cordillera.

Terrane Map of the Canadian Cordillera - cord2terr1.jpg

    The following figure illustrates the structural/stratigraphic relationships between Wrangellia (Skagit gneiss), Stikinia (Hozameen), and the Methow arc built on the western leading edge of Quesnellia.

The Skagit-Methow crustal section at the southern end of the Canadian Cordillera - cord2meth1.jpg

    The following figures illustrate the relationship between Wrangellia, Stikinia and Quesnellia in the Cascade region of Washington and British Columbia at the southern end of the Canadian Cordillera, as interpreted by M.F. McGroder (BGSA, 1991).

Regional tectonic map of the southern Canadian Cordillera/northwestern Washington - cord2mcgrod1.jpg

Regional cross section across the Southern Cordillera - cord2mcgrod2.jpg

Cross sections illustrating the development of the southern Canadian Cordillera - cord2mcgrod3.jpg

Paleogeographic setting of the southern Canadian Cordillera prior to the mid-Cretaceous orogeny - cord2mcgrod4.jpg


Structural Provinces of North America.


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