draft - university of toronto t-space · draft 1 cambrian detrital zircon signatures of the...

Draft

Cambrian detrital zircon signatures of the northern

Canadian Cordilleran passive margin, Liard area, Canada: evidence of sediment recycling, non-Laurentian ultimate

sources and basement denudation.

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2016-0127.R1

Manuscript Type: Article

Date Submitted by the Author: 21-Feb-2017

Complete List of Authors: McMechan, Margaret; Geological Survey of Canada, Currie, Lisel; Geological Survey of Canada – Calgary Ferri, Filippo; BC Ministry of Natural Gas Development, Tenure and Geoscience Branch Matthews, William; University of Calgary, Department of Geosciences O'Sullivan, Paul; Apatite To Zircon, Inc.; Geosep Services

Keyword: detrital zircon, Cambrian, sediment recycling, non-Laurentian sources, Cordilleran passive margin

Note: The following files were submitted by the author for peer review, but cannot be converted to PDF. You must view these files (e.g. movies) online.

cjes-2016-0127.R1-suplemental-2.xlsm

https://mc06.manuscriptcentral.com/cjes-pubs

Canadian Journal of Earth Sciences

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Cambrian detrital zircon signatures of the northern Cordilleran passive margin, Liard area,

Canada: evidence of sediment recycling, non-Laurentian ultimate sources and basement

denudation

Margot McMechan1, Lisel Currie2, Filippo Ferri3, William Matthews4 and Paul O’Sullivan5

1 Geological Survey of Canada – Calgary, 3303 33rd St. NW, Calgary, AB T2L 2A7;

[email protected]

2 Geological Survey of Canada – Calgary, 3303 33rd St. NW, Calgary, AB T2L 2A7;

[email protected]

3 Tenure and Geoscience Branch, British Columbia Ministry of Natural Gas Development

Victoria, BC; [email protected]

5 Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB

T2N 1N4; [email protected]

5 GeoSep Services, 1521 Pine Cone Rd, Moscow, Idaho 83843, USA;

[email protected]

Author responsible for correspondence:

Margot McMechan Geological Survey of Canada – Calgary, 3303 33rd St. NW, Calgary, AB

T2L 2A7; [email protected]; phone: 403-292-7154, fax 403-292-5377

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Cambrian detrital zircon signatures of the northern Cordilleran passive margin, Liard area,

Canada: evidence of sediment recycling, non-Laurentian ultimate sources and basement

denudation.

Margot McMechan, Lisel Currie, Filippo Ferri, William Matthews and Paul O’Sullivan

ABSTRACT

Detrital zircon U-Pb age probability distributions for the Cambrian Vizer formation (informal)

and Mount Roosevelt Formation (middle member) of the northern Canadian Cordilleran passive

margin indicate extensive recycling from ~1.7 to 1.6 Ga Paleoproterozoic sandstones and

Proterozoic and Lower Cambrian strata, respectively. The units have minor or no first cycle input

from Laurentian basement. The lower part of the Vizer formation contains North American

Magmatic Gap (1610 to1490 Ma) detrital zircons and lacks ultimate Grenvillian sourced grains,

indicating that the grains were likely sourced from a nearby Mesoproterozoic basin and have an

ultimate non-Laurentian source. Detrital zircon U-Pb ages of 670 to 640 Ma from the middle

member of the Mount Roosevelt Formation indicate associated volcanic clasts were locally

sourced, and are not of syn-sedimentary Middle Cambrian age. Provenance of these units was

indirectly impacted by the Liard Line basement feature.

Detrital zircon U-Pb age probability distributions from the northern Canadian Cordilleran

passive margin indicate sediments were sourced from the east in the Early Cambrian

(Terreneuvian; Vizer formation and correlatives) and the northeast during Early Cambrian

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(Series 2) deposition of Sekwi Formation and correlative strata. In the early Middle Cambrian

the middle member of the Mount Roosevelt Formation was primarily locally sourced, whereas

the upper member was derived from Laurentian basement to the east and southeast. The change

from reworked Paleoproterozoic cover in the Terrenuvian to primary basement sources in the

Middle Cambrian suggests significant denudation of the basement occurred southeast of the

Liard Line.

Keywords: detrital zircon, Cambrian, sediment recycling, non-Laurentian sources,

Cordilleran passive margin

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INTRODUCTION

The area now forming the western margin of Laurentia has had a protracted history of extension,

sediment accumulation and shortening. Rifting events in the middle and late Neoproterozoic

(Cryogenian , Ediacaran) established the margin (e.g. Stewart 1972; Arnott and Hein 1986; Ross

et al. 1995) and resulted in the deposition of two prominent sedimentary successions: the

Neoproterozoic Windermere Assemblage and the Ediacaran to Middle Devonian Cordilleran

passive margin. Several northeast-trending, basement-controlled fault zones affected

sedimentation within the Laurentian continental margin succession of the Canadian Cordillera.

The most prominent occurs near 60o N at a feature termed the Liard Line, which has been

interpreted as a Neoproterozoic and lower Paleozoic transfer fault zone separating a wide lower

plate margin on the north from a narrow upper plate margin on the south (Fig. 1; Cecile et al.

1997). This paper describes the detrital zircon U-Pb age signatures of the pre-Silurian quartz

arenite of theVizer formation (informal) and Middle Cambrian volcanic clast-bearing

conglomerates of the Mount Roosevelt formation exposed near the Liard Line and uses this

information together with published detrital zircon age information from the various units

described in the geological framework below to constrain their provenance and outline the major

changes in detrital zircon source areas during the Early and Middle Cambrian. Our results

indicate: 1) extensive recycling from the ~ 1.70 to 1.6 Ga Paleoproterozoic sedimentary blanket

deposited over northern Laurentia and a complete absence of ultimate Grenville sourced grains

in the Vizer formation and middle member of the Mount Roosevelt formation; 2) the component

of North American magmatic gap (1610 to 1490 Ma) aged zircons found in the lower part of the

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Vizer Formation were ultimately derived from non-Laurentian sources and most likely recycled

from a nearby Mesoproterozoic basin; 3) the Vizer formation is most likely Lower Cambrian

Terreneuvian in age; 4) the major change to first-cycle basement sources in the upper member of

the Mount Roosevelt Formation likely reflects denudation of the Laurentian basement; and 6)

stratigraphic changes associated with the Liard Line had an impact on the provenance of the

Vizer and Mount Roosevelt formations.

GEOLOGICAL FRAMEWORK

The ancestral North American continent Laurentia, comprising Archean to Early Proterozoic

microcontinents separated by collisional and magmatic orogenic belts, formed between 2.0 and

1.8 Ga (Hoffman 1989; Whitmeyer and Karlstom 2007) as part of a larger continental

amalgamation termed Columbia (Rogers and Santosh 2002). Between 1.7-1.68 Ga and 1.65-1.60

Ma juvenile orogens formed along the southeastern side of Laurentia (Whitmeyer and Karlstrom

2007) and thick skinned deformation of the Forward Orogeny occurred inboard of the northwest

Laurentia margin prior to 1.663 Ga (Cook and MacLean 1995). Rifting along the northwestern

margin of Laurentia around 1.65 Ga resulted in rapid deposition of the 13 km thick Wernecke

Supergroup (Furlanetto et al. 2016) and most likely the 6 km thick Muskwa assemblage (Fig. 2).

Detrital zircon studies record a predominant Laurentian provenance for both Wernecke

(Furlanetto et al. 2009, 2016) and Muskwa (Ross et al. 2001) strata. Paleocurrent indicators and

age constraints suggest they are the distal equivalents of a sandstone package derived from

westward flowing river systems that blanketed at least the northern part of Laurentia in the late

Paleoproterozoic. Eastern remnants of this package are now preserved in the Athabasca, Thelon,

and Hornby Bay basins (Fig. 1; Young 1978; Ross et al. 2001; Rainbird et al. 2005). Similar

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detrital zircon age distributions from the Athabasca and Muskwa basins support their correlation,

whereas, detrital zircon age distributions from the Dubawnt Supergroup of the Thelon Basin are

dissimilar and indicate a different provenance (Rainbird et al. 2005; Rainbird and Davies 2007).

Local intense deformation of the northwestern edge of Laurentia during the Racklan Orogeny

occurred after deposition of the Wernecke Supergroup and before intrusion of the Wernecke

breccia ca. 1595 Ma (Thorkelson et al. 2005; Furlanetto et al. 2013). By 1.5 Ga north Australia,

south Australia and eastern Antartica were firmly attached to the western margin of Laurentia

(Karlestrom et al. 2001; Thorkelson et al. 2005; Ross and Villeneuve 2003; Stewart et al. 2010;

Furlanetto et al. 2013; Medig et al. 2014).

Extension along the western margin of Laurentia between about 1490 to 1400 Ma did not

produce full continental separation. It is recorded in western Canada by the PR1 (basal Fifteen

Mile Group, Medig et al. 2014) and Belt-Purcell basins (Fig. 1; Ross and Villeneuve 2003).

Sometime after 1380 Ma, renewed subsidence of the northwestern margin of Laurentia initiated

deposition of the Pinguicula Group (Medig et al. 2010) and the roughly correlative Dismal Lakes

Group (Cook and MacLean, 1995). Extension along the northern margin of Laurentia resulted in

intrusion of the Mackenzie dyke swarm (1267 ± 2 Ma, LeCheminant and Heaman 1989) and the

extrusion of the Coppermine River basalts above the Dismal Lake Group. After a period of

planation, predominantly platformal strata of the Mackenzie Mountains Supergroup and Shaler

Group (Fig. 1) were deposited within an intracratonic basin developed along the northwest edge

of Laurentia between about 1000 Ma and 775 to 720 Ma (Heaman et al. 1992; Rainbird et al.

1996; Milton 2015). Thick sandstones in the lower part of the succession with 1600 to 1000 Ma

detrital zircons derived predominantly from the Grenville orogenic belt of eastern Laurentia were

deposited by west-northwest flowing rivers (Rainbird et al. 1997, 2012).

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The local extrusion of mantle sourced volcanic rocks at 775 Ma (Little Dal Basalts) in the

Mackenzie Mountains correlates with the Gunbarrel magmatic event and signals the initiation of

continental extension along this part of the western edge of Laurentia that would ultimately lead

to the deposition of the Windermere Supergroup (Milton, 2015). In northwest Laurentia, the first

narrow rift basin formed in the Mackenzie Mountains and was filled by the Coates Lake Group

whose uppermost strata have yielded a 732.2 ± 3.9 Ma Re-Os age (Rooney et al. 2014). The

onset of continental rifting along the length of the western margin of Laurentia to form either the

proto-Pacific Ocean (e.g. Stewart 1972; Arnott and Hein 1986; Ross et al. 1989; Ross et al.

1995) or a large intercontinental rift basin (Colpron et al. 2002) resulted in deposition of the

Windermere Supergroup. Along the segment north of 57o N sedimentation began sometime after

728 +8/-7 Ma (Evenchick et al. 1984) and before 717.43 ± 0.14 Ma (Macdonald et al. 2010). In

this same area local rift-related volcanism is recorded by the Gataga volcanics (689.1 ± 4.6 Ma;

Ferri et al. 1999).

In the late Ediacaran a major thermal and rifting event initiated deposition of the Ediacaran to

Middle Devonian Cordilleran passive margin succession (e.g. Bond and Kominz 1984), from

which our samples were obtained. In most areas along the eastern edge of this passive margin an

Ediacaran to Lower Cambrian sandstone package forms the basal unit (Gog Group and

correlatives). This facies appears to be offset 250 km to the northeast across the Liard Line

(Aitken 1993). Changes in older strata suggest this feature may have been established during

Cryogenian (Aitken 1993) or Paleoproterozoic(?) rifting events and reactivated in the Ediacaran

(Aitken, 1993). Local depositional thickening and volcanism within the Canadian Cordilleran

passive margin indicate widespread episodic extension beginning in the Middle Cambrian

(Goodfellow et al. 1995). In the Liard area this resulted in the development of the northwest-

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trending Roosevelt graben system above the western Liard Line and the local deposition of

coarse clastic strata of the Mount Roosevelt Formation (Taylor and Stott 1973; Fritz 1979, 1991;

Post and Long 2008).

SAMPLES ANALYSED

Samples were collected from two Lower Paleozoic horizons along the western part of the Liard

Line: the Vizer and Mount Roosevelt formations (Fig. 1).

Vizer formation (informal)

A quartz arenite unit exposed in the Cariboo Range immediately south of the B.C. – Yukon

border (Locality 3b in Fig. 1, 2) has been informally called the Vizer formation by Benjamin et

al. (2011), who studied the unit in detail as a potential source for fine-grained, pure (>97%)

quartz sands to be used by the petroleum industry in the fracking process. The Vizer formation is

comprised mainly of pale grey to white, fine- to medium-grained, thin- to thick- bedded, sub-

angular to subrounded quartz arenite (Benjamin et al. 2011). It is unconformably overlain by

Silurian carbonate and its base is not exposed because it lies in the immediate hangingwall of the

Larsen Fault (McMechan et al. 2012). One of our samples is from the lowermost exposures and

the other comes from the middle part. Taylor and Stott (1980) suggested a Lower and (?) Middle

Cambrian age and correlated these strata mainly with strata now called the Mount Roosevelt

Formation, whereas McMechan et al. (2012) suggested an Ediacaran to Lower Cambrian age

based on lithologic similarity with the undated quartz arenite unit underlying the Mount

Roosevelt Formation in the southwest Liard area, as shown in Figure 2. Recently, Fallas et al.

(2014) suggested these strata should be assigned to the uppermost Cambrian to Ordovician Crow

Formation. The Crow Formation comprises variably subarkosic sandstone, conglomerate,

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maroon siltstone, minor carbonate and local volcanics in exposures immediately northwest of the

Cariboo Range (Pigage 2009; Fig. 1, localities 2, 3a). From a sedimentology and compositional

perspective it seems unlikely that the nearly pure quartz arenite succession exposed in the

Cariboo Range is part of the variably subfeldspathic package comprising the Crow Formation,

particularly since crossbeds in the Crow Formation indicate a west to southwest transport

direction (Pigage, 2009). Detrital zircon U-Pb age results for 6 samples of the Crow Formation

reported by Pigage (2009) are compared with detrital zircon signatures from the Mount

Roosevelt and Vizer formations below.

Mount Roosevelt Formation

The lower Middle Cambrian Mount Roosevelt Formation (Fritz 1979; 1991) represents the

progradation of an alluvial fan delta into a marine environment (Post and Long 2008). Three

members comprise the up to 1500 m thick formation. The lower member is characterized by

ooid-bearing siltstone and sandstone, interbedded with carbonate and hematitic conglomerate.

The thick middle member comprises polymict, cobbly pebble conglomerate and the upper

member is comprised of karstified dolostone, calcareous cemented conglomerate and sandstone

and limestone. Deposition of the Mount Roosevelt Formation occurred in fault-controlled basins

with the thickness and distribution of the formation controlled by the location of active faults

(e.g. Fritz 1991; Ferri et al. 1999). The thickest development of the Mount Roosevelt Formation

occurs in the hanging wall of the Forcier fault immediately northwest of Muncho Lake (Post and

Long, 2008). Our sample (locality 3B in Fig. 1, 2) comes from a volcanic clast-bearing polymict

conglomerate in the middle member of the formation.

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Detrital zircons from a second sample of the Mount Roosevelt Formation were analysed by

Gehrels and Ross (1998) and reanalysed by Gehrels and Pecha (2014), who included this sample

in the Atan Group following the now discontinued terminology used by Taylor and Stott (1973).

This sample is from a coarse-grained to pebbly, carbonate-cemented quartz arenite horizon in a

clastic unit that is overlain by shale and limestone (Gehrels and Ross 1998). It comes from the

upper member of the Mount Roosevelt Formation exposed 14 km southeast of the middle

member sample location. In the Liard area, the Middle Cambrian Mount Roosevelt Formation

unconformably overlies Paleoproterozoic strata of the Muskwa assemblage in the east and up to

300 m of fine- to coarse-grained quartz arenite that likely correlates with the Vizer formation of

the Cariboo Range in the west (Fig. 2, see above).

METHODS

Detrital zircons from three new samples, two from the Vizer formation quartz arenite and one

from conglomerate of the Middle Cambrian Mount Roosevelt Formation, were processed and

analysed by AtoZ Incorporated, Bosie, Idaho using the LA- ICP-MS at the Geoanalytical

Laboratory, Washington State University, Pullman, Washington. Full details of the analytical

approach, grain descriptions and the data can be found in the Supplementary Information.

For grains that yield ages older than ca. 1000 Ma, the 207Pb/206Pb age is used, whereas for

younger grains the 206Pb/238U age is used. Analyses were filtered following the criteria of

Gehrels and Pecha (2014). Analyses with >10% uncertainty (1σ) in 206Pb/238U or the 206Pb/207Pb

age are not included in our analysis. Concordance is based on 206Pb/238U age/206Pb/207Pb age,

with 100% considered concordant. Analyses with >20% discordance (<80% concordance) or

>5% reverse discordance (>105% concordance) are not included.

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The resulting detrital zircon U-Pb age distributions for our samples and the Mount Roosevelt

Formation sample analysed by Gehrels and Pecha (2014) are compared with: 1) the U-Pb zircon

age distributions for other late Ediacaran and Cambrian aged strata; and 2) potential intermediate

sources (i.e. Proterozoic sedimentary strata through which grains may have been recycled) using

direct comparison of normalized probability plots (calculated using the Excel™ plug-in Isoplot

v. 4.15; Ludwig 1998, Ludwig 2012, Berkeley Geochronolgy Center, 2016) and

multidimentional scaling (MDS). MDS is a method of objectively interpreting large datasets.

Using the IsoplotR program of Vermeesch (2013; 2017) a ‘map’ of data points is produced on

which ‘dissimilar’ or unrelated samples plot far apart and ‘similar’ samples, such as samples

with similar provenance, or a sample and its ultimate or intermediate provenance, cluster closely

together. The ‘map’ is based on the D values (the maximum vertical separations between two

cumulative density functions) that are produced as part of the Kolmogorov-Smirnov test

(Vermeesch 2013). This study uses data from numerous sources including a few with small

sample sizes (n <50). Recent work by Pullen et al. (2014) suggests that the number of concordant

grains analysed for each sample needs to approach 300 for more meaningful statistical analysis.

Analyses from these other publications were also filtered using the criteria of Gehrels and Pecha

(2014).

DETRITAL ZIRCON GEOCHRONOLOGY

Results

Detrital zircons from two samples of the Vizer formation were analysed. Sample FF10-1 from

the lowest exposures of the unit contains a dominant 1900 to 1500 Ma age fraction with a lesser

2900 to 2500 Ma population. A distinct “shoulder” between 1700 and 1500 Ma is formed in part

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by 5 concordant grains with ages between 1605 and 1538 Ma that fall into a hiatus in Laurentian

magmatism between 1610 and 1490 Ma termed the North American magmatic gap (NAMG;

Ross and Villenueve 2003; Fig. 3). Sample 11EPF55A from the middle part of the formation has

a preponderance of 2000 to 1600 Ma grains with less common 3000 to 2200 Ma grains. Both

samples have a significant peak between 1900 and 1750 Ma. Neither contains zircons younger

than 1500 Ma and thus the zircon ages provide no useful information on the depositional age of

the Vizer formation. The samples are similar and have therefore been grouped together on the

normalized probability and MDS plots (Fig. 4, 5).

One sample from the middle member of the Middle Cambrian Mount Roosevelt Formation

(11EPF67A) yielded dominantly 2100 to 1600 Ma and 2800 to 2300 Ma grains, with two

concordant 700 to 600 Ma grains and one reliable ca. 3200 Ma grain. The probability plot has a

prominent peak between 1900 and 1700 Ma and a lesser peak between 2650 and 2500 Ma (Fig.

3). Zircons older than 2200 Ma make up a greater proportion of the zircons in this sample than in

the Vizer formation quartz arenites. There were no Early or Middle Cambrian (541 to 497 Ma)

grains.

DISCUSSION

Comparison with Cordilleran Passive Margin Cambrian to Ordovician Units

Detrital zircon results from our samples and the sample from the upper member of the Mount

Roosevelt Formation (Gehrels and Pecha, 2014) were compared with those of other Late

Ediacaran to Cambro-Ordovician units in the Canadian Cordilleran passive margin to determine

which units could have had similar detrital zircon provenances.

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Direct comparison of normalized probability plots (Fig. 4) for these units suggest the Vizer

formation has a different detrital zircon provenance from 1) the Franklin Mountain and Sekwi

formations and the Sekwi correlative unit because of the abundance of 1490 to 1000 Ma grains

and relative lack of 2000 to 1750 Ma grains in those samples; 2) the upper member of the Mount

Roosevelt Formation sample because of the abundance of 2500 to 2300 Ma grains and absence

of a strong 1880 to 1750 Ma peak in that sample; 3) the Crow Formation Northwest Liard

locality samples because of the presence of Ordovician aged zircon and the absence of 1750 to

1500 Ma grains in those samples; 4) the Yanks Peak Formation because of the lack of 1700 to

1600 Ma grains and presence of 1400 to 1000 Ma grains in that sample; and likely 5) the Crow

Formation Coal River locality samples because of the subdued 2000 to 1750 Ma peak and

component of 1400 to 600 Ma grains (8%) in those samples.

The MDS plot for comparison of detrital zircon signatures of Ediacaran to Cambro-Ordovician

units along the Canadian Cordilleran passive margin (Fig. 5) suggests the detrital zircon

signature of the Vizer formation is most similar to those of the McNaughton, Hamill, Vampire-

Narchilla units and the middle member of the Mount Roosevelt Formation. The similar detrital

zircon profiles of the Vizer formation with Lower Cambrian (Terrenevian) aged samples from

the McNaughton and Hamill formations suggests that the Vizer is most likely part of the

regionally extensive transgressive sandstone package at the base of the Cordilleran passive

margin succession. In the Mackenzie Mountains stratigraphic relationships (Aitken 1993;

MacNaughton et al. 2008) show that the Vampire interval is the basinal equivalent of nearshore

sandstones of the Backbone Ranges Formation. Comparable detrital zircon profiles of the

Vampire-Narchilla and Vizer formations in the Liard area suggests that a similar facies

relationship likely occurs between the Lower Cambrian (Terrenuevian; Pigage et al. 2015)

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Vampire-Narchilla formation and the nearshore sandstones of the Vizer formation. This would

also indicate a Terrenuevian Early Cambrian age for the quartz arenites of the Vizer formation.

Direct comparison of normalized probability plots of Ediacaran to Cambro-Ordovician units

along the Canadian Cordilleran passive margin (Fig. 4) suggest that our sample from the middle

member of the Mount Roosevelt Formation 1) is most similar in provenance to the Vizer

formation samples because of the width of the 2000 to 1600 Ma peak and subdued presence of

2500 to 2000 Ma grains, 2) has a different provenance from the Franklin Mountain and Sekwi

formations and Sekwi correlative unit because of the abundance of 1490 to 1000 Ma ultimate

Grenville sourced grains in those samples and 3) has a different provenance from the upper

member of the Mount Roosevelt Formation sample because of the relative abundance of 2400 to

2300 Ma aged grains and lack of a 1900 to 1700 Ma peak in that sample. The MDS plot (Fig. 5)

suggests the detrital zircon signature of the middle member of the Mount Roosevelt Formation

sample is most similar to the McNaughton, Hamill and Vampire-Narchilla units. Both direct

comparison of normalized probablility plots (Fig. 4) and the MDS plot (Fig. 5) suggest the

detrital zircon signature of the upper member of the Mount Roosevelt Formation differs from all

the other Ediacaran to Cambro-Ordovician units sampled to date in the Canadian Cordilleran

passive margin succession.

Comparison with Potential Intermediate Detrital Source Units

Due to its mechanical durability, zircon is commonly recycled from one sedimentary unit to

another without impacting the reliability of the U-Pb age determinations (e.g. Dickenson et al.,

2009). The significance of sedimentary recycling for Neoproterozoic and Cambrian strata in

northwestern Laurentia has been documented by Hadlari et al. (2012) and Lane and Gehrels

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(2014) who concluded most Neoproterozoic and Cambrian units in the Mackenzie – Wernecke

Mountains and adjacent Richardson Trough were recycled from intermediate (Proterozoic

sedimentary) sources. Almost all the Proterozoic successions mentioned previously in the

Geological Framework were exposed during the Cambrian (Fig. 1), making them potential

intermediate sources of detrital zircons found in the Vizer and Mount Roosevelt formations.

Direct comparison of normalized probability plots for the Vizer and Mount Roosevelt formation

with those from potential Proterozoic intermediate sources (Fig. 6) rules out the Neoproterozoic

Shaler, Mackenzie Mountains and Windermere supergroup units exposed in the Wernecke and

Mackenzie mountains and northwest Liard area (Fig. 1, 2, localities 1, 3b) as intermediate source

units for both the Mount Roosevelt and Vizer formations because they contain abundant 1490 to

1000 Ma (Grenville source) aged grains that the Vizer and Mount Roosevelt formations lack.

Unit Ps is not considered an important intermediate source for the Vizer formation because of the

abundant 2.0 to 1.9 Ga aged detrital zircons in that unit. Paleoproterozoic sandstones of the

Athabasca, Muskwa and Wernecke successions and Neoproterozoic deep water turbidites of the

Horsethief Creek Group and Ediacaran Yusezyu Formation are potential sources for the Vizer

formation. However, none of the potential intermediate source units contain the robust

contribution 2.5 to 2.2 Ga contribution found in the upper Mount Roosevelt Formation (Fig. 6).

Comparison with published probability density plots for samples from the Mesoproterozoic

Fifteen Mile and Pinguicula groups in the Hart Creek Inlier (Medig et al. 2012, 2014) suggest

that these would be unlikely intermediate sources for the Vizer and Mount Roosevelt formations

because they contain abundant detrital zircons with ages less than or equal to 1500 Ma (Fig. 7).

Whereas, the basal unit of the Pinguicula Group in the Wernecke inlier (Fig. 1, location 1a) has

very few <1500 Ma detrital zircon grains and could be a potential intermediate source (Fig. 7 A-

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C). Two of the three samples from this unit contained 1610 to 1490 Ma aged NAMG detrital

zircons (Fig. 7; Medig et al. 2012).

The MDS plot for comparison of detrital zircon signatures of the Vizer and Mount Roosevelt

formations with potential Proterozoic intermediate sources (Fig. 8) suggests that 1) the detrital

zircon signature of the Vizer formation is most similar to that of the Ediacaran Yusezyu

Formation; 2) the detrital zircon signature of the upper member of the Mount Roosevelt

Formation differs significantly from all the potential intermediate sources; and 3) the detrital

zircon signature of the middle member of the Mount Roosevelt Formation is similar to those of

the Paleoproterozoic Muskwa succession, Neoproterozoic Horsethief Creek Group and the

Ediacaran Yusezyu Formation. Data for the Pinguicula Group is not yet available for MDS

comparison.

The close similarity of detrital zircon signature for the Vizer formation to those of Proterozoic

intermediate sources suggests there is little if any first cycle Laurentian basement sourced

material in this unit. The abundance of 2500 to 2300 Ma zircons in the upper member of the

Mount Roosevelt Formation (25%, Fig. 4) as compared to the Muskwa (5%) implies a direct

cratonic source (Gehrels and Ross 1998). Magmatism between 2500 and 2300 Ma has a limited

distribution in western Canada (Fig. 1, Canadian Geochronology Knowledgebase 2013). The

most likely ultimate source for the 2500 to 2390 Ma grains are basement rocks in the western

Trans-Hudson Orogen. Other potential source areas include the La Ronge arc, Taltson magmatic

belt, Rae and Hearne provinces and eastern Trans-Hudson Orogen (Fig. 1). Abundant 2380 to

2300 Ma grains in the upper Mount Roosevelt Formation could have come from the Buffalo

Head, Thorsby or Wabamun terranes (Gehrels and Ross 1998) or rocks exposed near the western

margin of the Rae Province, north of the Athabasca basin (Fig. 1). Basement rocks in the eastern

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Trans-Hudson Orogen are considered a less likely source for 2500 to 2300 Ma grains because the

Trans-Hudson Orogen would provide a significant component of 1900 to 1800 Ma detrital

zircons, which are not observed in the upper Mount Roosevelt Formation sample. Recycled

zircons with 2500 to 2300 Ma ages occur in the northern Hottah Terrane (Davis et al. 2015). This

is considered to be an unlikely source since Cambrian sandstone samples unconformably

overlying the northern Hottah terrain at Great Bear Lake contain only a small component (~10%)

of these grains and a large component of 2000 to 1750 Ma grains (Hadlari, 2012). The 2050 to

1800 Ma grains in the upper Mount Roosevelt sample match well with plutons in several nearby

terranes to the east. The 2900 to 2500 Ma grains could have come from the Rae, Hearn or Slave

provinces (Fig. 1). The middle member of the Mount Roosevelt Formation contains a noticeable

component of 2500 to 2400 Ma aged detrital zircon grains that were ultimately derived from the

Laurentian basement areas mentioned above. They may indicate that a small component of first

cycle Laurentian basement material made its way into the Roosevelt graben or a lack of

sufficient sampling of zircon from feldspathic strata at the top of the underlying Muskwa

Assemblage (Tuchodi Formation, n = 19; Ross et al. 2001). Two concordant first-cycle

approximately 670 and 640 Ma detrital zircon grains occur in the middle Mount Roosevelt

Formation sample. Magmatism of this age is known from only two localities in western Canada

(Canadian Geochronology Knowledgebase, 2013; Yukon Geochronology Database, 2015). The

Gataga volcanics (689.1 ± 4.6 Ma; Ferri et al. 1999), which outcrop 75 km southwest of the

middle Mount Roosevelt Formation sample location and the Pool Creek Syenite (Fig. 2; 650 to

640 Ma, Pigage and Mortensen, 2004), located 150 km north of the middle Mount Roosevelt

sample locality. The older grain (669 ± 14 Ma) is intermediate in age while the younger (640 ±

10 Ma) detrital zircon grain is the same age as the Pool Creek Syenite. The erosion of volcanic

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and/or plutonic rocks associated with the Gataga Volcanics and the Pool Creek Syenite intrusion

form the likely sources. Occasional younger Neoproterozoic grains (690 to 640 Ma) are also

found in samples from the lower Cambrian Vampire-Narchilla and Cambro-Ordovician Crow

formations at the Coal River locality (Pigage 2009; Pigage et al. 2015). There was no detrital

zircon record of Middle Cambrian volcanism in the middle member of the Mount Roosevelt

Formation sample.

Potential Sources 1610 to 1490 Ma “North American Magmatic Gap” Grains, lower Vizer

formation

The detrital zircon age profile presented here for the lower Vizer formation is are the first

reported occurrence of NAMG detrital zircons (5% of accepted analyses) from the Cambrian

Laurentian margin succession not associated with Grenville aged grains (Fig. 3). This absence of

Grenville aged grains places serious doubt on the possibility that the NAMG zircons were

derived from eastern Laurentia, despite the occurance of 1520 and 1460 Ma magmatism in the

Pinware terrane (Fig. 1 inset map) of the easternmost Grenville orogen (Gower and Krogh 2002;

Heaman et al. 2004). The allochtonous Pinware terrane was accreted to the Archean and

Paleoproterozoic core of Laurentia during the (1250 to 980 Ma) Grenville Orogeny.

Consequently, any Pinwarian aged detrital zircon grains would be associated with younger (1350

to 1000 Ma) Grenville aged detrital zircon grains, as is found in the Shaler Group (Rayner and

Rainbird 2013). The complete absence of Grenville aged detrital zircon grains combined with the

older age range of the Vizer detrital zircon grains (1608 to 1532 Ma) as compared to the age of

Pinwarian magmatism (1520 to 1460 Ma) rule out Laurentia as a potential ultimate source.

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NAMG aged detrital zircons derived from non-Laurentian sources have been found from

northcentral Yukon to southern Arizona in Mesoproterozoic basins formed along the western

margin of Laurentia (Medig et al. 2014 and references therein). The ultimate source of the 1610

to 1490 Ma detrital zircon grains is thought to be the Mawson and North Australia cratons

(Stewart et al., 2010; Medig et al., 2014). Direct recycling from the three exposed Canadian

Laurentian margin Mesoproterozoic successions into the Cambrian Vizer Formation is unlikely.

First, the PR1 basin (Fig. 1; basal Fifteen Mile Group) located 900 km northwest of the Liard

area is characterized by a unimodal 1500 Ma detrital zircon population (Fig. 7D; Medig et al.

2014). These strata are directly overlain by younger Mesoproterozoic sediments of the Fifteen

Mile Group and were not available to provide material directly to Cambrian strata (Medig et al.

2014). Second, the basal unit of the Pinguicula Group (unit A) in the Wernecke Mountains 700

km northwest of the Liard area contain a small component of NAMG grains not associated with

younger grains (Fig. 7A-C; Medig et al. 2012). However, the Pinguicula Group in these areas is

unconformably overlain by the Neoproterozoic Mackenzie Mountains Supergroup (Medig et al.

2012) and was not available to provide material directly to Cambrian strata. Finally, the Belt-

Purcell basin, located 1200 km south of the Liard area (Fig. 1), is unconformably overlain by

Early Cambrian strata in northeastern exposures and potentially a source. The rarity of NAMG

grains in Ediacaran and Early Cambrian strata near the Belt-Purcell basin and to the north of this

basin (Gehrels and Pecha 2014; Matthews 2016) suggests the NAMG grains in the Vizer

formation were likely recycled from a more proximal source.

The absence of an exposed and therefore geologically viable source for the recycled NAMG

detrital zircon grains in the Vizer formation indicates that these grains most likely came from a

unit that has either been completely removed by lower Paleozoic erosion, is preserved only in the

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subsurface or has not yet been sampled. Unit Ps in the northwest Liard area provides evidence

for such a unit. Pigage (2009) suggested Proterozoic strata of unit Ps (Fig. 2) most likely

correlate with the Mesoproterozoic Pinguicula Group on the basis of a detrital zircon signature

that 1) lacks 1490 to 1000 Ma Grenville-sourced detrital zircons characteristic of the

Neoproterozoic Mackenzie Mountains and Shaler supergroups and eastern Windermere

Supergroup successions and 2) contains a strong 2000 to 1900 Ma peak that is absent in the

Paleoproteroic Wernecke, Athabasca and Muskwa successions but present in some Pinguicula

Group samples from the Wernecke Mountains (Fig. 6, 7). Although the exposed portion of unit

Ps could not be a source of NAMG grains in the lower part of the Cambrian Vizer formation

because it is overlain by Neoproterozoic strata, its presence does indicate that a Mesoproterozoic

succession younger than the Muskwa assemblage (Paleoproterozoic) and older than the

Mackenzie Mountain Supergroup (Neoproterozoic –Tonian) occurs in the subsurface of the

northwest Liard area. By analogy with Mesoproterozoic successions exposed along the western

edge of Laurentia, this succession probably contained a component of NAMG aged detrital

zircons.

During deposition of the lower part of the Vizer formation the postulated Mesoproterozoic

succession would have been progressively truncated eastward and available to provide detritus to

the basal Cambrian sandstone as it was progressively overlapped. Erosion and overlap of the

postulated Mesoproterozoic succession would also have happened in the southern part of the

Liard area as Cambrian or Silurian strata directly overlie the Muskwa assemblage. Progressive

removal of a Mesoproterozoic succession by sub-Cambrian erosion in the eastern and southern

part of the Liard area forms the most geologically feasible source for the NAMG detrital zircon

grains in the lower Vizer formation.

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Paleogeographic implications

New detrital zircon results from the Vizer and Mount Roosevelt formations combined with

previously published results show important changes in detrital zircon provenance occurred in

the northern Canadian Cordilleran passive margin succession during the Early and Middle

Cambrian. These changes are illustrated in Figure 9 using hypothetical drainage pathways for

four time intervals corresponding to deposition of the Vampire-Narchilla and Vizer formations

(Early Cambrian Terreneuvian series; Figure 9A); Sekwi Formation and correlatives (Early

Cambrian, Series 2; Figure 9B); middle member of the Mount Roosevelt Formation (early

Middle Cambrian; Figure 9C); and upper member of the Mount Roosevelt Formation (early

Middle Cambrian; Figure 9D) in the Coal River and Liard areas.

In the Canadian Cordilleran passive margin succession the Early Cambrian Terreneuvian and

Series 2 strata represent a major transgression that reached its maximum before the end of the

Early Cambrian. This was followed by a major regression represented by a disconformity at the

base of the Middle Cambrian and then a major Middle Cambrian transgression that progressively

onlapped the Laurentian craton (Aitken 1989; Gabrielse 1991). South of 55o N most of the

western Canadian Laurentian basement east of the passive margin was directly overlapped by

Middle Cambrian strata, whereas north of the Liard Line the Cambrian overlapped large regions

of Proterozoic sedimentary cover east of the passive margin (Fig. 1).

Detrital zircon age distributions for the basinal Vampire-Narchilla and the nearshore Vizer

formations (Fig. 4 -6; Terreneuvian) indicate extensive recycling from Paleoproterozoic

Athabasca-Muskwa sandstones exposed to the east and southeast, no recycling from the

Neoproterozoic Mackenzie Mountain/Shaler and Windermere successions exposed to the

northeast and no significant first cycle basement material. The Liard Line most likely impacted

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the detrital zircon provenance of the Vizer formation indirectly by controlling the southward

extent of the Mackenzie Mountains Supergroup (Aitken 1993). The minor component of NAMG

aged detrital zircon in the lower part of the Vizer formation was most likely recycled from

Mesoproterozoic strata exposed during the Terreneuvian in the eastern and southern Liard area

(discussed above). Further north in the Mackenzie Mountains, detrital zircon age distributions for

the lower and upper Backbone Ranges Formation (Fig. 4) indicate derivation mainly from

cratonic basement sources to the east, including the Hottah terrane, Great Bear magmatic zone,

Coronation Margin and the Slave craton (Fig. 9A; Leslie 2009; Lane and Gehrels 2014). The

detrital zircon provenance of all three formations resulted from a westward paleoflow. The

significant difference in detrital zircon signatures between the Vampire-Narchilla-Vizer and the

Backbone Ranges successions most likely reflects the greater amount of basement exposure east

of the Backbone Ranges localities in the Terreneuvian.

The detrital zircon age distribution for the Lower Cambrian Series 2 Sekwi Formation in the

Mackenzie Mountains indicates extensive recycling of ultimate Grenville orogeny sourced

grains. These most likely came from the Mackenzie Mountain Supergroup exposed to their

northeast in the Mackenzie Arch (Leslie 2009; Lane and Gehrels 2014). Northeastern source

areas are also indicated by the detrital zircon age distribution for the Sekwi correlative unit in the

Coal River area (Fig. 4, 9B), which has a broad spectrum of subdued peaks extending from 2800

to 1200 Ma that suggests derivation predominantly from the Mackenzie Mountain/Shaler

supergroup (1500 to 1200 Ma grains) and cratonic sources including the Slave craton, Hottah

terrane and Great Bear Magmatic zone (Pigage et al. 2015). Over most of the Liard area, Early

Cambrian Series 2 time is represented by a disconformity and no detrital zircon data is available.

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In the Liard area, Middle Cambrian strata are restricted to the syn-sedimentary Mount Roosevelt

graben. No detrital zircon data is available for Middle Cambrian deposits elsewhere along the

northern Canadian Cordilleran passive margin. The detrital zircon age distribution for the

conglomeratic middle member of the Mount Roosevelt Formation indicates a local provenance

consistent with the alluvial fan deposition model proposed by Post and Long (2008) with a minor

contribution from 2500 to 2400 Ma basement sources. Most detrital zircon grains were recycled

from the underlying Muskwa assemblage either directly or indirectly through Lower Cambrian

sandstones, and their provenance was indirectly influenced by the Proterozoic stratigraphic

changes associated with the Liard Line. The concordant 670 and 640 Ma detrital zircon grains

strongly suggest that volcanic clasts in the conglomerate were also derived locally as the only

magmatic rocks of this age near the Canadian Cordilleran passive margin are in the Liard area

(discussed above; Fig. 9C).

In contrast, the detrital zircon age distribution for the sandstone-dominated upper member of the

Mount Roosevelt Formation suggests derivation mainly from more distant first cycle cratonic

sources to the east or southeast (Fig. 9D). The upper member of the Mount Roosevelt Formation

contains a significant component of 2500 to 2300 Ma Laurentian basement sourced detrital

zircon not present in any of the intermediate sources. Magmatism of this age has a limited

distribution in western Canada (Figure 1, Canadian Geochronology Knowledgebase 2013). As

discussed above the most likely potential source areas for the 2500 to 2390 Ma grains are in or

near the western Trans-Hudson orogen (Fig. 1). The Buffalo Head, Thorsby or Wabamun

terranes and western edge of the Rae Province form the most likely source areas for 2380 to

2300 Ma grains (Fig. 1; Gehrels and Ross 1998) (Fig. 1). The younger 1825 to 1770 Ma grains

also indicate source areas to the east and southeast as intrusions of this age only occur southeast

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of the Snowbird tectonic zone in the Hearne Province, Trans-Hudson orogen and intervening

thrust-fold belt (Fig. 9D; Canadian Geochronology Knowledgebase 2013). The 2050 to 1830 Ma

grains match well with plutons in several nearby arcs and terranes and Archean grains could

have been derived from the Hearne, Slave or Rae provinces (Fig. 1; Gehrels and Ross 1998).

Both the Vizer and Vampire-Narchilla intervals and the upper member of the Mount Roosevelt

Formation were sourced from the east or southeast. The dramatic change in detrital zircon

provenance from recycled Paleoproterozoic blanket sandstone in the Terreneuvian to first cycle

Laurentian basement in the early Middle Cambrian strongly suggests significant erosion of the

Paleoproterozoic sedimentary cover and denudation of Laurentian basement occurred east of the

Liard area during late Early Cambrian and Middle Cambrian regression. Further stratigraphic

and detrital zircon provenance studies of Ediacaran and Cambrian strata along the northern

Canadian Cordilleran passive margin should be able to refine the evolution of drainage divides

and basement denudation.

CONCLUSIONS

The Vizer formation was derived primarily from Paleoproterozoic intermediate sources, with

little or no first cycle Laurentian basement input. The conglomeratic middle member of the

Mount Roosevelt Formation was derived primarily from Proterozoic and Lower Cambrian

intermediate sources, possibly with a minor component of first cycle Laurentian basement

material.

The North American Magmatic Gap aged detrital zircons in the lower part of the Vizer formation

were likely derived from a local Mesoproterozoic succession that was completely removed by

lower Paleozoic erosion or is preserved in the subsurface of the north central Liard area.

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An Early Cambrian Terreneuvian age is suggested for the nearshore Vizer formation based on

similar detrital zircon profiles with Terreneuvian transgressive sandstones to the south, the facies

relationships of Terreneuvian strata in the Mackenzie Mountains and the similarity of the Vizer

formation detrital zircon age distribution with that of the nearby basinal Vampire-Narchilla

Formation.

Volcanic clasts in the middle member of the Mount Roosevelt Formation were likely locally

sourced from the 689.1 ± 4.6 Ma Gataga volcanics (Ferri et al. 1999) and volcanic and/or

intrusive rocks related to the 650 to 640 Ma Pool Creek Syenite (Pigage and Mortensen 2004),

based on the presence of concordant 670 and 640 Ma detrital zircon grains. There is no detrital

zircon evidence to support syn-extensional volcanism associated with the Middle Cambrian

development of the Mount Roosevelt Graben.

The detrital zircon provenance of Early and Middle Cambrian strata deposited along the northern

Canadian Cordilleran passive margin indicates major variations in source area and paleoflow

occurred with time. Source areas were to the east when the Vizer, Vampire-Narchilla and

Backbone Ranges formations were deposited (Early Cambrian, Terreneuvian series) and changed

to the northeast as Sekwi Formation and Sekwi correlative strata formed (Early Cambrian, Series

2). The middle member of the Mount Roosevelt Formation (Middle Cambrian) in the Roosevelt

graben was primarily locally sourced, whereas the detritus that formed the upper member was

derived directly from Laurentian basement exposed over a large region to the east or southeast.

The change from recycled Paleoproterozoic sedimentary cover to primary basement sources

suggests that significant denudation of the cratonic basement occurred east of the Liard area in

the Early Cambrian and Middle Cambrian.

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Proterozoic stratigraphic changes associated with the Liard Line indirectly affected the

provenance of the Vizer formation and middle member of the Mount Roosevelt Formation.

ACKNOWLEDGEMENTS

This study was funded by the Geological Survey of Canada and the B.C. Ministry of Natural Gas

Development. Discussions with Thomas Hadlari, Tony Hamblin and Larry Lane are greatly

appreciated. Wing Chan and Kelsey Mah are thanked for their assistance with data manipulation.

This manuscript benefitted from the constructive comments and reviews of Thomas Hadlari,

associate editor Michael Rygel and two anonymous reviewers. Natural Resources Canada ESS

contribution number 0160262.

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Milton, J.E. 2015. Sedimentary rock hosted copper mineralization in the Neoproterozoic

Redstone Copperbelt, Mackenzie Mountains, Northwest Territories, Canada. Ph.D. thesis,

Department of Geological Siences, University of British Coulumbia, Vancouver. 396 p.

Nelson, J.L., Colpron, M. and Israel, S, 2013. The Cordillera of British Columbia, Yukon and

Alaska : tectonics and metallogeny : Society of Economic Geologists, Special Publication

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geochronology of Triassic and Jurassic sandstones on northwestern Axel Heiberg Island,

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Ootes, L. Davis, W. J., Jackson, V. A. and van Breemen O. 2015. Chronostratigraphy of the

Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and

exploration of a terrane translation model. Canadian Journal of Earth Sciences, 52: 1062-

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Pigage, L.C. 2009. Bedrock geology of NTS 95C/5 (Pool Creek) and NTS 95D/8 map sheets,

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Pigage, L.C. and Mortensen, J.K. 2004. Superimposed Neoproterozoic and early Tertiary

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Pigage, L.C., Roots, C.F. and Abbott, J.G. 2015. Regional bedrock geology for Coal River map

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(<850m.y.) Continental Separation. Geological Society of America Bulletin, 83: 1345-

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http://www.geology.gov.yk.ca/databases_gis.html#Databases

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Potential Intermediate

Sources

Reference

Athabasca Group Rayner et al. (2003)

Horsethief Creek Group Gehrels and Pecha (2014)

Mackenzie Mountain

Supergroup (Katherine

+Little Dal Grps)

Leslie (2009)

Keele Fm. (L+G) Lane and Gehrels (2014)

Keele Fm. (L) Leslie (2009)

Muskwa Group Ross et al. (2001)

Pa Pigage (2009)

Ps Pigage (2009)

Pinguicula Group Medig et al. (2012)

Rapitan Group (L+G) Lane and Gehrels (2014)

Toobally Formation Pigage (2009)

Wernecke Supergroup Furlanetto et al. (2016)

Yusezyu Formation Pigage et al. (2015)

Cambrian Units for

Comparison

Backbone Ranges Fm. Leslie (2009)

Crow Formation Pigage (2009)

Franklin Mountains Fm. Leslie (2009)

Hamill Group Gehrels and Pecha (2014)

McNaughton Formation

Mt. Roosevelt Fm. (middle)

Matthews (2016)

This study

Mt. Roosevelt Fm. (upper) Gehrels and Pecha (2014)

Sekwi Fm. correlative Pigage et al. (2015)

Sekwi Formation Leslie (2009)

Vampire-Narchilla unit

Vizer formation

Pigage et al. (2015)

This study

Yanks Peak Formation Matthews (2016)

McMechan et al Cambrian DZ Table 1

Table 1. References for detrital zircon age data used in Figures 4 - 6, 8. Fm. – formation, Grps. –

Groups.

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FIGURE CAPTIONS

Figure 1. Subcrop map at the base of the Paleozoic for northwest Laurentia showing distribution

of Cambrian sandstone, and Cambrian and Proterozoic detrital zircon localities palispastically

restored for Cordilleran deformation. Numbers correspond to sections in Figure 2. Sources of

information: Aitken 1993, Cook et al. 1999; Canadian Geochronology Knowledgebase 2013;

Cook and MacLean 2004; McMechan 2002; Ootes et al. 2015. Pugh 1975; Ross et al. 2001;

Slind et al. 1994; unpublished B.C. well logs. Palinspastic restoration based on: Campbell et al.

1982; K.M. Fallas, pers. comm. 2015; Fermor and Moffat 1992; Gabrielse and Taylor 1982;

Gordey 2013; Mair 2006; McMechan 1994, 2000, 2013, unpublished; Pigage et al. 2015; Price

and Fermor 1984. BP – Belt-Purcell basin; C – Coronation Margin; G – Great Bear magmatic

zone; H – Hamill Formation and Horsethief Creek Group; HBB – Horby Bay Basin; HCI – Hart

Creek Inlier; MM – Mackenzie Mountain Supergroup; Mn – McNaughton Formation; P –

Pinware terrane (inset map); PR1 = PR1 Basin; S-l – upper Coppermine River Group and lower

Shaler Supergroup; S-u – upper Shaler Supergroup; T – Thorsby terrane; W – Wabamun terrane;

Yp – Yanks Peak Formation.

Figure 2. Proterozoic to Middle Ordovician stratigraphic correlations and tectonic events along

the northern Canadian passive margin showing stratigraphic positions of detrital zircons samples

from this study or used for comparison purposes in Figures 4 to 8. See Table 1 for sources of

detrital zircon U-Pb age data. FO – Forward Orogeny; GB – Gunbarrel magmatic event; RO –

Racklan Orogeny.

Figure 3. U-Pb zircon probability density distributions and histograms for Vizer and Mount

Roosevelt formation samples.

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41

Figure 4. Normalized U-Pb zircon age probability plots for Ediacaran to Cambro-Ordovician

units in the Canadian Cordilleran passive margin succession. See Table 1 for sources of detrital

zircon U-Pb age data from other studies. Grey bars highlight age range of ultimate Grenville

Orogeny source area (Gren), NAMG (N) and 2500 to 2300 Ma. Edi – Ediacaran; eC2 – Early

Cambrian – series 2; eCT – Early Cambrian - Terrenuevian; lC- eO – Late Cambrian to Early

Ordovician; lC- mO – Late Cambrian to Middle Ordovician; mC – Middle Cambrian.

Figure 5. MDS plots (Vermeesh 2017) showing relative statistical similarity of detrital zircon age

distributions (based on the Kolmogorov-Smirnov test D value) for Ediacaran and Cambro-

Ordovician units in the Canadian Cordilleran passive margin succession. See Table 1 for sources

of detrital zircon U-Pb age data. BBl – lower Backbone Ranges Formation, BBu – upper

Backbone Ranges Formation. The thick pale grey dashed line separates samples with ultimate

Grenville sourced grains (to the right of the line) from those lacking or having very few

Grenville sourced zircons (to the left of the line).

Figure 6. Normalized U-Pb zircon age probability plots for potential sources of zircons found in

Mount Roosevelt and Vizer formation samples. See Table 1 for sources of detrital zircon U-Pb

age data. Grey bars highlight age range of ultimate Grenville Orogeny source area (Gren),

NAMG (N) and 2500 to 2300 Ma. eCT – Early Cambrian – Terrenuevian; mC – Middle

Cambrian; mP – Mesoproterozoic; nP – Neoproterozoic; pP – Paleoproterozoic. MM –

Mackenzie Mountain Supergroup; l Shaler – upper Coppermine River Group and lower Shaler

Supergroup; L – Leslie (2009); LG – Lane and Gehrels (2014).

Page 41 of 57



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42

Figure 7. U-Pb zircon age probability density distributions from samples of the basal Pinguicula

Group (unit A) exposed in the Wernecke Inlier, Wernecke Mountains, Yukon (A – C; Medig et

al. 2012) and the PR1 basin (D; Medig et al. 2014). Grey bar indicates age range of NAMG.

Figure 8. MDS plots (Versmeech, 2017) showing relative statistical similarity of detrital zircon

age distributions (based on the Kolmogorov-Smirnov test D value) for potential intermediate

sources of detrital zircons found in the Vizer and Mount Roosevelt formation. Samples from this

study are labelled in italics. See Table 1 for sources of detrital zircon U-Pb age data. HTC –

Horsethief Creek Group; L – Leslie (2009); LG – Lane and Gehrels (2014); MM – Mackenzie

Mountain Supergroup; Shaler- l – upper Coppermine River Group and lower Shaler Supergroup;

Shaler- u – Shaler Supergroup, upper part. Note: the lower part of the Shaler Supergroup

includes one sample from sandstone at top of Coppermine River Group.

Figure 9. Hypothetical drainage pathways suggested by observed detrital zircon signatures

superimposed on sub-Paleozoic subcrop map (see Figure 1 for details). A) Vampire-Narchilla

(VN), Vizer (V) and Backbone Ranges (BR) formations (Early Cambrian – Terreneuvian); B)

Sekwi Formation (S) and Sekwi correlative unit (SC) (Early Cambrian – Series 2); C) middle

member Mount Roosevelt Formation (Middle Cambrian – Series 3); D) upper member Mount

Roosevelt Formation (Middle Cambrian – Series 3). BHT – Buffalo Hills terrane; C –

Coronation Margin; G – Great Bear magmatic zone; H – Hottah terrane; LR – La Ronge arc; MA

– Mackenzie arch; MM- Mackenzie Mountains Supergroup; PRA – Peace River Arch; STZ –

Snowbird Tectonic zone; T – Thorsby terrane; TA – Taltson magmatic belt; W – Wabamun

terrane.

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Draft11

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TRANS-TRANS-HUDSONHUDSONOROGENOROGEN

TRANS-HUDSONOROGEN

SLAVE SLAVE PROVINCEPROVINCE

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2.1-1.85 Ga

1.87-1.85 Ga

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2.32-1.99 Ga

2.3-1.91 Ga

2.32 Ga

<2.3 Ga

1.96-1.90 Ga

1.85-1.78 Ga

2.00-1.92 Ga

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1.9-1.80 Ga thrust-fold belts

Archean (>2.5 Ga) crust

2.32-1.90 Ga accreted Proterozoic crust

2.3 Ga magmatic crust

1.9-1.8 Ga juvenile crust with ‘basement’ inliers

?

BP

ATHABASCAATHABASCA(BASIN)(BASIN)

ATHABASCA(BASIN)

DUBAWNTDUBAWNT(THELON(THELONBASIN)BASIN)

DUBAWNT(THELONBASIN)

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Neoproterozoic - Earliest CambrianWindermere Supergroup, Hyland Group

Neoproterozoic TonianMackenzie Mountains/ Shaler Supergroups

Mesoproterozoic Sedimentary Sequences

Paleoproterozoic 1760 - 1600 Ma Sedimentary Sequences

CORDILLERAN PASSIVE MARGINand Lower Cambrian sandstones

LiardLiardAreaAreaLiardArea

Cambrian detrital zircon sample locality, this study; other studies

Proterozoic detrital zircon sample locality other studies

300 km

Eastern limit of Mid

dle

Cam

brian strata


dle

Cam

brian strata


dle

Cam

brian strata

LIARD L

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LIARD L

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TERRANETERRANE

BUFFALOHEAD

TERRANE

2.5-1.89 Ga

G

Magmatism: 2.4 to 2.3 Ga, 2.5 to 2.4 Ga

WT

PR1PR1PR1

Eastern limit Cordilleran deformation

‘DISMAL‘DISMALLAKES’ LAKES’ ‘DISMALLAKES’

C

3b3b3b

para-autochtonous terranes



LaurentiaLaurentiaLaurentia

Liard AreaLiard AreaLiard Area

Arctic Islands

Arctic Islands

Arctic Islands

S-uS-uS-u

PPP

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Cam

brian

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500

550

650

750

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1350

1750

1600Muskwa Assemb.

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450

FranklinMountain Fm.

CL

Sekwi Fm.

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Risky Fm.

Vam-pire

Gametrail Fm.

Sheepbed Fm.

Ice Brook Fm.

Keele Fm.

Twitya Fm.

Rapitan Gp

Blueflower Fm.

Sekwi - correlative

Otter Ck Fm.

Rabbitkettle Fm.

Crow Fm.

Crow Fm.

Yusezyu Fm.

Vampire -Narchilla unit

Sunblood Sunblood Fm. Sunblood

+ +

unit Pa

base not exposed

base not exposed

base not exposed

base not exposed

base not exposed

base not exposed TooballyToobally Fm. Fm.

Toobally Fm.

Mt. Roosevelt

unnamedquartzite

Kechika Fm.Kechika Fm.Kechika Fm.

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nE

dia

cara

n

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???

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N. Mackenzie - WerneckeMountains

Coal River area

NW Liard area SW Liard area Tectonic Events

Vizer fm.

650 Ma650 Ma Pool Pool Creek Creek Syenite Syenite

650 Ma Pool Creek Syenite

Ma

1a 1b 2 3a 3b 4

???

Pinguicula Group

WSG

unit Ps

???

???

See Medig et al. (2012, 2014) and Fig. 7

This study

area 1 areas 2-4

FO

RO

GB

formation Cordilleranpassive margin

formationproto-Pacific margin?

Extension, rifting

Folding, reverse faulting

PR1

Unit with samples analysed for U-Pb detrital zircon ages and lacking Grenville age zircons

u

m

l

Other studies for comparison, seeFigs. 4-6, 8

Page 44 of 57



Draft

000 500 1000 1500 2000 2500 3000 3500

Re

lativ

e p

rob

ab

ility

Age (Ma)

Mount Roosevelt Formation

(middle mbr.)

11EPF67A (n = 96)

55

10

1015

1520

2025

2530

35 Vizer formation 11EPF55A (n = 94)

0 500 1000 1500 2000 2500 3000 3500 Age (Ma)

0

5

10

15

20

25

30

35

40Vizer formation FF10-1

(n = 99)

0 500 1000 1500 2000 2500 3000 3500

Nu

mb

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ins

Age (Ma)

Cariboo Range Cariboo Range

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500

1000

1500

2000

2500

3000

3500

4000

Ma

McNaughtonFormation

n=222

Yanks PeakFormation

n=112

Hamill Group

n=192

Vampire - Narchilla unit n = 230

Vizer formationn=194

lower Backbone Range Formation

upper Backbone Range Formation

n=48

n=57

Sekwi Correlativen=74

Sekwi Formationn=60

Mt. Roosevelt Formation (upper) n = 201

Mt. Roosevelt Fm. (middle)n=95

Franklin Mtn. Fm.n=45

Crow Formation NW Liard loc.(3A)

n=264

Crow Formation Coal River loc. n = 271

mC

mC

eC2

eC2

eCT

eCT

eCT

eCT

Unit Age

Edi

eCT

uC-eO

lC-mO

lC-mO

?

THIS STUDY

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GREN NNN

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-0.2 0 0.2 0.4 0.6

-0.2

0.0

0.2

V-N Mt. Roosevelt(middle)

McNaughton

Crow (NW Liard)

Yanks Peak

(Coal River)

SekwiSekwi correlative

Franklin Mountain

H

Vizer

Mount Roosevelt(upper)

BlBBuB

Unlikely correlatives of Vizer and Mount Roosevelt formations: units contain abundant Grenville age zircons

Crow

This Study

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INC

OM

PA

TIB

LE

VIZ

ER

FO

RM

AT

ION

SO

UR

CE

Wiin

derm

ere

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roup

Horsethief Creekn = 388

Wernecken = 275

Athabascan = 278

Muskwan = 102

Psn = 229

l Shaler n = 257

upper Shalern = 330

MMn = 101

Rapitann = 96

Pan = 98

Keele (L) n = 55

Keele (LG)n = 99

Toolballyn = 63

Yusezyun = 114

Vizer formationn = 194

middle Mt. Rooseveltn = 95

THIS STUDY

THIS STUDY

upper Mt. Roosevelt n = 201

mC

mC

eCT

nP

nP

nP

nP

nP

nP

nP

mP

pP

pP

pP

nP

nP

nP-mP

Unit Age

GREN NNN

500

1000

1500

2000

2500

3000

3500

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Pro

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900 1300 1700 2100 2500 2900 3300

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n= 53/77

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Basal Fifteen Mile Group

PR1 basin n= 83

D

Age (Ma)

Age (Ma)

Age (Ma)

Age (Ma)

0.005

0.005

0.003

0.003

0.003

0.001

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0.001

Page 49 of 57



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Potential intermediate sourceCambrian unit

Keele (L)Shaler-u

Keele (LG)

Rapitan

MMPa

HTC

Viser

Wernecke

Yusezyu

Mt. Roosevelt (upper)

Toobally

Shaler- lPs

Muskwa

Athabasca

Unlikely Sources:LikelySources

Mt.Roosevelt (middle)

Cambrian unitThis Study

units contain abundant Grenville age zircons

Page 50 of 57



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W

T

STZ


SLAVE PROVINCE


SLAVE PROVINCE


SLAVE PROVINCE


SLAVE PROVINCE

?

??

ATHABASCAATHABASCABASINBASIN

ATHABASCABASIN


ATHABASCABASIN

SHALERSHALERSHALER

SHALERSHALERSHALERSHALERSHALERSHALER

SHALERSHALERSHALER

MMMMMM

BRBRBR

VNVNVN

SSS

ScScSc

VVV

MMMMMMMMMMMM

MMMMMM

PR

APR

APR

A

PR

APR

APR

APR

APR

APR

A

PR

APR

APR

A

300 km

300 km300 km

300 km

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

LIARD L

INE

Neoproterozoic - Earliest CambrianWindermere Supergroup, Hyland Group

Neoproterozoic TonianMackenzie Mountains/ Shaler Supergroups

Mesoproterozoic Sedimentary Sequences

Paleoproterozoic 1760 - 1600 Ma Sedimentary Sequences

Inferred extent of Paleoproterozoic sedimentary cover

Magmatism: 2.4 to 2.3 Ga, 2.5 to 2.4 Ga

Detrital zircon sample

Upper Member MountRoosevelt Formation

Middle Member MountRoosevelt Formation

Sekwi Formation and correlatives

Vizer formation and correlatives

C


ATHABASCABASIN

GH

B

MA

MA

MA


ATHABASCABASIN

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2016, GeoSep Services, LLC

Zircon U-Pb Dating Methodology

Published Methods

Detailed descriptions of the methods followed by Geosep Services to produce and process their

ZrnUPb data have been presented in numerous peer-reviewed manuscripts. These include

Bradley et al. (2009), Hults et al. (2013), and Moore et al. (2015).

Sample Preparation

Zircon grains were isolated and prepared for LA-ICP-MS analysis using standard procedures

combined with specific customized procedures described by Donelick et al. (2005). These

customized procedures were designed to maximize recovery of: 1) all possible grain sizes

present within a sample by minimizing the potential loss of smaller grain sizes through the use of

water-table devices, and 2) complete grains with as close to full terminations by minimizing

grain breakage and/or fracturing inherent with the standard procedures typically used to separate

individual grains from the original rock material. Use of these procedures results in a

significantly greater range of recovered grain sizes, as well as a higher percentage of “complete”

grains being retained during the mineral separation process (Fig. 1).

Fig. 1. Example zircon separate from GSS Project 025, showing a wide range in grain-shapes and grain-sizes after

sample processing by GSS mineral separation procedures. Importantly, a significant number of tiny grains, as well

as complete grains were recovered.

Whole rock samples were first run multiple (minimum = 3) times through a Chipmunk brand jaw

crusher with the minimum jaw separation set to 2-3 mm. The crushed material was then sieved

through 300 µm nylon mesh, and the <300 µm size fraction washed with tap water and allowed

to dry at room temperature. Zircon grains were separated from other mineral species using a

combination of lithium metatungstate (density ~2.9 g/cm3), Frantz magnetic separator,

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diiodomethane (density ~3.3 g/cm3), and hand-panning separation procedures. Epoxy wafers (~1

cm x 1 cm) containing zircon grains for LA-ICP-MS were polished manually using 3.0 µm and

0.3 µm Al2O3 slurries to expose internal zircon grain surfaces. The polished zircon grain surfaces

were washed in 5.5 M HNO3 for 20 s at 21ºC in order to clean the grain surfaces prior to

introduction into the laser system sample cell.

LA-ICP-MS Session Details

LA-ICP-MS data collection was performed at the Geoanalytical Laboratory, Washington State

University, Pullman, Washington, U.S.A following conditions and parameters presented in Table

1. Individual zircon grains were targeted for data collection using a New Wave YP213 213 nm

solid state laser ablation system using a 20 µm diameter laser spot size, 5 Hz laser firing rate, and

ultra high purity He as the carrier gas. Isotopic analyses of the ablated zircon material were

performed using a ThermoScientific Element2 magnetic sector mass spectrometer using high

purity Ar as the plasma gas. The following masses (in amu) were monitored for 0.005 s each in

pulse detection mode(Pb, Th, and U isotopes): 202, 204, 206, 207, 208, 232, 235, and 238.

Table 1. ICP-MS and laser ablations system operating conditions and data acquisition parameters

ICP-MS: operating

conditions

Instrument Finnigan Element II Magnetic Sector

ICP-MS

Forward power 1.25 kW

Reflected power <5 W

Plasma gas Ar

Coolant flow 15 l/min

Carrier flow 1.0 l/min (Ar) 0.8 l/min (He)

Auxiliary flow 1.0 l/min

ICP-MS: data

acquisition parameters

Dwell time 24 milliseconds per peak point

Points per peak 3

Mass window 5%

Scans 200

Data acquisition time 29.5 sec

Data acquisition mode E scanning

Isotopes measured 43

Ca or 29

Si and 238

U

Laser ablation system:

operating conditions

Laser type New Wave Neodymium: YAG

Wavelength 213 nm

Laser mode Q switched

Laser output power 10 J/cm2

Laser warm up time 6 sec

Shot repetition rate 5 Hz

Sampling scheme spot (20 µm)

At time = 0.0 s, the mass spectrometer began monitoring signal intensities; at time = 6.0 s, the

laser began ablating zircon material; at time = 30.0 s, the laser was turned off and the mass

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spectrometer stopped monitoring signal intensities. A total of 200 data scans were collected for

each zircon spot analyzed comprising: approximately 55 background scans; approximately 20

transitions scans between background and background+signal, approximately 125

background+signal scans. A scheme was developed to check whether mass 238 experienced a

switch from pulse to analog mode during data collection and a correction procedure was

employed to ensure the use of good quality intensity data for masses 235 and 238 when such a

switch was observed.

UPb Data Analysis

Previous LA-ICP-MS studies of UPb zircon dating used the so-called intercept method, which

assumes that isotopic ratio varies linearly with scan number due solely to linearly varying

isotopic fractionation (Chang et al., 2006; Gerhels et al., 2008). The data modeling approach

favored here was the modeling of background-corrected signal intensities for each isotope at

each scan. Background intensity for each isotope was calculated using a fitted line (for

decreasing background intensity) or using the arithmetic mean (for non-decreasing background

intensity) at the global minimum of selected isotopes (206

Pb, 232

Th, and 238

U) for the spot.

Background+signal intensity for each isotope at each scan was calculated using the median of

fitted (2nd

-order polynomial) intensity values for a moving window (7 scans wide here) that

includes the scan. The precision of each background-corrected signal intensity value was

calculated from the precision of background intensity value and the precision of the

background+signal intensity value.

Zircon UPb age standards used during analysis are summarized in Table 2, including the

1099±0.6 Ma FC zircon (FC-1 of Paces and Miller, 1993) used here as the primary age standard.

Isotopic data for FC were used to calculate Pb/U fractionation factors and their absolute errors

for each FC data scan at each FC spot; these fractionation factors were smoothed session-wide

for each data scan using the median of fitted (1st-order polynomial) fractionation factor values for

a moving window that includes the current FC spot and scan.

Table 2. Zircon age standards.

Standard Standard U-Pb age (±2σ) Reference

FC Duluth complex 1099.0 ± 0.6 Ma Paces and Miller, 1993

F5 Duluth complex 1099.0 ± 0.6 Ma

(assumed equal to FC-1)

Paces and Miller, 1993

IF Fish Canyon Tuff 28.201 ± 0.012 Ma Lanphere et al., 2001; Kuiper et al.,

2008

MD Mount Dromedary 99.12 ± 0.14 Ma Renne et al., 1998

T2 Temora2, Middledale

gabbroic diorite 416.78 ± 0.33 Ma Black et al., 2004

TR Tardree Rhyolite 61.23 ± 0.11 Ma Dave Chew, personal communication

Pb/U Fractionation Factor

Under the operating conditions of LA-ICP-MS sessions, fractionation factors are occasionally

found to vary strongly with scan number, decreasing with increasing scan number (presumably

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due to increasing ablation pit depth and the effect this has on fractionation; e.g., Paton et al.,

2010). The zircon crystal lattice is widely known to accumulate α-radiation damage (e.g., Zhang

et al., 2009 and references therein). It is assumed that increased α-damage in a zircon leads to a

decrease in the hardness of the zircon; this in turn leads to a faster rate of laser penetration into

the zircon during ablation leading to dependence of isotopic fractionation on the degree of zircon

lattice radiation damage. Ages calculated for all zircon age standards, when those standards were

treated as unknowns, were used to construct a fractionation factor correction curve (exponential

form) in terms of accumulated radiation damage. The notion of matrix-matched zircon standard

and zircon unknown has been proposed largely on the basis of trace element chemistry (e.g.,

Black et al., 2004). In this study, time and lattice damage, parameters invisible to instruments

used to characterize trace element chemistry, were introduced and applied based on measured U

and Th chemistries to effectively matrix-match standard and unknown zircons.

Common Pb Correction

Common Pb was subtracted out using the Stacey and Kramer (1975) common Pb model for

Earth. Ages and common Pb ratio were determined iteratively using a pre-set, session-wide

minimum common Pb age value (default for each session was the age of the oldest age standard

which for both Ap and Zrn was 1099 Ma FC-1 and/or FC-5z).

Preferred Age

Uranium decay constants and the 238

U/235

U isotopic ratio reported in Steiger and Yäger (1977)

were used in this study. 207

Pb/235

Uc (235

Uc = 137.88238

U), 206

Pb/238

U, and 207

Pb/206

Pb ages were

calculated for each data scan and checked for concordance; concordance here was defined as

overlap of all three ages at the 1σ level (the use of 2σ level was found to skew the results to

include scans with significant common Pb). The background-corrected isotopic sums of each

isotope were calculated for all concordant scans. The precision of each isotopic ratio was

calculated by using the background and signal errors for both isotopes. The fractionation factor

for each data scan, corrected for the effect of accumulated α-damage, was weighted according to

the 238

U or 232

Th signal value for that data scan; an overall weighted mean fractionation factor for

all concordant data scans was used for final age calculation.

Ages and common Pb ratio were determined iteratively using a pre-set, session-wide minimum

common Pb age value (default for each session was the age of the oldest age standard which for

both Ap and Zrn was 1099 Ma FC-1 and/or FC-5z).

If the number of concordant data scans for a spot was greater than zero, then for grains that yield

ages older than ca. 1000 Ma, the 207

Pb/206

Pb age is used. For younger grains, the 206

Pb/238

U age is

used.

Analyses were filtered following the criteria of Gehrels and Pecha (2014). Analyses with >10%

uncertainty (1σ) in 206

Pb/238

U or the 206

Pb/207

Pb age are not included in our analysis.

Concordance is based on 206

Pb/238

U age/206

Pb/207

Pb age, with 100% = concordant. Analyses

with >20% discordance (<80% concordance) or >5% reverse discordance (>105% concordance)

are not included.

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Preferred Age Precision

Errors for the isotopic ratios 207

Pb/235

Uc (235

Uc = 137.88238

U), 206

Pb/238

U, and 207

Pb/206

Pb at each

scan included errors from the background-corrected signal values for each isotope, the

fractionation factor error, and an additional relative error term required to force 95% of the FC

ages to be concordant. Errors for the isotopic ratios 207

Pb/235

Uc (235

Uc = 137.88238

U), 206

Pb/238

U,

and 207

Pb/206

Pb at each scan included errors from the background-corrected signal values for

each isotope, the fractionation factor error, and an additional relative error term required to force

95% of the FC ages to be concordant. Asymmetrical negative-direction and positive-direction

age errors were calculated by subtracting and adding, respectively, the isotopic ratio errors in the

appropriate age equation (Chew and Donelick, 2012).

References Cited

Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R.,

Campbell, I.H., Korsch, R.J., Williams, I.S., and Foudoulis, C. 2004. Improved 206

Pb/238

U

microprobe geochronology by the monitoring of trace-element-related matrix effect; SHRIMP,

ID-TIMS, ELA-ICP-MS and oxygen isotope documentation for a series of zircon standards.

Chemical Geology, 205, p.15-140

Bradley, D., Haeussler, P., O’Sullivan, P., Friedman, R., Till, A., Bradley, D., and Trop, J., 2009,

Detrital zircon geochronology of Cretaceous and Paleogene strata across the south-central

Alaskan convergent margin, in Haeussler, P.J., and Galloway, J.P., Studies by the U.S.

Geological Survey in Alaska, 2007: U.S. Geological Survey Professional Paper 1760-F, 36 p.

Chang, Z., Vervoort, J.D., McClelland, W.C., and Knaack, C., 2006. UPb dating of zircon by

LA-ICP-MS. Geochemistry, Geophysics, Geosystems, American Geophysical Union, v. 7, n. 5,

14 p.

Chew, D.M. and Donelick, R.A., 2012. Combined apatite fission track and U-Pb dating by LA-

ICP-MS and its application in apatite provenance analysis. Mineralogical Association of Canada

Short Course, v. 42, 219-247.

Donelick, R. A., O'Sullivan, P. B., and Donelick, M. B., 2010, A Discordia-Based Method of

Zircon U-Pb Dating from LA-ICP-MS Analysis of Single Spots. Smart Science for Exploration

and Mining, v. 1 and 2, p. 276-278.

Donelick, R.A, O’Sullivan, P.B., Ketcham, R.A., 2005. Apatite fission-track analysis. Reviews in

Mineralogy and Geochemistry, Mineralogical Society of America, v. 58, p. 49-94.

Gehrels, G.E. and Pecha, M. 2014. Detrital zircon U-Pb geochronology and Hf isotope geochemistry

of Paleozoic and Triassic passive margin strata of western North America: Geosphere, 10: 49-65,

doi:10.1130/GES00889.

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Gehrels, G.E., Valencia, V.A., and Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and

spatial resolution of UPb ages by laser ablation-multicollector-inductively coupled plasma-mass

spectrometry. Geochemistry Geophysics Geosystems, American Geophysical Union, v. 9, 13 p.

Hults, C.P., Wilson, .H., Donelick , R.A., and O’Sullivan , P.B., 2013. Two flysch belts having

distinctly different provenance suggest no stratigraphic link between the Wrangellia composite

terrane and the paleo-Alaskan margin Lithosphere, December 2013, v. 5, p. 575-594, first

published on November 15, 2013, doi:10.1130/L310.1.

Kuiper, K.F., Deino, A., Hilgen, P.J., Krijgsman, W., Renne, P.R., and Wijbrans, J.R., 2008.

Synchronizing rock clocks of Earth history. Science, 320, p. 500-504.

Lanphere, M.A. and Baadsraard, H., 2001. Precise K-Ar, 40

Ar/39

Ar, Rb-Sr and U-Pb mineral ages

from the 27.5 Ma Fish Canyon Tuff reference standard. Chemical Geology, v. 175, p. 653-671.

Moore. T.E., O’Sullivan, P.B., Potter, C.J., and Donelick, R.A., 2015, Provenance and detrital

zircon geochonologic evolution of lower Brookian foreland basin deposits of the western Brooks

Range, Alaska, and implications for early Brookian tectonism: Geosphere, v. 11, p. 93–122,

doi:10.1130/GES01043.1.

Paces, J.B. and Miller, J.D., 1993. Precise UPb ages of Duluth Complex and related mafic

intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenic,

paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift

System. Journal of Geophysical Research, v. 98, no. B8, p. 13997-14013.

Paton, C., Woodhead, J.D., Hellstrom, J.C., Hergt, J.M., Greig, A., and Maas, R., 2010,

Improved laser ablation U-Pb zircon geochronology through robust downhole fractionation

correction, Geochem. Geophys. Geosyst., 11, Q0AA06, doi:10.1029/2009GC002618.

Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L., and DePaolo, D.J., 1998.

Intercalibration of standards, absolute ages and uncertainties in 40

Ar/39

Ar dating. Chemical

Geology, v. 45, p. 117-152.

Stacey J. S. and Kramer J. D., 1975. Approximation of terrestrial lead isotope evolution by a

two-stage model. Earth and Planetary Science Letters, v. 26, pp. 207-221

Steiger, R.H. and Jäger, E., 1977. Subcommission on geochronology: Convention on the use of

decay constants in geo- and cosmochronology. Earth and Planetary Science Letters, v. 36, p.

369-371.

Zhang, M., Ewing, R.C., Boatner, L.A., Salje, E.K.H., Weber, W.J., Daniel, P., Zhang, Y., and

Farnan, I., 2009, Pb* irradiation of synthetic zircon (ZrSiO4): Infrared spectroscopic study –

Reply. American Mineralogist, v. 94, pp. 856-858.

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