roundup 2010 poster
TRANSCRIPT
Natural ResourcesCanada
Ressources naturellesCanada
Geological Survey of Canada
Commission géologique du Canada
46721 m1 mm = 200 m
m a
sl
1 c
m =
200 m
x10 vertical exaggeration
X X’
500
700
900
1100
1300
Nechako Valley
Stewart Valley
extensive Chilcotin Group
?
093K/01 093J/04
093G/13093F/16
X
X’
bedrock (m asl)
400 1300850
drift thickness (m) = 7n 50
< 5 5 - 10 10 - 20
20 - 50 > 50
bedrock intersection point
“push down” point
10km0
1:500,000
Vanderhoof
Tachick Lake
Stewart Valley
Cluculz Lake
Nechako Valley
CO
AST
MTN
S
INTERIOR
PLATEAUS
CARIBOO
MTNS
ROCKY
MTNS
Distribution and Thickness of basalts and drift on the Interior PlateauDistribution et épaisseur des basaltes et des sédiments glaciaires de la région du plateau intérieur
1. Geological Survey of Canada, 625 Robson Street, Vancouver, British Columbia. V6B 5J3 Canada;2. EOS-UBC, 6339 Stores Road, Vancouver, British Columbia. V6T 1Z4 Canada3.
email: [email protected]
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario. K1A O8E Canada
Graham D.M. Andrews , Jackie Dohaney , Kelly Russell , Alain Plouffe , Robert G. Anderson1 2 2 3 1
093B/15 093B/16
093G/01093G/02
Quesnel
X
X’
24341 m1 mm = 200 m
900
700
500
300
m a
sl
1 c
m =
200 m
x10 vertical exaggeration
X X’
Fraser Valley
perchedremnantsof Chilcotin Group
bedrock (m asl)
400 1300850
drift thickness (m) =n 2150
< 10 10 - 20 20 - 50
50 - 100 > 100
bedrock intersection point
“push down” point
10km0
1:500,000
Fra
ser
Valle
y
Fra
ser V
alle
y
CO
AST
MTN
S
INTERIOR
PLATEAUS
CARIBOO
MTNS
ROCKY
MTNS
X
X’
1500
1300
1100
900
61360 m1 mm = 300 m
m a
sl
1 c
m =
300 m
x10 vertical exaggeration
X X’
Green Lake
Chilcotin Group veneer
092P/14092P/15
092P/11
092P/06
092P/07
092P/10
bedrock (m asl)
400 1300850
drift thickness (m) = 777n
< 5 5 - 10 10 - 20
20 - 50 > 50
10km0
1:500,000
100 Mile House
Lac la Hache
Forest Grove
Bridge Lake
70 Mile House
Lone Butte
Gre
enLake
Lac la Hache
Canim Lake
Rayfie
ldValle
y
CO
AST
MTN
S
INTERIOR
PLATEAUS
CARIBOO
MTNS
ROCKY
MTNS
“COVER”( ) Typical till veneer (<1 m) covering granitebedrock (092P). ( ) Forested till blanket (>1 m)covering “thin” (<20 m) Chilcotin Group basalt(092P). ( ) Gravel-rich esker (~10 m)deposited on an eroded bedrock surface. ( )“Thick” (>20 m) basalt lava pile filling apaleovalley at Chasm Provincial Park (092P).( ) Ancestral Chilcotin River filled by “thick”basalt and pillow-breccia succession nearAlexis Creek (093B).
AB
CD
E
A B
C
D
E
Quaternary deposits
basement -Mesozoic
sedimentary rocksbasement -Mesozoic
sedimentary rocks
subaerial lavassubaerial lavas
bedded hyaloclastitepillow breccia
Pliocene Chilcotin River valley floor
Quaternary deposits
Quaternary depositsPresent Chilcotin River valley floor
70 m
450 m
W E
Water Well Records ( = 10,486)n Bedrock Intersection Points ( = 3,189)n
V
PG
Q
100
WL
V
PG
Q
100
WL
092N 092O
092P
093C 093B 093A
093F 093G 093H
093K 093J 093I
0 50 km
V
PG
Q
100
WL
092N 092O
092P
093C 093B 093A
093F 093G 093H
093K 093J 093I
0 50 km
SkeenaDrainage
Basin
Colu
mbia
Dra
inage
Basi
n
0 km 100
Peace Drainage(Arctic)
‘Coastal’ Drainage
Basin
C - intraglacial >30 ka
alpine ice-cap
catchment boundary new canyon
river course
new river course
Dog Creek dam
abandoned channel
sea
impounded lake
decaying ice mass
continental divide
ice thickness (m)
SkeenaDrainage
Basin
0 km 100
Colu
mbia
Dra
inage
Basi
n
Fraser-PeaceDrainage Basin
(Arctic)
A - intraglacial c. 1.06 Ma
‘Coastal’ Drainage
Basin
0 km 100
B - deglaciation post-1.06 Ma
Prospectivity on the Interior Plateau has hitherto been hamperedby a lack of data to determine the areal distribution and verticalthickness of Chilcotin Group basalt lavas and Quaternary drift.Research at UBC supported by the GSC TGI-3 and MPB programsand Geoscience BC reveals that basalt cover is thinner and lessextensive than previously thought (<40%) across the InteriorPlateau. It is only thick (>20 m) in paleovalleys that can be readilyidentified in geological and geophysical surveys. Similarly,Quaternary drift, although areally extensive, is only thick inpaleovalleys. We have mapped cover thickness variations inseveral areas on the Interior Plateau (below) using a combinationof field observations, water well records, and archivedgeological, geochronological, geophysical, and MINFILE datasets; the results of which are presented here and will bepublished soon.
X
X’
092O/16
1000
800
600
28889 m1 mm = 200 m
m a
sl
1 c
m =
200 m
x10 vertical exaggeration
X X’Williams Lake
Creek
Chilcotin Group veneer
Williams Lake
150 Mile House
Miocene
McLeese Lake
Springhouse
Fra
se
r V
alle
y
bedrock (m asl)
400 1300850
drift thickness (m) =n 1954
< 5 5 - 10 10 - 20
20 - 50 > 50
bedrock intersection point
“push down” point
10km0
1:500,000
092P/13
093A/04093B/01
093A/05
093B/08
CO
AST
MTN
S
INTERIOR
PLATEAUS
CARIBOO
MTNS
ROCKY
MTNS
WATER WELL MODELINGY
Y’
X’
X
bedrock (m asl)
400 1300850
drift thickness (m) =n 1576
< 10 10 - 20 20 - 50
50 - 100 > 100
bedrock intersection point
“push down” point
10km0
1:500,000
Nechako Valley
Fra
ser
Valle
y
Fra
ser
Valle
y
Chi
lako
Val
ley
Prince George
Beaverley
Ferndale
093G/09
093G/10093G/11
093G/16093G/15
093G/14
093J/01093J/02093J/03
X’X
m a
sl
1 c
m =
200 m
400
600
800
1000
1200
48131 m1 mm = 200 m
Fraser ValleyChilako Valley
x10 vertical exaggeration
CO
AST
MTN
S
INTERIOR
PLATEAUS
CARIBOO
MTNS
ROCKY
MTNS
49167 m1 mm = 200 m
m a
sl
1 c
m =
200 m
Y Y’
800
600
Fraser Valley
Fraser Valley
x10 vertical exaggeration
buried paleochannel
buriedpaleochannel
buriedpaleochannel ?
buriedpaleochannel ?
Please see accompanying student posters by Jackie Dohaney (new map of Chilcotin basalt distribution) and Rebecca-Ellen Farrell (new map of Chasm Provincial Park)
1
2
3
45
1 - Quesnel area
3 - 100 Mile House area
2 - Williams Lakearea
4 - PrinceGeorge area
5 - Vanderhoof area
Water well logs recorded by the Province of BritishColumbia provide valuable subsurface data, in particularfor identifying the cover - bedrock surface. Wells areunevenly distributed across the Interior, concentratedaround cities and along major highways ( .
The base of the drift and the base of the Chilcotinbasalts have been identified in over 7,000 and 3,000wells respectively. These points can be interpolated toform bedrock elevation maps ( and )depicting the drift thickness (points). These maps areimproved by integration of outcrop and surficial geologymap data-sets. Cross-sections can be drawn to depictthe present-day and buried bedrock surfaces.
The take-home messages are:1. - the use of this data-set to constrain the depth to
bedrock (data and maps available soon!)2. - the discontinuous and thin nature of the Chilcotin
basalts, and thick drift only in major valleys.3. - the presence of abandoned valleys and major
erosion along the Fraser River after eruption ofbasalts and before the last glaciation (
).
above)
below right
see nextpanel - Reversal of the Fraser River
0 km 100
D - present-daypresent course
parallel ancient drainage
anti-parallel ancient drainage REVERSAL OF THE FRASER RIVERAnewly identified volcanic dam, formed at 1.06 Ma, indicates northward
flow of the Fraser River and the absence of the Fraser Canyon at that time.This requires reversal of the Fraser River’s flow and carving of the canyonin the last 1 million years. Erosion of the Fraser Canyon caused the baselevel of the drainage basin to drop, carving deep canyons in sometributaries, and abandoning others. We attribute the reversal to ice-damming during the end of a c. 1 Ma glaciation.
The implications of this for exploration are as follows:1. - Reversal means that the Fraser River and some tributaries
have changed their course in the last 1 Ma. Fluvialsediments and detrital minerals deposited before 1 Ma were transportedaway from source (e.g., mineral deposit) Tributariesin the west appear unchanged, but those in the east may be completelyreversed.
2. - Reversal probably occurred multiple times after initial reversal at c. 1Ma, therefore, detrital minerals may have been carried
3. - Contemporary and later glacial deposits recycled this alluvialsediment and redistributed it - therefore tills in the reversed valleys andadjacent areas, especially older tills, may have very complex detritalsource histories.
4. - This event abandoned channels of the old drainage on the InteriorPlateau, many subsequently buried. These are potential .
apparently upstream!
upstreamdownstream.
and
placer deposits
(e.g., theThompson River) the