TRIANGLE ZONES IN ACCRETIONARY WEDGES: EXAMPLES...
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Chambly-Fortierville Syncline GRENVILLE BASEMENT 47 o N 46 o 73 o 71 o W 20 km Montreal Joliette Trois Rivières Portneuf Neuville Quebec City Drummondville Saint- Dominique Chaudière Nappe Richardson Nappe N Normal fault Thrust fault Grenville basement Parautochthonous imbricate fault zone + + + + + + + + + + + + + Logan’s Line Aston Fault St. Lawrence Lowlands Autochthonous domain Appalachian thrusts Allochthonous domain c-c’ TRIANGLE ZONES IN ACCRETIONARY WEDGES: EXAMPLES FROM THE QUÉBEC APPALACHIANS AND PHYSICAL MODELING Elena Konstantinovskaya 1 , Diego Rodriguez 2 , Donna Kirkwood 3 , Lyal B. Harris 1 , Robert Theriault 4 1 - INRS-ETE, Quebec City, QC, Canada ([email protected]); 2 - Ecopetrol S.A., Bogota, Colombia; 3 - GSC-Quebec, Quebec City, QC, Canada; 4- MRNF, Quebec City, QC, Canada Research was funded by NSERC, CFI, MELS, and INRS-ETE 2 cm syn-orogenic sand layers décollement level SE NW 410 450 500 550 TRACE 2.0 0.0 0.4 0.8 1.2 1.6 TIME (s) 1km 5Q-33 ? JCF Neuville Fault Backthrust GB TZ Ni CFS Ni Tr Pts Lb Ut Bm PC PC PC Tr Lb Lb Ut 0.0 0.4 0.8 1.2 1.6 2.0 TIME (s) SE 155 205 255 305 355 405 455 TRACE 105 NW 1km 78-824 Aston Fault Logan’s Line A168 A161 Neuville Fault Neuville Fault Backthrust Ut-Tr Pts Bm PC Lt Ut-Tr PC CFS TZ GB Ni Lb Bt LF Bt Lb Lb Ni Ni Ni Bc Pg Pg Ni SE NW 20 15 10 05 TRACE 0.0 0.4 0.8 1.2 1.6 2.0 TIME (s) 1km M2001 Aston Fault Ct Logan’s Line A192 A167 A072 Bt GB PC PC Tr Ut Lb LF LF Pts Bm Tr Ut Ut Lb Lb Ut Lb CFS Ni SE NW 110 135 160 185 210 TRACE 1km 78-821 Aston Fault VQ 0.0 0.4 0.8 1.2 1.6 TIME (s) GB PC Pts Tr Ut Ut Ni LF Lb SE NW 50 100 150 200 250 300 350 400 450 TRACE 0.0 0.4 0.8 1.2 1.6 2.0 TIME (s) 1km 78-825 Aston Fault Ut Tr Pts Bm PC Backthrust GB Lb Ni Pg Ni LF TZ Lb Ni CFS Ni 0.6 cm 1.0-1.7 cm 2.2 cm Depth to basement: initial sand layers syn-orogenic sand layers basement On profiles: 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Max. shear strain, % a b c d e f g h i j a-a’ b-b’ c-c’ d-d’ e-e’ 2 cm syntectonic erosion backthrust 5 cm a-a’ 7 cm 6 cm 3 cm 2 cm f-f’ b-b’ d-d’ c-c’ e-e’ 2 cm a-a’ b-b’ d-d’ c-c’ f-f’ e-e’ detachment initial sand layers syn-orogenic sand layers post-orogenic sand layers basement On profiles: 0.5 cm 2.0 cm Depth to basement: a-a’ 5 cm 2 cm b-b’ c-c’ a-a’ b-b’ c-c’ 2 cm 3 cm 6 cm 7 cm syntectonic erosion backthrusts BTR basal detachment SERIES NW-SE SERIES SW-NE I II III IV V GEOLOGY OF THE APPALACHIAN FRONT IN THE QUEBEC CITY AREA GENERAL GEOLOGY OF THE SOUTHERN QUEBEC APPALACHIANS TIME STRUCTURE MAP OF THE PRECAMBRIAN BASEMENT 46 o 30' 46 o 45' 71 o 30' 71 o 00' 0 5 10 km St. Flavien Two-way time (s) N Light angle 300 o 0.1 0.5 1.0 2.0 3.0 3.5 1.5 2.5 GRENVILLE BASEMENT Montmorency Fault Neuville Fault Jacques Cartier Fault Deschambault Fault Saint Prosper Fault Quebec + + + + + + + + + + + + Syncline axial plane CFS Chambly-Fortierville Syncline Aston Fault Backthrust CFS 78-824 78-825 M2001 78-821 5Q-33 72 o 00' Declination 25 o Vertical exageration 10 x SEISMIC LINES ACROSS THE APPALACHIAN FRONT STRATIGRAPHIC CORRELATIONS BASED ON WELL LOG DATA MAP OF ELEVATIONS OF BASEMENT AND WELL LOCATIONS CONCEPTUAL MODEL OF BASEMENT GEOMETRY AND REGIONAL GEOLOGY RESULTS OF SANDBOX MODELING TRIANGLE ZONES IN MODEL THRUST WEDGES SYNTECTONIC SEDIMENTATION, EROSION, AND OBLIQUE RAMP IN BASEMENT SYNTECTONIC SEDIMENTATION SYNTECTONIC SEDIMENTATION, EROSION, AND ORTHOGONAL RAMP IN BASEMENT SYNTECTONIC SEDIMENTATION AND OBLIQUE RAMP IN BASEMENT: FRONTAL THRUST DEFLECTION PIV imaging of step-by-step frontal thrust deflection Geometry of deflected detachment TZ - triangle zone Lr Tr Lr Tr Tr Tr Lr Tr Pts Pts Lr Tr Lr Tr Lr Tr Lr Tr Lr Tr Pts Lr Tr Pts Lr Tr Pts Lr Tr Lr Tr Lr Tr Pts Lr Tr Lr Tr A187 C A D E SW NE NW SE NW SE SW NE PC Bm Chz Ut BR A175 A176 A167 A161 A010 A009 A072 A069 A167 A192 A016 A015 A069 A161 Ut Pts Ut Ut Ut BR Ut BR PC Ut Lr Ut B NW SE A072 A192 A167 PC Bm Chz Ut Ut Ut PC BR Pts Bm Ut Bm Ut BR Ut PC BR Chz Bm Ut Chz PC Ut PC Ut PC Ut BR PC PC PC BR BR 305 610 914 1219 1524 1829 890 244 015 549 m m 595 942 1525 1862 2427 2845 m 005 596 018 890 1667 2026 2661 3106 m 305 610 914 1219 1524 1829 m Lr Tr Pts Ct 46 o 30' 46 o 45' 71 o 30' 71 o 00' 72 o 00' Logan's Line St. Lawrence River Parautochthonous zone Queenston Group (Bécancour Fm) Lorraine Group Sainte-Rosalie Gr. (Lotbinière Fm) Utica Shale Pontgravé Fm. Nicolet Fm. Black River and Trenton groups GRENVILLE BASEMENT N Normal fault Thrust fault Syncline axial plane Anticline axial plane Sainte-Rosalie Gr. (Les Fonds Fm) Slope, rise siliclastics Reversely reactivated normal fault 0 5 10 km Chaudière Nappe Boyer River Nappe Bacchus Nappe Neuville Fault Jacques Cartier Fault Deschambault Fault CFS Chambly-Fortierville Syncline Montmorency Fault Saint Prosper Fault Aston Fault + + + + + + + + + + + + ? TZ Backthrust CFS LT PQT St Lawrence platform, Autochthonous domain Appalachian thrusts Allochthonous domain Saint Alban Fault Grondines Portneuf Neuville Chateau Richer Quebec City Neuville Fault Jacques Cartier Fault Deschambault Fault Montmorency Fault Saint Prosper Fault N 46 o 30' 46 o 45' 71 o 30' 71 o 00' 72 o 00' 0 5 10 km GRENVILLE BASEMENT Normal fault at surface Lineament at depth Stratigraphic contact A069 A190 A187 A015 A194 A160 A051 + + + + + + + + + + + + A168 A173 St. Flavien Two-way time (s) 0.5 1.0 2.0 1.5 2.5 I II III IV V A016 427 A072 549 A167 1862 A161 2845 A176 945 A175 942 A192 1050 A010 244 A167 1862 well number elevations of basement, m A009 290 OBLIQUE RAMP LATERAL RAMP Oblique basement escarpment Forward propagated detachment (glass microbeads) SHORTENING Deflection and rotation of detachment surface FIXED WALL MOVING WALL Well No. Well Name Latitude Latitude Longitude Longitude A009 Bald Mountain, Cap-Santé No 1 46° 40' 42,1" 46,6784 -71° 47' 01,4" -71,7837 A010 Bald Mountain, Cap-Santé No 2 46° 41' 48,1" 46,6967 -71° 47' 15,4" -71,7876 A015 Bald Mountain, Portneuf No 1 46° 40' 59,1" 46,6831 -71° 55' 17,4" -71,9215 A016 Bald Mountain, Portneuf No 2 46° 40' 58,1" 46,6828 -71° 55' 16,4" -71,9212 A069 Impérial Lowlands No 1 46° 32' 57,1" 46,5492 -71° 59' 55,4" -71,9987 A072 Impérial Lowlands No 4, Lotbinière 46° 36' 59,1" 46,6164 -71° 52' 02,4" -71,8673 A160 CPOG SOQUIP Sisque, Île d'Orléans No 1 46° 58' 29,1" 46,9748 -70° 55' 23,3" -70,9231 A161 Shell, Sainte-Françoise-Romaine No 1 46° 28' 25,1" 46,4736 -71° 54' 55,4" -71,9154 A167 SOQUIP Shell, Sainte-Croix No 1 46° 37' 17,6" 46,6216 -71° 42' 14,5" -71,704 A168 SOQUIP Shell, Villeroy No 1 46° 27' 55,1" 46,4653 -71° 54' 04,4" -71,9012 A173 SOQUIP et al., Villeroy No 2 46° 29' 47,0" 46,4964 -71° 51' 22,2" -71,8562 A175 SOQUIP et al., Les Saules No 1 46° 49' 05,1" 46,8181 -71° 20' 07,3" -71,3354 A176 SOQUIP et al., Ancienne-Lorette No 1 46° 46' 58,7" 46,783 -71° 23' 50,5" -71,3974 A187 SOQUIP et al., Du Chêne No 1 (Villeroy) 46° 25' 23,1" 46,4231 -71° 50' 26,4" -71,8407 A190 SOQUIP, Sainte-Françoise-Romaine No 1 46° 27' 04,1" 46,4511 -71° 54' 52,4" -71,9146 A192 SOQUIP, Sainte-Croix No 1 Lotbinière 46° 37' 38,1" 46,6272 -71° 46' 01,4" -71,7671 A194 SOQUIP, Pintendre No 1 Lévis 46° 46' 48,9" 46,7803 -71° 06' 29,1" -71,1081 WELL NAMES AND COORDINATES (NAD83) FROM THE PRESENT STUDY A triangle zone (lines 78-825, 78-824, 5Q-33) is bounded by backthrusts at the SE limb of the Chambly-Fortierville syncline and by imbricate faults of the Appala- chian thrust wedge and parau- tochthonous units. The basal de- tachment propagates forward under the triangle zone. Lateral and longitudinal variations in thicknesses of the St Lawrence platform units imply thickening from the NW to the SE and from the NE to the SW that likely confirm progres- sive synsedimentary subsidence during the Late Ordovician in the foreland basin. Triangle zone occurs in the thicker part of the foreland basin above the deeper-seated ba- sement and it is pinched out towards the lateral basement ramp. Geological data support that pre-existing basement structures, syntectonic sedimentation, and erosion appear to be responsible for the development of triangle zone and deflection of frontal thrusts in the Quebec Appalachians. ORDOVICIAN 443 449 458 464 470 485 495 AGE (Ma) LOWER MIDDLE UPPER ASHGILL CARADOC LLANDEIL LLANVIRN ARENIG TREMAD. Pts PC Bm Chz BR Lr Tr Utica Shale Trenton Black River Chazy Beekmantown Potsdam Grenville basement Lorraine SAUK DISCORDANCE Ste Rosalie Queenston argillaceous limestones turbi- dites molasse dolomites sandstones FORELAND BASIN PASSIVE MARGIN St Lawrence Lowlands sequence 545 CAMBR. 5 cm a-a’ e-e’ 2 cm 4 cm 7 cm 8 cm 9 cm b-b’ c-c’ d-d’ The Taconian fold and thrust belt of the Quebec Ap- palachians displays typical structures such as inver- ted normal faults, ramp and flat structures, sub-hori- zontal detachments, triangle zones and backthrusts. The development of these structures is not, howe- ver, consistent along the belt and seems to be spa- tially related to variations in palaeotopography and stratigraphic architecture of the Middle-Late Ordovi- cian foreland basin, which developed in front of the Taconian tectonic wedge. Our modelling results and geological data support the hypothesis that pre–existing basement struc- ture, syntectonic sedimentation, and erosion appear to be responsible for the development of triangle zones and frontal thrust deflection in the Quebec Appalachians. Syntectonic sedimentation in the foreland of the fold-thrust belt changes the dynamics of accretionary wedges and favors the activation of weak décollement layers (glass microbeads) at the base or within the cover. This leads to forward propagation of a décollement that induces the de- velopment of a piggy-back basin. 0.6 cm 1.2 cm 2.2 cm Depth to basement: initial sand layers syn-orogenic sand layers basement On profiles: Syntectonic erosion in accretionary wedges retards forward propagation of the wedge, enhances material transport across the wedge, and focuses the inter- nal deformation and exhumation close to the backstop. The presence of a rigid basement escarpment and along-strike variations in ini- tial thickness of sand layers in models influence the development of backthrusts and triangle zones in thrust wedges. Triangle zones occur in the thicker parts of models above the deeper-seated basement and they are pin- ched out towards the basement escarpments. The geometry of a growing thrust wedge is very sensitive to variations in base- ment surface topography. Deflection of the deformation front in thrust wedges occurs above oblique ramps in basement. Deflection is pronounced as a gradual propagation of forward mate- rial translation along the fault strike and counter-clockwise rotation of the hanging wall around a vertical axis caused by the differential forward slip Triangle zones form above the deeper-seated basement and pinch out towards basement highs in model wedges (see plan-view maps of the models B and C). c-c’ syn-orogenic sand layers basal detachment TRIANGLE ZONE BACKTHRUSTS syntectonic erosion and exhumation 2 cm 2 cm b-b’ CROSS-SECTION OF MODEL C MODEL A MODEL B CROSS-SECTION OF MODEL B MODEL C MODEL D Triangle zones develop between the frontal forward thrusts of accretionary wedges and foreland basins due to combined effect of syntectonic erosion and sedi- mentation affecting the wedges. Konstantinovskaya E.A., D. Rodriguez, D. Kirkwood, L.B. Harris, and R. Thériault. 2009. Effects of basement structure, sedimentation and erosion on thrust wedge geometry: an example from the Quebec Appalachians and analogue models. Bulletin of Canadian Petroleum Geology, 57 (1): 34–62 REFERENCES: The triangle zone is pin- ched out (lines M2001, 78-821) to the NE to- wards the Quebec City area because a lateral ramp is present in the Precambrian basement. after Castonguay et al. (2006) initial sand layers syn-orogenic sand layers basement A 40º-50º deflection of frontal thrusts relative to the general SW-NE strike of the orogen occurs against an oblique, deep-seated basement escarpment. TRIANGLE ZONE CFS - Chambly-Fortierville syncline BTR - Backthrust 10 km 1 2 0 CFS Logan’s Line Aston Fault Neuville Fault Bacchus Nappe BTR Depth, km SW NE The triangle zone pinches out to the northeast as the basement shallows. Extension related to the opening of the Iapetus ocean Shortening related to the Taconian orogeny SHORTENING SHORTENING Each step from a to j correspond to 1 mm of shortening HF/DL LF HF - high basal friction, LF - low basal friction DL - décollement level LF LF LF HF/DL LF LF HF - high basal friction, LF - low basal friction DL - décollement level LF - low basal friction BTR b-b’ décollement level TRIANGLE ZONE syntectonic erosion and exhumation high basal friction
Transcript of TRIANGLE ZONES IN ACCRETIONARY WEDGES: EXAMPLES...
Chambly-Fortie
rville Syn
cline
GRENVILLE BASEMENT
47oN
46o
73o 71oW
20 km
Montreal
Joliette
Trois Rivières
PortneufNeuville
Quebec City
Drummondville
Saint-Dominique
Chaud
ière N
appe
Richard
son N
appe
N
Normal fault
Thrust fault
Grenville basement
Parautochthonousimbricate fault zone
+ + + +
+ ++
+ + +
+
+ +
Logan’s Line
Aston F
ault
St. Lawrence LowlandsAutochthonous domain
Appalachian thrustsAllochthonous domain
c-c’
TRIANGLE ZONES IN ACCRETIONARY WEDGES: EXAMPLES FROM THE QUÉBEC APPALACHIANS AND PHYSICAL MODELING
Elena Konstantinovskaya1, Diego Rodriguez2, Donna Kirkwood3, Lyal B. Harris1, Robert Theriault4
1 - INRS-ETE, Quebec City, QC, Canada ([email protected]); 2 - Ecopetrol S.A., Bogota, Colombia; 3 - GSC-Quebec, Quebec City, QC, Canada; 4- MRNF, Quebec City, QC, Canada
Research was funded by NSERC, CFI, MELS, and INRS-ETE
2 cmsyn-orogenic sand layers
décollement level
SE NW410 450 500 550TRACE
2.0
0.0
0.4
0.8
1.2
1.6
TIM
E (s
)
1km 5Q-33
?
JCFNeuville FaultBackthrust
GB
TZNi CFS Ni
Tr
Pts
LbUt
Bm
PCPC
PC
Tr
Lb
LbUt
0.0
0.4
0.8
1.2
1.6
2.0
TIM
E (s
)
SE 155 205 255 305 355 405 455TRACE105 NW
1km 78-824
Aston FaultLogan’s LineA168 A161
Neuville Fault
Neuville Fault
Backthrust
Ut-Tr
Pts
BmPC
LtUt-Tr
PC
CFSTZ
GB
Ni
Lb
Bt
LF
Bt
Lb LbNi
NiNi
BcPg Pg
Ni
SE NW20 15 10 05TRACE0.0
0.4
0.8
1.2
1.6
2.0
TIM
E (s
)
1km M2001
Aston Fault
Ct
Logan’s LineA192A167 A072Bt
GB
PC
PC
Tr Ut
LbLF
LF
PtsBmTr
Ut
Ut
LbLbUt
LbCFS
Ni
SE NW110 135 160 185 210TRACE
1km 78-821
Aston Fault
VQ0.0
0.4
0.8
1.2
1.6
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E (s
)
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TrUt
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Ni
LFLb
SE NW50 100 150 200 250 300 350 400 450TRACE0.0
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0.8
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1.6
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E (s
)
1km 78-825
Aston Fault
UtTrPts Bm
PC
Backthrust
GB
Lb
Ni
Pg
Ni
LF TZ
Lb
Ni CFS
Ni
0.6 cm1.0-1.7 cm2.2 cm
Depth to basement:
initial sand layerssyn-orogenic sand layers
basement
On profiles:
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Max
. she
ar s
train
, %
a
b
c
d
e
f
g
h
i
j
a-a’
b-b’
c-c’
d-d’
e-e’
2 cm
syntectonic erosion
backthrust
5 cm
a-a’
7 cm
6 cm
3 cm
2 cm
f-f’
b-b’ d-d’
c-c’e-e’
2 cm
a-a’
b-b’
d-d’
c-c’
f-f’
e-e’
detachment
initial sand layerssyn-orogenic sand layers
post-orogenic sand layers
basement
On profiles:
0.5 cm2.0 cm
Depth to basement:
a-a’
5 cm
2 cm
b-b’
c-c’
a-a’
b-b’ c-c’
2 cm
3 cm
6 cm
7 cmsyntectonic erosion
backthrusts
BTR
basal detachment
SERIES NW-SE
SERIES SW-NE
I II III
IV V
GEOLOGY OF THE APPALACHIAN FRONT IN THE QUEBEC CITY AREA
GENERAL GEOLOGY OF THE SOUTHERN QUEBEC APPALACHIANS TIME STRUCTURE MAP OF THE PRECAMBRIAN BASEMENT
46o30'
46o45'
71o30'
71o00'
0 5 10 km
St. Flavien
Two-way time (s)
NLight angle 300o
0.10.51.0
2.0
3.03.5
1.5
2.5
GRENVILLE BASEMENT
Montmorency Fault
Neuvill
e Fau
lt
Jacques Cartier Fault
Deschambault Fault
Saint P
rospe
r Fau
lt
Quebec
+ + + +
+ +
+ + + ++
+
Syncline axial planeCFS Chambly-Fortierville Syncline
Aston Fault
Backthrust
CFS
78-824
78-825
M2001
78-821
5Q-33
72o00'
Declination 25o
Vertical exageration 10x
SEISMIC LINES ACROSS THE APPALACHIAN FRONT
STRATIGRAPHIC CORRELATIONS BASED ON WELL LOG DATA
MAP OF ELEVATIONS OF BASEMENT AND WELL LOCATIONS
CONCEPTUAL MODEL OF BASEMENT GEOMETRY AND REGIONAL GEOLOGY
RESULTS OF SANDBOX MODELING
TRIANGLE ZONES IN MODEL THRUST WEDGES
SYNTECTONIC SEDIMENTATION, EROSION, AND OBLIQUE RAMP IN BASEMENT
SYNTECTONIC SEDIMENTATION SYNTECTONIC SEDIMENTATION, EROSION, AND ORTHOGONAL RAMP IN BASEMENT
SYNTECTONIC SEDIMENTATION AND OBLIQUE RAMP IN BASEMENT: FRONTAL THRUST DEFLECTION
PIV imaging of step-by-step frontal thrust deflection
Geometry of deflected detachment
TZ - triangle zone
Lr
Tr
Lr
Tr
TrTr
Lr
Tr
Pts
Pts
Lr
Tr
Lr
Tr
Lr
Tr
Lr
Tr
Lr
Tr
Pts
Lr
Tr
Pts
Lr
Tr
Pts
Lr
Tr
Lr
TrLr
Tr
Pts
Lr
Tr
Lr
Tr
A187
CA
D E
SW NE
NW SE NW SE
SW NE
PC
BmChz
Ut
BR
A175A176A167A161A010A009A072A069
A167A192A016A015 A069 A161
UtPts
Ut Ut
Ut
BR
Ut
BR
PC
UtLr
Ut
B
NW SEA072 A192 A167
PC
BmChz
Ut
Ut
Ut
PCBR
PtsBm
UtBm
Ut
BR
Ut
PC
BRChz
Bm
Ut
Chz
PC
Ut
PC
Ut
PC
Ut
BR
PC
PC
PC
BR
BR
305
610
914
1219
1524
1829
890
244
015
549
m
m
595
942
1525
1862
2427
2845m
005
596
018
890
1667
2026
2661
3106m
305
610
914
1219
1524
1829m
Lr
Tr
Pts
Ct
46o30'
46o45'
71o30'
71o00'
72o00'
Logan's Line
St. Lawrence River
Parautochthonous zone
Queenston Group (Bécancour Fm)
Lorraine Group
Sainte-Rosalie Gr. (Lotbinière Fm)
Utica Shale
Pontgravé Fm.
Nicolet Fm.
Black River and Trenton groups
GRENVILLE BASEMENTNNormal fault
Thrust fault
Syncline axial plane
Anticline axial plane
Sainte-Rosalie Gr. (Les Fonds Fm)
Slope, rise siliclastics
Reversely reactivated normal fault
0 5 10 km
Chaudière Nappe
Boyer Rive
r Nappe
Bacchus N
appeNeu
ville F
ault
Jacques Cartier Fault
Deschambault FaultCFS Chambly-Fortierville Syncline
Montmorency Fault
Saint P
rospe
r Fau
lt
Aston Fault
+ + + +
+ +
+ + + ++
+
?
TZ
Backthrust
CFS
LT
PQT
St Lawrence platform, Autochthonous domain
Appalachian thrustsAllochthonous domain
Saint Alban Fault
Grondines
Portneuf
Neuville
Chateau Richer
Quebec City
Neuvill
e Fau
lt
Jacques Cartier Fault
Deschambault Fault
Montmorency Fault
Saint P
rospe
r Fau
lt
N
46o30'
46o45'
71o30'
71o00'
72o00'
0 5 10 km
GRENVILLE BASEMENTNormal fault at surface
Lineament at depth
Stratigraphic contact
A069
A190A187
A015
A194
A160
A051
+ + + +
+ +
++ + + +
+
A168
A173St. Flavien
Two-way time (s)
0.51.0
2.01.5
2.5
I
II
III
IV
VA016427
A072549
A1671862
A1612845
A176 945
A175 942
A1921050
A010 244
A1671862
well numberelevations of basement, m
A009290
OBL
IQUE
RAM
P
LATERAL RAMP
Oblique basement escarpment
Forward propagated detachment (glass microbeads)
SHORTENING
Deflection and rotation of detachment surface
FIXED WALL
MOVING WALL
Well No. Well Name Latitude Latitude Longitude Longitude A009 Bald Mountain, Cap-Santé No 1 46° 40' 42,1" 46,6784 -71° 47' 01,4" -71,7837 A010 Bald Mountain, Cap-Santé No 2 46° 41' 48,1" 46,6967 -71° 47' 15,4" -71,7876 A015 Bald Mountain, Portneuf No 1 46° 40' 59,1" 46,6831 -71° 55' 17,4" -71,9215 A016 Bald Mountain, Portneuf No 2 46° 40' 58,1" 46,6828 -71° 55' 16,4" -71,9212 A069 Impérial Lowlands No 1 46° 32' 57,1" 46,5492 -71° 59' 55,4" -71,9987 A072 Impérial Lowlands No 4, Lotbinière 46° 36' 59,1" 46,6164 -71° 52' 02,4" -71,8673 A160 CPOG SOQUIP Sisque, Île d'Orléans No 1 46° 58' 29,1" 46,9748 -70° 55' 23,3" -70,9231 A161 Shell, Sainte-Françoise-Romaine No 1 46° 28' 25,1" 46,4736 -71° 54' 55,4" -71,9154 A167 SOQUIP Shell, Sainte-Croix No 1 46° 37' 17,6" 46,6216 -71° 42' 14,5" -71,704 A168 SOQUIP Shell, Villeroy No 1 46° 27' 55,1" 46,4653 -71° 54' 04,4" -71,9012 A173 SOQUIP et al., Villeroy No 2 46° 29' 47,0" 46,4964 -71° 51' 22,2" -71,8562 A175 SOQUIP et al., Les Saules No 1 46° 49' 05,1" 46,8181 -71° 20' 07,3" -71,3354 A176 SOQUIP et al., Ancienne-Lorette No 1 46° 46' 58,7" 46,783 -71° 23' 50,5" -71,3974 A187 SOQUIP et al., Du Chêne No 1 (Villeroy) 46° 25' 23,1" 46,4231 -71° 50' 26,4" -71,8407 A190 SOQUIP, Sainte-Françoise-Romaine No 1 46° 27' 04,1" 46,4511 -71° 54' 52,4" -71,9146 A192 SOQUIP, Sainte-Croix No 1 Lotbinière 46° 37' 38,1" 46,6272 -71° 46' 01,4" -71,7671 A194 SOQUIP, Pintendre No 1 Lévis 46° 46' 48,9" 46,7803 -71° 06' 29,1" -71,1081
WELL NAMES AND COORDINATES (NAD83) FROM THE PRESENT STUDY
A triangle zone (lines 78-825, 78-824, 5Q-33) is bounded by backthrusts at the SE limb of the Chambly-Fortierville syncline and by imbricate faults of the Appala-chian thrust wedge and parau-tochthonous units. The basal de-tachment propagates forward under the triangle zone.
Lateral and longitudinal variations in thicknesses of the St Lawrence platform units imply thickening from the NW to the SE and from the NE to the SW that likely confirm progres-sive synsedimentary subsidence during the Late Ordovician in the foreland basin.
Triangle zone occurs in the thicker part of the foreland basin above the deeper-seated ba-sement and it is pinched out towards the lateral basement ramp. Geological data support that pre-existing basement structures, syntectonic sedimentation, and erosion appear to be responsible for the development of triangle zone and deflection of frontal thrusts in the Quebec Appalachians.
OR
DO
VIC
IAN
443
449
458
464
470
485
495
AGE (Ma)
LOW
ERM
IDD
LEU
PPER
ASH
GIL
LC
ARAD
OC
LLAN
DEI
LLL
ANVI
RN
AREN
IGTR
EMAD
.
Pts
PC
Bm
Chz
BR
Lr
TrUtica ShaleTrentonBlack River
Chazy
Beekmantown
Potsdam
Grenville basement
Lorraine
SAUK DISCORDANCE
Ste Rosalie
Queenston
argi
llace
ous
limes
tone
stu
rbi-
dite
s
molasse
dolomites
sandstones
FOR
ELAN
D B
ASIN
PASS
IVE
MAR
GIN
St Lawrence Lowlands sequence
545 CAMBR.
5 cm
a-a’ e-e’
2 cm
4 cm
7 cm
8 cm
9 cm
b-b’c-c’
d-d’
The Taconian fold and thrust belt of the Quebec Ap-palachians displays typical structures such as inver-ted normal faults, ramp and flat structures, sub-hori-zontal detachments, triangle zones and backthrusts.
The development of these structures is not, howe-ver, consistent along the belt and seems to be spa-tially related to variations in palaeotopography and stratigraphic architecture of the Middle-Late Ordovi-cian foreland basin, which developed in front of the Taconian tectonic wedge.
Our modelling results and geological data support the hypothesis that pre–existing basement struc-ture, syntectonic sedimentation, and erosion appear to be responsible for the development of triangle zones and frontal thrust deflection in the Quebec Appalachians.
Syntectonic sedimentation in the foreland of the fold-thrust belt changes the dynamics of accretionary wedges and favors the activation of weak décollement layers (glass microbeads) at the base or within the cover. This leads to forward propagation of a décollement that induces the de-velopment of a piggy-back basin. 0.6 cm
1.2 cm2.2 cm
Depth to basement:
initial sand layerssyn-orogenic sand layers
basement
On profiles:
Syntectonic erosion in accretionary wedges retards forward propagation of the wedge, enhances material transport across the wedge, and focuses the inter-nal deformation and exhumation close to the backstop.
The presence of a rigid basement escarpment and along-strike variations in ini-tial thickness of sand layers in models influence the development of backthrusts and triangle zones in thrust wedges. Triangle zones occur in the thicker parts of models above the deeper-seated basement and they are pin-ched out towards the basement escarpments.
The geometry of a growing thrust wedge is very sensitive to variations in base-ment surface topography. Deflection of the deformation front in thrust wedges occurs above oblique ramps in basement.
Deflection is pronounced as a gradual propagation of forward mate-rial translation along the fault strike and counter-clockwise rotation of the hanging wall around a vertical axis caused by the differential forward slip
Triangle zones form above the deeper-seated basement and pinch out towards basement highs in model wedges (see plan-view maps of the models B and C).
c-c’syn-orogenic sand layers
basal detachment
TRIANGLE ZONE
BACKTHRUSTS
syntectonic erosion and exhumation
2 cm 2 cm
b-b’CROSS-SECTION OF MODEL C
MODEL A MODEL B
CROSS-SECTION OF MODEL B
MODEL C MODEL D
Triangle zones develop between the frontal forward thrusts of accretionary wedges and foreland basins due to combined effect of syntectonic erosion and sedi-mentation affecting the wedges.
Konstantinovskaya E.A., D. Rodriguez, D. Kirkwood, L.B. Harris, and R. Thériault. 2009. Effects of basement structure, sedimentation and erosion on thrust wedge geometry: an example from the Quebec Appalachians and analogue models. Bulletin of Canadian Petroleum Geology, 57 (1): 34–62
REFERENCES:
The triangle zone is pin-ched out (lines M2001, 78-821) to the NE to-wards the Quebec City area because a lateral ramp is present in the Precambrian basement.
after Castonguay et al. (2006)
initial sand layerssyn-orogenic sand layers basement
A 40º-50º deflection of frontal thrusts relative to the general SW-NE strike of the orogen occurs against an oblique, deep-seated basement escarpment.
TRIANGLE ZONE
CFS - Chambly-Fortierville synclineBTR - Backthrust
10 km
1
2
0
CFS
Loga
n’s
Line
Aston Fault
Neuville Fault
Bacchus Nappe
BTR
Dep
th, k
m
SW
NE
The triangle zone pinches out to the northeast as the basement shallows.
Extension related to the opening of the Iapetus oceanShortening related to the Taconian orogeny
SHORTENING SHORTENING
Each step from a to j correspond to 1 mm of shortening
HF/DL LF
HF - high basal friction, LF - low basal frictionDL - décollement level
LF
LF
LF
HF/DL LF
LF
HF - high basal friction, LF - low basal friction DL - décollement level
LF - low basal friction
BTR
b-b’
décollement level
TRIANGLE ZONE
syntectonic erosion and exhumation
high basal friction
