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North-south compression, active uplift, and abyssal mantle exhumation of the Saint Peter and Saint Paul Rock, Equatorial Atlantic Ocean
North-south compression, active uplift, and abyssal mantle exhumation North-south compression, active uplift, and abyssal mantle exhumation of the Saint Peter and Saint Paul Rock, Equatorial Atlantic Oceanof the Saint Peter and Saint Paul Rock, Equatorial Atlantic Ocean
AGU Meeting of th Americas. Cancun, Mexico, 14-17 May 2013AGU Meeting of th Americas. Cancun, Mexico, 14-17 May 2013
Satellite-delivered gravimetry for the Vitória-Trindade Chain, Southeast Brazil, and its bearing on the volcanic seamount structure
1Motoki, A. (rochasornamentais@yahoo.com.br), 2 2Motoki, K.F. , Sichel, S.E. , 3Souza, K. , 4Bueno, G.V. ; 2) Federal Fluminense University, Brazil, 1) Rio de Janeiro State University, Brazil 3) Geological Survey of Brazil; 4) PETRBRAS, Brazil
1Motoki, A. (rochasornamentais@yahoo.com.br), 2 2Motoki, K.F. , Sichel, S.E. , 3Souza, K. , 4Bueno, G.V. ; 2) Federal Fluminense University, Brazil, 1) Rio de Janeiro State University, Brazil 3) Geological Survey of Brazil; 4) PETRBRAS, Brazil
2000 km
Brazil
200 km
NN
3040 38 36 34 32 28longitude (°W)
18
20
22
latitu
de
(°S
)
Atlantic OceanAtlantic Ocean
4000
3600
3200
2800
3200
280024
00
20001
600
1200
4000
3600
3200
2800
3200
280024
00
20001
600
1200
1
345
67
89
101
345
67
89
101
2
345
67
89
10
11
12
13
14
15
16
1718
19
11
12
13
14
15
16
1718
19
21
22
23
2425
21
22
23
2425
SM
VT
GPGP
1: Martim Vaz 2: South Trindade 3: North Trindade 4: East Columbia5: West Columbia6: E1 Dogaressa7: E2 Dogaressa8. W2 Dogaressa9. W1 Dogaressa
10: Davis11: Columbia Bank12: East Jaseur13: West Jaseur14: VT-2008-3610 15: Montange16: VT-2008-365317: Congress Bank18: Vitória Seamount
19: Champlain Bank20: Besnard Bank21: Almirante Saldanha22: São Tomé Seamount23: Hospur Seamount24: Abrolhos Seamount25: Minerva Seamount
ABR: AbrolhosCV: CaravelasSM: São MateusVT: VitóriaGP: Guarapari
South AmericaSouth America
CVABR
CVABR
Columbia Channel
Columbia Channel
São Mateus Off-shore
Vitória Off-shore
São Mateus Off-shore
4000
4000
3600
3600
Vitória Off-shore
2020
2
Abrolhos Continental Shelf
Abrolhos Continental Shelf
5000
3000
1000
0
he
igh
t (m
)
0 10 20 30
typical declivity (°)
A. Typical declivity vs. height
4000
2000
lava flows
21
22
1218
lava flows
21
22
121820
100
80
60
40
0
2220 1008060400 120
20
21
18
12 10
20
21
18
12 10
fla
t-to
p d
iam
ete
r (k
m)
base diamenter (km)
B. Base diamenter vs. flat-top diameter
normal size
large size
continental shelf fragmentnormal size
large size
continental shelf fragment
C. Longitude vs. height
38 30323436 28
longitude (°W) eastwest
2020
6000
5000
3000
1000
0
he
igh
t (m
) 4000
2000
6000
tectonic uplift
tectonic uplift
ocean floor deepning
ocean floor deepning
121220
1820
18 2222
2121
conical volcanic seamountelliptic volcanic seamountseamount out of the Vitória-Trindade Chaincontinental shelf fragment
10: Davis Bank (DVS)12: Jaseur Bank (JSR)18: Vitória-Congress Seamount (VTR-CGB)20: Besnard Bank (BSB)21: Almirante Saudanha Seamount (ASD)22: São Tomé Seamount (STM)
unconsolidated pyroclastics
unconsolidated pyroclastics
1. Vitória-Trindade Chain The Vitória-Trindade volcanic seamount chain is situated in the western side of South Atlantic Ocean, State of Espírito Santo, Brazil. It is of east-west trend, situated along 20°40'S, and about 950 km long.
200 km
N
3040 38 36 34 32 28
longitude (°W)
18
20
22
latit
ude (
°S)
SM
VT
GP
South AmericaSouth AmericaCVCV ABRABR
101218 101218
volcanic seamount
77
7: Dogaressa Bank10: Davos Bank12: Jaseur Bank18: Vitória Seamount
ABR: AbrolhosCV: CaravelasSM: São MateusVT: VitóriaGP: Guarapari
5000
4000
4000
3000
3000
1000
2000
2000
5000
4000
4000
3000
3000
1000
2000
2000
uplif
t
uplif
t
uplif
t
uplif
t
depth
(m
)
uplif
t
uplif
t
0
1000
2000
3000
4000
5000
MT
V
TR
N
CLS
DG
R
DV
S
JSR
VT
RV
TR
MTV: Martim VazTRN: TrindadeCLS: ColumbiaDGR: DogaressaDVS: DavisJSR: JaseurVTR: Vitória
base level surfacebase level surface
N
100
100
-100
-100
200 km
NN
1
2
345
67
89
10
20
GP
3040 38 36 34 32 28longitude (°W)
18
20
22
latit
ude (
°S)
ABRABR
0
0
0
0
0
9
2
367
8
10
0
451
0
0
0
0
1
2
345
67
89
10
0
00
100
0
21
22
23
2425
21
22
23
2425
12
1416
18
19
131517
1111
12
13
14
15
16
1718
1920
South America
CV
South America
CV
SM
VT
GPGP
00
SM
VT
GP
00
00
200
0
100200
0
SM-APSM-AP
VT-APVT-AP
Columbia Channel
Columbia Channel
SB2
SB3
SB5
SB9
SB1 SB2
SB3
SB5
SB9
SB1
Atlantic OceanAtlantic Ocean
local sedimentary basinSB1: Espírito Santo SB2: MucuriSB3: São Mateus SB5: Pedro CanárioSB9: Aracruz
local sedimentary basinSB1: Espírito Santo SB2: MucuriSB3: São Mateus SB5: Pedro CanárioSB9: Aracruz
200 km
NN
SM
VT
GPGP
SM
VT
GPGP
3040 38 36 34 32 28longitude (°W)
18
20
22
latit
ude (
°S)
1
2
345
67
89
10
11
12
13
14
15
16
1718
1920
21
22
23
2425
1
2
345
67
89
10
11
12
13
14
15
16
1718
1920
21
22
23
2425
Atlantic OceanAtlantic Ocean
30020
0
100
0
0 100
200
300
30020
0
100
0
0 100
200
300
Columbia Channel
Columbia Channel
CVABR
South America
CVABR
South America
PH
PH
PH
PH
PH
PH
PH
PH
SM-APSM-AP
VT-APVT-AP
US1
US2
US1
US2
SB2
SB3
SB5
SB9
SB1 SB2
SB3
SB5
SB9
SB1
Free-air anomaly
Bouguer anomaly
Free-air anomaly
Bouguer anomaly
A. Small volcano
sedimentary deposits lava
ρ = 2.6ρ = 2.6PH
PHPH
mantle
crust
mantle
crustρ = 2.85
ρ = 3.3
ρ = 2.85
ρ = 3.3
ML CH ML
CHρ = 2.85
gabbroic intrusions A
CHρ = 2.85
CH
ML ML
Bouguer anomaly profile
volcano rootvolcano root
B. Large volcanoCH: central highML: marginal lowPH: peripheral hight
crustal down-bucklingcrustal down-buckling
CH
ML ML
volcano rootvolcano root
gabbroic intrusions Bgabbroic intrusions B
gabbroic intrusions Cgabbroic intrusions C
PH ~3 km
CH
ML ML
PHPH
C. Veryh large volcano
18
20
22
latit
ude (
°S)
3040 38 36 34 32 28longitude (°W)
200 km
NN
200
300
0
100 200
300
0
100
100 km100 km
30°00'W
37°30'W
33°00'W
36°00'W
30°00'W
37°30'W
33°00'W
36°00'W
east
west
east
west20 m
Gal
60
10080
40
020 m
Gal
60
100
0
80
40
volcanic seamount continental shelf continent
north southnorth south
0-100 100 300free-air anomaly (mgal)
SH
Sm1: large seamountSM2: small seamountGY: seamount flat-topSH: continental shelfSL: continental slope
1000
depth
(m
) 2000
3000
4000
5000
0
6000200 400
SD
SD
SL
GY
AP
SH GY
SL
SM1
SD
-20~100 100~280
2000
4000
0
60000-100 100 300200 400
SL
CR
AP
SM2
SM1
no com
pensatio
nSM
2
SM1
SM2
full
isost
atic
com
pensa
tion
no isosta
tic co
mpensa
tion
fuu c
om
pensa
tion
CR
CR: continental riseSD: sedimentary depositAP: abyssal plane
SLSL
SD
SD
AP
SM2
SM1SM
2
SM1
CR
CR
Base level Bouguer anomaly mapBase level Bouguer anomaly map
5. Growth history of the volcanoesThese observations suggest the following growth history of the volcanic seamounts. At the initial stage, repeated central eruptions of lava flow construct the volcanic edifice. The weight of the volcano is sustained by mechanical firmness of the basement. The Bouguer anomaly is characterized by funnel-shaped depression. At the advanced stage, gabbroic radial dyke intrusion occurs along the central conduit in the upper level of the volcanic edifice, which is evidenced by the central Bouguer high. The seamount is supported mainly by mechanical firmness and partially by isostatic compensation of crustal down-buckling. At the highly advanced stage, the intrusion takes place into the lower level of the main volcanic edifice resulting lateral eruptions along its foot, which is shown by the bull's eye-like Bouguer lows. The crustal down-buckling and consequent isostatic compensation become relevant. The peripheral Bouguer high could be the rebound of the crustal down-buckling.
2. Volcanic seamountThe seamounts are generally of 30 km in base diameter, 10 km in flat-top diameter, and 2500 to 4000 m in relative height. The flat-tops are constant in depth, without evidence of basement subsidence.
4. Gravimetric anomalyThe volcanic seamounts usua l l y have Bougue r anomaly about 100 mGal lower than the adjacent area, showing funnel -shaped Bouguer depression. Large volcanoes show ring-like Bouguer structure composed of the central high and the marginal low. The marginal low is about 100 mGal lower than the adjacent abyssal plane and the central high is about 80 mGal higher than the marginal low. Very large volcanoes have bull's eye-like low Bouguer sites along the marginal low. On the foot of the volcanoes, there is the area with Bouguer anomaly 20 to 40 mGal higher, called peripheral high.
3. Basement upliftThe base level map (sekkokumen) of the interval of 15 km, which eliminates morphologic effects of the seamounts, shows that the western half of the chain shows basement elevation of 2000 m, which took place before the eruptions. The size and frequency of the seamounts become smaller to the east. Most of them have conical form of central eruptions, and some large ones are of elongated form of
5. Gravimetric interpretation diagramThe diagram of free-air anomaly vs. depth indicates that the morphologic elevations of the seamounts and the continental slope are sustained mainly by mechanical firmness of the basement, without isostatic compensation. On the other hand, the continental rise and abyssal plane are close to isostatic equilibrium.
2. Volcanic seamountThe seamounts are generally of 30 km in base diameter, 10 km in flat-top diameter, and 2500 to 4000 m in relative height. The flat-tops are constant in depth, without evidence of basement subsidence.
4. Gravimetric anomalyThe volcanic seamounts usua l l y have Bougue r anomaly about 100 mGal lower than the adjacent area, showing funnel -shaped Bouguer depression. Large volcanoes show ring-like Bouguer structure composed of the central high and the marginal low. The marginal low is about 100 mGal lower than the adjacent abyssal plane and the central high is about 80 mGal higher than the marginal low. Very large volcanoes have bull's eye-like low Bouguer sites along the marginal low. On the foot of the volcanoes, there is the area with Bouguer anomaly 20 to 40 mGal higher, called peripheral high.
3. Basement upliftThe base level map (sekkokumen) of the interval of 15 km, which eliminates morphologic effects of the seamounts, shows that the western half of the chain shows basement elevation of 2000 m, which took place before the eruptions. The size and frequency of the seamounts become smaller to the east. Most of them have conical form of central eruptions, and some large ones are of elongated form of
5. Gravimetric interpretation diagramThe diagram of free-air anomaly vs. depth indicates that the morphologic elevations of the seamounts and the continental slope are sustained mainly by mechanical firmness of the basement, without isostatic compensation. On the other hand, the continental rise and abyssal plane are close to isostatic equilibrium.
Satellite-delivered gravimetry for the Vitória-Trindade Chain, Satellite-delivered gravimetry for the Vitória-Trindade Chain, Southeast Brazil, and its bearing on the volcanic seamount structureSoutheast Brazil, and its bearing on the volcanic seamount structure
6. Regional Bouguer anomalyThe summit level (seppômen) map for Bouguer anomaly, which represent regional general Bouguer anomaly, suggests lithosphere thinning along the Vitória-Trindade Chain, which is relevant at the western end of the chain and becomes weak to east. The magmatism and tectonism of are strong at the western end of the chain and become less intense to the east.
6. Regional Bouguer anomalyThe summit level (seppômen) map for Bouguer anomaly, which represent regional general Bouguer anomaly, suggests lithosphere thinning along the Vitória-Trindade Chain, which is relevant at the western end of the chain and becomes weak to east. The magmatism and tectonism of are strong at the western end of the chain and become less intense to the east.
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