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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 of the Saint Peter and Saint Paul Rock, Equatorial Atlantic Ocean AGU Meeting of th Americas. Cancun, Mexico, 14-17 May 2013 AGU 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 1 Motoki, A. ([email protected]), 2 2 Motoki, K.F. , Sichel, S.E. , 3 Souza, K. , 4 Bueno, G.V. ; 2) Federal Fluminense University, Brazil, 1) Rio de Janeiro State University, Brazil 3) Geological Survey of Brazil; 4) PETRBRAS, Brazil 1 Motoki, A. ([email protected]), 2 2 Motoki, K.F. , Sichel, S.E. , 3 Souza, K. , 4 Bueno, 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 N N 30 40 38 36 34 32 28 longitude (°W) 18 20 22 latitude (°S) Atlantic Ocean Atlantic Ocean 4000 3600 3200 2800 3200 2800 2400 2000 1600 1200 4000 3600 3200 2800 3200 2800 2400 2000 1600 1200 1 3 4 5 6 7 8 9 10 1 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 11 12 13 14 15 16 17 18 19 21 22 23 24 25 21 22 23 24 25 SM VT GP GP 1: Martim Vaz 2: South Trindade 3: North Trindade 4: East Columbia 5: West Columbia 6: E1 Dogaressa 7: E2 Dogaressa 8. W2 Dogaressa 9. W1 Dogaressa 10: Davis 11: Columbia Bank 12: East Jaseur 13: West Jaseur 14: VT-2008-3610 15: Montange 16: VT-2008-3653 17: Congress Bank 18: Vitória Seamount 19: Champlain Bank 20: Besnard Bank 21: Almirante Saldanha 22: São Tomé Seamount 23: Hospur Seamount 24: Abrolhos Seamount 25: Minerva Seamount ABR: Abrolhos CV: Caravelas SM: São Mateus VT: Vitória GP: Guarapari South America South America CV ABR CV ABR Columbia Channel Columbia Channel São Mateus Off-shore Vitória Off-shore São Mateus Off-shore 4000 4000 3600 3600 Vitória Off-shore 20 20 2 Abrolhos Continental Shelf Abrolhos Continental Shelf 5000 3000 1000 0 height (m) 0 10 20 30 typical declivity (°) A. Typical declivity vs. height 4000 2000 lava flows 21 22 12 18 lava flows 21 22 12 18 20 100 80 60 40 0 22 20 100 80 60 40 0 120 20 21 18 12 10 20 21 18 12 10 flat-top diameter (km) base diamenter (km) B. Base diamenter vs. flat-top diameter normal size large size continental shelf fragment normal size large size continental shelf fragment C. Longitude vs. height 38 30 32 34 36 28 longitude (°W) east west 20 20 6000 5000 3000 1000 0 height (m) 4000 2000 6000 tectonic uplift tectonic uplift ocean floor deepning ocean floor deepning 12 12 20 18 20 18 22 22 21 21 conical volcanic seamount elliptic volcanic seamount seamount out of the Vitória-Trindade Chain continental 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 30 40 38 36 34 32 28 longitude (°W) 18 20 22 latitude (°S) SM VT GP South America South America CV CV ABR ABR 10 12 18 10 12 18 volcanic seamount 7 7 7: Dogaressa Bank 10: Davos Bank 12: Jaseur Bank 18: Vitória Seamount ABR: Abrolhos CV: Caravelas SM: São Mateus VT: Vitória GP: Guarapari 5000 4000 4000 3000 3000 1000 2000 2000 5000 4000 4000 3000 3000 1000 2000 2000 uplift uplift uplift uplift depth (m) uplift uplift 0 1000 2000 3000 4000 5000 MTV TRN CLS DGR DVS JSR VTR VTR MTV: Martim Vaz TRN: Trindade CLS: Columbia DGR: Dogaressa DVS: Davis JSR: Jaseur VTR: Vitória base level surface base level surface N 100 100 -100 -100 200 km N N 1 2 3 4 5 6 7 8 9 10 20 GP 30 40 38 36 34 32 28 longitude (°W) 18 20 22 latitude (°S) ABR ABR 0 0 0 0 0 9 2 3 6 7 8 10 0 4 5 1 0 0 0 0 1 2 3 4 5 6 7 8 9 10 0 0 0 100 0 21 22 23 24 25 21 22 23 24 25 12 14 16 18 19 13 15 17 11 11 12 13 14 15 16 17 18 19 20 South America CV South America CV SM VT GP GP 0 0 SM VT GP 0 0 0 0 200 0 100 200 0 SM-AP SM-AP VT-AP VT-AP Columbia Channel Columbia Channel SB2 SB3 SB5 SB9 SB1 SB2 SB3 SB5 SB9 SB1 Atlantic Ocean Atlantic Ocean local sedimentary basin SB1: Espírito Santo SB2: Mucuri SB3: São Mateus SB5: Pedro Canário SB9: Aracruz local sedimentary basin SB1: Espírito Santo SB2: Mucuri SB3: São Mateus SB5: Pedro Canário SB9: Aracruz 200 km N N SM VT GP GP SM VT GP GP 30 40 38 36 34 32 28 longitude (°W) 18 20 22 latitude (°S) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Atlantic Ocean Atlantic Ocean 300 200 100 0 0 100 200 300 300 200 100 0 0 100 200 300 Columbia Channel Columbia Channel CV ABR South America CV ABR South America PH PH PH PH PH PH PH PH SM-AP SM-AP VT-AP VT-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 = 2.6 ρ = 2.6 PH PH PH mantle crust mantle crust ρ = 2.85 ρ = 3.3 ρ = 2.85 ρ = 3.3 ML CH ML CH ρ = 2.85 gabbroic intrusions A CH ρ = 2.85 CH ML ML Bouguer anomaly profile volcano root volcano root B. Large volcano CH: central high ML: marginal low PH: peripheral hight crustal down-buckling crustal down-buckling CH ML ML volcano root volcano root gabbroic intrusions B gabbroic intrusions B gabbroic intrusions C gabbroic intrusions C PH ~3 km CH ML ML PH PH C. Veryh large volcano 18 20 22 latitude (°S) 30 40 38 36 34 32 28 longitude (°W) 200 km N N 200 300 0 100 200 300 0 100 100 km 100 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 west 20 mGal 60 100 80 40 0 20 mGal 60 100 0 80 40 volcanic seamount continental shelf continent north south north south 0 -100 100 300 free-air anomaly (mgal) SH Sm1: large seamount SM2: small seamount GY: seamount flat-top SH: continental shelf SL: continental slope 1000 depth (m) 2000 3000 4000 5000 0 6000 200 400 SD SD SL GY AP SH GY SL SM1 SD -20~100 100~280 2000 4000 0 6000 0 -100 100 300 200 400 SL CR AP SM2 SM1 no compensation SM2 SM1 SM2 full isostatic compensation no isostatic compensation fuu compensation CR CR: continental rise SD: sedimentary deposit AP: abyssal plane SL SL SD SD AP SM2 SM1 SM2 SM1 CR CR Base level Bouguer anomaly map Base level Bouguer anomaly map 5. Growth history of the volcanoes These 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 seamount The 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 anomaly The volcanic seamounts usually have Bouguer 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 uplift The 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 diagram The 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 seamount The 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 anomaly The volcanic seamounts usually have Bouguer 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 uplift The 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 diagram The 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, Southeast Brazil, and its bearing on the volcanic seamount structure 6. Regional Bouguer anomaly The 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 anomaly The 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.
