Embed Size (px)
Citation preview
61°W62°W63°W64°W
18°N
17°N
16°N
15°N
14°N
11°N
13°N
12°N
(1)(2)(3)
(4)
80
60
44
30
14
5
1460 Orinoco River44
-2000
-1000
500
0
-3000
1000
30002000
-4000
-5000
-6000
-8000
Elevation (m)
-7000
10°N
15°N
20°N
75°W 70°W 65°W 60°W
0 250 500 km
2 cm/y
1.8 cm/y
CARIBBEAN PLATE
SOUTH AMERICAN PLATE
NORTH AMERICAN PLATE
Grena
da
Basin
Ave
s Ri
dge
Lesser
Antilles
Arc
Bahamas Bank
Greater Antilles
Subduction trench
Fold-and-thrust belts
Strike-slip faults
Past locations of the subduction trench, ages in Ma(Modi�ed from Escalona & Mann, 2011)(5)
Past courses of the Orinoco River, ages in Ma(Modi�ed from Escalona & Mann, 2011)(5)
Current convergence rate (DeMets et al., 2000)(6)
Fig. 1: Present day tectonic boundaries of the Caribbean Plate and reconstruction of its relative eastward motion. Active volcanoes
Fig. 2: Location map of GARANTI cruise and previous studies used for seismic correlation
Gre
nada
Ba
sin
Lesser Antilles Arc
X
X
Fig. 3: Velocity model from wide-angle seismic pro�le GA02 (see �g. 2 for location). Modi�ed from
Klingelhoefer et al. (2018)(7).
Ave
s
Ridg
e
© GEBCO 2014
Acoustic Basement
III
II
I
Age (Ma)EpochSystem
Subcontinuous and hum-mocky, high frequency, medium-strong to strong re�ections.
Continuous to chaotic, strong re�ections.
Subcontinuous to chaotic, weak to medium-strong re�ections.
Syn-rift deposits
First post-rift deposits.Distal turbidites from the proto-Orinoco River
Arc-derived turbidites and pela-gic sedimentation.The basin is isolated from the Orinoco River by the uplift of the Northern Venezuelan Coas-tal Range.
Qua
tern
ary Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Neo
gene
Pal
eoge
ne
Upper
Cre
tace
ous
0.0117
2.58
5.33
23.03
33.9
56.0
66.0
Age
~12
~35
~48
Megasequences Facies Description
Transparent facies Pre-rift basement
Fig. 4: Seismic megasequences of the Grenada Basin and their tectono-stratigraphic signi�cance.
Geological interpretation
Study Area
Fig.9
GA02
GA34
GA29
SEA LEVEL
SEAFLOOR
Miocene-PlioceneUnconformity
Cretaceous-Paleocene Sediments
Middle PlioceneUnconformity
InternalDiscontinuity
~1000 m
0
1
2
3
~2 sec.(twt)
2 km
GA25C
ErosionalTruncation
TWT
(sec
onds
)
Fig. 11: Extract from MCS pro�le GA25C showing erosional truncations that could be related to a subae-rial erosion. See �g. 9 for location
Fig. 10: Microscopic analysis of a sample from DR07 (see �g. 9 for location).
Fig. 12: Estimation of Aves Ridge subsidence. A) schematic diagramm explaining the methodology used for paleo-bathymetry reconstruction. B) Present topographic pro�le (see �g. 9 for location); DR08 is projected on the pro�le, as well as older dredges(7)(8) and the DSDP 4-30 site.C) Paleo-topograhic reconstruction following the method explained in A).
Fig. 9: zoom in on the southeastern Aves Ridge
Fig. 12Projection of
DSDP 15-148(2)
11314(9)
11301(9)
(2)
(3)
Fig. 10
Oceanic crust
Dep
th (m
)
???
Oceanic crust
Grabens
Fig. 5: Iso-depth contour map of the top of the acoustic basement. Time-Depth conversion perfomed by velocity function V = V0 + KZ ; with V0 = 1500 m/s and K = 0.2 m/s/m
Fig. 8: Interpretation of MCS pro�le GA29 (see Fig.2 for location). Vertical exaggeration = 5
Fig. 7: Interpretation of MCS pro�le GA02 (see Fig.2 for location). Vertical exaggeration = 5
Fig. 6: Interpretation of MCS pro�le GA34 (see Fig.2 for location). Vertical exaggeration = 5
Unravelling the genetic relations between the Grenada Basin, the Aves Ridge, and the Lesser Antilles: a structural and stratigraphic analysis
Clément Garrocq1 ([email protected]), Serge Lallemand1, Boris Marcaillou2, Crelia Padron3, Frauke Klingelhoefer4, Jean-Frédéric Lebrun5, Mireille Laigle2, Laure Schenini2, Marie-Odile Beslier2, Aurélien Gay1, Philippe Münch1, Jean-Jacques Cornée1, Frédéric Quillévéré6, Bernard Mercier de Lépinay2, and Marcelle Boudagher-Fadel7
1Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France ([email protected]); 2GéoAzur, Université Côte d’Azur, CNRS, IRD, Observatoire de la Côte d’Azur, Valbonne, France; 3Departamento de Ciencias de la Tierra, Universidad Simon Bolivar, Caracas, Venezuela; 4IFREMER, Géosciences Marines, Plouzané, France; 5Géosciences Montpellier, Université des Antilles, Pointe-à-Pitre, France; 6Laboratoire de Géologie de Lyon, Université Lyon 1, Villeurbanne, France ; 7Department of Earth Sciences, University College London, London, United Kingdom
I. Study purposeLocated in the southeastern Caribbean, the Grenada Basin is bounded to the east by the active Lesser Antilles island arc, to the west by the Aves Ridge, commonly interpreted as a Cretaceous-Paleocene extinct volcanic arc, although its origin is unclear, and to the south by the transpressive plate boundary with South America (Fig. 1). As a result of the lack of data available so far in the Lesser Antilles back-arc area, the relations between the Grenada Basin, the Aves Ridge and the Lesser Antilles remains highly controversial. Our analysis of seismic re�ection and refraction data acqui-red during the GARANTI cruise (May-June 2017 onboard R/V L’Atalante) sheds light on basement nature and topogra-phy, depositional history and deformation of the sedimentary in�ll, including vertical motions, of the Lesser Antilles back-arc area. Correlations with well logs located on the northern Venezuelan shelf(1) and DSDP sites on the Aves Ridge(2)(3) also provide chronostratigraphic constraints.
III. Analysis of MCS pro�les
Key issues related to the Aves Ridge and the Grenada Basin 1. Has Aves Ridge hosted an island arc, and if so, what would be its relation with the active Lesser Antilles Arc? 2. Origin of the Grenada Basin: classical back-arc, atypical forearc spreading or trapped ‘‘Atlantic’’ crust? 3. How to quantify the vertical motions and what are their causes and consequences?
V. Conclusions1. The opening of the Grenada Basin is completed during the Eocene and no signi�-cant di�erential motion occured between the basin and the Aves Ridge since then.
2. The Southern Lesser Antilles Arc Platform has undergone a signi�cant uplift during the Miocene.
3. The Lesser Antilles Arc is not the conjugate of the Aves Ridge, which implies that the Grenada Basin was not simply formed by rifting of the Lesser Antilles. 4. The acoustic basement in the transition zone between Aves Ridge and the Gre-nada Basin shows evidences for strike-slip faulting. This tectonic event is recorded by Sequence 1 and sealed by Sequence 2, whose base is Late Eocene.
II. Deep structure
The velocity model along pro�le GA02 (Fig. 3) reveals a signi�cant asymmetry: the basement deepens from 5 to 10 km southeastwards while �at-lying sediment units thicken from 2 to 7 km. A 6.5 to 7 km thick oceanic crust underlies the southeastern half of the basin over a width of about 80 km. The seismic velocities along the Aves Ridge are compatible with an arc origin. The di�e-rence in the relative thicknesses and velocity gra-dients between the Aves Ridge and the Lesser Antilles suggest a di�erent origin of both arcs.
IV. Evidences for the emersion of the Aves Ridge
AcknowledgementsThis work is part of the ANR-17-CE31-0009GAARAnti Projecthttps://anr.fr/Projet-ANR-17-CE31-0009https://gaaranti.edu.umontpellier.fr/
References(1) Ysaccis, R. 1998, Tertiary Evolution of the Northeastern Venezuela O�shore, Rice University, TX, PhD thesis, 285 p., https://scholarship.rice.edu/handle/1911/19330(2)Edgar, N.T., et al., 1973, Site 148, Deep Sea Drilling Project Initial Reports, doi:10.2973/dsdp.proc.15.104.1973(3)Bader, R.G., et al., 1970, Site 30, Deep Sea Drilling Project Initial Reports, doi:10.2973/dsdp.proc.4.109.1970(4)Mann, P., Sawyer, D.S., et al., 2004, MCS line BOL30, EW0404 cruise, doi:10.1594/IEDA/500102(5)Escalona, A., and Mann, P., 2011, Tectonics, basin subsidence mechanisms, and paleogeogra-phy of the Caribbean-South American plate boundary zone, Marine and Petroleum Geology, vol. 28, p. 8-39, doi:10.1016/j.marpetgeo.2010.01.016(7)Klingelhoefer, F., et al., 2018, Deep structure of the Grenada Basin from wide-angle seismic, bathymetric and gravity data, AGU Fall Meeting, Washington D.C., 2018AGUFM.T21F0285K(8)Bouysse, P., et al., 1985, Aves Swell and Northern Lesser Antilles Ridge: rock-dredging results from Arcante3 cruise, Caribbean Geodynamics Symposium, Paris, 1985, Technip Editions(9)Fox, et al., 1985, The geology of the Caribbean crust: Tertiary sediments, granitic and basic rocks from the Aves ridge, Tectonophysics, vol. 12, p. 89-109,doi:10.1016/0040-1951(71)90011-4
Samples dredged at depths ranging from about 500 to 2000 m during GARANTI cruise along the east slope of Aves Ridge (see �g. 2 & 9 for location) reveal coral reef systems at 39.2-33.9 Ma and 23-15.9 Ma, which could have subsequently emerged at least once, as shown by dis-solution cavities (�g. 10). The Mio-Pliocene (8.6-3.8 Ma) pelagic mud that �lls those cavities allows to date the initiation of the last subsidence phase between 23-3.8 Ma for the longest possible time interval and between 15.9-8.6 Ma for the shortest possible time interval.
Tilt-block faulting
Upward bending
Signal loss due to the volcanic arc
Horizontal terminations
10 kmMOHO re�ections
Oceanic Crust
LESSER ANTILLES ARC
GRENADA BASIN
AVES RIDGE
Slope break
Shear zone?
0
1
2
3
4
5
6
7
8
9
10
TWT
(sec
.)
Upward bending
LESSER ANTILLES ARC
GRENADA BASIN
AVES RIDGE
10 km
0
1
2
3
4
5
6
7
8
TWT
(sec
.)
GA34Signal loss due to the volcanic arc
Shear zone?
Upward bending
Horizontal terminations
GRENADA BASIN
AVES RIDGE
10 km
GA29
GA02
0
1
2
3
4
5
6
7
8
9
10
TWT
(sec
.)
Oceanic Crust
‘‘Dog-tooth’’ calcite recrystallisation
Karstic cavity �lled bypelagic mud with
planktonic foraminifera8.6-3.8 Ma
Packstone/grainstone of red algae, benthicforaminifera, volcanic clasts.
Reef lagoon, 23-15.9 Ma
1 mm
DR08
DR08Early Miocene coral reef system
11314(9) 11303(9)
Pleis.Plio.Mio.
DSDP 4-30(4)
Distance (km)0 10 20 30 40 50 60 70 80 90 100
200400600800
0-200-400-600-800
-1000-1200-1400-1600-1800-2000-2200-2400-2600-2800-3000
Dep
th/e
leva
tion
(m)
0-200-400-600-800
-1000-1200-1400-1600-1800-2000-2200-2400-2600-2800-3000
Dep
th (m
)
DSDP 4-30(4)
11303(9) - Early Mioceneshallow carbonate shelf
11314(9) - Early Mioceneshallow carbonate shelf
~1000 m
Aves RidgeIsostatic
compensation
Sea level
Dredge sample Dredge sample
Present topography Removal of recent sediments
Dredge sample
Resetting the sample toits original bathymetry
Present
Early Miocene (23-16 Ma)
A)
B)
C)
W
W E
E
Pleis.Plio.Mio.
107D(8) - Early Miocene neritic
107D(8)
107D(8)
DR07Late Eocene and Early Miocenecoral reef systems
DR07
