The crustal nature of the Southern Mozambique Channel between Madagascar and Mozambique Extended abstract

Transcription

1 The crustal nature of the Southern Mozambique Channel between Madagascar and Mozambique Extended abstract

2 We have undertaken in the Central Mozambique Channel Basin (CMCB) observations regarding the nature of the crust. According to our interpretation the transition from continental to oceanic crust in the southern part of the Mozambique Channel developed further south from the volcanic cluster of Bassas da India and Europa. Our investigations allowed us to identify the presence of a large Jurassic depocenter situated west of the Davie Ridge and north of Europa island where sediments were deposited during Mesozoic and Tertiary in a large fan system. These features have important consequences for the existence of petroleum systems in this part of the Mozambique Channel. We can also note that we are involved in an application for a Petroleum Exploration License in the French territorial waters of Europa and Bassas da India and welcome interest from other parties in this venture. SPEC PARTNERS is a geophysical exploration company with projects in Indonesia, Spain, Unites States. AMPHORE ENERGY Inc. is a consulting company in frontier exploration areas. Yannis Bassias Amphore Energy Inc., Houston Trond Christoffersen Spec Partners Ltd, Oslo Glyn Roberts Spec Partners Ltd, London

3 The crustal nature of the Southern Mozambique Channel between Madagascar and Mozambique Yannis Bassias 1, Trond Christoffersen 2, Glyn Roberts 3 1 Amphore Energy Inc., USA 2, 3 Spec Partners Ltd, UK EXTENDED ABSTRACT A large sedimentary edifice (here named the Central Mozambique Channel Basin, CMCB) extends from the eastern border of the Beira High (off Mozambique) to the western border of Madagascar. As an integral part of Africa in pre-breakup and drift times, this feature developed at the northern border of the Mozambique Basin depocenter (Fig.1 & 2). Fig. 1 : The CMCB Is characterized by four main geological features from west to east. The Beira High and its eastern slope, the Zambezi Fan and Zambezi Canyon, the southern roots of the Davie Fracture Zone, and the volcanic cluster of Bassas da India and Europa. First mapping of the main morphology of the basement suggests the presence of a large Jurassic depocenter with important consequences for the presence of petroleum systems in this part of the Mozambique Channel. 1 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

4 We believe that true oceanic crust is emplaced further south than our study area this would correspond to the true abyssal plain (darkest blue in figure 2) seen south of the islands of Bassas da India and Europa. Our study is based on reconditioned vintage seismic data and suggests the presence of a large Jurassic depocenter with important consequences for the existence of petroleum systems in this part of the Mozambique Channel. It shows that the southern tail of the Davie Fracture Zone (DFZ) is not structurally very pronounced at these latitudes; that the effect of a barrier is attenuated; and that consequently the Zambezi canyon had the primary role of transporting, through the Mesozoic and Tertiary, sediments that were deposited in a large fan system situated west of the Davie Ridge (DR) and north of Europa island (Fig 1 and 2). Fig. 2 : Topographic map showing the main sea bottom features and including a conceptual representation of the modern day Mozambique Fan and Zambezi Fan. Note the DFZ position acting as a barrier (ridge) that modifies the direction of the transported sediments and that of the fan development. Geological setting The area extending from the Mozambique shore to western Madagascar is an important alluvial plain sourced by the proto-zambezi river system (Fig 1 and 2). The structural setting in the eastern part of the CMCB records the termination of the DFZ and that of the Zambezi Canyon with the bypass of coarse-grained siliciclastic sediment transported since Mesozoic into the deep basin by gravity-flow process. This is in contrast to the area to the north where 2 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

5 it is believed that the oblique angle of the transforms faults which cut the Davie Fracture Zone in this area were responsible for the creation of narrow continental uplifted blocks. In the CMCB the Mesozoic/Tertiary sedimentary pile is up to 4s thick to the east, decreasing to 3.5s towards the west. In the central part the Basin is penetrated by the volcanoes of the Hall and Jaguar Seamounts and the islands of Bassas da India and Europa (Fig. 3). Fig. 3: The Beira High is suggested to be a relic of the Early Jurassic failed-rift (Zambezi depression) during continental stretching between Africa and Antarctica (Klausen, 2009; Leinweber and Jokat, 2012; Mahanjane, 2012; Reeves and Mahanjane, 2013; Leinweber et al., 2013). Deep structuring of the basement is seen on the south-eastern edge of the Beira High at around 7 sec. To the southeast the basement depth and the thickness of the Mesozoic sediments each decrease by 1 sec. Fig. 4 : To the north and northeast, the basement depth and the thickness of the Mesozoic sediments each increase. These observations suggest that a large Jurassic depocenter was present in the area where the volcanic cluster was later generated. The presence of this Jurassic basin will constitute an important argument for the presence of a Jurassic source and petroleum system in the area. Fig. 5 : East of the DFZ, Pre-Tertiary igneous activity affected the area (extrusions and sills). The presence of similar volcanic activity has been documented onshore Madagascar. 3 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

6 A basin formed since Late Jurassic-Early Cretaceous A large Jurassic depocenter develops east of the Beira High above the continental basement. It has a ENE-WSW orientation that is perpendicular to the NNW-SSE lineaments detected from vertical gravity gradient (Fig. 1, 5, 8). Along the eastern part of the Beira High syn-rift tectonics developed under minor extensional regime, producing a series of half grabens that may contain potential Middle Jurassic syn-rift source rocks (Fig. 3, 4, 6). To the north and east this basin is bordered by the Davie Fracture Zone (DFZ), a ridge which has acted as a barrier since the Jurassic and favoured the development of the Zambezi fan. The Zambezi fan is an important geological feature with a continuous Mesozoic and Cenozoic history. Fig. 6 : The southwestern part of the Beira High shows a geometry similar to that of the central and northern parts with deep structuring of the basement at around 7 sec (Fig 3 and 4). Syn-rift tectonics developed a minor extensional regime producing a series of half grabens that may contain potential Middle Jurassic syn-rift source rocks. Section is 450 km in length. Two strong reflectors mark the base of Upper Cretaceous volcanics (green horizon in figure 3, 4, 5) and the base of the Tertiary nanno-oozes, clays, and siltstones with volcanic breccia (orange horizon) (Segoufin, 1978; Raillard, 1990). To the north, on the western flank of the DFZ similar volcanic breccia are cemented in a Middle Eocene carbonate matrix (Leclaire, Bassias et al., 1989; Bassias, 1992; Bassias and Bertagne, 2015). While deeper sediments, presumably of Jurassic age, overlay a faulted pre-rift basement; the continuity of these horizons is interrupted by the Hall and Jaguar Seamounts and the Bassas da India and Europa volcanoes of younger age. The Eocene strata are apparently affected by a thermal effect (bell shape) contouring the volcanic cluster. This observation underlines the possibility that the age of the volcanic cluster is younger than Eocene (Fig. 3 and 4). 4 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

7 x Fig. 7 and 7a : This N-S seismic line crosses the CMCB while staying parallel to the western side of the Zambezi Canyon. The Zambezi canyon had the primarily role transporting Mesozoic and Tertiary sediments that were deposited in a large fan system situated west of the Davie Ridge and north of the Europa island. The N-S section intersects the Zambezi fan sediments and show that incipient fan probably initiated since Early Cretaceous times (figure 7a). Section of figure 7 is 770 km in length. Cretaceous and Tertiary volcanic activity and sedimentation A series of sills are reported to the North of Europa and suggest that volcanism is present, however, without magnetic signature (Segoufin, 1978). East of the DFZ, Pre-Tertiary igneous activity with extrusions and sills affected the area (Figure 5, 9). The presence of similar volcanic activity has been documented onshore Madagascar. Recent publications based on modern data indicate that, below the volcanics in the Morondava Basin, that limit the resolution of our vintage data, there is a significant Mesozoic sequence above rifted continental basement. (Roberts et.al. 2013). Eocene extension and late fracturing of the basement seem to have affected the southwestern portion of Madagascar s offshore where the Davie Fracture Zone (DFZ) weakens and merges with Madagascar s continental slope. Indications of the transition between continental and oceanic crust The Mesozoic part of the sedimentary pile seems to be absent in the southern part of section in figure 7. The marker in light blue (and X in yellow) indicates the presence of a probable transition to oceanic crust (Fig 7). Dark brown markers indicate the presence of pre-tertiary volcanic intrusions (Fig 7). 5 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

8 Fig 8: A large Jurassic depocenter develops east of the Beira High above the continental basement. It has a ENE-WSW orientation that is perpendicular to the NNW-SSE lineaments detected from vertical gravity gradient. The lineaments are parallel to the DFZ and to the north-south branch of the Zambezi Canyon. The transition to oceanic crust was deduced from the interpretation of line MD Fig. 9 : The volcanic cluster (around the atoll of Bassas da India and the island of Europa) has a NW-SE orientation and develops above a Jurassic depocenter. The majority of the seismic lines show absence of onlap possibly indicating a young age (< 10 m.y) for the volcanism. Pre-Tertiary (green ) and post- Tertiary (yellow ) sills were also mapped and corroborate the presence of a Cretaceous volcanism in the Morondava basin. 6 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

9 Conclusions The thick Mesozoic sedimentary sequence (up to 4s) observed east of the Beira High, as well as east of Europa (3.5s), suggests that rifting and emplacement of oceanic crust happened further south and far from the Bassas da India and Europa volcanic islands. Syn-rift activity along the eastern part of Beira High appears to have developed under minor extensional crustal regimes, with gently dipping faults producing a series of half grabens containing synrift sediments with potential Middle Jurassic source rocks. We believe that liquid hydrocarbons have been generated in the CMCB. Our first work on the area was reported in the Appex-London Conference in March 2015 and is also backed by work reported from neighbouring areas (as described by Bertagne and Associates, Bassias and Bertagne, Mahanjane, Roberts et al., SA Petro and Tyrrell et al). Acknowledgements The seismic lines have been available courtesy of CNRS-IPGS/GeoAzur. Their interpretation allowed us to draw several geological conclusions; and to bring further reflection on the positioning of the limits between continental and oceanic crust and the repercussion that this may have for the generation and preservation of petroleum systems. We can also note that we are involved in an application of a Petroleum Exploration License in the French territorial waters of Europa and Bassas da India and welcome interest from other parties in this venture. References Bassias Y. and Bertagne R. (2015) Study updates uplift-erosion correlation, Davie fracture zone. Oil & Gas Journal, Sept. 7, 2015, p Bassias Y., Christoffersen T. and Roberts G. (2015) The crustal nature of the Southern Mozambique Channel between Madagascar and Mozambique (i.e the Central Mozambique Channel Basin) and observations concerning its petroleum potential APPEX Poster session, London, March Bassias Y., (1992) Petrological and geochemical investigation of rocks from the Davie fracture zone (Mozambique Channel) and some tectonic implications, Journal of African Earth Sciences and the Middle East, Volume 15, Issues 3 4, October November 1992, Pages Klausen, M.B., (2009) The Lebombo monocline and associated feeder dyke swarm: Diagnostic of a successful and highly volcanic rifted margin. Tectonophysics 468 p Leclaire L., Bassias Y., et al. (1989) La ride de Davie dans le Canal de Mozambique: approche stratigraphique et géodynamique.- C.R. Acad. Sci. Paris, 308, II: ; Paris. Leinweber V. and Jokat W. (2012) The Jurassic history of the Africa-Antarctica Corridor - new constraints from magnetic data on the conjugate continental margins, Tectonophysics, 530, p PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel

10 Leinweber V. et al. (2013) The crustal structure of the Central Mozambique continental margin Wide-angle seismic, gravity and magnetic study in the Mozambique Channel, Eastern Africa, Tectonophysics, 599, p Mahanjane, E.S. (2012) A geotectonic history of the northern Mozambique Basin including the Beira High - A contribution for the understanding of its development, Mar. and Petroleum Geology, Vol. 36, p Raillard, S. (1990) Les marges de l Afrique de l Est et les zones de fracture associées: Chaine Davie et Ridge du Mozambique-Campagne MD-60/MACA MO-11. PhD thesis. Université Pierre et Marie Curie, Paris, pp Reeves, C.V., and Mahanjane, E.S. (2013) Mozambique and its role in the downfall of Gondwana. Extended abstract. Geological Society of Houston/Petroleum exploration society of Great Britain, London, September Roberts G.F., Christoffersen T. et al., (2013) New insights on the prospectivity of the Morondava Basin, Offshore Madagascar, based on new seismic data. Poster paper, 12th PESGB/HGS Conference on African E & P. London, Sept Segoufin, J. (1978) Anomalies magnétiques mésozoïques dans le bassin de Mozambique, Comptes Rendus de l Académie des Sciences, Vol. 287, 1978, pp Vertical Gravity Map: Scripps Institute, Satellite derived vertical gravity gradient - Grey scale (+/- 60 EOTVOS units) represent variations associated with variations in mass inside the earth or beneath the ocean. Source: (David T. Sandwell, dsandwell@ucsd.edu). Extended abstract of a poster presented at the 14th PESGB/HGS Conference on African E & P - London, 2-4 September Contact details: Yannis Bassias Trond Christoffersen Glyn Roberts ybassias@amphorenergy.com tc@specpartners.net gfr@specpartners.net 8 PESGB/HGS - Sub-Saharan Africa - The crustal nature of the Southern Mozambique Channel