Mozambique Basin Research Articles

Tie points for Gondwana reconstructions from a structural interpretation of the Mozambique Basin, East Africa and the Riiser-Larsen Sea, Antarctica

Abstract. Movements within early East Gondwana dispersal are poorly constrained, and there is debate about conjugate geologic structures and the timing and directions of the rifting and earliest seafloor spreading phases. We present a combined structural interpretation of multichannel reflection seismic profiles from offshore of northern Mozambique (East Africa) and the conjugate Riiser-Larsen Sea (Antarctica). We find similar structural styles at the margins of both basins. At certain positions at the foot of the continental slope close to the continent–ocean transition, the basement is intensely deformed and fractured, a structural style very untypical for rifted continental margins. Sediments overlying the fractured basement are deformed and reveal toplap and onlap geometries, indicating a post-breakup deformation phase. We propose this unique deformation zone as a tie point for Gondwana reconstructions. Accordingly, we interpret the western flank of Gunnerus Ridge, Antarctica as a transform margin similar to the Davie Ridge offshore of Madagascar, implying that they are conjugate features. As the continental slope deformation is post-rift, we propose a two-phase opening scenario. A first phase of rifting and early seafloor spreading, likely in NW–SE direction, was subsequently replaced by a N–S-directed transform deformation phase overprinting the continent–ocean transition. From previously identified magnetic chrons and the sediment stratigraphy, this change in the spreading directions from NW–SE to N–S is suggested to have occurred by the late Middle Jurassic. We suggest that the second phase of deformation corresponds to the strike-slip movement of Madagascar and Antarctica and discuss implications for Gondwana breakup.

Contrasting hydrography and phytoplankton distribution in the upper layers of cyclonic eddies in the Mozambique Basin and Mozambique Channel

Hydrographic data collected in cyclonic eddies in the Mozambique Channel and Basin revealed notable differences in temperature and salinity at a depth of 100 m, the upper mixed layer, the nitracline depths, and vertical distribution of chlorophyll-a (Chl-a). Differences in temperature and salinity did not show any consistent patterns. In contrast, the differences in the upper mixed layer, nitracline depths and the vertical Chl-a profile appeared to be driven by combined effects of eddy dynamics (i.e. shoaling of isopleths) and the seasonal variation in light availability and mixing conditions in the upper layers. Cyclonic eddies studied during austral spring and summer in the Mozambique Channel exhibited shallower upper mixed layers and nitracline depths, and deeper euphotic zones. Distinct subsurface Chl-a maxima (SCM) were associated with the stratified conditions in the upper layers of these eddies. In contrast, a cyclonic eddy studied during mid-austral winter in the Mozambique Basin had a shallower euphotic zone, deeper upper mixed layer and uniform Chl-a profiles. Another eddy sampled in the Mozambique Basin toward the end of winter showed a less pronounced SCM and roughly equal euphotic zone and upper mixed layer depths, suggestive of a transition from a well-mixed upper layer during winter to stratified conditions in summer.

Petroleum systems of the deepwater Mozambique Basin

The Mozambique margin is relatively under explored with a small number of wells both onshore and offshore. Nine major gas fields have been identified to date (Brownfield et al., 2012), which are believed to contain a combined more than 150 trillion ft3 of natural gas. The discovery of large natural gas fields in the Rovuma basin represents one of the most exciting exploration successes of recent years and Mozambique is now considered to be a prolific hydrocarbon province (Hollebeek et al., 2015). This exploration study utilizes a modern, regional 2D seismic grid that was acquired in 2013 and processed to depth in 2015. It covers a large proportion of the Mozambique offshore province (Figure 1) and was used to assess hydrocarbon prospectivity in the region. Seven mega-sequences were identified based on stratigraphy from well ties (Uzcategui et al., 2014), the regional geology and seismic character and were interpreted throughout the study area. This interpretation provided a basin-scale, structural framework in which to model the petroleum systems. Structural and stratigraphic plays were mapped, assessed and built into a 3D model that assesses the viability and quality of petroleum systems offshore Mozambique.

Geochemistry of Petroleum Gases and Liquids from the Inhassoro, Pande and Temane Fields Onshore Mozambique

Although the first petroleum fields in the Mozambique basin were discovered more than 60 years ago, the composition and origin of petroleum fluids in this basin are largely unknown. We studied the geochemical composition of petroleum gases and liquids from the Inhassoro, Pande and Temane fields located onshore Mozambique. The gases are relatively dry (methane-dominated, average C1/(C1–C5) ratio is ~0.96), have pure thermogenic origin, originate predominantly from marine shale source organofacies and show no evidence of primary microbial gas or biodegradation. Most condensates have relatively high API gravity up to 76 degrees, are very mature and contain only traces of biomarkers, likely from migration contamination. However, biomarkers in the light oil from the Inhassoro field indicate that the oil derived from sub-oxic marine shales of the Late Cretaceous age. We suggest that the Aptian-Coniacian Domo Shale is the likely source rock for petroleum gases and liquids in the studied fields. Our geochemical data, including gas isotopes, as well as source-specific and age-specific biomarkers, exclude coals in the Late Carboniferous—Early Jurassic Karoo Supergroup as effective source rocks for the studied fields.

Phytoplankton communities and acclimation in a cyclonic eddy in the southwest Indian Ocean

A study of phytoplankton in a cyclonic eddy was undertaken in the Mozambique Basin between Madagascar and southern Africa during austral winter. CHEMTAX analysis of pigment data indicated that the community comprised mainly haptophytes and diatoms, with Prochlorococcus, prasinophytes and pelagophytes also being prominent to the east and west of the eddy. There was little difference in community structure, chlorophyll-specific absorption [a*ph(440)] and pigment:TChla ratios between the surface and the sub-surface chlorophyll maximum (SCM), reflecting acclimation to fluctuating light conditions in a well mixed upper layer. Values for a*ph(440) were low for diatom dominance, high where prokaryote proportion was high, and intermediate for flagellate dominated communities. Chlorophyll c and fucoxanthin:TChla ratios were elevated over most of the eddy, while 19′-hexanoyloxyfucoxanthin ratios increased in the eastern and western sectors. In a community comprising mainly flagellates and Prochlorococcus to the west of the eddy, there was high a*ph(440) at the surface and elevated ratios for divinyl chlorophyll a, chlorophyll b and 19′-hexanoyloxyfucoxanthin at the SCM. An increase in diadinoxanthin:TChla ratios and a decline in the quantum efficiency of photochemistry in PSII under high light conditions, indicated some photoprotection and photoinhibition at the surface even in a well mixed environment. Diadinoxanthin was the main photoprotective carotenoid within the eddy, while zeaxanthin was the dominant photoprotective pigment outside the eddy. The results of this study will be useful inputs into appropriate remote sensing models for estimating primary production and the size class distribution of phytoplankton in eddies in the southwest Indian Ocean.

Response of Cenozoic turbidite system to tectonic activity and sea-level change off the Zambezi Delta

Submarine fans and turbidite systems are important and sensitive features located offshore from river deltas that archive tectonic events, regional climate, sea level variations and erosional process. Very little is known about the sedimentary structure of the 1800 km long and 400 km wide Mozambique Fan, which is fed by the Zambezi and spreads out into the Mozambique Channel. New multichannel seismic profiles in the Mozambique Basin reveal multiple feeder systems of the upper fan that have been active concurrently or consecutively since Late Cretaceous. We identify two buried, ancient turbidite systems off Mozambique in addition to the previously known Zambezi-Channel system and another hypothesized active system. The oldest part of the upper fan, located north of the present-day mouth of the Zambezi, was active from Late Cretaceous to Eocene times. Regional uplift caused an increased sediment flux that continued until Eocene times, allowing the fan to migrate southwards under the influence of bottom currents. Following the mid-Oligocene marine regression, the Beira High Channel-levee complex fed the Mozambique Fan from the southwest until Miocene times, reworking sediments from the shelf and continental slope into the distal abyssal fan. Since the Miocene, sediments have bypassed the shelf and upper fan region through the Zambezi Valley system directly into the Zambezi Channel. The morphology of the turbidite system off Mozambique is strongly linked to onshore tectonic events and the variations in sea level and sediment flux.

Anomalous bathymetry and palaeobathymetric models of the Mozambique Basin and Riiser Larsen Sea

In this study we introduce a palaeobathymetric model for the conjugate Mozambique Basin and Riiser-Larsen Sea built by employing backstripping techniques, compensating for dynamic topography and plate motions. The model is presented at 0.2°×0.2° grid resolution, making it suitable for future oceanographic and climate simulation model experiments aimed at a better understanding of the climatic and oceanographic relevance of oceanic gateways in the southern ocean. At the present day, the seafloor next to the Mozambican continental margin is around 300 m shallower, and that in the central Mozambique Channel is almost 1300 m shallower, than their conjugate areas or the predictions of oceanic thermal subsidence models. The cause of this anomalous depth is difficult to determine confidently because of sparse data, in particular concerning sediment thickness, and because of the wide range of amplitudes in modelled present-day dynamic topography. The distribution of shallow seafloor suggests that it might be attributed to the presence of thicker-than-usual oceanic crust, which in turn can be attributed to the Paleogene passage of the Quathlamba plume beneath the basin. We portray these effects in our palaeobathymetric models. In contrast, the Riiser-Larsen Sea has experienced fairly stable subsidence since its formation in Jurassic times, with only slight observable changes attributable to the onset of Antarctic glaciation and during the middle Miocene climate transition. Both basins display flexure over half-wavelengths of ∼60–80 km with amplitudes of 1500 m towards their continental margins. This plays an important role in models of palaeobathymetry for times older than 100 Ma. Near the margins, isolated areas of transitional or debatable crustal composition, including Beira High and Gunnerus Ridge, are depicted to subside in a similar fashion to oceanic crust. Further into the Indian Ocean, oceanic lithosphere younger than 100 Ma on both plates has subsided to depths that are typical of thermal subsidence models. Finally, the new palaeobathymetry had distinct consequences for the current systems in the young Southern Ocean during the time periods. The onset of coast-parallel bottom currents and associated contourite deposition in the Mozambique Channel at palaeo water depths of 3500–4000 m may be a consequence of either an opening of a deep-water passage into the South Atlantic between Southwest Indian Ridge and Agulhas plateau or into the Tethys Ocean in the Late Cretaceous.

The crustal structure of Beira High, central Mozambique—Combined investigation of wide-angle seismic and potential field data

The timing and geometry of the initial Gondwana break-up between Africa and East Antarctica is still poorly known due to missing information about the continent-ocean boundaries along the rifted margins. In this context, the Beira High off central Mozambique forms a critical geological feature of uncertain crustal fabric. Based on new wide-angle seismic and potential field data across Beira High a P-wave velocity model, supported by amplitude and gravity modelling, provides constraints on the crustal composition of this area. In the Mozambique Basin mainly normal oceanic crust of 5.5–7km thickness with velocities of 6.5–7.0km/s in the lower crust is present. A sharp transition towards Beira High marks the continent-ocean boundary. Here the crust thickens to 23km at maximum. A small velocity-depth gradient and a constant increase in velocity with basal velocities of maximum 7.0km/s are in good agreement with typical velocities of continental crust and continental fragments. The density model indicates the existence of felsic material in greater depths and supports a fabric of stretched, but highly intruded continental crust below Beira High. A gradual decrease in crustal thickness characterizes the transition towards the Mozambican shelf area. Here, in the Zambezi Delta Depression 12km of sediments cover the underlying 7km thick crust. The presence of a high-velocity lower crustal body with velocities of 7.1–7.4km/s indicates underplated, magmatic material in this part of the profile. However, the velocity structure in the shelf area allows no definite interpretation because of the experimental setup. Thus, the crustal nature below the Zambezi Delta and consequently the landward position of the continent-ocean boundary remains unknown. The difference in stretching below the margins of Beira High suggests the presence of different thinning directions and a rift jump during the early rifting stage.

Reconstruction of the East Africa and Antarctica continental margins

AbstractThe Early Jurassic separation of Antarctica from Africa plays an important role in our understanding of the dispersal of Gondwana and Pangea. Previous reconstruction models contain overlaps and gaps in the restored margins that reflect difficulties in accurately delineating the continent‐ocean‐boundary (COB) and determining the amount and distribution of extended continental crust. This study focuses on the evolution of the African margin adjacent to the Mozambique Basin and the conjugate Antarctic margin near the Riiser‐Larsen Sea. Satellite‐derived gravity data have been used to trace the orientations and landward limits of fracture zones. A 3‐D gravity inversion has produced a crustal thickness model that reliably quantifies the extent and amount of stretched crust. Crustal thicknesses together with fracture zone terminations reveal COBs that are significantly closer to the African and Antarctic coasts than previously recognized. Correlation of fracture zone azimuths and identified COBs suggests Antarctica began drifting away from Africa at approximately 171 Ma in a roughly SSE direction. An areal‐balancing method has been used to restore the crust to a uniform prerift thickness so as to perform a nonrigid reconstruction for both nonvolcanic and volcanic margins. Both margins reveal a trend of increasing extension from east to west. Our results suggest Africa underwent extension of 60–120 km, while Antarctic crust was stretched by 105–180 km. Various models tested to determine the direction of extension during rifting suggest that Antarctica moved away from Africa in a WNW‐ESE direction during the period between 184 and 171 Ma prior to the onset of seafloor spreading.

New Somali Basin magnetic anomalies and a plate model for the early Indian Ocean

The oldest portions of the Indian Ocean formed via the breakup of Gondwana and the subsequent fragmentation of East Gondwana. We present a constrained plate model for this early Indian Ocean development for the time period from Gondwana Breakup until the start of the Cretaceous Normal Superchron. The motions of the East Gondwana terranes are determined using new geophysical observations in the Somali Basin and existing geophysical interpretations from other coeval Indian Ocean basins. Within the Somali Basin, recent satellite gravity data clearly resolve traces of an east–west trending extinct spreading ridge and north–south oriented fracture zones. A thorough compilation of Somali Basin ship track magnetic data allows us to interpret magnetic anomalies M24Bn through M0r about this extinct ridge. Our magnetic interpretations from the Somali Basin are similar in age, spreading rate, and spreading directions to magnetic anomalies previously interpreted in the neighboring Mozambique Basin and Riiser Larsen Sea. The similarity between the two magnetic anomaly datasets allows us to match both basin's older magnetic anomaly picks by defining a pole of rotation for a single and cohesive East Gondwana plate. However, following magnetic anomaly M15n, we find it is no longer possible to match magnetic picks from both basins and maintain plausible plate motions. In order to match the post-M15n geophysical data we are forced to model the motions of Madagascar/India and East Antarctica/Australia as independent plates. The requirement to utilize two independent plates after anomaly M15n provides strong circumstantial evidence that suggests East Gondwana breakup began around 135Ma.

Mesozoic and Early Cenozoic sediment influx and morphology of the Mozambique Basin

The Mozambique Basin is one of the oldest extensional sedimentary basins developed along the eastern African margin. The basin hosts a continuous record of sediments since the Jurassic separation of Antarctica from Africa. The objectives of this study were to extend the regional stratigraphic framework north of the Zambezi Delta into the deep abyssal plains and review the early evolution of the Mozambique Basin using nine multi-channel seismic reflection profiles.We identify six major stratigraphic units that were deposited in Jurassic, Early Cretaceous, Late Cretaceous, Paleogene, Neogene and Quaternary times. Mesozoic sedimentation rates of 5–10 cm/kyr and 1–3 cm/kyr during the Paleogene are calculated in the deeper basin. The presence of shales in neighbouring wells on the shelf implies an euxinic environment in the rapidly subsiding basin until Early Cretaceous times. The Mesozoic sediments have a high seismic velocity that exceeds 4.5 km/s, except in a distinct Early Cretaceous low-velocity (3.7 km/s) zone that may indicate the presence of undercompacted, overpressured shales. In spite of the fact that the Zambezi catchment was much smaller in pre-Miocene times, the high Late Cretaceous sedimentation rates can be attributed to rapid denudation of the African continent after a major tectonic uplift episode at approximately 90 Ma. Increased sediment influx into the basin from the Zambezi in Late Cretaceous times resulted in the formation of an elongated submarine fan lobe into the Mozambique Channel north of Beira High. Strong north-south bottom currents commenced within the channel in Late Cretaceous times, forcing the aggradation of sediments on the southern flank of the lobe. In addition, we observe several current-controlled sediment deposits in the deeper basin that are influenced by north-south bottom currents. Low Paleogene sedimentation rates are attributed to a sediment-starved basin during a relative quiet tectonic phase onshore.

Calculation of water saturation in low resistivity gas reservoirs and pay-zones of the Cretaceous Grudja Formation, onshore Mozambique basin

The water saturation of a hydrocarbon bearing formation is usually calculated via the conductivity of the formation water, as defined by Archie, 1942. However, in some formations such conventionally calculated water saturation contradicts values calculated from the Nuclear Magnetic Resonance (NMR) tool and from the Drill Stem Test (DST). Here we discuss such a case of low resistivity pay zones in the J- and K-Reservoirs, of the Lower Grudja Formation of Maastrichtian age, onshore Mozambique basin, in which conventional log analysis contradicts water saturation calculated from the NMR and by the Drill Stem Test.For both, the J-Reservoir and K-Reservoir, the water saturation (Sw) was calculated using the Archie equation and the Simandoux equation, that accounts for clay bound water but not for silt, and the results were compared to NMR-calculated water saturation. A new algorithm that improves the accuracy of water saturation calculation was introduced. This new algorithm takes into account the clay- and silt-bound water within the overall reservoir resistivity. It is demonstrated that the clay- and silt-bound water must be included in water saturation calculations, where the formations are rich in silt and clay. The Simandoux equation and the new algorithm yield significant improvement in water saturation results for the J- and K-Reservoirs, when compared to water saturation calculated using the Archie's equation.

Cretaceous–Cenozoic sedimentary budgets of the Southern Mozambique Basin: Implications for uplift history of the South African Plateau

In this study, data from 41 wells were used to quantify the evolution of the sedimentary budget in the Southern Mozambique passive margin basin, with a high temporal resolution for the Cenozoic period. We found that the drainage areas, which supplied sediments to the Southern Mozambique Basin, were eroded in two episodes. The first, of Mid–Late Cretaceous in age, is concordant with both thermochronological datation and sedimentary fluxes estimated by other studies in the Namibian and South African and Northern Mozambique margins. This erosion episode ended when the African surface, as defined by Burke and Gunnel (2008), had become flat and low-lying over most of the South African Plateau by ∼65Ma. Carbonate sediment deposition became more important in the shallow waters of the Mozambique basin after that time. The second erosion episode began at ∼23Ma and is likely due to an uplift event of the North-eastern part of the South African Plateau. It seems that the Limpopo catchment and the whole area sourcing the studied basin have inherited their present relief from two epeirogenic uplift pulses of Late Cretaceous and Miocene ages.

A new pathway for Deep water exchange between the Natal Valley and Mozambique Basin?

Although global thermohaline circulation pathways are fairly well known, the same cannot be said for local circulation pathways. Within the southwest Indian Ocean specifically there is little consensus regarding the finer point of thermohaline circulation. We present recently collected multibeam bathymetry and PARASOUND data from the northern Natal Valley and Mozambique Ridge, southwest Indian Ocean. These data show the Ariel Graben, a prominent feature in this region, creates a deep saddle across the Mozambique Ridge at ca. 28°S connecting the northern Natal Valley with the Mozambique Basin. Results show a west to east change in bathymetric and echo character across the northern flank of the Ariel Graben. Whereby eroded plastered sediment drifts in the west give way to aggrading plastered sediment drift in the midgraben, terminating in a field of seafloor undulations in the east. In contrast, the southern flank of the Ariel Graben exhibits an overall rugged character with sediments ponding in bathymetric depressions in between rugged sub/outcrop. It is postulated that this change in sea-floor character is the manifestation of deep water flow through the Ariel Graben. Current flow stripping, due to increased curvature of the graben axis, results in preferential deposition of suspended load in an area of limited accommodation space consequently developing an over-steepened plastered drift. These deposited sediments overcome the necessary shear stresses, resulting in soft sediment deformation in the form of down-slope growth faulting (creep) and generation of undulating sea-floor morphology. Contrary to previous views, our works suggests that water flows from west to east across the Mozambique Ridge via the Ariel Graben.

CO2 Storage Capacity Assessment of Deep Saline Aquifers in the Mozambique Basin

Abstract This study is the first of its kind that made an assessment of theoretical storage capacity within the deep saline aquifers in the Mozambique Basin. An integrated approach that involved geographic information systems analysis and field data assessment was adopted to estimate the storage capacity. Geological characterization was conducted based on available geological cross-sections supported by well stratigraphy data and data from well-logs. Four separate saline aquifers in the depth ranges of 800 m to 3,500 m below surface were recognized in the basin, each having its own sealing shale layers. The theoretical low- and high-end CO 2 storage capacity for the saline rock formations were estimated using volumetric approach. The integrated approach that involved use of GIS tools and field data has resulted in more robust estimates which reduced the spatial uncertainty and thus constrained CO 2 storage capacity estimations. It also avoided the unrealistic extrapolation throughout the basin, while promoting a proper accounting for the possibility to store CO 2 in multiple overlaying formations. We believe that the digital storage atlas developed should provide a basis for further work to reduce the uncertainty in the estimates and also provide support to policy makers on future planning of CCS projects in the country.

Hydrocarbon potential in the key basins in the East Coast of Africa

Abstract This paper analyzes the evolution and sedimentary filling characteristics of regional structures in the sedimentary basins in the east coast of Africa and discusses the different geological conditions of hydrocarbon accumulations (e.g. source rock, reservoir and cap-rock) and their exploration potential. These basins are superimposed basins developed on the Precambrian basement, they were successively filled with three sedimentary sequences, i.e. the late Carboniferous – early Jurassic intra-continental rifting continental sedimentary sequence, the mid/late Jurassic – early Cretaceous intra-continental weak rifting sedimentary sequence, and the late Cretaceous – Neogene passive margin marine sedimentary sequence, where different source-reservoir-caprock assemblages show good prospects for exploration. The comprehensive comparison and analysis has been conducted on such geological conditions in six key basins (Lamu, Somalia, Tanzania, Ruvuma, Mozambique and Morondava). It is considered that the Tanzania, Ruvuma and Somalia basins are highly potential for superior geological conditions, such as excellent source rocks and cap rocks, and good preservation later. The Mozambique basin is also favorable for exploration, but the Lamu and Morondava basins are unacceptable.

The crustal structure of the Central Mozambique continental margin — Wide-angle seismic, gravity and magnetic study in the Mozambique Channel, Eastern Africa

Abstract The continental margin of Mozambique formed during the initial dispersal of Gondwana about 180 Ma. Due to the lack of deep seismic and dense potential field data, many details of the timing and geometry of the early breakup in this region remained unknown to date. To close this gap, a research project (MoBaMaSis (“Mozambique Basin Marine Seismic Survey”) with the French research vessel R/V Marion Dufresne II was conducted in 2007. This paper presents the results of P-wave, magnetic and 2D-gravity modelling along two parallel seismic refraction profiles between 37° and 41° E, crossing the Mozambique rifted margin. The crust shows the characteristics of normal to slightly thickened oceanic crust. A lower crustal high-velocity-body with P-wave-velocities of 7.0–7.5 km/s is observed along both profiles. Its origin is discussed in the context of upper mantle convection and thermal properties. The existing magnetic anomaly identifications have been extended to older ages. We postulate that the oldest oceanic crust near the Central Mozambique continental margin has been formed around M41n (166 Ma). Closer to the coast a pronounced negative magnetic anomaly exists that we interpret to coincide with the continent–ocean-transition. This implies that the position of the continent–ocean-transition is located significantly closer to the shoreline than proposed before.

The Jurassic history of the Africa–Antarctica corridor — new constraints from magnetic data on the conjugate continental margins

Finding the best fit for East- and West-Gondwana requires a detailed knowledge of the initial Jurassic movements between Africa and Antarctica. This study presents results of systematic and densely spaced aeromagnetic measurements, which have been conducted in 2009/2010 across the Astrid Ridge (Antarctica) and in the western Riiser-Larsen Sea to provide constraints for the early seafloor spreading history between both continents. The data reveal different magnetic signatures of the northern and southern parts of the Astrid Ridge, which are separated by the Astrid Fracture Zone. The southern part is weakly magnetised, corresponding to the low amplitude anomaly field of the southwestern Riiser-Larsen Sea. In contrast, the northern Astrid Ridge bears strong anomalies of positive value. Furthermore, several sets of trends are visible in the data.In the Mozambique Channel, we extended the existing magnetic spreading anomaly identifications. Combined with the spreading anomalies in the conjugate Riiser-Larsen Sea, they were used to establish a new model of the relative movements of Africa and Antarctica after the breakup of Gondwana in Jurassic times. A detailed model for the emplacement of the Mozambique Ridge is now incorporated.The model postulates a tight fit between Africa and Antarctica and two stages of breakup, the first of which lasting until ~159Ma (M33n). During this stage, Antarctica rotated anticlockwise with respect to Africa. The Grunehogna Craton cleared the Coastal Plains of Mozambique to a position east of the Mozambique Fracture Zone. The southern Astrid Ridge is interpreted to consist of oceanic crust, also formed during this first stage, prior to the Riiser-Larsen Sea. During the second stage, Antarctica moved southward with respect to Africa forming the Mozambique Basin and the conjugate Riiser-Larsen Sea. The Mozambique Ridge and the Northern Natal Valley were formed at different spreading centres being active subsequently.

Thermochronological history of an orogen‐passive margin system: An example from northern Mozambique

In this paper, we present a conceptual model to describe the post‐Pan‐African (<∼500 Ma) basement cooling pattern for NE Mozambique. The cooling history is derived from combined low‐temperature thermochronological dating methods comprising titanite, zircon and apatite fission track data. After Pan‐African orogenesis (∼620–530 Ma) the Precambrian basement was subject to extensional tectonics and a relatively slow Lower Ordovician to Recent cooling with rates of ∼2.2°C to 0.1°C Myr−1. Basement rock cooling was mainly a response to Late Paleozoic to Mesozoic rifting between northern Mozambique and East Gondwana during the opening of the Rovuma and Mozambique sedimentary basins. Meanwhile, different dynamic margin and basin types evolved along the eastern and southern continental margins of NE Mozambique. During the Late Carboniferous–Triassic an intracontinental rift opened between NE Mozambique and East Antarctica, and the fastest denudation was focused along the present southern continental margin. Since the Middle Jurassic, tectonic denudation along the Rovuma margin was localized in a narrow zone, some 30 km wide, associated with erosion along strike‐slip faults. In contrast, the Jurassic‐Cretaceous opening and ocean crust formation in the Mozambique Basin were accompanied with an unusually uniform Late Cretaceous cooling pattern over a large area (∼150,000 km2) of the basin hinterland. This pattern can be explained by isostatic and erosional response to magmatic underplating or differential stretching, whereby the old Pan‐African lithospheric structure appears to have important controls on later events.

Human leukocyte antigen–A, –B, and –DRB1 allele and haplotype frequencies in the Mozambican population: A blood donor–based population study

Human leukocyte antigen (HLA) has been used for several decades as genetic markers for analyzing diversity of gene pool origin, platelet transfusion, tissue transplantation, disease susceptibility or resistance, and forensic and anthropological studies. In the present study, the allele and haplotype frequencies of HLA-A, -B, and -DRB1 were studied in 250 unrelated Mozambican individuals (black African from south of Mozambique Basin) by using a low-medium resolution polymerase chain reaction-Luminex typing method. A total of 18 A, 25 B, and 13 DRB1 alleles were identified. The most frequent HLA-A, -B, and -DRB1 alleles were HLA-A*30 (23.9%), HLA-B*15 (15.6%), and HLA-DRB1*13 (19.8%), respectively. The most frequent two-locus haplotypes were HLA-A*30-B*42 (7.4%) and HLA-B*42-DRB1*03 (5.4%), and three-locus haplotypes were HLA-A*30-B*42-DRB1*03 (4.9%), and HLA-A*02-B*58-DRB1*11 (4.1%). Allele distribution and haplotype analysis demonstrated that Mozambican population shares HLA patterns with sub-Saharan populations.