ALBERT

Description: The nickeliferous Madziwa Igneous Complex consists of several lenticular, mafic-ultramafic enclaves within late Archean gneissic terrain. The lenses of igneous rock are locally deformed and metamorphosed to lower greenschist grade. They are here interpreted to be remnants of a large, composite, magmatic structure with two main components: (1) a set of narrow (10s–100s of meters wide) dikes intruding the gneissic foliation, and (2) a large lopolith made up of leuconorite. Some dikes contain a differentiated and vertically oriented layered suite comprising a central pyroxenite layer, plus norite as both a continuous marginal layer and intermittent layers within the pyroxenite. The pyroxenite-norite suite has a preliminary U-Pb zircon age of 2684 Ma. Other dikes are made up of diorite and/or ferrodiorite; in places, the dioritic rocks also intrude the pyroxenite-norite suite. The leuconorite lopolith transects both the dikes and the gneissic country rocks, its basal contacts with the pyroxenite-norite suite varying locally from intrusive to gradational to (magmatic) erosional. Although modified in places by secondary mobilization, disseminated Ni-Cu sulfides are primarily hosted within the central (ortho- to mesocumulate) pyroxenite adjacent to internal norite layers. Whole-rock geochemical data establish the comagmatic origin of the principal rock types and indicate an Archean, D-type, basaltic source magma with ca. 8% MgO, the two dioritic rock types representing late, immiscible, silica- and Fe-Ti-P-rich derivatives of pyroxenite-norite(-leuconorite) crystallization. In addition to the major rock types, peridotites occur in several outlying dikes and may represent fractionates of a komatiitic precursor to the basalt. Geologic and geochemical evidence points to bulk assimilation of country rock gneiss by the Madziwa magma and sulfide segregation triggered by felsic contamination. These processes did not occur locally within the dikes but rather in the conduit system prior to the emplacement of the magma charged with sulfide droplets. The unusual vertical layering of the pyroxenite-norite sequence and the localization of the sulfide ores are attributed to the strong outward, cooling gradient across such narrow dikes and to large-scale, lateral movement of sulfide droplets through the solidifying, pyroxene crystal framework ahead of an advancing postcumulus plagioclase crystallization front.

Description: 〈p〉How food production first entered eastern Africa ~5000 years ago and the extent to which people moved with livestock is unclear. We present genome-wide data from 41 individuals associated with Later Stone Age, Pastoral Neolithic (PN), and Iron Age contexts in what are now Kenya and Tanzania to examine the genetic impacts of the spreads of herding and farming. Our results support a multiphase model in which admixture between northeastern African–related peoples and eastern African foragers formed multiple pastoralist groups, including a genetically homogeneous PN cluster. Additional admixture with northeastern and western African–related groups occurred by the Iron Age. These findings support several movements of food producers while rejecting models of minimal admixture with foragers and of genetic differentiation between makers of distinct PN artifacts.〈/p〉

Description: The hilly northern part of the north-northeast-trending Great Dyke – the Mvukwe Range – comprises a 300 km 2 , elongate mass of exposed serpentinite displaying remnants of two principal erosion surfaces: an arealy-dominant upper surface and a subordinate lower surface confined to a northerly location. Both surfaces, assigned to successive phases of the composite, continent-wide, mid-Cretaceous to end-Oligocene, African Surface, are represented by variably-preserved table-lands of plateaus, mesas, buttes, and accordant summits. To the east and west, inselberg-bearing, granitic plains form a composite, Miocene, Post-African etch surface at contrasting lower elevations, resulting in eccentric dispositions of African erosion surfaces and Post-African internal valleys, all attributed to the varying maturity of the main drainage systems either side of the Mvukwe Range, a probable regional watershed since pre-Karoo times. The lower and upper African surfaces have present-day elevations of ca. 1525 m and (mostly) ca. 1620 m, respectively, although an original vertical separation of ca. 200 m is estimated in the north. Complex northward variations in preservation and elevation of the upper surface, plus a general northward increase in modal olivine in the serpentinised dunite protolith, point to significant regional uplift, probably associated with Tertiary displacement of the Zambezi Escarpment horst active since the Triassic at the northern extremity of the Great Dyke, as well as possible re-activation of Zambezi belt-related Proterozoic faults. Preserved African Surface regoliths comprise (cliff-forming) horizontally-fractured serpentinite overlain by a composite silica cap of horizontally-fractured serpentinite with sheeted silica veins below ferruginous silicified serpentinite. The predominantly, goethite-chrysotile African regoliths carry nickel enrichments of 1 to 2% Ni (or more) to depths of up to 10 m (or more) in the fractured serpentinite and sheeted silica vein zones; other nickel enrichments occur more sporadically within the protolith. Three principal mineralogical associations are postulated for the contained nickel: (1) discrete, fracture-related, ‘garnieritic’ minerals (in both regolith and protolith), (2) nickeloan serpentine within drusy vugs associated with silica veins, and, probably, (3) pervasive enrichments associated with goethite and/or chrysotile. Cobalt, concentrated towards the top of the preserved regolith profile, is most likely linked to goethite via a primary association with Mn. The geomorphological and geological features of Great Dyke nickel laterites are closely analogous to those of classic, saprolite-type nickel laterite deposits in Brazil. Both groups probably formed in fundamentally similar ways, the lower grade/thickness of the Great Dyke deposits attributable to the slightly differing climatological and geomorphological histories of northern Zimbabwe and of equatorial and tropical Brazil.

Description: 〈p〉How food production first entered eastern Africa ~5000 years ago and the extent to which people moved with livestock is unclear. We present genome-wide data from 41 individuals associated with Later Stone Age, Pastoral Neolithic (PN), and Iron Age contexts in what are now Kenya and Tanzania to examine the genetic impacts of the spreads of herding and farming. Our results support a multi-phase model in which admixture between northeastern African-related peoples and eastern African foragers formed multiple pastoralist groups, including a genetically homogeneous PN cluster. Additional admixture with northeastern and western African-related groups occurred by the Iron Age. These findings support several movements of food producers, while rejecting models of minimal admixture with foragers and of genetic differentiation between makers of distinct PN artifacts.〈/p〉

Description: Set in ca. 74 km 2 of rugged terrain close to the Zambezi Escarpment, the Snake’s Head Platinum Project covers the northeastern half of the Musengezi Subchamber in the northern part of the Great Dyke. Here, the linear Great Dyke straddles the boundary between the Zimbabwe craton and the late Archaean Migmatitic Gneiss Terrain and is folded into a prominent S-shape adjacent to the Neoproterozoic-Phanerozoic Zambezi orogenic belt. Snake’s Head contains the northernmost remnant of the Great Dyke’s P1 Pyroxenite Layer, which hosts the economically-important, stratabound, PGE-rich Main Sulphide Zone (MSZ), as well as the lower grade (but petrogenetically very similar) Lower Sulphide Zone (LSZ), together containing one of the Great Dyke’s last undeveloped platinum resources (〉80 m oz). The original, gently-plunging, synclinal layered structure of the Musengezi Subchamber is preserved in the western part of Snake’s Head but is replaced in the east and north by several, contiguous, kilometre-scale structural blocks in different orientations and separated by curvilinear, brittle-ductile thrust zones suggestive of sequential stacking towards the west. Shearing and associated metasomatism increase from the generally pristine western blocks to the northern and eastern blocks where the structure is overlain above another major, south-directed thrust by the Marginal Gneiss Terrain of the Zambezi belt and the underlying, well-developed magnetite gabbro unit at the top of the Great Dyke sequence is mostly converted to mafic schist. The P1 Pyroxenite displays layer-thicknesses, mineral associations and textures, and other layering features, and the MSZ shows slight systematic variations in thickness, and in sulphide and metals contents, that all indicate (1) primary magma chamber locations varying from the axis (in the case of the western blocks) to midway between the axis and margins (eastern/northern blocks), and (2) an original magma chamber width that varied along its length but was significantly greater than in other parts of the Great Dyke. The MSZ and LSZ preserved at Snake’s Head are, unlike their correlatives elsewhere in the Great Dyke, broadly similar in thickness and metals content, probably because they formed along the axial to mid-axial/marginal facies of a very wide magma chamber where the horizontal rather than the vertical gradient dominated the cooling regime to a far greater extent than elsewhere in the Great Dyke. Emplacement of the 2.58 Ga year-old Great Dyke took place towards the end of late Archaean greenstone formation, granite intrusion and deformation along the northern edge of the Zimbabwe craton at ca. 2.57 to 2.62 Ga. Thrust deformation at Snake’s Head fits only the earliest (late Archaean) stage of deformation along the northern margin of the craton and so may have occurred soon after Great Dyke emplacement during the waning phase of Migmatitic Gneiss Terrain development and the final stabilisation of the craton. Folding of the Snake’s Head thrusts and thrust blocks may reflect cross-folding during extension of the Marginal Gneiss Terrain during the earliest stage of Zambezi belt orogenesis at 0.75 to 0.85 Ma. The marked north-south shortening of the northernmost part of the Great Dyke is likely the product of south-directed thrust movements during Zambezi contractional events at 0.85 to 1.10 Ga and/or 0.50 to 0.60 Ga.

Description: The Maths Learning Support Centre (MLSC) in the Dublin Institute of Technology (DIT) provides free mathematical support to all DIT students. This support is primarily delivered through a drop-in service, where students can receive one-to-one tuition, without an appointment, in any area of mathematics. In the first semester of the 2013/14 academic year, a significant proportion of students that availed of this drop-in service were mature students enrolled in Engineering programmes. This is of particular interest as mature students constitute a relatively small proportion of the total student body, motivating a deeper study of the reasons for the high levels of engagement in this cohort. To this end two focus groups were conducted, consisting of those who do and do not attend the MLSC. Particular interest was paid to the motivation of students who attend and the reasons given by those who do not. The motivations of mature students were found to be multifaceted whereas the reasons for non-engagement were mostly in line with the literature. In addition, some quantitative analysis was carried out to determine what effect the MLSC had on students’ academic performance.