The occurrence of several high-magnitude abrupt climatic changes during the last glacial period (~120-10 ka BP) was first recognised within the Greenland deep ice-core records. Subsequent identification of similar climatic variations has demonstrated the potential global significance of these events. Three of these millennial-scale events occurred during Marine Isotope Stage (MIS) 4 (~79-59 ka BP), a period characterised by cooler global temperatures. An understanding of the forcing mechanisms and the environmental responses to these events is currently unattainable due to chronological uncertainties and the inability to precisely synchronise disparate records. Tephrochronology, however, has the potential to facilitate high-precision ice-marine correlations by tracing isochronous horizons between different sequences spanning this period. This potential is demonstrated through the construction of the first tephrochronological framework for MIS 4 within the North Atlantic region. Fourteen cryptotephra horizons are identified within the NGRIP and GRIP ice-cores and the MD04-2822 marine core. Both major and trace element compositions are presented for these previously unknown tephra horizons and form the backbone of this framework. In addition, high-precision, independent age estimates have been assigned to the horizons identified within the ice-core sequences. This framework represents a significant first step towards the regional and potentially hemispheric synchronisation of MIS 4 climatic archives. As well as providing the first evidence for the activity of Icelandic volcanic systems during MIS 4, this framework also demonstrates the widespread dispersal of basaltic-trachybasaltic products from the Jan Mayen volcanic region and potentially the deposition of Japanese volcanic material over Greenland. In addition, investigations of laser ablation inductively coupled plasma mass spectrometry have demonstrated that reliable trace element characterisations can be obtained from tephra shards?20 ?m in diameter, which opens up new possibilities for the incorporation of this technique in distal tephra studies.

M.Sc. / The ca. 800 km2 Tete Complex of NW Mozambique is located at the eastern end of the 830 ±30 Ma Zambezi Belt, near the transition zone into the Neoproterozoic Mozambique Belt. The Complex is located just south of the Sanangoe Shear Zone where Mesozoic and Late Palaeozoic cover rocks obscure much of the region. Country rocks immediately in contact with the Tete Complex include amphibolitic gneiss, graphite-bearing marble, calcsilicate gneiss, muscovite and biotite schist and quartzite of the Chidue Group. The Tete Complex may have been intrusive into the Chidue Group, although there is evidence inferring tectonic emplacement. Those few contact exposures that exist are equivocal. Some of the rocks within the Tete Complex have been affected by metamorphism up to amphibolite grade, although large proportions of the rocks retain pristine magmatic mineralogy and texture. The Tete Complex contains mafic, ultramafic and anorthositic rocks, dolerite dykes and minor Fe-Ti oxide-rich rocks that occur as rubble. Pyroxenite occurs as thin (<1-2 m), cumulate layers within gabbroic rocks. Most exposed anorthositic rocks occur in the Nyangoma area in the eastern part of the Tete Complex. The anorthosites and leucotroctolites are massive, coarse grained (2-3 cm), and contain plagioclase (An47-An57) megacrysts up to 10 cm in length, interstitial olivine (Fo59-Fobs) and orthopyroxene (En59- En75, mean A1203 = 1.84 wt.%) rimmed by clinopyroxene (mean = Wo 46En38Fs i6), pyrite and Fe-Ti oxides. Secondary biotite, iddingsite, epidote and green spinet are present. The stable coexistence of olivine and plagioclase limits the depth of emplacement to <7-8 kbar, or <20- 25 km; a relatively shallow level of emplacement is favored by the generally fine grain size of the gabbroic and doleritic rocks. Compositions of coexisting plagioclase and mafic silicates (orthopyroxene and olivine) are similar to those of massif-type anorthosites. Previously unmapped meta-anorthosite occurs along the western and northern margin (within the Sanangoe Shear Zone) of the Tete Complex and has been metamorphosed to amphibolite grade. The rock contains plagioclase (An38-An39), with the more Ab-rich compositions related to the formation of garnet (mean = A1m67GrotsPYI6Sp2). Metamorphic orthopyroxene (Enso-En53), clinopyroxene (mean = Wo37En38Fs25), mizzonitic scapolite (Me63), amphibole, biotite and apatite are present. High Cl contents in amphibole, scapolite and biotite (e.g., up to 4.7 wt. % in amphibole), suggest that a Cl-rich metamorphic fluid infiltrated the western margin of the Tete Complex. Olivine melagabbro from the north-central part of the Tete Complex contains plagioclase (An70-An26), olivine (Fo82-Fos4) and clinopyroxene (mean = WanEn1Fs0.2, mean A1203 = 2.56 wt. %), with primitive compositions compared to those in Nyangoma anorthositic rocks and pyroxenites. Pyroxenites are modally dominated by clinopyroxene (mean = Wo46-48En36-39Fsi3-18) with accessory interstitial plagioclases (Ano-An45) and discrete and exsolved orthopyroxenes (En 56-En75). Clinopyroxenes with high A1203 contents up to 9 wt. % are similar to high-Al pyroxene megacrysts. One sample of pyroxenite contains orthopyroxene (En56-En60) and plagioclase (An40-An45) with more evolved compositions compared to those in Nyangoma anorthositic rocks and olivine melagabbro. Normal Fe4- and Na-enrichment trends accompanying fractionation from magmas that may be common to the Nyangoma anorthositic rocks, pyroxenites and olivine melagabbro, are associated with an increase in Al relative to Cr along a line of nearly constant relative Ti content. Gabbro contains olivine and plagioclase crystals that are commonly zoned, thus ranging widely in composition (Fool -Fos°, Anss-Ans2)• Clinopyroxene (mean = Wo36En47Fsi6) constitutes ca. 34 modal % of gabbro. New whole-rock (Nyangoma anorthosite and leucotroctolite) and mineral (plagioclase, clinopyroxene and orthopyroxene) Sm-Nd isotopic data yields ages between 975 ±33 Ma and 1041 ±131 Ma. The igneous crystallization age of the anorthositic rocks is estimated at 1025 ±79 Ma (9-point whole-rock regression). Rb-Sr isotopic compositions for whole-rock samples reveal no meaningful age relationships. Initial Nd isotopic compositions (calculated at 1.0 Ga) correspond to E Nd values between +3.5 and +4.5 (mean = +4.1) with Is, = 0.70276 — 0.70288 (mean = 0.70282), both inferring magmatic derivation from a depleted mantle source, possibly with little or no contamination by Archaean crustal components. TDM model ages range between 1074 and 1280 Ma (mean = 1148 Ma). There is a striking similarity between the Tete Complex anorthosites and those of SW Madagascar in terms of Nd isotopic compositions and the nature of country rocks; in both regions the anorthosites were emplaced either magmatically or tectonically into shelf-type supracrustal metasediments (marbles, quartzites, graphitic schists, etc.). Anorthosites intruded similar country rocks in Draining Maud Land, eastern Antarctica. Although anorthosites from Mozambique and Madagascar share a common depleted mantle signature with little or no contamination by Archaean crustal components, a direct stratigraphic correlation between these two areas (and possibly eastern Antarctica), awaits further geological and geochronological data.

M.Sc. / The Limpopo Complex (LC) of southern Africa is one of the best-studied Precambrian granulite facies terrains in the world, yet workers still disagree on fundamental aspects of the geological evolution of this complexly deformed high-grade terrain. Most workers agree that the two marginal zones were exhumed in the late-Archaean, but disagree on the timing of major tectono-metamorphic events that affected the Central Zone (CZ) of Limpopo Belt, and the mechanism/s of its formation. There are currently two main schools of thought: The first school regards the LC as a late-Archaean orogenic zone that resulted from a north-south collision of the Zimbabwe and Kaapvaal cratons. Granitic plutons throughout the entire LC are considered to be accurate time-markers for this orogeny. The second school suggests that the CZ evolved as a result of a major Paleoproterozoic tectono-metamorphic event based mainly on the interpretation of metamorphic mineral ages. The present study focuses on two aims, namely (i) to provide a synthesis of published data as a basis to understand the ongoing age controversy concerning the evolution of the CZ, and (ii) to show that specific fold types in the CZ can be related to either the late-Archaean or the Paleoproterozoic event. New age, structural, metamorphic, and petrographic data are presented to show that (i) major sheath folds reflect the peak tectono-metamorphic event that affected the CZ in the late-Archaean, while (ii) major cross folds developed as a result of a transpressive event in the Paleoproterozoic. The age of formation of the Avoca sheath fold located about 40 km west of Alldays is accurately constrained by the age of emplacement of different structural varieties of precursors to the Singelele Gneiss: penetratively deformed syn- to late-tectonic Singelele gneisses with a zircon SHRIMP age of 2651 ± 8 Ma, date the time of formation of the sheath fold that is characterized by a single population of linear elements that define the central fold axis. The Avoca sheath fold documents top-to-the-NNE movement of material during the exhumation of the high-grade CZ rocks. Weakly foliated late-tectonic L-tectonites with a zircon SHRIMP age of 2626.8 ± 5.4 Ma, outcrop near the centre of the sheath fold, and provide a minimum age for the shear deformation event. An almost undeformed (post-tectonic) variety of the Singelele Gneiss was emplaced after the shear event. A detailed metamorphic study of metapelitic gneisses from the large Baklykraal cross fold, located about 20 km east of the Avoca sheath fold, documents a single decompression-cooling (DC) P-T path for the evolution of this structure. Three studied metapelitic samples characterized by a single generation of garnet provide a Pb-Pb age of 2023 ± 11 Ma, that accurately constrain the time of formation of this major fold to the Paleoproterozoic. A metapelitic sample characterized by two generations of garnet provide a slightly older Pb-Pb age of 2173 ± 79 Ma, that is interpreted to also reflect the late-Archaean event. The Baklykraal cross fold is characterized by two populations of linear elements: the one population defines the shallow N-S oriented fold axes, while the second population is associated with top-to-the-NNE movement of material during exhumation, resulting in folds with a nappe-like geometry. A DC P-T path for the Campbell cross fold (Van Kal, 2004) located just west of Musina, suggests that cross folds developed under significantly lower P-T conditions than is the case with sheath folds, providing an explanation for the lack of significant anatexis associated with the Paleoproterozoic event. The late-Archaean orogeny in contrast, was accompanied by widespread anatexis during a major magmatic event that is characterized by an abnormal high radiogenic signature. This study, for the first time, provides evidence that link specific fold types, and thus deformational events, to different tectono-metamorphic events. The main conclusion is that the CZ was exhumed as the result of two distinct orogenies, one in the late-Archaean, and the other in the Paleoproterozoic.

Glacial till from the Mt. Achernar moraine (MAM) records pre- and post- last glacial maximum (LGM) compositional variability of an East Antarctic moraine sequence through time and space. Pebble lithology, detrital zircon geochronology, and till geochemistry were analyzed on samples from a 6.5 km transect. Hummocky topography occurs with the most recently exposed material along the active ice margin (Zone 1), followed by a relatively flat and low region (Zone 2), and then a series of ~2 m high parallel/sub-parallel ridges and troughs accompanied by distinct color changes that are directly related to the dominant lithology of the region (Zones 3–5). Zone 3 is dominated by ~38% more sedimentary rocks than adjacent zones and has an overall shape of a broad arch superimposed with smaller ridges. Zone 4 is composed of distinct colored bands that alternate between dominant sedimentary and mafic igneous lithologies. These dominant sedimentary and intermediate/mafic igneous rocks for all Zones are interpreted to be primarily the Beacon and Ferrar Supergroup rocks respectively. The U/Pb data from the till is consistent with a Beacon Supergroup source as samples consistently show significant populations from the Permian ~250-260 Ma, the Proterozoic ~565–600 Ma, ~950–1270 Ma, and ~2300-2320 Ma, as well as (and) the late Archean ~2700-2770 Ma. The Pagoda, Mackellar, Buckley, and Fremouw Formations are potential sources of the detrital zircons. When paired with surface exposure ages, the U/Pb data indicates that the debris source has been consistent over the past ~555 ka, implying relatively stable ice sheet behavior. However, ice sheet change is indicated by a trim line present on Mt. Achernar that can be traced back to the boundary between Zones 3 and 4, as well as a change in pebble lithology, geochemistry, and morphology of Zone 3. Zone 3 records a time of ice sheet thickening and a change in provenance during the LGM. Zone 4 is pre-LGM, Zone 2 records deglaciation, and Zone 1 is still actively connected to the Law Glacier. This study reveals the broader importance of using multiple provenance techniques when interpreting provenance changes in till over time.

No description available.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1981. / Microfiche copy available in Archives and Science / Includes bibliographies. / by Jon Eric Spencer. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 385-399. / by Christopher Scott Cameron. / Ph.D.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography : leaves 281-295. / by William John Olszewski, Jr. / Ph.D.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Vita. / Bibliography : leaves 248-259. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Accompanied by 7 folded plates inserted in back pocket. / Bibliography: leaves 256-263. / by John Michael Bartley. / Ph.D.