A pilot study was designed to evaluate the potential of zircon geochronology as a provenance indicator of till from the Lake Michigan, Saginaw, and Huron-Erie Lobes of the Laurentide Ice Sheet. Based on existing ice flow-path models, we hypothesized that till from each lobe would have different zircon age population distributions because the lobes originated from regions of the Canadian Shield with different bedrock ages. After correcting for zircon fertility, the majority of grains in all till samples are 1600–950 Ma, with ~30 % of ages >2500 Ma. This similarity means that till from the three lobes cannot be clearly differentiated based on their zircon populations. The dominant ages found and the homogeneity of distributions in the till indicates a non-Shield source and, instead, reflect an origin from some combination of underlying till and sedimentary bedrock in the Great Lakes region. Even though the datasets are small, the tills have similarities to zircon distributions in Michigan Basin rocks. This implies that a substantial fraction of zircon in till was not transported long distances from the Canadian Shield. Although zircon ages are not distinct between tills, the method provides a novel application to understand Laurentide Ice Sheet glacial erosion and transport.

Archaean zircon grains from the Oygarden Group of islands in Kemp Land, east Antarctica, record evidence for multiple episodes of recrystallisation, dissolution and growth from the Early to Middle Archaean to the Neoproterozoic. Zircon grains in layered felsic orthogneiss have an age of ∼3650 Ma, a minimum protolith age for this rock. These zircon grains were subsequently affected by a ∼3470 Ma Pb-loss event. Homogeneous felsic orthogneiss that cuts S1, but contains an intense S2 foliation, has disturbed ∼2780 Ma metamorphic zircon cores and rims that suggest a minimum age of ∼2780 Ma for the protolith to the orthogneiss. All zircon U-Pb data display considerable disturbance with further Pb-loss at ∼2400 Ma and ∼1600 Ma, and a major episode of isotopic resetting at ∼930 Ma. The highly disturbed data are related to complexly zoned zircon grains that developed through growth and modification during successive metamorphic events. Zircon cores with relic growth zoning patterns are inferred to have resulted from partial annealing or recrystallisation of older magmatic zircon. Highly luminescent zircon rims that embay cores along curved boundaries are interpreted to have formed through recrystallisation of zircon cores, and not new growth. The ages reported here confirm that central Kemp Land is composed of Archaean crust reworked during the Neoproterozoic Rayner Structural Episode.

We report ion-microprobe U-Pb zircon ages from charnockites of a large Proterozoic composite batholith, Mawson Coast, Australian Antarctic Territory. The charnockites crystallized from orogenic magmas of intermediate composition (mainly 54–68% SiO2) intruded into a granulite-facies metasedimentary gneiss sequence between the second and third recognized deformations. A sample of low-Ti charnockite provides an age of 954 ± 12 Ma and a high-Ti charnockite is dated at 985 ± 29 Ma (all ages quoted at 95% confidence). The age difference is not significant at the 95% confidence level. Both these ages were obtained from zircons with igneous zoning and/or morphology and thus are thought to date igneous crystallization. Zircons from a felsic gneiss xenolith within the charnockite have cores of various ages, many from 1.7 to 2.0 Ga, but with other grains between 1.0 and 1.5 Ga and a single 2.5 Ga zircon. These zircon cores are direct evidence for an early to middle Proterozoic age for the supracrustal basement sequence in this mobile belt. Many of these zircon cores are concordant but abundant discordant grains suggest a complex history of multiple Pb-loss events. Zircon rims grew at 921 ± 19 Ma, probably during the post-charnockite deformation (D3). Previously obtained Rb-Sr dates for charnockite of 886 ± 48 Ma and 910 ± 18 Ma were probably also rest during D3. A Rb-Sr isochron date of 1061 ± 36 Ma previously reported for high-Ti charnockite from Mawson Rock is thought to be erroneous, and a new date of 959 ± 58 Ma (consistent with both the igneous and reset dates above) is interpreted from those data.

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

Two new U-Pb zircon ages from the area immediately west of Denman Glacier in Antarctica show that its geological history differs from that of the Obruchev Hills and Bunger Hills, to the east of the glacier. A crystallization age of 516.0 ± 1.5 Ma for syenite is by far the youngest primary age reported for this region, whereas tonalitic orthogneiss from Cape Charcot, the oldest known local rock, was derived by the high-grade metamorphism and deformation at 2889 ± 9 Ma of a 3003 ± 8 Ma igneous precursor. Both major populations of zircon in this rock lost Pb at 500–600 Ma. Although the Sm-Nd characteristics of the entire region resemble those of the Albany Mobile Belt of Western Australia, the Sm-Nd systematics of the felsic gneisses and plutonics are too old to allow direct correlation with the rocks of the Naturaliste Block (Western Australia), a potential key element for Gondwana reconstruction. However, the possibility exists that there is an indirect relationship between the Naturaliste Block and the region immediately west of Denman Glacier.

Three granitoid types are recognised in the Famatinian magmatic belt of NW Argentina, based on lithology and new geochemical data: (a) a minor trondhjemite–tonalite–granodiorite (TTG) group, (b) a metaluminous I-type gabbro-monzogranite suite, and (c) S-type granites. The latter occur as small cordieritic intrusions associated with 1-type granodiorites and as abundant cordierite-bearing facies in large batholithic masses. Twelve new SHRIMP U-Pb zircon ages establish the contemporaneity of all three types in Early Ordovician times (mainly 470-490 Ma ago). Sr- and Nd-isotopic data suggest that, apart from some TTG plutons of asthenospheric origin, the remaining magmas were derived from a Proterozoic crust-lithospheric mantle section. Trace element modelling suggests that the TTG originated by variable melting of a depleted gabbroid source at 10-12kbar, and the I-type tonalite-granodiorite suite by melting of a more enriched lithospheric source at c. 5 kbar. The voluminous intermediate and acidic I-types involved hybridisation with lower and middle crustal melts. The highly peraluminous S-type granites have isotopic and inherited zircon patterns similar to those of Cambrian supracrustal metasedimentary rocks deposited in the Pampean cycle, and were derived from them by local anatexis. Other major components of the S-type batholiths involved melting of deep crust and mixing with the I-type magmas, leading to an isotopic and geochemical continuum.