Abstract The Dalradian Supergroup, comprising the Grampian (oldest), Appin, Argyll and Southern Highland (youngest) groups (Fig. 13) consists of lithologically diverse metasediments and typically mafic metavolcanic rocks. The supergroup is probably entirely late Precambrian in age and underlies an area of about 48000 km 2 in north and west Ireland, Scotland and Shetland. Neither the base nor the top of the Dalradian is seen but, taking the maximum thickness preserved for every group and making no allowance for tectonic thickening, it is calculated to have a total cumulative thickness of c. 25.5 km.

Abstract Geochemical data are used widely to help correlate lithostratigraphical sequences, particularly where they are unfossiliferous and/or affected by metamorphism and deformation. In this study, geochemical data for variably impure metamorphosed limestones from the Neoproterozoic – Cambrian Dalradian Supergroup of Scotland have been used to aid lithostratigraphical discrimination and correlation in a region where apparently similar sequences crop out in widely separated regions affected by major deformation. The key problem in the statistical analysis of geochemical data is that the data are constrained to a constant sum and cannot, therefore, be analysed in raw form by conventional statistical techniques. To overcome this problem, the data have been transformed into log-ratios. Subsequent statistical analysis of the transformed data focuses on determining the simplest sub-composition that effectively discriminates between the limestones. The results show that the Fe 2 O 3 –MgO–CaO subcomposition is sufficient in this regard, with the additional benefit that it reflects the composition of the carbonate component in the limestones. Mann–Whitney tests of the log-ratio Fe 2 O 3 /MgO show that limestones from most different lithostratigraphical levels are statistically different from each other at high levels of significance. The results have clarified interpretations of the lithostratigraphy and subsequent interpretations of the tectonic history of the region.

Abstract The Northern Highland and Grampian terranes together comprise an extensive tract of structurally complex and generally high-grade metamorphic rocks within the Caledonian orogenic belt of Scotland ( Fig. 4.1 ). This part of the orogen is dominated by two thick sequences of mainly Neoproterozoic metasedimentary rocks. The older sequence comprises the Moine Supergroup of the Northern Highland terrane, and possibly also the Dava Succession of the Grampian terrane. Both were deposited between c. 1000 Ma and c. 870 Ma, and subsequently affected by a controversial Knoydartian tectonothermal event at c. 800 Ma. The younger Dalradian Supergroup of the Grampian terrane accumulated between c. 800 Ma and the Early Cambrian during the break-up of the late Precambrian supercontinent Rodinia and the formation of the Iapetus Ocean. Inliers of Archaean to Palaeoproterozoic orthogneisses ( Fig. 4.1 ) probably represent fragments of the Laurentian continental basement on which the Moine and Dalradian successions accumulated. Caledonian orogenesis in the North Atlantic region resulted from the closure of the Iapetus Ocean and the convergence of three crustal blocks: Laurentia, Baltica and Avalonia (Soper & Hutton 1984; Pickering et al. 1988; Soper et al. 1992b). Early orogenic activity along the Iapetan margin of Laurentia resulted from an arc-continent collision that occurred during initial ocean closure in the Early to Mid-Ordovician. This phase of the Caledonian orogenic cycle is known as the Grampian event and it affected both the Northern Highland and Grampian terranes. Ocean closure and final amalgamation of crustal blocks occurred in the Late Silurian

Petrographic examination of temper sands in prehistoric Oceanian pottery collected by archaeologists from island groups spread across the tropical Pacific Ocean shows that the sands vary compositionally in geographic patterns that are governed by geotectonic setting and vagaries of local bedrock exposure on individual islands. The small islands serve as virtual point sources of sediment derived exclusively from the restricted array of rocks that form each island. Both natural and manually added tempers can be traced to bedrock sources by the same petrographic methodology, but independently sourcing clay bodies requires geochemical comparison of clay pastes with potential clay sources. Oceanian tempers include calcareous as well as terrigenous sands, but only the latter can be associated unequivocally with specific islands or island groups because the nature of reef tracts is similar throughout the tropical Pacific. Exotic tempers can be distinguished from indigenous tempers because their compositions are incompatible with the geology of the islands where the exotic sherds are found. Human migration into islands of the Pacific Ocean was the last main stage in human dispersal over the planet, with no human occupation of the small islands lying beyond island Southeast Asia and Australasia until 1500 B.C. The earliest inhabitants possessed a ceramic culture, and ceramic traditions evolved over subsequent centuries to produce a varied succession of ceramic phases. Lapita pottery, which is the oldest ware in southwest Pacific island groups, is especially notable because its production was limited to a time frame short enough to allow Lapita sherds to serve a role akin to index fossils. Temper sands in Lapita and post-Lapita sherds from the same locales are indistinguishable and show that salient temper contrasts are controlled by island geology rather than habits of ancient potters. Prehistoric collecting sites for temper sand were not necessarily identical to places where modern sand accumulates because of severe environmental changes on many islands. The compositions of terrigenous temper sands in Pacific Oceania reflect the complex pattern of circum-Pacific plate boundaries and intra-Pacific hotspot chains, and define oceanic basalt, andesitic arc, postarc-backarc, dissected orogen, and tectonic highland temper classes composed of different associations of grain types. The geographic distribution of different temper classes reflects not only the current geotectonic setting of each island group but also their paleotectonic settings when exposed rock assemblages were formed. Temper aggregates include beach, stream, and rarely dune sands, as well as grog (brokensherd) and crushed-rock particles in some island groups. Terrigenous grain types in Oceanian temper sands are subdivided by petrographic analysis into three main groups: light mineral grains including quartz and feldspars, heavyferromagnesian mineral grains including opaque iron oxides and ferromagnesian silicates, and a variety of polycrystalline lithic fragments that are dominantly of volcanic derivation in most temper suites. Useful triangular compositional diagrams plot relative proportions of grain types for populations of total terrigenous grains, mineral grains exclusive of lithic fragments, ferromagnesian silicate mineral grains, all non-ferromagnesian grains, only transparent mineral grains, and exclusively quartz and feldspar mineral grains. Supplemental grain parameters or indices express ratios of grain types among quartz and feldspar mineral grains, ferromagnesian grains, and lithic fragments. Oceanic basalt tempers are mineralogically simple volcanic sands derived from basaltic to basanitic volcanic assemblages of intraoceanic hotspot chains erupted in the interior of the Pacific plate in the eastern Caroline Islands, along the northern Melanesian borderland, in Samoa and American Samoa, and in the Marquesas Islands. Andesitic arc tempers are volcanic sands displaying more compositional variability and are the most abundant tempers within the region of Oceanian ceramic cultures, occurring along island arcs flanking the Philippine Sea plate, bounding the Banda Sea in eastern Indonesia, within the Bismarck Archipelago east of New Guinea, along the reversed-polarity Solomon and Vanuatu arcs, on the Fiji platform and the Lau remnant arc, and in Tonga. Postarc and backarc volcanic sand tempers, variously displaying affinities with both oceanic basalt and andesitic arc tempers, are known from the Bismarck Archipelago, the Vanuatu backarc region, the Horne Islands of the northern Melanesian borderland, and both the Fiji platform and the Lau remnant arc. All volcanic sand tempers of Pacific Oceania are composed of phenocrystic mineral grains and volcanic lithic fragments. Most are quartz-free or quartz-poor, but quartzose variants are present locally along island arcs where silicic eruptions accompanied more typical andesitic to basaltic activity, and within backarc settings where bimodal igneous assemblages are exposed. Most quartzose Oceanian temper sands are either dissected orogen tempers containing dominantly igneous but not exclusively volcanic detritus, or tectonic highland tempers containing recycled sedimentary detritus. Dissected orogen tempers with quartz-ose plutonic detritus occur in selected sherd suites from the Torres Strait Islands, the Bismarck Archipelago, and the Solomon Islands, but are especially characteristic from the south coast of Viti Levu in Fiji. Quartzose tectonic highland tempers occur in sherds from the outer Banda arc, the Aru Islands in the Arafura Sea, the D'Entrecasteaux Islands of the Solomon Sea, and New Caledonia. Nonquartzose tectonic highland tempers derived from ophiolitic rocks of uplifted oceanic crust are present in sherds from Yap and New Caledonia. Comparisons of temper compositions among temper classes indicate that oceanic basalt and basaltic backarc tempers contain significantly higher proportions of olivine mineral grains than arc and postarc tempers, which include a varied array of temper types containing different proportions of pyroxenes and hornblendes. Dissected orogen and quartzose andesitic arc tempers display varying proportions of quartz, plagioclase, and K-feldspar within the compositional field typical for circum-Pacific orogenic sands. Tectonic highland tempers contain distinctly higher proportions of nonigneous lithic fragments than other temper classes. The presence of exotic sherds containing temper sands incompatible with the geology of the islands from which they were recovered documents 106 instances of ceramic transfer between different islands, mostly lying within the same island groups, but also between island groups lying far apart. Two-thirds of the instances of ceramic transfer involved interisland distances of less than 200 km, and most of the remainder involved distances in the range of 200–600 km, but a few cases of ceramic transfer for 1000 km or more are known from temper analysis.