Abstract U–Pb detrital zircon age patterns in sandstones from the Wellington and eastern Cook Strait area have broad Permian–Triassic and Precambrian–early Paleozoic age groups that confirm a previously established Triassic Rakaia Terrane correlation. Along the western Cook Strait coast, meta-psammitic Marlborough Schist samples have zircon patterns with a single age group, either Late Triassic or Jurassic, indicating a Waipapa Terrane ancestry. Similar data from the central Cook Strait region suggest that Waipapa Terrane basement continues northeastwards from Marlborough through Fishermans Rock to Kapiti Island. The Rakaia–Waipapa terrane boundary thus lies east of Kapiti Island and Fishermans Rock. The position of a Caples–Waipapa terrane boundary within the Marlborough Schist is less certain but most of the eastern Marlborough Schist is Waipapa Terrane.

Abstract The tholeiitic basalt intrusives as sills and dykes from the Kutch region have been classified into high Ti and low Ti categories. The high-Ti basalts display characters comparable to the shield lavas of the Reunion Island with OIB type signature. The incompatible trace element patterns and ratios as well as the Sr-Nd composition of the high Ti-basalts support their generation from mixing of melts derived from both the convecting asthenospheric mantle (plume?) as the dominant source and the SCLM with little contribution from the continental crust. The petrographic and chemical data indicate dominant clinopyroxene and plagioclase fractionation and small olivine fractionation. In contrast, the low-Ti basalts exhibit trace element characters and Sr and Nd isotopic systematics similar to MORB with relatively more contribution from the SCLM, and less from Reunion like source that has been modified by variable contribution from the crustal contaminants. The variable amount of crustal interaction further divide the low Ti basalts into two subtypes viz. low-Ti-high Pb and low Ti-low Pb. The geochemical characters of both the high Ti and Low Ti basalts as well as the lava flows from Kutch do not correlate well with any of their southwestern counterparts identified in the main Deccan province and most probably represent lower levels. It is essential to treat these basalts therefore as separate stratigraphic unit as “Kutch Group” in the Deccan stratigraphy.

Abstract Spinel lherzolites and harzburgites from Mont-Briançon and Marais de Limagne in the Devès volcanic district display coarse-grained to porphyroclastic microstructures and the modal content of volatile-bearing phases increases with the degree of deformation. Clinopyroxene and/or spinel are partly or totally reacted to amphibole. The coupled interpretations of trace-element, rare earth element (REE) and O–Sr–Nd data for clinopyroxene and amphibole indicate that the metasomatized mantle beneath Devès is a mixture of depleted and enriched mantle associated with an alkaline, high field strength element poor, and light rare earth element, U- and Th-rich carbonate-rich silicate fluid–melt metasomatic agent. Oxygen isotope and REE data for clinopyroxene–amphibole pairs indicate a (La/Yb) N enrichment related to an increasing metasomatic agent/rock ratio.

Geochemical tomography sections based on mantle-derived pyrope garnet xenocrysts have been constructed for different tectonic domains along a southern transect crossing the Tasman Line. At the regional scale, these sections reveal thicker lithosphere and lower geothermal gradients with increasing tectonothermal age of the lithosphere domains. In a transect from the easternmost locality (Jugiong) in Phanerozoic eastern Australia to the Eyre Peninsula (Gawler Craton) in Proterozoic South Australia, the palaeogeotherm decreases from greater than 50 mW/m 2 at Jugiong to around 40 mW/m 2 In South Australia and the depth to the lithosphere-asthenosphere boundary changes from ∼100 to 180 km. Geochemical tomography sections for the Gawler Craton region sampled in the Permian and the Jurassic, indicate lithosphere thinning by about 10–15 km, attributed to the effect of Pangean rifting. These physical changes are paralleled by higher MgO and lower CaO and AI 2 O 3 contents in progressively older lithospheric mantle, consistent with the global secular variation in mantle composition previously documented. Olivine is the most abundant mantle mineral in all sections and the Fe/Mg ratio of olivine is important in controlling the physical properties of lithospheric regions (density, Vp, Vs). Because olivine is rarely preserved, an inversion of the garnet-olivine Fe-Mg-exchange geothermometer has been used to calculate the Fe/Mg of olivine coexisting with each garnet grain. Application of this inversion to the southern Australian transect shows high Mg# (Mg/(Mg+Fe)) for olivine in the shallow parts of the Proterozoic western sections and more Fe-rich olivine in the Phanerozoic eastern sections. There also is an overall trend to lower Mg# with increasing depth in each section, which may reflect infiltration by asthenospherlc melts near the lithosphere-asthenosphere boundary. Olivine density varies inversely with Mg#, and the Proterozoic lithosphere in this traverse therefore is more buoyant, relative to the asthenosphere, than the Phanerozoic sections despite the lower geotherm beneath the craton. Vp and Vs vary directly with Mg# (the higher the Mg#, the higher the Vp and Vs) and thus these compositional differences are important in the interpretation of seismic tomography.