In the Central Iberian Zone, the Cadomian orogenic collapse is represented by chaotic megabreccias, olistostromes and mélange deposits reflecting a drastic change from slope-related deposits, fed by denudation of the Cadomian arc, to offshore-dominant settings episodically punctuated by phosphogenetic processes. In the Ibor and Alcudia anticlines, the pre-rift unconformity is marked by paraconformable to angular discordant contacts separating variable tilted strata of the Ediacaran Lower Alcudian – Domo Extremeño Supergroup and the upper Ediacaran – lower Terreneuvian Ibor Group from the overlying Terreneuvian San Lorenzo and Fuentepizarra formations. The sedimentation of the San Lorenzo Formation reflects two palaeogeographic scenarios: (i) a low-angle stable basement recording shoaling-upward siliciclastic cycles, and (ii) perturbations of basement fault scarps feeding slope-related conglomeratic channels, with NE-directed palaeocurrents, and sourced from topographic palaeohighs controlled by the movement along synsedimentary normal fault systems, such as the so-called El Guijo Fault. The intra-Fortunian age of the pre-rift unconformity is constrained by the ichno- and microfossil content of the succession, and is bracketed between the first occurrence of Treptichnus pedum in the Arrocampo Formation (Ibor Group) and of Anabarella plana in the Fuentepizarra Formation.

We present a study on major and trace element geochemistry of some intermediate lithologies from the predominantly basaltic Tibbit Hill volcanic suite in the Humber Zone of the Quebec Appalachians. The intermediate rocks probably formed as lava flows in the volcanic sequence. Their presence shows that this rift-related, c. 554 Ma volcanic sequence is not bimodal (basaltic-comenditic) as previously thought, but consists of a spectrum of compositions ranging from mafic through intermediate to felsic lithologies. The entire volcanic sequence is poly-deformed and generally metamorphosed to greenschist facies conditions.

The intermediate rocks of the Tibbit Hill Formation are trachyandesitic, trachytic and comenditic in composition, and exhibit a wide range of SiO2 content (52 to 68 wt.%). Mg is highly depleted in most samples. Variations of silica versus the alkalis show that most of the samples are alkaline in nature. The rocks display a tholeiitic trend on a standard AFM diagram.

In general, the examined rocks also exhibit a wide range of Sr (15 to 174 ppm), Rb (0 to 156 ppm), Zr (155 to 899 ppm), Nb (18 to 123 ppm), and Y (18 to 94 ppm). The concentration of Hf and Ta are generally low (6.6–14.8 ppm, and 3.3–6.6 ppm, respectively), compared to those of Zr and Nb. Nevertheless, these rocks contain relatively high concentrations of the HFS elements, thus reflecting an enriched source. The suite is also relatively enriched in the rare earth elements (REE), and exhibits fractionated, subparallel REE pattems; the latter are generally uniform and conformable.

Chemical features of these volcanic rocks are typical of those of anorogenic A1 type suites, related to hotspots, mantle plumes, or continental rift zones. This is consistent with earlier interpretation of volcanism associated with an Iapetan RRR triple junction, occurring shortly before the onset of seafloor spreading. At that stage of crustal evolution, alkaline to transitional basaltic magma pierced into the crust, and experienced fractionation to produce the liquids of intermediate composition. Rare earth element geochemical modelling supports the hypothesis that the most evolved composition for which REE data are available (comendite; 67.9 wt.% SiO2) was produced by 20% fractional crystallization of the least evolved trachyandesite (56.7 wt.% SiO2) of this intermediate volcanic assemblage.

Jurassic dykes of western Dronning Maud Land (Antarctica) form a minor component of the Karoo large igneous province. An extensive local dyke swarm intrudes Neoproterozoic gneisses and Jurassic syenite plutons on the margins of the Jutulstraumen palaeo rift in the Svedrupfjella region. The dykes were intruded in three distinct episodes (~204, ~176 and ~170 Ma). The 204 Ma dykes are overwhelminglylow-Ti, olivine tholeiites including some primitive (picritic) compositions (MgO >12 wt.%; Fe2O3 >12 wt.%; Cr >1000 ppm; Ni >600 ppm). This 204 Ma event precedes the main Karoo volcanic event by~25 Ma, so anycorrelations to the wider province are difficult to make. However, it mayrecord the earliest phase of rift activity along the Jutulstraumen. The 176 Ma dyke event is more intimately associated with the two syenite plutons. The dykes are alkaline (basanite/ tephrite) and were small-degree melts from an enriched, locallyderived source and underwent at least some degree of interaction with a syenitic contaminant. This ~176 Ma dyke event is widespread elsewhere in the Karoo (southern Africa and Dronning Maud Land). Later-stage (170 Ma) felsic (phonolite–comendite) dykes intrude the 176 Ma basanite–tephrite suite and represent the last phase of magmatic activityin the region.

The Carboniferous Billefjorden rift basin is a well-known example of a suite of Carboniferous basins on the Barents Shelf and NE Greenland. The basin has a clastic, carbonate and evaporite fill with complex and disputed stratigraphic relationships, especially regarding the Ebbadalen and Minkinfjellet formations. Geometrically, the basin is considered a simple half-graben. A N–S-trending fault and monocline structure within the northern portion of the basin, the Løvehovden fault, has lithological and thickness differences across it within the Minkinfjellet and possibly Ebbadalen formations. The fault shows W-side-down movement, defining a sub-basin within the larger half-graben. Significant along-strike changes occur. Down-throw to the west is at least 150 metres and possibly 400 metres, as shown by across-fault thickness differences of Ebbadalen and/or Minkinfjellet formations. To the east of the fault, the contact between the Ebbadalen and Minkinfjellet formations is a disconformity with significant local relief, and is interpreted to represent exposure from footwall uplift, and associated near- or at-surface solution, producing basal stratiform breccias. A similar contact is not exposed west of the fault. Monoclinal deformation and thickening of the younger Wordiekammen Formation above and across the monocline constrain a later movement component. Kinematic data and the structural style clearly indicate the Løvehovden fault is a normal fault with associated tri-shear zone development, consistent with the regional Carboniferous rift setting. Earlier interpretations describe the Løvehovden fault and monocline as Tertiary contractional features. In contrast, our work advocates that they are an important architectural basin element, defining a sub-basin within the Billeforden Trough during Minkinfjellet Formation deposition, with insignificant, if any, Tertiary reactivation. The Løvehovden fault is aligned with and represents the southern termination of the Lemströmfjellet fault to the north. Thus, the Billefjorden basin changes from a narrow graben to a broader half-graben to the south. These along-strike changes have important implications for the stratigraphic architecture of the basin, and for palaeogeographic reconstructions. These results and application of 3-D models for extension related tri-shear zones may help inform interpretation of other Carboniferous basins on the Barents Shelf.

A geophysical data set including some 1400 km of reflection seismic profiles and 17000 km of gravity lines was recorded in the waters north-west of the Antarctic Peninsula during the austral spring cruise of RV Polarstern (October to December 1987). These data form a contribution to the earlier and continuing studies dealing with the tectonics of Bransfield Strait, the structure of the South Shetland Trench, and the segmentation of the adjacent oceanic crust. The seismic profiles and gravity data illustrate among other features the differential extension of Bransfield Strait and the structure and morphology of the former converging plate boundary, which vary corresponding to the time of the last ridge trench collision. Observations have been made about the active character of several oceanic fracture zones in time which meet the former plate boundary.

The Indus-Tsangpo suture and its adjoining tectonic zones are well displayed in the Ladakh Himalayas where four tectonic zones have been distinguished, viz. the Zanskar, Indus suture, Shyok suture and Karakoram zones. The Zanskar zone is made up of Precambrian basement of the Zanskar crystalline complex and overlying Phanerozic sediments including Upper Palaeozoic volcanic rocks of the Zanskar Supergroup; they form the northern margin of the Indian plate. The Indus suture zone consists of a remnant of tectonised oceanic lithosphere represented by the Shergol melange and the Nidar complex with a former volcanic arc indicated by the volcanogenic Dras and Khardung formations and the Ladakh plutonic complex. The Shyok suture zone does not represent a tectonic repetition of the Indus suture; it is interpreted as a relic of a back-arc basin. The Karakoram plutonic complex appears to be genetically related to the Ladakh plutonic complex; both were generated from the subducting Indian oceanic plate. It is proposed that the boundary between the Indian and Eurasian plates does not lie along the Indus and Shyok sutures, but is located further N at the junction of Central Pamir (Alpine-Himalayan) and North Pamir (Hercynian).