Results of an integrated geological mapping, geochronological, geochemical and airborne geophysics programme in NE Mozambique bring improved constraints on the sequence of events leading to the assembly of Gondwana along the East African Orogen (see Reference List). From the NW (foreland) to the SE (hinterland), a crustal transect across NE Mozambique shows division into 4 major lithotectonic units.

In their comment, Aslanian & Moulin argue that our model of South Atlantic opening is incompatible with several kinematic and geological constraints as recently evaluated in Moulin et al. They also claim that we have not appropriately referenced their work. We strongly disagree and in addressing their points will argue that our model is compatible with the most important constraints that have been assembled by the many scientists who have worked on the South Atlantic and that instead the interpretation by Moulin et al. suffers from serious flaws.

We present a revised model for the opening of the South Atlantic Ocean founded on a remapping of the continent–ocean boundaries and Aptian salt basins, the chronology of magmatic activity in and around the ocean basin and on the timing and character of associated intraplate deformation in Africa and South America. The new plate tectonic model is internally consistent and consistent with globally balanced plate motion solutions. The model includes realistic scenarios for intraplate deformation, pre-drift extension and seafloor spreading. Within the model, Aptian salt basins preserved in the South American (Brazilian) and African (Angola, Congo, Gabon) continental shelves are reunited in their original positions as parts of a single syn-rift basin in near subtropical latitudes (10°S–27°S). The basin was dissected at around 112 Ma (Aptian–Albian boundary) when the model suggests that seafloor spreading commenced north of the Walvis Ridge–Rio Grande Rise.

Extremely high thorium and considerable uranium concentrations are observed in carbonatite rocks of the Fen Complex—an alkaline intrusive complex in southern Norway. Since uranium- bearing bedrock and its weathering products are responsible for increased radon-222 concentrations in nearby dwellings, knowledge about the uranium concentrations of the individual rock types is important for evaluating the associated health risk. Earlier core-sample and ground-based scintillator measurements were limited in relating geological setting to indoor concentrations of radon-222 in such a region with very small-scale geological variations. We have performed airborne radiometric measurements over the entire Fen Complex and the nearby town of Ulefoss. The processed airborne data show that regions dominated by different carbonatite types vary significantly in mean thorium concentrations, but have similar uranium concentrations. Despite the complexity of the region, the obtained thorium/uranium ratios have proven to be a well-suited measure to distinguish regions that are dominated by specific carbonatite types. Furthermore, derived ground-concentration maps enable us to compare uranium ground concentrations directly with indoor radon concentrations of 139 individual dwellings in the Fen region. A positive correlation between local uranium concentrations and percentage of dwellings with indoor radon concentrations > 200 Bq m-3 was observed in regions where bedrock or its weathering material crops out. Similarly, high radon concentrations were observed for all carbonatites, indicating that the associated health hazard is largely independent of the dominant carbonatite type. In regions covered by clayey marine sediments, gamma radiation from bedrock is strongly attenuated. Also, indoor radon concentrations are predominantly low because radon transport is strongly limited by the low permeability of the marine sediments.

On the basis of large areal extent (similar to 0.5 x 10(6) km(2)), volume, brevity of eruption interval (+/-4 My) and convergent dyke swarms, the flare-up of igneous activity at 297 Ma in NW Europe marks a typical Large Igneous Province (LIP): The Skagerrak-Centered LIP (SCLIP). LfPs are widely but not universally considered products of deep-seated mantle plumes: We test the idea that a Skagerrak plume rose from the core-mantle-boundary (CMB) by restoring the center of SCLIP eruption, using a new reference frame, to its similar to 300 Ma position in a Pangea A type reconstruction. That position (similar to 11 degrees N, 16 degrees E, south of Lake Chad in Central Africa) lies vertically above the edge of the African Large Low Shear Velocity Province (LLSVP). It has previously been shown that eruption locations vertically above the edge of one or other of the Earth's two LLSVPs at the CMB characterize nearly all the Lips erupted since 200 Ma. A deep-sourced SCLIP plume source implies that the edge of the African LLSVP at the CMB has not moved significantly with respect to the spin axis of the Earth during the past 300 My. This is a 30% longer duration for the stability of a deep mantle structure than has been previously demonstrated and suggests that the African LLSVP was at least established by early Permian (Pangea) times. (C) 2007 Elsevier B.V. All rights reserved.

The paleomagnetic data sets from the British Tertiary Igneous Province (BTIP) have recently been criticized as being unreliable and discordant with data from elsewhere in the North Atlantic Igneous Province (NAIP) [Riisager et al. Earth Planet. Sci. Lett. 201 (2002) 261-276: Riisager et al. Earth Planet. Sci. Lett. 214 (2003) 409-4251. We offer new paleomagnetic data for the extensive lava flow sequence on the Isle of Mull, Scotland, and can confirm the paleomagnetic pole positions emanating from important earlier studies. Our new north paleomagnetic pole position for Eurasia at 59 +/- 0.2 Ma has latitude 73.3 degrees N, longitude 166.2 degrees E (dp/dm=5.2/7.0). A re-evaluation and an inter-comparison of the paleomagnetic database emanating from the NAIP were carried out to test for sub-province consistency. We find a general agreement between the Eurasian part of NAIP (BTIP and Faeroes) and East Greenland data. However a compilation of West Greenland data displays a large and unexplained dispersion. We speculate on if this is related to different sense of block rotation of the Tertiary West Greenland constituents. Combining all data from the NAIP constituents, give a pole position at 75.0 degrees N, 169.9 degrees E (N=25, K=84.3, Ag-95=3.2) in Eurasian reference frame. (C) 2008 Elsevier B.V. All rights reserved.

We test whether airborne gamma ray spectrometer measurements can be used to estimate levels of radon hazard in the Oslofjord region of Norway. We compile 43,000 line kilometres of gamma ray spectrometer data from 8 airborne surveys covering 10,000 km2 and compare them with 6326 indoor radon measurements. We find a clear spatial correlation between areas with elevated concentrations of uranium daughters in the near surface of the ground and regions with high incidence of elevated radon concentrations in dwellings. This correlation permits cautious use of the airborne data in radon hazard evaluation where direct measurements of indoor radon concentrations are few or absent. In radon hazard evaluation there is a natural synergy between the mapping of radon in indoor air, bedrock and drift geology mapping and airborne gamma ray surveying. We produce radon hazard forecast maps for the Oslofjord region based on a spatial union of hazard indicators from all four of these data sources. Indication of elevated radon hazard in any one of the data sets leads to the classification of a region as having an elevated radon hazard potential. This approach is inclusive in nature and we find that the majority of actual radon hazards lie in the assumed elevated risk regions.

Large Igneous Province (LIP) eruption sites of the past 300 My lie vertically above 1% slow shear wave velocity (V,) contours bounding the Afinican and Pacific Large Low Shear Velocity Provinces (LLSVPs) at the core-mantle boundary (CMB), or in the cases of the Siberian and Columbia River LIPs, bounding one or other of two smaller, Low Shear Velocity Provinces (LSVPs). Steep gradients in V-s at the CMB coincide with those 1% slow contours. The sites of 24 active hotspot volcanoes project down to the same narrowly defmed borders of the LLSVPs at the CMB. Plumes that have generated LIPs and major hotspot volcanoes have risen only from the immediate neighbourhoods of the 1% slow V-s contours at the CMB which thus define Plume Generation Zones (PGZs). PGZs projected vertically upward approximately match the + 10 m elevation contour of the geoid showing that the LLSVPs are a dominant control on the positively elevated geoid. Minima in the frequency distribution of shear wave velocities in the lowermost mantle near V-s = -1% indicate that regions with more negative velocities, forming similar to 2% of total mantle mass, are likely to be of material compositionally different from the rest of the mantle. Because all LIP eruption sites with ages younger than 300 Ma lie above the borders of LLSVPs or LSVPs at the CMB, PGZ footprints are inferred to have remained in the same places for the past 300 My. Because no plumes have risen from the interior of the LLSVPs and because no lithospheric slabs have penetrated those bodies the volumes of the LLSVPs are inferred to have also remained unchanged for the past 300 My. Because the LLSVPs are the dominant control on the positively elevated areas of the geoid those too must have remained as they now are since 300 Ma. The LLSVPs are not rising buoyant objects but stable features of the deep mantle. LIPs have been erupted throughout the past 2.5 Gy indicating that PGZs comparable to those of the past 0.3 Gy and LLSVPs (of which PGZs mark the margins at the CMB) have also existed for at least that long. LLSVPs could thus form the isolated reservoir invoked by some to explain the distinctive isotopic compositions of terrestrial rocks. PGZs lie at places where the boundaries of. (i) The outer core, (ii) one of the LLSVPs or LSVPs, and (iii) the seismically faster part of the deep mantle meet. Horizontal temperature gradients across the steeply inclined margins to the LLSVPs, the interiors of which are hotter than the surrounding mantle, at the CMB are key controls for the generation of plumes. Near the CMB the association of the high temperature of the outer core with an inclined thermal boundary layer at the margins of LLSVPs facilitates the generation of mantle plumes in the PGZs. (c) 2007 Elsevier B.V. All rights reserved.

B. Bingen, G. Viola, W. L. Griffin, J. Jacobs, R. Boyd, R.J. Thomas, E. Daudi, I.H.C. Henderson, E. Beyer, O. Skar, A. Engvik, R.M. Key, A. Solli, J.S. Sandstad, M. Smethurst, E. Tveten, T. Bjerkgard, V.A. Melezhik, D. Jamal, R. Smith, L.M. Hollick, P. Feito 1. Geological Survey of Norway, 7491 Trondheim, Norway, bernard.bingen@ngu.no 2. Department of Earth and Planetary Sciences, Macquarie University, NSW 2109 Australia 3. Department of Earth Science, University of Bergen, 5007 Bergen, Norway 4. British Geological Survey, NG125GG Keyworth, UK 5. National Directorate for Geology, Maputo, Mozambique 6. Eduardo Mondlane University, Maputo, Mozambique