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Basanites from theTertiary Siebengebirge area of Germany (part of the Central European Volcanic Province; CEVP) have high Mg# (40·60), moderate to high Cr (4 300 ppm) and Ni (4 200 ppm) contents and strong light rare earth element enrichment, but systematic depletion in Rb and K relative to trace elements of similar compatibility in anhydrous mantle. Rare earth element melting models can explain the petrogenesis of these basanites in terms of partial melting of a spinel peridotite source containing residual amphibole. It is inferred that amphibole, indicated by the relative K and Rb depletion and the melting model, was precipitated in the spinel peridotite lithospheric mantle beneath the Siebengebirge, by metasomatic fluids or melts from a rising mantle diapir or plume. Alkali basalts and more differentiated rocks have lower Mg# and lower abundances of Ni and Cr, and have undergone fractionation of mainly olivine, clinopyroxene, Fe^Ti oxides, amphibole and plagioclase. Most of the basanites and alkali basalts approach the Sr^Nd^Pb isotope compositions inferred for the European Asthenospheric Reservoir component. Trace element constraints (i.e. low Nb/U and Ce/Pb ratios) and the Sr^Nd^Pb isotope composition of the differentiated rocks indicate that assimilation of lower crustal material has modified the composition of the primary mantle-derived magmas. High 207 Pb/ 204 Pb ratios in the differentiated lavas point to assimilation of ancient lower crustal components having high U/Pb and Th/Pb ratios. Relatively shallow melting of inferred amphibole-bearing spinel peridotite sources may suggest an origin from the metasomatized part of the thermal boundary layer. Application of new thermobarometric equations for the basaltic magmas indicates relatively normal mantle potential temperatures (1300^14008C); thus the inferred mantle ‘baby plume’ or ‘hot finger’ is not thermally anomalous.

Dill et al. (2007) present laser ablation inductively coupled plasma mass spectrometry U-Pb data for torbernite, columbite, and limonite of the Hagendorf and Pleystein pegmatites. These pegmatites, which are intruded into a late Carboniferous granite, have been dated by Glodny (1997) to 317±3 Ma (2σ; 3-point Rb-Sr mineral isochron). Dill et al. (2007) report a torbernite age of 4.55±0.02 Ma, which is in line with earlier geochronological work in the region, showing the young redistribution of U and the formation of secondary U minerals (e.g. Carl and Dill, 1983; Wendt and Carl, 1985). Dill et al. (2007) present ages of 299.2±1.9 Ma and 302±3 Ma for ferrocolumbite from Hagendorf and Pleystein, respectively, that broadly agree with the Rb-Sr age of the Hagendorf pegmatite (Glodny, 1997). In addition, they present age data of ~345 to 380 Ma for four spot analyses on ferrocolumbite from the Pleystein pegmatite and a 549 ± 12 Ma discordia intercept age for limonite and torbernite mantling this limonite from the Hagendorf pegmatite. These ages are older than the rock hosting the dated minerals. Referring to older (Lower Ordovician) pegmatites in the Tepla-Barrandian (Glodny et al. , 1998), Dill et al. (2007) argue that the ages ~345 to ~380 Ma reflect the Devonian resetting of the U-Pb systematics of columbite from Lower Ordovician pegmatites and represent inherited domains in columbite. Apparently, Dill et al. (2007) were not aware that the Hagendorf and Pleystein pegmatites had emplaced into rocks of the Moldanubian Zone, which had an entirely different evolution than the Tepla-Barrandian from where Lower Ordovician pegmatites are known (e.g. Franke, 2000; Finger et al. , 2007). Furthermore, none of the numerous U-Pb TIMS studies on columbite from pegmatites (e.g. Romer and Wright, 1992; Romer and Smeds, 1994, 1996, 1997; Mauthner …

Fault-related veins and cements from two segments [Arava Fault (AF), Ghab Fault (GF)] and one branch [Serghaya Fault (SF)] of the major transform plate boundary between Africa and the Arabian plate, the Dead Sea Transform, were investigated geochemically. The results document considerable differences in the nature and degree of fluid–rock interactions among these faults. Within the area of the AF, fluid activity has neither led to intensive exchange reactions between fluids and rocks nor to notable cementation of the fault damage zones. Strontium and carbon and oxygen isotopes indicate infiltration of predominantly descending (meteoric water) and only subordinate involvement of ascending hydrothermal fluids from deep sources. For the SF, fluid-enhanced weakening mechanisms (chemical alteration processes) and fracture cementation are dominant. Along the GF, alteration processes and fracture healing by cementation are more intense than in the AF, but less intense than in the SF branch. For the SF and GF, δ18O, strontium isotopes, and major and minor element contents of veins indicate (i) near-surface, low-temperature meteoric fluids that show little or no interaction with carbonate host rocks; and (ii) meteoric fluids that were buffered by the surrounding host rocks. We suggest that the contrasting fluid–rock interactions along the Dead Sea Transform are related to local variations in climate (precipitation).

Geological and geochemical studies have been conducted on the Arava fault segment, which forms the major branch of the Dead Sea transform between the Dead Sea and the Gulf of Aqaba. Mesoscale to microscale faulting and veining related to this fault are described from limestone sequences of two locations (areas A and B) that represent different depth sections. In area A, pressure ridges expose the exhumed fault. Deformation mechanisms indicate that faulting took place at temperatures between 150°C and 300°C, which suggests faulting depths between 2 and 5 km with respect to published geothermal gradients. In area B, brittle fault damage forms a zone up to 150 m wide. The fault core is not exposed. Faulting took place at temperatures below 200°C (up to a 3‐km depth). In both areas, we found indications for a strong fault. Our kinematic analysis exhibits that the angle Ψ between δ1 and the strike of the Dead Sea transform immediately adjacent to the fault is ≤45°. The twin‐density technique yields di...

U-Pb isotopic analyses using TIMS and Laser Ablation-Multi Collector-ICP-MS were carried out on columbite-tantalite minerals from three suites of rare-element (Li, Cs, Ta) pegmatites in the Superior Province of Canada. Conventional TIMS analyses of these columbite-tantalite crystals produce scattered data and reverse discordance even after HF leaching of the grains prior to dissolution, possibly reflecting the incomplete removal of the open-system metamict segments during sample preparation. LA-MC-ICP-MS analyses of unleached, primary columbite free from inclusions and alteration give consistent and precise (

Auriferous skarns are associated with post- and late-kinematic Hercynian granites that intruded into Cambro-Ordovician to Devonian sediments of the central Pyrenees. We determined the age of the Andorra granite and the associated skarn at 305 ± 3 Ma by U-Pb dating titanite from the endo-skarn. The sulfur isotopic composition from sulfides in the skarn (Cardellach et al. 1992) shows a significant variation with isotopically light sulfur (δ34S ≈ +3) in the barren skarns and heavy sulfur (δ34S ≈ +11) in the gold-bearing skarns. Outwards, it increasingly resembles sulfur from arsenopyrite disseminations in the Cambro-Ordovician sediments. The lead isotopic composition from sulfides of the skarns is very homogeneous (206Pb/204Pb = 18.410, 207Pb/204Pb = 15.699, 208Pb/204Pb = 38.574) in contrast to the one in gold-bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments (e.g. 206Pb/204Pb varies from 18.54 to 30.36). Combined, sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite, whereas the sulfur is derived at variable portions from both the granite and the sediments.