Zircons from nine Palaeoproterozoic granitoid intrusions within the southern part of the Fennoscandian Shield have been studied by laser ablation inductively coupled plasma source mass spectrometry to obtain U-Pb ages (in the range 1.88-1.68 Ga) and Hf isotope compositions. Six granitoids are from the 1.85-1.65 Ga Transscandinavian Igneous Belt; during that period more than 10 6 km 3 of granitoid magma intruded the pre-existing crust. The large majority of magmatic zircons from the nine granitoids have a limited initial range, 176 Hf/ 177 Hf ¼ 0.2816-0.2818, and define an evolutionary trend given by an initial value of å Hf(1:88Ga) % +2 AE 3 at an average 176 Lu/ 177 Hf ¼ 0.015. These data show that a geographically extensive, long-lived, relatively homogeneous, and dominant magma source resided within 2.1-1.86 Ga Svecofennian juvenile crust between 1.88 and 1.68 Ga. Zircon xenocrysts (1.91-1.98 Ga) with initial å Hf ¼ +0 to +2.5 from one of the intrusions provide additional evidence for such a long-lived crustal source of granitic magmas in central Fennoscandia. The granitoids were emplaced during a period of active mafic underplating that supplied heat to the anatectic zone in the lower-middle crust, but little or no mantle-derived Hf to the granitic magmas, in contrast to many mixed intermediate rocks.

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The analytical problems of dating gypsum speleothems with the U-series technique are reviewed. Gypsum speleothems are, in general, very low in U content, challenging the limits of detection methods. Various approaches to dissolving gypsum and isolation of actinides from the matrix include ion-pairing dissolution with magnesium salts and using nitric acid. The most precise dating technique is Thermal Ionization Mass Spectrometry (TIMS), combined with Fe(OH) 3 scavenging and anionic exchange chromatography. Less satisfactory, but much quicker, is direct retention of actinides from HNO 3 by means of TRU resin and MC-ICP-MS detection. We have tested these methods on gypsum speleothems from the Sorbas karst in Spain and from the Naica caves in Mexico. be successfully dated, a potentially excellent source of palaeoenviromental and geomorphic information. For instance, many gypsum karsts, like Sorbas in southern Spain (Calaforra, 1998), the Gypsum area near Bologna in Italy (Forti & Rossi, 2003) and the New Mexico gypsum karst (Calaforra & Forti, 1994) contain gypsum speleothems (Klimchouk et al., 1997). There is also a great variability in gypsum speleothems with regards to their size, external shape, internal structure and development. Davis (2000) reports from Lechuguilla Cave (New Mexico, USA) gypsum stalactites, columns, hairs, "Candelieres" (up to 6 m long), flowers and needles (>1 m long). Korshunov and Shavrina (1998) focus on cryogenic gypsum speleothems and describe gypsum powder (formed after ice sublimation), gypsum yozh (with spherical, hemispherical, flat or amorphous shape, with development closely related to clay deposits), and spherical porous yozh with an unclear genesis. Gypsum trays have been reported by Calaforra & Forti (1994) and Doran & Hill (1998) as clusters of popcorn or grape coralloids ending in a flat surface. Gypsum nests has been described by Maltsev (1997) at Geophysicheskaya Cave, Turkmenistan, as a funnel-shaped mass of thousands of oriented gypsum needles with a hollow interior. Gypsum crusts in lava tubes have recently been dated by U-series technique (Dillon, 2009). Also, northern caves, even in relatively cold and wet regions like north Norway, contain evaporitic gypsum crusts (Lauritzen, 2002;Onac & Lauritzen, 1995 Keywords: Uranium series dating, gypsum, cave, methodology