Accessories in Kaiserstuhl carbonatites and related rocks as accurate and faithful recorders of whole rock age and isotopic composition

Abstract The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites carbonate-rich foidites the Kaiserstuhl are variously suited for in situ determination of their U–Pb ages Sr, Nd- Hf-isotope ratios by LA-ICP-MS. 143 Nd/ 144 Nd may be determined precisely all five phases, 176 Hf/ 177 Hf only 87 Sr/ 86 Sr perovskites pyrochlores. belong to one three magmatic groups that Schleicher et al. (1990) distinguished on basis Pb isotope ratios. Tephrites, phonolites essexites (nepheline monzogabbros) form second limburgites basanites) olivine nephelinites third. Our data overlap with carbonatite nephelinite fields defined but exhibit a much narrower range. These εNd εHf values plot along mantle array field oceanic island basalts relatively close mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar fission track lie between 16.2 17.8 Ma. They stem entirely geologically older tephrites, essexites. No existed so far younger except apatite age (15.8 Ma). We obtained precise zirconolites calzirtites 15.66, respectively 15.5 Ma (± 0.1 2 σ ) pyrochlores 15.35 ± 0.24 Only Badberg soevite yielded U–P concordia 14.56 0.86 while bergalites (haüyne melilitites) gave 206 Pb/ 238 U 208 232 Th 15.26 0.21, respectively, 15.28 0.48 main rock types were emplaced over time span 1.6 almost 1 million years before foidites. within 0.32