The genesis and age of the Grunehogna Granite and Rb–Sr and Sm–Nd chemistry of the Annandagstoppane Granite, Ahlmanryggen, Dronning Maud Land, Antarctica

Abstract

Interpretations of Rb–Sr and Sm–Nd data from the Grunehogna Granite demonstrate that anatexis of and mixing with Høgfonna Formation sedimentary rocks, caused by hot basic sills of ~1100 Ma Borgmassivet Suite, are consistent, with the granite εNdεSr100Ma data, partially overlapping Borgmassivet Suite data and are marginally displaced toward published data from the Høgfonna Formation. Upper intercept LA-ICPMS U–Pb data from the Grunehogna Granite and Borgmassivet Suite zircons are within error at 1088 ± 17Ma and 1088 ± 68Ma, and are consistent with with unpublished data for the gabbro of 1107Ma. Interpretations of syn-depositional anatexis of semi-consolidated sediments under, high pH2O, are consistent with deposition at ~1130-1107Ma for the Høgfonna Formation. Sm–Nd data define an age of 3058 ± 116Ma for the Annandagstoppane Granite, consistent with a reported U–Pb zircon age of 3067± 8Ma. Rb–Sr data for the Annandagstoppane Granite define an errorchron of 2252 ± 82Ma. Differences between Rb–Sr and Sm–Nd data suggest that Rb–Sr systematics in many samples from all units have experienced open system behaviour in contrast to Sm–Nd systematics from which no disturbance is apparent. Localised tonalitic partial melts of gabbro yield an upper intercept LA-ICPMS U–Pb age from zircon of 1114 ± 47Ma.