U-Pb zircon geochronology from Haag Nunataks, Coats Land and Shackleton Range (Antarctica): constraining the extent of juvenile Late Mesoproterozoic arc terranes

Understanding the accretionary stages of Rodinia evolution and the arrangement of cratons and arc terranes is dependent upon high-precision geochronology from key piercing points of Mesoproterozoic rocks. U-Pb zircon dating is presented here from the Mesoproterozoic Haag Nunataks gneiss complex of West Antarctica where the dominant granodiorite protolith was emplaced at 1238 ± 4 Ma, aplite/pegmatite sheets were intruded at 1064 ± 4 Ma and the final intrusive phase of microgranite sheets were emplaced at 1056 ± 8 Ma. A separate magmatic event at ∼1170 Ma is recorded as inherited zircons in the later stage intrusions. Based on field relationships, the main phase of deformation at Haag Nunataks is thought to have developed prior to the emplacement of the microgranite sheet at ∼1056 Ma but after the ∼1064 Ma aplite/pegmatite intrusive phase. Potentially correlative units from the Shackleton Range and Coats Land of East Antarctica are also dated to test supposed correlations with arc terranes and crustal blocks at the margins of Laurentia and the proto-Kalahari craton. An ice-transported granite pegmatite sample recovered from the Brunt Ice Shelf is used as a partial proxy for unexposed rocks of the ice-covered Coats Land block and has been dated at ∼1100 Ma. A diorite gneiss from the Shackleton Range was also analysed as it forms part of a magnetic domain shared with the Haag Nunataks crustal block. Core zircon ages of ∼2470 Ma were determined, and the age of migmatisation is interpreted at ∼1740 Ma and rules out any potential correlation with the Haag Nunataks gneiss complex. The magmatic precursors of the Haag Nunataks orthogneisses were emplaced in a juvenile arc setting. We argue that this arc was located in the Natal Embayment region, contiguous with the Namaqua-Natal-Maud belt of arc terranes typified by enhanced magmatism at ∼1240 Ma and ∼1170 Ma not associated with any significant deformation events. The later magmatic events at Haag Nunataks at ∼1060 Ma are more closely associated with collision of Laurentia with the proto-Kalahari craton and the associated deformation is correlated with the Ottawan phase of the Grenville orogeny.

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