The Ediacarian-Cambrian uplift history of western Dronning Maud Land: New ⁴⁰Ar-³⁹Ar and Sr/Nd data from Sverdrupfjella and Kirwanveggan, the source of the Urfjell Group and tectonic evolution of Dronning Maud Land within the Kuunga Orogeny and Gondwana amalgamation

Biotite ⁴⁰Ar/³⁹Ar ages from Mesoproterozoic gneisses from Kirwanveggan and Sverdrupfjella vary between 868–497 Ma and 547–326 Ma respectively. Hornblende ages from Kirwanveggan and Sverdrupfjella gneisses vary between 1067–480 Ma and 550–450 Ma respectively. The similar ages for hornblende and biotite from Sverdrupfjella are consistent with rapid uplift in a single event. The differences in ages between biotite and hornblende from Kirwanveggan imply differential heating southwards through Kirwanveggan and suggest heating over northern Kirwanveggan at ~500 Ma with central to southern Kirwanveggan preserving older Mesoproterozoic ⁴⁰Ar/³⁹Ar ages in hornblende. The heating is inferred to result from burial in the footwall of a nappe. Biotite ages throughout Sverdrupfjella and Kirwanveggan are similar to ages of deposition of Urfjell Group clastic sediments, with the Urfjell Group defining the southern limit of uplift and deposition at ~530 Ma. Radiogenic Nd/Sr isotope characteristics of the Urfjell Group are similar to basement gneisses from nearby Kirwanveggan and eastern Sverdrupfjella, Gjelsvikfjella and central Dronning Maud Land (CDML) but dissimilar to western Sverdrupfjella. In contrast detrital zircon patterns of the Urfjell Group suggest derivation from a source similar to distant CDML, ca. 500 km away. Tectonic analysis of Dronning Maud Land (DML), using available and new Sr/Nd radiogenic isotope and ⁴⁰Ar/³⁹Ar data, SHRIMP U/Pb zircon data, P-T-t estimates and structural analysis allow an interpretation that eastern Sverdrupfjella, Gjelsvikfjella and CDML comprise a nappe complex, emplaced toward S-SE over western Sverdrupfjella at ca. 500–480 Ma. The timing of the nappe complex emplacement is constrained by 510–490 Ma syn-D3 granitic intrusions and rapid uplift reflected by the ⁴⁰Ar/³⁹Ar data in Sverdrupfjella. Earlier top-to-the-NW D1-D2 folds and thrust faults preserved in the nappe complex predate the D3 nappe implacement. The emplacement of the nappe complex would position the Urfjell Group source much closer to its basin depository without intervening topography. The reach of the Kuunga Orogeny in DML is limited to central Kirwanveggan, with its southern limit being the Urfjell Group basin at ca. 530 Ma. Planar fabrics defined by hornblende and biotite, with older ages up to ~1100 Ma in southern Kirwanveggan, impliy dominantly Mesoproterozoic deformation in that area. with partial resetting of ⁴⁰Ar/³⁹Ar ages in northern Kirwanveggan. In contrast, D3 deformation in Sverdrupfjella is Cambrian in age. Integration of geochronological and geochemical data with published aeromagnetic and aerogravity data from WDML support the structural differences observed between Kirwanveggan and Sverdrupfjella and support a depth/heating gradient at ~530 Ma between N. Sverdrupfjella and S. Kirwanveggan. The absence of significant Neoproterozoic deformation in Kirwanveggan and the relatively undeformed nature of the ~530 Ma Urfjell Group rocks and Permian cover rocks, extending from southern Kirwanveggan to Vestfjella, indicate the Kuunga Orogeny is limited to Sverdrupfjella and possibly N. Kirwanveggan but is not continuous to Heimefrontfjella along the margin of the Grunehogna Craton.