10.6084/m9.figshare.3453137 Alan P. M. Vaughan Alan P. M. Vaughan Craig Storey Craig Storey Simon P. Kelley Simon P. Kelley Tiffany L. Barry Tiffany L. Barry Michael L. Curtis Michael L. Curtis Synkinematic emplacement of Lassiter Coast Intrusive Suite plutons during the Palmer Land Event: evidence for mid-Cretaceous sinistral transpression at the Beaumont Glacier in eastern Palmer Land Geological Society of London 2016 Palmer Land New Palmer Land Event deformation biotite Eastern Palmer Land Shear Zone emplacement Ma Beaumont Glacier shear zone Beaumont Glacier Phase 1 quartz tonalite cuts Lassiter Coast Intrusive Suite plutons transpression quartz tonalite sheet margin cooling NW sinistral evidence Lassiter Coast Intrusive Suite magmatism dyke Ar Geology 2016-06-21 11:10:11 Dataset https://geolsoc.figshare.com/articles/dataset/Synkinematic_emplacement_of_Lassiter_Coast_Intrusive_Suite_plutons_during_the_Palmer_Land_Event_evidence_for_mid-Cretaceous___sinistral_transpression_at_the_Beaumont_Glacier_in_eastern_Palmer_Land/3453137 <p>New structural and geochronological data from the Eastern Palmer Land Shear Zone, in the vicinity of Beaumont Glacier, provide the first evidence of dated structural control on emplacement of the 119–95 Ma, >13000 km<sup>2</sup> Cretaceous Lassiter Coast Intrusive Suite, during the accretionary mid-Cretaceous Palmer Land Event orogeny. A previously undated >100 m thick dyke-like quartz tonalite intrusion was emplaced at 116.5 ± 1.5 Ma (Ar–Ar biotite cooling age) along a NW–SE axis, coeval with NW–SE compressional deformation, and possibly controlled by sinistral transpression along the Beaumont Glacier shear zone. The quartz tonalite preserves two styles of deformation and was probably progressively deformed by normal-sinistral shearing during magmatic cooling with initial deformation of mafic enclaves in the dyke interior and final formation of proto-mylonite to mylonite on the dyke margin. The quartz tonalite cuts folding associated with Phase 1 of the Palmer Land Event, indicating that this folding is older than 116 Ma, extending the onset of Phase 1 back in time. Mylonite on the quartz tonalite sheet margin was subsequently thermally reset at <em>c</em>. 107 Ma (Ar–Ar biotite method), during a peak in Lassiter Coast Intrusive Suite magmatism. </p>