Kinematic history of western Marie Byrd Land, West Antarctica: direct evidence from Cretaceous mafic dykes

Abstract

AbstractIntracontinental deformation occurred in West Antarctica during the final stages of plate convergence along the Cretaceous Gondwana margin. In western Marie Byrd Land, 115 Ma to 95 Ma A-type granitoids and mafic dykes record a change in plate kinematics. The magmatism typically is viewed as a record of extension leading to orthogonal break-up between New Zealand and Marie Byrd Land by c. 67 Ma. This paper presents new kinmatic and 40Ar/39Ar age data for a mafic dyke array in the Ford Ranges, a region >1000 km2 dominated by plutonic and metamorphic bedrock. The mean dyke trend of N16W corresponds to a maximum finite strain axis orientated N74E, highly oblique to the N58E-trending margin and to on-land crustal structures defined from airborne geophysics. 40Ar/39Ar emplacement ages for most dykes fall between 114 Ma and 97 Ma, coeval with emplacement of a gneiss dome at 101-96 Ma and with development of mylonitic shear zones at 100–95 Ma in coastal western Marie Byrd Land. The oblique orientation of maximum finite strain with respect to large faults, geophysical lineaments and the rifted margin of western Marie Byrd Land is consistent with transcurrent tectonics along this segment of the Gondwana margin at c. 100 Ma.