Ascent of Ultrahigh-Pressure Rocks in Southeastern Papua New Guinea, as Revealed by Ti-in-Quartz Thermometry and Rb-Sr Dating

Debate concerns the timing of ultra-high pressure (UHP) metamorphism and the kinematics of exhumation of the world’s youngest known eclogite-facies rocks (U-Pb ages of 4 – 8 Ma) in the Woodlark Rift of southeastern Papua New Guinea. End-member kinematic models that have been proposed for the crustal exhumation of metamorphic gneiss domes that host these young eclogites include detachment-related (asymmetric) gneiss doming (metamorphic core complexes), and pure shear-dominated (symmetric or diapiric) gneiss doming. The former is predicted to exhume the deepest structural levels of the domes adjacent to a major normal fault. The latter is predicted to yield a concentric pattern of exhumation levels with the deepest rocks located near the center of the domes. As far as can be determined, there are no mappable field gradients with respect to either the high-pressure metamorphism or the later pervasive amphibolite-facies overprint in the lower crust. This apparent uniformity contributes to uncertainty regarding the distribution of vertical strain in the body, and thus to the mode of dome emplacement.