Actively rising surficial gneiss domes in Papua New Guinea

Abstract

Surficial gneiss domes are previously undescribed landforms two to three thousand metres high and tens of kilometres across, consisting of gneiss; they have the form of a dissected dome. On geomorphic grounds it is unlikely that the domes could be formed by differential erosion, so it is proposed that they emerged at the ground surface by shouldering the bounding rocks aside. Foliation in the gneiss is parallel to the dome surface, and therefore concentric in plan. Any small part of the dome surface looks like a fault scarp, but the ‘fault’ can be traced around the entire dome on Goodenough Island and around considerable arcs on other domes in southeast Papua New Guinea. We postulate that each dome originated by the pushing of a granite pluton and the foliation was created during the rise, whereas Davies (1978) has proposed that the domes are re‐folded thrust faults (which had earlier created the foliation) and that the granodiorite intrusions are later events only accidentally associated with the domes. In Davies’ hypothesis the topographic domes are created by differential erosion exposing orginally sub‐surface features, and some of the dome boundaries are fault‐line scarps. We consider that the topographic domes actually emerged at the ground surface, like a horst, and they are bounded by fault scarps. A review of the structural setting suggests that the domes may have been originally aligned as culminations on top of an elongated batholith rising beneath an axis of uplift along the Owen Stanley‐D'Entrecasteaux line. The domes are formed in an area of thick crust in a tensional environment.