A Devonian origin for the Princhester ophiolite, northern New England Orogen

Abstract

The Princhester Serpentinite of the Marlborough terrane of the northern New England Orogen (NEO) has been interpreted as the basal mantle section of an ophiolite that developed at an oceanic spreading centre about 560 Ma and was emplaced at the margin of the Australian continent 180 to 230 my. later. This interpretation is contrary to modern research which shows that ophiolites are formed from young, hot and thin oceanic lithosphere at spreading centres in a supra-subduction zone setting, and that emplacement follows genesis by 10 my. or less. An alternative model is proposed in which the Princhester Serpentinite was the mantle component of a Late Devonian ophiolite formed at intra-arc to back arc spreading centres above an east-dipping subduction zone. Blockage of the subduction zone by collision with the Australian continent reversed the direction of subduction, and trapped the ophiolite in a forearc position. This model is consistent with modern concepts of ophiolite genesis, is compatible with the primary mineral chemistry and rare earth element patterns of the Princhester Serpentinite, and illustrates the development of the NEO as an accretionary orogen.