A clastic dike‐sill assemblage in late Miocene (c. 6 Ma) strata, Annedale, Northern Wairarapa, New Zealand

Abstract

Abstract A glauconitic, sand‐filled, vertical clastic dike (>10 m high, base unexposed) and two associated sand‐filled sills in late Miocene mudstone (c. 6 Ma) near Annedale, Northern Wairarapa, New Zealand, pinches out upwards and thickens downwards. Relationships suggest that the mudstone remained solid while the glauconitic sand was fluidised during a penecontemporaneous earthquake event and was injected from below. After injection the margins of the clastic dike and sills were cemented by calcium carbonate. The cemented margins of the dike record at least two subsequent periods of shearing which are shown by subhorizontal and vertical slickensides on the dike walls. The clastic dike and the horizontal slickensides of the margin of the dike may have formed during two late Miocene dextral transtensional phases of faulting, whereas the vertical slickensides were probably formed during a short period when the subduction zone became locked. These features suggest that northeast Wairarapa had a similar tect...