2 June: Greetings from the Revelle! Today marks the half way point in the STINGS cruise and the science is flowing smoothly. We are currently measuring heat flow again after a successful seismic survey. The weather set us back 3+ days, but now the swells are low (<3 m) and the spirits are high again. There is more weather en route after a few days of calm seas, but it is not forecast to last. It does make deploying and recovering the heat probe a bit tricky, but we’ve got the process dialed in, thanks to our incredible ship crew and techs. We have a couple more heat flow transects in the area before heading to the southern coast of the North Island, where we will finish up more heat flow along with another seismic survey.
In my down time I have been reading about the geologic history of this area. It has become very clear to me why the work we are doing here is so important. The following is a very brief synopsis of what I’ve learned through the literature:
The Hikurangi Plateau is one piece of what is thought to be a massive large igneous province (3 – 5 million km3 of lava) consisting of the Hikurangi, Manihiki, and Ontong Java plateaus. There is much uncertainty about when the plateau formed and how (one hypothesis is a combination of a mantle plume and rifting). The three masses of flood basalt rifted apart ~120 Ma (Ontong Java first, followed by the separation of the other two), sending the Hikurangi southward toward the Chatham Rise margin of the Gondwana supercontinent. The collision occurred ~105 Ma, but the young, buoyant Hikurangi Plateau did not effectively subduct under the Chatham Rise, causing a slowing and eventual cessation of subduction. A fresh round of volcanism began ~99 Ma throughout the Hikurangi Plateau and Chatham Rise, producing a number of seamount ridges and guyots, lasting approximately 15 Ma. Spreading started again ~85 Ma, marking the beginning of the opening of the Southern Ocean. This reconstruction has been inferred by modeling, deep crustal reflection, dredging, and one drill hole. The real mystery at hand currently is what happens during the subduction of a large igneous province – this area is one of the only places on earth (if not the only) where this is occurring (now that the Hikurangi old and cold, it is subducting beneath the North Island of New Zealand). Our work here on STINGS is imperative to understanding the tectonic processes here, and our seismic and heat flow data will assist in the proposed drilling that will take place next year. We are all very excited to be a part of this cruise!