New insights on late stage volcanism in the Pigafetta basin, western Pacific

Abstract:

We document observations of late stage volcanism in the western Pacific Pigafetta Basin by integrating previously published and new multichannel seismic (MCS) reflection profiles, Ocean Drilling Program (ODP) drill core, and well log data. We examine data from three seismic experiments (FM35-12, MESOPAC II, and MTr5) conducted in the Pigafetta Basin, one of the oldest, deepest abyssal basins in the world, where crustal age is suggested to range from M29 (~157 Ma) to M44 (~169.8 Ma) based on Japanese Mesozoic magnetic lineations. We use a total of ~2150 km of MCS lines along with core and wire-line logging data from ODP Hole 801C. As a basis for our interpretation, we use previously defined seismic stratigraphy for the Pigafetta Basin, including Horizon B (basement) and lower transparent unit (volcaniclastic turbidites) terminology. We build synthetic seismograms from density and p-wave velocity logs using OpendTect v 4.6.0 tie well to seismic feature. We then incorporate energy and similarity attributes of the MCS profiles with the modeled seismogram to correlate reflectors to ODP Hole 801C lithostratigraphy. From this correlation, to be consistent with previous studies, we assign lithology and age to prominent sedimentary and basement reflectors throughout all survey lines. We characterize widely distributed deformation of Horizon B and lower sedimentary unit reflectors based on coherency of wiggle traces, lateral and vertical energy attenuation, and dip of reflectors over a range of scales (>10 km to <1 km). Our findings provide new evidence of late stage volcanism occurring in the Pigafetta Basin during the mid-Cretaceous (110 – 90 Ma). We classify late stage volcanism into 3 types of volcanic related features: (1) seamounts, (2) sills, and (3) vertical seismic disturbance zones (<<1 km wide) characterized by bilateral upward drag of reflectors (indicating a thin, vertical volcanic intrusion). The distribution of these features provide new insights into Cretaceous volcanism in the Pigafetta Basin: (i) late stage volcanism is more widely distributed and younger than previously reported, (ii) findings indicate a local source of magma, and (iii) the modes of volcanism differ from previously documented flood basalts and massive flows.