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Abstract

International Ocean Discovery Program (IODP) Expedition 371 drilled six sites in the Tasman Sea of the southwest Pacific between 27 July and 26 September 2017. The primary goal was to understand Tonga-Kermadec subduction initiation through recovery of Paleogene sediment records. Secondary goals involved understanding regional oceanography and climate since the Paleogene. Six sites were drilled, recovering 2506 m of cored sediment and volcanic rock in 36.4 days of on-site drilling during a total expedition length of 58 days. Wireline logs were collected at two sites. Shipboard observations made using cores and logs represent a substantial gain in fundamental knowledge about northern Zealandia, because only Deep Sea Drilling Project Sites 206, 207, and 208 had penetrated beneath upper Eocene strata within the region.The cored intervals at five sites (U1506-U1510) sampled nannofossil and foraminiferal ooze or chalk that contained volcanic or volcaniclastic intervals with variable clay content. Paleocene and Cretaceous sections range from more clay rich to predominantly claystone. At the final site (U1511), a sequence of abyssal clay and diatomite was recovered with only minor amounts of carbonate. The ages of strata at the base of each site were middle Eocene to Late Cretaceous, and our new results provide the first firm basis for defining formal lithostratigraphic units that can be mapped across a substantial part of northern Zealandia and related to onshore regions of New Caledonia and New Zealand.The material and data recovered during Expedition 371 enable primary scientific goals to be accomplished. All six sites provided new stratigraphic and paleogeographic information that can be put into context through regional seismic-stratigraphic interpretation and hence provide strong constraints on geodynamic models of subduction zone initiation. Our new observations can be directly related to the timing of plate deformation, the magnitude and timing of vertical motions, and the timing and type of volcanism. Secondary paleoclimate objectives were not all completed as planned, but significant new records of southwest Pacific climate were obtained.

Eocene (46–44 Ma) Onset of Australia‐Pacific Plate Motion in the Southwest Pacific Inferred From Stratigraphy in New Caledonia and New Zealand

“…Regional tectonic convergence is recorded across northern Zealandia and the Tasman Area immediately after this tectonic change (Sutherland et al, 2017(Sutherland et al, , 2018(Sutherland et al, , 2020. The combined evidence from across the southwest Pacific suggests onset of a new Australia-Pacific boundary at ~46-45 Ma, and that plate boundary was well developed by 43 Ma (Sutherland et al, 2020).…”

How to Create New Subduction Zones: A Global Perspective

“…Seismic reflection data across the Tasman Frontier reveal episodes of compression, uplift, and subsidence (Sutherland et al, 2017). Results from IODP Expedition 371 show regionally dramatic, Eoceneage vertical motions, with evidence for Eocene-Oligocene faulting and folding (Sutherland et al, 2018). Subduction inception along the proto-TK Arc may have involved elements of both spontaneous and induced elements.…”

Middle Miocene (∼14 Ma) and Late Miocene (∼6 Ma) Paleogeographic Boundary Conditions

“…In the South Pacific, since drilling cores and microfossil assemblages show that bathyal environments appeared in most parts of the Lord Howe Rise, Chatham Rise, and the Campbell Plateau during the middlelate Miocene (Carter et al, 1998;Sutherland et al, 2018). We assigned depths of ∼1,000 m in the middle and ∼2,000 m at the margin of these regions.…”