Exploring the coupling between plate tectonic and climate evolution: Eocene–Oligocene chronology of the southwest Pacific

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International Ocean Discovery Program (IODP) Exp. 371 (Tasman Frontier Subduction Initiation and Paleogene Climate, 27th July to 26th Sept. 2017) drilled six new sites recovering a total of 2506 m of Cretaceous to Pleistocene sediments and volcanic rocks. The record of Exp. 371 is integrated with the sediments recovered onshore in the Cadart borehole, which consists of ~1900 m of Upper Cretaceous–upper Eocene sediments drilled in 1999 near Bourail (central New Caledonia). The main objective of Exp. 371 is dating the widespread middle Eocene convergent deformation, reverse faulting, and uplift recorded in the area by analyses of seismic reflectors. This event, interpreted as the precursor of the Tonga-Kermadec subduction initiation, may also coincide with the global Eocene climate turnover from the warming trend peaking with the early Eocene climate optimum (EECO) to the ensuing general middle–late Eocene cooling. Pacific Plate westward-dominated subduction beneath oceanic crust, instead of subduction only occurring beneath the continental crust of the American cordillera, might have caused a significant drop in pCO2 and thus global cooling.The first objectives of this project are 1) the construction of a magnetic-polarity-based chronological framework of the sediments recovered during IODP Exp. 371 and sediments of the Cadart borehole, 2) use this framework to date the tectonic evolution of the Southwest Pacific area as reflected by the lithological variations (e.g. variations in clay content, volcanic material, and presence/absence of sedimentary high-energy structures like slumps).Data from Exp. 371 will be used to evaluate the intensity of chemical weathering on land during times of global climate variations. Chemical weathering of silicate minerals, followed by deposition of marine carbonate, is the only long-term mechanism buffering the atmospheric pCO2, which in turn modulates the average global temperatures. Preliminary data from Site U1511 (Tasman abyssal plain) shows a relative enrichment in sedimentary hematite (originated from the Australian continent) during the early Eocene (i.e. during the EECO), followed by a decrease over the ensuing middle–late Eocene. Following the idea proposed by Dallanave et al. [2010, Geochem. Geophys. Geosyst. 11(7)], variations of detrital hematite trace efficiently the rates of chemical weathering at the sediment source area. Objective 3) of this proposal is monitoring in detail the hematite content variations of the sediments deposited on the Tasman abyssal plain over the Eocene, evaluating the intensity of chemical weathering on the Australian continent.The integrated dataset obtained in this project will depict a complete tectonic and climate evolution picture placed in a common time frame, giving the possibility to shed light on the connection between large-scale tectonics and global climate.