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Logging Summary

IODP Expedition 340T:

Atlantis Massif Oceanic Core Complex

Expedition 340T Scientific Party

Introduction

    Figure 1. Location map of Atlantis Massif Core Complex Site U1309 and path of the Atlantic transit that took place during IODP Expedition 340T.

    IODP Expedition 340T returned to Hole U1309D to investigate hydration of the crust within the domal core of Atlantis Massif, located just west of the spreading axis of the Mid-Atlantic Ridge at 30°N. Prior seismic imaging showed considerable reflectivity within the footwall of this oceanic core complex. The results of Expedition 340T document the geologic explanation for at least some of the impedance contrast, confirming that borehole velocity of altered olivine-rich troctolite intervals at Site U1309 is sufficiently distinct from surrounding rock to produce a multichannel seismic reflection.

    Science operations for Expedition 340T were proposed in an ancillary project letter (APL), focusing primarily on completing the wireline logging of existing Hole U1309D with temperature and acoustic velocity measurements and a zero-offset vertical seismic profile (VSP). This work was carried out over ~5 days during a transit across the Atlantic Ocean between two full expeditions. During this time, the ~1415 m deep Hole U1309D was logged with the triple combo including the Modular Temperature Tool (MTT), a sonic tool string, a vertical seismic imager (VSI) tool string, and a magnetic susceptibility sonde (MSS-B) tool string.

    Scientific results for Expedition 340T (Atlantis Massif Oceanic Core Complex APL), which consist primarily of results from wireline logging, are summarized in the Expedition 340T Preliminary Report.


    Angela Slagle: Expedition Project Manager/Logging Staff Scientist, Borehole Research Group, Lamont-Doherty Earth Observatory of Columbia University, PO Box 1000, 61 Route 9W, Palisades, NY 10964, USA

    Gilles Guerin: Logging Staff Scientist, Borehole Research Group, Lamont-Doherty Earth Observatory of Columbia University, PO Box 1000, 61 Route 9W, Palisades, NY 10964, USA