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Ekspedycja IODP 360 : pierwszy etap odwiertu do płaszcza Ziemi

Ciążela J., Dick H. J. B., Mac-Leod Ch., Blum P.

Przegląd Geologiczny

2016

Vol. 64, nr 11

889--895

The aim of this paper is to provide a report on the IODP expedition 360 to the Polish geoscientific community. Expedition 360 to the Atlantis Bank along the Southwest Indian Ridge was Leg 1 of the SloMo Project. The primary objective of the SloMo Project is to test competing hypotheses on the nature of the Moho at the slow-spreading oceanic lithosphere. Based on a seismic survey and geologic mapping, the Moho beneath Atlantis Bank is believed to represent a serpentinization front, and not an igneous boundary between gabbro andperidotite. Expedition 360 started on November 30,2015 in Colombo (Sri Lanka), and ended on January 30,2015 in Port Louis (Mauritius). Hole U1473A was drilled 790 m through massive gabbro. Core recovery ranges from 44 to 96% towards the bottom of the hole, where excellent drilling conditions occurred. This deepest single-leg basement hole drilled into ocean crust is in overall good condition andcan be re-entered at Leg 2. For the first time, a Polish nominee has been selectedfor the scientific party of an oceanic IODP expedition. The mantle drilling project raised much attention in the Polish media. One hundred rock samples have been collected to investigate in Poland.

Mantle rock exposures at oceanic core complexes along mid-ocean ridges

Ciazela J., Koepke J., Dick H. J. B., Muszynski A.

Geologos

2015

Vol. 21, No. 4

207--231

The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites. The presence of plagioclase is usually linked to impregnation with late-stage melt. Based on the above, OCC peridotites away from segment ends and transforms can be treated as a new class of abyssal peridotites that differ from transform peridotites by a higher degree of partial melting and lower interaction with subsequent transient melt.