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Drilling to gabbro in intact ocean crust
Douglas S Wilson1, Damon A H Teagle, Jeffrey C Alt
1Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA. dwilson@geol.ucsb.edu
Science (New York, N.Y.)
|April 22, 2006
Summary
Scientists drilled into oceanic crust gabbro in the eastern Pacific, confirming melt lenses form shallower at faster spreading rates. This provides key insights into mid-ocean ridge crust formation.
Area of Science:
- Geology
- Oceanography
- Petrology
Background:
- Understanding oceanic crust formation at mid-ocean ridges requires sampling intact sequences of lavas, dikes, and gabbros.
- Accessing these deep crustal sections via scientific ocean drilling has been a long-standing challenge.
Purpose of the Study:
- To investigate the formation and evolution of oceanic crust at a superfast spreading rate.
- To sample gabbroic rocks, representing crystallized melt lenses beneath a mid-ocean ridge.
Main Methods:
- Scientific ocean drilling in Hole 1256D in the eastern Pacific Ocean.
- Geological sampling and analysis of recovered rock cores, including gabbros, dikes, and lavas.
Main Results:
- Gabbro was reached at 1157 meters depth within seismic layer 2 of the oceanic crust.
- The depth of gabbro confirms that melt lenses form at shallower positions under faster spreading conditions.
- The recovered gabbros intrude metamorphosed sheeted dikes and share compositional similarities with overlying lavas.
Conclusions:
- The findings support seismic predictions regarding the shallow occurrence of melt lenses at superfast spreading ridges.
- The sampled gabbros likely represent the crystallized melt lenses directly beneath the ridge axis.
- The study suggests that the penetrated melt lenses may not be the primary source for the cumulate lower oceanic crust.
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