Formation of fast-spreading lower oceanic crust as revealed by a new Mg–REE coupled geospeedometer
MetadataShow full item record
KeywordOceanic crust; Cooling rate; Crystallization temperature; Plagioclase; Clinopyroxene; Hess Deep
A new geospeedometer is developed based on the differential closures of Mg and rare earth element (REE) bulk-diffusion between coexisting plagioclase and clinopyroxene. By coupling the two elements with distinct bulk closure temperatures, this speedometer can numerically solve the initial temperatures and cooling rates for individual rock samples. As the existing Mg-exchange thermometer was calibrated for a narrow temperature range and strongly relies on model-dependent silica activities, a new thermometer is developed using literature experimental data. When the bulk closure temperatures of Mg and REE are determined, respectively, using this new Mg-exchange thermometer and the existing REE-exchange thermometer, this speedometer can be implemented for a wide range of compositions, mineral modes, and grain sizes. Applications of this new geospeedometer to oceanic gabbros from the fast-spreading East Pacific Rise at Hess Deep reveal that the lower oceanic crust crystallized at temperatures of 998–1353 °C with cooling rates of 0.003–10.2 °C/yr. Stratigraphic variations of the cooling rates and crystallization temperatures support deep hydrothermal circulations and in situ solidification of various replenished magma bodies. Together with existing petrological, geochemical and geophysical evidence, results from this new speedometry suggest that the lower crust formation at fast-spreading mid-ocean ridges involves emplacement of primary mantle melts in the deep section of the crystal mush zone coupled with efficient heat removal by crustal-scale hydrothermal circulations. The replenished melts become chemically and thermally evolved, accumulate as small magma bodies at various depths, feed the shallow axial magma chamber, and may also escape from the mush zone to generate off-axial magma lenses.
© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth and Planetary Science Letters 487 (2018): 165-178, doi:10.1016/j.epsl.2018.01.032.
Suggested CitationArticle: Sun, Chenguang, Lissenberg, C. Johan, "Formation of fast-spreading lower oceanic crust as revealed by a new Mg–REE coupled geospeedometer", Earth and Planetary Science Letters 487 (2018): 165-178, DOI:10.1016/j.epsl.2018.01.032, https://hdl.handle.net/1912/10307
The following license files are associated with this item:
Showing items related by title, author, creator and subject.
Drilling the oceanic lower crust and mantle : a global strategy for exploring the deep oceanic crust and mantle in the 1990's Workshop on Drilling the Oceanic Lower Crust and Mantle (Woods Hole Oceanographic Institution, 1989-03)This workshop was convened to follow up on the Second Conference on Scientific Ocean Drilling (COSOD II) to devise a specific plan for deep crustal and mantle drilling over the next decade. Since COSOD II, however, there ...
Swift, Stephen A.; Reichow, Marc; Tikku, Anahita; Tominaga, Masako; Gilbert, Lisa A. (American Geophysical Union, 2008-10-16)We examine shipboard physical property measurements, wireline logs, and vertical seismic profiles (VSP) from Ocean Drilling Program/Integrated Ocean Drilling Program Hole 1256D in 15 Ma ocean crust formed at superfast ...
Rohr, Kristin Marie Michener (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983-01)The lateral homogeneity of oceanic crust on the scale of a seismic experiment is a condition that most methods of seismic interpretation depend on. Whether this condition is in fact true is largely unknown and only ...