Mg in plagioclase: Experimental calibration of a new geothermometer and diffusion coefficients

Faak, K.; Chakraborty, Sumit; Coogan, L. A.

doi:10.1016/j.gca.2013.05.009

Cited by 49 publications

(75 citation statements)

References 27 publications

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“…Re-arranging Eq. (5) gives the following expression for a new thermometer based on Mg exchange between plagioclase and clinopyroxene, Faak et al (2013). Predicted temperatures in (a) were calculated using the thermometer of this study (Eq.…”

Section: Calibration Results and Model Testsmentioning

confidence: 99%

“…As two elements with different diffusivities have distinct closure temperatures, when considered together the two elements could uniquely constrain both the cooling rate and initial temperature. The initial concept was briefly discussed in for understanding the different temperatures derived from their REE-exchange thermometer and the Mg-exchange thermometer of Faak et al (2013). A similar concept has also been used in Watson and Cherniak (2015) with a focus on diffusive relaxation of stepwise concentration profiles in single crystals.…”

Section: Basic Conceptmentioning

confidence: 99%

“…Applying the closure temperature equation of Dodson (1973) to Ca in olivine, two research groups estimated cooling rates of oceanic gabbros from the Faak et al (2013) as a function of silica activity and (b) the differences of two existing silica activity models for a basaltic system. Light yellow region in (a) indicates the temperature calibration range for the thermometer of Faak et al (2013). A fixed Mg partition coefficient (K Mg = 0.01) and two plagioclase compositions (An 50 and An 80 ; An 50 denotes 50 mol% anorthite in plagioclase) were used in (a).…”

Section: Introductionmentioning

confidence: 99%

“…Inset in (b) shows the silica activity model expressions of Faak et al (2015) and Carmichael (2004), in which T is temperature in K, R is the gas constant, and X denotes the oxide molar fraction. The melt in (b) used for Carmichael's model has a typical basaltic composition (i.e., 022005-1522 used in Faak et al, 2013). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.…”

Section: Introductionmentioning

confidence: 99%

“…However, in addition to the Dodson-type assumptions, results of Faak et al (2015) are also likely subject to uncertainties from their Mgexchange thermometer (Faak et al, 2013) and 1-D plane sheet approximation. Particularly, Faak et al's thermometer has a strong dependence upon silica activities that can only be calculated using existing activity models .…”

Section: Introductionmentioning

confidence: 99%

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Formation of fast-spreading lower oceanic crust as revealed by a new Mg–REE coupled geospeedometer

Sun

Lissenberg

2018

Earth and Planetary Science Letters

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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.

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Section: Calibration Results and Model Testsmentioning

confidence: 99%

Section: Basic Conceptmentioning

confidence: 99%