Sun Chenguang

No Thumbnail Available
Last Name
Sun
First Name
Chenguang
ORCID

Filters

2014 - 2018 2
1 1
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Article
    Formation of fast-spreading lower oceanic crust as revealed by a new Mg–REE coupled geospeedometer
    (Elsevier, 2018-02-12) Sun, Chenguang ; Lissenberg, C. Johan
    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.
  • Preprint
    A REE-in-garnet–clinopyroxene thermobarometer for eclogites, granulites and garnet peridotites
    ( 2014-11) Sun, Chenguang ; Liang, Yan
    A REE-in-garnet-clinopyroxene thermobarometer for eclogites, granulites, and garnet peridotites has been developed on the basis of the temperature, pressure and mineral composition dependent partitioning of rare earth elements (REEs) between garnet and clinopyroxene. This new thermobarometer is derived from the garnet-clinopyroxene REE partitioning model of Sun and Liang (2014) that was calibrated against experimentally determined garnet-melt and clinopyroxene-melt partitioning data. It makes use of a group of trace elements that have similar geochemical behaviors at magmatic and subsolidus conditions, and allows one to invert temperature and pressure simultaneously using a least squares method. Application of the REE-in-garnet-clinopyroxene thermobarometer to REE partitioning data from laboratory experiments and field samples (quartz-bearing, graphite-bearing, and diamond-bearing granulites and eclogites; and well-equilibrated mantle eclogite xenoliths) published in the literature validates its reliability at both magmatic and subsolidus conditions. Application of the new thermobarometer to eclogites, garnet granulites and peridotites from various tectonic settings reveals an intriguing observation: temperatures derived from the REE-based thermobarometer are consistently higher than those derived from the widely used Fe-Mg thermometer of Krogh (1988) for samples that experienced cooling, but systematically lower than temperatures derived from the Fe-Mg thermometer for samples from thermally perturbed tectonic settings. The temperature discrepancies are likely due to the relative differences in diffusion rates between trivalent REEs and divalent Fe-Mg in garnet and clinopyroxene. Temperatures derived from the REE-based thermometer are closely related to closure temperatures for samples that experienced cooling, but are likely equilibrium or apparent re-equilibration temperatures at an early stage of heating for samples from thermally perturbed tectonic environments. The REE-in-garnet-clinopyroxene thermobarometer can shed new light on thermal histories of mafic and ultramafic rocks.