Rutile-bearing refractory eclogites: missing link between continents and depleted mantle

نویسندگان

  • Rudnick
  • Barth
  • Horn
  • McDonough
چکیده

A mass imbalance exists in Earth for Nb, Ta, and possibly Ti: continental crust and depleted mantle both have subchondritic Nb/Ta, Nb/La, and Ti/Zr, which requires the existence of an additional reservoir with superchondritic ratios, such as refractory eclogite produced by slab melting. Trace element compositions of minerals in xenolithic eclogites derived from cratonic lithospheric mantle show that rutile dominates the budget of Nb and Ta in the eclogites and imparts a superchondritic Nb/Ta, Nb/La, and Ti/Zr to the whole rocks. About 1 to 6 percent by weight of eclogite is required to solve the mass imbalance in the silicate Earth, and this reservoir must have an Nb concentration >/= 2 parts per million, Nb/La >/= 1.2, and Nb/Ta between 19 and 37-values that overlap those of the xenolithic eclogites. As the mass of eclogite in the continental lithosphere is significantly lower than this, much of this material may reside in the lower mantle, perhaps as deep as the core-mantle boundary.

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

An oxygen barometer for rutile–ilmenite assemblages: oxidation state of metasomatic agents in the mantle

Oxygen fugacity has been calculated for rutile–ilmenite assemblages from the reaction 2Fe2O3 (in ilmenite) C 4TiO2 (rutile) D 4FeTiO3 (in ilmenite) C O2. The equation log f O2 D 22:59 25925=T 3:09 log T C 0:0016535P C 48:836P=T 4 log a FeTiO3 C 2 log a Fe2O3 C 4 log a TiO2 , where T is in kelvin and P is in kbar, was derived from available thermodynamic data. The hypothetical end-member rutile–...

متن کامل

Metamorphic P–T conditions and thermal structure of Chinese Continental Scientific Drilling main hole eclogites: Fe–Mg partitioning thermometer vs. Zr-in-rutile thermometer

Core rocks recovered from the main hole (5158 m deep) of the Chinese Continental Scientific Drilling (CCSD-MH) project, southern Sulu UHP terrane, east-central China, consist of eclogites, various gneisses and minor metaperidotite cumulates; this lithological section underwent subduction-zone UHP metamorphism. Coesite-bearing eclogites are mainly present between the depths of 100–2000 m, but be...

متن کامل

Similarities between Archean high MgO eclogites and Phanerozoic arc-eclogite cumulates and the role of arcs in Archean continent formation

Some insights into the origin of cratonic mantle can be gained from “eclogite” (loosely defined here as an assemblage containing garnet and any pyroxene) xenoliths hosted in kimberlites erupted through Archean (~2.5­3.5 Gy) cratons. One subset of Archean eclogite xenoliths, the low MgO Archean xenoliths, is presently believed to represent metamorphosed fragments of ancient altered oceanic crust...

متن کامل

Eclogites in the Sclm: Are Any Subducted?

W.L. Griffin, Suzanne Y. O'Reilly and N.J. Pearson GEMOC, Dept of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia [email protected] It has become conventional wisdom that xenoliths of eclogite and garnet pyroxenite derived from cratonic subcontinental lithospheric mantle (SCLM) represent fragments of subducted ocean floor, implying that the SCLM has grown by a litho...

متن کامل

Geochemistry and magmatic history of eclogites and ultramafic rocks from the Chinese continental scientific drill hole: Subduction and ultrahigh-pressure metamorphism of lower crustal cumulates

Three distinct groups of eclogites (low-Mg–Ti eclogites, high-Ti eclogites and Mg-rich eclogites) and ultramafic rocks from the depth interval of 100–680 m of the Chinese Continental Scientific Drill Hole were studied. The lowMg#s (=100⁎molar Mg/(Mg+Fe)) (81–84%) and low Ni (1150–1220 ppm) and high Fe2O3 total (13–15 wt.%) contents of ultramafic rocks suggest a cumulate origin. Mgrich eclogites...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:
  • Science

دوره 287 5451  شماره 

صفحات  -

تاریخ انتشار 2000