Large peridotite massifs are scattered along the 1500 km length of the Yarlung-Zangbo Suture Zone (southern Tibet, China), the major suture between Asia and Greater India. Diamonds occur in the peridotites and chromitites of several massifs, together with an extensive suite of trace phases that indicate extremely low fO 2 (SiC, nitrides, carbides, native elements) and/or ultrahigh pressures (UHP) (diamond, TiO 2 II, coesite, possible stishovite). New physical and isotopic (C, N) studies of the diamonds indicate that they are natural, crystallized in a disequilibrium, high-T environment, and spent only a short time at mantle temperatures before exhumation and cooling. These constraints are difficult to reconcile with previous models for the history of the diamond-bearing rocks. Possible evidence for metamorphism in or near the upper part of the Transition Zone includes the following: (1) chromite (in disseminated, nodular and massive chromitites) containing exsolved pyroxenes and coesite, suggesting inversion from a high-P polymorph of chromite; (2) microstructural studies suggesting that the chromitites recrystallized from fine-grained, highly deformed mixtures of wadsleyite and an octahedral polymorph of chromite; (3) a new cubic Mg-silicate, with the space group of ringwoodite but an inverse-spinel structure (all Si in octahedral coordination); (4) harzburgites with coarsely vermicular symplectites of opx þ Cr-Al spinel 6 cpx; reconstructions suggest that these are the breakdown products of majoritic garnets, with estimated minimum pressures to > 13 GPa. Evidence for a shallow pre-metamorphic origin for the chromitites and peridotites includes the following: (1) trace-element data showing that the chromitites are typical of suprasubduction-zone (SSZ) chromitites formed by magma mixing or mingling, consistent with Hf-isotope data from magmatic (375 Ma) zircons in the chromitites; (2) the composition of the new cubic Mg-silicate, which suggests a low-P origin as antigorite, subsequently dehydrated; (3) the peridotites themselves, which carry the trace element signature of metasomatism in an SSZ environment, a signature that must have been imposed before the incorporation of the UHP and low-fO 2 phases. A proposed P-T-t path involves the original formation of chromitites in mantle-wedge

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words: 235 18 Abstract 25 We present high-precision Fe and Mg isotopic data for the Purang ophiolite, 26 southwestern Tibet, representing the first combined Fe and Mg isotopic study of the 27 oceanic lithosphere hitherto. The δ 56 Fe and δ 26 Mg values of the ophiolitic peridotite, 28 * Corresponding authors: Ben-Xun Su, subenxun@mail.igcas.ac.cn; Fang-Zhen Teng, fteng@u.washington.edu. Su et al. Page 2dunite and gabbro vary from -0.209 to 0.187‰ and from -0.28 to -0.14‰, respectively. 29The average δ 56 Fe of the peridotites is -0.030 ± 0.143‰ (2SD, n = 17), a value 30 indistinguishable from abyssal peridotites and chondrites, and lower than oceanic basalts. 31The average δ 26 Mg value of the peridotites is -0.20 ± 0.10‰, a value slightly higher than 32 both chondrites and oceanic basalts. Correlations between δ 56 Fe and indices of partial 33 melting indicate fractionation of 0.323‰ in δ 56 Fe between the oceanic lithospheric 34 mantle and the overlying mafic crust during an early episode of partial melting, 35presumably beneath a spreading centre. Subsequent metasomatism in a supra-subduction 36 zone caused elevated oxygen fugacity and heavy Fe isotopic compositions in the oceanic 37 lithospheric mantle. The dunite with high Ba/La, a proxy for oxygen fugacity, and high 38 δ 56 Fe values was likely formed during this process of sub-arc mantle-melt interaction. 39The negatively coupled Fe-Mg isotopic variations of the Purang ophiolite indicate that 40Mg isotope fractionation may also occur during high-temperature mantle processes. The 41 observed isotopic variations among different lithologies in the ophiolite may 42 satisfactorily account for the isotopic differences between arc lavas and mantle 43 peridotites with respect to oceanic basalts, thus providing implications for crust-mantle 44 differentiation. 45

We present high‐precision measurements of iron (Fe) and magnesium (Mg) isotopic compositions of olivine, orthopyroxene, and chromite separates from harzburgites, dunites, and chromitites in the mantle section of the Luobusa ophiolite, southern Tibet, to investigate the origins of podiform chromitite. Two harzburgites in the Zedong ophiolite, southern Tibet, are also reported for comparison. The olivine and orthopyroxene in the Luobusa and Zedong harzburgites have similar Fe and Mg isotopic compositions, with δ56Fe values ranging from 0‰ to +0.083‰ in olivine, from −0.034‰ to +0.081‰ in orthopyroxene and δ26Mg values ranging from −0.25‰ to −0.20‰ in olivine, from −0.29‰ to −0.26‰ in orthopyroxene, respectively. The olivines of two dunites from the Luobusa display small Fe and Mg isotopic variations, with δ56Fe values of +0.014‰ and +0.116‰ and δ26Mg values of −0.21‰ and −0.29‰. All chromites in the Luobusa chromitites have lighter Fe isotopic compositions than the coexisting olivines, with δ56Fe values ranging from −0.247‰ to +0.043‰ in chromite and from −0.146‰ to +0.215‰ in olivine (Δ56FeChr‐Ol = −0.294 to −0.101‰). The chromite δ26Mg values span a significant range from −0.41‰ to +0.14‰. Large disequilibrium Fe and Mg isotope fractionation between chromite and olivine, as well as positive correlation of chromite δ56Fe values with their MgO contents, could be attributed to Fe‐Mg exchange between chromite and olivine. In the disseminated chromitites, the higher modal abundances of olivine than chromite would result in a more extensive Fe‐Mg exchange, whereas chromite in the massive chromitite where olivine is rare could not be affected by this process.

Aluminate garnet phosphors Ca2GdZr2(AlO4)3:Ce(3+) (CGZA:Ce(3+)) for solid-state white lighting sources are reported. The crystal structure and Mulliken bonding population of the CGZA:Ce(3+) have been analyzed. The larger 5d ((2)D) barycenter shift εc and smaller phenomenological parameter 10Dq of Ce(3+) in CGZA are related to the larger covalent character of Ce-O. The tuning spectral properties of the Ce(3+)-doped CGZA-based isostructural phosphors are presented. The splitting of cubic crystal field energy level (2)Eg in Ca2REZr2(AlO4)3:Ce(3+) (CREZA:Ce(3+)) (RE = Lu, Y, and Gd) increases as the radius of RE(3+) increases, and the splitting of (2)Eg may dominate the difference of spectroscopic red-shift D(A) in CREZA:Ce(3+). The splitting of the (2)Eg in CaGd2ZrSc(AlO4)3:Ce(3+) (CGZSA:Ce(3+)) phosphors increases seemly due to the decreasing of the covalent character of Ce-O. Thermal quenching properties of Ce(3+)-doped CGZA-based isostructural phosphors are also presented and analyzed. For CREZA:Ce(3+) phosphors, the increasing of the radius of RE(3+) results in an enhancement of thermal quenching. The quenching of CGZSA:Ce(3+) is obviously stronger mainly due to the smaller energy difference between the lowest 5d excited state and 4f ground state.

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Detailed polarized spectral properties of Tm3+:NaLa(MoO4)2 crystal have been investigated. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves were measured at room temperature. The fluorescence decay mechanisms of the G14 and H34 multiplets were discussed. Spectroscopic parameters related to the laser operation at around 1.9 μm via the F34→H36 transition have been evaluated. Room-temperature quasi-cw 1.9 μm laser emission from a Ti:sapphire laser pumped Tm3+:NaLa(MoO4)2 crystal has been demonstrated. The maximum output power of 0.5 W has been achieved with a slope efficiency of 50%.