Inhomogeneous spinel in chromitite from the Iwanai-dake peridotite complex, Hokkaido, Japan : variations of spinel unmixing texture and chemical composition

Graduate School of Natural Science and Technology, Kanazawa UniversityDepartment of Earth Sciences, Kanazawa Universit

Geochemistry of clinopyroxene in peridotites from the Nukabira complex, Kamuikotan zone, Hokkaido, Japan : a LA-ICP-MS study

Department of Earth Sciences, Kanazawa UniversityDepartment of Earth Sciences, Kanazawa UniversityTrace-element compositions of clinopyroxene in peridotite from the Nukabira complex were examined to mainly discuss partial melting processes involved in their formation. The Nukabira complex in the Kamuikotan zone, Hokkaido, Japan, is mainly composed of mantle-derived peridotites with wide compositional variations. The Iherzolite (e.g., C# of spinel=0.18-0.34) and depleted harzburgite (e.g., Cr#=0.4-0.7) are predominant, and dunite is often surrounded by them. Samples of 8 Iherzolites, 3 harzburgites and 4 dunites from the complex were selected, and their clinopyroxene geochemical characteristics were determined by using LA-ICP-MS. Chondrite-normalized trace-element patterns of clinopyroxene in the Iherzolites except one sample are characterized by strong depletion of light-REE (LREE) and middle-REE (MREE) relative to high heavy-REE (HREE) (e.g., (Nd/Yb)_<0.004, Yb_N=2.7-6.1). One Iherzolite sample, on the other hand, has high REE abundances of clinopyroxene (e.g. Ce_N≈0.05, Yb_N≈5.3, (Ce/Yb)_N=0.02-0.06). The trace-element patterns of clinopyroxene in harzburgites are "spoon-shaped" being high in MREE and LREE and low in HREE abundance (e.g., (Nd/Yb)_N<0.09, Yb_N=1.0-1.7). The abundances of MREE and LREE are variable in each harzburgite sample (e.g., Ce_N=0.008-0.03, Nd_N=0.02-0.08). The dunites tend to be similar in clinopyroxene compositions to surrounding peridotites. The variations of Iherzolite can be ascribed not only to the difference of melting degree but also to conditions on melting, such as with or without residual garnet prior to spinel peridotite stability field melting. Most of the Iherzolites probably experienced the melting in the garnet peridotite stability field. The further melting of Iherzolites should generate the harzburgites. The clinopyroxene geochemistry, however, indicates that the harzburgite was produced by different melting processes from the Iherzolite formation. The melting assisted by LREE-rich hydrous fluid is more preferable to explain the harzburgite features and origin

DISCOVERY OF FERROPICRITES AND HIGH-MAGNESIAN ANDESITES FROM THE ERDENETSOGT FORMATION, CENTRAL MONGOLIA

New geochemical and petrological results are presented for greenstones from the Erdenetsogt Formation hosted by the Tsetserleg accretionary terrane in the Hangay region, with particular emphasis on newly found picritic and andesitic rocks. These rocks occur mostly in the lower portion of the Erdenetsogt Formation as massive lavas, sills, and dykes closely associated with varicolored bedded ribbon cherts and siltstones. The protoliths of the studied greenstones comprise (1) plume-derived tholeiitic greenstones with oceanic plateau basalt affinity, (2) arc-derived, calc-alkaline andesites. The plume-derived rocks are characterized by chemical signatures such as slight LREE enrichment similar to that of tholeiitic OIB and the existence of ferropicrite with high FeO* (&gt;14 wt%) and MgO (12–22 wt%), which is characteristic of large igneous provinces (LIPs), including oceanic plateaus. Therefore, their tholeiitic composition and high-Fe and -Ti contents require melting of the source mantle peridotite with addition of some recycled Fe- and Ti-rich basaltic material. The andesites are characterized by glassy texture, high MgO content (up to 7 wt%), and significant LREE enrichment with depletion in Nb and resemble sanukite type of high-magnesian andesite (HMAs). We infer that the Hangay tholeiitic greenstones probably represent an accreted upper section of an oceanic plateau that developed in the deep-water region of the Hangay-Henteypaleo-ocean in the Upper Silurian-Lower Devonian. The Hangay HMAs may have been produced by subduction of young oceanic plate after an oceanward back-stepping of the subduction zone that was a result of the collision during the Carboniferous of the oceanic plateau and the active continental margin of the Central Mongolian Massif

Residual mitral regurgitation after repair for posterior leaflet prolapse- Importance of preoperative anterior leaflet tethering

Background Carpentier's techniques for degenerative posterior mitral leaflet prolapse have been established with excellent long‐term results reported. However, residual mitral regurgitation ( MR ) occasionally occurs even after a straightforward repair, though the involved mechanisms are not fully understood. We sought to identify specific preoperative echocardiographic findings associated with residual MR after a posterior mitral leaflet repair. Methods and Results We retrospectively studied 117 consecutive patients who underwent a primary mitral valve repair for isolated posterior mitral leaflet prolapse including a preoperative 3‐dimensional transesophageal echocardiography examination. Twelve had residual MR after the initial repair, of whom 7 required a corrective second pump run, 4 underwent conversion to mitral valve replacement, and 1 developed moderate MR within 1 month. Their preoperative parameters were compared with those of 105 patients who had an uneventful mitral valve repair. There were no hospital deaths. Multivariate analysis identified preoperative anterior mitral leaflet tethering angle as a significant predictor for residual MR (odds ratio, 6.82; 95% confidence interval, 1.8–33.8; P =0.0049). Receiver operator characteristics curve analysis revealed a cut‐off value of 24.3° (area under the curve, 0.77), indicating that anterior mitral leaflet angle predicts residual MR . In multivariate regression analysis, smaller anteroposterior mitral annular diameter ( P &lt;0.001) and lower left ventricular ejection fraction ( P =0.002) were significantly associated with higher anterior mitral leaflet angle, whereas left ventricular and left atrial dimension had no significant correlation. Conclusions Anterior mitral leaflet tethering in cases of posterior mitral leaflet prolapse has an adverse impact on early results following mitral valve repair. The findings of preoperative 3‐dimensional transesophageal echocardiography are important for consideration of a careful surgical strategy. </jats:sec

The codes and the lattices of Hadamard matrices

It has been observed by Assmus and Key as a result of the complete classification of Hadamard matrices of order 24, that the extremality of the binary code of a Hadamard matrix H of order 24 is equivalent to the extremality of the ternary code of H^T. In this note, we present two proofs of this fact, neither of which depends on the classification. One is a consequence of a more general result on the minimum weight of the dual of the code of a Hadamard matrix. The other relates the lattices obtained from the binary code and from the ternary code. Both proofs are presented in greater generality to include higher orders. In particular, the latter method is also used to show the equivalence of (i) the extremality of the ternary code, (ii) the extremality of the Z_4-code, and (iii) the extremality of a lattice obtained from a Hadamard matrix of order 48.Comment: 16 pages. minor revisio

Measurement of whole-rock trace-element composition of Cr-rich rocks on fused glass by LA-ICP-MS: data reliability of chromite-bearing fused glass

Information from whole-rock trace-element compositions is significant for petrological studies. LA-ICP-MS technique can rapidly determine whole-rock trace-element compositions by fused glasses prepared by homogenization of rock powders. As already reported, several trace-element abundance (Sc, Ti, V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Ba, Th and REEs) of basaltic and andesitic rocks can be determined with high accuracy by the routine measurement on the flux-free fused glass using LA-ICP-MS in our laboratory. In this study, based on the previous report, whole-rock trace-element compositions of some Cr-rich rocks, mantle diopsidite and related rocks from the Oman ophiolite, were determined by the routine work. The mantle diopsidite is locally rich in chromite and its fused glass prepared includes quench crystals and residual grains of chromite. Here, we assessed the reliability and uncertainty of our data obtained from such incompletely homogenized fused glasses. High precision of 3-spot analyses supports that quench crystals of chromite were homogeneously distributed in the fused glass. This suggests that the analytical data obtained from spots unrelated to residual chromite grains are reliable for whole-rock trace-element compositions. The heterogeneity caused by residual chromite grains can be ignored in the measurement of incompatible elements (Sr, Y, Zr, and REEs). Our analytical results of 6 fused glass beads prepared from the diopsidite samples indicate that heterogeneity of the mantle diopsidite in terms of the abundance of chromite is scarcely reflected by incompatible-element compositions while the heterogeneity is clearly characterized by Cr abundance