Abstract— The Rumuruti meteorite shower fell in Rumuruti, Kenya, on 1934 January 28 at 10:43 p.m. Rumuruti is an olivine‐rich chondritic breccia with light‐dark structure. Based on the coexistence of highly recrystallized fragments and unequilibrated components, Rumuruti is classified as a type 3–6 chondrite breccia. The most abundant phase of Rumuruti is olivine (mostly Fa∼39) with about 70 vol%. Feldspar (∼14 vol%; mainly plagioclase), Ca‐pyroxene (5 vol%), pyrrhotite (4.4 vol%), and pentlandite (3.6 vol%) are major constituents. All other phases have abundances below 1 vol%, including low‐Ca pyroxene, chrome spinels, phosphates (chlorapatite and whitlockite), chalcopyrite, ilmenite, tridymite, Ni‐rich and Ge‐containing metals, kamacite, and various particles enriched in noble metals like Pt, Ir, arid Au. The chemical composition of Rumuruti is chondritic. The depletion in refractory elements (Sc, REE, etc.) and the comparatively high Mn, Na, and K contents are characteristic of ordinary chondrites and distinguish Rumuruti from carbonaceous chondrites. However, S, Se, and Zn contents in Rumuruti are significantly above the level expected for ordinary chondrites. The oxygen isotope composition of Rumuruti is high in δ17O (5.52 ‰) and δ18O (5.07 ‰). Previously, a small number of chondritic meteorites with strong similarities to Rumuruti were described. They were called Carlisle Lakes‐type chondrites and they comprise: Carlisle Lakes, ALH85151, Y‐75302, Y‐793575, Y‐82002, Acfer 217, PCA91002, and PCA91241, as well as clasts in the Weatherford chondrite. All these meteorites are finds from hot and cold deserts having experienced various degrees of weathering. With Rumuruti, the first meteorite fall has been recognized that preserves the primary mineralogical and chemical characteristics of a new group of meteorites. Comparing all chondrites, the characteristic features can be summarized as follows: (a) basically chondritic chemistry with ordinary chondrite element patterns of refractory and moderately volatile lithophiles but higher abundances of S, Se, and Zn; (b) high degree of oxidation (37–41 mol% Fa in olivine, only traces of Fe, Ni‐metals, occurrence of chalcopyrite); (c) exceptionally high Δ17O values of about 2.7 for bulk samples; (d) high modal abundance of olivine (∼70 vol%); (e) Ti‐Fe3+−rich chromite (∼5.5 wt% TiO2); (f) occurrence of various noble metal‐rich particles; (g) abundant chondritic breccias consisting of equilibrated clasts and unequilibrated lithologies. With Rumuruti, nine meteorite samples exist that are chemically and mineralogically very similar. These meteorites are attributed to at least eight different fall events. It is proposed in this paper to call this group R chondrites (rumurutiites) after the first and only fall among these meteorites. These meteorites have a close relationship to ordinary chondrites. However, they are more oxidized than any of the existing groups of ordinary chondrites. Small, but significant differences in chemical composition and in oxygen isotopes between R...
Pediatric GIST is a rare but considerable diagnosis in chronic anemia, which is the most frequent clinical finding with this tumor entity. Recent review articles focus on histopathologic criteria but omit clinical features and course of disease. In nonsyndromal CD117-positive GIST, girls tend to show more high-grade tumors and existing literature on pediatric GIST shows a 2.7-fold higher incidence in females. Altogether epithelioid cell tumors are most frequent, although in boys spindle-cell tumors are reported more often. Together with known differences in molecular changes and local as well as systemic tumor behavior this strongly suggests that pediatric GIST represents a different entity than adult GIST. After establishment of clear-cut pathologic features in the past, reports on preoperative diagnostic findings, long-term follow-up, and therapy have to be emphasized to clarify the relationship of these entities.
To evaluate the reliability of K-Ar ages on fresh basaltic rocks, various fractions and whole rocks were dated. The samples were chosen to obtain a variety of petrographic types representing several petrologic kindred and cooling environments. The dates provided no evidence of argon leakage. One sample of an unusual rock type (a troctolite) gave an anomalously high age, suggesting excess radiogenic argon. Nepheline separates from two rocks yielded ages equivalent to the ages of biotite and pyroxene. Introduction. Basaltic rocks have been dated by means of the potassium-argon method by numerous workers. Erickson and Kulp [1961] obtained encouraging but erratic results from measurements on the Palisades diabase and Watchung basalt. Since this initial work, numerous ages have been determined on basaltic rocks [e.Most of the previous work has been done on basalt flows. or diabases. Our investigation includes very diverse petrographic rock types of basaltic composition representing a number of cooling environments. We have made at least two argon analyses on each of eighteen rocks and mineral fractions of essentially known age in order to evaluate the method. Our results indicate that whole-rock determinations onpetrographically suitable mafic rocks are as reliable as any mineral fraction that can be dated. Analytical techniques. The radiogenic argon is measured by the isotope dilution method using Ar • spikes. These spikes are prepared in large batches on a manifold, so that they all have the same pressure. This pressure is determined by calibration against a spike of highly purified commercial air argon. Samples are fused by induction heating in tungsten or columbium crucibles. Purification involves the following steps: 1. Dry ice trap. 2. Copper oxide at 600øC. 3. Liquid nitrogen trap. 4. Calcium at 900øC. 5. Adsorption on charcoal at liquid nitrogen temperature in a break seal for transfer to the mass spectrometer. The typical blank is •10 -• tool of atmospheric argon; the best are about 3 X 10 -•2 mol. The mass spectrometer is a Reynolds [1956] type with Faraday cup collector. Flow runs are used for the larger samples and static runs for the smaller ones. Corrections for fractionation are made in both cases. POTASSIUM-ARGON DATING OF BASALTIC ROCKS 1083 flame measurements. Details of both flame tech-
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